A multi-demand-compatible energy feedback type split-capacitive three-phase power electronic load

Abstract

A kind of compatible multiple needs energy feedback type split capacitor three-phase power electronic load, main circuit uses AC / DC / AC two-stage back-to-back structure: the former stage is three-phase four-wire split capacitor PWM rectifier bridge, analog load;The latter stage is three-phase three-wire PWM inverter bridge, realizes energy feedback;Middle side uses split capacitor, and adopts flyback circuit and SPWM control strategy to carry out voltage control to capacitor both ends.Electricity control strategy is converted to the direct current signal in dq0 coordinate system by Park transformation and Clark transformation, three-phase alternating current signal under abc coordinate system, under decoupling condition, PI controller is used to signal no static difference tracking.The present application can use one circuit topology to realize multiple load simulation, in three-phase unbalanced load, unidirectional load, nonlinear load and other special cases, can maintain the stability of DC bus voltage, realizes current fast regulation, and will electric energy feedback power grid, has great practical value.

Description

Technical Field

[0001] This invention belongs to the field of power electronic load technology and relates to a power-feed type split capacitor three-phase power electronic load that is compatible with multiple needs. Specifically, it relates to a power-feed type power electronic load topology and control method that can realize static and dynamic simulation of linear loads and nonlinear loads, and also take into account the simulation needs of single-phase, three-phase three-wire, and three-phase four-wire loads. Background Technology

[0002] Traditional power loads include passive components such as resistors, capacitors, and inductors. However, traditional test loads suffer from drawbacks such as the inability to continuously adjust the load, limited load characteristics, low simulation accuracy, and high energy consumption. If a power electronic converter is connected to the power supply under test, and the phase and magnitude of the power supply's output current are precisely controlled, it is equivalent to running a real load from the power supply side, thus achieving the purpose of simulating a load. This is the concept of a power-feedback electronic load.

[0003] In 1990, an aging test device for UPS was proposed, with relatively fixed application scenarios. Subsequently, the regulation of active and reactive power in three-phase power supplies under test was gradually realized. Later, the application of various DC power supplies led experts to conduct extensive research on power electronic loads for testing. This progressed from using DC / AC converters connected to the grid to control the output power of the power supply under test, to adding Boost, Buck, and Cuk converters to add the function of feeding energy back to the grid, thus giving rise to the rudiments of energy-feedback power electronic loads. In 2012, an AC power electronic load composed of two-stage AC / DC converters was proposed. Its back-to-back structure gradually gained acceptance, laying the foundation for power electronic load research in recent years.

[0004] Existing research on energy-feedable AC electronic loads primarily focuses on single-phase or three-phase balanced operating conditions, making it difficult to simultaneously handle load testing under various operating conditions such as three-phase three-wire, three-phase four-wire, and single-phase systems. Therefore, further research is needed on energy-feedable AC electronic loads to ensure their input characteristics fully match the impedances of various typical loads in actual field conditions, flexibly simulating the steady-state operation and dynamic changes of single-phase, three-phase balanced, and three-phase unbalanced loads during load abrupt changes. Currently, how to flexibly simulate loads with various characteristics and simplify the circuit remains a crucial research area in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of traditional technologies and propose a power-feed type split capacitor three-phase power electronic load that is compatible with multiple needs. The purpose of this invention is achieved through the following technical solutions.

[0006] A three-phase power electronic load with a split capacitor and compatible with multiple needs is characterized in that the power electronic load includes a load simulation module, an energy feedback module, a DC module, and a control module; the load simulation module includes a three-phase filter inductor, six sets of first-stage power switching devices and six sets of first-stage diodes connected in anti-parallel to each of them, and two capacitors in the fourth bridge arm; the load simulation module consists of a three-phase four-wire bridge circuit composed of the six sets of first-stage power switching devices and the fourth bridge arm of the split capacitor; the energy feedback module includes a three-phase LCL filter, six sets of second-stage power switching devices and six sets of second-stage diodes connected in anti-parallel to each of them; the energy feedback module consists of a three-phase bridge circuit composed of the six sets of second-stage power switching devices; the DC module includes a DC capacitor; the control module includes a phase-locked loop module, a split capacitor voltage equalization module, a load simulation control module, and an energy feedback control module. The main circuit of this power electronic load uses a two-stage back-to-back AC / DC / AC structure: the front stage is a three-phase four-wire split capacitor PWM rectifier bridge to simulate loads under various operating conditions; the rear stage is a three-phase three-wire PWM inverter bridge to realize energy feedback to the grid and reduce energy waste; the middle stage uses a split capacitor structure and adopts a flyback circuit structure and SPWM control strategy to equalize the voltage across the split capacitor, which can simulate three-phase unbalanced loads, unidirectional loads and nonlinear loads.

