CN115483858B - Dead zone compensation method and system based on current zero crossing region variable PI control - Google Patents

Abstract

The invention discloses a dead zone compensation method and a dead zone compensation system based on current zero crossing region variable PI control, and belongs to the field of permanent magnet synchronous motor control. The variable PI control dead zone compensation method based on the current zero crossing region only needs to additionally carry out segmentation judgment and PI parameter adjustment and selection, and when a motor enters or exits from the current zero crossing region, smooth transition of an output voltage vector before and after region switching is realized through the linearly-changed PI parameter value. Compared with the traditional dead zone compensation method, the dead zone compensation method based on the current zero crossing region variable PI control can realize effective compensation of zero current clamping phenomenon under the condition that a current filter is not additionally added.

Description

A dead zone compensation method and system based on current zero-crossing region variable PI control

Technical Field

The present invention belongs to the field of permanent magnet synchronous motor control, and more specifically, relates to a dead zone compensation method and system based on current zero-crossing region variable PI control.

Background Art

In a two-level voltage source inverter, each phase controls the output of pulse voltage through the on-off control of the upper and lower power switch tubes. Due to the asymmetric on-off delay of power devices, if the upper and lower power tubes are driven directly according to the ideal switch pulse, the bridge arm will be short-circuited. In order to avoid the upper and lower power tubes from being directly turned on, it is necessary to insert a delay opening time based on the original switch pulse to leave enough safety margin for the upper and lower tube switching process. This inserted delay time is called dead time. During the dead time, the upper and lower power switch tubes remain in the off state, and the bridge arm current continues through the diode. At this time, the output voltage polarity is determined by the output current polarity rather than the voltage command, which will cause the output voltage and current to be distorted. The effect of voltage and current distortion caused by the dead time is called the dead time effect.

The distorted voltage pulses generated by the dead zone effect will cause the voltage amplitude and phase to be distorted at the same time, thereby introducing current harmonics and causing motor torque pulsation. Therefore, compensation for the dead zone effect is required in actual control. Dead zone compensation methods can be divided into compensation methods based on model observation and compensation methods based on principle calculation. The model observation-based method combines the motor model and the observer model to estimate the dead zone error voltage and compensate for it. This method has high requirements for sampling and control delays, and the algorithm implementation is generally more complex; the dead zone compensation method based on principle calculation derives the dead zone distortion voltage or distortion pulse width according to the dead zone error principle and then compensates. This method is relatively simple to implement, but its compensation effect is very dependent on the accurate judgment of current polarity. Since current sampling noise and current ripple are easy to cause current polarity misjudgment in the zero current region, which leads to the occurrence of miscompensation, it will further increase current harmonics.

When the motor runs at low speed, the effective action time of the voltage vector is often short, and the error voltage generated by the dead zone effect will dominate. Therefore, when the motor runs in the zero current area, the motor phase voltage will be dominated by the dead zone error voltage. At this time, the phase voltage is clamped to the no-load back electromotive force value of the phase motor, which will keep the zero-crossing phase current at around zero current until the effective voltage vector regains the dominant position of the output voltage and the zero-crossing phase current can get rid of the clamping state. This phenomenon is called zero current clamping. The zero current clamping phenomenon will cause serious distortion of the voltage synthesis vector, causing the other phase currents to be distorted as well. Therefore, the dead zone effect is often more serious when the motor runs at low speed. During the zero current clamping period, the polarity of the zero-crossing phase current will change many times due to the freewheeling phenomenon of the dead zone effect. At this time, the direct current polarity compensation method will be miscompensated in the zero current area due to inaccurate polarity judgment. The miscompensated voltage will make the dead zone effect in the zero current area more serious.

