Bidirectional four-port three-phase DC-AC converter and modulation strategy thereof

Abstract

The invention belongs to the technical field of power equipment, and particularly provides a bidirectional four-port three-phase DC-AC converter and a modulation strategy thereof, and the converter comprises a DC-DC converter, a dual-output converter, a low-voltage DC port Vdc1, a high-voltage DC port Vdc2, and two AC voltage ports Vac1 and Vac2. The converter can operate in a single-input single-output working mode, a single-input double-output working mode, a double-input single-output working mode or a double-input double-output working mode by controlling the switch module, compared with a traditional two-stage structure, the power capacity, the loss and the volume cost of the DC-AC converter are effectively reduced, and the DC-AC converter can be well applied to a hybrid AC-DC micro-grid.

Description

Technical Field

[0001] The invention belongs to the technical field of electric power equipment, and in particular relates to a bidirectional four-port three-phase DC-AC converter and a modulation strategy thereof. Background Art

[0002] In recent years, with the global attention and development of renewable energy, the large-scale access of distributed energy such as solar energy and wind energy, and the application needs in the modern hybrid AC / DC microgrid environment, the structure and operation mode of the power grid have undergone profound changes. Traditional power grids mainly rely on centralized power generation and unidirectional power transmission, that is, power is transmitted from power stations to power grids at all levels and then to end users. In this mode, the direction of power flow is single and the power conversion process is relatively simple. In the modern energy structure, renewable energy and distributed power generation systems have gradually become the mainstream. They have the characteristics of unstable output voltage and power, and require flexible and efficient power conversion and management technologies to adapt to their volatility and intermittency. Hybrid AC / DC microgrid is one of the important technical paths to meet this challenge. It organically combines DC power supply and AC power supply, can more efficiently utilize various types of power supply, and improve the flexibility and stability of the power grid. In this context, traditional DC-AC converters can no longer meet actual needs. These converters can usually only handle a single type of voltage conversion, and have limited efficiency and flexibility, making it difficult to perform ideally in complex applications with multiple ports and multiple modes.

[0003] In addition, with the development of smart grids and energy internet, the requirements for power quality and conversion efficiency are becoming higher and higher. Research on multi-port converters and multi-mode working modes has become a hot topic, in order to improve the overall performance and adaptability of the converter by optimizing the control strategy without increasing the hardware cost. This requires that the new converter topology can not only achieve efficient power conversion, but also be able to flexibly switch between different working modes and adapt to a variety of voltage and power requirements. In this context, the development of a bidirectional DC-AC converter that can flexibly handle multi-port and multi-mode has become an urgent technical need. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a bidirectional four-port three-phase DC-AC converter and a modulation strategy thereof to solve the above-mentioned technical problems.

[0005] In a first aspect, the present invention provides a bidirectional four-port three-phase DC-AC converter, comprising a DC-DC converter, a dual-output converter, a low-voltage DC port V dc1 , High voltage DC port V dc2 and two AC voltage ports V ac1 、V ac2 ; Low voltage DC port Vdc1 Connected to the energy storage battery, low voltage DC port V dc1 A capacitor C1 is connected in parallel between the positive and negative electrodes; The first end of the DC-DC converter and the first end of the dual output converter are both connected to the low voltage DC port V dc1 The positive pole of the DC-DC converter and the second end of the dual output converter are connected to the high voltage DC port V dc2 The positive pole, high voltage DC port V dc2 The positive electrode is also connected to the positive terminal P of the DC bus. The third terminal of the DC-DC converter, the low-voltage DC port V dc1 The negative pole, the third terminal of the dual output converter and the high voltage DC port V dc2 The negative poles of the two terminals are grounded, and the high voltage DC port V dc2 The negative pole of the dual output converter is also connected to the negative terminal N of the DC bus. The fourth terminal of the dual output converter is connected to the negative terminal N of the DC bus. ac1 Connected to the external three-phase load, the fifth terminal of the dual output converter is connected to the AC voltage port V ac2 Connect to the external power grid; The dual-output converter includes three-phase bridge arms, namely, phase A bridge arm, phase B bridge arm and phase C bridge arm. Each phase bridge arm consists of 6 switch modules S x1 ~S x6 Composition, where x∈{A, B, C}.

[0006] A further improvement of the technical solution is that the DC-DC converter includes an inductor L1, an insulated gate bipolar transistor S1, an insulated gate bipolar transistor S2 and a capacitor C2, and the first end of the inductor L1 is connected to the low voltage DC port V dc1 The positive electrode of the inductor L1, the second end of the inductor L1 is connected to the emitter of the insulated gate bipolar transistor S1 and the collector of the insulated gate bipolar transistor S2, the collector of the insulated gate bipolar transistor S1 and the first end of the capacitor C2 are both connected to the high voltage DC port V dc2 The positive electrode of the insulated gate bipolar transistor S2, the emitter of the insulated gate bipolar transistor S2 and the second end of the capacitor C2 are all grounded.

[0007] A further improvement of the technical solution is that the A phase bridge arm includes an insulated gate bipolar transistor S A1 , Insulated Gate Bipolar Transistor S A2 , Insulated Gate Bipolar Transistor S A3 , Insulated Gate Bipolar Transistor S A4 , Insulated Gate Bipolar Transistor S A5 and IGBT S A6 ; Insulated Gate Bipolar Transistor S A1 The collector is connected to the high voltage DC port V dc2 The positive electrode of the insulated gate bipolar transistor SA1 The emitter of the insulated gate bipolar transistor S A2 The collector of the external three-phase load and the A-phase input terminal, the insulated gate bipolar transistor S A2 The emitter of the insulated gate bipolar transistor S A4 The collector and insulated gate bipolar transistor S A5 The collector of the insulated gate bipolar transistor S A4 The emitter of the insulated gate bipolar transistor S A3 The emitter of the insulated gate bipolar transistor S A3 The collector is connected to the low voltage DC port V dc1 The positive electrode of the insulated gate bipolar transistor S A5 The emitter of the insulated gate bipolar transistor S A6 The collector of the insulated gate bipolar transistor S A5 The emitter of a A phase line connected to the external power grid, insulated gate bipolar transistor S A6 The emitter is grounded.