[0007] As a preferred embodiment of the energy-feed type split capacitor three-phase power electronic load compatible with multiple requirements described in this invention, the phase-locked loop module includes a Clark transformation stage, a Park transformation stage, a PI control stage, and a phase change stage.

[0008] As a preferred embodiment of the energy-feeding split capacitor three-phase power electronic load compatible with multiple needs described in this invention, the split capacitor voltage equalization module includes an upper split capacitor, a lower split capacitor, two sets of third-stage power switching devices, and two sets of third-stage diodes, coupling inductor Le1, and coupling inductor Le2 connected in reverse parallel with them respectively. The split capacitor voltage equalization module is composed of an upper split capacitor, a lower split capacitor, two sets of third-stage power switching devices, and two sets of third-stage diodes, coupling inductor Le1, and coupling inductor Le2 connected in reverse parallel with them respectively, forming a flyback voltage equalization circuit.

[0009] As a preferred embodiment of the energy-feed type split capacitor three-phase power electronic load compatible with multiple needs described in this invention, wherein: the first-stage power switching device, the second-stage power switching device, and the third-stage power switching device are all insulated-gate bipolar transistors.

[0010] As a preferred embodiment of the energy-feed type split capacitor three-phase power electronic load compatible with multiple requirements described in this invention, the load simulation control module includes a first-stage coordinate transformation stage, a first-stage PI control stage, a first-stage decoupling stage, and a first-stage SPWM control stage.

[0011] As a preferred embodiment of the energy-feeding split capacitor three-phase power electronic load compatible with multiple requirements described in this invention, the energy feedback control module includes a second-level coordinate transformation stage, a second-level PI control stage, a second-level decoupling stage, and a second-level SPWM control stage.

[0012] As a preferred embodiment of the energy-feed type split capacitor three-phase power electronic load compatible with multiple requirements described in this invention, wherein: the first-stage coordinate transformation stage and the second-stage coordinate transformation stage are both composed of Clark transformation and Park transformation.

[0013] As a preferred embodiment of the energy-feed type split capacitor three-phase power electronic load compatible with multiple requirements described in this invention, wherein: the phase change link changes the obtained grid phase to form the phase requirements when simulating resistive, capacitive and inductive loads, and uses the obtained phase to generate a three-phase unbalanced given current.

[0014] As a preferred embodiment of the energy-feeding split capacitor three-phase power electronic load compatible with multiple needs described in this invention, it further includes a current-setting circuit for simulating a nonlinear load. The current-setting circuit for simulating a nonlinear load includes six diodes and six resistors connected in parallel with them. The current-setting circuit for simulating a nonlinear load consists of a three-phase bridge circuit composed of the six diodes.

[0015] The present invention has the following advantages over the prior art: 1. This invention addresses the problems of traditional three-phase power electronic loads being unable to simultaneously simulate single-phase loads and three-phase unbalanced loads, and having poor simulation effects on nonlinear loads. It proposes an energy-feeding three-phase four-wire power electronic load based on SPWM control using a front-end split capacitor rectifier and its control method, which can effectively simulate three-phase balanced, three-phase unbalanced, nonlinear, and single-phase load conditions.

[0016] 2. In terms of control, the three-phase AC quantity is converted to DC quantity in the dq0 coordinate system through coordinate transformation, resulting in faster adjustment speed and better tracking effect.