In order to solve the problem of the difficulty in accurately judging the current polarity, there are two common methods: current filtering and leading power factor angle judgment. Current filtering often leads to phase deviation. In order to achieve the filtering effect with low phase delay, a more complex filter is often designed. The leading power factor angle method observes the motor power factor angle or uses the command current instead of the actual current as the basis for polarity judgment. This method also needs to take measures to improve the sampling accuracy against the influence of current sampling noise, which also increases the complexity of the algorithm. And when the zero current clamping phenomenon of the motor is more prominent, the error voltage in the zero-crossing area of the motor current will mainly depend on the difference between the motor reverse potential and the command voltage, which will result in that even if the current polarity judgment method is improved, a better compensation effect cannot be achieved. Therefore, it is of great practical significance to propose a simple method that can effectively compensate for the dead zone of the zero current clamping phenomenon of the motor.

Summary of the invention

In view of the defects of the prior art, the purpose of the present invention is to provide a dead zone compensation method and system based on variable PI control in the current zero-crossing region, aiming to solve the technical problem that conventional dead zone compensation methods of motors have poor compensation effect on zero current clamping phenomenon.

To achieve the above purpose, the present invention provides a dead zone compensation method based on variable PI control in the current zero-crossing region, which can realize the dead zone compensation of the zero current clamping phenomenon without adding additional filtering. The basic idea is: based on the current ripple and sampling error current measured without dead zone compensation as the segmentation basis, the current zero-crossing phase output voltage is compensated by the amplified PI parameters in the current zero-crossing region, thereby realizing effective compensation for the zero current clamping phenomenon.

Based on the above ideas, the dead zone compensation method based on current zero-crossing region variable PI control proposed by the present invention to achieve the purpose of the invention includes:

(1) Run the motor without dead zone compensation, record the zero-crossing current ripple amplitude and the controller sampling noise amplitude during operation, and set the dead zone compensation segmentation threshold I _threshold accordingly.

(2) The dead zone error voltage vector amplitude is calculated based on the measured three-phase current values, and then the dead zone compensation voltage value U _com is calculated based on the working conditions.

(3) Compare the minimum current amplitude of the three-phase current with I _threshold , apply different current loop PI parameter values according to the segmentation results, and add the current loop output voltage value to the dead zone compensation voltage value calculated in step (2) to obtain the output voltage vector, and then obtain the three-phase duty cycle signal to be output through SVPWM modulation.

(4) The three-phase duty cycle signal is updated synchronously with the carrier cycle, and the compensated voltage pulse signal with dead zone is output to realize the dead zone compensation control of the motor.

Furthermore, the step (1) comprises:

The zero-crossing current ripple amplitude increases with the increase of load and speed, and the zero-crossing current ripple amplitude can be obtained under rated working conditions. The controller current sampling noise amplitude can be determined by comparing the error between the controller current sampling value and the oscilloscope current probe calibration value in the voltage positioning mode.

Furthermore, the step (2) comprises:

(201) In each sampling period, the dead zone error voltage _Uerr is calculated according to the polarity of the three-phase current, and then the minimum amplitude of the three-phase current value is compared with the compensation segmentation threshold _Ithreshold . If it is less than or equal to _Ithreshold , the motor is running in the current zero-crossing area, and step 202 is executed. Otherwise, the motor is running in the non-current zero-crossing area, and step 203 is executed.

(202) According to the proportional relationship between the minimum amplitude of the three-phase current values and I _threshold , the calculated U _err is proportionally reduced and multiplied by negative 1 to obtain the voltage vector to be compensated U _com and execute step 204.

(203) Multiply the calculated U _err by negative 1 to obtain the voltage vector to be compensated U _com and execute step 204.

(204) Decompose the U _com voltage vector calculated in step 202 or 203 to the αβ axis to obtain U _comα and U _comβ .

Furthermore, the step (3) comprises:

(301) According to the comparison result of 201, if the motor is located in the zero current region, execute step 302, otherwise execute step 303.

