A single bridge arm power electronic transformer topology and method

Abstract

This invention discloses an improved single-arm power electronic transformer topology, belonging to the field of power electronic converters, which includes a three-phase AC filter inductor L. g The topology consists of a main bridge arm circuit, a three-phase common half-bridge circuit, a high-frequency series inductor and capacitor L1 / C1, a high-frequency isolation transformer, a low-voltage side rectifier, and a common-isolation DC-DC converter. This single-stage topology requires only one bridge arm per phase, directly employing hybrid frequency conversion to achieve AC / DC power transfer, reducing the number of components in the power electronic transformer and lowering costs. The introduction of the three-phase common half-bridge circuit reduces the multi-frequency coupling of the bridge arms, simplifying control. Combined with reasonable circuit parameter design and optimized main bridge arm sub-module number, efficiency is improved. This topology is suitable for all applications requiring medium-voltage AC to low-voltage DC conversion.

Description

Technical Field

[0001] This invention belongs to the field of power electronic converters, and specifically relates to a single-arm power electronic transformer topology and method. Background Technology

[0002] "Intelligentization," "cleanliness," and "power electronics" will be the inevitable development trends of future power grid systems. Traditional power frequency transformers, due to their inherent defects such as fixed voltage and frequency transformation, inflexible adjustment methods, large size and weight, and poor disturbance and harmonic resistance, are no longer sufficient to meet the needs and challenges of future power grids. Power electronic transformers, as a new type of power electronic device, possess rich functions such as adjustable voltage transformation, reactive power management, harmonic elimination, and unbalanced operation, and can significantly reduce size and weight, making them a powerful alternative to traditional power frequency transformers. Power electronic transformers can be classified into AC-AC conversion type, AC-DC conversion type, and DC-DC conversion type according to the input and output port types. This invention focuses on the AC-DC type, with the input AC port connecting to the medium- and high-voltage AC power grid and the output DC port connecting to the low-voltage DC bus, suitable for applications requiring DC connection such as data center power supply, new energy grid connection, supercharging stations, and AC / DC hybrid distribution networks.

[0003] Existing AC-DC power electronic transformer topologies are mainly divided into two-stage and single-stage structures. Two-stage structures typically employ a series H-bridge or modular multilevel structure. These topologies often have a large number of transformation stages, a large number of modules (devices), and numerous passive components such as capacitors, inductors, and high-frequency transformers, significantly increasing the cost and size of the device. Single-stage topologies can effectively reduce the number of components by reducing the number of power conversion stages, but often result in some loss of device efficiency and increased control and implementation complexity. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a single-arm power electronic transformer topology and method. The aim is to improve existing power electronic transformer topologies, reduce the number of components, lower costs, and simplify control. Combined with appropriate circuit parameter design, efficiency is enhanced. This topology is suitable for all applications requiring medium-voltage AC to low-voltage DC conversion.

[0005] To achieve the above objectives, the present invention employs the following technical means:

[0006] In a first aspect, the present invention provides a single-bridge-arm power electronic transformer topology, comprising: a three-phase AC filter inductor L gThe circuit consists of a three-phase main bridge arm circuit, a three-phase common half-bridge circuit, a high-frequency series inductor and capacitor L1 / C1, a high-frequency isolation transformer, a low-voltage side rectifier, and a common isolation DC-DC converter.

[0007] The three-phase AC filter inductor Lg is used to filter out high-frequency harmonics in the three-phase AC current.

[0008] The main bridge arm circuit uses a hybrid frequency conversion to convert three-phase AC power into high-frequency AC power.

[0009] A three-phase common half-bridge circuit is used to assist the main bridge arm circuit of the auxiliary phase to perform voltage and current conversion.

[0010] The high-frequency series inductor and capacitor L1 / C1 are used to filter out the power frequency fundamental wave and high-frequency PWM harmonics generated by the main bridge arm circuit and the three-phase common half-bridge circuit;

[0011] High-frequency isolation transformers are used to achieve electrical isolation and voltage transformation, transmitting high-frequency alternating current from the primary side to the secondary side.

