Three-phase solid-state transformer topology and split modulation method to reduce duty cycle loss

Abstract

The present invention discloses a three-phase solid-state transformer topology and a separate modulation method for reducing duty cycle loss, which is a novel three-phase current type AC-AC high-frequency chain matrix power electronic transformer topology and an auxiliary resonant circuit separate control strategy for reducing duty cycle loss. The topology is mainly composed of a three-phase AC power supply, an input filter, a front-stage matrix converter, an auxiliary resonant circuit, a high-frequency transformer, a rear-stage matrix converter, an output filter and a load connection; the auxiliary resonant circuit is composed of two common collector connected switch tubes S2 and S1 and a parallel capacitor C r By combining the idea of ​​zero vector bridge arm direct pass in current-type space vector with the idea of ​​current zero crossing in resonant period, a separate control strategy is adopted for the auxiliary resonant circuit, which can effectively reduce duty cycle loss, reduce power loss, and improve transmission efficiency.

Description

Technical Field

[0001] The invention relates to a three-phase solid-state transformer topology and a separate modulation method for reducing duty cycle loss, and belongs to the field of power electronic power converter topology and modulation thereof. Background Art

[0002] Compared with traditional transformers, power electronic transformers have the advantages of small size, light weight, and controllable voltage and frequency. They can be widely used in distribution networks, microgrids, photovoltaic power generation and energy routers.

[0003] Power electronic transformers are also called solid-state transformers. They can be divided into single-stage and multi-stage solid-state transformers according to the number of transformation stages. Multi-stage solid-state transformers have a DC link and can be connected to renewable energy or storage systems. However, due to the multi-stage nature of the system structure, multi-stage solid-state transformers have the disadvantages of low efficiency, low power density, and poor reliability. The single-stage power electronic transformer composed of a matrix converter has fewer transformation levels and high efficiency. It also has the advantages of adjustable voltage amplitude and adjustable output frequency. In this system, since there is no DC link in the matrix converter, electrolytic capacitors with short service life are not required. Therefore, this type of topology has the advantages of long service life, small size, and high efficiency.

[0004] Space vector modulation is a commonly used modulation method for three-phase single-stage power electronic transformers. Some space vector modulation strategies will cause the problem of duty cycle loss. In response to the problem of duty cycle loss in current-type three-phase matrix power electronic transformers, the invention patent with the publication number of CN112436733A and the name of "Three-phase resonant topology and auxiliary switch modulation method for reducing duty cycle loss" discloses a three-phase power electronic transformer topology and an integrated control method for auxiliary resonant circuit that can reduce duty cycle loss; in this patented technology, the auxiliary resonant circuit consists of a bidirectional switch tube connected to a common emitter, a parallel capacitor C r , resistor R r The bidirectional switch tube adopts integrated control; in the patented technology, the auxiliary bidirectional switch tube integrated modulation scheme used has the problem of making the parallel capacitor C r At the moment of short circuit, the current spike of the capacitor will be caused. To solve this problem, the patent proposes an improved auxiliary resonant circuit, that is, to give C r A smaller resistor R is connected in series r , Figure 5 , Figure 6 and Figure 7 Although this patented technology can achieve the purpose of reducing duty cycle loss, due to the resistance R r Absorbing active power will result in power loss.

[0005] The patent of the present invention optimizes the above patent, including the optimization of the auxiliary resonant circuit structure and the optimization of the auxiliary resonant circuit control method, which can not only solve the problem of current spikes, but also solve the problem of power loss caused by resistance, and can also achieve the purpose of reducing duty cycle loss. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a three-phase solid-state transformer topology and a separate modulation method for reducing duty cycle loss, thereby reducing duty cycle loss by adding an auxiliary resonant circuit, increasing transmission power, reducing grid-side current distortion factor, and improving the sinusoidality of output voltage and current waveforms.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0008] Three-phase solid-state transformer topology with reduced duty cycle loss, including a three-phase AC power supply u a 、u b 、u c , three-phase LC input filter, high-frequency transformer primary side matrix converter, auxiliary resonant circuit, high-frequency transformer, high-frequency transformer secondary side matrix converter, three-phase CL output filter and three-phase load R a , R b , R c ;

[0009] Three-phase AC power supply a 、u b 、u c The three-phase LC input filter is connected to the input end of the primary matrix converter of the high-frequency transformer; the output end of the primary matrix converter of the high-frequency transformer and the emitter of the switch tube S2 in the auxiliary resonant circuit and the parallel capacitor C r Connected, C r The other end of and the emitter of the switch tube S1 are connected to the primary side of the high-frequency transformer; the secondary side of the high-frequency transformer is connected to the input end of the secondary side matrix converter of the high-frequency transformer; the output end of the secondary side matrix converter of the high-frequency transformer is connected to the three-phase CL output filter, and the three-phase CL output filter is connected to the three-phase load R a , R b , R c connected.