(302) According to the proportional relationship between the minimum current amplitude and I _threshold , the linearly amplified current loop proportional parameters k _pdzero and k _pqzero are calculated, and under the condition of sharing the dq axis integral output value, the unamplified PI parameters k _pd and k _pq and the amplified PI parameters k _pdzero and k _pqzero are substituted respectively to calculate the current loop output voltage values U _d1 , U _q1 , U _d2 , and U _q2 respectively, and execute step 304.

(303) Using the unamplified proportional parameters k _pd , k _pq as the current loop proportional parameter values, the output values U _d , U _q are calculated through the current loop PI link and step 305 is executed.

(304) The current loop output voltage values U _d1 , U _q1 , U _d2 , and U _q2 are transformed into dq-αβ coordinates and then added to U _comα and U _comβ calculated in step (2) to obtain the voltage vector to be output. After SVPWM modulation, the two sets of current loop output values are respectively calculated to obtain the three-phase duty ratios duty _x1 (x＝a, b, c) and duty _x2 (x＝a, b, c). According to the phase corresponding to the zero-crossing current determined in step 201, duty _x1 is assigned to the two non-zero-crossing phases, and duty _x2 is assigned to the zero-crossing phase to obtain the three-phase duty ratio duty _x (x＝a, b, c) to be output.

(305) After the dq-αβ coordinate transformation, the current loop output values _Ud and _Uq are added to _{the Ucomα} and _Ucomβ calculated in step (2) to obtain the output voltage vector. After SVPWM modulation, the current loop output values are calculated to obtain the three-phase duty ratio duty _x (x＝a, b, c).

The present invention proposes a variable PI dead zone compensation method with segmented compensation, which uses the motor current ripple and sampling error current measured when not compensated as segmentation basis, and divides the compensation interval into a current zero-crossing region and a non-current zero-crossing region. The current loop PI parameter value is amplified in the current zero-crossing region, and the amplified current regulator output is only effective for the zero-crossing phase voltage, and does not affect the voltage output of the other two phases. The output voltage is calculated using the unamplified PI parameter value in the non-current zero-crossing region. On the other hand, in the non-current zero-crossing region, the dead zone compensation voltage is directly calculated according to the current polarity judgment, while in the current zero-crossing region, the dead zone compensation voltage decreases linearly as the current decreases. The present invention realizes a dead zone compensation method based on variable PI control in the current zero-crossing region, which can quickly increase the current zero-crossing phase effective voltage output value by increasing the current loop PI value, so that the current can get rid of the zero current clamping region faster, thereby reducing the output voltage distortion caused by the zero current clamping effect, and realizing effective compensation for the zero current clamping phenomenon without adding an additional filter.

Another aspect of the present invention provides a dead zone compensation system based on current zero-crossing region variable PI control, comprising: a computer-readable storage medium and a processor;

The computer-readable storage medium is used to store executable instructions;

The processor is used to read the executable instructions stored in the computer-readable storage medium to execute the above-mentioned dead zone compensation method based on current zero-crossing region variable PI control.

Compared with the prior art, the above technical solution conceived by the present invention can achieve the following beneficial effects:

(1) Compared with the traditional dead zone compensation method, the dead zone compensation method based on variable PI control in the current zero-crossing region proposed in the present invention can effectively compensate for the zero current clamping phenomenon without adding an additional current filter.

(2) When the motor enters or exits the current zero-crossing region, a smooth transition of the output voltage vector before and after the region switching is achieved through the linear change of the PI parameter value.

(3) The dead zone compensation method based on variable PI control in the current zero-crossing region proposed in the present invention only requires additional segmented judgment and PI parameter adjustment and selection, and is suitable for implementation in a low-cost control chip.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of a dead zone compensation method based on variable PI control in the current zero-crossing region.

FIG2 is a schematic diagram of output voltage pulse distortion caused by the dead zone effect, where (a) is the output voltage pulse when the bridge arm current is greater than 0, and (b) is the output voltage pulse when the bridge arm current is less than 0.