[0017] 3. By using a split capacitor as the fourth bridge arm and controlling the voltage across the split capacitor, the stability of the DC bus voltage can be ensured under simulated load conditions such as three-phase unbalanced load and nonlinear load. Attached Figure Description

[0018] Figure 1 This is a circuit diagram of a three-phase power electronic load with a split capacitor that is compatible with various needs.

[0019] Figure 2 This is a flowchart of the phase-locked loop (PLL) component in a multi-functional, energy-feeding, split-capacitor three-phase power electronic load.

[0020] Figure 3 This is a circuit diagram of the voltage equalization section of the split capacitor in a three-phase power electronic load with a split capacitor that is compatible with various needs.

[0021] Figure 4 This is a flowchart of the control section for the voltage equalization part of the split capacitor in a three-phase power electronic load with a power feed type that is compatible with various needs.

[0022] Figure 5 This is a flowchart of a load simulation control module for a power-feed type split capacitor three-phase power electronic load that is compatible with various needs.

[0023] Figure 6 This is a control flowchart for an energy feedback control module in a three-phase power electronic load with a split capacitor that is compatible with various needs.

[0024] Figure 7 This is a current-feeding circuit for simulating nonlinear loads in a power-feed type split capacitor three-phase power electronic load that is compatible with various needs.

[0025] Figure 8 This is a circuit diagram simulating a single-phase load in a three-phase power electronic load with a split capacitor that is compatible with various needs.

[0026] Figure 9 This is a DC bus voltage waveform diagram for simulating a three-phase unbalanced load in a power-feed type split capacitor three-phase power electronic load that is compatible with various needs. Implementation

[0027] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention. Example 1

[0028] Reference Figures 1-3This is the first embodiment of the present invention, which provides an energy-feedable split-capacitor three-phase power electronic load capable of simulating three-phase unbalanced loads, unidirectional loads, and nonlinear loads. The load simulation module 100, DC module 200, energy feedback module 300, and control module 400 are included. The control module 400 generates control signals to control the on / off states of various switching devices, thereby achieving various types of load simulation. The energy feedback module 300 feeds electrical energy back to the power grid, thereby improving energy utilization efficiency.

[0029] The load simulation module includes a three-phase filter inductor 101, six sets of first-stage power switching devices 102, and six sets of first-stage diodes 103 connected in reverse parallel with each of them. The fourth bridge arm uses two capacitors 104. The load simulation module 100 is a three-phase four-wire bridge circuit composed of six sets of first-stage power switching devices 102 and the fourth bridge arm of the split capacitors 104. The DC module 200 includes a DC capacitor 201. The energy feedback module includes a three-phase LCL filter 301, six sets of second-stage power switching devices 302, and six sets of second-stage diodes 303 connected in reverse parallel with each of them. The energy feedback module 300 is a three-phase bridge circuit composed of six sets of second-stage power switching devices 302 and six sets of second-stage diodes 303 connected in reverse parallel with each of them. The control module 400 includes a phase-locked loop module 401, a split capacitor voltage equalization module 402, a load simulation control module 403, and an energy feedback control module 404.

[0030] The phase-locked loop module 401 includes a Clark transformation stage 401.a, a Park transformation stage 401.b, a PI control stage 401.c, and a phase change stage 401.d.

[0031] The first-stage power switching device 102, the second-stage power switching device 302, and the third-stage power switching device 402.c are all insulated-gate bipolar transistors.

[0032] The split capacitor voltage equalization module 402 includes an upper split capacitor 402.a, a lower split capacitor 402.b, two sets of third-stage power switching devices, and two sets of third-stage diodes 402.c, coupling inductors Le1 and Le2 402.d connected in reverse parallel with them. The split capacitor voltage equalization module 402 is composed of the upper split capacitor 402.a, the lower split capacitor 402.b, the two sets of third-stage power switching devices, and two sets of third-stage diodes 402.c, coupling inductors Le1 and Le2 402.d connected in reverse parallel with them to form a flyback voltage equalization circuit.

