A method and system for suppressing starting inrush current of a three-phase grid-connected converter

Abstract

The present invention belongs to the technical field of power electronics, and specifically relates to a method and system for suppressing starting impact current of a three-phase grid-connected converter, comprising: controlling the on-off of an AC relay based on a three-phase AC relay switch in the three-phase grid-connected converter; adding a PWM wave generator switch for controlling the on-off of a PWM wave generator and a closed-loop controller switch for controlling the state of a closed-loop controller in a control circuit of the three-phase grid-connected converter; performing coordinate transformation on an inverter side current and a three-phase voltage at a common connection point of a power grid to obtain a current tracking command value and a voltage feedforward command value respectively; combining a proportional-integral controller, a current tracking command value and a voltage feedforward command value, sequentially adjusting the states of the closed-loop controller switch, the PWM wave generator switch and the three-phase AC relay switch to suppress the impact current during the starting process of the three-phase grid-connected converter.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and in particular relates to a method and system for suppressing starting inrush current of a three-phase grid-connected converter. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art.

[0003] The applications of wind, solar and other renewable energy grid-connected power generation and energy storage require three-phase grid-connected converters to be connected to the grid to complete the energy conversion from AC to DC or DC to AC. During the startup process of the three-phase grid-connected converter, there is an inrush current on the AC side, which needs to be suppressed by hardware or software.

[0004] According to the inventors, the existing hardware suppression method for inrush current usually uses an additional current limiting resistor. Before the grid-connected converter is started, the AC relay is closed to suppress the inrush current through the current limiting resistor. After the AC capacitor (or DC side capacitor) is charged, the current limiting resistor is bypassed by an additional relay to avoid its power loss. However, the current limiting resistor and the bypass relay inevitably increase the volume, cost, and weight of the grid-connected converter system, while increasing the complexity of the system and reducing the reliability of the circuit. By accurately detecting the zero-crossing point of the AC voltage and independently closing the three-phase AC relays near the zero-crossing point, the inrush current can be limited; however, the three-phase AC relays of the actual grid-connected converter often use a unified signal control, which makes it difficult to achieve independent control.

[0005] For three-phase grid-connected converters without current limiting resistors, overcurrent is very likely to occur during the startup process, posing a severe challenge to the normal operation of AC relays and power switches, leading to grid connection failure and converter failure, reducing the reliability and safety of the system. Summary of the invention

[0006] In order to solve the above problems, the present disclosure proposes a method and system for suppressing the starting impact current of a three-phase grid-connected converter, which does not require additional hardware such as current limiting resistors and bypass relays, can significantly reduce the starting impact current of the grid-connected converter, avoid the additional system cost, volume and weight introduced by current limiting resistors and bypass relays, simplify the system structure, increase system reliability and robustness, and has the advantage of simple implementation.

[0007] According to some embodiments, a first solution of the present disclosure provides a method for suppressing startup inrush current of a three-phase grid-connected converter, using the following technical solution:

[0008] A method for suppressing starting inrush current of a three-phase grid-connected converter, comprising:

[0009] Based on the three-phase AC relay switch in the three-phase grid-connected converter, the AC relay is controlled to be on and off;

[0010] A PWM wave generator switch for controlling the on and off of the PWM wave generator and a closed-loop controller switch for controlling the state of the closed-loop controller are added to the three-phase grid-connected converter control circuit;

[0011] Perform coordinate transformation on the inverter side current and the three-phase voltage at the common connection point of the power grid to obtain the current tracking command value and the voltage feedforward command value respectively;

[0012] In combination with a proportional-integral controller, a current tracking command value and a voltage feedforward command value, the states of the closed-loop controller switch, the PWM wave generator switch and the three-phase AC relay switch are adjusted in sequence to suppress the inrush current during the startup of the three-phase grid-connected converter.

[0013] As a further technical limitation, the three-phase grid-connected converter includes a power semiconductor switch, a three-phase LCL filter and a three-phase AC relay connected in sequence; the power semiconductor switch adopts a three-phase bridge power semiconductor switch, including a first bridge arm, a second bridge arm and a third bridge arm, the first bridge arm includes a first power switch device and a fourth power switch device, the second bridge arm includes a third power switch device and a sixth power switch device, and the third bridge arm includes a second power switch device and a fifth power switch device.

[0014] Furthermore, the first power switch device, the second power switch device, the third power switch device, the fourth power switch device, the fifth power switch device and the sixth power switch device are all switch tube units, and the switch tube unit includes a triode and a diode connected in reverse parallel between the collector and the emitter of the triode, the anode of the diode is connected to the emitter of the triode, and the cathode of the diode is connected to the collector of the triode.