FIG3 is a schematic diagram of segmented PI parameter adjustment.

FIG4 is a flow chart of duty cycle calculation of the dead zone compensation method.

FIG5 is a block diagram of a dead zone compensation control system.

Figure 6 is a schematic diagram of the phase current compensation effect of a low-inductance permanent magnet synchronous motor when running at a low speed of 30Hz.

DETAILED DESCRIPTION

In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

The embodiment of the present invention provides a dead zone compensation method based on current zero-crossing region variable PI control, and the compensation method flow chart is shown in FIG1 , which specifically includes:

Step 1: Set the switching frequency f _sw , bus voltage V _dc and dead time t _d according to system requirements, and run the motor without dead zone compensation. At this time, the output voltage distortion caused by the dead zone effect is shown in Figure 2. When the current flows out of the inverter, the voltage pulse distortion is shown in Figure 2 (a); when the current flows into the inverter, the voltage pulse distortion is shown in Figure 2 (b). Figure 2 only shows a dead zone generation method. This method can also effectively compensate for other types of dead zones. Record the zero-crossing current ripple amplitude I _ripple . Position the motor in the voltage positioning mode, and determine the sampling noise amplitude I _noise by comparing the controller current sampling value with the current probe recording value. Determine the dead zone compensation segmentation threshold I _threshold based on the measured I _ripple and I _noise . The purpose of selecting I _threshold is to prevent the voltage vector from being incorrectly compensated in the zero current area. Its value should meet the following requirements:

I _threshold >I _ripple +I _noise

Step 2: Calculate the dead zone error voltage vector U _err , the amplitude of U _err is denoted as |U _err |, and T _s is the carrier period:

Record the dead zone error time t _err , the power device turn-on time t _on , and the power device turn-off time t _off . The power device turn-on time includes the turn-on delay time and the rise time, and the power device turn-off time includes the turn-off delay time and the fall time. When only considering the impact of the asymmetric rise and fall time of the power device on t _err , t _err is expressed as:

t _err = t _d + t _on - t _off

From this |U _err | we can calculate:

The U _err angle is determined by the polarity of the three-phase current. It is defined that the current polarity is positive when the current flows into the motor. When the phase current polarity is positive, it is represented by the number 1, and when it is negative, it is represented by the number 0. The current polarity phase sequence is arranged in the abc phase sequence. According to the polarity of the three-phase current, the voltage component of U _err in the αβ axis coordinate system can be calculated, as shown in Table 1.

Table 1 Dead zone error voltage vector calculation

Step 3: Calculate the minimum amplitude of the three-phase current according to the three-phase current values I _a I _b I _c , and define the phase current corresponding to the minimum as I _min . Divide the compensation interval into segments according to the comparison result of I _min and I _threshold . When |I _min |＜I _threshold , the motor is running in the current zero-crossing area, otherwise it is considered to be running in the non-current zero-crossing area.

When the motor runs in the current zero-crossing region, in order to avoid miscompensation, according to the proportional relationship between the minimum current amplitude and I _threshold , the U _err vector calculated in step 2 is linearly scaled down and multiplied by negative 1 to obtain the voltage vector to be compensated U _com :

When the motor is running in the non-current zero-crossing region, U _err is multiplied by negative 1 to obtain U _com :

U _com = -U _err

After U _com is calculated, if the motor is running in the current zero-crossing region, execute step 4; otherwise, execute step 5.

Step 4: The original PI parameters of the current loop are recorded as k _pd , k _id , k _pq and k _iq , respectively. k _pd is the d-axis current loop proportional parameter; k _id is the d-axis current loop integral parameter; k _pq is the q-axis current loop proportional parameter; k _iq is the q-axis current loop integral parameter. When the motor is running in the current zero-crossing region, the current loop proportional parameter is amplified, and the amplified dq-axis proportional parameters are recorded as k _pdzero and k _pqzero . In order to avoid sudden changes in the current loop output value when switching regions, k _pdzero and k _pqzero are set to change linearly. The proportional parameter amplification factor is recorded as k _pscale . Excessive proportional parameter values will cause the motor system to become unstable. In the program, the upper limit saturation value of the proportional parameter can be set to avoid excessive proportional parameter values.

