CN106877467B

CN106877467B - Discharge circuit and discharge control method

Info

Publication number: CN106877467B
Application number: CN201710114891.7A
Authority: CN
Inventors: 吕剑; 孙景; 沈得贵; 袁庆民; 茹永刚
Original assignee: Xian Tgood Intelligent Charging Technology Co Ltd
Current assignee: Xi'an Telai Intelligent Charging Technology Co ltd
Priority date: 2017-02-28
Filing date: 2017-02-28
Publication date: 2020-06-19
Anticipated expiration: 2037-02-28
Also published as: CN106877467A

Abstract

The invention relates to a discharge circuit and a discharge control method, wherein the discharge control method comprises the following steps: judging whether the discharge condition is met, if so, acquiring the discharge starting voltage of the current discharge period when each discharge period starts, judging whether the discharge starting voltage of the current discharge period is greater than a set voltage, if so, generating a pulse signal of the current discharge period according to the discharge starting voltage of the current discharge period, wherein the generated pulse signal enables the discharge energy of the discharge resistor in the effective pulse discharge time and the average power of the discharge resistor in the discharge period to meet the derating requirement of the discharge resistor; and outputting a pulse signal to the switching tube to control the on-off of the switching tube so as to realize the discharge function of the current discharge period. By implementing the technical scheme of the invention, the reliable discharge of the discharge circuit of the direct current charging module is ensured, the discharge time can be effectively shortened, the model selection range of the discharge resistor is expanded, and the cost of devices is favorably reduced.

Description

Discharge circuit and discharge control method

Technical Field

The invention relates to the field of direct current charging, in particular to a discharging circuit and a discharging control method.

Background

In the intelligent group charging system, a large number of direct current charging modules are arranged to realize the conversion from alternating current input to direct current and provide electric energy for charging the electric automobile. According to the national standard, the upper limit of the output voltage of some direct current charging modules is higher, and can reach 750V generally. In order to reduce output ripples, the dc charging module is generally configured with a filter capacitor with a certain capacity at its output port. However, when the filter capacitor is turned off in a no-load mode under the condition of outputting high voltage, the self-discharge speed of the port voltage is very slow, the application of a direct current charging module in an intelligent charging system is influenced, and a special discharge circuit needs to be designed to complete the rapid reduction of the output port voltage under a specified working condition.

The main functions of the discharge circuit of a general dc charging module are two points:

(1) when the direct current charging module is separated from the charging system (pulled out), the voltage of the output port is required to be rapidly reduced to be lower than the set voltage;

(2) the direct current charging module in the intelligent charging system realizes active discharging when the direct current charging module is positioned in the intelligent charging system according to the state of the system, and realizes related functions by matching with the intelligent charging system.

A conventional discharging circuit of a dc charging module is shown in fig. 1, and a discharging enable signal is used to control whether the discharging circuit operates. When the direct current charging module is in the system, the discharging enabling signal is at a low level, the switching tube S is disconnected, and the discharging circuit does not act; when the direct current charging module is separated from the system, the discharging enabling signal is at a high level, the switching tube S is conducted, and the discharging circuit starts to discharge.

Although the discharge circuit is simple to control, the discharge speed is high. However, since the output voltage is high, when the dc charging module outputs 750V, the energy stored in the capacitor C1 can reach 134 joule, and a large current is applied to the discharge resistor R1 during discharging, which causes a large amount of heat accumulation in the discharge resistor R1. This discharge control has two disadvantages:

(1) in order to enable the discharge resistor R1 to bear heat accumulation generated by transient large current, a high-power resistor device needs to be selected, which means that a high-cost and large-volume power resistor needs to be selected, and even the discharge resistor needs to be considered in the design of the air duct, so that the complexity of the module design is increased indirectly;

(2) the output discharge is controlled by a hardware discharge enable signal, and the discharge action is executed only when the module is separated from the system, so that the active discharge of the output end in the charging system cannot be realized, and the system function is influenced.

Disclosure of Invention

The present invention is directed to a discharge circuit and a discharge control method, which are provided to overcome the above-mentioned drawbacks of the prior art.

The technical scheme adopted by the invention for solving the technical problems is as follows: a discharge control method is constructed, and is used for controlling the discharge of the voltage on a filter capacitor through a discharge resistor and a switch tube, and the discharge resistor is connected with the switch tube in series and then connected with the filter capacitor in parallel, and the discharge control method is characterized by comprising the following steps:

s10, judging whether a discharging condition is met, and if so, executing the next step;

s20, when each discharge period starts, acquiring a discharge starting voltage of the current discharge period, judging whether the discharge starting voltage of the current discharge period is greater than a set voltage, and if so, executing the next step;

s30, generating a pulse signal of the current discharge period according to the discharge starting voltage of the current discharge period, wherein the generated pulse signal enables the discharge energy of the discharge resistor in the effective pulse discharge time and the average power of the discharge resistor in the discharge period to meet the derating requirement of the discharge resistor;

and S40, outputting the pulse signal to the switching tube to control the on-off of the switching tube so as to realize the discharge function of the current discharge period.

Preferably, the step S30 includes:

and acquiring the current effective pulse discharge time according to the discharge starting voltage of the current discharge period, and generating a pulse signal of the current discharge period according to the preset discharge period time and the acquired current effective pulse discharge time.

Preferably, the obtaining of the current effective pulse discharge time according to the discharge start voltage of the current discharge cycle specifically includes:

calculating the current effective pulse discharge time according to equation 1:

wherein, t_onFor the current effective pulse discharge time, R is the discharge powerResistance value of resistor, Q_RmaxIs the maximum discharge energy, k, sustainable by the discharge resistor_cTo a derating factor, V_oIs the discharge start voltage of the current discharge period.

step S301, a discharge starting voltage array and an effective pulse discharge time array are stored in advance, and the discharge starting voltage in the discharge starting voltage array and the effective pulse discharge time in the effective pulse discharge time array satisfy the following relations:

wherein, V_oiIs the discharge starting voltage in the discharge starting voltage array, and the discharge starting voltage is selected from the minimum discharge cut-off voltage to the highest voltage needing to be discharged, t_oniIs the effective pulse discharge time in the effective pulse discharge time array, R is the resistance value of the discharge resistor, Q_RmaxIs the maximum discharge energy, k, sustainable by the discharge resistor_cIs a derating coefficient;

step S302, a target discharge starting voltage is determined from the discharge starting voltage array according to the discharge starting voltage of the current discharge period, a target effective pulse discharge time corresponding to the target discharge starting voltage is determined from the effective pulse discharge time array, and the target effective pulse discharge time is used as the current effective pulse discharge time, wherein the determined target discharge starting voltage is higher than the discharge starting voltage of the current discharge period, and the difference value is minimum.