[0015] Furthermore, the three-phase LCL filter includes a three-phase inverter side inductor, a three-phase grid side inductor and a three-phase filter capacitor; one side of the three-phase inverter side inductor is respectively arranged in the middle of the first bridge arm, the second bridge arm and the third bridge arm, and the other side is respectively connected to the three-phase grid side inductor; one end of the three-phase filter capacitor is respectively connected to the three-phase inverter side inductor and the three-phase grid side inductor, and the other end is respectively short-circuited.

[0016] As a further technical limitation, the three-phase AC relay switch S g_relay It includes two states: 0 and 1. g_relay =1 means the AC relay is closed; S g_relay =0 means the AC relay is disconnected;

[0017] The PWM wave generator switch S g_pwm It includes two states: 0 and 1. g_pwm=1 means the PWM wave generator is turned on, allowing the generation of PWM waves; S g_pwm =0 means the PWM generator is turned off and all PWM waves are at low level;

[0018] The closed-loop controller switch S g_cl It includes two states: 0 and 1. g_cl =1 means the closed loop controller is turned on; S g_cl =0 means the closed-loop controller is closed.

[0019] As a further technical limitation, in the process of suppressing the impact current during the startup of the three-phase grid-connected converter, the three-phase AC relay switch and the closed-loop controller switch are opened, and the PWM wave generator switch is closed to make the three-phase grid-connected converter run in an open loop; after the first operating time, the PWM wave generator switch is adjusted to be disconnected, that is, the PWM wave generator is turned off, so that the three-phase filter capacitor in the three-phase grid-connected converter is charged; after the second operating time, the three-phase AC relay switch is adjusted to be closed, the AC relay is energized, and the three-phase filter capacitor is reversely discharged, thereby reducing the impact current generated during the startup of the three-phase grid-connected converter.

[0020] Furthermore, the first operating time is not less than 5 ms; and the time difference between the second operating time and the first operating time is an integer multiple of the fundamental wave period of the power grid.

[0021] According to some embodiments, a second solution of the present disclosure provides a three-phase grid-connected converter startup inrush current suppression system, which adopts the following technical solution:

[0022] A three-phase grid-connected converter startup inrush current suppression system, comprising:

[0023] A switch module is configured to control the on / off of an AC relay based on a three-phase AC relay switch in a three-phase grid-connected converter; a PWM wave generator switch for controlling the on / off of a PWM wave generator and a closed-loop controller switch for controlling the state of a closed-loop controller are added to the control circuit of the three-phase grid-connected converter;

[0024] A coordinate transformation module is configured to perform coordinate transformation on the inverter-side current and the three-phase voltage at the common connection point of the power grid to obtain a current tracking command value and a voltage feedforward command value respectively;

[0025] The suppression module is configured to combine the proportional-integral controller, the current tracking command value and the voltage feed-forward command value to sequentially adjust the states of the closed-loop controller switch, the PWM wave generator switch and the three-phase AC relay switch to suppress the impact current during the startup process of the three-phase grid-connected converter.

[0026] According to some embodiments, a third solution of the present disclosure provides a computer-readable storage medium, which adopts the following technical solution:

[0027] A computer-readable storage medium stores a program, which, when executed by a processor, implements the steps of the method for suppressing starting inrush current of a three-phase grid-connected converter as described in the first aspect of the present disclosure.

[0028] According to some embodiments, a fourth solution of the present disclosure provides an electronic device, which adopts the following technical solution:

[0029] An electronic device comprises a memory, a processor and a program stored in the memory and executable on the processor, wherein when the processor executes the program, the steps in the method for suppressing startup inrush current of a three-phase grid-connected converter as described in the first aspect of the present disclosure are implemented.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention does not require additional hardware such as current limiting resistors and bypass relays, and can significantly reduce the startup impact current of the grid-connected converter; at the same time, the method of the present invention uniformly controls the AC relays, is simple to implement, and has universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings constituting a part of the present disclosure are used to provide a further understanding of the present disclosure. The illustrative embodiments of the present disclosure and their descriptions are used to explain the present disclosure and do not constitute an improper limitation on the present disclosure.