The errors between the dq axis current loop input command and the actual input value are recorded as I _derr and I _qerr respectively, and the dq axis current loop integral output values are defined as Int _d and Int _q respectively. Under the conditions of sharing Int _d and Int _q, the dq axis proportional parameters before and after the increase are used to calculate the current loop output values U _d1 , U _q1 , U _d2 , and U _q2 respectively, and step 6 is executed.

Step 5: When the motor runs in the non-current zero-crossing region, the PI parameters remain unchanged, and the output values U _d and U _q are obtained through current loop calculation and step 7 is executed. Finally, the proportional parameter value in the dq axis PI parameter value changes as shown in FIG3 .

Step 6: After dq-αβ coordinate transformation, U _d1 , U _q1 , U _d2 , and U _q2 are added to U _com calculated in step 4. After SVPWM modulation, the three-phase duty ratios duty _x1 (x＝a, b, c) and duty _x2 (x＝a, b, c) can be calculated respectively. Duty _x1 is assigned to the two non-current zero-crossing phases, and duty _x2 is assigned to the current zero-crossing phase to obtain the three-phase duty ratio duty _x (x＝a, b, c) to be output and execute step 8. The duty ratio assignment process represented by step 6 is shown in Figure 4.

Step 7: U _d and U _q are transformed into dq-αβ coordinates and added to U _com calculated in step 4. After SVPWM modulation, the three-phase duty ratio duty _x (x=a, b, c) can be calculated and step 8 is executed.

Step 8: Bring the three-phase duty cycle duty _x (x＝a, b, c) into the dead zone module to generate a three-phase complementary PWM signal with dead zone output.

To better illustrate the dead zone compensation effect, the present invention further provides an embodiment:

Take a three-phase low-inductance permanent magnet synchronous motor as an example, the number of motor pole pairs is 6, L _d = 42μH, L _q = 51μH, the dead time is set to 2us, the switching frequency is set to 20kHz, and the DC bus voltage is set to 300V. The effects before and after dead zone compensation are simulated in MATLAB/Simulink software, and the dead zone compensation control system block diagram is built as shown in Figure 5.

Figure 6 shows the phase current compensation effect of the low-inductance permanent magnet synchronous motor at low speed 30Hz. Without dead zone compensation, the simulated current THD is 11.18% when the motor is running at 300rpm and the load current is 166A effective value, of which the proportion of the 5th harmonic is 9.71% and the proportion of the 7th harmonic is 6.40%. The 5th and 7th harmonic components caused by the dead zone effect are the main sources of current harmonics. Assuming _kpscale is 30 and _Ithreshold is 10A, when the dead zone compensation method proposed in this patent is used, the simulated current THD under the same working condition is reduced to 1.86%, of which the proportion of the 5th harmonic is 0.33% and the proportion of the 7th harmonic is 0.90%, the zero current clamping time is greatly shortened, and the 5th and 7th harmonics caused by the dead zone are well suppressed. The simulation results prove that the dead zone compensation method proposed in this patent can effectively compensate for the zero current clamping phenomenon, thereby reducing current ripple distortion and improving current quality.