[0008] A further improvement of the technical solution is that the B-phase bridge arm includes an insulated gate bipolar transistor S B1 , Insulated Gate Bipolar Transistor S B2 , Insulated Gate Bipolar Transistor S B3 , Insulated Gate Bipolar Transistor S B4 , Insulated Gate Bipolar Transistor S B5 and IGBT S B6 ; Insulated Gate Bipolar Transistor S B1 The collector is connected to the high voltage DC port V dc2 The positive electrode of the insulated gate bipolar transistor S B1 The emitter of the insulated gate bipolar transistor S B2 The collector of the insulated gate bipolar transistor S is connected to the B-phase input terminal of the external three-phase load. B2 The emitter of the insulated gate bipolar transistor S B4 The collector and insulated gate bipolar transistor S B5 The collector of the insulated gate bipolar transistor S B4 The emitter of the insulated gate bipolar transistor S B3 The emitter of the insulated gate bipolar transistor S B3 The collector is connected to the low voltage DC port V dc1 The positive electrode of the insulated gate bipolar transistor S B5 The emitter of the insulated gate bipolar transistor S B6 The collector of the insulated gate bipolar transistor S B5 The emitter of bThe B-phase line connected to the external power grid, the insulated gate bipolar transistor S B6 The emitter is grounded.

[0009] A further improvement of the technical solution is that the C-phase bridge arm includes an insulated gate bipolar transistor S C1 , Insulated Gate Bipolar Transistor S C2 , Insulated Gate Bipolar Transistor S C3 , Insulated Gate Bipolar Transistor S C4 , Insulated Gate Bipolar Transistor S C5 and IGBT S C6 ; Insulated Gate Bipolar Transistor S C1 The collector is connected to the high voltage DC port V dc2 The positive electrode of the insulated gate bipolar transistor S C1 The emitter of the insulated gate bipolar transistor S C2 The collector of the external three-phase load and the C-phase input terminal, the insulated gate bipolar transistor S C2 The emitter of the insulated gate bipolar transistor S C4 The collector and insulated gate bipolar transistor S C5 The collector of the insulated gate bipolar transistor S C4 The emitter of the insulated gate bipolar transistor S C3 The emitter of the insulated gate bipolar transistor S C3 The collector is connected to the low voltage DC port V dc1 The positive electrode of the insulated gate bipolar transistor S C5 The emitter of the insulated gate bipolar transistor S C6 The collector of the insulated gate bipolar transistor S C5 The emitter of c Connected to the C phase line of the external power grid, the insulated gate bipolar transistor S C6 The emitter is grounded.

[0010] A further improvement of the technical solution is that the first inverter stage is composed of three output ports of the A-phase bridge arm, the B-phase bridge arm and the C-phase bridge arm connected to the external three-phase load, and the second inverter stage is composed of three output ports of the A-phase bridge arm, the B-phase bridge arm and the C-phase bridge arm connected to the external power grid.

[0011] In a second aspect, the present invention provides a triangular carrier modulation strategy for a bidirectional four-port three-phase DC-AC converter based on any one of the above, comprising: Get switch module S x1 ~S x6 The opening status of According to the switch module S x1 ~S x6The opening condition determines the output phase voltage of the output port corresponding to the first inverter stage and the second inverter stage; According to the low voltage DC port V dc1 and high voltage DC port V dc2 The level at modulates the triangular carrier; The three-phase modulation wave is modulated according to the modulated triangular carrier and the determined two output phase voltages in combination with the modulation constraint conditions; The switch drive signal of each phase bridge arm is generated according to the modulated triangular carrier and three-phase modulation.

[0012] A further improvement of the technical solution is that the modulation constraint condition is: during modulation, the output phase voltage of the bridge arm in the first inverter stage cannot be less than the output phase voltage of the bridge arm in the second inverter stage.

[0013] A further improvement of this technical solution is that when V dc1 >1 / 2V dc2 When , the three-phase modulation wave of the first inverter stage is: ; A further improvement of this technical solution is that when V dc1 >1 / 2V dc2 When , the three-phase modulation wave of the second inverter stage is: ; Among them, m1 and m2 are modulation degrees, and the linear value range is 0 to 1; and is the output angular frequency, and is the initial phase angle, and is the DC offset.

[0014] The beneficial effect of the present invention is that the present invention discloses a novel bidirectional four-port three-phase DC-AC converter topology structure for a hybrid AC / DC microgrid. For a hybrid AC / DC microgrid system, the topology structure of the present invention has two DC ports and two three-phase AC ports, i.e., a low-voltage DC port V dc1 , a high voltage DC port V dc2 and two AC voltage ports V ac1 and V ac2 By controlling the switch module, the converter can operate in single-input single-output, single-input dual-output, dual-input single-output or dual-input dual-output working modes. Compared with the traditional two-stage structure, it effectively reduces the power capacity, loss and volume cost of the DC-AC converter, and can be well applied to hybrid AC / DC microgrids.

[0015] In addition, the invention has a reliable design principle, a simple structure and a very broad application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 This is a topological diagram of the bidirectional four-port three-phase DC-AC converter of the present invention.

[0018] Figure 2 (a) is the schematic diagram of switch state 1.

[0019] Figure 2 (b) is the schematic diagram of switch state 2.

[0020] Figure 2 (c) is the schematic diagram of switch state 3.

[0021] Figure 2 (d) is the schematic diagram of switch state 4.

[0022] Figure 2 (e) is the schematic diagram of switch state 5.

[0023] Figure 2 (f) is the schematic diagram of switch state 6.

[0024] Figure 3 (a) is a schematic diagram comparing the upper and lower groups of triangular carrier and modulation waves with the same amplitude and frequency and symmetrical distribution.

[0025] Figure 3 (b) is a schematic diagram comparing the triangular carrier and modulation wave corresponding to Vdc1>1 / 2Vdc2.

