Subsynchronous oscillation suppression system

Abstract

A subsynchronous oscillation suppression system disclosed by the present invention comprises a coupling transformer and a subsynchronous oscillation suppressor, a first DC power supply is connected with a power grid through a new energy power generation device, and a connection line of the new energy power generation device and the power grid is connected in series with a secondary side of the coupling transformer. The primary side of the coupling transformer is connected with the output end of the subsynchronous oscillation suppressor; the subsynchronous oscillation suppressor detects the output current of the new energy power generation equipment and judges whether subsynchronous oscillation occurs or not, if the subsynchronous oscillation occurs, the frequency of current oscillation is detected, and based on the frequency band, virtual negative inductive reactance is constructed through the coupling transformer to suppress the subsynchronous oscillation of the current; the method has the advantage that the current subsynchronous oscillation condition of new energy grid-connected power generation equipment such as a fan converter and a photovoltaic inverter can be inhibited.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of subsynchronous oscillation suppression, in particular to a subsynchronous oscillation suppression system. BACKGROUND

[0002] At present, in order to cope with global warming and the depletion of fossil energy, low-carbon energy such as wind, light, storage, electricity and hydrogen will become more and more popular. However, with the popularization of low-carbon energy, the power electronics of the power distribution network will also become higher and higher. The current commonly used wind turbine converter, photovoltaic inverter and other new energy grid-connected power generation equipment adopt LC or LCL filter on the grid side to reduce the output switching frequency level ripple current of the wind turbine converter, photovoltaic inverter and other new energy grid-connected power generation equipment.

[0003] However, at present, most grid-connected inverters adopt control strategies based on the DQ synchronous rotating coordinate system. When dealing with weak power grids, the system may introduce subsynchronous oscillation. The paper "Analysis and Phase-locked Loop Parameter Optimization Design of Direct-driven Wind Farm Subsynchronous Oscillation Based on Sequence Impedance" (Proceedings of the Chinese Society of Electrical Engineering, 2017, 37 (23)) discloses a method for optimizing the parameters of the phase-locked loop to suppress the subsynchronous oscillation of the grid-connected inverter system. However, this scheme can only reduce the probability of subsynchronous oscillation and cannot completely suppress the subsynchronous oscillation of the grid-connected inverter system. SUMMARY

[0004] The technical problem to be solved by the present application is how to suppress the subsynchronous current oscillation of the wind turbine converter, photovoltaic inverter and other new energy grid-connected power generation equipment.

[0005] The present application solves the above technical problems by the following technical means: a subsynchronous oscillation suppression system, comprising a coupling transformer and a subsynchronous oscillation suppressor, a first direct current power supply is connected with the grid through a new energy power generation equipment, a secondary side of the coupling transformer is connected in series on the connection line between the new energy power generation equipment and the grid, a primary side of the coupling transformer is connected with an output end of the subsynchronous oscillation suppressor, and a second direct current power supply supplies power to the subsynchronous oscillation suppressor; a controller of the subsynchronous oscillation suppressor detects the output current of the new energy power generation equipment, judges whether there is subsynchronous oscillation, if there is subsynchronous oscillation, detects the frequency of the current subsynchronous oscillation, and constructs a virtual negative inductance through the coupling transformer in the frequency band to suppress the current subsynchronous oscillation.

[0006] The present application sets a coupling transformer on the connection line between the new energy power generation equipment and the grid. When the controller of the subsynchronous oscillation suppressor detects subsynchronous oscillation, a virtual negative inductance is constructed through the coupling transformer to suppress the current subsynchronous oscillation. The control logic of this scheme is simple. When subsynchronous oscillation needs to be suppressed, a coupling transformer and a subsynchronous oscillation suppressor are set on the corresponding line, which is not limited to a single new energy power generation equipment.

[0007] Further, the controller of the subsynchronous oscillation suppressor detects the output current of the new energy power generation device, judges whether the subsynchronous oscillation occurs, and if the subsynchronous oscillation occurs, detects the frequency of the current subsynchronous oscillation, comprising: The controller of the subsynchronous oscillation suppressor collects the current at the output end of the new energy power generation device, performs frequency spectrum analysis, and when the current at a certain subsynchronous frequency band exceeds a threshold value, it is considered that there is a subsynchronous oscillation at the subsynchronous frequency band.