Preferably, the step S30 includes:

and acquiring the current discharge period time according to the discharge starting voltage of the current discharge period, and generating a pulse signal of the current discharge period according to the preset effective pulse discharge time and the acquired current discharge period time.

Preferably, the obtaining of the current discharge cycle time according to the discharge start voltage of the current discharge cycle specifically includes:

calculating the current discharge cycle time according to equation 2:

wherein T is the current discharge cycle time, V_oIs the discharge starting voltage of the current discharge period, R is the resistance value of the discharge resistor, P_eIs the rated power of the discharge resistor, t_onEffective pulse discharge time, k_cFor derating factor, k is the maximum pulse power multiple that the discharge resistor can bear in a predetermined discharge period.

step S303, a discharge starting voltage array and a discharge period time array are stored in advance, and the discharge starting voltage in the discharge starting voltage array and the discharge period time in the discharge period time array satisfy the following relationship:

wherein, V_oiIs the discharge starting voltage in the discharge starting voltage array, and the discharge starting voltage is selected from the minimum discharge cut-off voltage to the highest voltage required for discharge, T_iIs the discharge cycle time in the discharge cycle time array, R is the resistance value of the discharge resistor, P_eIs the rated power of the discharge resistor, t_onEffective pulse discharge time, k_cFor derating coefficient, k is the maximum pulse power multiple which can be borne by the discharge resistor in a predetermined discharge period;

step S304, determining a target discharge starting voltage from the discharge starting voltage array according to the discharge starting voltage of the current discharge period, determining a target discharge period time corresponding to the target discharge starting voltage from the discharge period time array, and taking the target discharge period time as the current discharge period time, wherein the determined target discharge starting voltage is higher than the discharge starting voltage of the current discharge period and the difference value is minimum.

Preferably, the step S40 includes:

step S401, judging whether a fault flag bit is set, if so, executing step S410; if not, executing step S402;

s402, starting timing by a timer;

s403, judging whether the timing time reaches the effective pulse discharge time of the current discharge period, if not, executing S404; if yes, go to step S405;

s404, outputting a high level to control the conduction of a switching tube, and then executing the step S403;

s405, outputting a low level to control the switch tube to be turned off;

s406, judging whether the timing time reaches the current discharge cycle time, and if not, executing the step S405; if yes, go to step S407;

s407, resetting a timer;

step S408, acquiring a discharge starting voltage and a discharge cut-off voltage of the current discharge period, judging whether the ratio of the discharge cut-off voltage and the discharge starting voltage of the current discharge period is greater than a preset value, if so, generating a single fault that an external high voltage is continuously applied to an output port, and executing step S409; if not, starting to perform the next discharge period;

s409, setting the fault flag bit;

and S410, stopping discharging.

Preferably, in the step S30, the generated pulse signal enables both the discharge energy of the discharge resistor in the effective pulse discharge time and the average power of the discharge resistor in the discharge period to satisfy the derating requirement of the discharge resistor, specifically:

the effective pulse discharge time and the discharge cycle time satisfy the following conditions:

wherein Q is the discharge energy of the discharge resistor within the current effective pulse discharge time, V_oIs the discharge initial voltage of the current discharge period, R is the resistance value of the discharge resistor, tau is the charge-discharge time constant and is the product of the resistance value of the discharge resistor and the capacitance value of the filter capacitor, t_onThe current effective pulse discharge time, T the current discharge period time, P the average power of discharge resistors in the current discharge period, k the predetermined maximum pulse power multiple of the discharge resistors in the current discharge period, and k_cTo derate the coefficient, P_eIs rated power of the discharge resistor, Q_RmaxThe maximum discharge energy which can be borne by the discharge resistor.

The invention also constructs a discharge circuit which is connected with the filter capacitor and comprises a discharge resistor, a switch tube and a controller, wherein the first end of the discharge resistor is connected with the first end of the filter capacitor, the second end of the discharge resistor is connected with the first end of the switch tube, and the second end of the switch tube is connected with the second end of the filter capacitor;

the controller is used for acquiring a discharge starting voltage of a current discharge period when the discharge condition is met and each discharge period is started, if the discharge starting voltage is larger than a set voltage, generating a pulse signal of the current discharge period according to the discharge starting voltage, and outputting the pulse signal to the switching tube to control the on-off of the switching tube so as to realize a discharge function of the current discharge period, wherein the generated pulse signal enables the discharge energy of the discharge resistor in an effective pulse discharge time and the average power of the discharge resistor in the discharge period to meet the derating requirement of the discharge resistor.

Preferably, the controller is further configured to obtain a discharge cut-off voltage of the current discharge cycle when each discharge cycle is ended, and if it is determined that a ratio of the discharge cut-off voltage of the current discharge cycle to a discharge start voltage of the current discharge cycle is greater than a preset value, a single fault in which an external high voltage is continuously applied to the output port occurs, and the discharge is stopped.

When the technical scheme of the invention is implemented, the controller generates a pulse signal according to the discharge starting voltage of the current discharge period (such as the voltage of the output port of the DC charging module detected currently) when judging that the discharge condition is met, and the pulse signal enables the discharge energy of the discharge resistor in the effective pulse discharge time and the average power of the discharge resistor in the discharge period to meet the derating requirement of the discharge resistor, and then the pulse signal is output to the switching tube to control the switching tube to be conducted discontinuously, so that the heat accumulation generated by bearing instantaneous large current on the discharge resistor is avoided, the reliable discharge of the discharge circuit is ensured, the voltage on the filter capacitor can be quickly reduced, the model selection range of the discharge resistor is expanded, and the cost of devices is reduced. In addition, the discharging circuit can be applied to the situation that the direct current charging module is separated from the charging system (is pulled out), and can also realize the active discharging of the direct current charging module in the system according to the requirement of the system, thereby expanding the application range of the discharging circuit.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts. In the drawings:

fig. 1 is a circuit diagram of a filter capacitor and a discharging circuit at an output port of a dc charging module in the prior art;

FIG. 2 is a circuit diagram of a filter capacitor and a discharging circuit of an output port of a DC charging module according to a first embodiment of the present invention;

FIG. 3 is a schematic diagram of the pulse signal and the output port voltage of the DC charging module according to the present invention;

FIG. 4 is a flowchart of a first embodiment of a discharge control method according to the present invention;

FIG. 5 is a graph of the pulse power characteristic of the discharge resistor;

FIG. 6 is a graph of discharge time versus discharge start voltage for a first embodiment of an effective pulse;

FIG. 7 is a diagram of a second embodiment of a discharge time versus discharge start voltage curve of an effective pulse;

FIG. 8 is a voltage waveform diagram of a first embodiment of an output port of a DC charging module during discharging at different voltage levels;

FIG. 9 is a graph of discharge cycle time versus discharge start voltage according to a first embodiment;

FIG. 10 is a voltage waveform diagram of a second embodiment of the output port of the DC charging module during discharging at different voltage levels;

fig. 11 is a flowchart of a first embodiment of step S40 in fig. 4.

