A topology of a swiss type three-phase single-stage isolated AC / DC bidirectional converter

Abstract

The application relates to a topology structure of a SWISS type three-phase single-stage isolated AC / DC bidirectional converter, which comprises a low-frequency sector selection circuit, a high-frequency isolated resonant conversion circuit and an output switch network; wherein the input end of the low-frequency sector selection circuit is connected with a three-phase AC power grid, and is used for rectifying and folding input three-phase power frequency AC voltage into a direct current voltage with three times power frequency pulsation characteristics; the input end of the high-frequency isolated resonant conversion circuit is connected with the output end of the low-frequency sector selection circuit, and is used for converting the direct current voltage with the pulsation characteristics into an isolated direct current output voltage; and the output switch network is connected with the output end of the high-frequency isolated resonant conversion circuit, and is used for switching according to the output voltage and power to adjust the series or parallel connection of the output port. The application can realize high-efficiency work, wide-range output and high electric energy quality, simultaneously guarantees the soft switching of all switch tubes and the optimization of transformer peak current, and improves the efficiency of the converter.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a topology of a SWISS-type three-phase single-stage isolated AC / DC bidirectional converter. Background Technology

[0002] With the rapid development of new energy power generation, electric vehicles, energy storage systems, and microgrid technologies, three-phase AC / DC bidirectional converters, as the core interface device between the power grid and DC loads / energy storage units, directly affect the efficiency, reliability, and power quality of the entire system. In practical applications, these converters must simultaneously meet multiple requirements, including electrical isolation, high efficiency, wide voltage range output, high power density, and fast dynamic response.

[0003] Currently, most mainstream three-phase AC / DC bidirectional converters adopt a two-stage topology, where a front-stage three-phase PWM rectifier circuit is cascaded with a rear-stage isolated DC / DC converter. The front-stage is responsible for power factor correction (PFC) and DC bus voltage stabilization, while the rear-stage provides electrical isolation and output voltage regulation. However, this two-stage architecture has the following inherent drawbacks: the two power conversions limit overall efficiency; the large number of components and complex control increase system cost and size; and the need for coordinated control between the front and rear stages limits dynamic response speed.

[0004] To simplify the structure, single-stage topologies that have emerged in recent years can reduce the number of power conversion stages, but most of them have significant shortcomings: non-isolated topologies lack electrical isolation, resulting in insufficient safety and anti-interference capabilities; in traditional single-stage rectification schemes, the switching transistors operate in a hard-switching state, leading to high switching losses and severe electromagnetic interference (EMI); the output voltage regulation range is narrow, making it difficult to adapt to the changing requirements of applications such as high-voltage fast charging and wide-voltage energy storage. In addition, existing single-stage topologies are prone to severe oscillations and stress spikes in resonant cavity current and voltage during sudden load changes, especially during the transition from light load to heavy load, making transient control difficult. This not only threatens device safety but may also cause a significant drop in output voltage, affecting power supply quality.

[0005] In summary, existing technologies in the field of three-phase AC / DC bidirectional conversion still face the following core challenges: two-stage structures struggle to balance efficiency and power density; single-stage topologies have shortcomings in soft-switching implementation, output range, and dynamic performance; and traditional solutions cannot simultaneously meet the multiple requirements of high efficiency, wide-range output, and fast transient response. Therefore, there is an urgent need for a novel topology that can achieve full-condition soft-switching, flexible output configuration, and excellent dynamic performance based on single-stage power conversion, in order to meet the development needs of next-generation power electronic systems. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing three-phase AC / DC bidirectional converters in that it is difficult to balance efficiency, dynamic performance and output flexibility, and to provide a topology of a SWISS-type three-phase single-stage isolated AC / DC bidirectional converter that enables soft switching across the full power range, wide-range adjustable output, and offline switching of output port connections.

