A high current DC / DC converter with low voltage side bridge arms in parallel

Abstract

The present invention discloses a high-current DC / DC converter with low-voltage side bridge arms in parallel, the converter comprises a full-bridge submodule bridge arm, a bridge arm inductor, a thyristor valve group and a diode valve group, wherein: the full-bridge submodule bridge arm comprises bridge arm A1 to bridge arm A2. i , i=1, 2, 3, 4; the bridge arm A i One end of the inductor is connected to the positive electrode of the low voltage side, and the bridge arm A i The other end of the inductor is connected to bridge arm A i One end of the bridge is connected to i The other end leads to two branches, one of which passes through the diode D i Connected to the positive pole of the high voltage side, the other branch passes through the thyristor T i The DC / DC converter can not only realize high-voltage and large-capacity DC transformation without the need for additional filters, but also realize the distribution of high current on the low-voltage side among multiple bridge arms based on the parallel connection of the low-voltage side bridge arms, thereby improving the current transmission capacity of the DC / DC converter.

Description

Technical Field

[0001] The invention relates to a DC / DC converter, in particular to a high-current DC / DC converter with low-voltage side bridge arms connected in parallel. Background Art

[0002] In long-distance and large-capacity power transmission, DC transmission technology has higher efficiency and lower cost than AC transmission technology. In high-voltage and large-capacity DC transmission, the voltage levels of each DC line may be inconsistent, so DC / DC converters are needed to achieve DC transformation and interconnect DC transmission lines of different voltage levels. Summary of the invention

[0003] The purpose of the present invention is to provide a high-current DC / DC converter with low-voltage side bridge arms connected in parallel. The DC / DC converter can not only realize high-voltage and large-capacity DC transformation without the need for additional filters, but also realize the distribution of high current on the low-voltage side among multiple bridge arms based on the parallel connection of low-voltage side bridge arms, thereby improving the current transmission capacity of the DC / DC converter.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] A high current DC / DC converter with low voltage side bridge arms in parallel connection, comprising a full bridge submodule bridge arm, a bridge arm inductor, a thyristor valve group and a diode valve group, wherein:

[0006] The bridge arms of the full bridge submodule include bridge arms A1 to A i , i = 1, 2, 3, 4, the voltage and current of two adjacent bridge arms are 90° out of phase and have the same amplitude;

[0007] The bridge arm inductance includes bridge arm A1 inductance ~ bridge arm A i inductance;

[0008] The thyristor valve group includes thyristors T1 to T1. i ;

[0009] The diode valve group includes diodes D1 to D i ;

[0010] The bridge arm A i One end of the inductor is connected to the positive electrode of the low voltage side, and the bridge arm A i The other end of the inductor is connected to bridge arm A i One end of the bridge is connected to i The other end leads to two branches, one of which passes through the diode D i Connected to the positive pole of the high voltage side, the other branch passes through the thyristor T i They are respectively connected to the negative electrode on the low voltage side and the negative electrode on the high voltage side.

[0011] Compared with the prior art, the present invention has the following advantages:

[0012] 1. When the DC / DC converter is in any working state, there are always two bridge arms connected in parallel with the low voltage side, and one bridge arm connected in series between the low voltage side and the high voltage side. In this way, the current on the low voltage side will be distributed among the three bridge arms, and the current on each bridge arm connected in parallel with the low voltage side is reduced to (I L -I H ) / 2.

[0013] 2. The four sub-module bridge arms of the DC / DC converter are connected to the high-voltage side through a diode valve group. When the sub-module bridge arm is connected in series between the low-voltage side and the high-voltage side, the diode valve group is subjected to positive pressure and conducts; when the sub-module bridge arm is connected in parallel with the low-voltage side, the diode valve group is subjected to the high-voltage side voltage U H The advantages of the diode valve group in terms of high pressure resistance, strong flow capacity and low cost are fully utilized.

[0014] 3. The four sub-module bridge arms of the low-voltage side parallel DC / DC converter are connected to the low-voltage side through the thyristor valve group, and the thyristor valve group is triggered on and off to ensure its normal operation according to the designed working sequence. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a low voltage side bridge arm parallel DC / DC converter topology;

[0016] Figure 2 It is the theoretical waveform of the low voltage side bridge arm parallel DC / DC converter;

[0017] Figure 3 Dynamic simulation waveform of the low-voltage side bridge arm parallel DC / DC converter;

[0018] Figure 4 This is the steady-state simulation waveform of the 30MW DC / DC converter in parallel with the low-voltage side bridge arm;

[0019] Figure 5 This is the steady-state simulation waveform of the 90MW DC / DC converter in parallel with the low-voltage side bridge arm. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described below in conjunction with the accompanying drawings, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0021] The present invention provides a high-current DC / DC converter with low-voltage side bridge arms in parallel, and provides the circuit topology, theoretical waveform and working timing of the DC / DC converter. The following points are considered in the design of this topology:

[0022] 1. When the proposed topology is working, two submodule bridge arms will be connected in parallel with the low-voltage side, and one submodule bridge arm will be connected in series between the low-voltage side and the high-voltage side. In this way, the current on the low-voltage side will be distributed among the three bridge arms, which can greatly reduce the current stress of the low-voltage side bridge arm. In addition, in order to maintain the charge and discharge energy balance of the submodule bridge arm, another submodule bridge arm needs to be introduced for commutation.

