An open-winding transformer-type multi-active bridge converter

Abstract

This invention pertains to the fields of DC power transmission and distribution networks and DC microgrids, specifically disclosing an open-winding transformer-type multi-active bridge converter for medium- and low-voltage DC distribution networks and DC microgrids. After a DC port fault occurs, DC fault ride-through can be quickly achieved by bypassing the fault-side converter submodule. Due to the open-winding structure of the transformer, the transformer flux linkage will not feed power to the faulty DC port after bypassing the submodule. Simultaneously, utilizing the fast switching characteristics of power semiconductor devices, a significant amount of fault clearing time is saved compared to mechanical circuit breakers. Meanwhile, the non-faulty submodules can continue to operate normally without interrupting power transmission. This invention provides an effective and feasible DC fault ride-through solution for medium- and low-voltage DC distribution networks and DC microgrids based on dual-active bridge or multi-active bridge converters.

Description

Technical Field

[0001] This invention belongs to the field of DC power transmission and distribution networks and DC microgrids, and more specifically, relates to an open-winding transformer type multi-active bridge converter. Background Technology

[0002] Medium and low voltage DC power distribution based on DC solid-state transformers is a new generation of DC power distribution technology. Because it uses DC power transmission, it has advantages such as no harmonic losses, no eddy current losses, no in-phase issues, and low voltage ripple, making it suitable for small- to medium-scale renewable energy aggregation, islanded power supply, and urban DC distribution networks. Dual-active-bridge converters (DABs) and multiple-active-bridge converters (MABs) have become the preferred solution for DC solid-state transformers due to their simple structure, seamless bidirectional power flow switching, high power density, and simple control. Compared to AC systems, DC systems have relatively lower damping, faster fault propagation speeds, require shorter fault monitoring and control response times, and present greater challenges in relay protection design. Therefore, DC-side fault protection and control is a pressing issue that needs to be addressed in current DC transformer engineering.

[0003] Currently, most faults on the DC side are cleared by DC-side circuit breakers. However, the DC voltage does not cross zero, making it difficult to extinguish DC fault currents and extremely challenging to interrupt them, which places very high demands on the arc-extinguishing chamber. In addition, the long arcing time of DC fault currents will cause significant erosion of the contacts of mechanical circuit breakers, resulting in a shorter lifespan for DC circuit breakers.

[0004] In recent years, power semiconductor solid-state circuit breakers have solved the problems of arcing and contact erosion in mechanical circuit breakers. However, the current and voltage withstand capability of a single power device is limited. Therefore, a series-parallel structure of multiple devices is often used to improve the voltage and current withstand capability, which greatly increases the additional hardware cost and losses.

[0005] In summary, existing solutions cannot balance cost-effectiveness and speed, and their technologies are not yet mature. This, to some extent, limits the system reliability of DC distribution networks and DC microgrids, and their practical application and development. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide an open-winding transformer-type multi-active bridge converter for use in DC distribution networks and DC microgrids, eliminating the need for DC circuit breakers. In the event of a DC fault, fault isolation can be quickly achieved without interrupting power transmission by simply controlling the power devices within the topology itself, thereby improving the system's power supply stability.

[0007] An open-winding transformer type multi-active bridge converter includes an open-winding transformer and N M-phase inverters; the open-winding transformer has N*M / 2 windings; the M-phase inverters include bridge arms B1~B1. M With capacitor C, each bridge arm includes two semiconductor switching devices connected in series in the same direction, bridge arms B1~B1. M After being connected in parallel, it is then connected in parallel with capacitor C. The two ends of the parallel connection form a DC port; the bridge arms B1~B of the first M-phase inverter. M The series connection point of the semiconductor switching device is connected in sequence to windings R1~R M The same-named terminals; windings R1~R M The different-named terminals are connected sequentially to the bridge arms B1~B1 of the second M-phase inverter. M The series connection point of the semiconductor switching devices; the bridge arms B1~B of the third M-phase inverter. M The series connection point of the semiconductor switching device is sequentially connected to the winding R. M+1 ~R 2M The same-named terminal, winding R M+1 ~R 2M The opposite-named terminals; sequentially connected to bridge arms B1~B of the fourth M-phase inverter. M The semiconductor switching devices are connected in series; and so on; all windings are wound on the same M-phase transformer core, and windings in the same phase are wound on the same magnetic column, and any two windings are coupled.