[0010] The further improvement of the technical solution of the present invention is that: the specific circuit connection relationship is as follows: three-phase AC power supply u a 、u b 、u cThe three-phase input filter inductor L1, L2, L3 is connected to the three-phase input filter capacitor C1, C2, C3, and the three-phase bridge arm of the primary side matrix converter of the high-frequency transformer is connected to points a, b, and c respectively; the six groups of bidirectional switch tubes of the three-phase bridge arm of the primary side matrix converter of the high-frequency transformer are all connected with a common emitter, and the lower tube S of the bidirectional switch tube in the upper bridge arm of the three-phase bridge arm pah , S pbh , S pch The collector of the three-phase bridge arm is connected to the upper tube S of the bidirectional switch tube in the lower bridge arm nah , S nbh , S nch The collector of the high-frequency transformer is connected to the output of the primary matrix converter and the emitter of the switch tube S2 in the auxiliary resonant circuit and the parallel capacitor C r Connected, C r The other end of and the emitter of the switch tube S1 are connected to the primary side of the high-frequency transformer; the secondary side of the high-frequency transformer is connected to the input end of the secondary side matrix converter of the high-frequency transformer, and the primary side matrix converter of the high-frequency transformer is connected in the same way as the secondary side matrix converter of the high-frequency transformer; the output end of the secondary side matrix converter of the high-frequency transformer is connected to the three-phase CL output filter, and the three-phase CL output filter is connected to the three-phase load R a , R b , R c connected.

[0011] A further improvement of the technical solution of the present invention is that: the auxiliary resonant circuit comprises two switch tubes S2 and S1 connected with a common collector and a parallel capacitor C r .

[0012] A further improvement of the technical solution of the present invention is that the high-frequency transformer primary matrix converter and the high-frequency transformer secondary matrix converter are both composed of 6 common-emitter bidirectional switch tubes.

[0013] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0014] A separate modulation method for a three-phase solid-state transformer topology that reduces duty cycle loss, a high-frequency transformer primary matrix converter and a high-frequency transformer secondary matrix converter both use decoupled vector modulation with low switching voltage stress, and the specific process is: first, the decoupling idea is adopted to decouple the three-phase current-type matrix power electronic transformer into two three-phase-three-phase AC conversion circuits composed of unidirectional switching tubes, and then low-voltage stress space vector modulation and a high-frequency square wave signal with a duty cycle of 50% are used to generate modulation signals of the primary and secondary matrix converter switches of the high-frequency transformer in the three-phase current-type matrix power electronic transformer topology according to the idea of ​​current-type coupling.

[0015] A further improvement of the technical solution of the present invention is that when a certain phase bridge arm of the primary side matrix converter of the high-voltage and high-frequency transformer is directly connected, the switch tubes S2 and S1 in the auxiliary resonant circuit are controlled separately, and by adding an auxiliary resonant circuit and modulating the auxiliary bidirectional switch tube, the duty cycle loss is reduced and the power transmission is improved.

[0016] Due to the adoption of the above technical solution, the technical progress achieved by the present invention is:

[0017] The present invention reduces duty cycle loss, increases transmission power, reduces grid-side current distortion factor, and improves the sinusoidality of output voltage and current waveforms by adding an auxiliary resonant loop.

[0018] The present invention optimizes the patent in the background technology, including the optimization of the auxiliary resonant circuit structure and the optimization of the auxiliary resonant circuit control method, which can not only solve the problem of current spikes, but also solve the problem of power loss caused by resistance, and can also achieve the purpose of reducing duty cycle loss.