[0023] 2. Since the submodule bridge arm of the proposed topology needs to maintain a charge and discharge energy balance, a reasonable working sequence needs to be designed. The present invention provides a working sequence design of the submodule bridge arm.

[0024] 3. In the proposed topology, the four submodule bridge arms are connected to the high voltage side through a diode valve group. When the bridge arm is connected in series between the low voltage side and the high voltage side, the diode valve group is subjected to positive pressure and conducts; when the bridge arm is connected in parallel with the low voltage side, the diode valve group is subjected to the high voltage side voltage U H The advantages of diode valve group in withstanding high pressure and strong flow capacity are fully utilized, and the cost of diode is relatively low, which can reduce the construction cost of equipment.

[0025] 4. In the proposed topology, the four sub-module bridge arms are connected to the low-voltage side through a thyristor valve group. When the thyristor valve group connected to the bridge arm is turned off, the diode valve group is turned on by the positive voltage, and the sub-module bridge arm is connected in series between the low-voltage side and the high-voltage side. The thyristor valve group is subjected to the high-voltage side voltage U H When the thyristor valve group connected to the bridge arm is turned on, the diode valve group is turned off due to the reverse pressure, and the sub-module bridge arm is connected in parallel with the low-voltage side.

[0026] like Figure 1 As shown in the figure, the low-voltage side bridge arm parallel DC / DC converter consists of 4 full-bridge sub-module bridge arms, 4 bridge arm inductors, 4 thyristor valve groups and 4 diode valve groups. In this topology, one end of the i-th bridge arm inductor is connected to the positive electrode of the low-voltage side, and the other end is connected to the bridge arm A. i Bridge arm A i The other end leads to two branches, one of which passes through the diode D i Connected to the positive pole of the high voltage side, the other branch passes through the thyristor T i They are connected to the negative pole of the low voltage side and the negative pole of the high voltage side respectively (i=1,2,3,4). Among them, the four full-bridge sub-module bridge arms are composed of N full-bridge sub-modules in series. The positive direction of the relevant electrical quantity is as follows Figure 1 As indicated in the markings.

[0027] like Figure 2As shown in the figure, the four full-bridge sub-module bridge arms of the low-voltage bridge arm parallel DC / DC converter remain symmetrical, and the voltage and current phases of two adjacent bridge arms are 90° apart and have the same amplitude. This topology can realize power transmission from the low-voltage side to the high-voltage side. When it is working, the theoretical waveforms of the voltage and current of the four bridge arms are as follows: Figure 2 As shown. This topology needs to go through 9 working states in one working cycle, and needs to go through 4 commutations on the low-voltage side and the high-voltage side respectively. Its working sequence table is shown in Table 1. In any working state of this topology, there are always two bridge arms connected in parallel with the low-voltage side, and one bridge arm connected in series between the low-voltage side and the high-voltage side. In this way, the current on the low-voltage side will be distributed among the three bridge arms, which can greatly reduce the current stress of the low-voltage side bridge arm, thereby meeting the working requirements of high-voltage and large-capacity conditions.

[0028] Table 1 Working sequence of low voltage side bridge arm parallel DC / DC converter

[0029]

[0030] Figure 2 The voltage and current waveforms of the four bridge arms of the low-voltage side bridge arm parallel DC / DC converter in one working cycle are given and a specific analysis is given below.

[0031] Initially, the low-voltage side bridge arm parallel DC / DC converter is in working state 1. At this time, bridge arm A1 and bridge arm A2 are connected in parallel to the low-voltage side for charging, and the charging current amplitude is (I L -I H ) / 2, the charging voltage is -U L ; Bridge arm A3 is in the disconnected state, its current is 0 and its voltage is -U L ; Bridge arm A4 is connected in series between the low voltage side and the high voltage side for discharge, and its discharge current amplitude is I H , the discharge voltage is U H -U L , where: U L is the low voltage side voltage, U H is the high voltage side voltage, I L is the low voltage side current, I H is the high voltage side current.

[0032] During [0, t1], thyristor T3 is triggered and turned on, and the low-voltage side bridge arm parallel DC / DC converter enters the low-voltage side commutation stage 1. Bridge arm A1 and bridge arm A3 commutate on the low-voltage side, bridge arm A2 is connected in parallel on the low-voltage side and remains unchanged, and bridge arm A4 is connected in series between the low-voltage side and the high-voltage side and remains unchanged. At this time, the bridge arm A1 voltage u A1 Equal to -U L -U0, bridge arm A3 voltage u A3 Equal to -U L+U0, the voltage difference 2U0 between bridge arm A1 and bridge arm A3 is applied to the bridge arm inductance 2L of the two bridge arms, so that the current i A1 At a change rate of 2U0 / 2L from (I L -I H ) / 2 linearly decreases to 0, the bridge arm A3 current i A3 Increase linearly from 0 to (I L -I H ) / 2, thus completing the low-voltage side commutation stage 1, where: U0 is the low-voltage side commutation voltage.