[0008] Furthermore, the semiconductor switching device is a fully controlled semiconductor device, or two or more fully controlled semiconductor devices connected in series, or two or more fully controlled semiconductor devices connected in parallel, or two fully controlled semiconductor devices connected in antiparallel, or two fully controlled semiconductor devices connected in antiseries.

[0009] The beneficial effects of this invention are as follows: Flexible DC transmission systems and medium- and low-voltage DC distribution networks employing open-winding transformer-type dual-modular multilevel converter topologies can quickly achieve DC fault ride-through after a DC port fault occurs by bypassing the fault-side converter submodule. Due to the open-winding structure of the transformer, the transformer flux linkage will not feed power to the faulty DC port after bypassing the submodule. Simultaneously, utilizing the fast switching characteristics of power semiconductor devices, a significant amount of fault clearing time is saved compared to mechanical circuit breakers. Furthermore, the non-faulty submodule can continue to operate normally without interrupting power transmission. This invention provides an effective and feasible DC fault ride-through solution for medium- and low-voltage DC distribution networks and DC microgrids based on dual active bridge or multi-active bridge converters. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the topology of an open-winding transformer type active bridge converter.

[0011] Figure 2 The diagram shows an example of a semiconductor switch, where (a) represents a power semiconductor device, (b) represents a series combination of power semiconductor devices, and (c) represents a parallel combination of power semiconductor devices.

[0012] Figure 3 This is a control block diagram for an open-winding transformer type multi-active bridge converter.

[0013] Figure 4 This is a schematic diagram of DC fault ride-through control for an open-winding transformer type multi-active bridge converter.

[0014] Figure 5 This is a schematic diagram of the topology of an open-winding transformer type three-phase four-active-bridge converter.

[0015] Figure 6 This is a schematic diagram of DC fault ride-through control for an open-winding transformer type three-phase four-active-bridge converter.

[0016] Figure 7 The simulation waveform diagram for DC fault ride-through of an open-winding transformer type three-phase four-active-bridge converter. Detailed Implementation

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0018] An open-winding transformer type active bridge converter topology is as follows: Figure 1 As shown, its structure is as follows:

[0019] This DC-DC converter includes three types of devices: semiconductor power switches, coupling inductors (transformers), and capacitors, and has N ports; each port has an M-phase inverter or rectifier composed of 2M semiconductor switches; it also includes a coupling M-phase inductor (transformer). DC capacitor at the port The coupling coefficient between every two coupled inductors is .

[0020] In an M-phase open-winding transformer, both ends of any winding are connected to the same phase bridge arm of two inverters or rectifiers.

[0021] Each group of M-phase coupled inductors is connected to the same two inverters or rectifiers.

[0022] The M-phase open-winding transformer can be composed of M single-phase N / 2 winding transformers, or it can be composed of one M-phase N / 2 winding transformer, two M-phase N / 4 winding transformers, etc.

[0023] The M-phase open-winding transformer can be composed of a leakage inductance transformer or an external inductor and a high coupling coefficient transformer.

[0024] In an open-winding transformer-type active bridge converter topology, 2M*N semiconductor switches represent power semiconductor switching devices and their combinations that perform switching functions, such as... Figure 2 As shown, including but not limited to:

[0025] Switch combination 1: Fully controlled or semi-controlled power semiconductor devices and their series, parallel, anti-parallel, and anti-series combinations, etc.

[0026] Switch combination 2: power diodes and their series and parallel combinations, etc.

[0027] Switch combination 3: series, parallel, anti-parallel, and anti-series combinations of switch combination 1 and switch combination 2.

[0028] Device types: diodes, insulated gate bipolar transistors (IGBTs), power MOSFETs, junction field-effect transistors (JFETs), thyristors (SCRs), gate turn-off thyristors (GTOs), gate injection enhancement-mode transistors (IEGTs), integrated gate commutated thyristors (IGCTs), high electron mobility transistors (HEMTs), etc.

[0029] Device materials: silicon (Si), gallium nitride (GaN), silicon carbide (SiC), gallium arsenide (GaAs), etc.

[0030] Any combination of the above-mentioned device materials, types, and combinations.

[0031] A control method for an open-winding transformer type multi-active bridge converter, as follows: Figure 3 As shown:

[0032] It employs outer-loop voltage control and inner-loop power control; the outer-loop voltage controller selectively controls the DC voltage at the control port. , , , The control objective of the inner-loop power controller is the active power at each DC port. , , , .