It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims (3)

1. The dead zone compensation method based on the current zero crossing region variable PI control is characterized by comprising the following steps of:

(1) Setting a dead zone compensation segmentation threshold I _threshold according to the zero crossing point current ripple amplitude and the sampling noise amplitude when the motor operates; the dead zone compensation segmentation threshold I _threshold has a value satisfying:

I_threshold＞I_ripple+I_noise

wherein, I _ripple is zero current ripple amplitude, and I _noise is sampling noise amplitude;

(2) Calculating dead zone error voltage vector amplitude according to the measured three-phase current value, and calculating dead zone compensation voltage value U _com according to working conditions; comprising the following steps:

(201) Each sampling period is calculated according to the polarity of the three-phase current to obtain a dead zone error voltage U _err, then the minimum amplitude of the three-phase current value is compared with a compensation segmentation threshold I _threshold, if the minimum amplitude of the three-phase current value is smaller than or equal to I _threshold, step 202 is executed, otherwise step 203 is executed;

(202) According to the proportional relation between the minimum amplitude value of the three-phase current value and I _threshold, the calculated U _err is scaled down and multiplied by minus 1 to obtain a voltage vector U _com to be compensated, and the step 204 is executed;

(203) Multiplying the calculated U _err by minus 1 to obtain a voltage vector U _com to be compensated and executing step 204;

(204) Decomposing a voltage vector U _com to be compensated to an alpha beta axis to obtain U _comα and U _comβ;

(3) Comparing the minimum current amplitude of the three-phase current value with I _threshold, respectively applying different current loop PI parameter values according to the segmentation result, adding the current loop PI output voltage value and the dead zone compensation voltage value calculated in the step (2) to obtain a voltage vector to be output, and obtaining a three-phase duty ratio signal to be output through SVPWM modulation; comprising the following steps:

(301) According to the comparison result of (201), if the motor is located in the zero current region, executing step 302, otherwise executing step 303;

(302) According to the proportional relation between the minimum amplitude value of the three-phase current value and I _threshold, calculating to obtain a linear amplified current loop proportional parameter k _pdzero、k_pqzero, substituting an unamplified PI parameter k _pd、k_pq and an amplified PI parameter k _pdzero、k_pqzero respectively under the condition of sharing dq axis integral output values, calculating to obtain a current loop output voltage value U _d1、U_q1、U_d2、U_q2 respectively, and executing step 304;

(303) Using the un-amplified proportional parameter k _pd、k_pq as a current loop proportional parameter value, calculating to obtain an output value U _d、U_q through a current loop PI link, and executing step 305;

(304) The current loop output voltage value U _d1、U_q1、U_d2、U_q2 is transformed by dq-alpha beta coordinates and then added with the U _comα and the U _comβ calculated in the step (2) to obtain a voltage vector to be output; after SVPWM modulation, the output values of the two sets of current loops are respectively calculated to obtain a three-phase duty _x1 (x=a, b, c) and a duty _x2 (x=a, b, c); assigning duty _x1 (x=a, b, c) to two non-zero-crossing phases, assigning duty _x2 (x=a, b, c) to zero-crossing phases so as to obtain a duty _x (x=a, b, c) of three phases to be output, bringing the duty _x1 (x=a, b, c) into a dead zone module, and generating three-phase complementary band dead zone PWM signals for output;

(305) The current loop output value U _d、U_q is transformed by dq-alpha beta coordinates and then added with the U _comα and the U _comβ calculated in the step (2) to obtain a voltage vector to be output, the current loop output value is calculated to obtain a three-phase duty _x (x=a, b, c) after SVPWM modulation, and the three-phase duty _x is brought into a dead zone module to generate a three-phase complementary PWM signal output with a dead zone;

(4) And synchronously updating the three-phase duty ratio signals along with the carrier period, and outputting the compensated voltage pulse signals with dead zones to realize dead zone compensation control of the motor.

2. The dead zone compensation method of claim 1 wherein the zero crossing current ripple magnitude is taken at nominal operating conditions.

3. A dead zone compensation system based on current zero crossing region PI control, comprising: a computer readable storage medium and a processor;

The computer-readable storage medium is for storing executable instructions;

the processor is configured to read executable instructions stored in the computer readable storage medium and execute the dead zone compensation method based on current zero crossing region PI control according to claim 1 or 2.