Detailed Description

Fig. 2 is a circuit diagram of a first embodiment of the output port filter capacitor and the discharging circuit of the present invention, the dc charging module of the embodiment includes a voltage converting circuit (not shown), a filter capacitor C1 and a discharging circuit, wherein the voltage converting circuit is used for converting ac mains supply into dc power and supplying electric energy to the electric vehicle. A filter capacitor C1 is set at the output port of the dc charging module and is used to reduce the ripple of the output voltage. The discharge circuit comprises a discharge resistor R1, a switch tube S and a controller U1. The discharging resistor R1 preferably has a power resistor with a certain impact resistance, the first end of the discharging resistor R1 is connected to the first end of the filter capacitor C1, the second end of the discharging resistor R1 is connected to the first end of the switching tube S, the second end of the switching tube S is connected to the second end of the filter capacitor C1, the controller U1 is connected to the control end of the switching tube S, and the controller U1 is configured to obtain the voltage at the output port of the dc charging module at the beginning of each discharging cycle when the discharging condition is detected to be met, and use the voltage as the discharging start voltage of the current discharging cyclePressure V_oIf the discharge starting voltage is greater than the set voltage, a pulse signal of the current discharge period is generated according to the discharge starting voltage, and the pulse signal is output to the switching tube S to control the on-off of the switching tube S, so that the discharge function of the current discharge period is realized, specifically: when the pulse signal is at a high level, the switching tube S is conducted, and the discharge circuit starts to discharge; when the pulse signal is at a low level, the switching tube S is turned off, and the discharge circuit stops discharging. In addition, the generated pulse signal enables the discharge energy of the discharging resistor R1 in the effective pulse discharge time and the average power of the discharging resistor R1 in the discharge period to meet the derating requirement of the discharging resistor R1.

Referring to FIG. 3, the discharge period of the generated pulse signal is T, and the effective pulse discharge time is T_onDischarge pulse interval time of t_offAnd T ═ T_on+t_off. When the controller U1 outputs a pulse signal to the open tube S, t₁Sending out high level signal at the moment, and discharging time t of effective pulse_onThe inner switch tube S is continuously conducted until t₂The voltage at the output port of the time direct current charging module is V₀Down to V₁When the pulse signal is changed from high level to low level, the switch tube S is turned off, and the voltage of the output port of the direct current charging module is in the discharge pulse interval time t_offInternal holding V₁And does not change until the next discharge pulse arrives.

In this embodiment, the pulse signal is generated such that the discharge energy of the discharging resistor R1 in the effective pulse discharge time and the average power of the discharging resistor R1 in the discharge period both satisfy the de-rating requirement of the discharging resistor, that is, the following two conditions are satisfied: the discharge energy of the discharge resistor R1 in the effective pulse discharge time does not exceed the maximum bearing capacity of the discharge resistor R1; the average power of the discharge resistor R1 in the discharge period does not exceed the pulse power de-rating of the discharge resistor R1.

In addition, the discharge conditions of this embodiment include, for example: the direct current charging module is separated (pulled out) from the charging system, and the voltage of an output port of the direct current charging module is greater than the set voltage; alternatively, the dc charging module actively discharges according to the requirements of the charging system, for example, the system where the dc charging module is located requires a rapid reduction in module voltage to perform a specific function.

By implementing the technical scheme of the embodiment, when the controller judges that the discharging condition is met, a pulse signal is generated according to the voltage of the output port of the direct current charging module detected currently, the pulse signal enables the discharge energy of the discharging resistor R1 in the effective pulse discharging time and the average power of the discharging resistor R1 in the discharging period to meet the derating requirement of the discharging resistor R1, and then the pulse signal is output to the switching tube S to control the switching tube S to be conducted intermittently, so that heat accumulation generated by bearing instantaneous large current on the discharging resistor R1 can be avoided, the voltage of the output port of the direct current charging module can be rapidly reduced, the discharging time can be effectively shortened while the discharging circuit of the direct current charging module is ensured to discharge reliably, the type selection range of the discharging resistor is expanded, and the cost of devices is reduced. In addition, the discharging circuit can be applied to the situation that the direct current charging module is separated from the charging system (pulled out), and can also realize the active discharging of the direct current charging module when the direct current charging module is in place according to the requirement of the charging system, so that the application range of the discharging circuit is expanded.

In a preferred embodiment, the controller U1 is further configured to, at the end of each discharge cycle, acquire a voltage at the output port of the dc charging module, and use the voltage as a discharge cut-off voltage of the current discharge cycle, and if it is determined that a ratio of the discharge cut-off voltage of the current discharge cycle to a discharge start voltage of the current discharge cycle is greater than a preset value, a single fault occurs in which an external high voltage is continuously applied to the output port, and the discharge is stopped.

By implementing the technical scheme of the embodiment, the controller can also perform fault diagnosis at the end of the discharge period, so that the reliability of the pulse discharge circuit can be effectively improved, and the overheating damage of the discharge resistor R1 can be avoided.

It should be noted that, the above embodiments are described by taking the application of the discharging circuit to the dc charging module as an example, it should be understood that the discharging circuit of the present invention can also be applied to other devices with a filter capacitor, and when the voltage of the filter capacitor needs to be rapidly decreased, the discharging circuit can be used to discharge the filter capacitor.

Fig. 4 is a schematic flow chart of a first embodiment of a discharge control method according to the present invention, where the discharge control method is used to perform discharge control on a voltage across a filter capacitor through a discharge resistor and a switching tube, and the discharge resistor is connected in series with the switching tube and then connected in parallel with the filter capacitor, and the discharge control method includes the following steps:

s20, when each discharge period starts, acquiring a discharge starting voltage of the current discharge period, judging whether the discharge starting voltage of the current discharge period is greater than a set voltage, and if so, executing the next step; if not, stopping discharging;

and S40, outputting a pulse signal to the switching tube to control the on-off of the switching tube so as to realize the discharge function of the current discharge period.