[0033] During [t1, t2], the low-voltage side bridge arm parallel DC / DC converter enters working state 2. At this time, bridge arm A2 and bridge arm A3 are connected in parallel to the low-voltage side for charging, and the charging current amplitude is (I L -I H ) / 2, the charging voltage is -U L ; Bridge arm A1 is in the disconnected state, its current is 0, and its voltage is -U L The additional output is longer than the thyristor reverse turn-off time t q The back pressure U RE , so that the thyristor T1 is reliably turned off. After that, the voltage u A1 By -U L Switch to U step by step H -U L , creating conditions for diode D1 to conduct; bridge arm A4 is connected in series between the low-voltage side and the high-voltage side for discharge, and its discharge current amplitude is I H , the discharge voltage is U H -U L .

[0034] During [t2, t3], thyristor T1 is turned off, diode D1 is turned on by positive voltage, and the low-voltage side bridge arm parallel DC / DC converter enters the high-voltage side commutation stage 1. Bridge arm A4 and bridge arm A1 commutate on the high-voltage side, and bridge arm A2 and bridge arm A3 are connected in parallel on the low-voltage side and remain unchanged. At this time, the bridge arm A4 voltage u A4 Equal to U H -U L -U1, bridge arm A1 voltage u A1 Equal to U H -U L +U1, the voltage difference 2U1 between the A4 bridge arm and the A1 bridge arm is applied to the bridge arm inductance 2L of the two bridge arms, so that the bridge arm A1 current i A1 Increase linearly from 0 to I at a rate of 2U1 / 2L H , bridge arm A4 current i A4 At the same rate of change from I HIt decreases linearly to 0, thus completing the high-voltage side commutation stage 1, where: U1 is the high-voltage side commutation voltage.

[0035] During [t3, t4], the low-voltage side bridge arm parallel DC / DC converter enters working state 3. At this time, bridge arm A2 and bridge arm A3 are connected in parallel to the low-voltage side for charging, and the charging current amplitude is (I L -I H ) / 2, the charging voltage is -U L ; Bridge arm A4 is in the disconnected state, its current is 0, and its voltage is -U L On the basis of additional output of the reverse pressure U for a period of time RE , ensuring that diode D4 is reliably turned off. After that, the voltage u A4 By -U L Switch to U step by step H -U L , creating conditions for the thyristor T4 to turn on; the bridge arm A1 is connected in series between the low-voltage side and the high-voltage side for discharge, and its discharge current amplitude is I H , the discharge voltage is U H -U L .

[0036] During [t4, t5], thyristor T4 is triggered and turned on, and the low-voltage side bridge arm parallel DC / DC converter enters the low-voltage side commutation stage 2. Bridge arm A2 and bridge arm A4 commutate on the low-voltage side, bridge arm A3 remains unchanged in parallel on the low-voltage side, and bridge arm A1 remains unchanged in series between the low-voltage side and the high-voltage side. At this time, the bridge arm A2 voltage u A2 Equal to -U L -U0, bridge arm A4 voltage u A4 Equal to -U L +U0, the voltage difference 2U0 between bridge arm A2 and bridge arm A4 is applied to the bridge arm inductance 2L of the two bridge arms, so that the current i A2 At a change rate of 2U0 / 2L from (I L -I H ) / 2 linearly decreases to 0, and the bridge arm A4 current i A4 Increase linearly from 0 to (I L -I H ) / 2, thus completing the low-voltage side commutation stage 2.

[0037] During [t5, t6], the low-voltage side bridge arm parallel DC / DC converter enters working state 4. At this time, bridge arm A3 and bridge arm A4 are connected in parallel to the low-voltage side for charging, and the charging current amplitude is (I L -I H ) / 2, the charging voltage is -U L; Bridge arm A2 is in the disconnected state, its current is 0, and its voltage is -U L The additional output is longer than the thyristor reverse turn-off time t q The back pressure U RE , so that the thyristor T2 is reliably turned off. After that, the voltage u A2 By -U L Switch to U step by step H -U L , creating conditions for diode D2 to conduct; bridge arm A1 is connected in series between the low-voltage side and the high-voltage side for discharge, and its discharge current amplitude is I H , the discharge voltage is U H -U L .

[0038] During [t6, t7], thyristor T2 is turned off, diode D2 is turned on by positive voltage, and the low-voltage side bridge arm parallel DC / DC converter enters the high-voltage side commutation stage 2. Bridge arm A1 and bridge arm A2 commutate on the high-voltage side, and bridge arm A3 and bridge arm A4 are connected in parallel on the low-voltage side and remain unchanged. At this time, the bridge arm A1 voltage u A1 Equal to U H -U L -U1, bridge arm A2 voltage u A2 Equal to U H -U L +U1, the voltage difference 2U1 between the A1 bridge arm and the A2 bridge arm is applied to the bridge arm inductance 2L of the two bridge arms, so that the bridge arm A2 current i A2 Increase linearly from 0 to I at a rate of 2U1 / 2L H , bridge arm A1 current i A1 At the same rate of change from I H It decreases linearly to 0, thus completing the high-voltage side commutation stage 2.

[0039] During [t7, t8], the low-voltage side bridge arm parallel DC / DC converter enters working state 5. At this time, bridge arm A3 and bridge arm A4 are connected in parallel to the low-voltage side for charging, and the charging current amplitude is (I L -I H ) / 2, the charging voltage is -U L ; Bridge arm A1 is in the disconnected state, its current is 0, and its voltage is -U L On the basis of additional output of the reverse pressure U for a period of time RE , ensuring that diode D1 is reliably turned off. After that, the voltage u A1 By -U L Switch to U step by step H -U L, creating conditions for the thyristor T1 to turn on; the bridge arm A2 is connected in series between the low-voltage side and the high-voltage side for discharge, and its discharge current amplitude is I H , the discharge voltage is U H -U L .