[0019] The present invention combines the idea of ​​bridge arm direct-pass brought by the zero vector in the current-type space vector with the idea of ​​current zero crossing in a complete resonant cycle, and proposes a three-phase power electronic transformer topology that reduces duty cycle loss and a separate modulation strategy suitable for auxiliary resonant circuit switch tubes, which can effectively reduce duty cycle loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a topological diagram of an auxiliary resonant three-phase current-type matrix power electronic transformer for reducing duty cycle loss according to the present invention;

[0021] Figure 2 This is a schematic diagram of the low switching voltage stress decoupling space vector modulation principle of the present invention;

[0022] Figure 3 This is the auxiliary resonance circuit diagram of the present invention;

[0023] Figure 4 It is the working mode diagram of the auxiliary resonant circuit of the separate control of the present invention;

[0024] Figure 5 It is a comparison diagram of the auxiliary resonant circuit of the background art patent and the present invention;

[0025] Figure 6 It is a comparison diagram of the working modes of the auxiliary resonant circuit of the background technology patent and the present invention;

[0026] Figure 7 It is an auxiliary resonance circuit diagram improved by the background technology patent;

[0027] Figure 8It is a working state diagram of the first sector of the three-phase current type matrix power electronic transformer for reducing duty ratio loss of the present invention;

[0028] Fig. 9 It is the equivalent diagram of mode 1 of the present invention;

[0029] Fig.10 It is the equivalent diagram of mode 2 of the present invention;

[0030] Fig.11 It is the equivalent diagram of mode 3 of the present invention;

[0031] Fig.12 It is the equivalent diagram of mode 4 of the present invention;

[0032] Fig.13 is the mode 5 equivalent diagram of the present invention;

[0033] Fig.14 It is the equivalent diagram of mode 6 of the present invention;

[0034] Fig.15 It is the equivalent diagram of mode 7 of the present invention;

[0035] Fig.16 It is the equivalent diagram of mode 8 of the present invention;

[0036] Fig.17 It is the equivalent diagram of mode 9 of the present invention;

[0037] Fig.18 It is the equivalent diagram of mode 10 of the present invention;

[0038] Fig.19 This is a duty cycle loss diagram when the auxiliary resonant circuit is not added in the present invention;

[0039] Fig. 20 This is a diagram showing how the duty cycle loss is reduced when an auxiliary resonant circuit is added to the present invention. DETAILED DESCRIPTION

[0040] The present invention is further described in detail below in conjunction with embodiments:

[0041] The patent of this invention combines the idea of ​​bridge arm direct-pass brought by the zero vector in the current-type space vector with the idea of ​​current zero crossing in a complete resonant cycle, and proposes a three-phase power electronic transformer topology that reduces duty cycle loss and a separate modulation strategy suitable for auxiliary resonant circuit switch tubes, which can effectively reduce duty cycle loss.

[0042] Figure 1 To reduce the duty cycle loss, the auxiliary resonant three-phase current-source matrix power electronic transformer topology diagram is shown. a 、u b 、u cIt is connected to the three-phase input filter inductor L1, L2, L3, which is connected to the three-phase input filter capacitor C1, C2, C3, and is connected to the three-phase bridge arm of the high-frequency transformer primary matrix converter at points a, b, and c. The six groups of bidirectional switch tubes in the three-phase bridge arm of the high-frequency transformer primary matrix converter are all connected to the common emitter, and the lower tube S of the bidirectional switch tube in the upper bridge arm of the three-phase bridge arm pah , S pbh , S pch The collector of the three-phase bridge arm is connected to the upper tube S of the bidirectional switch tube in the lower bridge arm nah , S nbh , S nch The collector of the high-frequency transformer is connected to the output of the primary matrix converter and the emitter of the switch tube S2 in the auxiliary resonant circuit and the parallel capacitor C r Connected, C r The other end of and the emitter of the switch tube S1 are connected to the primary side of the high-frequency transformer. The secondary side of the high-frequency transformer is connected to the input end of the high-frequency transformer secondary side matrix converter, and the primary and secondary side matrix converters of the high-frequency transformer are connected in the same way. The output end of the high-frequency transformer secondary side matrix converter is connected to the three-phase CL output filter, and the three-phase CL output filter is connected to the three-phase load.

[0043] Figure 2 This is a schematic diagram of the low switching voltage stress decoupling space vector modulation principle of the present invention. + SV1 - SV2 + SV2 - SV3 + SV3 - is the driving signal generated by the vector modulation part, V p 、V n The six-way driving signal generated by the vector modulation part is connected to V p 、V n Decoupling logic synthesis is performed to generate the driving signal of the switch tube. The primary and secondary matrix converters of the high-frequency transformer are composed of 6 bidirectional switch tubes. The driving signals of the upper and lower tubes in each bidirectional switch tube are the same. Figure 2 Only 6 unidirectional switch tube signals are given.

