Bidirectional dc / dc converter with interphase and intraphase twice branching and control method

Abstract

This invention relates to the field of DC transformers and describes a bidirectional DC / DC converter with both phase-to-phase and intra-phase current shunting. The converter consists of symmetrical and identical four-phase parallel connections, with each phase including a full-bridge arm FB, a half-bridge arm HB, and two arm inductors L. FB L HB Three anti-parallel thyristors and diodes T j1 / D j1 T j2 / D j2 T j3 / D j3 Given j = a, b, c, d, this DC / DC converter utilizes a multi-phase interphase current shunting and intraphase half-bridge and full-bridge arm parallel current shunting method to achieve two current shunting operations for the large low-voltage side, one between phases and one within a phase, thereby reducing the current stress on the bridge arms. The employed control method ensures that the four phases of the DC / DC converter maintain symmetrical alternating operation, achieving bidirectional power transmission. When high power is transmitted, the current stress between the bridge arms decreases, and switching losses decrease, increasing the capacity of the non-isolated transformer, reducing cost, and decreasing size.

Description

Technical Field

[0001] This invention relates to the field of DC transformers, and more specifically to a bidirectional DC / DC converter and control method with phase-to-phase and phase-to-phase current splitting. Background Technology

[0002] DC transformers are key equipment in DC power grids. With the continuous increase in DC transmission capacity, DC transformers need to withstand voltages of several kV, and their capacity needs to reach MW or even GW. Currently, DC transformers are mainly divided into isolated transformers and non-isolated transformers. While isolated transformers can utilize AC transformers to achieve high-voltage, high-power transmission, they are large and expensive, making them unsuitable for offshore flexible DC transmission scenarios. Non-isolated transformers, although having advantages in size, need to withstand several kA of current on the low-voltage side, resulting in excessive bridge arm current stress and switching losses, limiting their power delivery capacity. Therefore, how to improve the capacity, reduce cost, and decrease the size of non-isolated transformers has become a hot research topic. Summary of the Invention

[0003] This invention addresses the problems of large capacity, high cost, and large size of non-isolated transformers by providing a bidirectional DC / DC converter and control method with two-stage current splitting between phases and within phases.

[0004] The technical solution adopted in this invention is:

[0005] A bidirectional DC / DC converter with phase-to-phase and phase-to-phase shunt, it includes a low-voltage side DC voltage U L DC voltage U on the high-voltage side H The converter consists of four identical symmetrical phases (phase a, phase b, phase c, and phase d) connected in parallel. Each phase includes a full-bridge arm (FB), a half-bridge arm (HB), and two arm inductors (L). FB L HB ), three anti-parallel thyristors and diodes (T) j1 / D j1 T j2 / D j2 T j3 / D j3 (j = a, b, c, d);

[0006] Taking phase a as an example, the negative terminal of half-bridge arm HB is connected to the arm inductor L. HB With T a3 / D a3 Thyristor T a3 The positive terminal is connected to the positive terminal, and the negative terminal of the full-bridge arm FB is connected through the arm inductor L. FB With T a3 / D a3 Thyristor Ta3 The positive terminals are connected, T a3 / D a3 Thyristor T a3 The negative terminal and the low-voltage side DC voltage U L The negative terminal and the DC voltage U on the high-voltage side H The negative terminal is connected;

[0007] The positive terminal of the full-bridge arm FB and T a1 / D a1 Diode D a1 The positive and low-voltage side DC voltage U L The positive terminals are connected, T a1 / D a1 Diode D a1 The negative electrode is simultaneously connected to the positive electrode of the half-bridge arm HB and T. a2 / D a2 Diode D a2 The positive terminals are connected, T a2 / D a2 Diode D a2 The negative terminal and the high-voltage side DC voltage U H The positive terminals are connected.

[0008] Preferably, the four phases (a, b, c, and d) of the DC / DC converter maintain symmetrical alternating operation.

[0009] Preferably, this DC / DC converter is suitable for both forward and reverse power transmission; the inductance of the half-bridge arm and the full-bridge arm are set to be equal, i.e., L HB =L FB =L; The commutation voltages U2 and U3 of the half-bridge arm are equal in magnitude to the commutation voltages U1 and U0 of the full-bridge arm, that is, |U2| = |U1|, |U3| = |U0|.

[0010] Its forward transmission process is as follows:

[0011] Initially, the full-bridge arms and half-bridge arms of phases c and d are connected in parallel to the low-voltage side for charging. The charging current for both the full-bridge arms and half-bridge arms is (Ic). L -I H ) / 4, the charging voltage is U L Phase b is in a disconnected state, with both its full-bridge arm current and half-bridge arm current being 0. The full-bridge arm and half-bridge arm of phase a are connected in series between the low-voltage side and the high-voltage side for discharge. The discharge current of the full-bridge arm is I. H The full-bridge arm output voltage is -(U H -U L ) / 2; The discharge current of the half-bridge arm is -I H The output voltage of the half-bridge arm is (U H -UL ) / 2;

[0012] During the period [0, t1], phase a and phase b undergo commutation on the high-voltage side. At this time, the output voltage of the full-bridge arm in phase a is -(U H -U L The output voltage of the half-bridge arm is (U) / 2+U1. H -U L The output voltage of the full-bridge arm in phase b is -(U) / 2-U1. H -U L ) / 2-U1, the output voltage of the half-bridge arm is (U H -U L The voltage difference 4U1 between phase a and phase b is applied to the bridge arm inductance 4L of the two phases, causing the full-bridge arm current in phase a to change from I at a rate of 4U1 / 4L. H As the current linearly decreases to 0, the half-bridge arm current changes from -I at a rate of 4U1 / 4L. H As the current increases linearly to 0, the full-bridge arm current in phase b also increases linearly from 0 to I at the same rate. H The half-bridge arm current decreases linearly from 0 to -I at the same rate of change. H ;

[0013] During the period [t1,t2], phase a is in a disconnected state, and its full-bridge arm current and half-bridge arm current are both 0. To reduce switching losses, the low-voltage side thyristor T is kept in a state of no connection. a3 When the ZVS turn-on condition is met, the output voltage of the full-bridge arm is changed from -(U H -U L ) / 2 Step-by-step switch to U L The output voltage of the half-bridge arm is determined by (U) H -U L ) / 2 Step-by-step switch to U L ;

[0014] During the period [t2,t3], thyristor T a3 When the circuit is triggered, phase c and phase a commutate on the low-voltage side; at this time, the output voltage of both the full-bridge arm and the half-bridge arm in phase a is U. L -U0, the output voltage of both the full-bridge arm and the half-bridge arm in phase c is U L +U0, diode D a1 Under positive voltage conduction, the voltage difference 2U0 between phase c and phase a is applied to the bridge arm inductance 2L of the two phases, causing both the full-bridge arm current and the half-bridge arm current in phase a to increase linearly from 0 to (I) at a rate of 2U0 / 2L. L -I H In phase c, both the full-bridge arm current and the half-bridge arm current change at a rate of 2U0 / 2L from (I) / 4. L-I H ) / 4 decreases linearly to 0;

[0015] During [t3,t4], the full-bridge arms and half-bridge arms of phases a and d are connected in parallel to the low-voltage side for charging. The charging current of both the full-bridge arm and the half-bridge arm is (I L -I H ) / 4, the charging voltage is U L ;

[0016] During the period [t4,t5], phase a and phase c undergo commutation on the low-voltage side. At this time, the output voltage of both the full-bridge arm and the half-bridge arm in phase a is U. L +U0, the output voltage of both the full-bridge arm and the half-bridge arm in phase c is U L -U0, diode D c1 Under positive voltage conduction, the voltage difference 2U0 between the bridge arms of phases a and c is applied to the bridge arm inductance 2L of the two phases, causing both the full-bridge arm current and the half-bridge arm current in phase a to change at a rate of 2U0 / 2L from (I... L -I H As the current decreases linearly from 0 to 0, the full-bridge arm current and half-bridge arm current in phase c both increase linearly from 0 to 0 at a rate of 2U0 / 2L. L -I H ) / 4;

[0017] During the period [t5,t6], phase a is in a disconnected state, and its full-bridge arm current and half-bridge arm current are both 0. Its full-bridge arm voltage and half-bridge arm voltage first reach U... L In addition, a reverse voltage U is output that is longer than the reverse turn-off time of the thyristor. RE Ensure thyristor T a3 To ensure reliable turn-off and reduce switching losses, the high-voltage side diode D... a2 The ZVS activation conditions are met, and the output voltage of its full-bridge arm is determined by U. L Switch step by step to -(U H -U L ) / 2, the output voltage of the half-bridge arm is determined by U L Switch step by step to (U) H -U L ) / 2;

