CN112803758A

CN112803758A - Non-isolated high-voltage direct current-direct current converter with fault blocking function and method

Info

Publication number: CN112803758A
Application number: CN202110056024.9A
Authority: CN
Inventors: 刘进军; 陈海宇; 杜思行
Original assignee: Xian Jiaotong University
Current assignee: Xian Jiaotong University
Priority date: 2021-01-15
Filing date: 2021-01-15
Publication date: 2021-05-14
Anticipated expiration: 2041-01-15
Also published as: CN112803758B

Abstract

The invention discloses a non-isolated high-voltage direct current-direct current converter with fault blocking and a method thereof, wherein the converter comprises at least one single-pole converter, and the single-pole converter comprises four sub-module strings, a filter inductor and a series switch string; wherein the filter inductance L₁And a high-voltage side full-bridge sub-module string HVSM, a fault blocking sub-module string BLSM, a middle half-bridge sub-module string MCSM and a filter inductor L₂The low-voltage side full-bridge sub-module strings LVSM are sequentially connected in series to form a series structure; high-voltage side series switch string S_HWith the switching string S in series at the low-voltage side_LOne end of the half-bridge module is respectively connected with a positive point and a negative point of the MCSM in the middle half-bridge sub-module string, and the other end of the half-bridge module string is directly connected to form a half-bridge structure; the middle point of the half-bridge structure is a low-voltage side anode, and the cathode of the low-voltage side full-bridge submodule string is a cathode of the low-voltage side. The converter can effectively reduce the switch required by the system while realizing the DC fault blocking performanceThe number of devices and the capacitance value of the capacitor, thereby reducing the cost and the volume of the system.

Description

Non-isolated high-voltage direct current-direct current converter with fault blocking function and method

Technical Field

The invention relates to the technical field of converters, in particular to a non-isolated high-voltage direct current-direct current converter with fault blocking and a method.

Background

The high-voltage direct current-direct current converter is key equipment for engineering application occasions such as open sea wind power plant access, high-voltage direct current transmission line interconnection and the like. In the existing high-voltage direct current-direct current converter topology, the non-isolated topology is particularly suitable for the interconnection occasion of the high-voltage direct current transmission line due to the advantages of high efficiency and small size. Under the condition that the current high-voltage direct-current circuit breaker is not in commercial use, a high-voltage direct-current-direct-current converter with a direct-current fault blocking function is the key point of research, and the converter with the direct-current fault blocking function has an electric energy conversion function and the capacity of clearing direct-current short-circuit faults. In the existing non-isolated high-voltage direct current-direct current converter topology, the topology with the fault blocking function is few, and the topology with the fault blocking function usually uses a two-phase or three-phase structure to create an alternating current circulating path or maintain the continuity of input and output currents, so that the number of switching devices required by the system and the total capacitance value are increased more, and the system has the problems of high cost and large volume.

Disclosure of Invention

The invention aims to provide a non-isolated high-voltage direct current-direct current converter with a direct current fault blocking function and a method.

In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:

a non-isolated high-voltage direct current-direct current converter with fault blocking comprises at least one single-pole converter, wherein the single-pole converter comprises four sub-module strings, a filter inductor and a series switch string;

the four sub-module strings are a high-voltage side full-bridge sub-module string HVSM, a fault blocking sub-module string BLSM, a middle half-bridge sub-module string MCSM and a low-voltage side full-bridge sub-module string LVSM; the filter inductor comprises a filter inductor L₁Filter inductor L₂(ii) a The series switch string comprises a high-voltage side series switch string S_HAnd a low-side series switch string S_L；

Filter inductance L₁And a high-side full-bridge sub-module string HVSM, a fault blocking sub-module string BLSM,Middle half-bridge submodule string MCSM and filter inductor L₂The low-voltage side full-bridge sub-module strings LVSM are sequentially connected in series to form a series structure;

high-voltage side series switch string S_HWith the switching string S in series at the low-voltage side_LOne end of the half-bridge module is respectively connected with a positive point and a negative point of the MCSM in the middle half-bridge sub-module string, and the other end of the half-bridge module string is directly connected to form a half-bridge structure; the middle point of the half-bridge structure is a low-voltage side anode, and the cathode of the low-voltage side full-bridge submodule string is a cathode of the low-voltage side.

Filter inductance L₁And a high-voltage side full-bridge submodule string HVSM, a middle half-bridge submodule string MCSM and a filter inductor L₂The low-voltage side full-bridge sub-module strings LVSM are sequentially connected in series to form a series structure;

high-voltage side series switch string S_HWith the switching string S in series at the low-voltage side_LOne end of the first half-bridge is respectively connected with the positive point and the negative point of the middle half-bridge submodule string MCSM, and the high-voltage side is connected with the switch string S in series_HAfter the fault blocking sub-module string BLSM is connected in series, the other end of the fault blocking sub-module string is connected with the low-voltage side series switch string S_LThe other end is directly connected to form a half-bridge structure, the midpoint of the half-bridge structure is a low-voltage side anode, and the cathode of the low-voltage side full-bridge sub-module string is a cathode of the low-voltage side.

As a further improvement of the present invention, when applied to the unipolar type field, the series structure formed by the unipolar type current transformer is connected in parallel with the high-voltage side;

when the bipolar type converter is applied to a bipolar occasion, a series structure formed by the two unipolar type converters is connected in series in opposite directions and then connected with the high-voltage side in parallel.

