A subsynchronous oscillation suppression system

Abstract

The application discloses a kind of subsynchronous oscillation suppression systems, including coupling transformer and subsynchronous oscillation suppressor, first DC power supply is connected with power grid through new energy power generation equipment, new energy power generation equipment and the connecting line of power grid are connected with the secondary side of coupling transformer in series, the primary side of coupling transformer is connected with the output end of subsynchronous oscillation suppressor;Subsynchronous oscillation suppressor detects the output current of new energy power generation equipment, judge whether there is subsynchronous oscillation, if there is subsynchronous oscillation, the frequency of current oscillation is detected, and based on the frequency band, virtual negative inductance is constructed by coupling transformer to suppress current subsynchronous oscillation;The application has the advantages that: it can suppress the current subsynchronous oscillation of wind turbine converter, photovoltaic inverter and other new energy grid-connected power generation equipment.

Description

Technical Field

[0001] This invention relates to the field of subsynchronous oscillation suppression, and more specifically to a subsynchronous oscillation suppression system. Background Technology

[0002] Currently, to address global warming and the depletion of fossil fuels, low-carbon energy sources such as wind, solar, energy storage, electricity, and hydrogen are becoming increasingly prevalent. However, with the widespread adoption of low-carbon energy, the power distribution network will also become increasingly electronic. Currently, commonly used grid-connected power generation equipment such as wind turbine converters and photovoltaic inverters employs LC or LCL filters on the grid side to reduce the ripple current at the output switching frequency level of these devices.

[0003] However, currently, grid-connected inverters mostly adopt control strategies based on the DQ synchronous rotating coordinate system. When dealing with weak grids, this may introduce subsynchronous oscillations in the system. The paper "Analysis of Subsynchronous Oscillations in Direct-Drive Wind Farms Based on Sequence Impedance and Optimization Design of Phase-Locked Loop Parameters" (Proceedings of the CSEE, 2017, 37(23)) discloses a method for optimizing phase-locked loop parameters to suppress subsynchronous oscillations in grid-connected inverter systems. However, this scheme can only reduce the probability of subsynchronous oscillations and cannot completely suppress them. Summary of the Invention

[0004] The technical problem to be solved by this invention is how to suppress the subsynchronous current oscillation of new energy grid-connected power generation equipment such as wind turbine converters and photovoltaic inverters.

[0005] The present invention solves the above-mentioned technical problems through the following technical means: a subsynchronous oscillation suppression system, comprising a coupling transformer and a subsynchronous oscillation suppressor, wherein a first DC power supply is connected to the power grid via a new energy power generation device, the secondary side of the coupling transformer is connected in series on the connection line between the new energy power generation device and the power grid, the primary side of the coupling transformer is connected to the output terminal of the subsynchronous oscillation suppressor, and a second DC power supply supplies power to the subsynchronous oscillation suppressor; the controller of the subsynchronous oscillation suppressor detects the output current of the new energy power generation device to determine whether subsynchronous oscillation has occurred, and if subsynchronous oscillation has occurred, the frequency of the current subsynchronous oscillation is detected, and a virtual negative inductance is constructed through the coupling transformer within this frequency range to suppress the current subsynchronous oscillation.

[0006] This invention involves installing a coupling transformer on the connection line between the new energy power generation equipment and the power 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. Furthermore, the control logic of this scheme is simple. When it is necessary to suppress subsynchronous oscillation, a coupling transformer and a subsynchronous oscillation suppressor can be installed on the corresponding line, which is not limited to a single new energy power generation equipment.

[0007] Furthermore, the controller of the subsynchronous oscillation suppressor detects the output current of the new energy power generation equipment to determine whether subsynchronous oscillation has occurred. If subsynchronous oscillation occurs, the frequency of the current subsynchronous oscillation is detected, including:

[0008] The controller of the subsynchronous oscillation suppressor collects the current at the output end of the new energy power generation equipment and performs spectrum analysis. When the current in a certain subsynchronous frequency band exceeds the threshold, it is considered that there is subsynchronous oscillation in that subsynchronous frequency band.