[0026] Figure 3 (c) is a schematic diagram comparing the triangular carrier and modulation wave corresponding to Vdc1<1 / 2Vdc2.

[0027] Figure 4 Schematic diagram of the triangular carrier PWM strategy for the FPTPC co-frequency and co-phase working mode.

[0028] Figure 5 Schematic diagram of the triangular carrier PWM strategy for the FPTPC co-frequency and out-of-phase working mode.

[0029] Figure 6 The logic circuit diagram for generating the A-phase bridge arm switch drive signal in FPTPC.

[0030] Figure 7 Schematic diagram for comparing the triangular carrier and modulation wave of the FPTPC modulation strategy.

[0031] Figure 8 The output port outputs three-phase voltage waveform for the FPTPC modulation strategy.

[0032] Fig. 9 The output port outputs three-phase current waveform for the FPTPC modulation strategy.

[0033] Fig.10 The three-phase voltage waveform output by the output port under the FPTPC modulation strategy.

[0034] Fig.11 The three-phase current waveform output by the output port under the FPTPC modulation strategy.

[0035] Fig.12 This is a schematic diagram comparing the triangular carrier and the modulation wave of the first non-sinusoidal modulation strategy.

[0036] Fig.13 The output port outputs a three-phase voltage waveform for the first non-sinusoidal modulation strategy.

[0037] Fig.14 The output port outputs a three-phase current waveform for the first non-sinusoidal modulation strategy.

[0038] Fig.15 The three-phase voltage waveform output by the output port under the first non-sinusoidal modulation strategy.

[0039] Fig.16 The three-phase current waveform output by the output port under the first non-sinusoidal modulation strategy.

[0040] Fig.17 The output port outputs active and reactive waveforms for the first non-sinusoidal modulation strategy.

[0041] Fig.18 The output port outputs active and reactive waveforms under the first non-sinusoidal modulation strategy.

[0042] Fig.19 This is a schematic diagram comparing the triangular carrier and the modulation wave of the second non-sinusoidal modulation strategy.

[0043] Fig. 20 The output port outputs a three-phase voltage waveform for the second non-sinusoidal modulation strategy.

[0044] Fig.21 The output port outputs a three-phase current waveform for the second non-sinusoidal modulation strategy.

[0045] Fig. 22The three-phase voltage waveform output by the output port under the second non-sinusoidal modulation strategy.

[0046] Fig.23 The three-phase current waveform output by the output port under the second non-sinusoidal modulation strategy.

[0047] Fig.24 The output port outputs active and reactive waveforms for the second non-sinusoidal modulation strategy.

[0048] Fig.25 The output port outputs active and reactive waveforms under the second non-sinusoidal modulation strategy.

[0049] Fig.26 This is a schematic diagram comparing the triangular carrier and modulation wave of the third non-sinusoidal modulation strategy.

[0050] Fig. 27 The output port outputs a three-phase voltage waveform for the third non-sinusoidal modulation strategy.

[0051] Fig.28 The output port outputs a three-phase current waveform for the third non-sinusoidal modulation strategy.

[0052] Fig.29 The three-phase voltage waveform output by the output port under the third non-sinusoidal modulation strategy.

[0053] Fig.30 The three-phase current waveform output by the output port under the third non-sinusoidal modulation strategy.

[0054] Fig.31 The output port outputs active and reactive waveforms for the third non-sinusoidal modulation strategy.

[0055] Fig.32 The output port outputs active and reactive waveforms under the third non-sinusoidal modulation strategy. DETAILED DESCRIPTION

[0056] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0057] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0058] like Figure 1 As shown, the present invention provides a bidirectional four-port three-phase DC-AC converter, including a DC-DC converter, a dual-output converter, a low-voltage DC port V dc1 , High voltage DC port V dc2 and two AC voltage ports V ac1 、V ac2 ; Low voltage DC port V dc1 Connected to the energy storage battery, low voltage DC port V dc1 A capacitor C1 is connected in parallel between the positive and negative electrodes of the DC-DC converter; the first end of the DC-DC converter and the first end of the dual output converter are both connected to the low voltage DC port V dc1 The positive pole of the DC-DC converter and the second end of the dual output converter are connected to the high voltage DC port V dc2 The positive pole, high voltage DC port V dc2 The positive electrode is also connected to the positive terminal P of the DC bus. The third terminal of the DC-DC converter, the low-voltage DC port V dc1 The negative pole, the third terminal of the dual output converter and the high voltage DC port V dc2 The negative poles of the two terminals are grounded, and the high voltage DC port V dc2 The negative pole of the dual output converter is also connected to the negative terminal N of the DC bus. The fourth terminal of the dual output converter is connected to the negative terminal N of the DC bus. ac1 Connected to the external three-phase load, the fifth terminal of the dual output converter is connected to the AC voltage port V ac2 The dual output converter includes three-phase bridge arms, namely, phase A bridge arm, phase B bridge arm and phase C bridge arm, and each phase bridge arm consists of 6 switch modules S x1 ~S x6 Composition, where x∈{A, B, C}.

[0059] The dual output converter is a four-port three-phase converter (FPTPC), and the dual output converter part is based on the dual output T-type three-level converter topology structure and is improved. It provides four voltage ports at the same time, namely a low voltage DC port V dc1 , a high voltage DC port V dc2 and two AC voltage ports V ac1and Vac2. The high-voltage DC port is connected to the intermediate DC bus, while the low-voltage DC port is directly connected to the energy storage battery. When AC and DC energy interact through the low-voltage DC port, only a single-stage conversion is required, and when energy interacts through the high-voltage DC port, it must first be boosted by the DC-DC converter before energy interaction. The output voltage amplitude and frequency of the two AC voltage ports can be flexibly adjusted. When power is transferred from DC to AC, it is defined as an inverter mode, and vice versa when it is transferred from AC to DC, it is defined as a rectifier mode. Taking the inverter mode as an example, part of the power P dc1 The power is directly transmitted to the AC side through FPTPC, while the other part of the power P dc2 It is transmitted to the AC side through two conversion stages: the boost DC-DC converter and the FPTPC.