In an alternative embodiment, with reference to fig. 2, the discharge starting voltage of the current discharge cycle is obtained, and may be a voltage at an output port of the dc charging module, and the voltage is used as the discharge starting voltage of the current discharge cycle.

In step S30, the generated pulse signal enables both the discharge energy of the discharge resistor within the effective pulse discharge time and the average power of the discharge resistor within the discharge period to satisfy the derating requirement of the discharge resistor, which is specifically:

wherein Q is the discharge energy of the discharge resistor in the current effective pulse discharge time, V_oIs the discharge starting voltage of the current discharge period, R is the resistance value of the discharge resistor, tau is the charge-discharge time constant and is the product of the resistance value of the discharge resistor and the capacitance value of the filter capacitor, t_onThe current effective pulse discharge time, T the current discharge period time, P the average power of the discharge resistor in the current discharge period, k the predetermined maximum pulse power multiple of the discharge resistor in the current discharge period, and k_cTo derate the coefficient, P_eRated power for discharge resistor, Q_RmaxThe maximum discharge energy which can be borne by the discharge resistor.

Regarding step S30, in an alternative embodiment, step S30 specifically includes: and acquiring the current effective pulse discharge time according to the discharge starting voltage, and generating a pulse signal of the current discharge period according to the preset discharge period time and the acquired current effective pulse discharge time. In this embodiment, the discharge period time T may be set according to hardware parameters of the dc charging module (e.g., the capacitance C of the filter capacitor C1, the resistance R of the discharge resistor R1, etc.), i.e., the discharge period time T is fixed. And an effective pulse discharge time t in each discharge period_onThe discharge control method is set according to the voltage at the output port of the dc charging module, that is, the discharge control method in this embodiment is a pulse discharge control method with a fixed frequency and an adaptive pulse width. In particular, by t_on＝F(V_o) Obtaining the voltage V between the discharge period and the discharge start voltage_oCorresponding effective pulse discharge time t_onSo as to achieve the purpose of rapidly discharging the port voltages of different levels.

By implementing the technical scheme of the embodiment, the reliability of the discharge circuit is ensured, and meanwhile, the voltage of the output port can be released to be lower than the set voltage in the shortest time. Meanwhile, the discharge starting voltage in each discharge period is detected in real time, and the effective pulse discharge time in the discharge period is updated in real time, so that the method has better adaptability.

Referring to fig. 2, if the capacitance of the filter capacitor C1 is C, the maximum voltage at the output port of the dc charging module is V_maxThen the energy stored by the filter capacitor C1 can be up to:

during discharging, the energy can only be discharged in the form of heat energy through the discharge resistor R1, so the discharge resistor R1 generally adopts a power resistor with certain impact resistance.

Assume discharge resistor R1 has a power rating of P_eThen, a pulse discharge strategy satisfying the derating of the discharge resistor R1 can be designed according to the pulse power characteristic curve of the discharge resistor shown in fig. 5. In fig. 5, the horizontal axis t represents the discharge pulse time, i.e., the discharge cycle time, and the vertical axis k represents the maximum pulse power multiple that can be sustained by the discharge resistor during the discharge pulse t. As can be seen, the shorter the discharge pulse time, the more pulse power the discharge resistor can withstand, but the energy discharged from the discharge resistor does not change (i.e., k P) during the discharge pulse time_eT is a constant) is the maximum discharge energy that the discharge resistor can withstand.

According to the pulse power characteristic curve of the discharge resistor, the maximum discharge energy Q bearable by the discharge resistor in the discharge process can be calculated_Rmax：

Q_Rmax＝k·P_e·t

For the selected type of discharge resistor R1, the maximum allowable discharge energy is fixed, i.e. Q_RmaxIs a constant. Taking into account the external voltage V that may occur in the DC charging module_oThe constant frequency self-adaptive pulse width pulse discharge control method needs to ensure the effective pulse discharge time t when the fault occurs_onThe internal discharge resistor R1 is not broken. If a fault condition that external voltage is continuously applied to the output port of the direct current charging module occurs, and the discharging circuit discharges in a fixed-frequency self-adaptive pulse width mode, the energy consumed on the discharging resistor R1 in a single discharging period is as follows:

taking discharge resistance R1 as k_cThe coefficient de-rating can calculate the effective pulse discharge time t in each discharge period in the constant frequency self-adaptive pulse width pulse discharge control method_on：

Namely, when the fault condition that the external voltage is continuously applied to the output port occurs in the direct current charging module, the discharging time t is even the effective pulse discharging time in a short time_onThe pulse discharge is carried out, the discharge resistor still meets the energy and power derating, and the discharge resistor R1 cannot be damaged.

When the type of the discharge resistor R1 is selected, the resistance R of the discharge resistor R1 and the maximum discharge energy Q bearable by the discharge resistor R1_RmaxAnd a derating coefficient k of the discharge resistor R1_cAll are constant, then effective pulse discharge time t_onAnd a discharge start voltage V_oThe relationship is a power function, and as shown in fig. 6, the higher the discharge start voltage, the shorter the allowable effective pulse discharge time. Meanwhile, it can be seen that even if the discharging circuit is continuously turned on, the voltage at the output port of the dc charging module cannot be quickly lowered to 0V, so that a voltage needs to be set in the discharging control method, and when the discharging start voltage is not greater than the set voltage, discharging is stopped to prevent pulse discharging from circulating indefinitely.

When the current effective pulse discharge time is obtained according to the discharge starting voltage of the current discharge period, there are two implementation manners, which are specifically described below:

the implementation mode is as follows: and directly calculating the current effective pulse discharge time according to a formula.

In this implementation, the current active pulse discharge time is calculated according to equation 1:

wherein, t_onFor the current effective pulse discharge time, R is the resistance of discharge resistor R1, Q_RmaxIs the maximum discharge energy, k, that the discharge resistor R1 can bear_cTo a derating factor, V_oIs the discharge start voltage of the current discharge period.