[0018] During [t6,t7], phase d and phase a undergo commutation on the high-voltage side. At this time, the full-bridge arm output voltage of phase a is -(U H -U L ) / 2-U1, the output voltage of the half-bridge arm is (U H -U L The output voltage of the full-bridge arm in phase d is -(U) / 2+U1. H -U LThe output voltage of the half-bridge arm is (U) / 2+U1. H -U L The voltage difference 4U1 between phase d and phase a is applied to the bridge arm inductance 4L of the two phases, causing the full-bridge arm current in phase a to increase linearly from 0 to I at a rate of 4U1 / 4L. H The half-bridge arm current decreases linearly from 0 to -I at a rate of 4U1 / 4L. H The full-bridge arm current in phase d also changes at the same rate from I... H As the current linearly decreases to 0, the half-bridge arm current changes from -I at the same rate. H Increasing linearly to 0,

[0019] During [t7,t8], the full-bridge arm and half-bridge arm of phase a are connected via diode D. a2 Discharge is connected in series between the high-voltage side and the low-voltage side, and the discharge current of the entire bridge arm is I. H The full-bridge arm output voltage is -(U H -U L The discharge current of the half-bridge arm is -I / 2. H The output voltage of the half-bridge arm is (U H -U L ) / 2,

[0020] A bidirectional DC / DC converter with two phase-to-phase and intra-phase current splits completes one duty cycle T. s .

[0021] Preferably, the DC / DC converter is suitable for both forward and reverse power transmission;

[0022] Its reverse transmission process is as follows:

[0023] During reverse transmission, the high-voltage side current I H and low-voltage side current I L All are negative values. Initially, the full-bridge arm and half-bridge arm of phases c and d are connected in parallel to the low-voltage side for discharge, and the discharge current of both the full-bridge arm and the half-bridge arm is (I L -I H ) / 4, the discharge voltage is U L Phase b is in a disconnected state, with both its full-bridge arm current and half-bridge arm current being 0. The full-bridge arm and half-bridge arm of phase a are connected in series between the low-voltage side and the high-voltage side for charging, with the charging current of the full-bridge arm being I. H The full-bridge arm output voltage is -(U H -U L ) / 2; The charging current of the half-bridge arm is -I H The output voltage of the half-bridge arm is (U H -U L ) / 2;

[0024] During the period [0, t1], phase a and phase b undergo commutation on the high-voltage side. At this time, the output voltage of the full-bridge arm in phase a is -(U H -U L ) / 2-U1, the output voltage of the half-bridge arm is (U H -U L The output voltage of the full-bridge arm in phase b is -(U) / 2+U1. H -U L The output voltage of the half-bridge arm is (U) / 2+U1. H -U L The voltage difference 4U1 between phase a and phase b is applied to the bridge arm inductance 4L of the two phases, causing the full-bridge arm current in phase a to change from I at a rate of 4U1 / 4L. H As the current increases linearly to 0, the half-bridge arm current changes from -I at a rate of 4U1 / 4L. H As the current decreases linearly to 0, the full-bridge arm current in phase b also decreases linearly from 0 to I at the same rate. H The half-bridge arm current increases linearly from 0 to -I at the same rate of change. H ;

[0025] During the period [t1,t2], phase a is in a disconnected state, and its full-bridge arm current and half-bridge arm current are both 0. Its full-bridge arm voltage first reaches -(U... H -U L In addition to the ) / 2, an extra reverse voltage -U is output, longer than the thyristor's reverse turn-off time. RE The voltage of the half-bridge arm is (U H -U L Output reverse voltage U based on ) / 2 RE Ensure thyristor T a2 Reliable turn-off. To reduce switching losses, the low-voltage side diode D... a3 When the ZVS turn-on condition is met, the output voltage of the full-bridge arm is changed from -(U H -U L ) / 2 Step-by-step switch to U L The output voltage of the half-bridge arm is determined by (U) H -U L ) / 2 Step-by-step switch to U L ;

[0026] During the period [t2,t3], thyristor T a1 Trigger conduction, diode D a3 When the circuit is turned on, phase c and phase a undergo commutation on the low-voltage side; at this time, the output voltage of both the full-bridge arm and the half-bridge arm in phase a is U. L +U0, the output voltage of both the full-bridge arm and the half-bridge arm in phase c is U L-U0, the voltage difference 2U0 between the bridge arms of phase c and phase a is applied to the bridge arm inductance 2L of the two phases, thereby causing both the full-bridge arm current and the half-bridge arm current in phase a to decrease linearly from 0 to (I) at a rate of 2U0 / 2L. L -I H In phase c, both the full-bridge arm current and the half-bridge arm current change at a rate of 2U0 / 2L from (I) / 4. L -I H ) / 4 increases linearly to 0;

[0027] During [t3,t4], the full-bridge arm and half-bridge arm of phase a and phase d are connected in parallel to the low-voltage side for discharge. The discharge current of both the full-bridge arm and the half-bridge arm is (I L -I H ) / 4, the discharge voltage is U L ;

[0028] During the period [t4,t5], phase a and phase c undergo commutation on the low-voltage side. At this time, the output voltage of both the full-bridge arm and the half-bridge arm in phase a is U. L -U0, the output voltage of both the full-bridge arm and the half-bridge arm in phase c is U L +U0, thyristor T c1 When the circuit is triggered, the voltage difference 2U0 between the bridge arms of phases a and c is applied to the bridge arm inductance 2L of the two phases, causing both the full-bridge arm current and the half-bridge arm current in phase a to change at a rate of 2U0 / 2L from (I... L -I H As the current increases linearly from 0 to 0, both the full-bridge arm current and the half-bridge arm current in phase c decrease linearly from 0 to (I) at a rate of 2U0 / 2L. L -I H ) / 4;

[0029] During the period [t5,t6], phase a is in a disconnected state, and its full-bridge arm current and half-bridge arm current are both 0. Its full-bridge arm voltage and half-bridge arm voltage first reach U... L In addition, a reverse voltage -U is output that is longer than the reverse turn-off time of the thyristor. RE Ensure thyristor T a1 To ensure reliable turn-off and reduce switching losses, the high-voltage side thyristor T... a2 The ZVS activation conditions are met, and the output voltage of its full-bridge arm is determined by U. L Switch step by step to -(U H -U L ) / 2, the output voltage of the half-bridge arm is determined by U L Switch step by step to (U) H -U L ) / 2;

[0030] During [t6,t7], phase d and phase a undergo commutation on the high-voltage side. At this time, the full-bridge arm output voltage of phase a is -(U H -U L The output voltage of the half-bridge arm is (U) / 2+U1. H -U L The output voltage of the full-bridge arm in phase d is -(U) / 2-U1,d. H -U L ) / 2-U1, the output voltage of the half-bridge arm is (U H -U L The voltage difference 4U1 between phase d and phase a is applied to the bridge arm inductance 4L of the two phases, causing the full-bridge arm current in phase a to decrease linearly from 0 to I at a rate of 4U1 / 4L. H The half-bridge arm current increases linearly from 0 to -I at a rate of 4U1 / 4L. H The full-bridge arm current in phase d also changes at the same rate from I... H As the current increases linearly to 0, the half-bridge arm current changes from -I at the same rate. H Decrease linearly to 0,

[0031] During [t7,t8], the full-bridge arm and half-bridge arm of phase a are connected via thyristor T. a2 The charging is connected in series between the high-voltage side and the low-voltage side, and the charging current of the entire bridge arm is I. H The full-bridge arm output voltage is -(U H -U L ) / 2. The current in the half-bridge arm is -I H The output voltage of the half-bridge arm is (U H -U L ) / 2. This completes the transfer of power from the high-voltage side to the low-voltage side.

[0032] Preferably, since the bidirectional DC / DC converter with two phase-to-phase shunts operates in a symmetrical and staggered manner, the voltage and current waveforms of the full-bridge arm and half-bridge arm of adjacent phases have the same shape and are 90° out of phase.

[0033] A control method for a bidirectional DC / DC converter based on phase-to-phase and phase-to-phase current splitting is proposed. This control method comprises five parts: bridge arm energy balance control, bridge arm current control, bridge arm voltage feedforward control, thyristor converter valve on / off control, submodule capacitor voltage equalization, and carrier phase shift modulation. The bridge arm energy balance control, bridge arm current control, and bridge arm voltage feedforward control are respectively applicable to full-bridge and half-bridge bridge arms, i.e., full-bridge bridge arm energy balance control, full-bridge bridge arm current control, full-bridge bridge arm voltage feedforward control, half-bridge bridge arm energy balance control, half-bridge bridge arm current control, and half-bridge bridge arm voltage feedforward control.