[0044] Figure 3 The auxiliary resonant circuit of the present invention is shown in FIG. The auxiliary resonant circuit is composed of two switch tubes S2 and S1 connected with a common collector and a parallel capacitor C r Composition. gk is the current flowing from point g to point k, i s is the current flowing through the switch tubes S2 and S1, i cr is the current flowing through the parallel capacitor C rThe current, u cr The parallel capacitor C r The voltage at both ends, the directions marked in the figure are all reference directions.

[0045] Figure 4 This is the working mode diagram of the auxiliary resonant circuit of the separate control of the present invention. Now select a high-frequency switching cycle [t0-t6] for analysis. At [t0-t1], the current i gk In the positive half cycle from g to k, S1 is opened. At this time, the capacitor C r The voltage at both ends is negative on the left and positive on the right. S2 clamped, so the current i gk First through the capacitor C r Flow from g to k, giving C r Charge until C r The voltage across the two ends is 0. At [t1-t2], the current i gk Through the diode D S2 The current i flows from g to k with the switch tube S1. At [t2-t3], the switch tubes S2 and S1 are both in the off state, and the current i gk Through the capacitor C r Flow from g to k, giving C r Charging. At [t3-t4], the current i gk Flow from k to g, open S2, then the capacitor voltage u cr The left side is positive and the right side is negative. S1 clamped, so the current i gk First through the capacitor C r Flow from k to g, giving C r Charge until C r The voltage across the two ends is 0. At [t4-t5], the current i gk Through the diode D S1 The current i flows from k to g with the switch tube S2. At [t5-t6], the switch tubes S2 and S1 are both in the off state, and the current i gk Through the capacitor C r Flow from k to g, giving C r Charging. Switch tubes S2 and S1 are both turned on at ZVZCS.

[0046] Figure 5 It is a comparison diagram of the auxiliary resonant circuit of the disclosed patent and the present invention. Figure 5 (a) is a diagram of the auxiliary resonant circuit of the disclosed patent. The auxiliary resonant circuit consists of two common emitter connected switches S1 and S2 and a parallel capacitor C r composition. Figure 5 (b) is an auxiliary resonant circuit diagram of the present invention, wherein the auxiliary resonant circuit is composed of two switches S1 and S2 connected to the same collector and a parallel capacitor C rComposition. gk is the current flowing from point g to point k, i s is the current flowing through the switch tubes S2 and S1, i cr is the current flowing through the parallel capacitor C r The current, u cr The parallel capacitor C r The voltage at both ends, the directions marked in the figure are all reference directions. Figure 5 (a) with Figure 5 (b) It can be seen that the connection methods of the switch tubes in the two figures are different.

[0047] Figure 6 It is a comparison diagram of the modal analysis of the auxiliary resonant circuit of the disclosed patent and the present invention. Figure 6 (a) is the working mode diagram of the auxiliary resonant circuit of the integrated control mentioned in the patent disclosure. Now we select a high-frequency switching cycle [t0-t4] for analysis. At [t0-t1], the current i gk In the positive half cycle from g to k, at time t0, the switches S1 and S2 are turned on. At this time, the capacitor C r The voltage at both ends is negative on the left and positive on the right. The capacitor is connected to the diode D through the switch tube S2. S1 Instantaneous discharge, capacitor C r is short-circuited, i cr At this time, a current spike will appear. Then the current i gk Through the switch tube S1 and the diode D S2 Flows from g to k. [t1-t2] At time t1, the switch tubes S1 and S2 are turned off, and the current i gk Through the capacitor C r Flow from g to k, giving C r Charging, charging to a certain level, current i gk Reverse, C r Discharge. [t2-t3] At time t2, the switches S1 and S2 are turned on. At this time, the capacitor C r The voltage at both ends is positive on the left and negative on the right. The capacitor is connected to the diode D through the switch tube S1. S2 Instantaneous discharge, capacitor C r is short-circuited, i cr At this time, a current spike will appear. Then the current i gk Through the switch tube S2 and the diode D S1 Flows from k to g. [t3-t4] At time t3, the switch tubes S1 and S2 are turned off, and the current i gk Through the capacitor C r Flow from k to g, giving C r Charging, charging to a certain level, current i gk Reverse, C r Discharge. Figure 6(b) is the working mode diagram of the auxiliary resonant circuit of the separate control mentioned in the present invention. Figure 6 (a) It can be seen that the integral control has a moment when the capacitor is short-circuited, which will cause a current spike, and Figure 6 The split control mentioned in (b) effectively solves this problem.