[0060] Specifically, the DC-DC converter includes an inductor L1, an insulated gate bipolar transistor S1, an insulated gate bipolar transistor S2 and a capacitor C2. The first end of the inductor L1 is connected to the low voltage DC port V dc1 The positive electrode of the inductor L1, the second end of the inductor L1 is connected to the emitter of the insulated gate bipolar transistor S1 and the collector of the insulated gate bipolar transistor S2, the collector of the insulated gate bipolar transistor S1 and the first end of the capacitor C2 are both connected to the high voltage DC port V dc2 The positive electrode of the insulated gate bipolar transistor S2, the emitter of the insulated gate bipolar transistor S2 and the second end of the capacitor C2 are all grounded.

[0061] Among them, the A phase bridge arm includes an insulated gate bipolar transistor S A1 , Insulated Gate Bipolar Transistor S A2 , Insulated Gate Bipolar Transistor S A3 , Insulated Gate Bipolar Transistor S A4 , Insulated Gate Bipolar Transistor S A5 and IGBT S A6 ; Insulated Gate Bipolar Transistor S A1 The collector is connected to the high voltage DC port V dc2 The positive electrode of the insulated gate bipolar transistor S A1 The emitter of the insulated gate bipolar transistor S A2 The collector of the external three-phase load and the A-phase input terminal, the insulated gate bipolar transistor S A2 The emitter of the insulated gate bipolar transistor S A4 The collector and insulated gate bipolar transistor S A5 The collector of the insulated gate bipolar transistor S A4 The emitter of the insulated gate bipolar transistor S A3 The emitter of the insulated gate bipolar transistor S A3 The collector is connected to the low voltage DC port V dc1 The positive electrode of the insulated gate bipolar transistor S A5The emitter of the insulated gate bipolar transistor S A6 The collector of the insulated gate bipolar transistor S A5 The emitter of a A phase line connected to the external power grid, insulated gate bipolar transistor S A6 The emitter is grounded.

[0062] In addition, the B-phase bridge arm includes an insulated gate bipolar transistor S B1 , Insulated Gate Bipolar Transistor S B2 , Insulated Gate Bipolar Transistor S B3 , Insulated Gate Bipolar Transistor S B4 , Insulated Gate Bipolar Transistor S B5 and IGBT S B6 ; Insulated Gate Bipolar Transistor S B1 The collector is connected to the high voltage DC port V dc2 The positive electrode of the insulated gate bipolar transistor S B1 The emitter of the insulated gate bipolar transistor S B2 The collector of the insulated gate bipolar transistor S is connected to the B-phase input terminal of the external three-phase load. B2 The emitter of the insulated gate bipolar transistor S B4 The collector and insulated gate bipolar transistor S B5 The collector of the insulated gate bipolar transistor S B4 The emitter of the insulated gate bipolar transistor S B3 The emitter of the insulated gate bipolar transistor S B3 The collector is connected to the low voltage DC port V dc1 The positive electrode of the insulated gate bipolar transistor S B5 The emitter of the insulated gate bipolar transistor S B6 The collector of the insulated gate bipolar transistor S B5 The emitter of b The B-phase line connected to the external power grid, the insulated gate bipolar transistor S B6 The emitter is grounded.

[0063] In addition, the C phase bridge arm includes an insulated gate bipolar transistor S C1 , Insulated Gate Bipolar Transistor S C2 , Insulated Gate Bipolar Transistor S C3 , Insulated Gate Bipolar Transistor S C4 , Insulated Gate Bipolar Transistor S C5 and IGBT S C6 ; Insulated Gate Bipolar Transistor S C1 The collector is connected to the high voltage DC port V dc2 The positive electrode of the insulated gate bipolar transistor S C1The emitter is connected to the insulated gate bipolar transistor S C2 The collector and the C-phase input terminal of the external three-phase load, the insulated gate bipolar transistor S C2 The emitter is connected to the insulated gate bipolar transistor S C4 The collector and the insulated gate bipolar transistor S C5 The collector of, the insulated gate bipolar transistor S C4 The emitter is connected to the insulated gate bipolar transistor S C3 The emitter of, the insulated gate bipolar transistor S C3 The collector is connected to the positive pole of the low-voltage DC port V dc1 of, the insulated gate bipolar transistor S C5 The emitter is connected to the insulated gate bipolar transistor S C6 The collector of, the insulated gate bipolar transistor S C5 The emitter is connected to the C-phase line of the external power grid through the inductor L c of, the insulated gate bipolar transistor S C6 The emitter is grounded.

[0064] Among them, the first inverter stage is composed of three output ports of the A-phase bridge arm, B-phase bridge arm, and C-phase bridge arm that are connected to the external three-phase load, and the second inverter stage is composed of three output ports of the A-phase bridge arm, B-phase bridge arm, and C-phase bridge arm that are connected to the external power grid. The first inverter stage is connected to the external three-phase load, and the second inverter stage is connected to the external power grid through the inductor L a inductor L b connected and inductor L c connected to the external power grid to complete grid connection.

[0065] As Figure 2 shown, the bidirectional four-port three-phase DC-AC converter has a total of 6 switching states. Since the voltage V dc1 of the low-voltage DC port is not a constant value, it is expressed in a general form as kU (0 < k ≤ 2) here, where k = 2V dc1 / V dc2 . Taking the A-phase bridge arm as an example, the six switching states of the converter are described as follows: Operating state 1: The insulated gate bipolar transistors S A1 , the insulated gate bipolar transistors S A2 , the insulated gate bipolar transistors S A3 and the insulated gate bipolar transistors S A5 are turned on. The current paths between the DC link and node A1 (the output port corresponding to A in the first inverter stage) and node A2 (the output port corresponding to A in the second inverter stage) are as Figure 2 (a) shown. At this time, the output phase voltage V A1N of A in the first inverter stage is 2U, and the output phase voltage VA2N 2U.