[0007] To achieve the above objectives, the present invention provides the following solution: A topology of a SWISS-type three-phase single-stage isolated AC / DC bidirectional converter includes: a low-frequency sector selection circuit, a high-frequency isolation resonant converter circuit, and an output switching network; The low-frequency sector selection circuit is connected to a three-phase AC power grid at its input terminal, and is used to rectify and fold the input three-phase power frequency AC voltage into a DC voltage with three times the power frequency pulsation characteristics. The input terminal of the high-frequency isolated resonant converter circuit is connected to the output terminal of the low-frequency sector selection circuit, and is used to convert the pulsating DC voltage into an isolated DC output voltage. The output switch network is connected to the output terminal of the high-frequency isolation resonant converter circuit and is used to switch according to the output voltage and power to adjust the output ports to be connected in series or in parallel.

[0008] Optionally, the low-frequency sector selection circuit includes a three-phase full-bridge switch and a power frequency injection bidirectional switch. , , , , , A three-phase bridge structure is adopted, with each phase arm containing two switching transistors (upper and lower), and the midpoints of each phase arm are respectively connected to the three-phase AC input terminals A, B, and C; the power frequency injection bidirectional switching transistor... and , and , and The two transistors are connected in reverse series, with their source electrodes electrically connected.

[0009] Optionally, the input side of the low-frequency sector selection circuit is directly connected to the three-phase AC power grid or connected to the three-phase AC power grid after being filtered by the three-phase EMC circuit.

[0010] Optionally, the low-frequency switching transistor selectively turns on according to the real-time sector of the three-phase AC input voltage, folding the three-phase AC voltage into an approximate triangular waveform three times the power frequency.

[0011] Optionally, the high-frequency isolated resonant converter circuit includes a primary-side full-bridge circuit, a secondary-side full-bridge circuit, a resonant inductor Lr, a resonant capacitor Cr, and a high-frequency transformer. The primary-side full-bridge circuit includes two sets of four full-bridge switching transistors. The midpoints of the bridge arms are electrically connected to the primary side of the high-frequency transformer. The resonant inductor Lr includes the leakage inductance of the high-frequency transformer and an external inductor. The secondary full-bridge circuit includes two sets of four full-bridge switching transistors. The midpoints of the bridge arms are electrically connected to the secondary side of the high-frequency transformer.

[0012] Optionally, the high-frequency isolated resonant converter circuit includes a series resonant dual active bridge structure and an LLC topology.

[0013] Optionally, the high-frequency isolation resonant converter circuit is optimized using a multi-degree-of-freedom modulation strategy, with the optimization objectives being soft switching of all switching transistors, minimum resonant current, and minimum reactive power, to achieve optimal modulation of the high-frequency isolation resonant converter circuit.

[0014] Optionally, the input and output terminals of the high-frequency isolation resonant converter circuit are connected to filter capacitors.

[0015] The beneficial effects of the present invention are as follows: the topology of the present invention can achieve low THD control of grid-side current and wide-range adjustable power factor by controlling the input current of two high-frequency isolated resonant converter circuits; power can flow in both forward and reverse directions by changing the external phase angle; and wide-range DC output can be achieved by closing the DC voltage loop.

[0016] This invention enables high-efficiency operation, wide-range output, and high power quality, while ensuring soft switching of all switching transistors and optimization of transformer peak current, thereby improving converter efficiency. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the topology of a SWISS-type three-phase single-stage isolated AC / DC bidirectional converter according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the simulation results of the output current waveform of the low-frequency sector selection circuit according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the simulation results of the output port voltage waveform of the low-frequency sector selection circuit according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the simulation results of the grid-side voltage and current waveforms in an embodiment of the present invention; Figure 5 This is a schematic diagram of the simulation results of the resonant cavity voltage and current of the high-frequency isolation resonant converter circuit according to an embodiment of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] like Figure 1 As shown, this embodiment proposes a topology for a SWISS-type three-phase single-stage isolated AC / DC bidirectional converter, including: a low-frequency sector selection circuit, a high-frequency isolation resonant converter circuit, and an output switching network; The low-frequency sector selection circuit is connected to the three-phase AC power grid at its input terminal. It is used to rectify and fold the input three-phase power frequency AC voltage into a DC voltage with three times the power frequency pulsation characteristics. The input terminal of the high-frequency isolated resonant converter circuit is connected to the output terminal of the low-frequency sector selection circuit to convert the pulsating DC voltage into an isolated DC output voltage. The output switch network is connected to the output terminal of the high-frequency isolation resonant converter circuit and is used to switch according to the output voltage and power to adjust the output ports to be connected in series or in parallel.