As a further improvement of the invention, the high-voltage side full-bridge sub-module string HVSM and the low-voltage side full-bridge sub-module string LVSM are both formed by connecting a plurality of full-bridge sub-modules FB in series; the full-bridge sub-module FB is composed of four IGBTs and a capacitor, the four IGBTs are connected in series in pairs and then connected in parallel with the capacitor to form two bridge arms, and two output points of the bridge arms are respectively located at the middle points of the two bridge arms.

As a further improvement of the invention, the middle half-bridge submodule string MCSM is formed by connecting a plurality of half-bridge submodules HB in series, each half-bridge submodule HB is formed by two IGBTs and a capacitor, the two IGBTs are connected in series and then connected in parallel with the capacitor to form a half-bridge arm, and two output points of the half-bridge arm are respectively positioned at the middle point of the arm and the negative end of the capacitor.

As a further improvement of the present invention, the fault blocking sub-module string BLSM is formed by connecting a plurality of fault protection sub-modules BL in series, each fault protection sub-module BL is formed by connecting two IGBTs, one resistor, one diode and one capacitor in series, the diode is connected with one IGBT in series to form a high tube which is a diode, a low tube which is a half-bridge arm of the IGBT is connected in parallel with the capacitor, and the other IGBT is connected in series with the resistor and then also connected in parallel with the capacitor, and two output points thereof are respectively located at a midpoint of the arm containing the diode and at a negative end of the capacitor.

As a further development of the invention, the series-connected switching string S_H,S_LThe IGBT is formed by directly connecting a plurality of IGBTs in series.

As a further improvement of the invention, the fault blocking sub-module string BLSM is formed by connecting a plurality of fault protection sub-modules BL in series, each fault protection sub-module BL is formed by two IGBTs, a resistor and a capacitor, the two IGBTs are connected in series to form a half-bridge structure and are connected in parallel with the capacitor, the resistor is connected in parallel with the low-tube IGBT, and two output points of the sub-modules are respectively positioned at the middle point of a bridge arm and the negative end of the capacitor.

A control method of a non-isolated high-voltage direct current-direct current converter with fault blocking comprises the following steps:

state 1: when the high-voltage side is connected in series with the switch S_HConducting, low-voltage side series switch S_LWhen the circuit is turned off, the high-voltage side full-bridge submodule string outputs U_H-U_LVoltage, fault blocking sub-module string BLSM keeps bypass output 0 voltage, middle half-bridge sub-module string MCSM outputs high level U_CSM1Low voltage side full bridge submodule series output- (U)_CSM1-U_L) A voltage; at the moment, the high-voltage side transmits energy to the low-voltage side through the high-voltage side full-bridge submodule string, and the high-voltage side full-bridge submodule string is charged; the middle half-bridge sub-module string discharges to the low-voltage side and low-voltage side half-bridge sub-module strings, the middle half-bridge sub-module string discharges, and the low-voltage side full-bridge sub-module string charges;

state 2: maintaining high side series switch S_HConducting, low-voltage side series switch S_LTurning off, and synchronously changing the output voltage of the middle half-bridge sub-module string and the low-voltage side full-bridge sub-module string; ensuring that the sum of the output voltages of the two is U_LUnder the premise of (1), the half-bridge submodules of the middle half-bridge submodule string are bypassed one by one, and the output voltage of the half-bridge submodules is measured by U_csm1Changing the voltage into 0, bypassing the full-bridge submodules of the low-voltage side full-bridge submodule string one by one and outputting opposite voltages, wherein the integral output voltage is formed by- (U)_CSM1-U_L) Is changed into U_L(ii) a High-voltage side full-bridge submodule string output U_H-U_LThe voltage is charged, the middle half-bridge submodule string outputs 0 voltage, and the low-voltage side full-bridge submodule string outputs U_LThe voltage is discharged to the low-voltage side, and the fault blocking sub-module string BLSM keeps the bypass to output 0 voltage; series switch string S_HAnd S_LThe voltage at the two ends of the switch is 0, and the zero-voltage soft switching condition is met;

state 3: zero voltage conduction S_LSwitching the string, then switching off the high-side series switch S at zero voltage_HSwitching the string to complete the commutation process;

and 4: maintaining high side series switch S_HOff, low side series switch S_LConducting; and synchronously changing the output voltage of the middle half-bridge sub-module string and the high-voltage side full-bridge sub-module string. Ensuring that the sum of the output voltages of the two is U_H-U_LUnder the premise of (1), the half-bridge submodules of the middle half-bridge submodule string are connected one by one, and the output voltage of the half-bridge submodules is changed from 0 to U_csm2Simultaneously bypassing the full-bridge submodules of the high-voltage side full-bridge submodule string one by one and outputting the phasesReverse voltage, the overall output voltage being from U_H-U_LBecome- (U)_csm2+U_L-U_H) (ii) a High-voltage side full-bridge submodule series output- (U)_csm2+U_L-U_H) Voltage discharge, intermediate half-bridge submodule string output U_csm2Voltage, low-voltage side full-bridge submodule series output U_LThe voltage is discharged to the low-voltage side, and the fault blocking sub-module string BLSM keeps the bypass to output 0 voltage;

and finally, the operation is carried out from the state 4 to the state 3 and the state 2, and then the operation returns to the state 1, so that the cycle operation is carried out, and the electric energy conversion is completed.