[0008] Further, the virtual negative inductance is constructed by the coupling transformer to suppress the current oscillation, comprising: The controller of the subsynchronous oscillation suppressor performs frequency spectrum analysis on the harmonic current of the new energy power generation device at a certain frequency band, and when the harmonic current is greater than a threshold value, the controller of the subsynchronous oscillation suppressor multiplies the difference between the target value of the amplitude of the subsynchronous current oscillation and the amplitude of the subsynchronous oscillation current output by the new energy power generation device and the output current of the new energy power generation device after the first and second regulators to obtain the output voltage command of the secondary side of the coupling transformer. After the difference between the output voltage command of the secondary side of the coupling transformer and the actual voltage of the secondary side of the coupling transformer is subtracted and passed through the third regulator, the modulation voltage command of the H-bridge of the primary side is obtained. Then, the subsynchronous oscillation suppressor sends corresponding driving signals to the switches of the H-bridge of the primary side according to the modulation voltage command of the H-bridge of the primary side.

[0009] Further, the virtual negative inductance is constructed by the coupling transformer to suppress the current oscillation, comprising: The controller of the subsynchronous oscillation suppressor performs frequency spectrum analysis on the harmonic current of the new energy power generation device at a certain frequency band, and when the harmonic current is greater than a threshold value, the controller of the subsynchronous oscillation suppressor multiplies the difference between the target value of the amplitude of the subsynchronous current oscillation and the amplitude of the subsynchronous oscillation current output by the new energy power generation device and the output current of the new energy power generation device after the first and second regulators to obtain the output voltage command of the secondary side of the coupling transformer. After the difference between the output voltage command of the secondary side of the coupling transformer and the actual voltage of the secondary side of the coupling transformer is subtracted and passed through the fourth regulator, the modulation voltage command of the H-bridge of the primary side is obtained. Then, the subsynchronous oscillation suppressor sends corresponding driving signals to the switches of the H-bridge of the primary side according to the modulation voltage command of the H-bridge of the primary side.

[0010] Further, the transfer function of the second regulator is , is a complex variable, is a fundamental frequency, is a frequency coefficient.

[0011] Further, the first regulator is a P regulator or a PI regulator.

[0012] Further, the third regulator is a P regulator, a PI regulator, a PR regulator or a PIR regulator.

[0013] Further, the fourth regulator and the fifth regulator are P regulators, PI regulators, PR regulators or PIR regulators.

[0014] Further, the subsynchronous oscillation suppression system further comprises a bypass switch, which is connected in parallel with the secondary side of the coupling transformer, and when the controller of the subsynchronous oscillation suppressor detects that the new energy power generation device does not have subsynchronous oscillation, the subsynchronous oscillation suppressor is bypassed by closing the bypass switch.

[0015] Further, the subsynchronous oscillation suppression system is two-phase or three-phase, and when the subsynchronous oscillation suppression system is two-phase, the coupling transformer and the corresponding subsynchronous oscillation suppressor are arranged in any one of the two phases, and when the subsynchronous oscillation suppression system is three-phase, the coupling transformer and the corresponding subsynchronous oscillation suppressor are arranged in each phase.

[0016] Further, the first direct current power supply and the new energy power generation device have one or more groups of parallel connection, and the parallel output end is connected with the secondary side of the coupling transformer in series on the connection line of the power grid.

[0017] Further, the new energy power generation device is a fan converter or a photovoltaic inverter.

[0018] The advantages of the present application are that: (1) The present application sets the coupling transformer on the connection line of the new energy power generation device and the power grid, constructs a virtual negative inductance to suppress the current subsynchronous oscillation through the coupling transformer when subsynchronous oscillation is detected, and the control logic of the scheme is simple, and the coupling transformer and the subsynchronous oscillation suppressor are arranged on the corresponding line when the subsynchronous oscillation needs to be suppressed, which is not limited to a single new energy power generation device.

[0019] (2) The present application applies a high-pass filter to simulate a low-frequency negative inductance when there is subsynchronous oscillation, which can suppress low-frequency subsynchronous oscillation and avoid affecting the LC filter parameters of the middle and high frequency bands.