[0034] When applied to the full bridge arm, this method can be called the full bridge arm control method, which includes the following steps:

[0035] Step 1: First, based on the system's power control requirements, use the formula P = U H I H =U L I L The charging current amplitude (I) of each phase bridge arm is obtained. L -I H ) / 4 and discharge current amplitude I H ;

[0036] Step 2: Set the discharge current amplitude I H Multiplying this by waveform generator 2 yields the reference waveform of the discharge current for each phase of the full-bridge arm, i. FB_out_ref ;

[0037] Step 3: Introduce full-bridge arm energy balance control to reduce losses generated during power transmission in the DC / DC converter; the full-bridge arm energy balance control controls the total capacitor voltage u of each full-bridge arm submodule. C_sum_FB Its reference value U C_sum_ref The deviation is fed into the proportional-integral (PI) controller, which outputs a modulation signal to adjust the current amplitude during arm charging, so as to keep the total energy of the arm balanced.

[0038] Step 4: Introduce the charging current amplitude (I) of the bridge arm L -I H ) / 4, used to achieve rapid control of the energy balance of the entire bridge arm; the charging current amplitude (I) of the entire bridge arm L -I H 4. The sum of the modulation signals obtained in step 3 is then multiplied by waveform generator 1 to obtain the reference signal i for the charging current of each phase full-bridge arm. FB_in_ref ;

[0039] Step 5: Use the discharge current reference waveform i of the full-bridge arm described in Step 2. FB_out_ref ; and the reference signal i of the charging current of each phase full-bridge arm mentioned in step four. FB_in_ref By adding them together, we obtain the current reference signal i for each phase of the full-bridge arm. FB_ref ;

[0040] Step Six: Introduce full-bridge arm current control to ensure that the actual current of each phase full-bridge arm can track its reference signal; the full-bridge arm current control is to use the current reference signal i of each phase full-bridge arm... FB_ref With actual current i FB The difference is calculated and fed into a proportional-integral (PI) controller to obtain the bridge arm voltage regulation value u. FB_PI;

[0041] Step 7: Introduce commutation voltage feedforward signals U0 / U1 and arm voltage feedforward control to achieve rapid tracking of arm current; this part of the control measures the voltage amplitude U during arm charging. L Multiplying by waveform generator 3 yields the input voltage feedforward signal u for each phase of the full-bridge arm. FB_in_fw Voltage amplitude during discharge - (U H -U L Multiplying 1 / 2 by waveform generator 4 yields the output voltage feedforward signal u for each phase of the full-bridge arm. FB_out_fw ;

[0042] Step 8: Introduce thyristor converter valve turn-on / turn-off control to provide the trigger signal and reverse turn-off voltage U of the thyristor valve group. RE ;

[0043] Step 9: Combine the commutation voltage feedforward signal U0 / U1 and the input voltage feedforward signal u of each phase full-bridge arm from Step 7. FB_in_fw The output voltage feedforward signal u of each phase full-bridge arm FB_out_fw The trigger signal and reverse turn-off voltage U of the thyristor valve group RE Add them together to obtain its voltage reference signal u. FB_ref The reference signal is then fed into the submodule capacitor voltage equalization and carrier phase shift modulation to obtain the IGBT drive signal of each submodule of each phase full-bridge arm.

[0044] A control method for a bidirectional DC / DC converter based on phase-to-phase and phase-to-phase current splitting is proposed. This control method comprises five parts: bridge arm energy balance control, bridge arm current control, bridge arm voltage feedforward control, thyristor converter valve on / off control, submodule capacitor voltage equalization, and carrier phase shift modulation. The bridge arm energy balance control, bridge arm current control, and bridge arm voltage feedforward control are respectively applicable to full-bridge and half-bridge bridge arms, i.e., full-bridge bridge arm energy balance control, full-bridge bridge arm current control, full-bridge bridge arm voltage feedforward control, half-bridge bridge arm energy balance control, half-bridge bridge arm current control, and half-bridge bridge arm voltage feedforward control.

[0045] When applied to a half-bridge arm, this method can be called a half-bridge arm control method. Taking power transfer from the low-voltage side to the high-voltage side as an example, it includes the following steps:

[0046] Step 1: First, based on the system's power control requirements, use the formula P = U H I H =U L I L The charging current amplitude (I) of each phase bridge arm is obtained. L -I H ) / 4 and discharge current amplitude IH ;

[0047] Step 2: Set the discharge current amplitude I H Multiplying this by waveform generator 2 yields the reference waveform of the discharge current for each phase half-bridge arm, i. HB_out_ref ;

[0048] Step 3: Introduce half-bridge arm energy balance control to reduce losses generated during power transmission in the DC / DC converter; the half-bridge arm energy balance control adjusts the total capacitor voltage u of the half-bridge arm submodules. C_sum_HB Its reference value U C_sum_ref The deviation is fed into the proportional-integral (PI) controller, which outputs a modulation signal to adjust the current amplitude during arm charging, so as to keep the total energy of the arm balanced.

[0049] Step 4: Introduce the charging current amplitude (I) of each phase bridge arm. L -I H ) / 4, used to achieve rapid control of energy balance of the half-bridge arm; the charging current amplitude (I) of the arm is... L -I H 4. The sum of the modulation signals obtained in step 3 is then multiplied by waveform generator 1 to obtain the reference signal i for the charging current of each phase half-bridge arm. HB_in_ref ;

[0050] Step 5: Use the discharge current reference waveform i of the half-bridge arm mentioned in Step 2. HB_out_ref ; and the reference signal i of the charging current of each phase half-bridge arm mentioned in step four. HB_in_ref By adding them together, we obtain the current reference signal i for each phase of the full-bridge arm. HB_ref ;

[0051] Step Six: Introduce half-bridge arm current control to ensure that the actual current of each phase half-bridge arm can track its reference signal; the full-bridge arm current control is to use the current reference signal i of each phase half-bridge arm. HB_ref With actual current i HB The difference is calculated and fed into a proportional-integral (PI) controller to obtain the bridge arm voltage regulation value u. HB_PI ;

[0052] Step 7: Introduce negative commutation voltage feedforward signals U2 / U3 and arm voltage feedforward control to achieve rapid tracking of arm current, where commutation voltage U2 = U0, U3 = -U1; this part of the control is to control the voltage amplitude U during arm charging. L Multiplying by waveform generator 3 yields the input voltage feedforward signal u for each phase half-bridge arm. HB_in_fw Voltage amplitude during discharge (U) H -UL Multiplying 1 / 2 by waveform generator 4 yields the output voltage feedforward signal u for each phase half-bridge arm. HB_out_fw ;

[0053] Step 8: Introduce thyristor converter valve turn-on / turn-off control to provide the trigger signal and reverse turn-off voltage U of the thyristor valve group. RE ;

[0054] Step 9: Combine the negative commutation voltage feedforward signal U2 / U3 and the input voltage feedforward signal u of each phase half-bridge arm from Step 7. HB_in_fw The output voltage feedforward signal u of each phase half-bridge arm HB_out_fw The trigger signal and reverse turn-off voltage U of the thyristor valve group RE Add them together to obtain its voltage reference signal u. HB_ref The reference signal is then fed into the submodule capacitor voltage equalization and carrier phase shift modulation to obtain the IGBT drive signal of each submodule in each phase half-bridge arm.

[0055] Beneficial Effects: This invention proposes a bidirectional DC / DC converter with phase-to-phase and intra-phase current shunting, and provides its circuit topology. This DC / DC converter can achieve DC-DC transformation under high-current conditions, and can withstand a maximum current of 3600*5A on the low-voltage side (taking an existing IGBT with a current stress of 3600A as an example). Based on multi-phase phase-to-phase current shunting and parallel current shunting of half-bridge and full-bridge arms within each phase, this DC / DC converter achieves phase-to-phase and intra-phase current shunting of large currents on the low-voltage side, thereby reducing the current stress on the bridge arms.

[0056] This topology has the following characteristics and advantages:

[0057] 1. To reduce the current stress on the bridge arms and achieve high-power transmission, this topology is based on the principle of symmetrical staggered operation of four-phase bridge arms. Three-phase bridge arms share the low-voltage side current, and within each phase bridge arm, a method is employed such as... Figure 1 The connection method shown allows the current of the two phases connected in parallel with the low-voltage side to be evenly distributed within the full-bridge arm and half-bridge arm of each phase, thereby reducing the current stress in each phase arm to (I L -I H ) / 4.

[0058] 2. In order to achieve bidirectional high-power transmission while reducing device cost and losses, this topology uses a switching device consisting of a diode and a thyristor connected in anti-parallel.