Furthermore, in one implementation, the controller U1 is a microcontroller with strong computing power, and the software designs the fitting curve, i.e., t_on＝F(V_o) Of variable V_oIs the discharge starting voltage of the detected current discharge period, F is a power function shown in the above formula 1, and the effective pulse discharge time t in the current discharge period is calculated cycle by detecting the discharge starting voltage_on。

The implementation mode two is as follows: the method comprises the following steps of obtaining the current effective pulse discharge time according to the discharge starting voltage of the current discharge period:

wherein, V_oiIs the discharge start voltage in the discharge start voltage array, and the discharge start voltage is selected from the minimum discharge cut-off voltage to the highest voltage required to be discharged, in the embodiment shown in fig. 2, the highest voltage required to be discharged may be the highest voltage at the output port of the dc charging module, t_oniThe effective pulse discharge time is in the effective pulse discharge time array;

step S302, a target discharge starting voltage is determined from a discharge starting voltage array according to the discharge starting voltage of the current discharge period, a target effective pulse discharge time corresponding to the target discharge starting voltage is determined from an effective pulse discharge time array, and the target effective pulse discharge time is used as the current effective pulse discharge time, wherein the determined target discharge starting voltage is higher than the discharge starting voltage of the current discharge period, and the difference value is minimum.

In the second implementation, the power function shown in formula 1 is first discretized into an array sequence, t_oni＝Fn(V_oi) And if i is 1, 2, 3 and …, Fn is a discretization array expression, the software firstly obtains the detected discharge starting voltage, and inquires the effective pulse discharge time in the current discharge period cycle by cycle, so that the maximum effective pulse discharge time can be obtained according to the currently output discharge starting voltage, the output discharge time is shortened, the operation of the formula 1 can be avoided, and the calculation expense of the controller is saved.

When the current effective pulse discharge time is obtained according to the discharge starting voltage of the current discharge period, the difference between the two implementation modes is only reflected in that: the former adopts software to calculate in real time to obtain t_onThe latter uses software table look-up method to obtain t_on. The following description will be given by taking only the second implementation as an example:

the highest voltage that the direct current charging module can output is V_maxMinimum discharge cutoff voltage is V_endCan be at V_maxAnd V_endX points are selected to form a discharge start voltage array { V }_max，V₁，V₂，...，V_xThe corresponding effective pulse discharge time array is { t }_on0，t_on1，t_on2，...，t_onx}. Wherein, t_on0Is as a V_maxEffective pulse discharge time, t, being the discharge initiation voltage_onxIs as a V_xAn effective pulse discharge time which is a discharge start voltage, and has:

V_max＞V₁＞V₂＞…＞V_x＞V_end

t_on0＜t_on1＜t_on2＜…＜t_onx

obtaining an array of effective pulse discharge times t_on0，t_on1，t_on2，...，t_onxAfter the discharge is completed, each discharge start voltage array is required to be countedThe energy and average power discharged from the discharge resistor in each discharge period.

For example, the voltage at the output port of the DC charging module is V_xFor example, the energy Q discharged from the discharging resistor R1 in the discharging period is:

the average power P of the discharge resistor in the discharge cycle is:

during the whole discharging process, the energy Q discharged from the discharging resistor R1 in each discharging period is less than Q_Rmax*k_cThe average power P on the discharge resistor R1 in each discharge period is less than k × P_e*k_c。

When the direct current charging module meets the discharging condition, the controller obtains the discharging initial voltage grade of the output port of the direct current charging module, and selects effective discharging pulse time which is larger than or equal to the current discharging initial voltage as the effective discharging pulse time in the current discharging period so as to ensure that the discharging resistor cannot be damaged due to over power.

In one embodiment, it is assumed that the capacitance C of the filter capacitor C1 is 475uF, the discharge period T is 0.2s, the resistance R of the discharge resistor R1 is 440ohm, and the rated power P of the discharge resistor R1_e12W, the maximum pulse power multiple k which can be borne by the discharge resistor R1 in 200ms is 20, and the derating coefficient k of the discharge resistor R1_c0.8, the maximum discharge energy Q that the discharge resistor R1 can bear_RmaxComprises the following steps:

Q_Rmax＝k·P_e·t＝20*12W*200ms＝48J

in addition, the highest voltage V which can be output by the direct current charging module is set_max750V, minimum discharge cut-off voltage is V_endIs 50V, at V_maxAnd V_endTaking 14 points in between (i.e. interval 50V) to obtain discharge start voltage array {750V, 700V, 650V.., 100V },and calculating a corresponding effective pulse discharge time array {30ms, 34ms, 40ms,. once, 200ms } according to the maximum discharge energy bearable by the discharge resistor R1. Also, in this embodiment, the discharge start voltage versus the effective pulse discharge time is shown in fig. 7.

In addition, when the discharge starting voltage is lower than 291V, the effective pulse discharge time t corresponding to the discharge starting voltage can be obtained by calculating through the formula 1_onWhen the discharge period time T is longer, that is, the discharge start voltage is lower than 291V, even if the pulse discharge is performed at a 100% duty ratio, the discharge resistor R1 is not damaged by excessive power.

In addition, the calculated effective pulse discharge time and discharge starting voltage in the effective pulse discharge time array need to be checked for discharge energy and average power.

The energy discharged from the discharge resistor R1 in the first discharge cycle is:

the average power of the discharge resistor in the first discharge period is:

similarly, it can be verified that the effective pulse discharge time of all discharge cycles in this example meets the de-rating requirement of discharge resistor R1.

If the port voltage of the direct current charging module meeting the discharging condition is 750V, the effective pulse discharging time in the first discharging period is t through searching the discharging initial voltage array_on0Is 30ms, and takes the time as the effective pulse discharge time of the first discharge period. The discharge start voltage at the time of the second discharge period was 649.598V (i.e., the discharge cut-off voltage at the end of the first discharge period), and V was found by searching the discharge start voltage array₃(600V)<649.598V<V₂(650V) according to the principle that the voltage is large, the effective pulse discharge time in the second discharge period is 40ms, and the time is used as the effective pulse discharge time of the second discharge period. In the same way, the effective pulse discharge time corresponding to the discharge starting voltage in each discharge period can be obtained.

The process of discharging the pulse with the port voltage of 620V when the dc charging module satisfies the discharging condition is similar to the above process, and is not described herein again.

By adopting the fixed-frequency adaptive pulse width pulse discharge control method described in this embodiment, discharge control is performed on output port voltages of 750V and 620V, respectively, and voltage waveforms of the output ports of the dc charging module are shown in fig. 8.