[0040] During [t8, t9], thyristor T1 is triggered and turned on, and the low-voltage side bridge arm parallel DC / DC converter enters the low-voltage side commutation stage 3. Bridge arm A3 and bridge arm A1 commutate on the low-voltage side, bridge arm A4 is connected in parallel on the low-voltage side and remains unchanged, and bridge arm A2 is connected in series between the low-voltage side and the high-voltage side and remains unchanged. At this time, the bridge arm A3 voltage u A3 Equal to -U L -U0, bridge arm A1 voltage u A1 Equal to -U L +U0, the voltage difference 2U0 between bridge arm A3 and bridge arm A1 is applied to the bridge arm inductance 2L of the two bridge arms, so that the current i A3 At a change rate of 2U0 / 2L from (I L -I H ) / 2 linearly decreases to 0, the bridge arm A1 current i A1 Increase linearly from 0 to (I L -I H ) / 2, thus completing the low-voltage side commutation stage 3.

[0041] [t9,t 10 ], the low voltage side bridge arm parallel DC / DC converter enters working state 6. At this time, bridge arm A4 and bridge arm A1 are connected in parallel to the low voltage side for charging, and the charging current amplitude is (I L -I H ) / 2, the charging voltage is -U L ; Bridge arm A3 is in the disconnected state, its current is 0, and its voltage is -U L The additional output is longer than the thyristor reverse turn-off time t q The back pressure U RE , so that the thyristor T3 is reliably turned off. After that, the voltage u A3 By -U L Switch to U step by step H -U L , creating conditions for diode D3 to conduct; bridge arm A2 is connected in series between the low-voltage side and the high-voltage side for discharge, and its discharge current amplitude is I H , the discharge voltage is U H -U L .

[0042] [t 10 ,t 11] During this period, the thyristor T3 is turned off, the diode D3 is turned on by the positive voltage, and the low-voltage side bridge arm parallel DC / DC converter enters the high-voltage side commutation stage 3. Bridge arm A2 and bridge arm A3 commutate on the high-voltage side, and bridge arm A4 and bridge arm A1 are connected in parallel on the low-voltage side and remain unchanged. At this time, the bridge arm A2 voltage u A2 Equal to U H -U L -U1, bridge arm A3 voltage u A3 Equal to U H -U L +U1, the voltage difference 2U1 between the A2 bridge arm and the A3 bridge arm is applied to the bridge arm inductance 2L of the two bridge arms, so that the bridge arm A3 current i A3 Increase linearly from 0 to I at a rate of 2U1 / 2L H , bridge arm A2 current i A2 At the same rate of change from I H It decreases linearly to 0, thus completing the high-voltage side commutation stage 3.

[0043] [t 11 ,t 12 ], the low voltage side bridge arm parallel DC / DC converter enters working state 7. At this time, bridge arm A4 and bridge arm A1 are connected in parallel to the low voltage side for charging, and the charging current amplitude is (I L -I H ) / 2, the charging voltage is -U L ; Bridge arm A2 is in the disconnected state, its current is 0, and its voltage is -U L On the basis of additional output of the reverse pressure U for a period of time RE , ensuring that diode D2 is reliably turned off. After that, the voltage u A2 By -U L Switch to U step by step H -U L , creating conditions for the thyristor T2 to turn on; the bridge arm A3 is connected in series between the low-voltage side and the high-voltage side for discharge, and its discharge current amplitude is I H , the discharge voltage is U H -U L .

[0044] [t 12 ,t 13 ], the thyristor T2 is triggered and turned on, and the low-voltage side bridge arm parallel DC / DC converter enters the low-voltage side commutation stage 4. Bridge arm A4 and bridge arm A2 commutate on the low-voltage side, bridge arm A1 remains unchanged in parallel on the low-voltage side, and bridge arm A3 remains unchanged in series between the low-voltage side and the high-voltage side. At this time, the bridge arm A4 voltage u A4 Equal to -U L -U0, bridge arm A2 voltage u A2 Equal to -UL +U0, the voltage difference 2U0 between bridge arm A4 and bridge arm A2 is applied to the bridge arm inductance 2L of the two bridge arms, so that the current i A4 At a change rate of 2U0 / 2L from (I L -I H ) / 2 linearly decreases to 0, the bridge arm A2 current i A2 Increase linearly from 0 to (I L -I H ) / 2, thus completing the low-voltage side commutation stage 4.

[0045] [t 13 ,t 14 ], the low-voltage side bridge arm parallel DC / DC converter enters working state 8. At this time, bridge arm A1 and bridge arm A2 are connected in parallel to the low-voltage side for charging, and the charging current amplitude is (I L -I H ) / 2, the charging voltage is -U L ; Bridge arm A4 is in the disconnected state, its current is 0, and its voltage is -U L The additional output is longer than the thyristor reverse turn-off time t q The back pressure U RE , so that the thyristor T4 is reliably turned off. After that, the voltage u A4 By -U L Switch to U step by step H -U L , creating conditions for diode D4 to conduct; bridge arm A3 is connected in series between the low-voltage side and the high-voltage side for discharge, and its discharge current amplitude is I H , the discharge voltage is U H -U L .