[0033] Figure 1 is a flow chart of a method for suppressing a starting inrush current of a three-phase grid-connected converter in Embodiment 1 of the present disclosure;

[0034] Figure 2 is a schematic diagram of the circuit structure of a three-phase grid-connected converter in Embodiment 1 of the present disclosure;

[0035] Figure 3 is a schematic diagram of the control structure of a three-phase grid-connected converter in Embodiment 1 of the present disclosure;

[0036] Figure 4 When the PWM wave of the three-phase grid-connected converter in the first embodiment of the present disclosure is turned off (S g_pwm =0) control structure diagram;

[0037] Figure 5 is the three-phase grid-connected converter in the first embodiment of the present disclosure in open-loop operation (S g_pwm =1, S g_cl =0) control structure diagram;

[0038] Figure 6 is the three-phase grid-connected converter in the first embodiment of the present disclosure in closed-loop operation (S g_pwm =1, S g_cl=1) Schematic diagram of control structure;

[0039] Figure 7 is a control logic diagram of starting current surge suppression of a three-phase grid-connected converter in Embodiment 1 of the present disclosure;

[0040] Figure 8 is a time series diagram of the starting current impulse suppression control of the three-phase grid-connected converter in the first embodiment of the present disclosure;

[0041] Fig. 9 is a waveform diagram of a startup experiment of a three-phase grid-connected converter in Embodiment 1 of the present disclosure;

[0042] Fig.10 It is a structural block diagram of the three-phase grid-connected converter starting inrush current suppression system in the second embodiment of the present disclosure. DETAILED DESCRIPTION

[0043] The present disclosure is further described below in conjunction with the accompanying drawings and embodiments.

[0044] It should be noted that the following detailed descriptions are all illustrative and are intended to provide further explanation of the present disclosure. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present disclosure belongs.

[0045] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present disclosure. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0046] In the absence of conflict, the embodiments in the present disclosure and the features in the embodiments may be combined with each other.

[0047] Embodiment 1

[0048] Embodiment 1 of the present disclosure introduces a method for suppressing startup inrush current of a three-phase grid-connected converter.

[0049] like Figure 1 A method for suppressing starting impact current of a three-phase grid-connected converter is shown, comprising:

[0050] Based on the three-phase AC relay switch in the three-phase grid-connected converter, the AC relay is controlled to be on and off;

[0051] A PWM wave generator switch for controlling the on and off of the PWM wave generator and a closed-loop controller switch for controlling the state of the closed-loop controller are added to the three-phase grid-connected converter control circuit;

[0052] Perform coordinate transformation on the inverter side current and the three-phase voltage at the common connection point of the power grid to obtain the current tracking command value and the voltage feedforward command value respectively;

[0053] In combination with a proportional-integral controller, a current tracking command value and a voltage feedforward command value, the states of the closed-loop controller switch, the PWM wave generator switch and the three-phase AC relay switch are adjusted in sequence to suppress the inrush current during the startup of the three-phase grid-connected converter.

[0054] like Figure 2 The common three-phase two-level grid-connected converter shown in FIG. 1 includes six power switching devices (S g1 , S g2 , S g3 , S g4 , S g5 , S g6 ), 1 three-phase LCL filter (consisting of 3 inverter-side inductors L gi , 3 grid-side inductors L gg , 3 filter capacitors C gf ), 1 three-phase AC relay; wherein the three-phase AC relay is switched by the switch signal S g_relay Control: S g_relay =1, the relay is closed; S g_relay = 0, the relay is disconnected. Figure 2 The three-phase two-level grid-connected converter shown in FIG. samples the three-phase voltage v at the common connection point of the grid. gabc , the three-phase current i on the inverter side giabc , DC side voltage v gdc Provides information to the controller.

[0055] like Figure 3 The three-phase grid-connected converter controller structure described above performs error-free tracking of the command value through a proportional integral (PI) controller, that is, the inverter side current i in the dq0 coordinate system is respectively set to gid and i giq Track its instruction value i gid_ref and i giq_ref ; The phase-locked loop (PLL) provides accurate phase θ for abc / dq0 coordinate system transformation g . Three-phase voltage v at the public connection point of the power grid gabc By transforming the abc / dq0 coordinate system, we can get v gd and v gq , as a feedforward instruction; S g_cl and S g_pwm The additional control signal switch added in this embodiment; S g_cl =1, enable closed-loop control; S g_cl=0, the closed-loop control is turned off and the open-loop control is entered. g_pwm =1, enable PWM wave generation; S g_pwm When =0, the PWM wave is turned off and all PWM waves are at low level.