By adopting the pulse discharge control method of the fixed-frequency self-adaptive pulse width, the effective pulse discharge time in the current discharge period can be obtained by searching the discharge initial voltage array and the effective pulse discharge time array (or calculating in real time) according to the discharge initial voltage of the output port of the direct-current charging module in each discharge period.

Regarding step S30, in an alternative embodiment, step S30 specifically includes: and acquiring the current discharge period time according to the discharge starting voltage of the current discharge period, and generating a pulse signal of the current discharge period according to the preset effective pulse discharge time and the acquired current discharge period time. In this embodiment, the effective pulse discharge time t_onCan be designed according to the worst working condition of the maximum voltage output by the direct current charging module, namely, the effective pulse discharge time t_onAnd is fixed. The discharge period time T is set according to the voltage at the output port of the dc charging module, that is, the discharge control method in this embodiment is a pulse discharge control method with a fixed pulse width adaptive period. In particular, by T ═ f (V)_o) Obtaining and discharging an initial voltage V_oAnd corresponding discharge cycle time is adopted, so that the purpose of quickly discharging the port voltages of different levels is achieved.

By implementing the technical scheme of the embodiment, the reliability of the discharge circuit is ensured, and meanwhile, the voltage of the output port can be released to be lower than the set voltage in the shortest time. Meanwhile, the discharge starting voltage in each discharge period is detected in real time, and the discharge period time is updated in real time, so that the method has better adaptability.

Referring to fig. 2, if the capacitance of the filter capacitor C1 is C, the maximum voltage at the output port of the dc charging module is V_maxThe resistance value of the discharge resistor R1 is R, and the rated power of the discharge resistor R1 is P_eAccording to FIG. 5, the maximum discharge energy that can be borne by the discharge resistor R1 is Q_RmaxThe derating coefficient of the discharge resistance is k_c. Considering that the highest external voltage V may occur in the DC charging module_maxThe fault condition continuously applied to the output port, in the pulse discharge control method with fixed pulse width self-adapting period, it is necessary to ensure that the discharge resistor R1 is not damaged in each discharge period when the fault occurs. If a fault condition that external high voltage is continuously applied to the output port of the direct current charging module occurs, and the discharging circuit discharges in a fixed pulse width mode, the energy consumed on the discharging resistor R1 in a single discharging period is constant:

the discharge period time T at this time is required to ensure that the average power across the resistor meets the de-rating requirement. Taking the maximum pulse power multiple which can be borne by the discharge resistor in the discharge period as k, the following steps are provided:

that is to say that the first and second electrodes,

when the current discharge cycle time is obtained according to the discharge start voltage of the current discharge cycle, there are two implementation manners, which are specifically described below:

the implementation mode is as follows: the current discharge cycle time is calculated directly according to a formula.

In this implementation, the current discharge cycle time is calculated according to equation 2:

wherein T is the current discharge cycle time, V_oIs the discharge start voltage of the current discharge cycle, R is the resistance of the discharge resistor R1, P_eRated power, t, of discharge resistor R1_onEffective pulse discharge time, k_cFor the derating coefficient, k is the maximum pulse power multiple that can be borne by the discharge resistor in the predetermined discharge period, and it should be noted here that, when k is determined, a discharge period time is estimated, a corresponding k value is determined according to the estimated discharge period time, and then the estimated discharge period time and the corresponding k value are continuously corrected through the calculation of the energy and the average power discharged from the discharge resistor in the discharge period, so that the estimated discharge period time is closest to the discharge period time calculated by formula 2.

Furthermore, in one implementation, the controller U1 is a microcontroller with high computing power, and the fitting curve is designed by software, i.e., T ═ F (V)_o) Of variable V_oThe discharge starting voltage of the detected current discharge period is F is a power function shown in the formula 2, and the current discharge period time is calculated cycle by detecting the discharge starting voltage;

the implementation mode two is as follows: obtaining the current discharge period time according to the discharge starting voltage of the current discharge period, which specifically comprises the following steps:

step S303, pre-storing a discharge starting voltage array and a discharge period time array, wherein the discharge starting voltage in the discharge starting voltage array and the discharge period time in the discharge period time array satisfy the following relationship:

wherein, V_oiThe discharge start voltage is selected from a minimum discharge cut-off voltage to a maximum voltage required for discharge, and in the embodiment shown in FIG. 2, the maximum voltage required for discharge may be the DC charging moduleMaximum voltage at output port, T_iIs the discharge cycle time in the discharge cycle time array;

step S304, determining a target discharge starting voltage from a discharge starting voltage array according to the discharge starting voltage of the current discharge period, determining a target discharge period time corresponding to the target discharge starting voltage from a discharge period time array, and taking the target discharge period time as the current discharge period time, wherein the determined target discharge starting voltage is higher than the discharge starting voltage of the current discharge period, and the difference is minimum.

In the second implementation mode, the power function curve shown in formula 2 is first discretized into an array sequence, T_i＝Fn(V_oi) When the discharge starting voltage is detected, the software searches the discharge period time corresponding to the current discharge period cycle by cycle, namely, i is 1, 2, 3 and …, and Fn is a discretization array expression; and the operation of formula 2 can be avoided, and the calculation overhead of the controller is saved.

When the current discharge cycle time is obtained according to the discharge starting voltage of the current discharge cycle, the difference between the two implementation manners is only reflected in that: the former adopts software to calculate in real time to obtain T, and the latter adopts a software table look-up method to obtain T, which is not described in detail hereinafter, and the following description only takes the implementation mode two as an example:

the highest voltage that the direct current charging module can output is V_maxMinimum discharge cutoff voltage is V_endCan be at V_maxAnd V_endX points are selected to form an array { V } of discharge start voltages_max，V₁，V₂，...，V_xThe corresponding discharge period time array is { T }₀，T₁，T₂，...，T_x}. Wherein, T₀Is as a V_maxDischarge period time, T, being the discharge starting voltage_xIs as a V_xA discharge cycle time which is a discharge start voltage, and having:

V_max＞V₁＞V₂＞…＞V_x＞V_end

T₀＞T₁＞T₂＞…＞T_x

thus, a pulse discharge period time array { T } corresponding to the discharge start voltage array is obtained₀，T₁，T₂，...，T_x}. Then, the corresponding discharge starting voltage array is needed to calculate the energy and the average power discharged from the discharge resistor in each discharge period.

the average power P of the discharge resistor in the discharge cycle is:

during the whole discharging process, the energy and the average power discharged from the discharging resistor R1 in each discharging period both need to meet the derating requirement.