[0046] [t 14 ,t 15 ] During this period, thyristor T4 is turned off, diode D4 is turned on by positive voltage, and the low-voltage side bridge arm parallel DC / DC converter enters the high-voltage side commutation stage 4. Bridge arm A3 and bridge arm A4 commutate on the high-voltage side, and bridge arm A1 and bridge arm A2 are connected in parallel on the low-voltage side and remain unchanged. At this time, the bridge arm A3 voltage u A3 Equal to U H -U L -U1, bridge arm A4 voltage u A4 Equal to U H -U L +U1, the voltage difference 2U1 between the A3 bridge arm and the A4 bridge arm is applied to the bridge arm inductance 2L of the two bridge arms, so that the bridge arm A4 current i A4 Increase linearly from 0 to I at a rate of 2U1 / 2L H, bridge arm A3 current i A3 At the same rate of change from I H It decreases linearly to 0, thus completing the high-voltage side commutation stage 4.

[0047] [t 15 ,t 16 ], the low-voltage side bridge arm parallel DC / DC converter enters working state 9, which is the same as working state 1. At this time, bridge arm A1 and bridge arm A2 are connected in parallel to the low-voltage side for charging, and the charging current amplitude is (I L -I H ) / 2, the charging voltage is -U L ; Bridge arm A3 is in the disconnected state, its current is 0, and its voltage is -U L On the basis of additional output of the reverse pressure U for a period of time RE , ensuring that diode D3 is reliably turned off. After that, the voltage u A3 By -U L Switch to U step by step H -U L , creating conditions for the thyristor T3 to turn on; the bridge arm A4 is connected in series between the low-voltage side and the high-voltage side for discharge, and its discharge current amplitude is I H , the discharge voltage is U H -U L .

[0048] Through the above analysis, we can get the voltage and current waveforms of the four bridge arms of the low-voltage side bridge arm parallel DC / DC converter in one working cycle, as shown in Figure 2 As shown. Figure 2 It can be seen that the four full-bridge sub-module bridge arms (bridge arm A1, bridge arm A2, bridge arm A3, bridge arm A4) of the low-voltage side bridge arm parallel DC / DC converter remain symmetrical, and the voltage and current phases of two adjacent bridge arms differ by 90° and have the same amplitude.

[0049] In order to verify the function of the low-voltage side bridge arm parallel DC / DC converter, a low-voltage side bridge arm parallel DC / DC converter model with a rated transmission power of P = 90MW was built in Simulink for simulation verification. The low-voltage side and high-voltage side DC grids are simulated with fixed voltage sources, which are designed as U L =100kV and U H =300kV. In the four-phase bridge arm, each phase bridge arm has 180 full-bridge sub-modules, and the rated capacitance voltage of each full-bridge sub-module is U C The simulation parameters are shown in Table 2.

[0050] Table 2 Simulation parameters of low voltage side bridge arm parallel DC / DC converter

[0051]

[0052] Figure 3 The dynamic simulation results of the low-voltage side bridge arm parallel DC / DC converter are shown. In the time [0.1s, 0.3s], the power transmitted from the low-voltage side to the high-voltage side is 30MW. At this time, the low-voltage side current I L =300A, high voltage side current I H =100A. In [0.3s, 0.5s], the power transmitted from the low voltage side to the high voltage side increases linearly from 30MW to 90MW, and the current I L The current on the high-voltage side increases linearly from 300A to 900A. H It increases linearly from 100A to 300A. In [0.5s, 0.8s], the power transmitted from the low-voltage side to the high-voltage side is 90MW. At this time, the current I L =900A, high voltage side current I H =300A. During the entire dynamic process, the total voltage of the bridge arm A1 submodule capacitor U C_sum Can be stabilized at its reference value U C_sum_ref =360kV, with fluctuation of about 10kV.

[0053] Figure 4 The steady-state simulation results of the low-voltage side bridge arm parallel DC / DC converter in the time [0.2s, 0.22s] are shown. At this time, bridge arm A i The charging current and discharging current of (i=1,2,3,4) are both (I L -I H ) / 2=I H =100A trapezoidal wave, bridge arm A i The voltage u Ai At charging voltage -U L =-100kV and discharge voltage U H -U L =200kV switching back and forth. Figure 5 The steady-state simulation results of the low-voltage side bridge arm parallel DC / DC converter in the time [0.6s, 0.62s] are shown. At this time, bridge arm A i The charging current and discharging current of (i=1,2,3,4) are both (I L -I H ) / 2=I H = 300A trapezoidal wave, bridge arm A i The voltage u Ai Still charging voltage -U L =-100kV and discharge voltage U H -U L =200kV switching back and forth. In addition, from the four-phase bridge arm current (i A1,i A2 ,i A3 ,i A4 ) and the four-phase bridge arm voltage (u A1 ,u A2 ,u A3 ,u A4 ) waveform, it can be seen that the current and voltage of the four-phase bridge arms differ by 90° electrical angle, making the input and output DC current waveforms continuous and smooth without the need for additional filters.