[0009] Furthermore, the method of constructing a virtual negative inductance through a coupling transformer to suppress current oscillations includes:

[0010] The controller of the subsynchronous oscillation suppressor analyzes the spectrum and determines if the harmonic current of the new energy power generation equipment exceeds a threshold at a certain frequency range. It then multiplies the difference between the target value of the subsynchronous current oscillation amplitude and the amplitude of the subsynchronous oscillation current output by the new energy power generation equipment, along with the output current of the new energy power generation equipment, through the first and second regulators respectively, to obtain the output command for the secondary voltage of the coupling transformer. The difference between the output command and the actual voltage of the secondary side of the coupling transformer is then passed through the third regulator to obtain the modulation voltage command for the primary H-bridge. Based on the modulation voltage command of the primary H-bridge, the subsynchronous oscillation suppressor sends corresponding drive signals to each switch of the primary H-bridge.

[0011] Furthermore, the method of constructing a virtual negative inductance through a coupling transformer to suppress current oscillations includes:

[0012] The controller of the subsynchronous oscillation suppressor analyzes the frequency spectrum to determine if the harmonic current of the new energy power generation equipment exceeds a threshold at a certain frequency range. The controller then multiplies the target value of the subsynchronous current oscillation amplitude with the difference between the output subsynchronous oscillation current amplitude of the new energy power generation equipment and the output current of the new energy power generation equipment through the first and second regulators respectively to obtain the secondary voltage output command of the coupling transformer. The difference between the secondary voltage output command of the coupling transformer and the actual secondary voltage of the coupling transformer is then passed through the fourth regulator to obtain the primary current command of the coupling transformer. The difference between the primary current command of the coupling transformer and the actual primary current of the coupling transformer is then passed through the fifth regulator to obtain the modulation voltage command of the primary H-bridge. Finally, the subsynchronous oscillation suppressor sends corresponding drive signals to each switch of the primary H-bridge according to the modulation voltage command of the primary H-bridge.

[0013] Furthermore, the transfer function of the second regulator is , For complex variables, The fundamental frequency, For frequency coefficients.

[0014] Furthermore, the first regulator is a P regulator or a PI regulator.

[0015] Furthermore, the third regulator is a P regulator, PI regulator, PR regulator, or PIR regulator.

[0016] Furthermore, the fourth and fifth regulators are P regulators, PI regulators, PR regulators, or PIR regulators.

[0017] Furthermore, the subsynchronous oscillation suppression system also includes a bypass switch, which is connected in parallel with the secondary side of the coupling transformer. When the controller of the subsynchronous oscillation suppressor detects that there is no subsynchronous oscillation in the new energy power generation equipment, it bypasses the subsynchronous oscillation suppressor by closing the bypass switch.

[0018] Furthermore, the subsynchronous oscillation suppression system is two-phase or three-phase. When the subsynchronous oscillation suppression system is two-phase, a coupling transformer and a corresponding subsynchronous oscillation suppressor are provided in any one of the two phases. When the subsynchronous oscillation suppression system is three-phase, a coupling transformer and a corresponding subsynchronous oscillation suppressor are provided in each phase.

[0019] Furthermore, the first DC power supply and the new energy power generation equipment are connected in parallel in one or more groups, and the secondary side of the coupling transformer is connected in series on the connection line between the parallel output terminal and the power grid.

[0020] Furthermore, the new energy power generation equipment is a wind turbine converter or a photovoltaic inverter.

[0021] The advantages of this invention are:

[0022] (1) The present invention sets up a coupling transformer on the connection line between the new energy power generation equipment and the power grid. When subsynchronous oscillation is detected, a virtual negative inductance is constructed through the coupling transformer to suppress the current subsynchronous oscillation. Moreover, the control logic of this scheme is simple. When it is necessary to suppress subsynchronous oscillation, a coupling transformer and a subsynchronous oscillation suppressor can be set on the corresponding line. It is not limited to a single new energy power generation equipment.

[0023] (2) In the case of subsynchronous oscillation, the present invention uses a high-pass filter to simulate the negative inductance in the low-frequency band, which can suppress the subsynchronous oscillation in the low-frequency band and avoid the influence on the LC filter parameters in the mid-to-high frequency band.