[0066] Working state 2: Insulated gate bipolar transistor S A1 , Insulated Gate Bipolar Transistor S A3 , Insulated Gate Bipolar Transistor S A4 and IGBT S A5 The current paths between the DC link and the nodes A1 and A2 are as follows: Figure 2 (b) At this time, the output phase voltage V of phase A in the first inverter stage is A1N is 2U, the output phase voltage V of phase A in the second inverter stage A2N is kU.

[0067] Working state 3: Insulated gate bipolar transistor S A1 , Insulated Gate Bipolar Transistor S A3 , Insulated Gate Bipolar Transistor S A4 and IGBT S A6 The current paths between the DC link and the nodes A1 and A2 are as follows: Figure 2 (c) At this time, the output phase voltage V of phase A in the first inverter stage is A1N is 2U, the output phase voltage V of phase A in the second inverter stage A2N is 0.

[0068] Working state 4: Insulated gate bipolar transistor S A2 , Insulated Gate Bipolar Transistor S A3 , Insulated Gate Bipolar Transistor S A4 and IGBT S A5 The current paths between the DC link and the nodes A1 and A2 are as follows: Figure 2 (d) At this time, the output phase voltage V of phase A in the first inverter stage is A1N kU, the output phase voltage V of phase A in the second inverter stage A2N is kU.

[0069] Working state 5: Insulated gate bipolar transistor S A2 , Insulated Gate Bipolar Transistor S A3 , Insulated Gate Bipolar Transistor S A4 and IGBT S A6 The current paths between the DC link and the nodes A1 and A2 are as follows: Figure 2 (e) At this time, the output phase voltage V of phase A in the first inverter stage is A1N kU, the output phase voltage V of phase A in the second inverter stage A2N is 0.

[0070] Working state 6: Insulated gate bipolar transistor SA2 , Insulated Gate Bipolar Transistor S A4 , Insulated Gate Bipolar Transistor S A5 and IGBT S A6 The current paths between the DC link and the nodes A1 and A2 are as follows: Figure 2 (f) At this time, the output phase voltage V of phase A in the first inverter stage is A1N is 0, the output phase voltage V A2N is 0.

[0071] Table 1 summarizes the working principle of the insulated gate bipolar transistor S according to the above switch module. A1 ~S A6 The potentials of the upper and lower output ends of the A-phase bridge arm relative to point N in each working state corresponding to different on and off states.

[0072] Table 1 Relationship between FPTPC switch state and output phase voltage

[0073] The bidirectional four-port three-phase DC-AC converter includes 7 working modes, which are divided into 4 categories. The first category is the single-input single-output operation mode, which can be divided into 3 modes, namely mode 1-V dc1 Input V ac2 Output, Mode 2-V dc2 Input V ac1 Output, Mode 3-V dc2 Input V ac2 Output; The second type is single input dual output operation mode, which is mode 4-V dc2 Input V ac1 and V ac2 Output; The third category is the dual-input single-output operation mode, which corresponds to two operation modes, namely mode 5-V dc1 and V dc2 Input V ac1 Output, Mode 6-V dc1 and V dc2 Input V ac2 Output; The last category is dual-input dual-output operation mode, that is, mode 7-V dc1 and V dc2 Input V ac1 and V ac2Output. For the single-input single-output mode and the single-input dual-output mode, since their corresponding equivalent topologies are the equivalent three-phase voltage source inverter and the nine-switch inverter respectively, the carrier PWM modulation strategy is adopted; for the dual-input single-output mode, which belongs to the three-level converter, its modulation strategy adopts the carrier stacked pulse width modulation method; the following is a detailed analysis of an improved carrier PWM modulation suitable for FPTPC in the dual-input dual-output operation mode.

[0074] The present invention provides a triangular carrier modulation strategy for a bidirectional four-port three-phase DC-AC converter based on any one of the above, comprising: Step 210: Obtain switch module S x1 ~S x6 The opening status of Step 220: According to the switch module S x1 ~S x6 The opening condition determines the output phase voltage of the output port corresponding to the first inverter stage and the second inverter stage; Step 230: According to the low voltage DC port V dc1 and high voltage DC port V dc2 The level at modulates the triangular carrier; Step 240, modulating the three-phase modulation wave according to the modulated triangular carrier and the determined two output phase voltages in combination with the modulation constraint conditions; Step 250: Generate a switch drive signal for each phase bridge arm according to the modulated triangular carrier and three-phase modulation.

[0075] Specifically, since the voltage of the low-voltage DC port of the FPTPC is no longer always 1 / 2 of the voltage of the high-voltage DC port, the traditional carrier stacking PWM strategy uses two sets of triangular carriers with the same amplitude and frequency and symmetrical distribution to intersect with the modulation wave to generate a switching signal, such as Figure 3 The situation shown in (a) will no longer apply. c1 and U c2 There are two groups of carriers, V A is the A-phase modulation wave. It is necessary to study the carrier stacking method that changes with the low-voltage DC port level. When FPTPC adopts the carrier modulation strategy, its carrier amplitude needs to be based on the level V dc1 and V dc2 Make adjustments, refer to Figure 3 (b) is V dc1 >1 / 2V dc2 The corresponding carrier amplitude, the calculation formula for the carrier peak and valley value is: .

[0076] Reference Figure 3 (c) is V dc1 <1 / 2Vdc2 The corresponding carrier amplitude, the calculation formula for the carrier peak and valley value is: .

[0077] V dc1 >1 / 2V dc2 The proposed FPTPC carrier PWM strategy is derived from the corresponding carrier situation. The modulation constraint condition must be met during modulation. The modulation constraint condition is: during modulation, the output phase voltage of the bridge arm in the first inverter stage cannot be less than the output phase voltage of the bridge arm in the second inverter stage. Therefore, adding a DC offset to the two sets of sinusoidal modulation waves expands the operating range of the converter. Therefore, the three-phase modulation wave of the first inverter stage is: ; Correspondingly, the three-phase modulation wave of the second inverter stage is: ; Among them, m1 and m2 are modulation degrees, and the linear value range is 0 to 1; and is the output angular frequency, and is the initial phase angle, and is the DC offset, and its values ​​are: .