[0012] The low-voltage side rectifier, located on the secondary side of the high-frequency isolation transformer, is used to convert high-frequency AC power into low-voltage DC power, transmit most of the power of the circuit, and maintain the stability of the bus voltage.

[0013] A common-isolation DC-DC converter is used to supplement the transmission of the remaining power and maintain voltage stability at both ends.

[0014] As a further improvement of the present invention, the phase main bridge arm circuit is composed of N sub-modules connected in series, where N is a positive integer greater than or equal to 1; each sub-module is a full-bridge circuit composed of four switching transistors and a DC-side capacitor, with the upper and lower switching transistors conducting complementaryly, and the midpoints of the two half-bridges respectively leading out external ports Q1 / Q2; wherein, the Q2 port of one sub-module is connected to the Q1 port of another sub-module, and they are connected in series to form the phase main bridge arm.

[0015] As a further improvement of the present invention, the three main bridge arms of phases a, b, and c have the same structure. Phase a main bridge arm leads out the upper and lower ports Ma1 / Ma2, phase b main bridge arm leads out the upper and lower ports Mb1 / Mb2, and phase c main bridge arm leads out the upper and lower ports Mc1 / Mc2.

[0016] As a further improvement of the present invention, the upper port of the main bridge arm is connected to the three-phase medium-voltage AC power grid through a filter inductor: for phase a, port Ma1 is connected to phase a power grid va through filter inductor Lg; for phase b, port Mb1 is connected to phase b power grid vb through filter inductor Lg; for phase c, port Mc1 is connected to phase c power grid vc through filter inductor Lg.

[0017] The upper port of the main bridge arm is also connected to the high-frequency isolation transformer via a high-frequency series inductor and capacitor: for phase a, port M a1 The high-frequency isolation transformer T is connected via a high-frequency series inductor and capacitor L1 / C1. a Port; for phase b, port M b1 The high-frequency isolation transformer T is connected via a high-frequency series inductor and capacitor L1 / C1. b Port; for phase c, port M c1 The high-frequency isolation transformer T is connected via a high-frequency series inductor and capacitor L1 / C1. c port.

[0018] As a further improvement of the present invention, the three-phase common half-bridge circuit includes three half-bridges composed of six switching transistors, and the three half-bridges have a common DC side port; the midpoints of the three half-bridges are respectively connected to the M-axis of the three-phase main bridge arms a, b, and c. a2 / M b2 / M c2 The ports are connected, with their common DC-side port connected to the input port P of the common isolated DC-DC converter. com / N com Connected.

[0019] As a further improvement of the present invention, the common isolation DC-DC converter is a DC-DC converter with isolation and bidirectional power flow functions;

[0020] The common isolation DC-DC converter is selected from all DC-DC converters that meet the functions of isolation and bidirectional power flow, such as dual active bridge converters and CLLC resonant converters.

[0021] As a further improvement of the present invention, the primary side of the high-frequency isolation transformer includes ports Ta, Tb, Tc, and Tcom, and the secondary side includes ports S1~S2. i , where i is a positive integer greater than 1;

[0022] The Tcom port on the primary side is the common port of the three primary windings, and this port is connected to the DC side Ncom port of the three-phase common half-bridge circuit; the S1~S on the secondary side i The port is connected to the low-voltage side rectifier.

[0023] As a further improvement of the present invention, the high-frequency isolation transformer is selected from three independent two-winding transformers, a six-winding transformer with three inputs and three outputs, or a four-winding transformer with three inputs and one output.

[0024] As a further improvement of the present invention, the low-voltage side rectifier structure can be either a three-full-bridge DC-side parallel structure or a single full-bridge structure, depending on the number of secondary side ports of the high-frequency isolation transformer.