[0024] (3) In the absence of subsynchronous oscillation, the present invention bypasses the subsynchronous oscillation suppressor by bypassing the circuit through a bypass switch, thereby avoiding interference from the subsynchronous oscillation suppressor to the circuit when the circuit is running normally. Attached Figure Description

[0025] Figure 1This is a block diagram illustrating the principle of a subsynchronous oscillation suppression system disclosed in Embodiment 1 of the present invention;

[0026] Figure 2 This is a circuit diagram of a subsynchronous oscillation suppression system disclosed in Embodiment 1 of the present invention;

[0027] Figure 3 This is a schematic diagram of a method for generating the inverter reference voltage in a subsynchronous oscillation suppression system disclosed in Embodiment 1 of the present invention;

[0028] Figure 4 This is a schematic diagram of another method for generating the inverter reference voltage in a subsynchronous oscillation suppression system disclosed in Embodiment 1 of the present invention;

[0029] Figure 5 This is a circuit diagram of a subsynchronous oscillation suppression system disclosed in Embodiment 2 of the present invention;

[0030] Figure 6 This is a circuit diagram of a subsynchronous oscillation suppression system disclosed in Embodiment 3 of the present invention;

[0031] Figure 7 This is a circuit diagram of a subsynchronous oscillation suppression system disclosed in Embodiment 4 of the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] like Figure 1As shown, Embodiment 1 of the present invention provides a subsynchronous oscillation suppression system, including a coupling transformer 4 and a subsynchronous oscillation suppressor 5. A first DC power supply 1 is connected to the power grid 3 via a new energy power generation device 2. The secondary side of the coupling transformer 4 is connected in series on the connection line between the new energy power generation device 2 and the power grid 3. The primary side of the coupling transformer 4 is connected to the output terminal of the subsynchronous oscillation suppressor 5. A second DC power supply 6 supplies power to the subsynchronous oscillation suppressor 5. In this embodiment, the new energy power generation device 2 is a wind turbine converter or a photovoltaic inverter. The principle of the present invention is that the controller of the subsynchronous oscillation suppressor 5 collects the current at the output terminal of the new energy power generation device 2 and performs spectrum analysis. When the current in a certain low-frequency band exceeds a threshold, it is considered that there is subsynchronous oscillation in that frequency band. The frequency of the current oscillation is detected, and based on that frequency band, a virtual negative inductance is constructed through the coupling transformer 4 to suppress the current subsynchronous oscillation. The method and process of suppressing subsynchronous oscillation are described in detail below:

[0034] like Figure 2 As 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 installed in either of the two phases. The controller of the subsynchronous oscillation suppressor 5, through spectrum analysis, determines that if the subsynchronous harmonic current of the new energy power generation device 2 in the subsynchronous frequency band exceeds a threshold, then the controller of the subsynchronous oscillation suppressor 5 will control the inverter voltage of the H-bridge on the primary side of the transformer, making the secondary voltage of the coupling transformer 4 approximately equivalent to a negative inductive voltage drop. This indirectly reduces the grid-side impedance of the input port of the single new energy power generation device 2, thereby suppressing the subsynchronous oscillation of the system.

[0035] The controller of the aforementioned subsynchronous oscillation suppressor 5 controls the inverter voltage of the H-bridge on the primary side of the transformer, making the secondary voltage of the coupling transformer 4 approximately equivalent to a negative inductive voltage drop. This indirectly reduces the grid-side impedance of the input port of a single new energy power generation device 2, thereby suppressing the subsynchronous oscillation of the system. This is achieved through the following two methods, one of which is as follows: Figure 3 As shown, the controller of the subsynchronous oscillation suppressor 5 multiplies the difference between the target value of the subsynchronous current oscillation amplitude and the output subsynchronous oscillation current amplitude of the new energy power generation equipment 2, and the output current of the new energy power generation equipment 2, after passing through the first regulator and the second regulator respectively, to obtain the secondary voltage output command of the coupling transformer 4. The difference between the secondary voltage output command of the coupling transformer 4 and the actual secondary voltage of the coupling transformer 4 is passed through the third regulator to obtain the modulation voltage command of the primary H-bridge of the subsynchronous oscillation suppressor 5. Then, according to the modulation voltage command of the primary H-bridge of the subsynchronous oscillation suppressor 5, the subsynchronous oscillation suppressor sends corresponding drive signals to each switch of the primary H-bridge of the subsynchronous oscillation suppressor 5.