Claims

1. A high current DC / DC converter with low voltage side bridge arms connected in parallel, characterized in that The DC / DC converter includes a full-bridge submodule bridge arm, a bridge arm inductor, a thyristor valve group and a diode valve group, wherein: The bridge arms of the full bridge submodule include bridge arms A1 to A1. i , i =1, 2, 3, 4, the voltage and current phases of two adjacent bridge arms differ by 90° and have the same amplitude; The bridge arm inductor includes the bridge arm A1 inductor ~ bridge arm A i inductance; The thyristor valve group includes thyristors T1 to T1. i ; The diode valve group includes diodes D1 to D i ; The bridge arm A i One end of the inductor is connected to the positive electrode of the low voltage side, and the bridge arm A i The other end of the inductor is connected to bridge arm A i One end of the bridge is connected to i The other end leads to two branches, one of which passes through the diode D i Connected to the positive pole of the high voltage side, the other branch passes through the thyristor T i They are respectively connected to the negative electrode on the low voltage side and the negative electrode on the high voltage side; The DC / DC converter goes through the following 9 working states and 4 commutation stages in one working cycle: Initially, the low-voltage side bridge arm parallel DC / DC converter is in working state 1. At this time, bridge arm A1 and bridge arm A2 are connected in parallel to the low-voltage side for charging, and the charging current amplitudes are both ( I L - I H ) / 2, the charging voltage is - U L ; Bridge arm A3 is in the disconnected state, its current is 0 and its voltage is - U L ; Bridge arm A4 is connected in series between the low voltage side and the high voltage side for discharge, and its discharge current amplitude is I H , the discharge voltage is U H - U L ,in: U L is the low voltage side voltage, U H is the high voltage side voltage, I L is the low voltage side current, I H is the high voltage side current; [0, t During the period 1], the thyristor T3 is triggered and turned on, and the low-voltage side bridge arm parallel DC / DC converter enters the low-voltage side commutation stage 1. Bridge arm A1 and bridge arm A3 commutate on the low-voltage side, bridge arm A2 is connected in parallel on the low-voltage side and remains unchanged, and bridge arm A4 is connected in series between the low-voltage side and the high-voltage side and remains unchanged. At this time, the bridge arm A1 voltage u A1 equal- U L - U 0, bridge arm A3 voltage u A3 equal- U L + U 0, the voltage difference between bridge arm A1 and bridge arm A3 is 2 U 0 bridge arm inductance applied to these two bridge arms 2 L So that the bridge arm A1 current i A1 With 2 U 0 / 2 L The speed of change from ( I L - I H ) / 2 linearly decreases to 0, the bridge arm A3 current i A3 Increase linearly from 0 to ( I L - I H ) / 2, thus completing the low-voltage side commutation stage 1, where: U 0 is the commutation voltage on the low voltage side; [ t 1, t 2], the low-voltage side bridge arm parallel DC / DC converter enters working state 2. At this time, bridge arm A2 and bridge arm A3 are connected in parallel to the low-voltage side for charging, and the charging current amplitudes are both ( I L - I H ) / 2, the charging voltage is - U L ; Bridge arm A1 is in the disconnected state, its current is 0, and its voltage is - U L The additional output is longer than the thyristor reverse turn-off time t q Back pressure U RE , so that the thyristor T1 is reliably turned off, after which the bridge arm A1 voltage u A1 Depend on- U L Switch to U H - U L , creating conditions for diode D1 to conduct; bridge arm A4 is connected in series between the low-voltage side and the high-voltage side for discharge, and its discharge current amplitude is I H , the discharge voltage is U H - U L ; [ t 2, t 3], the thyristor T1 is turned off, the diode D1 is turned on by the positive voltage, and the low-voltage side bridge arm parallel DC / DC converter enters the high-voltage side commutation stage 1. The bridge arm A4 and the bridge arm A1 are commutated on the high-voltage side, and the bridge arm A2 and the bridge arm A3 are connected in parallel on the low-voltage side and remain unchanged. At this time, the bridge arm A4 voltage u A4 equal U H - U L - U 1. Bridge arm A1 voltage u A1 equal U H - U L + U 1. Voltage difference between A4 bridge arm and A1 bridge arm 2 U 1 Bridge arm inductance applied to these two bridge arms 2 L So that the bridge arm A1 current i A1 With 2 U 1 / 2 L The speed of change increases linearly from 0 to I H , bridge arm A4 current i A4 At the same rate of change from I H Linearly decreases to 0, thus completing the high-voltage side commutation stage 1, where: U 1 is the commutation voltage on the high-voltage side; [ t 3, t 4], the low-voltage side bridge arm parallel DC / DC converter enters working state 3. At this time, bridge arm A2 and bridge arm A3 are connected in parallel to the low-voltage side for charging, and the charging current amplitudes are both ( I L - I H ) / 2, the charging voltage is - U L ; Bridge arm A4 is in the disconnected state, its current is 0, and its voltage is - U L Output back pressure for a period of time on the basis of U RE , to ensure that diode D4 is reliably turned off, then the bridge arm A4 voltage u A4 Depend on- U L Switch to U H - U L , creating conditions for the thyristor T4 to turn on; the bridge arm A1 