A soft start control method of a distributed energy storage grid-connected converter

Abstract

This invention discloses a soft-start method for a grid-connected converter for distributed energy storage. No starting resistor is connected to the AC side of the converter, and a thyristor anti-parallel diode module is installed in the upper arm of the three phases. During startup, the fully controlled devices are kept in a locked state, the initial value of the thyristor firing angle α is set to 120°, and the DC side voltage U is detected. dc Less than the DC side voltage threshold U set And the peak value of the bridge arm current I brig Less than the bridge arm current threshold I set If so, the firing angle α will be gradually reduced in 1° intervals during the next control cycle; when the peak value of the bridge arm current I... brig Greater than or equal to the bridge arm current threshold I set If the trigger angle α remains unchanged in the next control cycle, then the DC side voltage U... dc Reaching the DC-side voltage threshold U set At this time, a continuous conduction signal is supplied to the thyristor to make it equivalent to a diode. The fully controlled devices in the converter are then controlled using PWM to raise the DC-side voltage to the rated voltage. This method avoids the problems of bridge arm overcurrent or excessively long start-up time without exceeding the bridge arm current limit.

Description

Technical Field

[0001] This invention relates to the field of power equipment technology, and in particular to a soft-start control method for a grid-connected converter for distributed energy storage. Background Technology

[0002] With the increasing integration of new elements such as high-proportion distributed power sources, 5G, and charging piles, the random fluctuations and instantaneous impacts of power at distribution network nodes are growing, making energy storage a crucial solution. Currently, most grid-connected converters for distributed energy storage employ two-level voltage source converters (VSCs), with a starting resistor connected to the AC side. During startup, the starting resistor is first connected to limit the startup current. Once the DC side voltage is established, the starting resistor is bypassed, and the system enters normal operation. The resistance value of this startup method is not adjustable. When the equivalent capacitance of the DC system changes, the starting resistor and capacitor become mismatched, leading to problems such as bridge arm overcurrent or excessively long startup times.

[0003] Existing traditional VSC devices and their AC-side startup resistors involve the following startup process: First, the IGBT is locked out and the startup resistor is connected to the system, gradually increasing the DC-side capacitor voltage to the peak AC-side line voltage. Then, the IGBT voltage is increased to its rated voltage via PWM control. Finally, the startup resistor is bypassed, completing the startup process. If the startup resistor is too small, an extremely high inrush current will occur within the uncontrolled rectifier; if the startup resistor is too large, the startup process will take a very long time. In particular, the equivalent capacitance of the DC system changes dynamically with the number and capacity of the converters, making it impossible to guarantee real-time matching between the startup resistor and the equivalent capacitance of the DC system. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a soft-start control method for a grid-connected converter for distributed energy storage. This method can quickly establish DC voltage without exceeding the limit of the bridge arm current, thus avoiding problems such as bridge arm overcurrent or excessively long start-up time.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A soft-start method for a grid-connected converter for distributed energy storage.

[0007] No starting resistor is connected to the AC side of the converter, and a thyristor anti-parallel diode module is installed in the upper three-phase bridge arm;

[0008] During startup, keep the fully controlled devices in the latched state, set the initial value of the thyristor firing angle α to 120°, and detect the DC side voltage U. dc Less than the DC side voltage threshold U set And the peak value of the bridge arm current I brig Less than the bridge arm current threshold Iset When the bridge arm current peak I brig is greater than or equal to the bridge arm current threshold I set , the trigger angle a is kept unchanged in the next control cycle.

[0009] When the bridge arm current peak I brig is greater than or equal to the bridge arm current threshold I set , the trigger angle a is kept unchanged in the next control cycle.

[0010] When the DC side voltage U dc reaches the DC side voltage threshold U set , the thyristor conduction signal is continuously given to make it equivalent to a diode, and the full-controlled device in the PWM control converter is used to make the DC side voltage rise to the rated voltage.

[0011] Preferably, the full-controlled device is a full-controlled power electronic switch tube S1-S6, specifically IGBT, IGCT, GCT, IEGT and GTO, which can actively control the conduction and turn-off current; the thyristor SCR1-SCR3 is a semi-controlled power electronic switch tube, which can accurately control the time of conduction current.

[0012] Preferably, the DC side voltage threshold Uset is the line voltage peak value of the three-phase alternating voltage.