[0036] The transfer function of the second regulator can be , The fundamental frequency, For frequency coefficients, The variable is a complex variable. Since subsynchronous oscillations are generally located at low frequencies, a high-pass filter is used to simulate the negative inductive reactance in the low-frequency region. This reduces interference from the derivative and minimizes the impact of high-frequency bands on the LC filter parameters.

[0037] Another way is as follows Figure 4 As shown, the controller of the subsynchronous oscillation suppressor 5 multiplies the difference between the target value of the subsynchronous current oscillation amplitude and the amplitude of the subsynchronous oscillation current output by the new energy power generation equipment 2, and the output current of the new energy power generation equipment 2, after passing through the first regulator and the second regulator respectively, to obtain the secondary voltage output command of the coupling transformer 4. The difference between the secondary voltage output command of the coupling transformer 4 and the actual secondary voltage of the coupling transformer 4 is passed through the fourth regulator to obtain the primary current command of the coupling transformer 4. The difference between the primary current command of the coupling transformer 4 and the actual primary current of the coupling transformer 4 is then passed through the fifth regulator to obtain the modulation voltage command of the primary H-bridge of the subsynchronous oscillation suppressor 5. Then, according to the modulation voltage command of the primary H-bridge of the subsynchronous oscillation suppressor 5, the subsynchronous oscillation suppressor sends corresponding drive signals to each switch of the primary H-bridge of the subsynchronous oscillation suppressor 5. The fourth and fifth regulators can be P regulators, PI regulators, PR regulators, or PIR regulators.

[0038] In the two implementation methods above, the first regulator can be a P regulator or a PI regulator; the third regulator can be a P regulator, a PI regulator, a PR regulator, or a PIR regulator.

[0039] It should be noted that the coupling transformer 4 of this invention is simply a transformer, and its specific structure is not particularly limited. The circuit principle and structure of the subsynchronous oscillation suppressor 5 of this invention are not particularly limited, as long as it can achieve the voltage output obtained by multiplying the first and second regulators. The specific circuit structure can adopt... Figure 2 The structure is not described in detail here, but other circuit principles and structures can also be used, such as half-bridge inverter, Heric circuit and H5 inverter circuit, etc.

[0040] Through the above technical solution, the present invention sets up a coupling transformer 4 on the connection line between the new energy power generation equipment 2 and the power grid 3. When oscillation is detected, a virtual negative inductance is constructed through the coupling transformer 4 to suppress current oscillation. Moreover, the control logic of this solution is simple. When it is necessary to suppress subsynchronous oscillation, the coupling transformer 4 and the subsynchronous oscillation suppressor 5 can be set on the corresponding line. It is not limited to a single new energy power generation equipment 2.

[0041] Example 2

[0042] like 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.

[0043] Example 3

[0044] 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.

[0045] Example 4

[0046] 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.