[0033] The load simulation control module 403 includes a first-stage coordinate transformation stage 403.a, a first-stage PI control stage 403.b, a first-stage decoupling stage 403.c, and a first-stage SPWM control stage 403.d.

[0034] The energy feedback control module 404 includes a second-level coordinate transformation stage 404.a, a second-level PI control stage 404.b, a second-level decoupling stage 404.c, and a second-level SPWM control stage 404.d. Example 2

[0035] Reference Figures 1-9 This is the second embodiment of the present invention. In the previous embodiment, the energy-feeding split-capacitor three-phase power electronic load, capable of accommodating various load requirements, includes a load simulation module 100, an energy feedback module 300, a DC module 200, and a control module 400. The control module 400 generates control signals to control the on and off states of various switching devices, thereby achieving various types of load simulation. The energy feedback module 300 feeds electrical energy back to the power grid, thereby improving energy utilization efficiency.

[0036] In simulating a three-phase unbalanced load, a given current is first generated through a three-phase unbalanced current generation circuit to achieve the simulation effect. Simultaneously, the switching signals of the first-stage power switching devices are generated through the first-stage coordinate transformation stage 403.a, the first-stage PI control stage 403.b, the first-stage decoupling stage 403.c, and the first-stage SPWM control stage 403.d, controlling their switching states so that the entire load simulation module 100 can simulate the specified load requirements. Throughout the process, the two switching devices in the split capacitor voltage equalization stage switch their switching states according to the switching signals generated by the voltage requirements at their terminals to maintain the balance of the upper and lower capacitor voltages and the stability of the DC bus voltage.

[0037] The energy feedback module is a three-phase bridge inverter. When performing energy feedback, the phase of the grid is first obtained through a phase-locked loop, and the DC bus voltage and inverter output current are sampled. Through the second-stage coordinate transformation stage 404.a, the second-stage PI control stage 404.b, the second-stage decoupling stage 404.c, and the second-stage SPWM control stage 404.d, the current is made to meet the grid connection requirements.

[0038] When performing single-phase load simulation, disconnect any two phases of the three-phase load, and at the same time disconnect the corresponding two-phase bridge arms according to the selected two phases. At this time, the midpoint of the split capacitor is connected to the midpoint of the power supply, and forms a complete circuit with the aforementioned power supply phase and bridge arm. At this time, the front-end structure of the circuit is a single-phase half-bridge rectifier to realize the simulation of single-phase load.

[0039] During nonlinear load simulation, the current-setting circuit 500 for nonlinear load simulation includes six diodes 501 and six resistors 502 connected in parallel with them. The current-setting circuit 500 for nonlinear load simulation forms a three-phase bridge circuit with the six diodes 501 and the six resistors 502 connected in parallel with them. Since the three-phase input currents are unbalanced, the circuit topology is consistent with that of the unbalanced three-phase load. Modifying the given current waveform to match the current waveform corresponding to the nonlinear load allows the circuit front-end to operate under the simulated nonlinear load condition. At this time, because the sum of the three-phase currents is not zero (i.e., there is current in the neutral line), there will be an imbalance in the voltage of the two split capacitors on the DC side. This phenomenon will adversely affect the load simulation performance, grid connection performance, and system lifespan of the device. Therefore, the split capacitor voltage equalization module is still needed to reduce the voltage difference between the two split capacitors, thereby improving simulation performance and power quality.

[0040] When performing voltage equalization control of split capacitors, the voltage of one side of the split capacitor is subtracted from 0.5 times the DC bus voltage. This difference is then passed through a PI controller and compared with a triangular wave to output a corresponding drive signal, which drives the two switching transistors to turn on and off, thereby controlling the voltage across the split capacitor.

[0041] refer to Figure 9 , Figure 9 The x-axis represents time t (s), and the y-axis represents voltage Udc (V). It can be seen that when simulating a three-phase unbalanced load, due to the use of a split capacitor voltage equalization circuit, the DC bus voltage rises rapidly and quickly stabilizes near the given value, demonstrating good regulation. This provides a relatively stable DC bus voltage for the entire experiment.