[0025] Secondly, the present invention provides a method for operating a single-bridge-arm power electronic transformer topology, characterized in that it includes:

[0026] The three-phase AC power supply enters the main phase bridge arm circuit after filtering out high-frequency harmonics through the three-phase AC filter inductor Lg. The main phase bridge arm circuit and the three-phase common half-bridge circuit convert the three-phase AC power into high-frequency AC power through a hybrid frequency conversion control, and the energy is transferred through a resonant circuit composed of high-frequency series inductor and capacitor L1 / C1.

[0027] High-frequency alternating current is electrically isolated and transmitted through a high-frequency isolation transformer, and a corresponding high-frequency alternating current is generated on the secondary side.

[0028] The low-voltage side rectifier converts high-frequency AC power into low-voltage DC power, undertakes the main power transmission, and controls and stabilizes the bus voltage; the common isolation DC-DC converter connects the three-phase common half-bridge DC side to the low-voltage DC bus, transmits the remaining small part of the power, and controls and maintains the voltage at both ends to be stable.

[0029] The present invention has the following technical effects:

[0030] In the power electronic transformer of this invention, three-phase AC power enters the main bridge arm circuit through a three-phase AC filter inductor Lg. The main bridge arm circuit and the three-phase common half-bridge circuit convert the three-phase AC power into high-frequency AC power through a hybrid frequency conversion, and the energy is transferred through a resonant circuit composed of a high-frequency series inductor and capacitor L1 / C1. The high-frequency AC power is electrically isolated and transmitted through a high-frequency isolation transformer, and a corresponding high-frequency AC power is generated on the secondary side. The low-voltage side rectifier converts the high-frequency AC power into low-voltage DC power, transferring most of the power, maintaining the stability of the low-voltage DC bus, and supplementing the remaining power in conjunction with a common isolation DC-DC converter, further ensuring system stability. Through the high-frequency resonant circuit and optimized control strategy, the transmission efficiency of the power electronic transformer is improved. The number of conversion stages is reduced, the power density is increased, and the entire system is more compact and lightweight. The high-frequency isolation transformer achieves electrical isolation between the input and output, improving system safety. Different high-frequency isolation transformers and low-voltage side rectifier structures can be selected according to specific application requirements to meet different conversion needs. This invention belongs to a single-stage structure, requiring only one bridge arm per phase, with fewer components and a cost advantage. Meanwhile, by introducing a three-phase common half-bridge module, the multi-frequency coupling of the bridge arms is reduced, simplifying the control implementation. Potentially, with optimized circuit parameter design, the efficiency of this topology can be further improved. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 A diagram of an improved single-arm power electronic transformer topology;

[0033] Figure 2 Submodule SM structure diagram;

[0034] Figure 3 Commonly isolated DC-DC converter: Dual active bridge converter;

[0035] Figure 4 Commonly isolated DC-DC converter: CLLC resonant converter;

[0036] Figure 5 High-frequency isolation transformer structure 1;

[0037] Figure 6 High-frequency isolation transformer structure 2;

[0038] Figure 7 High-frequency isolation transformer structure 3;

[0039] Figure 8 Low-voltage side rectifier structure 1: Three full-bridge DC sides connected in parallel;

[0040] Figure 9 Low-voltage side rectifier structure 2: Single full bridge;

[0041] Figure 10 Specific embodiments of the present invention;

[0042] Figure 11 Steady-state operating waveforms in specific embodiments of the present invention. Detailed Implementation

[0043] To make the objectives and technical solutions of this invention clearer and easier to understand, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0044] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. 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 the present invention.

[0045] To promote the better application of power electronic transformers, a topology that is low-cost, easy to control, and highly efficient has become an urgent need. This invention proposes an improved single-arm power electronic transformer topology, suitable for all applications requiring medium-voltage AC to low-voltage DC conversion. The topology is as follows: Figure 1 As shown, it includes a three-phase AC filter inductor L g The circuit consists of a three-phase main bridge arm circuit, a three-phase common half-bridge circuit, a high-frequency series inductor and capacitor L1 / C1, a high-frequency isolation transformer, a low-voltage side rectifier, and a common isolation DC-DC converter.