The method also comprises a bidirectional direct current side fault blocking step:

no matter what state the converter has high-voltage side short-circuit fault, the high-voltage side series switch string S is kept_HIn series with the low-voltage side switch S_LKeeping the bypass state of the fault blocking sub-module string unchanged, and immediately blocking all the sub-modules of the high-voltage side full-bridge sub-module string, the low-voltage side full-bridge sub-module string and the middle half-bridge sub-module string, namely effectively inhibiting the circulation of fault current;

the method also comprises the following steps of low-voltage side fault blocking:

when the low-voltage side short-circuit fault occurs in the series-connected switch string S only_LAt the moment of conduction, the series string S is maintained after a fault_HAnd S_LKeeping the bypass state of the fault blocking sub-module string unchanged, and immediately blocking all the sub-modules of the high-voltage side full-bridge sub-module string, the low-voltage side full-bridge sub-module string and the middle half-bridge sub-module string, namely effectively inhibiting the circulation of fault current;

when the short-circuit fault of the low-voltage side occurs in S only_HConducting or S_H、S_LMaintaining the series switch string S in a simultaneously conducting state_HAnd S_LThe state is unchanged, all the submodules of the fault blocking submodule string are blocked on the basis of blocking all the submodules of the high-voltage side full-bridge submodule string, the low-voltage side full-bridge submodule string and the middle half-bridge submodule string, and circulation of fault current is effectively inhibited.

Compared with the prior art, the invention has the following beneficial effects:

the non-isolated high-voltage direct current-direct current converter with the direct current fault blocking function comprises two single-pole type converters consisting of four sub-module strings, a filter inductor and a series switch string, wherein when the non-isolated high-voltage direct current-direct current converter is applied to a single-pole type field, a series structure formed by the single-pole type converters is connected with a high-voltage side in parallel; when the bipolar type converter is applied to a bipolar occasion, a series structure formed by the two unipolar type converters is connected in series in opposite directions and then connected with the high-voltage side in parallel. The medium-high voltage medium-high power direct current conversion can be realized, the bidirectional direct current fault blocking function is realized, and the method is suitable for the fields of high-voltage direct current transmission line interconnection, offshore wind power access, direct current distribution networks, full electric ships and the like. Most of the existing high-voltage direct-current converter topology can normally operate only by a two-phase or three-phase structure, and the invention realizes electric energy conversion only by adopting a single-phase structure, thereby effectively reducing the number of switching devices required by the system and the integral capacitance value of the capacitor compared with the existing topology, and further effectively reducing the cost and the volume of the system.

Drawings

Fig. 1 is a unipolar topology diagram of a non-isolated high voltage dc-dc converter with dc fault blocking according to the present invention;

FIG. 2 is a bipolar topology of a non-isolated HVDC-DC converter with DC fault blocking according to the present invention;

fig. 3 is another unipolar topology diagram of a non-isolated high voltage dc-dc converter with dc fault blocking according to the present invention;

FIG. 4 is another bipolar topology of a non-isolated HVDC-DC converter with DC fault blocking according to the present invention;

fig. 5 is a waveform diagram corresponding to the operation of the present invention.

Detailed Description

The invention is described in further detail below with reference to the accompanying drawings:

as shown in fig. 1, the non-isolated high voltage dc-dc converter with dc fault blocking function of the present invention includes four sub-module strings, a filter inductor and a series switch string. Four strings of the Chinese character' pinThe sub-module strings are a high-voltage side full-bridge sub-module string (HVSM), a fault blocking sub-module string (BLSM), a middle half-bridge sub-module string (MCSM) and a low-voltage side full-bridge sub-module string (LVSM) respectively; the required filter inductor comprises an inductor L₁，L₂(ii) a The series switch string comprises a high-voltage side series switch string S_HAnd a low-side series switch string S_L。

All four sub-module strings and two filter inductors are connected in series to form a series structure and then are connected with the high-voltage side in parallel, and the series structure is provided with filter inductors L from top to bottom respectively₁High-voltage side full-bridge sub-module string (HVSM), fault blocking sub-module string (BLSM), middle half-bridge sub-module string (MCSM), and filter inductor L₂And a low side full bridge sub-module string (LVSM). High-voltage side series switch string S_HWith the switching string S in series at the low-voltage side_LOne end of the half-bridge module is respectively connected with a positive point and a negative point of a middle half-bridge sub-module string (MCSM), and the other end of the half-bridge module string is directly connected to form a half-bridge structure. The middle point of the half-bridge structure is a low-voltage side anode, and the cathode of the low-voltage side full-bridge submodule string is a cathode of the low-voltage side. The high-voltage side full-bridge submodule string and the low-voltage side full-bridge submodule string in the topology are formed by serially connecting full-bridge submodules, the middle half-bridge submodule string is formed by serially connecting half-bridge submodules, and the fault blocking submodule string is formed by serially connecting half-bridge submodule strings with a discharge passage.

The operation principle of this topology is explained as follows, taking the example of power transmission from the high voltage side to the low voltage side. Hereinafter U_HRepresenting the high side voltage, U_LRepresenting the low side voltage.

State 1: when S is_HConduction, S_LWhen the circuit is turned off, the high-voltage side full-bridge submodule string outputs U_H-U_LVoltage, fault blocking sub-module string (BLSM) keeps bypass output 0 voltage, middle half-bridge sub-module string (MCSM) outputs high level U_CSM1Low voltage side full bridge submodule series output- (U)_CSM1-U_L) A voltage. At the moment, the high-voltage side transmits energy to the low-voltage side through the high-voltage side full-bridge submodule string, and the high-voltage side full-bridge submodule string is charged. The middle half-bridge sub-module string discharges to the low-voltage side and the low-voltage side half-bridge sub-module strings. Discharging the middle half-bridge submodule in series and charging the low-voltage side full-bridge submodule in seriesAnd (4) electricity.