[0059] 3. Within each phase, the full-bridge arm and half-bridge arm are connected via anti-parallel diodes and thyristors. When power is transferred from the low-voltage side to the high-voltage side, the diodes conduct under forward voltage; when power is transferred from the high-voltage side to the low-voltage side, the thyristors are triggered and conduct, and the half-bridge arm outputs an additional reverse voltage U longer than the thyristor's reverse turn-off time. RE To achieve reliable turn-off of the thyristor.

[0060] The control method adopted in this invention enables the four phases (a, b, c, and d) of the DC / DC converter to maintain symmetrical alternating operation, achieving bidirectional power transmission. Furthermore, with this topology and control method, the current stress between the bridge arms and the switching loss are reduced when high power is transmitted, thereby increasing the capacity of the non-isolated transformer, reducing costs, and decreasing size. Attached Figure Description

[0061] Figure 1 This is a schematic diagram of a bidirectional DC / DC converter topology with two-stage current splitting: interphase and intraphase.

[0062] Figure 2 yes Figure 1 A schematic diagram showing the current flow direction (j=a,b,c,d) when each phase is connected in parallel on the low-voltage side;

[0063] Figure 3 This is a schematic diagram showing the current flow direction (j=a,b,c,d) when each phase is connected in series between the high and low voltage sides;

[0064] Figure 4 The theoretical waveform diagram of each bridge arm of phase a during forward transmission;

[0065] Figure 5 This is a schematic diagram of the theoretical waveforms of each arm of phase a during reverse transmission;

[0066] Figure 6 This is a schematic diagram of the dynamic simulation waveform for ±1500MW;

[0067] Figure 7 This is a schematic diagram of the steady-state simulation waveform for 1500MW.

[0068] Figure 8 This is a schematic diagram of the steady-state simulation waveform at -1500MW.

[0069] Figure 9 This is a schematic diagram of a bidirectional DC / DC converter control method that involves two phase-to-phase and intra-phase current splitting. Detailed Implementation

[0070] Detailed Implementation Method 1, Refer to Figures 1 to 9 This embodiment specifically describes a bidirectional DC / DC converter with phase-to-phase and phase-to-phase current splitting.

[0071] 1. Topology of a bidirectional DC / DC converter with phase-to-phase and phase-to-phase current splitting

[0072] U L U is the low-voltage side DC voltage. H The DC / DC converter topology is as follows: (This refers to the DC voltage on the high-voltage side.) Figure 1 As shown, it consists of four identical symmetrical phases (phase a, phase b, phase c, and phase d) connected in parallel. Each phase includes a full-bridge arm (FB), a half-bridge arm (HB), two arm inductors (L), and three anti-parallel thyristors and diodes (T). j1 / D j1 T j2 / D j2 T j3 / D j3 (j = a, b, c, d). The positive directions of the relevant electrical quantities are all marked in the diagram. Taking phase a as an example, the negative terminals of the half-bridge arm HB and the full-bridge arm FB are connected to T through the arm inductance L. a3 / D a3 Thyristor T a3 The positive terminals are connected, T a3 / D a3 Thyristor T a3 The negative terminal of the bridge arm FB is connected to the negative terminals of the high and low voltage sides. The positive terminal of the bridge arm FB is connected to T. a1 / D a1 Diode D a1 The positive electrode of the high-voltage side is connected to the positive electrode of the low-voltage side, T a1 / D a1 Diode D a1 The negative electrode and the positive electrode of the half-bridge arm HB and T a2 / D a2 Diode D a2 The positive terminals are connected. T a2 / D a2 Diode D a2 The negative electrode is connected to the positive electrode on the high-voltage side.

[0073] 2. Operating waveforms of a bidirectional DC / DC converter with phase-to-phase and phase-to-phase current splitting.

[0074] The four phases (phase a, phase b, phase c, and phase d) of this DC / DC converter operate symmetrically and alternately. This topology enables bidirectional power transfer. Figure 4 and Figure 5 The theoretical voltage and current waveforms of the full-bridge arm and half-bridge arm in phase a are given for both forward (forward rotation) and reverse (reverse rotation) power transmission. The theoretical waveform of phase a during forward power transmission is as follows: Figure 4 As shown, I L and I HAll are positive, and the current flow direction of the two phases in parallel with the low-voltage side is as follows: Figure 2 As shown by the black arrow, current is flowing through diode D at this time. a1 and thyristor T a3 The current flowing through each phase is (I L -I H The current flowing through both the full-bridge arm and the half-bridge arm is (I) / 2. L -I H ) / 4; The current flow direction of the bridge arm phase connected in series between the high and low voltage sides is as follows Figure 3 As shown by the black arrow, current is flowing through diode D at this time. a2 The current flowing through this phase is I. H The current flowing through all the bridge arms is I. H The current flowing through the half-bridge arm is -I H During reverse transmission, the theoretical waveform of phase a is as follows: Figure 5 As shown, I L and I H All are negative, and the current flow direction of the two phases in parallel with the low-voltage side is as follows: Figure 2 As indicated by the gray arrow, current is flowing through diode T at this time. a1 and thyristor D a3 The current flowing through each phase is (I L -I H The current flowing through both the full-bridge arm and the half-bridge arm is (I) / 2. L -I H ) / 4. The bridge arm current of one phase connected in series between the high and low voltage sides is as follows: Figure 4 As indicated by the gray arrow, current is flowing through thyristor T at this time. a2 The current flowing through this phase is I. H The current flowing through all the bridge arms is I. H The current flowing through the half-bridge arm is -I H .

[0075] Effect:

[0076] To verify the effectiveness of the high-current bidirectional DC / DC converter with phase-to-phase and phase-to-phase current splitting as described in this invention, simulation software was used for verification. Specifically, a bidirectional DC / DC converter model with a rated transmission power P = ±1500MW and phase-to-phase and phase-to-phase current splitting was built in Simulink for simulation verification. The low-voltage side and high-voltage side DC grid were simulated using fixed voltage sources, designed as U... L =100kV and U H =500kV. Each phase consists of a full-bridge arm and a half-bridge arm, and each full-bridge arm and half-bridge arm is composed of 120 sub-modules connected in series. Simulation parameters are shown in Table 1.

[0077] Table 1 Simulation parameters of the bidirectional DC / DC converter with phase-to-phase and phase-to-phase current splitting.

[0078]

[0079] Figure 6 The dynamic simulation results of bidirectional power transmission are presented. Initially, the power transmitted from the low-voltage side to the high-voltage side is P = 1500MW, and the current on the low-voltage side is I. L =15000A, high-voltage side current I H =3000A. Afterwards, the power transferred from the low-voltage side to the high-voltage side changes linearly from 1500MW to -1500MW, and the low-voltage side current I... L The high-voltage side current I changes linearly from 3000A to -3000A. H The voltage changes linearly from 15000A to -15000A. Throughout the entire power change process, the total capacitor voltage u of the a-phase full-bridge submodule... C_sum_FB and the sum of the capacitor voltages of the half-bridge submodule u C_sum_HB All can remain stable at their reference value U C_sum_ref = Around 300kV, the capacitor voltage fluctuates by about 20kV.

[0080] Figure 7 The steady-state simulation results of a bidirectional DC / DC converter with phase-to-phase and phase-to-phase current splitting are presented at a transmission power of 1500MW. At this time, the charging current and discharging current of the full-bridge arm in phase a are both of magnitude (I L -I H ) / 4=I H =3000A trapezoidal waveform, full-bridge arm voltage u aFB At charging voltage U L =100kV and discharge voltage -(U H -U L ) / 2=-200kV switching; the charging current of the half-bridge arm in phase a is controlled to I H =3000A trapezoidal wave, the discharge current is controlled to be -(I L -I H A trapezoidal waveform of -3000A is generated by ) / 4, and the half-bridge arm voltage u aHB At charging voltage U L =100kV and discharge voltage (U H -U L ) / 2=200kV switching back and forth.

[0081] Figure 8 The steady-state simulation results of a bidirectional DC / DC converter with phase-to-phase and phase-to-phase current splitting are presented at a transmission power of -1500MW. At this time, the charging current and discharging current of the full-bridge arm in phase a are both of magnitude I. H=(I L -I H A trapezoidal waveform of -3000A is generated by ) / 4, and the full-bridge arm voltage u aFB At charging voltage -(U H -U L ) / 2 = -200kV and discharge voltage U L =100kV switching; the charging current of the half-bridge arm in phase a is controlled to -I H =3000A trapezoidal wave, the discharge current is controlled to be (I L -I H A trapezoidal waveform of -3000A is generated by ) / 4, and the half-bridge arm voltage u aHB At charging voltage (U H -U L ) / 2 = 200kV and discharge voltage U L =100kV switching back and forth.