[0022] Specifically, the low-frequency sector selection circuit and the high-frequency isolation resonant converter circuit are connected by a capacitor with a small capacitance value.

[0023] The topology can control the low-frequency and high-frequency switching transistors through various optimized modulation strategies, achieving soft switching of all transistors and optimizing the peak current of the high-frequency transformer. It can realize multiple functions such as bidirectional power flow, power factor correction, and wide-range adjustable output.

[0024] Furthermore, the low-frequency sector selection circuit includes six three-phase full-bridge switches and three sets of power frequency injection bidirectional switches. , , , , , A three-phase bridge structure is adopted, with each phase arm containing two switching transistors (upper and lower), and the midpoints of each phase arm are respectively connected to the three-phase AC input terminals A, B, and C; power frequency injection bidirectional switching transistors are used. and , and , and Reverse series connection, two transistors with source terminals electrically connected; power frequency injection bidirectional switching transistor , , , , , Discrete MOSFETs, IGBTs, and SCRs can also be bidirectional power devices. This embodiment uses a discrete SiC MOSFET as an example.

[0025] Furthermore, the input side of the low-frequency sector selection circuit is directly connected to the three-phase AC power grid or connected to the three-phase AC power grid after being filtered by the three-phase EMC circuit. The three-phase EMC circuit includes, but is not limited to, filters such as three-phase common-mode inductors and three-phase differential-mode inductors.

[0026] Furthermore, the power frequency injection bidirectional switching transistor in the low-frequency sector selection circuit , , , , , The switching frequency is equal to or close to the power frequency (50Hz / 60Hz), and selective conduction is performed according to the real-time sector of the three-phase AC input voltage, folding the three-phase AC voltage at the PY and YN ports into an approximate triangular waveform three times the power frequency.

[0027] Furthermore, the input terminals of two high-frequency isolation resonant converter circuits with identical structures and parameters are connected to the output terminals of the low-frequency sector selection circuit, with a small-value filter capacitor in between. , To filter out high-frequency ripple, each output terminal of the high-frequency isolation resonant converter circuit is connected to an output filter capacitor. , It is connected to the load via an output switch network.

[0028] The high-frequency isolated resonant converter circuit includes a primary-side full-bridge circuit, a secondary-side full-bridge circuit, a resonant inductor Lr, a resonant capacitor Cr, and a high-frequency transformer. The primary-side full-bridge circuit includes two sets of four full-bridge switches. The midpoints of the bridge arms are electrically connected to the primary side of the high-frequency transformer. The resonant inductor Lr includes the leakage inductance of the high-frequency transformer and an external inductor. The secondary full-bridge circuit includes two sets of four full-bridge switching transistors. The midpoints of the bridge arms are electrically connected to the secondary side of the high-frequency transformer. The high-frequency transformer magnetizing inductance Lm is either negligible or participates in resonance. That is, the high-frequency isolation resonant converter circuit topology includes a series resonant dual active bridge structure and an LLC topology.

[0029] The resonant cavity (i.e., resonant inductor Lr, resonant capacitor Cr, and magnetizing inductor Lm) can be placed on the primary or secondary side of the high-frequency isolation resonant converter circuit according to the magnitude of the current stress.

[0030] Furthermore, the high-frequency isolation resonant converter circuit can be optimized using various multi-degree-of-freedom modulation strategies such as intra-bridge phase shifting, inter-bridge phase shifting, and frequency conversion, with optimization targets such as soft switching of all switching transistors, minimum resonant current, and minimum reactive power, to achieve optimal modulation of the high-frequency isolation resonant converter circuit.

[0031] Furthermore, the output switching network, including switching switches K1 to K3, can use various devices such as relays, SCRs, IGBTs, and MOSFETs. It can switch offline according to the output voltage and power requirements, and dynamically configure the series or parallel connection of the output ports to meet various output scenarios such as high voltage and high current.