[0013] Preferably, the bridge arm current threshold Iset is the peak value of the three-phase alternating side phase current.

[0014] The advantages and technical effects of the present application are:

[0015] The soft start method of the distributed energy storage grid-connected converter of the present application, when starting, the full-controlled power electronic switch tube S1-S6 is locked, and the initial trigger angle of the thyristor SCR1-SCR3 is set to 120°, and the trigger angle is gradually reduced during the starting process, so that the DC side voltage can be quickly established without exceeding the bridge arm current.

[0016] The soft start method of the distributed energy storage grid-connected converter of the present application can be used in the starting process without the need to install a starting resistor on the alternating side, saving land occupation and investment. The problem of bridge arm overcurrent or long starting time is avoided, and the converter operates in different control modes during starting and normal operation, so that the DC side voltage can be quickly established without exceeding the bridge arm current, and the shortcomings of the existing starting method that cannot balance the bridge arm overcurrent and starting speed are avoided.

[0017] The soft start method of the distributed energy storage grid-connected converter of the present application can be used in the starting process without the need to install a starting resistor on the alternating side, saving land occupation and investment. The problem of bridge arm overcurrent or long starting time is avoided, and the converter operates in different control modes during starting and normal operation, so that the DC side voltage can be quickly established without exceeding the bridge arm current, and the shortcomings of the existing starting method that cannot balance the bridge arm overcurrent and starting speed are avoided. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 A topology diagram of a traditional VSC device and its AC side starting resistor;

[0019] Figure 2 A topology diagram of a distributed energy storage grid-connected converter of the present application;

[0020] Figure 3 A soft start control method of a distributed energy storage grid-connected converter of the present application. DETAILED DESCRIPTION

[0021] In order to further understand the content, characteristics and effects of the present application, the following examples are given, and are described in detail below with reference to the accompanying drawings. It should be noted that the present examples are descriptive, not limiting, and cannot limit the protection scope of the present application.

[0022] A soft start method of a distributed energy storage grid-connected converter,

[0023] The converter AC side is not connected to the starting resistor, and a thyristor anti-parallel diode module is arranged in the upper bridge arm of the three-phase;

[0024] During starting, the full-controlled device is kept in the blocking state, the initial value of the thyristor trigger angle a is set to 120°, the DC side voltage U dc is detected, and the DC side voltage threshold U set is set to 400V, the bridge arm current peak I brig is detected, and the bridge arm current threshold I set is set to 20A;

[0025] When the bridge arm current peak I brig is greater than or equal to the bridge arm current threshold I set , the trigger angle a is kept unchanged in the next control period;

[0026] When the DC side voltage U dc reaches the DC side voltage threshold U set , the thyristor conduction signal is continuously given to make it equivalent to the diode, and the full-controlled device in the PWM controlled converter is used to make the DC side voltage rise to the rated voltage.

[0027] Preferably, the full-controlled device is a full-controlled power electronic switch tube S1-S6, specifically IGBT, IGCT, GCT, IEGT and GTO, which can actively control the conduction and turn-off current; the thyristor SCR1-SCR3 is a semi-controlled power electronic switch tube, which can accurately control the time of conduction current.

[0028] Preferably, the DC side voltage threshold Uset is the line voltage peak value of the three-phase AC voltage.

[0029] Preferably, the bridge arm current threshold Iset is the peak value of the three-phase AC phase current.

[0030] To more clearly describe the specific embodiments of the present invention, an example is provided below:

[0031] like Figure 2 As shown, the distributed energy storage grid-connected converter includes fully controlled power electronic switches S1-S6, thyristors SCR1-SCR3, and diodes D1-D9. S1-S6 are anti-parallel to D1-D6, and SCR1-SCR3 are anti-parallel to D6-D9. S1-S3 are placed on the upper arm of the three-phase bridge, and S4-S6 are placed on the lower arm of the three-phase bridge. The collectors of S1 and S3 are connected together to form a DC positive electrode, which is electrically connected to the positive electrode of the energy storage unit. The emitters of S4-S6 are connected together to form a DC negative electrode, which is electrically connected to the negative electrode of the energy storage unit. The cathodes of SCR1-SCR3 are connected to the emitters of S1-S3, and their anodes are connected to the collectors of S4-S6.