State 2: retention of S_HConduction, S_LAnd turning off, and synchronously changing the output voltage of the middle half-bridge sub-module string and the low-voltage side full-bridge sub-module string. Ensuring that the sum of the output voltages of the two is U_LUnder the premise of (1), the half-bridge submodules of the middle half-bridge submodule string are bypassed one by one, and the output voltage of the half-bridge submodules is measured by U_csm1Changing the voltage into 0, bypassing the full-bridge submodules of the low-voltage side full-bridge submodule string one by one and outputting opposite voltages, wherein the integral output voltage is formed by- (U)_CSM1-U_L) Is changed into U_L. The system reaches a second state, and the high-voltage side full-bridge submodule string outputs U_H-U_LThe voltage is charged, the middle half-bridge submodule string outputs 0 voltage, and the low-voltage side full-bridge submodule string outputs U_LThe voltage is discharged to the low side and the fault blocking sub-module string (BLSM) keeps bypassing the output 0 voltage. Series switch string S_HAnd S_LThe voltage at the two ends of the switch is 0, and the zero-voltage soft switching condition is met.

State 3: zero voltage conduction S_LSwitching the string, then switching off S at zero voltage_HAnd switching the string to complete the commutation process.

And 4: retention of S_HOff, S_LAnd conducting. And synchronously changing the output voltage of the middle half-bridge sub-module string and the high-voltage side full-bridge sub-module string. Ensuring that the sum of the output voltages of the two is U_H-U_LUnder the premise of (1), the half-bridge submodules of the middle half-bridge submodule string are connected one by one, and the output voltage of the half-bridge submodules is changed from 0 to U_csm2Simultaneously, the full-bridge submodules of the high-voltage side full-bridge submodule string are bypassed one by one and output opposite voltages, and the integral output voltage is measured by U_H-U_LBecome- (U)_csm2+U_L-U_H). The system reaches a fourth state, and the high-voltage side full-bridge submodule string outputs (U)_csm2+U_L-U_H) Voltage discharge, intermediate half-bridge submodule string output U_csm2Voltage, low-voltage side full-bridge submodule series output U_LThe voltage is discharged to the low side and the fault blocking sub-module string (BLSM) keeps bypassing the output 0 voltage.

Similarly, the system may run from state 4 to state 3, to state 2, and back to state 1, using the corresponding opposite run rule. The system can well complete the function of electric energy conversion by the regular cycle operation.

The corresponding operation waveform diagram of the above operation process is shown as 5.

Further to U_csm1And U_csm2Is derived.

The currents flowing through the high-voltage side full-bridge submodule in the topological operation process are all high-voltage side currents I_HThe current flowing through the low-voltage side full-bridge submodule is I_L-I_HIn which I_LFor low voltage current, for ensuring I_HAnd I_LThe ripple contained is small, so that the current flowing through the high-side full-bridge submodule string and the low-side full-bridge submodule string is substantially constant in each operating state.

According to the working principle of the topology, in order to ensure the power balance of two full-bridge sub-module strings at the high-low voltage side in one switching period, the system should satisfy the following equation

In the formula D_rHThe ratio of the single edge time of the positive level of the high-voltage side full-bridge submodule string to the total switching cycle time is represented; d_nHThe proportion of the single edge time of the negative level of the high-voltage side full-bridge submodule string to the total switching cycle time is represented; in the same way, D_rLThe ratio of the single edge time of the positive level of the low-voltage side full-bridge submodule string to the total switching cycle time is represented; d_nLThe proportion of the single edge time of the negative level of the low-voltage side full-bridge submodule string to the total switching cycle time is represented; d_zIndicating S in one commutation_HAnd S_LMeanwhile, the conducting time accounts for the proportion of the total switching period time; d₁' represents the output of the low-voltage side full-bridge submodule string — (U)_CSM1-U_L) The time of the level is proportional to the total switching cycle time; d₂' represents the high-voltage side full-bridge submodule string output- (U)_csm2+U_L-U_H) The time of the level is a proportion of the total switching cycle time. D₁’、D₂’、D_rH、D_nH、D_rL、D_nLAnd D_zIs defined as shown in the waveform diagram.

Can be easily seen

D′₁+D′₂+2D_z+2D_rH+2D_nH+2D_rL+2D_nL＝1

Thus, U can be deduced_csm1And U_csm2Is of the formula

To satisfy the power balance of the middle half-bridge sub-module string, the system should satisfy the following equation

I_LVSMU_CSM1(D′₁+D_rL+D_nL)＝I_HVSMU_CSM2(D′₂+D_rH+D_nH)

In the formula I_HVSMFor the current flowing through the high-side full-bridge sub-module string, I_LVSMIs the current flowing through the low side full bridge sub-module string. The following two formulas can be obtained through the analysis of the topological structure

I_LVSM＝I_L-I_H

I_HVSM＝I_H

In the formula I_LRepresents the low side current flow, I_HThe input current at the high-voltage side is expressed, and the two equations are substituted into an equation to obtain

Since P is I_LU_L＝I_HU_HThus, therefore, it is

Due to D_nL＜＜D′₁,D_rL＜＜D′₁,D_nH＜＜D′₂,D_rH＜＜D′₂Thus the above formula can be simplified into

This formula shows when U_csm1And U_csm2When the output is carried out according to the formula (1), the converter can maintain the power balance of the high-low voltage side full-bridge sub-module string and the middle half-bridge sub-module string. It can be seen that the input-output voltage transformation ratio of the topology is independent of the duty ratio, and D is achieved at a certain transformation ratio₁' optional selection according to D₁' calculation of D₂' and obtaining corresponding U according to the formula (1)_csm1And U_csm2Voltage and in accordance with D₁’、D₂’、U_csm1And U_csm2And a selected high side voltage U_HAnd low side voltage U_LGenerating respective sub-block strings and S_H，S_LAnd connecting the driving signals of the switch strings in series and driving the corresponding parts of the converter to operate according to the operation rule, so that the converter can work under the target input and output voltage. D1' is generally selected in consideration of the cost and dc fault blocking performance of the system.