[0032] like Figure 2 As shown, from top to bottom, the port currents of P, Y, and N are respectively, which are used as reference current waveforms for controlling the input current of the high-frequency isolation resonant converter circuit (when PF=1).

[0033] like Figure 3 The figure shows the voltage waveform of the three-phase grid voltage after passing through the low-frequency sector selection circuit of the SWISS structure. From top to bottom, they are the voltages of the PY and YN ports, which are used to generate the reference signal for the high-frequency isolation resonant converter circuit.

[0034] like Figure 4 The figures from top to bottom represent the voltage and current of the three-phase AC grid A, B, and C, respectively, indicating that this topology can achieve good power factor and grid current THD control effects under the corresponding control strategies described above.

[0035] like Figure 5 The figures, from top to bottom, represent the midpoint voltages of the two primary arms, the midpoint voltages of the two secondary arms, the primary resonant cavity current, and the secondary resonant cavity current in the high-frequency isolated resonant converter circuit, respectively, to indicate the operating state of the resonant cavity in this topology.

[0036] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A topology of a Swiss-type three-phase single-stage isolated AC / DC bidirectional converter, characterized in that, include: Low-frequency sector selection circuit, high-frequency isolation resonant converter circuit, and output switching network; The low-frequency sector selection circuit is connected to a three-phase AC power grid at its input terminal, and is used to rectify and fold the input three-phase power frequency AC voltage into a DC voltage with three times the power frequency pulsation characteristics. The input terminal of the high-frequency isolated resonant converter circuit is connected to the output terminal of the low-frequency sector selection circuit, and is used to convert the pulsating DC voltage into an isolated DC output voltage. The output switch network is connected to the output terminal of the high-frequency isolation resonant converter circuit and is used to switch according to the output voltage and power to adjust the output ports to be connected in series or in parallel.

2. The topology according to claim 1, characterized in that, The low-frequency sector selection circuit includes a three-phase full-bridge switch and a power frequency injection bidirectional switch. , , , , , A three-phase bridge structure is adopted, with each phase arm containing two switching transistors (upper and lower), and the midpoints of each phase arm are respectively connected to the three-phase AC input terminals A, B, and C; the power frequency injection bidirectional switching transistor... and , and , and The two transistors are connected in reverse series, with their source electrodes electrically connected.

3. The topology according to claim 1, characterized in that, The input side of the low-frequency sector selection circuit is directly connected to the three-phase AC power grid or connected to the three-phase AC power grid after being filtered by the three-phase EMC circuit.

4. The topology according to claim 1, characterized in that, The low-frequency switching transistor selectively conducts according to the real-time sector of the three-phase AC input voltage, folding the three-phase AC voltage into an approximate triangular waveform three times the power frequency.

5. The topology according to claim 1, characterized in that, The high-frequency isolated resonant converter circuit includes a primary-side full-bridge circuit, a secondary-side full-bridge circuit, a resonant inductor Lr, a resonant capacitor Cr, and a high-frequency transformer. The primary-side full-bridge circuit includes two sets of four full-bridge switches. The midpoints of the bridge arms are electrically connected to the primary side of the high-frequency transformer. The resonant inductor Lr includes the leakage inductance of the high-frequency transformer and an external inductor. The secondary full-bridge circuit includes two sets of four full-bridge switching transistors. The midpoints of the bridge arms are electrically connected to the secondary side of the high-frequency transformer.

6. The topology according to claim 1, characterized in that, The high-frequency isolated resonant converter circuit includes a series resonant dual active bridge structure and an LLC topology.

7. The topology according to claim 1, characterized in that, The high-frequency isolation resonant converter circuit is optimized through a multi-degree-of-freedom modulation strategy, with the optimization objectives of soft switching of all switching transistors, minimum resonant current, and minimum reactive power, to achieve optimal modulation of the high-frequency isolation resonant converter circuit.

8. The topology according to claim 1, characterized in that, The high-frequency isolation resonant converter circuit has filter capacitors connected to its input and output terminals.

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