[0032] Figure 3 This diagram illustrates a soft-start control method for a grid-connected converter for distributed energy storage, provided in an embodiment of the present invention. Figure 3 As shown in the specific embodiment of the soft-start control method for distributed energy storage grid-connected converters provided by the present invention, during startup, the fully controlled devices S1 to S6 are kept in a locked state, and the initial firing angle α of thyristors SCR1 to SCR3 is set to 120°; the DC side voltage U is detected. dc Less than threshold U set And the peak current of the bridge arm I brig Less than threshold I set If so, the firing angle α will be gradually reduced in 1° intervals during the next control cycle; when the peak value of the bridge arm current I... brig Greater than or equal to threshold I set If the trigger angle α remains unchanged in the next control cycle, then the DC side voltage U... dc Reaching threshold U set At that time, a continuous conduction signal is given to the thyristor to make it equivalent to a diode. The fully controlled device in the converter is controlled by PWM to raise the DC side voltage to the rated voltage, and the soft start process is completed.

[0033] In a specific embodiment of the soft-start control method for a grid-connected converter for distributed energy storage provided by the present invention, the fully controlled power electronic switching transistors S1 to S6 can be IGBTs, IGCTs, GCTs, IEGTs, GTOs, etc., which can actively control the on and off currents; the thyristors are semi-controlled power electronic switching transistors, which can precisely control the timing of the on-current.

[0034] In the embodiment of the soft start control method of the distributed energy storage grid-connected converter provided by the application, the line voltage peak value of the three-phase alternating voltage is taken as the DC side voltage threshold U set ;

[0035] In the embodiment of the soft start control method of the distributed energy storage grid-connected converter provided by the application, the line voltage peak value of the three-phase alternating voltage is taken as the DC side voltage threshold U set .

[0036] In addition, other configurations and functions of the soft start control method of the distributed energy storage grid-connected converter in the embodiment of the application are known to those skilled in the art, and in order to reduce redundancy, they will not be described here.

[0037] Finally, the unfinished parts of the application all adopt mature products and mature technical means in the prior art.

[0038] It should be understood that, for those skilled in the art, the above description can be improved or changed, and all these improvements and changes shall belong to the protection scope of the appended claims of the application.

Claims

1. A soft start method of a distributed energy storage grid-connected converter, characterized in that: no starting resistor is connected to the AC side of the converter, and a thyristor anti-parallel diode module is arranged in the upper three-phase bridge arm; wherein the converter comprises fully-controlled power electronic switching tubes S1-S3 of the upper three-phase bridge arm, and thyristor SCR1-SCR3 anti-parallel diode modules, the cathodes of the thyristors SCR1-SCR3 are connected to the emitters of S1-S3 respectively, and the anodes are connected to the collectors of the fully-controlled power electronic switching tubes S4-S6 of the lower bridge arm respectively; At the start, keep the full-controlled power electronic switch S1-S6 in the blocking state, set the initial value of the thyristor trigger angle α as 120°, detect the DC side voltage U dc less than the DC side voltage threshold value U set , and the bridge arm current peak value I brig less than the bridge arm current threshold value I set , then the trigger angle α is gradually reduced by 1° in the next control period. When the bridge arm current peak I brig is greater than or equal to the bridge arm current threshold I set , the trigger angle a is kept unchanged in the next control period. When the DC side voltage U dc reaches the DC side voltage threshold U set , the thyristor conducting signal is continuously given to make it equivalent to a diode, and the DC side voltage is raised to the rated voltage by using PWM control of the full-controlled devices in the inverter. 2.The soft start method of a distributed energy storage grid-connected converter according to claim 1, characterized in that: the fully-controlled devices are fully-controlled power electronic switching tubes S1-S6, specifically IGBT, IGCT, GCT, IEGT and GTO, which can actively control the conduction and turn-off current; the thyristors SCR1-SCR3 are semi-controlled power electronic switching tubes, which can accurately control the timing of the conduction current. 3.The soft start method of a distributed energy storage grid-connected converter according to claim 1, characterized in that: the DC side voltage threshold Uset is the line voltage peak value of the three-phase AC voltage.

4. The soft start method of a distributed energy storage grid-connected converter according to claim 1, characterized in that: the bridge arm current threshold Iset is the phase current peak value of the three-phase AC side.

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