The fault blocking function of the topology is further explained. The invention has the function of bidirectional DC side fault blocking.

The high side fault blocking function is explained first. From the previous analysis, the level of the output required by the high-voltage side full-bridge submodule is (U) when the system is in normal operation_H-U_L) And (U)_csm2+U_L-U_H) In order to ensure that the system has the function of blocking the high-side direct-current fault, the high-side full-bridge submodule string at least contains the power supply U_LFull bridge submodule of voltage, when U_L<＝U_HPer 2 hour, high-pressure side full-bridge sub-dieHigh level voltage U that the block string needs to output_H-U_LGreater than U_LAnd the requirements are met. When U is formed_L>U_HAt/2, U is required_csm2+U_L-U_H>＝U_LI.e. U_csm2>＝U_HD is generally selected₁All can make U_csm2This requirement is met. At this time, no matter what state the converter has the high-voltage side short-circuit fault, the series switch string S is kept_HAnd S_LThe state is unchanged, the bypass state of the fault blocking sub-module string is kept unchanged, all sub-modules of the high-voltage side full-bridge sub-module string, the low-voltage side full-bridge sub-module string and the middle half-bridge sub-module string are immediately blocked, and the circulation of fault current can be effectively inhibited.

And when the low-voltage side has a short-circuit fault, the specific protection measures are related to the operation state of the converter.

If a fault occurs in the series-only switching string S_LAt the moment of conduction, the series switch string S is maintained_HAnd S_LThe state is unchanged, the bypass state of the fault blocking sub-module string is kept unchanged, all sub-modules of the high-voltage side full-bridge sub-module string, the low-voltage side full-bridge sub-module string and the middle half-bridge sub-module string are immediately blocked, the circulation of fault current can be effectively inhibited, and at the moment, the high-voltage side full-bridge sub-module string and the middle half-bridge sub-module string output U together_HThe voltage suppresses the flow of the fault current.

And if the fault occurs in S only_HConducting or S_H、S_LIn the simultaneously conducting state, the series switch string S still needs to be maintained_HAnd S_LThe state is unchanged, and all the submodules of the fault blocking submodule string are further blocked on the basis of blocking all the submodules of the high-voltage side full-bridge submodule string, the low-voltage side full-bridge submodule string and the middle half-bridge submodule string, so that the circulation of fault current can be effectively inhibited. When the fault occurs in S-only_HWhen the high-voltage side full-bridge submodule string is conducted, the high-voltage side full-bridge submodule string and the fault blocking submodule string output U together_HThe voltage suppresses the flow of the fault current. When the fault occurs in S_H、S_LWhen the high-voltage side full-bridge submodule is conducted at the same time, the high-voltage side full-bridge submodule is connected in series and is in fault resistanceThe broken sub-module string and the middle half-bridge sub-module string output U together_HThe voltage suppresses the flow of the fault current.

Therefore, the voltage required to be output by the fault blocking sub-module string is U_H-max(U_H-U_L,U_csm2+U_L-U_H) At this time, it and the high-voltage side full-bridge submodule string can output U together_HThe voltage of (c). In addition, the fault blocking sub-module string absorbs certain electric energy in the process of inhibiting the fault, so that the capacitor voltage of the sub-module slightly rises, and the capacitor voltage needs to be restored to an initial value before the next fault comes. When the power of the converter is transmitted from the low-voltage side to the high-voltage side, the fault blocking submodule string can discharge to the high-voltage side through the main circuit, but when the power is transmitted from the high-voltage side to the low-voltage side, the power cannot be discharged through the main circuit, and the power needs to be discharged through the auxiliary discharge branch of each submodule.

The invention is described in detail below with reference to the drawings and the detailed description, including presenting the base topology of fig. 1 and the conversion topologies of fig. 2-4.

Example 1

As shown in fig. 1, the unipolar topology of the non-isolated high voltage dc-dc converter with dc fault blocking function according to the present invention includes four strings of sub-module strings, a filter inductor, and a series switch string. The four sub-module strings are respectively a high-voltage side full-bridge sub-module string (HVSM), a fault blocking sub-module string (BLSM), a middle half-bridge sub-module string (MCSM) and a low-voltage side full-bridge sub-module string (LVSM); the required filter inductor comprises an inductor L₁，L₂(ii) a The series switch string comprises a high-voltage side series switch string S_HAnd a low-side series switch string S_L。

The high-voltage side Full-Bridge submodule string HVSM and the low-voltage side Full-Bridge submodule string are formed by connecting a plurality of Full-Bridge submodules (Full bridges, FB) in series, the Full-Bridge submodule structure is shown as FB in fig. 1, it can be seen that the Full-Bridge submodule structure is formed by four Insulated Gate Bipolar Transistors (IGBTs) and a capacitor, and two output points of the Full-Bridge submodule string HVSM and the low-voltage side Full-Bridge submodule string are respectively located at the middle points of two Bridge arms. High-voltage side full-bridge submodule is connected in series at S_HWhen conductingDrawing electric energy from the high-voltage side and at S_LWhen conducting, electric energy is released to the middle half-bridge submodule string. Otherwise, the low-voltage side full-bridge submodule is connected in series at S_HAbsorbing electric energy from the middle half-bridge sub-module string when conducting, and at S_LWhen conducting, the electric energy is released to the low-voltage side. The change of output level is realized by switching the states of single full-bridge submodule one by one and matching with the middle half-bridge submodule string to realize S_H，S_LAnd the zero-voltage soft switches of the two series controllable switch strings are connected.