When the direct current charging module meets the discharging condition, the controller obtains the discharging initial voltage grade of the output port of the direct current charging module, and selects the discharging period time which is larger than or equal to the discharging period time corresponding to the current discharging initial voltage as the discharging period time of the pulse discharging so as to ensure that the discharging resistor cannot be damaged due to over power.

In an embodiment, assuming that the capacitance C of the filter capacitor C1 on the output side of the dc charging module is 475uF, the resistance R of the discharging resistor R1 is 440ohm, and the rated power P of the discharging resistor R1 is P_e12W, the derating coefficient k of the discharge resistor R1_c0.8, the maximum pulse power multiple k which can be borne by the resistor R in 200ms is 20 in the initial pick-and-place process, and the maximum discharge energy Q which can be borne by the resistor in the discharging process_RmaxComprises the following steps:

Q_Rmax＝k·P_e·t＝20*12W*200ms＝48J

effective pulse discharge time t in pulse discharge period is designed according to the worst working condition of the maximum voltage output by the direct current charging module_onThen, there are:

in the fixed-pulse-width adaptive-period pulse discharge control method of this embodiment, the effective pulse discharge time is designed to be 30ms, and on this basis, discharge period time arrays corresponding to the discharge start voltage arrays one to one are designed.

In addition, the highest voltage V which can be output by the direct current charging module is set_max750V, minimum pulse discharge cut-off voltage is V_endIs 50V, at V_maxAnd V_end14 points (namely, the interval of 50V) are taken to obtain a discharge starting voltage array {750V, 700V, 650V.., 100V }, and a corresponding discharge cycle time array {200ms, 174ms, 150 ms.., 30ms } is obtained by calculation according to the maximum discharge energy bearable by the discharge resistor R1. Also, in this embodiment, the discharge start voltage versus discharge cycle time is shown in fig. 9.

In addition, when the discharge start voltage is lower than 291V, the calculated discharge cycle time is already smaller than the effective pulse discharge time, that is, when the discharge start voltage is lower than 291V, even if pulse discharge is performed at a 100% duty ratio, the discharge resistor is not over-powered and damaged.

At this time, the average power of the discharge cycle time and the discharge start voltage in the calculated discharge cycle time array is also calculated. Average power P across discharge resistor R1 during discharge cycle₀Comprises the following steps:

similarly, it can be verified that when the discharge start voltage is higher than 291V, the calculated average power of the discharge resistor in the discharge cycle time is 166.691W, and the average power meets the power derating requirement of the discharge resistor R1.

If the port voltage is 750V when the module meets the discharge condition, the initial discharge period time T can be obtained by searching the discharge initial voltage array₀Is 200ms, and takes the time as the first discharge period time. The discharge start voltage at the time of the second discharge period was 649.598V (i.e., the discharge cut-off voltage at the end of the first discharge period), and V was found by searching the discharge start voltage array₃(600V)<649.598V<V₂(650V), the second pulse discharge cycle time is 150ms as the voltage increases, and this time is used as the second discharge cycle time. Similarly, the discharge period time corresponding to the discharge start voltage can be obtained.

With the fixed-pulse-width adaptive-period pulse discharge control method according to this embodiment, the voltage waveform of the output port when discharge control is performed for output port voltages of 750V and 620V, respectively, is shown in fig. 10.

By adopting the pulse discharge control method with the fixed pulse width self-adaptive period, on the premise that the effective pulse discharge time is fixed, the discharge period time of the current discharge period can be obtained by searching the discharge initial voltage array and the discharge period time array (or calculating in real time) according to the discharge initial voltage at the beginning of each discharge period, so that the average power of the discharge resistors in the discharge period is equal, the reliability is ensured, the utilization rate of the discharge resistors is improved, and the voltage of an output port is reduced to be below the safety voltage in the shortest time.

Regarding step S40, in an alternative embodiment, with reference to fig. 11, step S40 specifically includes the following steps:

s402, starting timing by a timer;

s405, outputting a low level to control the switch tube to be turned off;

s407, resetting a timer;

s409, setting a fault flag bit;

and S410, stopping discharging.

Regarding the preset values in step S408, it should be noted that:

when the single fault that the external high voltage is continuously applied to the output port of the direct current charging module occurs, even if the discharging circuit of the output port passes through a discharging cycle, the voltage of the output port of the direct current charging module still keeps unchanged, and the expected voltage drop of the output port does not occur, the situation that the single fault that the external high voltage is continuously applied to the output port of the direct current charging module at the moment can be judged, and the action of the discharging circuit is forbidden at the moment.

When the output port of the DC charging module is normally discharged, the discharge time t is in the effective pulse_onIn the method, the voltage of the output port of the dc charging module is gradually reduced from V0 (discharge start voltage) to V1 (discharge cut-off voltage), and the two satisfy the following relation:

as can be seen from the above formula, the discharge cut-off voltage and the discharge are generated during the discharge periodRatio of initial voltage to effective pulse discharge time t_onRelated, t_onThe longer the time, the smaller the ratio of the discharge cut-off voltage to the discharge start voltage.

For the pulse signal with fixed frequency and self-adaptive pulse width, the effective pulse discharge time t in the first discharge period_onIn the shortest time, the ratio of the discharge pulse cut-off voltage to the discharge pulse start voltage is also the largest, for example, in the above embodiment, the ratio of the discharge cut-off voltage to the discharge start voltage in the first discharge period is 0.866, and the ratio is gradually decreased as the number of discharge periods increases. Therefore, in this case, the preset value of the discharge failure detection may be set according to the maximum value of the ratio of the discharge cut-off voltage to the discharge start voltage during discharge, and may be set to 0.9, for example.

For pulse signals with fixed pulse width and self-adaptive period, the discharge time t is shortened due to effective pulse_onFixed, e.g. effective pulse discharge time t in the above-described embodiments_onThe discharge start voltage is fixed to be 30ms, so that the ratio of the discharge cut-off voltage to the discharge start voltage in each discharge period is also fixed to be 0.866 in the whole discharge process, and therefore, in this case, the preset value for detecting the discharge fault can be set to be 0.866 by directly referring to the ratio of the discharge cut-off voltage to the discharge start voltage.

If k is_fAnd detecting the preset value of the set discharge fault. At the end of each discharge period, comparing the discharge cut-off voltage and the discharge start voltage in the discharge period, if the discharge cut-off voltage is greater than k of the discharge start voltage_fWhen the voltage is doubled, the single fault that the external high voltage is continuously applied to the output port occurs in the direct current charging module at the moment can be judged, namely the discharge failure fault occurs in the direct current charging module, the relevant mark is set, and the pulse discharge of the next discharge period is forbidden. In addition, it should be noted that the fault detection logic is executed in a nested manner in the discharge control.