[0048] Figure 7 This is a diagram of the auxiliary resonance circuit improved by the disclosed patent. Due to the integral modulation scheme used in the auxiliary resonance circuit of the disclosed patent, the parallel capacitor C r At the moment of short circuit, the current spike of the capacitor will be caused. To solve this problem, an improved auxiliary resonant circuit is proposed in the patent disclosure, that is, to give C r A smaller resistor R is connected in series r Although this solves the current spike problem caused by capacitor short circuit, the series resistor R r Active power will be absorbed, resulting in power loss. The auxiliary resonant circuit with two switch tubes connected to the common collector and controlled separately mentioned in the present invention solves the problem of current spikes and the problem of power loss caused by resistance, thereby achieving the purpose of reducing duty cycle loss.

[0049] Figure 8 The working state diagram of the first sector of the three-phase current matrix power electronic transformer that can reduce the duty cycle loss. pah , S nah , S pbh , S nbh , S pch , S nch is the driving signal of the switch tube of the matrix converter on the primary side of the high-frequency transformer, and S2 and S1 are the driving signals of the switch tube in the auxiliary resonant circuit. p is the primary voltage waveform of the high-frequency transformer, u s is the secondary voltage waveform of the high-frequency transformer, i p is the primary current waveform of the high-frequency transformer, i cr is the current flowing through the parallel capacitor C r The current, u cr The parallel capacitor C r The driving signal of the switch tube of the matrix converter on the secondary side of the high-frequency transformer is generated in the same way as the driving signal of the switch tube on the primary side.

[0050] Fig. 9 is the equivalent diagram of mode 1. Mode 1 corresponds to Figure 8 [t0-t1] time period, at time t0, turn off the switch tube S pal , turn on the switch tube S pcl . Primary side matrix converter switch tube S nch , S pcl , Snal With S pah There are driving signals, but only S pah With S pcl The auxiliary resonant circuit switch tube S1 has a driving signal but is not turned on. The current flows through the switch tube S pah , S pcl With diode D nal , D nch And the parallel capacitor C in the auxiliary resonant circuit r Flow. Diode D nal , D nch For the switch tube S nal , S nch The anti-parallel diode has a similar symbol. At time t0, the capacitor voltage u cr The right side is positive and the left side is negative. S2 clamped, so the primary current i p Give C first r Charge until C r The voltage across the terminals is 0.

[0051] Fig.10 is the equivalent diagram of mode 2. Mode 2 corresponds to Figure 8 [t1-t2] time period, at time t1, C r The voltage across the two ends is 0, and the auxiliary resonant circuit switch S1 is turned on. The current flows through the switch S pah , S pcl With diode D nal , D nch And the auxiliary resonant circuit D S2 , S1 flows. This is the process of transferring energy from the front stage to the back stage.

[0052] Fig.11 is the equivalent diagram of mode 3. Mode 3 corresponds to Figure 8 [t2-t3] time period, at time t2, turn off the switch tube S pcl , turn on the switch tube S pbl At this time, the primary matrix converter switch tube S pah , S nal , S nbh With S pbl There are driving signals, but only S pah With S pbl The auxiliary resonant circuit switch S1 is turned on, and the current flows through the switch S pah , S pbl , S1 and diode D nal , D nbh , D s2 This is the process of transferring energy from the front stage to the back stage.

[0053] Fig.12 is the equivalent diagram of mode 4. Mode 4 corresponds to Figure 8 [t3-t4] time period, at time t3, turn off the switch tube S pbl , turn off the auxiliary resonant circuit switch S1, turn on the switch S pal . Primary side matrix converter switch tube S pah , S nal , S nah With S pal There are driving signals, but only S pah With S pal The current flows through the switch tube S pah , S pal With diode D nal , D nah And the parallel capacitor C in the auxiliary resonant circuit r The primary a-phase bridge arm is directly connected. At this time, the transformer leakage inductance L r With the parallel capacitor C r Resonance, primary current i p Decrease until it reaches 0.