[0042] Compared to existing technologies, current power electronic loads cannot simulate special load conditions such as three-phase unbalanced loads and nonlinear loads, and their effect on stabilizing DC bus voltage is poor. Furthermore, traditional control methods based on the abc coordinate system have significant errors and poor adjustment performance. This invention can simulate various load conditions, including three-phase unbalanced, nonlinear, and single-phase loads, using the same circuit topology. To address the DC bus voltage fluctuation problem caused by unbalanced loads, a split capacitor is used as the fourth bridge arm for voltage equalization control to maintain bus voltage stability. In terms of control, coordinate transformation is used to convert the three-phase AC quantities to the dq0 coordinate system for control, resulting in faster adjustment speed and better tracking performance.

[0043] Although embodiments of the present invention have been shown and described above, it is understood that these embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and alterations to the above embodiments within the scope of the present invention without departing from its principles and spirit. The scope of protection of the present invention is defined by the claims and their equivalents.

Claims

1. A multi-demand-compatible, energy-feeding, split-capacitive, three-phase power electronic load, characterized in that, The power electronic load includes a load simulation module (100), a DC module (200), an energy feedback module (300), and a control module (400). The load simulation module includes a three-phase filter inductor (101), six sets of first-stage power switching devices (102) and six sets of first-stage diodes (103) connected in reverse parallel with them respectively. The fourth bridge arm uses two capacitors (104). The load simulation module (100) is a three-phase four-wire bridge circuit composed of six sets of first-stage power switching devices (102) and split capacitors (104) and the fourth bridge arm. The DC module (200) includes a DC capacitor (201); The energy feedback module includes a three-phase LCL filter (301), six sets of second-stage power switching devices (302) and six sets of second-stage diodes (303) connected in reverse parallel with each other. The energy feedback module (300) is composed of six sets of second-stage power switching devices (302) and six sets of second-stage diodes (303) connected in reverse parallel with each other to form a three-phase bridge circuit. The control module (400) includes a phase-locked loop module (401), a split capacitor voltage equalization module (402), a load simulation control module (403), and an energy feedback control module (404). The split capacitor voltage equalization module (402) includes an upper split capacitor (402.a), a lower split capacitor (402.b), two sets of third-stage power switching devices, and two sets of third-stage diodes (402.c), coupling inductors Le1 and Le2 (402.d) connected in reverse parallel with them respectively. The split capacitor voltage equalization module (402) is composed of an upper split capacitor (402.a), a lower split capacitor (402.b), two sets of third-stage power switching devices, and two sets of third-stage diodes (402.c), coupling inductors Le1 and Le2 (402.d) connected in reverse parallel with them respectively, forming a flyback voltage equalization circuit. It also includes a current-setting circuit (500) for simulating a nonlinear load, which includes six diodes (501) and six resistors (502) connected in parallel with them respectively. The current-setting circuit (500) for simulating a nonlinear load consists of six diodes (501) and six resistors (502) connected in parallel with them respectively, forming a three-phase bridge circuit.

2. The power electronic load according to claim 1, characterized in that, The phase-locked loop module (401) includes a Clark transformation stage (401.a), a Park transformation stage (401.b), a PI control stage (401.c), and a phase change stage (401.d).

3. The power electronic load according to claim 1, characterized in that, The first-stage power switching device (102), the second-stage power switching device (302), and the third-stage power switching device (402.c) are all insulated-gate bipolar transistors.

4. The power electronic load according to claim 1, characterized in that, The load simulation control module (403) includes a first-stage coordinate transformation stage (403.a), a first-stage PI control stage (403.b), a first-stage decoupling stage (403.c), and a first-stage SPWM control stage (403.d).

5. The power electronic load according to claim 1, characterized in that, The energy feedback control module (404) includes a second-level coordinate transformation stage (404.a), a second-level PI control stage (404.b), a second-level decoupling stage (404.c), and a second-level SPWM control stage (404.d).

6. The power electronic load according to claim 2, characterized in that, The phase change step (401.d) changes the obtained grid phase to form the phase requirements when simulating resistive, capacitive and inductive loads, and uses the obtained phase to generate a three-phase unbalanced given current.

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