[0046] Three-phase AC filter inductor Lg: Used to filter out high-frequency harmonics in three-phase AC current, ensuring the quality of the grid current at the input of the power electronic transformer.

[0047] Phase main bridge arm circuit: Each phase is equipped with a main bridge arm circuit, which, together with the three-phase common half-bridge circuit, is used to convert three-phase AC power into high-frequency AC power. These main bridge arm circuits are typically composed of multiple switching devices (such as IGBTs or MOSFETs), and use a hybrid frequency conversion strategy to control the switching on and off of the switching devices, thereby realizing voltage and current conversion.

[0048] Three-phase common half-bridge circuit: This is a key improvement. Traditional single-stage power electronic transformers contain multiple high and low frequency components in their bridge arms, leading to complex module equalization control. This invention introduces a three-phase common half-bridge circuit, which distributes the frequency coupling of the main bridge arms, simplifies control, and improves system reliability. The common half-bridge circuit is also composed of switching devices and works in conjunction with the main bridge arm circuit to achieve voltage and current conversion.

[0049] High-frequency series inductor and capacitor L1 / C1: These components form a bandpass filter to filter out the power frequency fundamental wave and high-frequency PWM harmonics generated by the main bridge arm circuit and the three-phase common half-bridge circuit, ensuring that the current flowing into the high-frequency transformer is only the set high-frequency AC current.

[0050] High-frequency isolation transformer: This is one of the core components of power electronic transformers. It is used to achieve electrical isolation and voltage transformation, transmitting high-frequency alternating current from the primary side to the secondary side. High-frequency isolation transformers have advantages such as small size and light weight, and are key to achieving higher power density in power electronic transformers compared to power frequency transformers.

[0051] Low-voltage side rectifier: Located on the secondary side of the high-frequency isolation transformer, it is used to convert high-frequency alternating current (AC) into low-voltage direct current (DC). The rectifier consists of active switching transistors (such as MOSFETs), which convert AC to DC through rectification.

[0052] Common-isolation DC-DC converter: Used to connect the DC side of a three-phase common half-bridge to the low-voltage DC bus, stabilizing the voltage across both ends. Multiple topologies are available. Common-isolation DC-DC converters also feature electrical isolation, ensuring system safety and stability.

[0053] Furthermore, the main bridge arm circuit consists of N sub-modules (SMs) connected in series, where N is a positive integer greater than or equal to 1. The sub-module structure is as follows: Figure 2 As shown, this is a full-bridge circuit consisting of four switching transistors and a DC-side capacitor. The upper and lower switching transistors operate complementaryly, and the midpoints of the two half-bridges are respectively connected to external ports Q1 and Q2. The Q2 port of one submodule is connected to the Q1 port of another submodule, and so on in series to form the main bridge arm. The three main bridge arms a, b, and c have the same structure. Finally, the upper and lower ports M of the a-phase main bridge arm are connected. a1 / M a2 The upper and lower ports M of the main bridge arm of phase b are led out. b1 / M b2 c-phase main bridge arm leads out upper and lower ports M c1 / M c2 .

[0054] In the above scheme, the phase main bridge arm circuit proposed in this invention is designed with N sub-modules (SMs) connected in series, providing greater flexibility and scalability for power electronic transformers. Each sub-module consists of four switching transistors (such as IGBTs or MOSFETs) and a DC-side capacitor forming a full-bridge circuit. The upper and lower switching transistors operate complementaryly, ensuring circuit stability and efficiency. The midpoints of the two half-bridges are respectively led out to external ports Q1 and Q2 for series connection between sub-modules. The Q2 port of one sub-module is connected to the Q1 port of another sub-module, forming a series chain. This approach allows the phase main bridge arm to be composed of any number of sub-modules as needed, improving design flexibility.