is connected in series between the low-voltage side and the high-voltage side for discharge, and its discharge current amplitude is I H , the discharge voltage is U H - U L ; [ t 4, t 5], thyristor T4 is triggered and turned on, and the low-voltage side bridge arm parallel DC / DC converter enters the low-voltage side commutation stage 2. Bridge arm A2 and bridge arm A4 commutate on the low-voltage side, bridge arm A3 is connected in parallel on the low-voltage side and remains unchanged, and bridge arm A1 is connected in series between the low-voltage side and the high-voltage side and remains unchanged. At this time, the bridge arm A2 voltage u A2 equal- U L - U 0, bridge arm A4 voltage u A4 equal- U L + U 0, the voltage difference between bridge arm A2 and bridge arm A4 is 2 U 0 bridge arm inductance applied to these two bridge arms 2 L So that the bridge arm A2 current i A2 With 2 U 0 / 2 L The speed of change from ( I L - I H ) / 2 linearly decreases to 0, the bridge arm A4 current i A4 Increase linearly from 0 to ( I L - I H ) / 2, thus completing the low-voltage side commutation stage 2; [ t 5, t 6], the low-voltage side bridge arm parallel DC / DC converter enters working state 4. At this time, bridge arm A3 and bridge arm A4 are connected in parallel to the low-voltage side for charging, and the charging current amplitudes are both ( I L - I H ) / 2, the charging voltage is - U L ; Bridge arm A2 is in the disconnected state, its current is 0, and its voltage is - U L The additional output is longer than the thyristor reverse turn-off time t q Back pressure U RE , so that the thyristor T2 is reliably turned off, after which the bridge arm A2 voltage u A2 Depend on- U L Switch to U H - U L , creating conditions for diode D2 to conduct; bridge arm A1 is connected in series between the low-voltage side and the high-voltage side for discharge, and its discharge current amplitude is I H , the discharge voltage is U H - U L ; [ t 6, t 7], the thyristor T2 is turned off, the diode D2 is turned on by the positive voltage, and the low-voltage side bridge arm parallel DC / DC converter enters the high-voltage side commutation stage 2, the bridge arm A1 and the bridge arm A2 are commutated on the high-voltage side, and the bridge arm A3 and the bridge arm A4 are connected in parallel on the low-voltage side and remain unchanged. At this time, the bridge arm A1 voltage u A1 equal U H - U L - U 1. Bridge arm A2 voltage u A2 equal U H - U L + U 1. Voltage difference between A1 bridge arm and A2 bridge arm 2 U 1 Bridge arm inductance applied to these two bridge arms 2 L So that the bridge arm A2 current i A2 With 2 U 1 / 2 L The speed of change increases linearly from 0 to I H , bridge arm A1 current i A1 At the same rate of change from I H Linearly decreases to 0, thus completing the high-voltage side commutation stage 2; [ t 7, t 8], the low-voltage side bridge arm parallel DC / DC converter enters working state 5. At this time, bridge arm A3 and bridge arm A4 are connected in parallel to the low-voltage side for charging, and the charging current amplitudes are both ( I L - I H ) / 2, the charging voltage is - U L ; Bridge arm A1 is in the disconnected state, its current is 0, and its voltage is - U L Output back pressure for a period of time on the basis of U RE , to ensure that diode D1 is reliably turned off, then the bridge arm A1 voltage u A1 Depend on- U L Switch to U H - U L , creating conditions for the thyristor T1 to turn on; the bridge arm A2 is connected in series between the low-voltage side and the high-voltage side for discharge, and its discharge current amplitude is I H , the discharge voltage is U H - U L ; [ t 8, t 9], the thyristor T1 is triggered and turned on, and the low-voltage side bridge arm parallel DC / DC converter enters the low-voltage side commutation stage 3. The bridge arm A3 and the bridge arm A1 are commutated on the low-voltage side, the bridge arm A4 is connected in parallel on the low-voltage side and remains unchanged, and the bridge arm A2 is connected in series between the low-voltage side and the high-voltage side and remains unchanged. At this time, the bridge arm A3 voltage u A3 equal- U L - U 0, bridge arm A1 voltage u A1 equal- U L + U 0, the voltage difference between bridge arm A3 and bridge arm A1 is 2 U 0 bridge arm inductance applied to these two bridge arms 2 L So that the bridge arm A3 current i A3 With 2 U 0 / 2 L The speed of change from ( I L - I H ) / 2 linearly decreases to 0, the bridge arm A1 current i A1 Increase linearly from 0 to ( I L - I H ) / 2, thus completing the low-voltage side commutation stage 3; [ t 9, t 10 ], the low-voltage side bridge arm parallel DC / DC converter enters working state 6. At this time, bridge arm A4 and bridge arm A1 are connected in parallel to the low-voltage side for charging, and the charging current amplitudes are both ( I L - I H ) / 2, the charging voltage is - U L ; Bridge arm A3 is in the disconnected state, its current is 0, and its voltage is - U L The additional output is longer than the thyristor reverse turn-off time t q Back pressure U RE , so that the thyristor T3 is reliably turned off, after which the bridge arm A3 voltage u A3 Depend on- U L Switch to U H - U L , creating conditions for diode D3 to conduct; bridge arm A2 is connected in series between the low-voltage side and the high-voltage side for discharge, and its discharge current amplitude is I H , the discharge voltage is U H - U L ; [ t 10 , t 11 ], the thyristor T3 is turned