[0078] When the first inverter stage and the second inverter stage operate at the same frequency and phase, = , = For the first inverter stage, if the modulation wave V mA1 Greater than carrier U C1 , the first inverter output phase voltage V A1N is 2U; if the modulation wave V mA1 Less than carrier U C1 , the first inverter output phase voltage V A1N is 0; otherwise, the first inverter stage output phase voltage V A1N For the second inverter stage, if the modulation wave V mA2 Greater than U C2 , the second inverter output phase voltage V A2N is 2U; if the modulation wave V mA2 Less than carrier U C2 , the second inverter output phase voltage V A2N is 0; otherwise, the second inverter output phase voltage V A2N The output phase voltage of phase B and phase C can be obtained in the same way.

[0079] In the same frequency working mode, refer to Figure 4 , modulation wave V mA1 and V mA2 The peak moments of the modulation indices m1 and m2 are the same and a DC offset is added so that the values ​​of the modulation indices m1 and m2 do not affect each other: .

[0080] When the first inverter stage and the second inverter stage operate at the same frequency but different phases, = = , ≠ The modulation wave V of the first inverter stage mA1 , the modulation wave V of the second inverter stage mA2 And two carriers U C1 , U C2 Reference Figure 5 The value range of m2 can be obtained as: .

[0081] The carrier PWM modulation strategy of FPTPC determines the output phase voltage by comparing the modulation wave and the carrier. The following specifically describes how to generate the switch drive signal of each phase bridge arm based on the modulation wave and the carrier.

[0082] Still taking the A phase bridge arm as an example: Figure 6 It is the logic circuit diagram for generating the A-phase bridge arm switch drive signal in FPTPC. A1 ~S A6 They represent the driving signals of the six switches of the A-phase bridge arm. Among them, || represents the logic OR gate operation, && represents the logic AND gate operation, and ! represents the logic NOT gate operation. The on-off logic of each switch module can be obtained: ; ; ; ; ; ; ; ;

[0083] .

[0084] In order to analyze the power flow of FPTPC, the current i flowing through the low-voltage DC port under the carrier PWM strategy is first derived. dc1 When the modulation ratio of the first inverter stage is greater than k / 2, the modulation waves of the first inverter stage and 2V dc1 / V dc2 -1 determines 6 regions R1 to R6. Similarly, the low-voltage DC port current i of the first inverter stage in the regions R1 to R6 can be obtained: dc11 The value of low voltage DC port current i in different regions dc11 The values ​​are shown in the following table: .

[0086] When the modulation ratio of the first inverter stage is less than k / 2, each modulation wave of the first inverter stage is greater than 2Vdc1 / Vdc2-1, so the calculation of the low-voltage DC port current idc11 of the first inverter stage no longer needs to be solved in different regions, and the expression of the low-voltage DC port current idc11 of the first inverter stage is as follows: .

[0087] It can be seen that the low-voltage DC port current i in two cases dc11 The average value in one cycle is less than 0, so the upper DC bias reduces the output power of the low-voltage DC port. Similarly, it can be found that the lower DC bias increases the output power of the low-voltage DC port. Therefore, in order to increase the output power of the DC low-voltage port, the lower DC bias is injected into the two sets of inverter stages at the same time. At the same time, in order to meet the constraint that the output phase voltage of the bridge arm of the first inverter stage cannot be less than the output phase voltage of the bridge arm of the second inverter stage, the modulation ratio of the first inverter stage is required to be greater than or equal to the modulation ratio of the second inverter stage.

[0088] Three non-sinusoidal carrier PWM modulation strategies for increasing the output power of the DC low-voltage port include: The first modulation strategy injects a zero-sequence voltage 1 / 2 (V max +V min ). Therefore, the reference signal for the four-port three-phase DC-AC converter is corrected as follows: ; ; The modulation degrees m1' and m2' range from 0 to 1.15.

[0089] Then the zero-sequence components in the three-phase sinusoidal reference signals injected into the above two sets of formulas are v10 and v20, which are calculated as follows: ; .

[0090] Similar to the sine-based carrier PWM of FPTPC, the necessary DC components Vbia1' and Vbia2' offsets are also added in this scheme, which are calculated as follows: ; .

[0091] The modulation wave signal corresponding to the proposed first non-sinusoidal modulation wave carrier PWM modulation strategy can be calculated: ; .

[0092] The second modulation strategy is to inject zero-sequence voltage -1-vmin into the three-phase sinusoidal reference signals of the two sets of inverter stages. Therefore, the zero-sequence components in the three-phase sinusoidal reference signals injected into the formula are v10 and v20, which are calculated as follows: ; .

[0093] Since the non-sinusoidal CBPWM modulation strategy based on the second zero-sequence voltage injection directly clamps the modulation signal to the lowest end, it does not require a DC bias. According to the formula, the modulation wave signal corresponding to the proposed second non-sinusoidal modulation wave carrier PWM modulation strategy can be obtained as follows: ; .

[0094] The second non-sinusoidal carrier PWM modulation strategy can maximize the output power of the low-voltage DC port, which can effectively reduce the number of switching actions of the FPTPC and reduce the loss of the switching device. The first non-sinusoidal carrier PWM modulation strategy can make the voltage waveforms of the two groups of outputs better.

[0095] The third modulation strategy: In order to make full use of the advantages corresponding to the above two non-sinusoidal carrier PWM modulation strategies, the present invention proposes a third non-sinusoidal carrier PWM modulation strategy, namely, hybrid modulation. In order to meet the constraint that the output phase voltage of the bridge arm of the first inverter stage cannot be less than the output phase voltage of the bridge arm of the second inverter stage, the proposed hybrid modulation is that the first inverter stage adopts the first non-sinusoidal carrier PWM modulation strategy, and the second inverter stage adopts the second non-sinusoidal carrier PWM modulation strategy, which can combine the advantages of the above two, that is, one group of output voltage waveforms has better quality, and the other group can maximize the output power of the low-voltage DC port. Since both groups of inverter stages use down bias, for the proposed hybrid modulation, the non-sinusoidal carrier PWM modulation strategies adopted by the two groups of inverter stages must be as specified above and cannot be interchanged, otherwise the output waveform will be severely distorted.