[0055] Furthermore, the three main bridge arms a, b, and c have the same structure, each consisting of N sub-modules connected in series. Each main bridge arm has upper and lower ports (e.g., M... a1 / M a2 M b1 / M b2 M c1 / M c2The modular design simplifies the manufacturing and maintenance of power electronic transformers. The capacity and performance of the transformer can be adjusted by adding or removing submodules to meet different application requirements. The series connection of submodules allows for easy expansion of the capacity of the main bridge arm. This enables power electronic transformers to adapt to power systems of different sizes, increasing their applicability. The modular design also provides redundancy; if a submodule fails, it can be bypassed or replaced without affecting the operation of the entire system. This improves system reliability and stability and reduces the risk of power outages due to faults.

[0056] Specifically, the upper port of the main bridge arm is connected to the three-phase medium-voltage AC power grid via a filter inductor: for phase a, port M a1 The phase a power grid va is connected via a filter inductor Lg; for phase b, port M... b1 The b-phase power grid VB is connected via the filter inductor Lg; for the c-phase, port Mc1 is connected to the c-phase power grid VC via the filter inductor Lg.

[0057] Meanwhile, the upper port of the main bridge arm is also connected to the high-frequency isolation transformer via a high-frequency series inductor and capacitor: for phase a, port M a1 The high-frequency isolation transformer T is connected via a high-frequency series inductor and capacitor L1 / C1. a Port; for phase b, port M b1 The high-frequency isolation transformer T is connected via a high-frequency series inductor and capacitor L1 / C1. b Port; for phase c, port M c1 The high-frequency isolation transformer T is connected via a high-frequency series inductor and capacitor L1 / C1. c port.

[0058] Specifically, the three-phase common half-bridge circuit includes three half-bridges composed of six switching transistors, all three half-bridges sharing a common DC-side port. The midpoints of the three half-bridges are respectively connected to the M-axis of the three-phase main bridge arms a, b, and c. a2 / M b2 / M c2 The ports are connected, with their common DC-side port connected to the input port P of the common isolated DC-DC converter. com / N com Connected.

[0059] The circuit consists of six switching transistors, divided into three half-bridges, each containing two switching transistors. These three half-bridges share a common DC-side port, P. com and N com The midpoint of each half-bridge is respectively connected to the M of the three-phase main bridge arm (a, b, c). a2 M b2 M c2The ports are connected. This connection method allows for independent control of the three-phase current through a half-bridge circuit. A common-isolation DC-DC converter is a power electronic device with isolation and bidirectional power flow capabilities. Its input port P... com and N com It is connected to the common DC side port of a three-phase common half-bridge circuit. The output ports DC+ and DC- are used to provide a stable DC voltage or current to meet the needs of subsequent circuits or loads.

[0060] Specifically, the common-isolation DC-DC converter can be any DC-DC converter with isolation and bidirectional power flow capabilities, such as a dual active bridge converter or a CLLC resonant converter, with structures as follows: Figure 3 , Figure 4 As shown, but not limited to, these two types of isolated DC-DC converters. The input port of the common isolated DC-DC converter is P. com and N com The output ports are DC+ and DC-. Figure 3 Commonly isolated DC-DC converter: Dual active bridge converter; Figure 4 Commonly isolated DC-DC converter: CLLC resonant converter.

[0061] In the above scheme, the three-phase common half-bridge circuit and the common-isolation DC-DC converter only need to handle a small portion of the total system power, requiring small component capacity, low losses, and low cost. Meanwhile, the high efficiency of the common-isolation DC-DC converter ensures the high efficiency of the entire system. The bidirectional power flow function of the common-isolation DC-DC converter allows the system to flexibly adapt to different load demands and operating modes.

[0062] Specifically, the primary side of the high-frequency isolation transformer includes ports Ta, Tb, Tc, and Tcom, while the secondary side includes ports S1~S2. i Where i is a positive integer greater than 1, and the value of i depends on the specific form of the high-frequency isolation transformer. The high-frequency isolation transformer can be three independent two-winding transformers, a three-input three-output six-winding transformer, or a three-input single-output four-winding transformer, as shown below. Figure 5 , Figure 6 , Figure 7 As shown. Original side T com The port is the common port of the primary three windings, and this port is connected to the DC side N of the three-phase common half-bridge circuit. com The ports are connected. S1~S on the secondary side. i The port is connected to the low-voltage side rectifier. Figure 5 High-frequency isolation transformer structure 1; Figure 6 High-frequency isolation transformer structure 2; Figure 7 High-frequency isolation transformer structure 3.