[0082] 2. Advantages of bidirectional DC / DC converters with phase-to-phase and phase-to-phase current splitting:

[0083] 1. In any operating state, this DC / DC converter always has one phase's full-bridge arm and half-bridge arm connected in series to bear the voltage difference between the high and low voltage sides and the high-voltage side current. The other two phases' full-bridge arms and half-bridge arms share the low-voltage side voltage and the high-low voltage side current difference. This distributes the low-voltage side current among the three phase arms, and it is further divided among the full-bridge arms and half-bridge arms of the two phases connected in parallel with the low-voltage side. This achieves both inter-phase and intra-phase current shunting. Thus, the anti-parallel thyristors (T...) connected to the negative terminals of the high and low voltage sides... j3 ) and diode (D j3 The current stress will be reduced to (I) L -I H The current stress of each phase bridge arm submodule IGBT will be reduced to (I) / 2. L -I H ) / 4.

[0084] 2. The four phases of the bidirectional DC / DC converter with phase-to-phase and phase-to-phase splitting are all composed of full-bridge arms and half-bridge arms. Each phase achieves bidirectional high-power transmission through three sets of anti-parallel thyristor and diode valve groups, with low loss and cost, and no need for bulky and expensive transformers.

[0085] 3. When the converter is working, one-third of the power on the low-voltage side is directly output to the high-voltage side, which can reduce the energy storage requirements of the bridge arm.

[0086] 1. Timing of a bidirectional DC / DC converter with phase-to-phase and phase-to-phase current splitting

[0087] Figure 4 and Figure 5 The voltage and current waveforms of the full-bridge arm and half-bridge arm in phase a of the DC / DC converter are given for both forward and reverse power transmission. The following section uses... Figure 4 We will take the theoretical waveform shown in the figure as an example for specific analysis.

[0088] Initially, the full-bridge arms and half-bridge arms of phases c and d are connected in parallel to the low-voltage side for charging. The charging current for both the full-bridge arms and half-bridge arms is (Ic). L -I H ) / 4, the charging voltage is U L Phase b is in a disconnected state, with both its full-bridge arm current and half-bridge arm current being 0. The full-bridge arm and half-bridge arm of phase a are connected in series between the low-voltage side and the high-voltage side for discharge. The discharge current of the full-bridge arm is I. H The full-bridge arm output voltage is -(U H -U L The discharge current of the half-bridge arm is -I / 2. H The output voltage of the half-bridge arm is (U H -U L ) / 2.

[0089] During the period [0, t1], phase a and phase b undergo commutation on the high-voltage side. At this time, the output voltage of the full-bridge arm in phase a is -(U H -U L The output voltage of the half-bridge arm is (U) / 2+U1. H -U L The output voltage of the full-bridge arm in phase b is -(U) / 2-U1. H -U L ) / 2-U1, the output voltage of the half-bridge arm is (U H -U L The voltage difference 4U1 between phase a and phase b is applied to the bridge arm inductance 4L of the two phases, causing the full-bridge arm current in phase a to change from I at a rate of 4U1 / 4L. H As the current linearly decreases to 0, the half-bridge arm current changes from -I at a rate of 4U1 / 4L. H As the current increases linearly to 0, the full-bridge arm current in phase b also increases linearly from 0 to I at the same rate. H The half-bridge arm current decreases linearly from 0 to -I at the same rate of change. H .

[0090] During the period [t1,t2], phase a is in a disconnected state, and its full-bridge arm current and half-bridge arm current are both 0. To reduce switching losses, the low-voltage side thyristor T is kept in a state of no connection. a3 When the ZVS turn-on condition is met, the output voltage of the full-bridge arm is changed from -(U H -U L) / 2 Step-by-step switch to U L The output voltage of the half-bridge arm is determined by (U) H -U L ) / 2 Step-by-step switch to U L .

[0091] During the period [t2,t3], thyristor T a3 When the circuit is triggered, phase c and phase a begin commutation on the low-voltage side. At this time, the output voltage of both the full-bridge arm and the half-bridge arm in phase a is U. L -U0, the output voltage of both the full-bridge arm and the half-bridge arm in phase c is U L +U0, diode D a1 Under positive voltage conduction, the voltage difference 2U0 between phase c and phase a is applied to the bridge arm inductance 2L of the two phases, causing both the full-bridge arm current and the half-bridge arm current in phase a to increase linearly from 0 to (I) at a rate of 2U0 / 2L. L -I H In phase c, both the full-bridge arm current and the half-bridge arm current change at a rate of 2U0 / 2L from (I) / 4. L -I H It decreases linearly from 0 to 0.

[0092] During [t3,t4], the full-bridge arms and half-bridge arms of phases a and d are connected in parallel to the low-voltage side for charging. The charging current of both the full-bridge arm and the half-bridge arm is (I L -I H ) / 4, the charging voltage is U L .

[0093] During the period [t4,t5], phase a and phase c undergo commutation on the low-voltage side. At this time, the output voltage of both the full-bridge arm and the half-bridge arm in phase a is U. L +U0, the output voltage of both the full-bridge arm and the half-bridge arm in phase c is U L -U0, diode D c1 Under positive voltage conduction, the voltage difference 2U0 between the bridge arms of phases a and c is applied to the bridge arm inductance 2L of the two phases, causing both the full-bridge arm current and the half-bridge arm current in phase a to change at a rate of 2U0 / 2L from (I... L -I H As the current decreases linearly from 0 to 0, the full-bridge arm current and half-bridge arm current in phase c both increase linearly from 0 to 0 at a rate of 2U0 / 2L. L -I H ) / 4.

[0094] During the period [t5,t6], phase a is in a disconnected state, and its full-bridge arm current and half-bridge arm current are both 0. Its full-bridge arm voltage and half-bridge arm voltage first reach U... LIn addition, a reverse voltage U is output that is longer than the reverse turn-off time of the thyristor. RE Ensure thyristor T a3 To ensure reliable turn-off and reduce switching losses, the high-voltage side diode D... a2 The ZVS activation conditions are met, and the output voltage of its full-bridge arm is determined by U. L Switch step by step to -(U H -U L ) / 2, the output voltage of the half-bridge arm is determined by U L Switch step by step to (U) H -U L ) / 2.

[0095] During [t6,t7], phase d and phase a undergo commutation on the high-voltage side. At this time, the output voltage of the full-bridge arm in phase a is -(U H -U L ) / 2-U1, the output voltage of the half-bridge arm is (U H -U L The output voltage of the full-bridge arm in phase d is -(U) / 2+U1. H -U L The output voltage of the half-bridge arm is (U) / 2+U1. H -U L The voltage difference 4U1 between phase d and phase a is applied to the bridge arm inductance 4L of the two phases, causing the full-bridge arm current in phase a to increase linearly from 0 to I at a rate of 4U1 / 4L. H The half-bridge arm current decreases linearly from 0 to -I at a rate of 4U1 / 4L. H The full-bridge arm current in phase d also changes at the same rate from I... H As the current linearly decreases to 0, the half-bridge arm current changes from -I at the same rate. H It increases linearly to 0.

[0096] During [t7,t8], the full-bridge arm and half-bridge arm of phase a are connected via diode D. a2 Discharge is connected in series between the high-voltage side and the low-voltage side, and the discharge current of the entire bridge arm is I. H The full-bridge arm output voltage is -(U H -U L The discharge current of the half-bridge arm is -I / 2. H The output voltage of the half-bridge arm is (U H -U L ) / 2.

[0097] In this way, the bidirectional DC / DC converter with phase-to-phase and phase-to-phase current splitting completes one duty cycle T. s During reverse transmission, the theoretical voltage and current waveforms of the full-bridge arm and half-bridge arm in phase a are as follows: Figure 5As shown, the process is similar to that of forward transmission, and will not be repeated here. Because the bidirectional DC / DC converter operates with four-phase symmetrical interleaving, which splits current twice between phases and within a phase, the voltage and current waveforms of the full-bridge arm and half-bridge arm of adjacent phases have the same shape and are 90° out of phase.

[0098] 2. Control scheme for a bidirectional DC / DC converter with phase-to-phase and phase-to-phase current splitting

[0099] The control block diagram of a bidirectional DC / DC converter with phase-to-phase and phase-to-phase splitting is shown below. Figure 9 As shown, the control scheme consists of five parts. For both full-bridge and half-bridge arms, it includes arm energy balance control, arm current control, and arm voltage feedforward control. In addition, it includes thyristor converter valve on / off control, submodule capacitor voltage equalization, and carrier phase-shift modulation. The following analysis uses the control scheme for the full-bridge arm during forward transmission as an example.