[0020] (3) The present application bypasses the subsynchronous oscillation suppressor through the bypass switch when there is no subsynchronous oscillation, which avoids the interference of the subsynchronous oscillation suppressor on the line during normal operation of the circuit. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The principle block diagram of the subsynchronous oscillation suppression system disclosed in Embodiment 1 of the present application is shown in the figure; Figure 2A circuit schematic of a subsynchronous oscillation suppression system disclosed in Embodiment 1 of the present application; Figure 3 A schematic diagram of a generation mode of an inverter reference voltage in a subsynchronous oscillation suppression system disclosed in Embodiment 1 of the present application; Figure 4 A schematic diagram of another generation mode of an inverter reference voltage in a subsynchronous oscillation suppression system disclosed in Embodiment 1 of the present application; Figure 5 A circuit schematic of a subsynchronous oscillation suppression system disclosed in Embodiment 2 of the present application; Figure 6 A circuit schematic of a subsynchronous oscillation suppression system disclosed in Embodiment 3 of the present application; Figure 7 A circuit schematic of a subsynchronous oscillation suppression system disclosed in Embodiment 4 of the present application. DETAILED DESCRIPTION

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will combine the embodiments of the present application to make a clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0023] As shown in Figure 1 Embodiment 1 of the present application provides a subsynchronous oscillation suppression system, which comprises a coupling transformer 4 and a subsynchronous oscillation suppressor 5. A first direct current power supply 1 is connected with a power grid 3 through a new energy power generation device 2. The connection line of the new energy power generation device 2 and the power grid 3 is connected in series with a secondary side of the coupling transformer 4. A primary side of the coupling transformer 4 is connected with an output end of the subsynchronous oscillation suppressor 5. A second direct current power supply 6 supplies power to the subsynchronous oscillation suppressor 5. In the embodiment, the new energy power generation device 2 is a fan converter or a photovoltaic inverter. The principle of the present application is that a controller of the subsynchronous oscillation suppressor 5 collects a current at an output end of the new energy power generation device 2, then performs frequency spectrum analysis, considers that there is a subsynchronous oscillation in a certain low frequency band when the current in the frequency band exceeds a threshold value, detects a frequency of the current oscillation, and constructs a virtual negative inductance through the coupling transformer 4 to suppress the current subsynchronous oscillation based on the frequency band. The following will introduce the method process of suppressing the subsynchronous oscillation in detail. As shown in Figure 2As shown, when the above principle of suppressing subsynchronous oscillation is applied to a single new energy power generation device 2 and the line is two-phase, a coupling transformer 4 and a corresponding subsynchronous oscillation suppressor 5 are arranged in any one of the two phases. The controller of the subsynchronous oscillation suppressor 5 analyzes the subsynchronous harmonic current of the new energy power generation device 2 at the subsynchronous frequency band through spectrum analysis. If the subsynchronous harmonic current is greater than a threshold value, the controller of the subsynchronous oscillation suppressor 5 will control the inverter voltage of the transformer primary side H-bridge, so that the secondary side voltage of the coupling transformer 4 is approximately equivalent to a voltage drop on a negative inductance, thereby indirectly reducing the grid-side impedance of the input port of the single new energy power generation device 2 to suppress the subsynchronous oscillation of the system.

[0024] The controller of the above subsynchronous oscillation suppressor 5 controls the inverter voltage of the transformer primary side H-bridge, so that the secondary side voltage of the coupling transformer 4 is approximately equivalent to a voltage drop on a negative inductance, thereby indirectly reducing the grid-side impedance of the input port of the single new energy power generation device 2 to suppress the subsynchronous oscillation of the system. This is achieved in two ways, one of which is as shown in Figure 3 As shown, the controller of the subsynchronous oscillation suppressor 5 multiplies the difference between the subsynchronous current oscillation amplitude target value and the amplitude of the subsynchronous oscillation current output by the new energy power generation device 2, and the new energy power generation device 2 output flow after passing through the first and second adjusters to obtain the coupling transformer 4 secondary side voltage output instruction. The coupling transformer 4 secondary side voltage output instruction is subtracted from the actual voltage of the coupling transformer 4 secondary side, and then passed through the third adjuster to obtain the modulation voltage instruction of the primary side H-bridge of the subsynchronous oscillation suppressor 5. Then, the subsynchronous oscillation suppressor sends corresponding drive signals to each switch tube of the primary side H-bridge of the subsynchronous oscillation suppressor 5 according to the modulation voltage instruction of the primary side H-bridge of the subsynchronous oscillation suppressor 5.