[0054] Fig.13 is the equivalent diagram of mode 5. Mode 5 corresponds to Figure 8 [t4-t5] time period, at time t4, the primary current i p Decreases to 0, and the primary current i p The primary matrix converter switch tube S pah , S nal , S nah With S pal There are driving signals, at this time S nal With S nah The current flows through the switch tube S nal , S nah With diode D pah , D pal And the parallel capacitor C in the auxiliary resonant circuit r The primary side a phase bridge arm is directly connected, and the transformer leakage inductance L r With the parallel capacitor C r resonance.

[0055] Fig.14 is the equivalent diagram of mode 6. Mode 6 corresponds to Figure 8 [t5-t6] time period, at time t5, turn off the switch tube S nal , turn on the switch tube S ncl , giving a driving signal to the auxiliary resonant circuit switch tube S2, but S2 is not turned on. pch , S ncl , Snah With S pal There are driving signals, only S nah With S ncl The current flows through the switch tube S nah , S ncl With diode D pal , D pch And the parallel capacitor C in the auxiliary resonant circuit r Flow. Since at time t5, the capacitor voltage u cr The left side is positive and the right side is negative. S1 clamped, so the primary current i p Give C first r Charge until C r The voltage across the terminals is 0.

[0056] Fig.15 is the equivalent diagram of mode 7. Mode 7 corresponds to Figure 8 [t6-t7] time period, at time t6, C r The voltage across the two ends is 0, and the auxiliary resonant circuit switch S2 is turned on. The current flows through the switch S nah , S ncl With diode D pal , D pch And the auxiliary resonant circuit D S1 , S2 flows. This period of time is the process of power supply energy transfer to the next stage, and the transformer primary voltage u p Reverse.

[0057] Fig.16 is the equivalent diagram of mode 8. Mode 8 corresponds to Fig.10 [t7-t8] time period, at time t7, turn off the switch tube S ncl , turn on the switch tube S nbl . Primary side matrix converter switch tube S pbh , S nbl , S nah With S pal There are driving signals, but only S nah With S nbl The current flows through the switch tube S nah , S nbl With diode D pbh , D pal And the auxiliary resonant circuit D S1 , S2 flows. This period of time is the process of power supply energy transferring to the next stage.

[0058] Fig.17 is the equivalent diagram of mode 9. Mode 9 corresponds to Figure 8 [t8-t9] time period, at time t8, turn off the switch tube S nbl, turn off the auxiliary resonant circuit switch tube S2, turn on the switch tube S nal . Primary side matrix converter switch tube S nal , S pah , S nah With S pal There are driving signals, but only S nal With S nah The transformer primary current flows through S nal , D pah , S nah , D pal And the parallel capacitor C in the auxiliary resonant circuit r The primary a-phase bridge arm is directly connected. At this time, the transformer leakage inductance L r With the parallel capacitor C r Resonance, primary current i p Decrease until it reaches 0.

[0059] Fig.18 is the equivalent diagram of mode 10. Mode 10 corresponds to Figure 8 [t9-t 10 ] time period, at time t9, the primary current i p Decreases to 0, and the primary current i p The primary matrix converter switch tube S nal , S pah , S nah With S pal There are driving signals, but at this time S pal With S pah The transformer primary current flows through S pal , D nah , S pah , D nal And the parallel capacitor C in the auxiliary resonant circuit r The primary side a phase bridge arm is directly connected, and the transformer leakage inductance L r With capacitor C r resonance.

[0060] Fig.19 The high-frequency transformer primary and secondary matrix converter of the present invention adopts the same three-phase decoupled vector modulation method. When the auxiliary resonant circuit is not added, in each high-frequency cycle, when the primary current of the transformer switches between positive and negative, the leakage inductance current cannot pass zero in time, resulting in duty cycle loss. Fig.19 As shown. Where T0 is the zero vector action time, T x With T y is the effective vector action time, D x With D y is the duty ratio loss. p and ip are the transformer primary voltage and current respectively. At time T0, the current i p Cannot cross zero, then at T x At this moment, the duty cycle will be lost, such as Fig.19 Middle D x With D y shown.