[0100] First, based on the system's power control requirements, the formula P = U H I H =U L I L The charging current amplitude (I) of each phase full-bridge arm is obtained. L -I H ) / 4 and discharge current amplitude I H The discharge current amplitude I H Multiplying this by waveform generator 2 yields the reference discharge current waveform i for each phase of the full-bridge arm. FB_out_ref Because this DC / DC converter incurs losses during power transmission, bridge arm energy balance control is required. This control part adjusts the total capacitor voltage u of each bridge arm submodule. C_sum_FB Its reference value U C_sum_ref The deviation is fed into a proportional-integral (PI) controller, whose output is used to adjust the current amplitude during arm charging, thereby maintaining the total energy balance of the arms. Simultaneously, to achieve rapid control of the full-bridge arm energy balance, a current feedforward value (If) during full-bridge arm charging needs to be introduced. L -I H ) / 4. Multiplying the charging current amplitude obtained from this part of the control by waveform generator 1, the reference signal i of the charging current of each phase full-bridge arm can be obtained. FB_in_ref Furthermore, the current reference signal i for each phase full-bridge arm is synthesized. FB_ref Furthermore, to ensure that the actual current of each phase full-bridge arm can track its reference signal, arm current control needs to be introduced. This control involves using the previously obtained current reference signal i of each phase full-bridge arm. FB_ref Its actual current i FB The difference is calculated and fed into a proportional-integral (PI) controller to obtain the bridge arm voltage regulation value u.FB_PI Simultaneously, to achieve rapid tracking of the bridge arm current, it is necessary to introduce commutation voltage feedforward U0 / U1 and bridge arm voltage feedforward control. This part of the control involves controlling the voltage amplitude U0 / U1 during full-bridge arm charging. L and the voltage amplitude during discharge - (U H -U L ) / 2 is multiplied by waveform generator 3 and waveform generator 4 respectively to obtain the voltage feedforward signal of each phase full bridge arm.

[0101] The control of each phase's half-bridge arm is similar to that of the full-bridge arm, and will not be elaborated here. In addition, thyristor commutator valve turn-on / turn-off control needs to be introduced to provide the trigger signal for the thyristor valve group and the reverse turn-off voltage U. RE Finally, by adding the voltage regulation signals and feedforward signals of each phase full-bridge arm and half-bridge arm, the voltage reference signal u can be obtained. FB_ref and u HB_ref By sending the reference signal into the submodule capacitor voltage equalization and carrier phase shift modulation, the IGBT drive signals of each submodule of each phase full-bridge arm and half-bridge arm can be obtained.

[0102] This invention has been illustrated through several specific embodiments. Those skilled in the art will understand that various modifications and equivalent substitutions can be made to this invention without departing from its scope. Furthermore, various modifications can be made to this invention for specific situations or circumstances without departing from its scope. Therefore, this invention is not limited to the specific embodiments disclosed, but should include all embodiments falling within the scope of the claims.

Claims

1. A bidirectional DC / DC converter with phase-to-phase and phase-to-phase current splitting, characterized in that, It includes low-voltage side DC voltage U L DC voltage on the high-voltage side U H The converter consists of four identical symmetrical phases (a, b, c, and d) connected in parallel. Each phase includes a full-bridge arm (FB), a half-bridge arm (HB), and two arm inductors. L FB , L HB Three anti-parallel thyristors and diodes T j1 / D j1 T j2 / D j2 T j3 / D j3 , j =a,b,c,d; Taking phase a as an example, the negative terminal of half-bridge arm HB is connected through the arm inductor. L HB With T a3 / D a3 Thyristor T a3 The positive terminal is connected to the positive terminal, and the negative terminal of the full-bridge arm FB is connected through the arm inductor. L FB With T a3 / D a3 Thyristor T a3 The positive terminals are connected, T a3 / D a3 Thyristor T a3 The negative terminal and the low-voltage side DC voltage U L negative terminal and high voltage side DC voltage U H The negative terminal is connected; The positive terminal of the full-bridge arm FB and T a1 / D a1 Diode D a1 DC voltage on the positive and low voltage sides U L The positive terminals are connected, T a1 / D a1 Diode D a1 The negative electrode is simultaneously connected to the positive electrode of the half-bridge arm HB and T. a2 / D a2 Diode D a2 The positive terminals are connected, T a2 / D a2 Diode D a2 The negative terminal and the DC voltage on the high-voltage side U H The positive terminals are connected; This DC / DC converter is suitable for both forward and reverse power transmission; the inductance of the half-bridge arm and the full-bridge arm are set to be equal, i.e. L HB = L FB = L Half-bridge arm commutation voltage U 2. U 3. Commutation voltage of the full-bridge arm U 1. U 0 are equal in size, that is, | U 2|=| U 1|,| U 3|=| U 0|.

2. The bidirectional DC / DC converter with interphase and intraphase twice shunt according to claim 1, characterized in that, The four phases a, b, c, and d of this DC / DC converter operate symmetrically and alternately.

3. The bidirectional DC / DC converter with phase-to-phase and phase-to-phase dual current splitting according to claim 2, characterized in that, Its forward transmission process is as follows: Initially, the full-bridge arms and half-bridge arms of phases C and D are connected in parallel to the low-voltage side for charging. The charging current of both the full-bridge arms and half-bridge arms is ( I L - I H ) / 4, the charging voltage is 1 / 4. U L Phase b is in a disconnected state, with both its full-bridge arm current and half-bridge arm current being 0. The full-bridge arm and half-bridge arm of phase a are connected in series between the low-voltage side and the high-voltage side for discharge. The discharge current of the full-bridge arm is... I H The full-bridge arm output voltage is -( U H - U L ) / 2; The discharge current of the half-bridge arm is - I H The output voltage of the half-bridge arm is ( U H - U L ) / 2; [0, t During [1], phase a and phase b undergo commutation on the high-voltage side. At this time, the output voltage of the full-bridge arm in phase a is -( U H - U L ) / 2+ U 1. The output voltage of the half-bridge arm is ( U H - U L ) / 2- U 1. The output voltage of the full-bridge arm in phase b is -( U H - U L ) / 2- U 1. The output voltage of the half-bridge arm is ( U H - U L ) / 2+ U 1. The voltage difference between phase a and phase b is 4. U 1. Bridge arm inductance applied to two phases 4 L This causes the full-bridge arm current in phase a to be 4 U 1 / 4 L The rate of change from I H The current in the half-bridge arm decreases linearly to 0, with a current of 4 U 1 / 4 L The rate of change from - I H As the current increases linearly to 0, the full-bridge arm current in phase b also increases linearly from 0 to 0 at the same rate. I H The half-bridge arm current decreases linearly from 0 to - at the same rate of change. I H ; [ t 1, t During [2], phase a is in a disconnected state, and its full-bridge arm current and half-bridge arm current are both 0. To reduce switching losses, the low-voltage side thyristor T is kept in a state of no connection. a3 When the ZVS activation conditions are met, the output voltage of the full-bridge arm is changed from -( U H - U L ) / 2 Step-by-step switch to U L The output voltage of the half-bridge arm is determined by ( U H - U L ) / 2 Step-by-step switch to U L ; [ t 2, t During [3], thyristor T a3 When the circuit is triggered, phase c and phase a commutate on the low-voltage side; at this time, the output voltage of both the full-bridge arm and the half-bridge arm in phase a is... U L - U The output voltages of both the full-bridge arm and the half-bridge arm in phase 0 and c are... U L + U 0, Diode D a1 Under positive voltage, the voltage difference between phase c and phase a in the bridge arm is 2. U 0. Bridge arm inductance applied to two phases 2 L This causes both the full-bridge arm current and the half-bridge arm current in phase a to increase by 2%. U 0 / 2 L The rate of change increases linearly from 0 to ( I L - I H In phase c, both the full-bridge arm current and the half-bridge arm current are 2 U 0 / 2 L The rate of change from ( I L - I H ) / 4 decreases linearly to 0; [ t 3, t During this period, the full-bridge arms and half-bridge arms of phases a and d are connected in parallel to the low-voltage side for charging, and the charging current of both the full-bridge arms and half-bridge arms is ( I L - I H ) / 4, the charging voltage is 1 / 4. U L ; [ t 4, t During [5], phase a and phase c undergo commutation on the low-voltage side. At this time, the output voltage of both the full-bridge arm and the half-bridge arm in phase a is [missing value]. U L + U The output voltages of both the full-bridge arm and the half-bridge arm in phase 0 and c are... U L - U 0, Diode D c1 Under positive voltage, the voltage difference between phase a and phase c of the bridge arm is 2. U 0. Bridge arm inductance applied to two phases 2 L This causes both the full-bridge arm current and the half-bridge arm current in phase a to increase by 2%. U 0 / 2 L The rate of change from ( I L - I H As the current decreases linearly from 0 to 0, the current in both the full-bridge arm and the half-bridge arm of phase c decreases by 2. U 0 / 2 L The rate of change increases linearly from 0 to ( I L - I H ) / 4; [ t 5, t During [6], phase a is in a disconnected state, and its full-bridge arm current and half-bridge arm current are both 0. Its full-bridge arm voltage and half-bridge arm voltage first […]. U L In addition, a reverse voltage longer than the thyristor's reverse turn-off time is output. U RE Ensure thyristor T a3 To ensure reliable turn-off and reduce switching losses, the high-voltage side diode D... a2 The ZVS activation conditions are met, and the output voltage of its full-bridge arm is determined by... U L Switch step by step to -( U H - U L ) / 2, the output voltage of the half-bridge arm is determined by U L Switch to (level by level) U H - U L ) / 2; [ t 6, t During [7], phase d and phase a undergo commutation on the high-voltage side. At this time, the output voltage of the full-bridge arm in phase a is -( U H - U L ) / 2- U 1. The output voltage of the half-bridge arm is ( U H - U L ) / 2+ U 1. The output voltage of the full-bridge arm in phase d is -( U H - U L ) / 2+ U 1. The output voltage of the half-bridge arm is ( U H - U L ) / 2- U 1. The voltage difference between phase d and phase a is 4. U 1. Bridge arm inductance applied to two phases 4 L This causes the full-bridge arm current in phase a to be 4 U 1 / 4 L The rate of change increases linearly from 0 to I H The half-bridge arm current is 4 U 1 / 4 L The rate of change decreases linearly from 0 to - I H The current in the full-bridge arm of phase d also changes at the same rate from I H As the current linearly decreases to zero, the half-bridge arm current changes from - I H Increasing linearly to 0, [ t 7, t During [8], the full-bridge arm and half-bridge arm of phase a are connected via diode D. a2 Discharge is connected in series between the high-voltage side and the low-voltage side, and the discharge current of the entire bridge arm is... I H The full-bridge arm output voltage is -( U H - U L The discharge current of the half-bridge arm is - ) / 2. I H The output voltage of the half-bridge arm is ( U H - U L ) / 2, The bidirectional DC / DC converter with twice branch current in phase and out of phase completes a working cycle T s .