[0025] The transfer function of the second adjuster can be , is the fundamental frequency, is the frequency coefficient, is a complex variable. Because subsynchronous oscillation is generally located at low frequency, a high-pass filter is used to simulate the negative inductance in the low frequency region. First, it can reduce the interference caused by differentiation. Second, it reduces the impact of high frequency on the parameters of the LC filter.

[0026] The other way is as shown in Figure 4As shown, the controller of the subsynchronous oscillation suppressor 5 obtains the difference between the subsynchronous current oscillation amplitude target value and the subsynchronous oscillation current amplitude output by the new energy power generation device 2, multiplies the new energy power generation device 2 output flow after passing through the first regulator and the second regulator, respectively, to obtain the coupling transformer 4 secondary side voltage output instruction; the coupling transformer 4 secondary side voltage output instruction is subtracted from the coupling transformer 4 secondary side actual voltage, and then passes through the fourth regulator to obtain the coupling transformer 4 primary side current instruction, the coupling transformer 4 primary side current instruction is subtracted from the coupling transformer 4 primary side actual current, and then passes through the fifth regulator to obtain the modulation voltage instruction of the primary side H-bridge of the subsynchronous oscillation suppressor 5, and then the subsynchronous oscillation suppressor sends corresponding driving signals to each switch tube of the primary side H-bridge of the subsynchronous oscillation suppressor 5 according to the modulation voltage instruction of the primary side H-bridge of the subsynchronous oscillation suppressor 5. The fourth and fifth regulators can be P regulators, PI regulators, PR regulators or PIR regulators.

[0027] In the above two implementation manners, the first regulator can be a P regulator or a PI regulator; and the third regulator can be a P regulator, a PI regulator, a PR regulator or a PIR regulator.

[0028] It should be noted that the coupling transformer 4 of the present application is a transformer, and its specific structure is not particularly limited. The circuit principle structure of the subsynchronous oscillation suppressor 5 of the present application is not particularly limited, as long as the voltage output obtained after the multiplication of the first regulator and the second regulator can be achieved, and the specific circuit structure can adopt the structure in Figure 2 , which will not be repeated here, and other circuit principle structures such as half-bridge inverter, Heric circuit and H5 inverter circuit can also be adopted.

[0029] Through the above technical scheme, the coupling transformer 4 is arranged on the connection line between the new energy power generation device 2 and the power grid 3, a virtual negative inductance is constructed by the coupling transformer 4 to suppress current oscillation when oscillation is detected, and the control logic of the scheme is simple, the coupling transformer 4 and the subsynchronous oscillation suppressor 5 are arranged on the corresponding line when the subsynchronous oscillation needs to be suppressed, and the present application is not limited to a single new energy power generation device 2.

[0030] Embodiment 2 As shown in Figure 5As shown, Embodiment 2 of the present invention differs from Embodiment 1 in that the subsynchronous oscillation suppression system further includes a bypass switch. The bypass switch is connected in parallel with the secondary side of the coupling transformer 4. When no oscillation is detected in the circuit, the bypass switch is closed to bypass the subsynchronous oscillation suppressor 5. This control method allows for timely disconnection of the subsynchronous oscillation suppressor 5 when no oscillation is detected, preventing the negative inductance of the subsynchronous oscillation suppressor 5 from affecting the circuit during normal operation. Conversely, when oscillation is detected, the bypass switch is opened, ensuring that the subsynchronous oscillation suppressor 5 is promptly connected to the circuit, effectively suppressing subsynchronous oscillations, thus achieving on-demand setting.

[0031] Example 3 like Figure 6 As shown, the difference between Embodiment 3 and Embodiment 1 is that the subsynchronous oscillation suppression device is three-phase, with a coupling transformer 4 and a corresponding subsynchronous oscillation suppressor 5 installed in each phase. This arrangement ensures that subsynchronous oscillations can be detected and suppressed in each phase, guaranteeing safe and stable circuit operation.

[0032] Example 4 like Figure 7 As shown, Embodiment 4 of the present invention differs from Embodiment 1 in that multiple sets of the first DC power supply 1 and the new energy power generation equipment 2 are connected in parallel, and the secondary side of the coupling transformer 4 is connected in series on the connection line between the parallel output terminal and the power grid 3. In this embodiment, two sets of new energy power generation equipment 2 are connected in parallel, but in practical applications, more sets of new energy power generation equipment 2 can be connected in parallel. Thus, when multiple wind turbine converters, photovoltaic inverters, and other new energy grid-connected power generation equipment are connected in parallel, or under low short-circuit ratios, at the grid connection common point of the new energy equipment, subsynchronous oscillations can be effectively suppressed by the subsynchronous oscillation suppressor 5 and the coupling transformer 4.