[0056] The control structure diagram of the PWM mode is as follows: Figure 4 As shown, S g_pwm = 0, turn off the PWM wave, and all power switch drive levels are low; the control structure diagram in the open-loop operation mode is as follows Figure 5 As shown, S g_pwm =1 and S g_cl = 0, the grid-connected converter operates in open-loop mode; the control structure diagram in closed-loop operation mode is as follows Figure 6 As shown, S g_pwm =1 and S g_cl =1, the grid-connected converter operates in closed-loop mode.

[0057] The control logic diagram of the starting current surge suppression of the three-phase grid-connected converter is as follows: Figure 7 As shown in Figure 1, the inrush current suppression strategy adds a control sequence between shutdown (turning off PWM) and closing the AC relay. In the process of suppressing the inrush current, first, Figure 5 The open loop mode shown in the figure is run for a while, and then Figure 4 The PWM mode shown runs for a while, and then closes the AC relay (S g_relay =1), and finally Figure 6 The closed-loop mode shown in the figure is operating normally. The time series diagram of the starting current impact suppression control of the three-phase grid-connected converter is as follows Figure 8 As shown in Figure 1, the typical timing of this inrush current suppression strategy is to run in open loop for 50ms, run in PWM mode for 20ms, and then close the AC relay (S g_relay =1). The three-phase grid-connected converter startup test waveform is shown in Fig. 9 As shown, it is verified that the method proposed in this embodiment can effectively limit the inrush current.

[0058] This embodiment does not require additional hardware such as current limiting resistors and bypass relays, and can significantly reduce the startup impact current of the grid-connected converter; at the same time, the method disclosed in the present invention uniformly controls the AC relays, which is simple to implement and has universality.

[0059] Embodiment 2

[0060] Embodiment 2 of the present disclosure introduces a three-phase grid-connected converter startup inrush current suppression system.

[0061] like Fig.10 A three-phase grid-connected converter startup inrush current suppression system is shown, comprising:

[0062] A switch module is configured to control the on / off of an AC relay based on a three-phase AC relay switch in a three-phase grid-connected converter; a PWM wave generator switch for controlling the on / off of a PWM wave generator and a closed-loop controller switch for controlling the state of a closed-loop controller are added to the control circuit of the three-phase grid-connected converter;

[0063] A coordinate transformation module is configured to perform coordinate transformation on the inverter-side current and the three-phase voltage at the common connection point of the power grid to obtain a current tracking command value and a voltage feedforward command value respectively;

[0064] The suppression module is configured to combine the proportional-integral controller, the current tracking command value and the voltage feed-forward command value to sequentially adjust the states of the closed-loop controller switch, the PWM wave generator switch and the three-phase AC relay switch to suppress the impact current during the startup process of the three-phase grid-connected converter.

[0065] The detailed steps are the same as those of the method for suppressing startup inrush current of a three-phase grid-connected converter provided in the first embodiment, and will not be repeated here.

[0066] Embodiment 3

[0067] A third embodiment of the present disclosure provides a computer-readable storage medium.

[0068] A computer-readable storage medium stores a program, which, when executed by a processor, implements the steps of the method for suppressing starting inrush current of a three-phase grid-connected converter as described in the first embodiment of the present disclosure.

[0069] The detailed steps are the same as those of the method for suppressing startup inrush current of a three-phase grid-connected converter provided in the first embodiment, and will not be repeated here.

[0070] Embodiment 4

[0071] A fourth embodiment of the present disclosure provides an electronic device.

[0072] An electronic device comprises a memory, a processor and a program stored in the memory and executable on the processor, wherein when the processor executes the program, the steps of the method for suppressing starting impact current of a three-phase grid-connected converter as described in the first embodiment of the present disclosure are implemented.

[0073] The detailed steps are the same as those of the method for suppressing startup inrush current of a three-phase grid-connected converter provided in the first embodiment, and will not be repeated here.

[0074] The above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure. For those skilled in the art, the present disclosure may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.

[0075] Although the above describes the specific implementation methods of the present disclosure in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present disclosure. Technical personnel in the relevant field should understand that on the basis of the technical solution of the present disclosure, various modifications or variations that can be made by those skilled in the art without creative work are still within the scope of protection of the present disclosure.