[0061] Fig. 20 This is a graph showing how the duty ratio is reduced when an auxiliary resonant circuit is added. Fig. 20 As shown in the figure, when the auxiliary resonant circuit is added, the primary leakage inductance L r and the parallel capacitor C in the auxiliary resonant circuit r Resonance makes the primary current i p The duty cycle loss of the proposed converter can be minimized by crossing zero and changing the current polarity during the direct-through period of the upper and lower bridge arms of the primary matrix converter. This reduces the power loss caused by the loss of duty cycle, while also increasing the transmission efficiency and reducing the grid-side current distortion factor.

Claims

1. A three-phase solid-state transformer topology for reducing duty cycle loss, characterized in that: Includes three-phase AC power supply u a , u b , u c , three-phase LC Input filter, high frequency transformer primary side matrix converter, auxiliary resonant circuit, high frequency transformer, high frequency transformer secondary side matrix converter, three phase CL Output filter and three-phase load R a , R b , R c ; Three-phase AC power supply u a , u b , u c It is connected to the three-phase LC input filter, which is connected to the input end of the primary matrix converter of the high-frequency transformer; the positive output end of the primary matrix converter of the high-frequency transformer and the emitter of the switch tube S2 in the auxiliary resonant circuit and the parallel capacitor C r Connected, C r The other end of and the emitter of the switch tube S1 are connected to one end of the primary side of the high-frequency transformer, and the negative output end of the primary side matrix converter is connected to the other end of the primary side of the high-frequency transformer; the secondary side of the high-frequency transformer is connected to the input end of the secondary side matrix converter of the high-frequency transformer; the output end of the secondary side matrix converter of the high-frequency transformer is connected to the three-phase CL output filter, and the three-phase CL output filter is connected to the three-phase load R a , R b , R c connected; The specific circuit connection relationship is as follows: three-phase AC power supply u a , u b , u c With three-phase input filter inductor L 1. L 2. L 3 one end connected to the three-phase input filter inductor L 1. L 2. L 3 The other end is connected to the three-phase input filter capacitor C 1. C 2. C 3, and are respectively connected to points a, b, and c with the three-phase bridge arm of the primary matrix converter of the high-frequency transformer; the six groups of bidirectional switch tubes in the three-phase bridge arm of the primary matrix converter of the high-frequency transformer are all connected with a common emitter, and the lower tube S of the bidirectional switch tube in the upper bridge arm of the three-phase bridge arm pah , S pbh , S pch The collector of the three-phase bridge arm is connected to the upper tube S of the bidirectional switch tube in the lower bridge arm nah , S nbh , S nch The collector of the high-frequency transformer is connected; the secondary side of the high-frequency transformer is connected to the input end of the secondary side matrix converter of the high-frequency transformer, and the primary side matrix converter of the high-frequency transformer is connected in the same way as the secondary side matrix converter of the high-frequency transformer; the output end of the secondary side matrix converter of the high-frequency transformer is connected to the three-phase CL Output filter connected, three-phase CL Output filter and three-phase load R a , R b , R c connected; The auxiliary resonant circuit includes two switch tubes S2 and S1 connected with a common collector and a parallel capacitor C r ; The high-frequency transformer primary side matrix converter and the high-frequency transformer secondary side matrix converter are both composed of 6 common-emitter bidirectional switch tubes.

2. A split modulation method for a three-phase solid-state transformer topology to reduce duty cycle loss according to claim 1, characterized in that: Both the primary side matrix converter of the high-frequency transformer and the secondary side matrix converter of the high-frequency transformer adopt decoupled vector modulation with low switching voltage stress. The specific process is: first, the decoupling idea is adopted to decouple the three-phase current-type matrix power electronic transformer into two three-phase-three-phase AC conversion circuits composed of unidirectional switching tubes, and then low-voltage stress space vector modulation and a high-frequency square wave signal with a duty cycle of 50% are adopted to generate the modulation signal of the primary and secondary side matrix converter switching tubes of the high-frequency transformer in the three-phase current-type matrix power electronic transformer topology according to the current-type coupling idea.

3. The split modulation method of three-phase solid-state transformer topology with reduced duty cycle loss according to claim 2, characterized in that: When a certain phase bridge arm of the primary side matrix converter of the high-voltage and high-frequency transformer is directly connected, the switch tubes S2 and S1 in the auxiliary resonant circuit are controlled separately. By adding the auxiliary resonant circuit and modulating the auxiliary bidirectional switch tube, the duty cycle loss is reduced and the power transmission is improved.

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