[0096] In order to verify the feasibility of the novel bidirectional four-port three-phase DC-AC converter topology and the effectiveness of its carrier modulation strategy, simulation verification was carried out through MATLAB / Simulink.

[0097] A novel bidirectional four-port three-phase DC-AC converter dual-input dual-output three-level simulation modulation strategy: The three-phase modulation wave U A1 , U B1 , U C1 The amplitude is 300V, the frequency is 50Hz, and the offset is 0; the triangular carrier U c1 , U c2 The parameter design is as follows Figure 7 As shown, the peak value of the upper carrier is 1, and the peak value of the lower carrier is 0.2. dc1 360V, V dc2 The upper AC output is connected to a three-phase resistive-inductive load with a resistance of 10Ω and an inductance of 10mH; the lower AC output is connected to a three-phase resistive-inductive load with a resistance of 10Ω and an inductance of 10mH. Figure 8 , 10 They are the three-phase voltage waveform and three-phase current waveform output from the upper output port respectively. Fig. 9 , 11 They are the three-phase voltage waveform and three-phase current waveform output from the lower output port respectively.

[0098] The first non-sinusoidal modulation strategy is implemented by injecting a zero-sequence voltage of 1 / 2 (Vmax+Vmin) into the three-phase sinusoidal reference signals of the two sets of inverter stages. The modulation index m1 of the upper output port is 1.1, and the modulation index m2 of the lower output port is 1. The comparison between the carrier and the modulated wave is shown in the figure. Fig.12 shown. Fig.13 , 151 and 17 are the three-phase voltage waveform, three-phase current waveform and the output active and reactive power of the upper output port respectively. Fig.14 , 16 , 18 are the three-phase voltage waveform, three-phase current waveform and output active and reactive power of the lower output port respectively.

[0099] The second modulation strategy uses zero-sequence extreme value injection, which is achieved by injecting zero-sequence voltage -1-Vmin into the three-phase sinusoidal reference signal of the two sets of inverter stages, with an offset of 0; the modulation wave works in the same frequency and phase state. The modulation index m1 of the upper output port is 1.1, and the modulation index m2 of the lower output port is 1; the carrier setting is also the same as above; the DC input terminal V dc1 360V, V dc2 The comparison between the carrier wave and the modulated wave is shown in Fig.15 As shown, the output three-phase voltage waveform of the upper output port is as follows Fig.16 As shown, the output three-phase voltage waveform of the lower output port is as follows Fig.19 As shown, Fig. 20 , 22 , 24 are the three-phase voltage waveform, three-phase current waveform and output active and reactive power of the upper output port respectively. Fig.21 , 23 , 25 are the three-phase voltage waveform, three-phase current waveform and output active and reactive power of the lower output port respectively.

[0100] The third modulation strategy is hybrid modulation. The first inverter stage adopts the first non-sinusoidal carrier PWM modulation strategy, and the second inverter stage adopts the second non-sinusoidal carrier PWM modulation strategy. The modulation index m1 of the upper output port is 1.1, and the modulation index m2 of the lower output port is 1; the carrier setting is the same as above. DC input terminal V dc1 is 120V, Vdc2 is 200V. The comparison between the carrier wave and the modulated wave is as follows Fig.26 As shown, Fig. 20 , 22 , 24 are the three-phase voltage waveform, three-phase current waveform and output active and reactive power of the upper output port respectively. Fig.21 , 23 , 25 are the three-phase voltage waveform, three-phase current waveform and output active and reactive power of the lower output port respectively.

[0101] The above simulation results show that the unique down-biasing strategy of the dual-output DC-AC of a novel bidirectional four-port three-phase DC-AC converter and its carrier modulation strategy of the present invention can increase the output power of the low-voltage DC port, and a sinusoidal CBPWM modulation strategy and three non-sinusoidal CBPWM modulation strategies simultaneously increase the output power of the low-voltage DC port and the DC bus voltage utilization rate.

[0102] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention.

Claims

1. A bidirectional four-port three-phase DC-AC converter, characterized in that: Including DC-DC converter, dual output converter, low voltage DC port V dc1 , High voltage DC port V dc2 and two AC voltage ports V ac1 、V ac2 ; Low voltage DC port V dc1 Connected to the energy storage battery, low voltage DC port V dc1 A capacitor C1 is connected in parallel between the positive and negative electrodes; The first end of the DC-DC converter and the first end of the dual output converter are both connected to the low voltage DC port V dc1 The positive pole of the DC-DC converter and the second end of the dual output converter are connected to the high voltage DC port V dc2 The positive pole, high voltage DC port V dc2 The positive electrode is also connected to the positive terminal P of the DC bus. The third terminal of the DC-DC converter, the low-voltage DC port V dc1 The negative pole, the third terminal of the dual output converter and the high voltage DC port V dc2 The negative poles of the two terminals are grounded, and the high voltage DC port V dc2 The negative pole of the dual output converter is also connected to the negative terminal N of the DC bus. The fourth terminal is connected to the AC voltage port V ac1 Connected to the external three-phase load, the fifth terminal of the dual output converter is connected to the AC voltage port V ac2 Connect to the external power grid; The dual-output converter includes three-phase bridge arms, namely, phase A bridge arm, phase B bridge arm and phase C bridge arm. Each phase bridge arm consists of 6 switch modules S x1 ~S x6 Composition, where x∈{A, B, C}.

2. A bidirectional four-port three-phase DC-AC converter according to claim 1, characterized in that: The DC-DC converter includes an inductor L1, an insulated gate bipolar transistor S1, an insulated gate bipolar transistor S2 and a capacitor C2. The first end of the inductor L1 is connected to the low voltage DC port V dc1 The positive electrode of the inductor L1, the second end of the inductor L1 is connected to the emitter of the insulated gate bipolar transistor S1 and the collector of the insulated gate bipolar transistor S2, the collector of the insulated gate bipolar transistor S1 and the first end of the capacitor C2 are both connected to the high voltage DC port V dc2 The positive electrode of the insulated gate bipolar transistor S2, the emitter of the insulated gate bipolar transistor S2 and the second end of the capacitor C2 are all grounded.