4. The bidirectional DC / DC converter with interphase and intraphase twice shunt according to claim 2, characterized in that, This DC / DC converter is suitable for both forward and reverse power transmission; Its reverse transmission process is as follows: During reverse transmission, the high-voltage side current I H and low-voltage side current I L Both are negative. Initially, the full-bridge arm and half-bridge arm of phases c and d are connected in parallel to the low-voltage side for discharge. The discharge current of both the full-bridge arm and the half-bridge arm is ( I L - I H ) / 4, the discharge voltage is 1 / 4. U L Phase b is in an unconnected state, with both its full-bridge arm current and half-bridge arm current being 0. The full-bridge arm and half-bridge arm of phase a are connected in series between the low-voltage side and the high-voltage side for charging. The charging current of the full-bridge arm is... I H The full-bridge arm output voltage is -( U H - U L ) / 2; The charging current of the half-bridge arm is - I H The output voltage of the half-bridge arm is ( U H - U L ) / 2; [0, t During [1], phase a and phase b undergo commutation on the high-voltage side. At this time, the output voltage of the full-bridge arm in phase a is -( U H - U L ) / 2- U 1. The output voltage of the half-bridge arm is ( U H - U L ) / 2+ U 1. The output voltage of the full-bridge arm in phase b is -( U H - U L ) / 2+ U 1. The output voltage of the half-bridge arm is ( U H - U L ) / 2- U 1. The voltage difference between phase a and phase b is 4. U 1. Bridge arm inductance applied to two phases 4 L This causes the full-bridge arm current in phase a to be 4 U 1 / 4 L The rate of change from I H The current in the half-bridge arm increases linearly to 0, with a 4 U 1 / 4 L The rate of change from - I H As the current in the bridge arm of phase b decreases linearly to 0, it also decreases linearly from 0 to 0 at the same rate. I H The half-bridge arm current increases linearly from 0 to - at the same rate of change. I H ; [ t 1, t During [2], phase a is in a disconnected state, and its full-bridge arm current and half-bridge arm current are both 0. Its full-bridge arm voltage is first at -( U H - U L In addition to the 1 / 2, an extra reverse voltage longer than the thyristor's reverse turn-off time is output. U RE The voltage of the half-bridge arm is ( U H - U L Output reverse voltage based on ) / 2 U RE Ensure thyristor T a2 To ensure reliable turn-off and reduce switching losses, the low-voltage side diode D... a3 When the ZVS activation conditions are met, the output voltage of the full-bridge arm is changed from -( U H - U L ) / 2 Step-by-step switch to U L The output voltage of the half-bridge arm is determined by ( U H - U L ) / 2 Step-by-step switch to U L ; [ t 2, t During [3], thyristor T a1 Trigger conduction, diode D a3 When the circuit is turned on, phase c and phase a undergo commutation on the low-voltage side; at this time, the output voltage of both the full-bridge arm and the half-bridge arm in phase a is... U L + U The output voltages of both the full-bridge arm and the half-bridge arm in phase 0 and c are... U L - U 0, the voltage difference between phase c and phase a bridge arm is 2. U 0. Bridge arm inductance applied to two phases 2 L This causes both the full-bridge arm current and the half-bridge arm current in phase a to increase by 2%. U 0 / 2 L The rate of change decreases linearly from 0 to ( I L - I H In phase c, both the full-bridge arm current and the half-bridge arm current are 2 U 0 / 2 L The rate of change from ( I L - I H ) / 4 increases linearly to 0; [ t 3, t During this period, the full-bridge arm and half-bridge arm of phases a and d are connected in parallel to the low-voltage side for discharge, and the discharge current of the full-bridge arm and half-bridge arm are both ( I L - I H ) / 4, the discharge voltage is 1 / 4. U L ; [ t 4, t During [5], phase a and phase c undergo commutation on the low-voltage side. At this time, the output voltage of both the full-bridge arm and the half-bridge arm in phase a is [missing value]. U L - U The output voltages of both the full-bridge arm and the half-bridge arm in phase 0 and c are... U L + U 0, thyristor T c1 Trigger conduction, the voltage difference between phase A and phase C bridge arms is 2. U 0. Bridge arm inductance applied to two phases 2 L This causes both the full-bridge arm current and the half-bridge arm current in phase a to increase by 2%. U 0 / 2 L The rate of change from ( I L - I H As the current increases linearly from 0 to 0, the current in both the full-bridge arm and the half-bridge arm of phase c increases by 2. U 0 / 2 L The rate of change decreases linearly from 0 to ( I L - I H ) / 4; [ t 5, t During [6], phase a is in a disconnected state, and its full-bridge arm current and half-bridge arm current are both 0. Its full-bridge arm voltage and half-bridge arm voltage first […]. U L In addition, an extra reverse voltage longer than the thyristor's reverse turn-off time is output. U RE Ensure thyristor T a1 To ensure reliable turn-off and reduce switching losses, the high-voltage side thyristor T... a2 The ZVS activation conditions are met, and the output voltage of its full-bridge arm is determined by... U L Switch step by step to -( U H - U L ) / 2, the output voltage of the half-bridge arm is determined by U L Switch to (level by level) U H - U L ) / 2; [ t 6, t During [7], phase d and phase a undergo commutation on the high-voltage side. At this time, the output voltage of the full-bridge arm in phase a is -( U H - U L ) / 2+ U 1. The output voltage of the half-bridge arm is ( U H - U L ) / 2- U 1. The output voltage of the full-bridge arm in phase d is -( U H - U L ) / 2- U 1. The output voltage of the half-bridge arm is ( U H - U L ) / 2+ U 1. The voltage difference between phase d and phase a is 4. U 1. Bridge arm inductance applied to two phases 4 L This causes the full-bridge arm current in phase a to be 4 U 1 / 4 L The rate of change decreases linearly from 0 to I H The half-bridge arm current is 4 U 1 / 4 L The rate of change increases linearly from 0 to - I H The current in the full-bridge arm of phase d also changes at the same rate from I H As the current increases linearly to 0, the half-bridge arm current changes from - I H Decrease linearly to 0, [ t 7, t During [8], the full-bridge arm and half-bridge arm of phase a are connected via thyristor T a2 The charging is connected in series between the high-voltage side and the low-voltage side, and the charging current of the entire bridge arm is... I H The full-bridge arm output voltage is -( U H - U L The current in the half-bridge arm is - ) / 2. I H The output voltage of the half-bridge arm is ( U H - U L ) / 2.