[0033] The output of the outer loop voltage controller is the power command value of the inner loop power controller. , , , The output of the inner-loop power controller is the phase shift angle 0° of the N three-phase inverter modules relative to module 1. , , .

[0034] After giving the initial phase shift angle, detect the active power at each DC port. , , , , and power command value , , , The result of the subtraction is fed into a PI (Proportional Integral) error controller for error-free adjustment. The N pulse generators are based on the phase shift angle θ... , , The generated pulses control the switching transistors in the three-phase inverter modules 1-N respectively.

[0035] Specifically, if a module uses an uncontrolled bridge composed of diodes, it is not controlled; instead, it is modulated by a fully controlled bridge connected to the other end of the same winding.

[0036] A DC fault ride-through control method for an open-winding transformer type multi-active bridge converter, specifically:

[0037] After a DC port fault occurs, turn on M lower bridge arms of the inverter to which the faulty port belongs, and turn off M upper bridge arms of the inverter to which the faulty port belongs. Figure 4 As shown, the bypass fault inverter module is equivalent to a short circuit in phase M on this side; the outer loop voltage controller and inner loop power controller are switched to an N-1 port multi-active bridge controller to achieve fault-tolerant operation.

[0038] Example 1:

[0039] This embodiment provides a topology for an open-winding transformer-type four-active-bridge converter with self-clearing capability for DC port faults, such as... Figure 5As shown, the system includes an open-winding leakage inductance transformer and three-phase inverter modules 1-4. The primary winding of the open-winding transformer A-phase has two terminals A1 and A2, and the secondary winding has two terminals U1 and U2; the primary winding of the open-winding transformer B-phase has two terminals B1 and B2, and the secondary winding has two terminals V1 and V2; the primary winding of the open-winding transformer C-phase has two terminals C1 and C2, and the secondary winding has two terminals W1 and W2. Terminals A1, B1, and C1 are connected to the three-phase AC ports of three-phase inverter module 1; terminals A2, B2, and C2 are connected to the three-phase AC ports of three-phase inverter module 2; terminals U1, V1, and W1 are connected to the three-phase AC ports of three-phase inverter module 3; and terminals U2, V2, and W2 are connected to the three-phase AC ports of three-phase inverter module 4. The inductance of the primary winding of the open-winding leakage inductance transformer is... The secondary winding inductance is The coupling coefficient between the two windings in each phase is .

[0040] according to Figure 3 The control method shown can be used to adjust the power of each port.

[0041] After a DC port fault occurs, the three lower arms of the inverter corresponding to the faulty port are turned on, and the three upper arms of the inverter corresponding to the faulty port are turned off, bypassing the faulty inverter module, such as... Figure 6 As shown, this is equivalent to a three-phase short circuit on that side. Therefore, the open-winding transformer type four-active-bridge converter is transformed into a three-active-bridge converter. According to... Figure 3 The control method shown can be used to adjust the power of each port.

[0042] It is worth noting that Embodiment 1 of the present invention only schematically provides a four-port open-winding transformer type active bridge converter. Other cases, such as five-port and six-port converters, will not be elaborated here. The control scheme is not limited to the given strategy; other control strategies can still be applied to this topology.

[0043] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. "A plurality of" means two or more, unless otherwise explicitly specified.

[0044] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. An open-winding transformer type multi-active bridge converter, characterized in that, Includes open-winding transformers and N M-phase inverters; The open-winding transformer has N*M / 2 windings; The M-phase inverter includes bridge arms B1~B1. M With capacitor C, each bridge arm includes two semiconductor switching devices connected in series in the same direction, bridge arms B1~B1. M After being connected in parallel, it is then connected in parallel with capacitor C. The two ends of the parallel connection form a DC port. The bridge arms B1~B of the first M-phase inverter M The series connection point of the semiconductor switching device is connected in sequence to windings R1~R M The same-named terminals; windings R1~R M The different-named terminals are connected sequentially to the bridge arms B1~B1 of the second M-phase inverter. M The series connection point of semiconductor switching devices; The bridge arms B1~B of the third M-phase inverter M The series connection point of the semiconductor switching device is sequentially connected to the winding R. M+1 ~R 2M The same-named terminal, winding R M+1 ~R 2M The opposite-named terminals; sequentially connected to bridge arms B1~B of the fourth M-phase inverter. M The series connection point of semiconductor switching devices; All windings are wound on the same M-phase transformer core, and windings of the same phase are wound on the same magnetic column. Any two windings are coupled. The semiconductor switching device is a fully controllable semiconductor device.

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