In one embodiment, if the circuit parameters shown in the above embodiments are adopted, when the dc charging module fails to apply the external high voltage to the output port continuously, the first effective pulse discharge time is passedt_onAnd then, the voltage of the output port of the direct current charging module still keeps 750V unchanged, and in the first effective pulse discharging time, the energy discharged from the discharging resistor R1 is as follows:

derating coefficient k of pick-and-place resistor R1_cAverage power P across discharge resistor R1, 0.8₁Comprises the following steps:

even if the direct current charging module has a single fault that external high voltage is continuously applied, when the direct current charging module performs discharge control on the voltage at the output port of the direct current charging module by using the discharge control method of the above embodiment, the derating requirement of the discharge resistor R1 is still met in the first discharge period, so that the discharge resistor has no risk as long as the occurrence of the fault can be judged in time.

The fault detection method of the embodiment is suitable for all occasions adopting pulse discharge control, can effectively improve the reliability of a pulse discharge circuit, and avoids the discharge resistor from being damaged due to overheating.

In addition, the application of the discharge control method is not limited to the direct current charging module, and the discharge control method is applicable to the application of filter capacitor discharge in the field.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A discharge control method is used for controlling discharge of voltage on a filter capacitor through a discharge resistor and a switch tube, wherein the discharge resistor is connected with the switch tube in series and then connected with the filter capacitor in parallel, and the discharge control method is characterized by comprising the following steps:

step S30, generating a pulse signal of the current discharge period according to the discharge starting voltage of the current discharge period, wherein the generated pulse signal enables the discharge energy of the discharge resistor in the effective pulse discharge time and the average power of the discharge resistor in the discharge period to meet the following conditions: the discharge energy of the discharge resistor in the effective pulse discharge time does not exceed the maximum bearing capacity of the discharge resistor; the average power of the discharge resistor in the discharge period does not exceed the pulse power de-rating of the discharge resistor;

s40, outputting the pulse signal to the switching tube to control the on-off of the switching tube so as to realize the discharge function of the current discharge period;

wherein the step S30 includes:

acquiring current discharge cycle time according to the discharge starting voltage of the current discharge cycle, and generating a pulse signal of the current discharge cycle according to preset effective pulse discharge time and the acquired current discharge cycle time;

moreover, obtaining the current discharge cycle time according to the discharge starting voltage of the current discharge cycle specifically includes:

calculating the current discharge cycle time according to equation 2:

wherein T is the current discharge cycle time, V_oIs the discharge starting voltage of the current discharge period, R is the resistance value of the discharge resistor, P_eIs the rated power of the discharge resistor, t_onEffective pulse discharge time, k_cFor derating coefficient, k is the maximum pulse power multiple which can be borne by the discharge resistor in a predetermined discharge period;

or,

obtaining the current discharge cycle time according to the discharge starting voltage of the current discharge cycle, specifically comprising:

2. The discharge control method according to claim 1, wherein the step S30 includes:

3. The discharge control method according to claim 2, wherein obtaining the current effective pulse discharge time according to the discharge start voltage of the current discharge cycle specifically includes:

calculating the current effective pulse discharge time according to equation 1:

wherein, t_onFor the current effective pulse discharge time, R is the resistance of the discharge resistor, Q_RmaxIs the maximum discharge energy, k, sustainable by the discharge resistor_cTo a derating factor, V_oIs the discharge start voltage of the current discharge period.

4. The discharge control method according to claim 2, wherein obtaining the current effective pulse discharge time according to the discharge start voltage of the current discharge cycle specifically includes:

5. The discharge control method according to any one of claims 1 to 4, wherein the step S40 includes:

s402, starting timing by a timer;

s405, outputting a low level to control the switch tube to be turned off;

s407, resetting a timer;

s409, setting the fault flag bit;

and S410, stopping discharging.

6. The discharge control method according to claim 1, wherein in the step S30, the generated pulse signal enables both a discharge energy of a discharge resistor in a discharge period of the effective pulse and an average power of the discharge resistor in a discharge period to satisfy a derating requirement of the discharge resistor, specifically:

7. A discharge circuit is connected with a filter capacitor and is characterized by comprising a discharge resistor, a switch tube and a controller, wherein a first end of the discharge resistor is connected with a first end of the filter capacitor, a second end of the discharge resistor is connected with a first end of the switch tube, and a second end of the switch tube is connected with a second end of the filter capacitor;

the controller is configured to, when it is detected that a discharge condition is met, obtain a discharge start voltage of a current discharge cycle at the start of each discharge cycle, generate a pulse signal of the current discharge cycle according to the discharge start voltage if the discharge start voltage is greater than a set voltage, and output the pulse signal to the switching tube to control on/off of the switching tube, so as to implement a discharge function of the current discharge cycle, where the generated pulse signal enables discharge energy of the discharge resistor within an effective pulse discharge time and average power of the discharge resistor within the discharge cycle to meet the following conditions: the discharge energy of the discharge resistor in the effective pulse discharge time does not exceed the maximum bearing capacity of the discharge resistor; the average power of the discharge resistor in the discharge period does not exceed the pulse power de-rating of the discharge resistor;

wherein, according to the discharge starting voltage, generating the pulse signal of the current discharge period comprises:

calculating the current discharge cycle time according to equation 2:

or,

the method comprises the following steps of storing a discharge starting voltage array and a discharge cycle time array in advance, wherein the discharge starting voltage in the discharge starting voltage array and the discharge cycle time in the discharge cycle time array satisfy the following relations:

determining a target discharge starting voltage from the discharge starting voltage array according to the discharge starting voltage of the current discharge period, determining a target discharge period time corresponding to the target discharge starting voltage from the discharge period time array, and taking the target discharge period time as the current discharge period time, wherein the determined target discharge starting voltage is higher than the discharge starting voltage of the current discharge period, and the difference is minimum.

8. The discharge circuit of claim 7,

the controller is further configured to obtain a discharge cut-off voltage of the current discharge cycle when each discharge cycle is ended, and if it is determined that a ratio of the discharge cut-off voltage of the current discharge cycle to a discharge start voltage of the current discharge cycle is greater than a preset value, a single fault in which an external high voltage is continuously applied to the output port occurs, and discharge is stopped.