[0047] 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 in that, The system includes a coupling transformer and a subsynchronous oscillation suppressor. A first DC power supply is connected to the power grid via a new energy power generation device. The secondary side of the coupling transformer is connected in series on the connection line between the new energy power generation device and the power grid. The primary side of the coupling transformer is connected to the output terminal of the subsynchronous oscillation suppressor. A second DC power supply powers the subsynchronous oscillation suppressor. The subsynchronous oscillation suppressor detects the output current of the new energy power generation device to determine whether subsynchronous oscillation has occurred. If subsynchronous oscillation is detected, the frequency of the current subsynchronous oscillation is detected, and based on the frequency range, a virtual negative inductance is constructed through the coupling transformer to suppress the current oscillation. The controller of the subsynchronous oscillation suppressor detects the output current of the new energy power generation equipment and determines whether subsynchronous oscillation has occurred. If subsynchronous oscillation occurs, the frequency of the current subsynchronous oscillation is detected. This includes: the controller of the subsynchronous oscillation suppressor collects the current and voltage at the output terminal of the new energy power generation equipment and performs spectrum analysis. When the current in a certain frequency range exceeds the threshold, it is determined that there is subsynchronous oscillation in that frequency range. The method of constructing a virtual negative inductance through a coupling transformer to suppress current oscillation includes: The controller of the subsynchronous oscillation suppressor analyzes the spectrum and finds that the harmonic current of the new energy power generation equipment is greater than the threshold at a certain frequency range. Then, it multiplies the difference between the target value of the subsynchronous current oscillation amplitude and the output subsynchronous oscillation current amplitude of the new energy power generation equipment, and the output current of the new energy power generation equipment, after passing through the first regulator and the second regulator respectively, to obtain the output command of the secondary voltage of the coupling transformer. The difference between the output command of the secondary voltage of the coupling transformer and the actual voltage of the secondary side of the coupling transformer is passed through the third regulator to obtain the modulation voltage command of the primary H-bridge. Then, the subsynchronous oscillation suppressor sends corresponding drive signals to each switch of the primary H-bridge according to the modulation voltage command of the primary H-bridge. Alternatively, the method of constructing a virtual negative inductance through a coupling transformer to suppress current oscillations includes: The controller of the subsynchronous oscillation suppressor analyzes the frequency spectrum to determine if the harmonic current of the new energy power generation equipment exceeds a threshold at a certain frequency range. The controller then multiplies the target value of the subsynchronous current oscillation amplitude with the difference between the output subsynchronous oscillation current amplitude of the new energy power generation equipment and the output current of the new energy power generation equipment through the first and second regulators respectively to obtain the secondary voltage output command of the coupling transformer. The difference between the secondary voltage output command of the coupling transformer and the actual secondary voltage of the coupling transformer is then passed through the fourth regulator to obtain the primary current command of the coupling transformer. The difference between the primary current command of the coupling transformer and the actual primary current of the coupling transformer is then passed through the fifth regulator to obtain the modulation voltage command of the primary H-bridge. Finally, the subsynchronous oscillation suppressor sends corresponding drive signals to each switch of the primary H-bridge according to the modulation voltage command of the primary H-bridge.

2. The subsynchronous oscillation suppression system according to claim 1, characterized in that, The transfer function of the second regulator is , For complex variables, The fundamental frequency, For frequency coefficients.

3. The subsynchronous oscillation suppression system according to claim 1, characterized in that, The first regulator is a P regulator or a PI regulator.

4. The subsynchronous oscillation suppression system according to claim 1, characterized in that, The third regulator is a P regulator, PI regulator, PR regulator, or PIR regulator.

5. The subsynchronous oscillation suppression system according to claim 1, characterized in that, The fourth and fifth regulators are P regulators, PI regulators, PR regulators, or PIR regulators.

6. The subsynchronous oscillation suppression system according to claim 1, characterized in that, It also includes a bypass switch, which is connected in parallel with the secondary side of the coupling transformer. When the controller of the subsynchronous oscillation suppressor detects that there is no subsynchronous oscillation in the new energy power generation equipment, it bypasses the subsynchronous oscillation suppressor by closing the bypass switch.

7. The subsynchronous oscillation suppression system according to claim 1, characterized in that, The subsynchronous oscillation suppression system is two-phase or three-phase. When the subsynchronous oscillation suppression system is two-phase, a coupling transformer and a corresponding subsynchronous oscillation suppressor are installed in any one of the two phases. When the subsynchronous oscillation suppression system is three-phase, a coupling transformer and a corresponding subsynchronous oscillation suppressor are installed in each phase.

8. The subsynchronous oscillation suppression system according to claim 1, characterized in that, The first DC power supply and the new energy power generation equipment are connected in parallel in one or more groups, and the secondary side of the coupling transformer is connected in series on the connection line between the parallel output terminal and the power grid.

9. The subsynchronous oscillation suppression system according to claim 1, characterized in that, The new energy power generation equipment is a wind turbine converter or a photovoltaic inverter.

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