5. The bidirectional DC / DC converter with interphase and intraphase twice shunt according to claim 3 or 4, characterized in that, Because the bidirectional DC / DC converter operates with four-phase symmetrical interleaving, which splits current twice between phases and within a phase, the voltage and current waveforms of the full-bridge arm and half-bridge arm of adjacent phases have the same shape and are 90° out of phase.

6. The control method of the bidirectional DC / DC converter with interphase and intraphase twice splitting according to claim 1, characterized in that, The control method comprises five parts: bridge arm energy balance control, bridge arm current control, bridge arm voltage feedforward control, thyristor converter valve on / off control, submodule capacitor voltage equalization and carrier phase shift modulation. The bridge arm energy balance control, bridge arm current control, and bridge arm voltage feedforward control are respectively applicable to full-bridge bridge arms and half-bridge bridge arms, namely, full-bridge bridge arm energy balance control, full-bridge bridge arm current control, full-bridge bridge arm voltage feedforward control, half-bridge bridge arm energy balance control, half-bridge bridge arm current control, and half-bridge bridge arm voltage feedforward control. When applied to the entire bridge arm, this method can be called the control method for the entire bridge arm. Taking the transfer of power from the low-voltage side to the high-voltage side as an example, it includes the following steps: Step 1: First, based on the system's power control requirements, use the formula... P = U H I H = U L I L The charging current amplitude of each phase bridge arm is obtained. I L - I H ) / 4 and discharge current amplitude I H ; Step 2: Adjust the discharge current amplitude I H Multiplying this by waveform generator 2 yields the reference waveform of the discharge current for each phase of the full-bridge arm. i FB_out_ref ; Step 3: Introduce full-bridge arm energy balance control to reduce losses generated during power transmission in the DC / DC converter; the full-bridge arm energy balance control controls the total capacitor voltage of each full-bridge arm submodule. u C_sum_FB Its reference value U C_sum_ref The deviation is fed into the proportional-integral (PI) controller, which outputs a modulation signal to adjust the current amplitude during arm charging, so as to keep the total energy of the arm balanced. Step 4: Introduce the charging current amplitude of the bridge arm ( I L - I H ) / 4, used to achieve rapid control of the energy balance of the entire bridge arm; the charging current amplitude of the entire bridge arm ( I L - I H 4. The sum of the modulation signals obtained in step 3 is then multiplied by waveform generator 1 to obtain the reference signal for the charging current of each phase full-bridge arm. i FB_in_ref ; Step 5: Use the discharge current reference waveform of the full-bridge arm mentioned in Step 2. i FB_out_ref ; and the reference signal of the charging current of each phase full-bridge arm mentioned in step four. i FB_in_ref By adding them together, we obtain the current reference signals for each phase of the full-bridge arm. i FB_ref ; Step Six: Introduce full-bridge arm current control to ensure that the actual current of each phase full-bridge arm can track its reference signal; the full-bridge arm current control is to use the current reference signal of each phase full-bridge arm... i FB_ref With actual current i FB The difference is calculated and fed into a proportional-integral (PI) controller to obtain the bridge arm voltage regulation. u FB_PI ; Step 7: Introduce the commutation voltage feedforward signal U 0 / U 1. And arm voltage feedforward control, used to achieve fast tracking of arm current; this part of the control measures the voltage amplitude during arm charging. U L Multiplying this signal by waveform generator 3 yields the input voltage feedforward signal for each phase of the full-bridge arm. u FB_in_fw Voltage amplitude during discharge - ( U H - U L Multiplying 2 by waveform generator 4 yields the output voltage feedforward signal for each phase of the full-bridge arm. u FB_out_fw ; Step 8: Introduce thyristor converter valve turn-on / turn-off control to provide trigger signals and reverse turn-off voltages for the thyristor valve group. U RE ; Step 9: The commutation voltage feedforward signal from Step 7 U 0 / U 1. Input voltage feedforward signal for each phase full-bridge arm u FB_in_fw Output voltage feedforward signal of each phase full-bridge arm u FB_out_fw Trigger signal and reverse turn-off voltage of thyristor valve group U RE Add them together to obtain the voltage reference signal. u FB_ref The reference signal is then fed into the submodule capacitor voltage equalization and carrier phase shift modulation to obtain the IGBT drive signal of each submodule of each phase full-bridge arm.

7. A control method for a bidirectional DC / DC converter with phase-to-phase and phase-to-phase dual current splitting as described in claim 1, characterized in that, The control method comprises five parts: bridge arm energy balance control, bridge arm current control, bridge arm voltage feedforward control, thyristor converter valve on / off control, submodule capacitor voltage equalization and carrier phase shift modulation. The bridge arm energy balance control, bridge arm current control, and bridge arm voltage feedforward control are respectively applicable to full-bridge bridge arms and half-bridge bridge arms, namely, full-bridge bridge arm energy balance control, full-bridge bridge arm current control, full-bridge bridge arm voltage feedforward control, half-bridge bridge arm energy balance control, half-bridge bridge arm current control, and half-bridge bridge arm voltage feedforward control. When applied to a half-bridge arm, this method can be called a half-bridge arm control method. Taking power transmission from the low-voltage side to the high-voltage side as an example, it includes the following steps: Step 1: First, based on the system's power control requirements, use the formula... P = U H I H = U L I L The charging current amplitude of each phase bridge arm is obtained. I L - I H ) / 4 and discharge current amplitude I H ; Step 2: Adjust the discharge current amplitude I H Multiplying this by waveform generator 2 yields the reference waveform of the discharge current for each phase half-bridge arm. i HB_out_ref ; Step 3: Introduce half-bridge arm energy balance control to reduce losses generated during power transmission in the DC / DC converter; the half-bridge arm energy balance control controls the total capacitor voltage of each half-bridge arm submodule. u C_sum_HB Its reference value U C_sum_ref The deviation is fed into the proportional-integral (PI) controller, which outputs a modulation signal to adjust the current amplitude during arm charging, so as to keep the total energy of the arm balanced. Step 4: Introduce the charging current amplitude of each phase bridge arm ( I L - I H ) / 4, used to achieve rapid control of energy balance in the half-bridge arm; the charging current amplitude of the arm ( I L - I H 4. The sum of the modulation signals obtained in step 3 is then multiplied by waveform generator 1 to obtain the reference signal for the charging current of each phase half-bridge arm. i HB_in_ref ; Step 5: Use the discharge current reference waveform of the half-bridge arm mentioned in Step 2. i HB_out_ref ; and the reference signal of the charging current of each phase half-bridge arm mentioned in step four. i HB_in_ref By adding them together, we obtain the current reference signals for each phase of the full-bridge arm. i HB_ref ; Step Six: Introduce half-bridge arm current control to ensure that the actual current of each phase half-bridge arm can track its reference signal; the full-bridge arm current control uses the current reference signal of each phase half-bridge arm. i HB_ref With actual current i HB The difference is calculated and fed into a proportional-integral (PI) controller to obtain the bridge arm voltage regulation. u HB_PI ; Step 7: Introduce negative commutation voltage feedforward signal U 2 / U 3. And arm voltage feedforward control, used to achieve fast tracking of arm current, wherein the commutation voltage... U 2= U 0, U 3=- U 1; This part of the control is to control the voltage amplitude during bridge arm charging. U L Multiplying by waveform generator 3 yields the input voltage feedforward signal for each phase half-bridge arm. u HB_in_fw Voltage amplitude during discharge ( U H - U L Multiplying 2 by waveform generator 4 yields the output voltage feedforward signal for each phase half-bridge arm. u HB_out_fw ; Step eight: introducing thyristor converter valve turn-on and turn-off control for providing a trigger signal and a reverse blocking voltage for the thyristor valve group U RE ; Step 9: Feed the negative commutation voltage forward signal from Step 7. U 2 / U 3. Input voltage feedforward signal for each phase half-bridge arm u HB_in_fw Output voltage feedforward signal of each phase half-bridge arm u HB_out_fw Trigger signal and reverse turn-off voltage of thyristor valve group U RE Add them together to obtain the voltage reference signal. u HB_ref The reference signal is then fed into the submodule capacitor voltage equalization and carrier phase shift modulation to obtain the IGBT drive signal of each submodule in each phase half-bridge arm.

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