[0063] As a specific solution, the low-voltage side rectifier structure can be either a three-full-bridge DC-side parallel structure or a single full-bridge structure, depending on the number of secondary terminals of the high-frequency isolation transformer. The former can be adapted to high-frequency transformer structures 1 and 2, such as... Figure 8 As shown; the latter can be adapted to high-frequency transformer structure 3, such as Figure 9 As shown. The low-voltage side rectifier output ports are DC+ and DC-.

[0064] As an example, the structure of the low-voltage side rectifier will also differ depending on the number of secondary ports of the high-frequency isolation transformer. Three-bridge DC-side parallel structure: suitable for high-frequency isolation transformers with multiple secondary ports, ensuring that each port can effectively output power. Single-bridge structure: suitable for high-frequency isolation transformers with only one secondary port, offering a simpler structure.

[0065] It should be noted that the switching transistors in the embodiments of the present invention include all fully controllable active switching devices, such as metal-oxide-semiconductor field-effect transistors (MOSFETs), insulated-gate bipolar transistors (IGBTs), etc.

[0066] High-frequency isolation transformers are devices that transmit high-frequency voltage and current. They are suitable for high-frequency electronic equipment and switching power supplies. Due to their high operating frequency, their size can be greatly reduced. The number of windings and connection methods vary depending on the application requirements. Three independent two-winding transformers: Each winding has independent input and output ports, making the transformer easy to design and manufacture. Three-input, three-output six-winding transformer: Multiple windings share a single magnetic core, resulting in a more compact structure, but more complex manufacturing. Three-input, single-output four-winding transformer: Multiple input windings jointly drive one output winding. In these structures, the T on the primary side... com The port is the common port of the three windings, typically connected to the DC side N of a three-phase common half-bridge circuit. com The ports are connected. And on the secondary side, S1~S... i The port is connected to the low-voltage side rectifier.

[0067] As an example, the high efficiency of high-frequency isolation transformers makes them suitable for various high-power electronic devices and switching power supplies. Electrical isolation between input and output is achieved through electromagnetic induction, improving circuit safety. Different winding numbers and connection methods can meet various complex circuit requirements.

[0068] Ultimately, all DC+ ports of the common-isolated DC-DC converter and the low-voltage side rectifier are connected to form a positive low-voltage DC bus, and all DC- ports are connected to form a negative low-voltage DC bus, outputting a DC voltage v. Ldc . Figure 8 Low-voltage side rectifier structure 1: Three full-bridge DC sides connected in parallel; Figure 9Low-voltage side rectifier structure 2: single full bridge.

[0069] The single-arm power electronic transformer topology described above in this invention includes the following steps in its operation:

[0070] Input stage: The three-phase AC power supply is filtered by the three-phase AC filter inductor Lg and then enters the main bridge arm circuit.

[0071] High-frequency conversion stage: The main bridge arm circuit and the three-phase common half-bridge circuit convert the three-phase AC power into high-frequency AC power through hybrid frequency conversion control, and the energy is transferred through the resonant circuit composed of high-frequency series inductor and capacitor L1 / C1.

[0072] Isolation and transmission stage: High-frequency AC power is electrically isolated and transmitted through a high-frequency isolation transformer, and corresponding high-frequency AC power is generated on the secondary side.

[0073] Rectification and output stage: The low-voltage side rectifier converts high-frequency AC power into low-voltage DC power, controls and stabilizes the DC bus voltage, and, in conjunction with the common isolation DC-DC converter, ensures the stability of the DC side of the three-phase common half-bridge circuit.