[0033] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A subsynchronous oscillation suppression system, characterized by, The first DC power supply is connected with the power grid through the new energy power generation equipment, a secondary side of a coupling transformer is connected in series on a connection line of the new energy power generation equipment and the power grid, a primary side of the coupling transformer is connected with an output end of a subsynchronous oscillation suppressor, and a second DC power supply supplies power to the subsynchronous oscillation suppressor.

2. A system for subsynchronous oscillation suppression according to claim 1, wherein, The controller of the subsynchronous oscillation suppressor detects the output current of the new energy power generation equipment, judges whether the subsynchronous oscillation occurs, and if the subsynchronous oscillation occurs, detects the frequency of the current subsynchronous oscillation, and includes: The controller of the subsynchronous oscillation suppressor collects the current and voltage at the output end of the new energy power generation equipment, performs frequency spectrum analysis, and determines that the subsynchronous oscillation occurs at a certain frequency band when the current at the frequency band exceeds a threshold value.

3. A system for subsynchronous oscillation suppression according to claim 2, wherein, The coupling transformer constructs a virtual negative inductance to suppress the current oscillation, including: The controller of the subsynchronous oscillation suppressor performs frequency spectrum analysis on the harmonic current of the new energy power generation equipment at a certain frequency band, and if the harmonic current is greater than a threshold value, the controller of the subsynchronous oscillation suppressor multiplies the difference between a target value of the amplitude of the subsynchronous current oscillation and the amplitude of the subsynchronous oscillation current output by the new energy power generation equipment and the output current of the new energy power generation equipment after the first and second regulators to obtain a voltage output instruction of the secondary side of the coupling transformer.

4. The system of claim 2, wherein, The coupling transformer constructs a virtual negative inductance to suppress the current oscillation, including: The controller of the subsynchronous oscillation suppressor performs frequency spectrum analysis on the harmonic current of the new energy power generation equipment at a certain frequency band, and if the harmonic current is greater than a threshold value, the controller of the subsynchronous oscillation suppressor multiplies the difference between a target value of the amplitude of the subsynchronous current oscillation and the amplitude of the subsynchronous oscillation current output by the new energy power generation equipment and the output current of the new energy power generation equipment after the first and second regulators to obtain a voltage output instruction of the secondary side of the coupling transformer.

5. A system for subsynchronous oscillation suppression according to claim 3 or 4, c h a r a c t e r i z e d b y that The transfer function of the second regulator is , is a complex variable, is the fundamental frequency, is the frequency coefficient.

6. A system for subsynchronous oscillation suppression according to claim 3 or 4, c h a r a c t e r i z e d b y that The first regulator is a P regulator or a PI regulator.

7. The system of claim 3, wherein the system is configured to: The third regulator is a P regulator, a PI regulator, a PR regulator or a PIR regulator.

8. The system for subsynchronous oscillation suppression of claim 4, wherein, The fourth regulator and the fifth regulator are P regulators, PI regulators, PR regulators or PIR regulators.

9. The system for subsynchronous oscillation suppression of claim 1, wherein, The bypass switch is connected in parallel with the secondary side of the coupling transformer, and when the controller of the subsynchronous oscillation inhibitor detects that the new energy power generation device does not have subsynchronous oscillation, the subsynchronous oscillation inhibitor is bypassed by closing the bypass switch.

10. The system for subsynchronous oscillation suppression of claim 1, wherein, The subsynchronous oscillation inhibition system is two-phase or three-phase, when the subsynchronous oscillation inhibition system is two-phase, the coupling transformer and the corresponding subsynchronous oscillation inhibitor are arranged in any one of the two phases, and when the subsynchronous oscillation inhibition system is three-phase, the coupling transformer and the corresponding subsynchronous oscillation inhibitor are arranged in each phase.

11. The system for subsynchronous oscillation suppression of claim 1, wherein, The first direct-current power supply and the new energy power generation device have one or more groups of parallel connection, and the parallel output end is connected with the secondary side of the coupling transformer in series on the connection line of the power grid.

12. The system for subsynchronous oscillation suppression of claim 1, wherein, The new energy power generation device is a fan converter or a photovoltaic inverter.

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