off, the diode D3 is turned on by the positive voltage, and the low-voltage side bridge arm parallel DC / DC converter enters the high-voltage side commutation stage 3, the bridge arm A2 and the bridge arm A3 are commutated on the high-voltage side, and the bridge arm A4 and the bridge arm A1 are connected in parallel on the low-voltage side and remain unchanged. At this time, the bridge arm A2 voltage u A2 equal U H - U L - U 1. Bridge arm A3 voltage u A3 equal U H - U L + U 1. Voltage difference between A2 bridge arm and A3 bridge arm 2 U 1 Bridge arm inductance applied to these two bridge arms 2 L So that the bridge arm A3 current i A3 With 2 U 1 / 2 L The speed of change increases linearly from 0 to I H , bridge arm A2 current i A2 At the same rate of change from I H Linearly decreases to 0, thus completing the high-voltage side commutation stage 3; [ t 11 , t 12 ], the low-voltage side bridge arm parallel DC / DC converter enters working state 7. At this time, bridge arm A4 and bridge arm A1 are connected in parallel to the low-voltage side for charging, and the charging current amplitudes are both ( I L - I H ) / 2, the charging voltage is - U L ; Bridge arm A2 is in the disconnected state, its current is 0, and its voltage is - U L Output back pressure for a period of time on the basis of U RE , to ensure that diode D2 is reliably turned off, then the bridge arm A2 voltage u A2 Depend on- U L Switch to U H - U L , creating conditions for the thyristor T2 to turn on; the bridge arm A3 is connected in series between the low-voltage side and the high-voltage side for discharge, and its discharge current amplitude is I H , the discharge voltage is U H - U L ; [ t 12 , t 13 ], the thyristor T2 is triggered and turned on, and the low-voltage side bridge arm parallel DC / DC converter enters the low-voltage side commutation stage 4. The bridge arm A4 and the bridge arm A2 are commutated on the low-voltage side, the bridge arm A1 is connected in parallel on the low-voltage side and remains unchanged, and the bridge arm A3 is connected in series between the low-voltage side and the high-voltage side and remains unchanged. At this time, the bridge arm A4 voltage u A4 equal- U L - U 0, bridge arm A2 voltage u A2 equal- U L + U 0, the voltage difference between bridge arm A4 and bridge arm A2 is 2 U 0 bridge arm inductance applied to these two bridge arms 2 L So that the bridge arm A4 current i A4 With 2 U 0 / 2 L The speed of change from ( I L - I H ) / 2 linearly decreases to 0, the bridge arm A2 current i A2 Increase linearly from 0 to ( I L - I H ) / 2, thus completing the low-voltage side commutation stage 4; [ t 13 , t 14 ], the low-voltage side bridge arm parallel DC / DC converter enters working state 8. At this time, bridge arm A1 and bridge arm A2 are connected in parallel to the low-voltage side for charging, and the charging current amplitudes are both ( I L - I H ) / 2, the charging voltage is - U L ; Bridge arm A4 is in the disconnected state, its current is 0, and its voltage is - U L The additional output is longer than the thyristor reverse turn-off time t q Back pressure U RE , so that the thyristor T4 is reliably turned off, after which the bridge arm A4 voltage u A4 Depend on- U L Switch to U H - U L , creating conditions for diode D4 to conduct; bridge arm A3 is connected in series between the low-voltage side and the high-voltage side for discharge, and its discharge current amplitude is I H , the discharge voltage is U H - U L ; [ t 14 , t 15 ], thyristor T4 is turned off, diode D4 is turned on by positive voltage, and the low-voltage side bridge arm parallel DC / DC converter enters the high-voltage side commutation stage 4, bridge arm A3 and bridge arm A4 commutate on the high-voltage side, bridge arm A1 and bridge arm A2 are connected in parallel on the low-voltage side and remain unchanged. At this time, the bridge arm A3 voltage u A3 equal U H - U L - U 1. Bridge arm A4 voltage u A4 equal U H - U L + U 1. Voltage difference between A3 bridge arm and A4 bridge arm 2 U 1 Bridge arm inductance applied to these two bridge arms 2 L So that the bridge arm A4 current i A4 With 2 U 1 / 2 L The speed of change increases linearly from 0 to I H , bridge arm A3 current i A3 At the same rate of change from I H Linearly decreases to 0, thus completing the high-voltage side commutation stage 4; [ t 15 , t 16 ], the low-voltage side bridge arm parallel DC / DC converter enters working state 9, which is the same as working state 1. At this time, bridge arm A1 and bridge arm A2 are connected in parallel to the low-voltage side for charging, and the charging current amplitudes are both ( I L - I H ) / 2, the charging voltage is - U L ; Bridge arm A3 is in the disconnected state, its current is 0, and its voltage is - U L Output back pressure for a period of time on the basis of U RE , to ensure that diode D3 is reliably turned off, then the bridge arm A3 voltage u A3 Depend on- U L Switch to U H - U L , creating conditions for the thyristor T3 to turn on; the bridge arm A4 is connected in series between the low-voltage side and the high-voltage side for discharge, and its discharge current amplitude is I H , the discharge voltage is U H - U L .

2. The high-current DC / DC converter with low-voltage side bridge arms in parallel according to claim 1 is characterized in that The bridge arms of the full-bridge sub-modules are each composed of N full-bridge sub-modules connected in series.

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