[0074] To verify the feasibility of the present invention, the proposed topology is further described herein with reference to specific embodiments. The topology of the specific embodiments is as follows: Figure 10 As shown, each of the three-phase main bridge arms consists of N full-bridge sub-modules connected in series. The upper port of the main bridge arm is connected to the three-phase AC power grid via inductor Lg, and the lower port is connected to the three-phase common half-bridge. The upper port is also connected to a high-frequency transformer via inductor and capacitor L1C1. The high-frequency isolation transformer uses three independent two-winding transformers. The secondary side of the transformer is connected to a low-voltage side rectifier, which uses a three-full-bridge DC-side parallel structure. The DC side of the three-phase common half-bridge circuit is connected to a common isolation DC-DC converter, which is a CLLC resonant converter operating at its resonant point. All the outputs of the low-voltage side rectifiers and the CLLC resonant converter are connected in parallel to form the low-voltage DC bus.

[0075] Table 1 Circuit parameters of the embodiment

[0076]

[0077] Table 1 shows the specific circuit parameters of this embodiment: the three-phase AC side is connected to a 10 kV power grid, and the rated power is set to 1 MVA; each phase main bridge arm consists of 11 sub-modules, the rated voltage of each sub-module is set to 1.1 kV, and the equivalent switching frequency on the AC side is 20 kHz; the AC filter inductance is 10 mH; the low-voltage DC side outputs 1 kV voltage, and the low-voltage side switching frequency is 10 kHz; the high-frequency transformer turns ratio is 3.3:1. Based on the above parameters, this invention uses Matlab / Simulink to build a simulation of the power electronic transformer, and obtains the steady-state operating waveform of this embodiment, as shown below. Figure 11 As shown, Figure 11 Steady-state operating waveforms in specific embodiments of the present invention.

[0078] Figure 11 From top to bottom, the figures represent the three-phase AC grid voltage, three-phase AC grid current, three-phase main bridge arm submodule voltage, low-voltage DC bus voltage, and low-voltage DC bus current. As can be seen from the figure, the topology can stably achieve power transmission on both the AC and DC sides, ensuring excellent sinusoidal characteristics of the three-phase AC current with low harmonic content. Simultaneously, the submodule voltages of each phase main bridge arm can be stabilized at the rated voltage of 1.1kV, the low-voltage DC bus voltage is stabilized at 1kV, and the low-voltage DC bus current is 1kA.

[0079] Based on the above description, the improved single-arm power electronic transformer topology proposed in this invention has multiple advantages such as high efficiency, high power density, electrical isolation, and flexibility, and can be widely used in various applications requiring medium-voltage AC to low-voltage DC conversion. This topology is suitable for all applications requiring medium-voltage AC to low-voltage DC conversion, such as smart grids, electric vehicle charging stations, and data centers.