The middle Half-Bridge submodule string MCSM is formed by connecting a plurality of Half-Bridge submodules (Half Bridge, HB) in series, the structure diagram of the Half-Bridge submodule is shown as HB in fig. 1, and it can be seen that the Half-Bridge submodule is formed by two IGBTs and a capacitor, and two output points of the Half-Bridge submodule are respectively located at the middle point of a Bridge arm and the negative end of the capacitor. Middle half-bridge submodule string MCSM at S_HWhen the module is conducted, electric energy is released to the low-voltage side and the low-voltage side full-bridge submodule string, and S is carried out_LWhen the high-voltage side full-bridge submodule is conducted, electric energy is absorbed from the high-voltage side full-bridge submodule string and the high-voltage side full-bridge submodule string.

The fault Blocking sub-module string BLSM is formed by serially connecting a plurality of fault protection sub-modules (Blocking cells, BL), and the structure diagram of the fault protection sub-modules is shown in BL in fig. 1, which shows that a capacitor discharge branch is added on the basis of a half-bridge sub-module to recover the capacitor voltage to a rated value after fault protection. The fault blocking sub-module string only generates short-circuit fault on the low-voltage side of the converter series switch string S_HIndividually conducting or series-connecting switch strings S_H、S_LAnd the current of the fault current is required to be switched in and restrained when the current is switched on at the same time, and the bypass state is kept under the other conditions.

Series switch string S_H,S_LA plurality of IGBTs are directly connected in series to realize higher voltage-resistant level, and S is realized in the topological operation process_HAnd S_LThe zero voltage soft switch, therefore, the two series switch strings do not have the problem of dynamic voltage sharing, and the engineering realization is easy.

Example 2

A topological structure diagram of the non-isolated high-voltage direct current-direct current converter with the direct current fault blocking function applied to the bipolar field is shown in the attached figure 2. The bipolar structure consists of an upper part and a lower partA single-pole converter, two single-pole converters having U-shaped high-voltage anodes_H ⁺And U_H ^-The positive electrodes of the low-voltage sides are respectively U_L ⁺And U_L ^-The negative poles at the high and low voltage sides are connected with the ground. The operating principle of the single unipolar current transformer is identical to that described above. The bipolar topological structure has a phase displacement angle theta at the upper and lower current conversion time relative to the unipolar structure, namely the upper and lower current transformer series switch string S_H1And S_H2The phase of the phase difference between the drive signals. Because the current conversion process and the current conversion time of the upper converter and the lower converter are consistent under the normal condition, S_H1And S_H2Phase of phase difference between driving signals and S_L1And S_L2The phase difference between the driving signals is the same, and is theta.

Setting different theta angles will affect the fault blocking capability of the bipolar topology and the ripple of the voltage between the input and output pole pairs. If the angle theta is set, S in the upper converter is enabled_H1And S_L1The moment of simultaneous conduction is not equal to S in the lower converter_H2And S_L2The moment of simultaneous conduction is coincident, when the bipolar topology has a low-voltage side electrode-to-electrode short circuit fault, the whole output voltage max (U) of the full-bridge submodule string at the high-voltage side of the upper converter and the lower converter is only needed_H-U_L,U_csm2+U_L-U_H) Greater than U_HAnd/2, fault blocking can be realized without the need of serial access of the fault blocking submodule. Therefore, only when a single-pole earth fault occurs on the low-voltage side and the fault moment is the corresponding converter S_HConducting alone or S_HAnd S_LAnd in the on state, the fault blocking sub-module string corresponding to the converter needs to act to inhibit the circulation of fault current. And because the whole topology is a bipolar structure, when one pole fails, the operation of the other pole cannot be influenced.

In addition, the ripple content of the voltage between the high-voltage side and the low-voltage side pole pair can be changed by adjusting the theta angle, and the ripple value of the voltage between the high-voltage side and the low-voltage side pole pair can be effectively reduced by selecting the proper theta angle, so that the electric energy quality is further improved.

Example 3

Another unipolar topology structure diagram of the non-isolated high voltage dc-dc converter with dc fault blocking function of the present invention is shown in fig. 3. It can be seen that the structure is substantially the same as that in fig. 1, except that the position of the fault blocking sub-module string is changed from being in series with the high-side full-bridge sub-module string HVSM to being in series with the series switch string S_HAre connected in series. It is noted that the fault blocking sub-module in the structure shown in fig. 3 has two optional forms, and the main difference is that the discharge resistance of the capacitor voltage is different, and the discharge resistance in the structure 1 of the fault blocking sub-module is R_sAnd the discharge resistance of the No. 2 structure is R_dThe difference between the two will be explained below. S in two fault blocking submodules₁The switches all control the access of the submodules, and S₂The switch is responsible for discharging the capacitor voltage to a nominal value, S, after the fault has cleared₂The off state is maintained under normal conditions. Due to S₁The switch and the diode connected in series therewith determine the fault clearing speed of the system, so that S₁It is necessary to use fast switching power semiconductor devices such as IGBTs. And S in structure No. 2₂The speed requirement of the switch is not high, and therefore, the switch can be realized by using a switch such as a relay.