Claims

1. A method for suppressing starting inrush current of a three-phase grid-connected converter, characterized in that: include: Based on the three-phase AC relay switch in the three-phase grid-connected converter, the AC relay is controlled to be on and off; A PWM wave generator switch for controlling the on and off of the PWM wave generator and a closed-loop controller switch for controlling the state of the closed-loop controller are added to the three-phase grid-connected converter control circuit; Perform coordinate transformation on the inverter side current and the three-phase voltage at the common connection point of the power grid to obtain the current tracking command value and the voltage feedforward command value respectively; In combination with a proportional-integral controller, a current tracking command value and a voltage feedforward command value, the states of the closed-loop controller switch, the PWM wave generator switch and the three-phase AC relay switch are adjusted in sequence to suppress the inrush current during the startup of the three-phase grid-connected converter; The three-phase grid-connected converter comprises a power semiconductor switch, a three-phase LCL filter and a three-phase AC relay connected in sequence; the power semiconductor switch adopts a three-phase bridge power semiconductor switch, including a first bridge arm, a second bridge arm and a third bridge arm, the first bridge arm comprises a first power switch device and a fourth power switch device, the second bridge arm comprises a third power switch device and a sixth power switch device, and the third bridge arm comprises a second power switch device and a fifth power switch device; The three-phase LCL filter includes a three-phase inverter side inductor, a three-phase grid side inductor and a three-phase filter capacitor; one side of the three-phase inverter side inductor is respectively arranged in the middle of the first bridge arm, the second bridge arm and the third bridge arm, and the other side is respectively connected to the three-phase grid side inductor; one end of the three-phase filter capacitor is respectively connected to the three-phase inverter side inductor and the three-phase grid side inductor, and the other end is respectively short-circuited; The three-phase AC relay switch S g_relay It includes two states: 0 and 1. g_relay =1 means the AC relay is closed; S g_relay =0 means the AC relay is disconnected; The PWM wave generator switch S g_pwm It includes two states: 0 and 1. g_pwm =1 means the PWM wave generator is turned on, allowing the generation of PWM waves; S g_pwm =0 means the PWM generator is turned off and all PWM waves are at low level; The closed-loop controller switch S g_cl It includes two states: 0 and 1. g_cl =1 means the closed loop controller is turned on; S g_cl =0 means the closed loop controller is closed; In the process of suppressing the impact current during the startup of the three-phase grid-connected converter, the three-phase AC relay switch and the closed-loop controller switch are turned on, and the PWM wave generator switch is closed to make the three-phase grid-connected converter run in an open loop; after the first operation time, the PWM wave generator switch is adjusted to be disconnected, that is, the PWM wave generator is turned off, so that the three-phase filter capacitor in the three-phase grid-connected converter is charged; after the second operation time, the three-phase AC relay switch is adjusted to be closed, the AC relay is energized, and the three-phase filter capacitor is reversely discharged, thereby reducing the impact current generated during the startup of the three-phase grid-connected converter.

2. A method for suppressing starting inrush current of a three-phase grid-connected converter as claimed in claim 1, characterized in that: The first power switch device, the second power switch device, the third power switch device, the fourth power switch device, the fifth power switch device and the sixth power switch device are all switch tube units, and the switch tube unit includes a triode and a diode connected in reverse parallel between the collector and the emitter of the triode, the anode of the diode is connected to the emitter of the triode, and the cathode of the diode is connected to the collector of the triode.

3. A method for suppressing starting inrush current of a three-phase grid-connected converter as claimed in claim 1, characterized in that: The first operating time is no less than 5 ms; and the time difference between the second operating time and the first operating time is an integer multiple of the fundamental wave period of the power grid.

4. A three-phase grid-connected converter startup inrush current suppression system, using the three-phase grid-connected converter startup inrush current suppression method as claimed in any one of claims 1 to 3, characterized in that: include: A switch module is configured to control the on / off of an AC relay based on a three-phase AC relay switch in a three-phase grid-connected converter; a PWM wave generator switch for controlling the on / off of a PWM wave generator and a closed-loop controller switch for controlling the state of a closed-loop controller are added to the control circuit of the three-phase grid-connected converter; A coordinate transformation module is configured to perform coordinate transformation on the inverter-side current and the three-phase voltage at the common connection point of the power grid to obtain a current tracking command value and a voltage feedforward command value respectively; The suppression module is configured to combine the proportional-integral controller, the current tracking command value and the voltage feed-forward command value to sequentially adjust the states of the closed-loop controller switch, the PWM wave generator switch and the three-phase AC relay switch to suppress the impact current during the startup process of the three-phase grid-connected converter.

5. A computer-readable storage medium having a program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method for suppressing starting inrush current of a three-phase grid-connected converter as described in any one of claims 1 to 3 are implemented.

6. An electronic device comprising a memory, a processor, and a program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the steps of the method for suppressing startup inrush current of a three-phase grid-connected converter as described in any one of claims 1 to 3 are implemented.

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