3. A bidirectional four-port three-phase DC-AC converter according to claim 1, characterized in that: The A phase bridge arm includes an insulated gate bipolar transistor S A1 , Insulated Gate Bipolar Transistor S A2 , Insulated Gate Bipolar Transistor S A3 , Insulated Gate Bipolar Transistor S A4 , Insulated Gate Bipolar Transistor S A5 and IGBT S A6 ; Insulated Gate Bipolar Transistor S A1 The collector is connected to the high voltage DC port V dc2 The positive electrode of the insulated gate bipolar transistor S A1 The emitter of the insulated gate bipolar transistor S A2 The collector of the external three-phase load and the A-phase input terminal, the insulated gate bipolar transistor S A2 The emitter of the insulated gate bipolar transistor S A4 The collector and insulated gate bipolar transistor S A5 The collector of the insulated gate bipolar transistor S A4 The emitter of the insulated gate bipolar transistor S A3 The emitter of the insulated gate bipolar transistor S A3 The collector is connected to the low voltage DC port V dc1 The positive electrode of the insulated gate bipolar transistor S A5 The emitter of the insulated gate bipolar transistor S A6 The collector of the insulated gate bipolar transistor S A5 The emitter of a A phase line connected to the external power grid, insulated gate bipolar transistor S A6 The emitter is grounded.

4. A bidirectional four-port three-phase DC-AC converter according to claim 3, characterized in that: The B-phase bridge arm includes an insulated gate bipolar transistor S B1 , Insulated Gate Bipolar Transistor S B2 , Insulated Gate Bipolar Transistor S B3 , Insulated Gate Bipolar Transistor S B4 , Insulated Gate Bipolar Transistor S B5 and IGBT S B6 ; Insulated Gate Bipolar Transistor S B1 The collector is connected to the high voltage DC port V dc2 The positive electrode of the insulated gate bipolar transistor S B1 The emitter of the insulated gate bipolar transistor S B2 The collector of the insulated gate bipolar transistor S B2 The emitter of the insulated gate bipolar transistor S B4 The collector and insulated gate bipolar transistor S B5 The collector of the insulated gate bipolar transistor S B4 The emitter of the insulated gate bipolar transistor S B3 The emitter of the insulated gate bipolar transistor S B3 The collector is connected to the low voltage DC port V dc1 The positive electrode of the insulated gate bipolar transistor S B5 The emitter of the insulated gate bipolar transistor S B6 The collector of the insulated gate bipolar transistor S B5 The emitter of b The B-phase line connected to the external power grid, the insulated gate bipolar transistor S B6 The emitter is grounded.

5. A bidirectional four-port three-phase DC-AC converter according to claim 4, characterized in that: The C phase bridge arm includes an insulated gate bipolar transistor S C1 , Insulated Gate Bipolar Transistor S C2 , Insulated Gate Bipolar Transistor S C3 , Insulated Gate Bipolar Transistor S C4 , Insulated Gate Bipolar Transistor S C5 and IGBT S C6 ; Insulated Gate Bipolar Transistor S C1 The collector is connected to the high voltage DC port V dc2 The positive electrode of the insulated gate bipolar transistor S C1 The emitter of the insulated gate bipolar transistor S C2 The collector of the external three-phase load and the C-phase input terminal, the insulated gate bipolar transistor S C2 The emitter of the insulated gate bipolar transistor S C4 The collector and insulated gate bipolar transistor S C5 The collector of the insulated gate bipolar transistor S C4 The emitter of the insulated gate bipolar transistor S C3 The emitter of the insulated gate bipolar transistor S C3 The collector is connected to the low voltage DC port V dc1 The positive electrode of the insulated gate bipolar transistor S C5 The emitter of the insulated gate bipolar transistor S C6 The collector of the insulated gate bipolar transistor S C5 The emitter of c Connected to the C phase line of the external power grid, the insulated gate bipolar transistor S C6 The emitter is grounded.

6. A bidirectional four-port three-phase DC-AC converter according to claim 5, characterized in that: The first inverter stage is composed of three output ports of the A-phase bridge arm, the B-phase bridge arm and the C-phase bridge arm connected to the external three-phase load, and the second inverter stage is composed of three output ports of the A-phase bridge arm, the B-phase bridge arm and the C-phase bridge arm connected to the external power grid.

7. A triangular carrier modulation strategy for a bidirectional four-port three-phase DC-AC converter according to any one of claims 1 to 6, characterized in that: include: Get switch module S x1 ~S x6 The opening status of According to the switch module S x1 ~S x6 The opening condition determines the output phase voltage of the output port corresponding to the first inverter stage and the second inverter stage; According to the low voltage DC port V dc1 and high voltage DC port V dc2 The level at modulates the triangular carrier; The three-phase modulation wave is modulated according to the modulated triangular carrier and the determined two output phase voltages and in combination with the modulation constraint conditions; The switch drive signal of each phase bridge arm is generated according to the modulated triangular carrier and three-phase modulation.

8. The triangular carrier modulation strategy of the bidirectional four-port three-phase DC-AC converter according to claim 7, characterized in that: The modulation constraint condition is: during modulation, the output phase voltage of the bridge arm in the first inverter stage cannot be less than the output phase voltage of the bridge arm in the second inverter stage.

9. The triangular carrier modulation strategy of the bidirectional four-port three-phase DC-AC converter according to claim 7, characterized in that: When V dc1 >1 / 2V dc2 When , the three-phase modulation wave of the first inverter stage is: 。 10. The triangular carrier modulation strategy of the bidirectional four-port three-phase DC-AC converter according to claim 9, characterized in that: When V dc1 >1 / 2V dc2 When , the three-phase modulation wave of the second inverter stage is: ； Among them, m1 and m2 are modulation degrees, and the linear value range is 0 to 1; and is the output angular frequency, and is the initial phase angle, and is the DC offset.

Images