The operation process of the structure shown in fig. 3 is basically the same as that of the structure shown in fig. 1 in normal operation, except that when the fault blocking sub-module string in the structure shown in fig. three fails, the S in the sub-module is not failed₁With switches as series-connected switch strings S_HOne series switch of (2) is operated. Simultaneously when a high-voltage side short-circuit fault or a low-voltage side short-circuit fault occurs in S_LWhen the sub-module string is conducted independently, the fault blocking sub-module string does not need to act at the moment, so that S of the fault blocking sub-module₁The switch is still according to S_HOne series switch of (2) is operated. When short-circuit fault occurs on the low-voltage side and the fault occurs on the series switch string S_HConducting alone or S_H、S_LWhen the two-way switch is turned on simultaneously, the system needs to act the fault blocking submodule to inhibit the circulation of fault current, and at the moment, the S1 switch of the fault blocking submodule does not follow S any more_HThe series switch of (2) is operated, and after a fault occurs, S is kept_H、S_LThe state of the switch string is unchanged, the IGBTs of all the sub-module strings are blocked immediately, namely S of each fault blocking sub-module is included₁The switch, and therefore the fault protection sub-modules, are connected in series to inhibit the flow of fault current.

Because the capacitor voltage of the fault blocking sub-module will rise to a certain extent in the fault clearing process, the capacitor voltage needs to be discharged in order to prevent the capacitor voltage from exceeding the allowable range in the operation process. As mentioned above, when power is transmitted from the high voltage side to the low voltage side, the fault blocking sub-module cannot bleed voltage through the main circuit, and thus a discharge resistor needs to be provided in the sub-module. In the topology of FIG. 3 the string of fault blocking sub-modules has multiplexed S₁Switching devices of the series-switched string, whereby S is present₁Switch is also provided with S_HThe function of the series switch device is realized by using a static voltage equalizing resistor in engineering for realizing the static voltage equalizing of the series switch device, such as the fault interrupting submodule and the S₁Resistor R with parallel switches_sAs shown. Therefore, the No. 1 fault blocking submodule is in the form of using the static voltage-sharing resistor R_sDischarging the capacitor as a discharge resistor, turning off S after the fault has cleared₁Switch for conducting S of submodule₂The switch can reduce the capacitor voltage. While the No. 2 fault blocking submodule form uses a single discharge resistor R_dTo discharge electricity. Compared with the two forms, the No. 1 form has the advantages of less switching devices and resistance and lower cost, but the static voltage-sharing effect and the discharging effect are required to be considered simultaneously when the static voltage-sharing resistor is selected, so that the resistance value is difficult to determine. In the form 2, the two problems are respectively corresponding to two resistors, so that the resistance value design is simpler. In addition, the sub-module of the form 1 is at S₁When the switch is turned on, the switch cannot discharge, so that the system needs to be powered on again after the capacitor discharge is finished or the circuit runs in S₁The gap of the switch can be switched on S₂A discharge operation is performed. For the sub-module of No. 2, the capacitor is only discharged by S₂Influence of the switch and S₁Status independence and thus system re-installation when using sub-modules of the form number 2Continuous use of S in the course of electricity₂The switch discharges the capacitor without influencing the operation of the system, obviously, the method reduces the influence of the discharge on the system and improves the speed of restarting the system due to faults.

It will be readily seen that the fundamental variation of the architecture of figure 3 from that of figure 1 is that the fault blocking sub-module string multiplexes the series switch string S_HS with series switch as fault blocking submodule₁And (4) switching. The method further reduces the number of switching devices required by the topology, reduces the number of switching devices flowing through large current in the main circuit, further reduces the conduction loss of the system, and improves the efficiency of the system.

Example 4

Another bipolar topology structure diagram of the non-isolated high voltage dc-dc converter with dc fault blocking function of the present invention is shown in fig. 4. The bipolar structure of fig. 4 is formed by combining two unipolar structures of fig. 3 in the same manner as fig. 1 forms fig. 2. The high-voltage side anodes of the two unipolar current transformers are respectively U_H ⁺And U_H ^-The positive electrodes of the low-voltage sides are respectively U_L ⁺And U_L ^-The negative poles at the high and low voltage sides are connected with the ground. The operating principle of the single-pole current transformer of fig. 3 is identical to that described above. The bipolar topology shown in fig. 4 also has a phase shift angle θ at the upper and lower commutation times, and the selection of an appropriate phase shift angle θ can also enhance the fault blocking performance of the topology and reduce the ripple of the voltage between the input and output pole pairs.

The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A non-isolated high-voltage direct current-direct current converter with fault blocking is characterized by comprising at least one single-pole converter, wherein the single-pole converter comprises four sub-module strings, a filter inductor and a series switch string;

Filter inductance L₁And a high-voltage side full-bridge sub-module string HVSM, a fault blocking sub-module string BLSM, a middle half-bridge sub-module string MCSM and a filter inductor L₂The low-voltage side full-bridge sub-module strings LVSM are sequentially connected in series to form a series structure;

2. A non-isolated high-voltage direct current-direct current converter with fault blocking is characterized by comprising at least one single-pole converter, wherein the single-pole converter comprises four sub-module strings, a filter inductor and a series switch string;

high-voltage side series switch string S_HWith the switching string S in series at the low-voltage side_LOne end of the half-bridge is respectively connected with the positive point and the negative point of the MCSM in the middle half-bridge submodule string, and the high-voltage sideSeries switch string S_HAfter the fault blocking sub-module string BLSM is connected in series, the other end of the fault blocking sub-module string is connected with the low-voltage side series switch string S_LThe other end is directly connected to form a half-bridge structure, the midpoint of the half-bridge structure is a low-voltage side anode, and the cathode of the low-voltage side full-bridge sub-module string is a cathode of the low-voltage side.