[0080] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for operating a single-arm power electronic transformer topology, characterized in that, The topology of a single-bridge power electronic transformer includes: a three-phase AC filter inductor L g The circuit consists of a three-phase main bridge arm circuit, a three-phase common half-bridge circuit, a high-frequency series inductor and capacitor L1 / C1, a high-frequency isolation transformer, a low-voltage side rectifier, and a common isolation DC-DC converter. The three-phase AC filter inductor Lg is used to filter out high-frequency harmonics in the three-phase AC current. The main bridge arm circuit is used to convert three-phase AC power into high-frequency AC power using hybrid frequency conversion. A three-phase common half-bridge circuit is used to assist the main bridge arm circuit of the auxiliary phase to perform voltage and current conversion. The high-frequency series inductor and capacitor L1 / C1 are used to filter out the power frequency fundamental wave and high-frequency PWM harmonics generated by the main bridge arm circuit and the three-phase common half-bridge circuit; High-frequency isolation transformers are used to achieve electrical isolation and voltage transformation, transmitting high-frequency alternating current from the primary side to the secondary side. The low-voltage side rectifier, located on the secondary side of the high-frequency isolation transformer, is used to convert high-frequency alternating current into low-voltage direct current, transmitting most of the power of the circuit. A common-isolation DC-DC converter is used to supplement the transmission of the remaining power; The phase main bridge arm circuit is composed of N sub-modules connected in series, where N is a positive integer greater than or equal to 1; each sub-module is a full-bridge circuit consisting of four switching transistors and a DC-side capacitor, with the upper and lower switching transistors conducting complementaryly, and external ports Q1 / Q2 respectively leading out from the midpoints of the two half-bridges; wherein, the Q2 port of one sub-module is connected to the Q1 port of another sub-module, and they are connected in series to form the phase main bridge arm. The three main bridge arms of phases a, b, and c have the same structure; phase a main bridge arm leads out upper and lower ports Ma1 / Ma2, phase b main bridge arm leads out upper and lower ports Mb1 / Mb2, and phase c main bridge arm leads out upper and lower ports Mc1 / Mc2. The upper port of the main bridge arm is connected to the three-phase medium-voltage AC power grid through a filter inductor: for phase a, port Ma1 is connected to phase a power grid va through filter inductor Lg; for phase b, port Mb1 is connected to phase b power grid vb through filter inductor Lg; for phase c, port Mc1 is connected to phase c power grid vc through filter inductor Lg. The upper port of the main bridge arm is also connected to the high-frequency isolation transformer via a high-frequency series inductor and capacitor: for phase a, port M a1 The high-frequency isolation transformer T is connected via a high-frequency series inductor and capacitor L1 / C1. a Port; for phase b, port M b1 The high-frequency isolation transformer T is connected via a high-frequency series inductor and capacitor L1 / C1. b Port; for phase c, port M c1 The high-frequency isolation transformer T is connected via a high-frequency series inductor and capacitor L1 / C1. c port; The three-phase common half-bridge circuit includes three half-bridges composed of six switching transistors, and the three half-bridges have a common DC side port; the midpoints of the three half-bridges are respectively connected to the M-axis of the three-phase main bridge arms a, b, and c. a2 / M b2 / M c2 The ports are connected, with their common DC-side port connected to the input port P of the common isolated DC-DC converter. com / N com Connected; The primary side of the high-frequency isolation transformer includes ports Ta, Tb, Tc, and Tcom, and the secondary side includes ports S1~S2. i , where i is a positive integer greater than 1; The Tcom port on the primary side is the common port of the three primary windings, and this port is connected to the DC side Ncom port of the three-phase common half-bridge circuit; the S1~S on the secondary side i The port is connected to the low-voltage side rectifier; The low-voltage side rectifier structure can be either a three-full-bridge DC-side parallel structure or a single full-bridge structure, depending on the number of secondary ports of the high-frequency isolation transformer. Working methods, including: The three-phase AC power supply filters out high-frequency harmonic currents through the three-phase AC filter inductor Lg and enters the main bridge arm circuit. The main bridge arm circuit and the three-phase common half-bridge circuit convert the three-phase AC power into high-frequency AC power through a hybrid frequency conversion control, and the energy is transferred through a resonant circuit composed of a high-frequency series inductor and capacitor L1 / C1. High-frequency alternating current is electrically isolated and transmitted through a high-frequency isolation transformer, and a corresponding high-frequency alternating current is generated on the secondary side. The low-voltage side rectifier converts high-frequency AC power into low-voltage DC power for power transmission and controls the low-voltage DC bus voltage stability; the common isolation DC-DC converter connects the three-phase common half-bridge DC side to the low-voltage DC bus, transmits the remaining small portion of power, and maintains the voltage stability at both ends.

2. The single-arm power electronic transformer topology according to claim 1, characterized in that, The common isolation DC-DC converter is a DC-DC converter with isolation and bidirectional power flow functions; The common isolation DC-DC converter is selected from: dual active bridge converter and CLLC resonant converter.

3. The single-arm power electronic transformer topology according to claim 1, characterized in that, The high-frequency isolation transformer is selected from three independent two-winding transformers, a six-winding transformer with three inputs and three outputs, or a four-winding transformer with three inputs and one output.

Images