3. The non-isolated high voltage dc-dc converter with fault blocking according to claim 1 or 2, wherein when applied to a unipolar type application, the unipolar type converter forms a series structure in parallel with the high voltage side;

4. The non-isolated high-voltage direct current-direct current converter with fault blocking according to claim 1 or 2, wherein the high-voltage side full-bridge submodule string HVSM and the low-voltage side full-bridge submodule string LVSM are formed by connecting a plurality of full-bridge submodules FB in series; the full-bridge sub-module FB is composed of four IGBTs and a capacitor, the four IGBTs are connected in series in pairs and then connected in parallel with the capacitor to form two bridge arms, and two output points of the bridge arms are respectively located at the middle points of the two bridge arms.

5. The non-isolated high-voltage direct current-direct current converter with the fault blocking function according to claim 1 or 2, wherein the middle half-bridge submodule string MCSM is formed by connecting a plurality of half-bridge submodules HB in series, each half-bridge submodule HB is formed by connecting two IGBTs and a capacitor in parallel, each two IGBTs are connected in series and then connected in parallel to form a half-bridge arm, and two output points of each half-bridge submodule string MCSM are located at the middle point of the arm and the negative end of the capacitor.

6. The non-isolated high-voltage direct current-direct current converter with the fault blocking function according to claim 1 or 2, wherein the fault blocking submodule string BLSM is formed by serially connecting a plurality of fault protection submodules BL, each fault protection submodule BL is formed by two IGBTs, a resistor, a diode and a capacitor, the diode is serially connected with one IGBT to form a high-voltage tube which is a diode, the low-voltage tube is a half-bridge arm of the IGBT and then is parallelly connected with the capacitor, the other IGBT is serially connected with the resistor and then is also parallelly connected with the capacitor, and two output points of the IGBT are respectively located at the middle point of the arm containing the diode and the negative end of the capacitor.

7. Non-isolated hvdc-dc converter with fault blocking according to claim 1 or 2, characterized in that said series switch string S_H,S_LThe IGBT is formed by directly connecting a plurality of IGBTs in series.

8. The non-isolated high-voltage direct current-direct current converter with the fault blocking function according to claim 2 is characterized in that the fault blocking submodule string BLSM is formed by serially connecting a plurality of fault protection submodules BL, each fault protection submodule BL is formed by two IGBTs, a resistor and a capacitor, the two IGBTs are serially connected to form a half-bridge structure and are connected with the capacitor in parallel, the resistor is connected with the low-tube IGBT in parallel, and two output points of each submodule are respectively located at the middle point of a bridge arm and the negative end of the capacitor.

9. The control method of the non-isolated high-voltage direct current-direct current converter with fault blocking according to claim 1 or 2, characterized by comprising the following steps:

state 2: maintaining high side series switch S_HConduction ofLow voltage side series switch S_LTurning off, and synchronously changing the output voltage of the middle half-bridge sub-module string and the low-voltage side full-bridge sub-module string; ensuring that the sum of the output voltages of the two is U_LUnder the premise of (1), the half-bridge submodules of the middle half-bridge submodule string are bypassed one by one, and the output voltage of the half-bridge submodules is measured by U_csm1Changing the voltage into 0, bypassing the full-bridge submodules of the low-voltage side full-bridge submodule string one by one and outputting opposite voltages, wherein the integral output voltage is formed by- (U)_CSM1-U_L) Is changed into U_L(ii) a High-voltage side full-bridge submodule string output U_H-U_LThe voltage is charged, the middle half-bridge submodule string outputs 0 voltage, and the low-voltage side full-bridge submodule string outputs U_LThe voltage is discharged to the low-voltage side, and the fault blocking sub-module string BLSM keeps the bypass to output 0 voltage; series switch string S_HAnd S_LThe voltage at the two ends of the switch is 0, and the zero-voltage soft switching condition is met;

and 4: maintaining high side series switch S_HOff, low side series switch S_LConducting; synchronously changing the output voltage of the middle half-bridge sub-module string and the high-voltage side full-bridge sub-module string; ensuring that the sum of the output voltages of the two is U_H-U_LUnder the premise of (1), the half-bridge submodules of the middle half-bridge submodule string are connected one by one, and the output voltage of the half-bridge submodules is changed from 0 to U_csm2Simultaneously, the full-bridge submodules of the high-voltage side full-bridge submodule string are bypassed one by one and output opposite voltages, and the integral output voltage is measured by U_H-U_LBecome- (U)_csm2+U_L-U_H) (ii) a High-voltage side full-bridge submodule series output- (U)_csm2+U_L-U_H) Voltage discharge, intermediate half-bridge submodule string output U_csm2Voltage, low-voltage side full-bridge submodule series output U_LThe voltage is discharged to the low-voltage side, and the fault blocking sub-module string BLSM keeps the bypass to output 0 voltage;

10. The method for controlling a non-isolated hvdc-dc converter with fault blocking according to claim 9 further comprising the step of fault blocking the bi-directional dc side: