An oscillation suppression method and system suitable for black-gray box power system

Abstract

The present invention proposes an oscillation suppression method and system suitable for a black-gray box power system, which relates to the field of power generation oscillation suppression. The method comprises: obtaining real-time acquisition parameters of a new energy power system, and obtaining the resonant frequency of the new energy power system current based on the real-time acquisition parameters and the black-gray box parameter identification algorithm, and calculating the system resistance value and the grid reactance value at the resonant frequency; inputting the resonant frequency, the system resistance value and the grid reactance value obtained based on the real-time acquisition parameters and the black-gray box parameter identification algorithm into a coupling coefficient calculator, so that the coupling coefficient calculator outputs the system coupling coefficient, and respectively calculates the coupling amplitude and the coupling phase angle corresponding to the system coupling coefficient based on the system coupling coefficient; using the coupling amplitude, the coupling phase angle and the system resonant frequency as design parameters of a proportional phase shift controller, obtaining the phase lag and the time constant of the proportional phase shift controller, and correspondingly outputting the resonant frequency current signal of the proportional phase shift controller; obtaining the AC-DC axis reference current signal corresponding to the resonant frequency current signal based on the Park transformation, so as to adjust the reference value of the current inner loop in the parallel converter, so that the parallel converter is coupled with the new energy power system, so as to suppress subsynchronous oscillation. The present invention helps to improve the adaptability and coordination of the system to different time-varying working conditions and control strategies.

Description

Technical Field

[0001] The present invention relates to the field of power generation oscillation suppression, and in particular to an oscillation suppression method and system suitable for a black-grey box power system. Background Art

[0002] With the continuous development of power electronics technology, large-scale wind power, photovoltaic and other new energy units have begun to be connected to the power grid. However, new energy units based on power electronic equipment may interact with the power grid, causing subsynchronous oscillation accidents with time-varying amplitude and frequency. Subsynchronous oscillation accidents can easily cause serious consequences such as new energy units disconnecting from the grid and equipment damage, which brings great challenges to the safe and stable operation of new energy systems.

[0003] The Chinese patent with publication number CN114597911A discloses a method and system for suppressing oscillation of new energy power generation, including: real-time acquisition of instantaneous voltage and current at the unit port, and obtaining oscillation components of different frequency bands such as subsynchronous, medium frequency band, and high frequency band through online FFT analysis, triggering alarm signals through oscillation identification and judgment, starting online adjustment of control parameters, and adjusting multi-loop control parameters such as phase-locked loop, current loop, and DC voltage loop of wind turbine units. However, the above scheme relies on customized solutions under specific accident scenarios, which is difficult to adapt to the expansion of system scale and complex topological structure of new energy power system, and the control strategy and parameters of new energy units may be difficult to obtain. Therefore, it is very necessary to provide an oscillation suppression method and system suitable for black-gray box power system, which can evaluate the system resonant frequency and grid impedance online, and adjust the coupling relationship between parallel converter and grid in real time, so as to improve the system's adaptability and coordination to different time-varying working conditions and control strategies. Summary of the invention

[0004] In view of this, the present invention proposes an oscillation suppression method and system suitable for black-gray box power systems. The adaptive coupling reshaping control is composed of three parts: black-gray box parameter identification algorithm, coupling coefficient calculator and proportional phase shift controller, so that the system can evaluate the system resonant frequency and grid impedance online, and adjust the coupling relationship between the parallel converter and the grid in real time, so as to improve the system's adaptability and coordination to different time-varying working conditions and control strategies.

[0005] The present invention provides an oscillation suppression method applicable to a black-gray box power system, the method comprising:

[0006] Acquire the real-time acquisition parameters of the new energy power system, and acquire the resonant frequency of the new energy power system current based on the real-time acquisition parameters and the black-gray box parameter identification algorithm, and calculate the system resistance value and the grid reactance value at the resonant frequency;

[0007] The resonant frequency, the system resistance value and the grid reactance value obtained based on the real-time acquisition parameters and the black-gray box parameter identification algorithm are input into a coupling coefficient calculator, so that the coupling coefficient calculator outputs a system coupling coefficient, and calculates a coupling amplitude and a coupling phase angle corresponding to the system coupling coefficient based on the system coupling coefficient;

[0008] The coupling amplitude, the coupling phase angle and the system resonant frequency are used as design parameters of a proportional phase-shift controller, a phase lag and a time constant of the proportional phase-shift controller are obtained, and a resonant frequency current signal of the proportional phase-shift controller is output accordingly;

[0009] Based on the Park transformation, an AC-DC axis reference current signal corresponding to the resonant frequency current signal is obtained to adjust the reference value of the current inner loop in the parallel converter, so that the parallel converter is coupled with the new energy power system to suppress subsynchronous oscillation.

[0010] On the basis of the above technical solution, preferably, the real-time acquisition parameters of the new energy power system are acquired, and the resonant frequency of the new energy power system current is acquired based on the real-time acquisition parameters and the black-gray box parameter identification algorithm, and the system resistance value and the grid reactance value at the resonant frequency are calculated, specifically including:

[0011] Obtaining a system resonant voltage and a system resonant current of the new energy power system;

[0012] Obtaining a system resonant frequency of the new energy power system at the resonant frequency according to the system resonant current, a Fourier transform algorithm based on a sliding time window, and a three-point phasor interpolation method;

[0013] According to the system resonant voltage, system resonant current and grid impedance online identification algorithm, obtaining the grid equivalent impedance and grid equivalent capacitive reactance of the new energy power system at the resonant frequency;

[0014] The system grid impedance is calculated based on the system resonant frequency, the grid equivalent impedance and the grid equivalent capacitive reactance.

[0015] On the basis of the above technical solution, preferably, the resonant frequency, the system resistance value and the grid reactance value obtained based on the real-time acquisition parameters and the black-gray box parameter identification algorithm are input into the coupling coefficient calculator, specifically including:

[0016] Determine whether the system oscillation current amplitude is greater than 5% of the fundamental frequency current amplitude, and whether the system resonant frequency change is greater than 0.1 Hz;

[0017] If the system oscillation current amplitude is greater than 5% of the fundamental frequency current amplitude, and the system resonant frequency change is greater than 0.1 Hz, then updating the estimated value of the resonant frequency and the system resistance value and grid reactance value at the resonant frequency;

[0018] If the system oscillation current amplitude is greater than 5% of the fundamental frequency current amplitude, the resonant frequency, the system resistance value and the grid reactance value obtained based on the real-time acquisition parameters and the black-gray box parameter identification algorithm are input into the coupling coefficient calculator;

[0019] The coupling coefficient calculator calculates the coupled grid impedance, the admittance of the parallel converter and the system coupling coefficient according to the resonant frequency, the system resistance value and the grid reactance value obtained based on the real-time acquisition parameters and the black-gray box parameter identification algorithm.

[0020] More preferably, the expression of the coupled grid impedance is:

[0021]

[0022]

[0023] Z ge (s n )=R g (s n )+ΔR-jX g (s n )

[0024] in, represents the operator for taking the imaginary part, R g (s n ) represents the grid resistance, ΔR represents the newly added resistance in the new energy power system, represents the operator for taking the real part, Z ge (s n ) represents the coupled grid impedance, Z g (s n ) represents the grid impedance, ΔR represents the virtual resistance in series in the grid only at the resonant frequency, and X g (s n ) represents the grid capacitive reactance.

[0025] More preferably, the expression of the system resistance value is:

[0026]

[0027]

[0028] Among them, Z sys (s n) represents the system coupling impedance model at the resonant frequency, Z r (s n ) represents the equivalent impedance of the new energy station at the resonant frequency, Z g (s n ) represents the equivalent impedance of the power grid at the resonant frequency, k represents the system coupling coefficient, and Z ge (s n ) represents the equivalent coupled grid impedance after considering the coupling relationship, represents the operator for taking the real part, R sys (s n ) represents the system resistance value.

[0029] More preferably, the coupling amplitude, the coupling phase angle and the system resonant frequency are used as design parameters of a proportional phase shift controller to obtain a phase lag and a time constant of the proportional phase shift controller, specifically including:

[0030] Based on the system resonant frequency, the grid oscillation frequency and the control parameters of the PI controller, a band-stop filter, a band-pass filter and a transfer function of the current inner loop of the parallel converter are respectively constructed;

[0031] The coupling amplitude is used as the gain coefficient of the proportional phase-shift controller, and the coupling phase angle is used as the phase-shift angle of the proportional phase-shift controller to obtain the phase lag and time constant of the proportional phase-shift controller.

[0032] More preferably, the band-stop filter and the band-pass filter are expressed as follows:

[0033]

[0034] Among them, G BSF (s) represents the transfer function of the band-stop filter, s represents the Laplace operator, ω0 represents the grid oscillation frequency, ζ0 represents the damping coefficient of the band-stop filter, G BPF (s) represents the transfer function of the bandpass filter, ω n represents the system resonant frequency, ζ n Represents the damping coefficient of the bandpass filter.

[0035] More preferably, the transfer function of the current inner loop of the parallel converter is expressed as:

[0036]

[0037] Among them, s represents the Laplace operator, G c (s) represents the transfer function of the current inner loop of the parallel converter, k p represents the proportional parameter of the PI controller in the current inner loop of the parallel converter, ki represents the integral parameter of the PI controller in the current inner loop of the parallel converter, L s Represents the filter inductance of the grid-connected converter, T s Represents the switching cycle.

[0038] More preferably, the expression of the time constant is:

[0039] θ PS =θ d -(θ BSF +θ c )

[0040]

[0041] Among them, θ PS represents the phase shift angle of the phase shifter after compensation, θ d represents the phase of the coupling coefficient k, θ BSF represents the phase difference caused by the band-stop filter, θ c represents the phase difference caused by the inner loop of the parallel converter current, T represents the time constant of the phase shifter, s n represents the Laplace operator at the resonant frequency.

[0042] In a second aspect of the present application, an oscillation suppression system applicable to a black-gray box power system is provided, wherein the oscillation suppression system comprises a black-gray box system parameter identification module, a coupling processing module and an oscillation suppression module connected in sequence, wherein:

[0043] The black-gray box system parameter identification module is used to obtain the real-time acquisition parameters of the new energy power system, and obtain the resonant frequency of the new energy power system current based on the real-time acquisition parameters and the black-gray box parameter identification algorithm, and calculate the system resistance value and the grid reactance value at the resonant frequency;

[0044] The coupling processing module is used to input the resonant frequency, the system resistance value and the grid reactance value obtained based on the real-time acquisition parameters and the black-gray box parameter identification algorithm into the coupling coefficient calculator, so that the coupling coefficient calculator outputs the system coupling coefficient, and calculates the coupling amplitude and coupling phase angle corresponding to the system coupling coefficient based on the system coupling coefficient, and uses the coupling amplitude, the coupling phase angle and the system resonant frequency as design parameters of the proportional phase shift controller, obtains the phase lag and time constant of the proportional phase shift controller, and outputs the resonant frequency current signal of the proportional phase shift controller accordingly;

[0045] The oscillation suppression module is used to obtain the AC and DC axis reference current signals corresponding to the resonant frequency current signal based on Park transformation, so as to adjust the reference value of the current inner loop in the parallel converter, so as to couple the parallel converter with the new energy power system to suppress subsynchronous oscillations.

[0046] The oscillation suppression method and system for a black-gray box power system provided by the present invention have the following beneficial effects compared with the prior art:

[0047] (1) The adaptive coupling reshaping control is composed of three parts: a black / gray box parameter identification algorithm, a coupling coefficient calculator, and a proportional phase shift controller. The black / gray box parameter identification algorithm estimates the system resonant frequency and the grid impedance at the resonant frequency online according to the oscillating voltage and current signals appearing in the system. The coupling coefficient calculator updates the amplitude and phase angle of the coupling coefficient according to the real-time estimated system resonant frequency and grid impedance. The proportional phase shift controller updates the center frequency of the BPF according to the system resonant frequency, and updates the gain coefficient and the time constant of the phase shifter according to the amplitude and phase angle of the coupling coefficient. The generated resonant frequency current signal is transformed into a reference current signal through Park transformation and superimposed on the reference value of the current inner loop of the parallel converter to achieve the desired coupling relationship between the parallel converter and the grid, so that the system can evaluate the system resonant frequency and grid impedance online, and adjust the coupling relationship between the parallel converter and the grid in real time, so as to improve the system's adaptability and coordination to different time-varying working conditions and control strategies.

[0048] (2) The Fourier transform algorithm based on the sliding window provides continuous and real-time frequency monitoring, enabling the system to respond to frequency changes in a timely manner and adjust the control strategy accordingly to suppress oscillations. The use of the sliding window makes the algorithm more sensitive to instantaneous changes in the signal, which helps to improve the monitoring accuracy and response speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0050] Figure 1 A flow chart of an oscillation suppression method applicable to a black-gray box power system provided by the present invention;

[0051] Figure 2 A simplified schematic diagram of a new energy power system with integrated parallel converters provided by the present invention;

[0052] Figure 3A coupling impedance model of a new energy power system with integrated parallel converters provided by the present invention;

[0053] Figure 4 A schematic diagram of the mechanism of the subsynchronous oscillation suppression strategy based on coupling reshaping provided by the present invention;

[0054] Figure 5 The impedance / admittance phasor diagram of the subsystem at the resonant frequency provided by the present invention;

[0055] Figure 6 The modified IEEE subsynchronous resonance first standard model provided by the present invention;

[0056] Figure 7 The resistance-frequency and reactance-frequency characteristic curves of the system provided by the present invention;

[0057] Figure 8 This is a test result diagram of the adaptive coupling reshaping control under different series compensation degrees provided by the present invention;

[0058] Fig. 9 This is a test result diagram of the adaptive coupling reshaping control under different wind speeds provided by the present invention;

[0059] Fig.10 This is a test result diagram of the adaptive coupling remodeling control under different numbers of online fans provided by the present invention;

[0060] Fig.11 The test result diagram of the conventional voltage feedforward-based adaptive damping control provided by the present invention under different numbers of online fans;

[0061] Fig.12 This is a schematic diagram of the structure of the oscillation suppression system provided by the present invention.

[0062] Explanation of the reference numerals: 1. Oscillation suppression system; 11. Black-gray box system parameter identification module; 12. Coupling processing module; 13. Oscillation suppression module. DETAILED DESCRIPTION

[0063] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0064] The present invention discloses an oscillation suppression method applicable to a black-gray box power system, referring to Figure 1 The method includes steps S1 to S4.

[0065] Step S1, obtaining real-time acquisition parameters of the new energy power system, and obtaining the resonant frequency of the new energy power system current based on the real-time acquisition parameters and the black-gray box parameter identification algorithm, and calculating the system resistance value and the grid reactance value at the resonant frequency.

[0066] In this step, a simplified schematic diagram of a renewable energy power system with integrated parallel converters is shown in Figure 2 As shown. Among them, i r 、i c and g They represent the new energy station current, grid current and parallel converter current respectively, u p is the voltage at the point of common coupling (PCC), Z r With Z g is the equivalent impedance between the new energy station and the power grid, such as Figure 2 In the topology shown, the parallel converter and the renewable energy power system are coupled to each other through branch currents, and this current coupling relationship may hide a specific relationship between the parallel converter impedance and the renewable energy station impedance or the grid impedance.

[0067] When the shunt converter is integrated into the power system, the current i c With the grid current i g The ratio can be calculated as:

[0068] k=i c (ω n ) / i g (ω n )

[0069] k=k d cosθ d +jk d sinθ d

[0070] Among them, ω n is the system resonant frequency, and the ratio k is defined as the system coupling coefficient, which is used to quantitatively describe the coupling relationship between the parallel converter and the power system. The system coupling coefficient k is a vector and is expressed in k. d With θ d Represents the amplitude and phase angle of the system coupling coefficient k.

[0071] At this time, the impedance Z of the parallel converter c It can be calculated through the impedance of the coupled system and its coupling coefficient, without relying on the inherent control strategy of the parallel converter.

[0072]

[0073] Among them, sn is the Laplace operator s at the resonant frequency n =jω n .

[0074] It should be noted that when the impedance of the coupled subsystem (here, the grid impedance) and the coupling coefficient are used to describe the impedance of the parallel subsystem, the parallel converter is equivalent to a controlled current source. If the parallel converter and its coupled subsystem are divided into two subsystems, the coupling relationship may be destroyed and the effectiveness of the analysis may be affected. Therefore, the parallel converter and its coupled subsystem are divided into one subsystem.

[0075] The coupling impedance model of the renewable energy power system with integrated parallel converters is as follows: Figure 3 As shown in the figure, the analytical expression of the coupling impedance model of the new energy power system with integrated parallel converters at the resonant frequency can be derived as follows:

[0076]

[0077] In the formula, Z ge (s n ) is the equivalent coupled grid impedance after considering the coupling relationship. According to the negative resistance criterion, if the resistance of the system at the resonant frequency is greater than 0, the oscillation converges, otherwise the oscillation diverges. The system impedance model is constructed by a state variable that can be measured in real time (i.e., the current coupling relationship k between the parallel converter and the power system), which makes it possible to reveal the dynamic interaction mechanism between the parallel converter and the power system in the black-gray box system.

[0078] In this embodiment, steps S11 to S13 are also included.

[0079] Step S11, obtaining the system resonant voltage and system resonant current of the new energy power system.

[0080] Step S12, obtaining the system resonant frequency of the new energy power system at the resonant frequency according to the system resonant current, a Fourier transform algorithm based on a sliding time window, and a three-point phasor interpolation method.

[0081] In this step, the resonant frequency estimation algorithm consists of a low-pass filter (LPF), a band-stop filter, and an oscillation frequency monitoring algorithm. Since the harmonic content in the grid current is much higher than the PCC point voltage, the grid current is selected as the input signal of the resonant frequency estimation algorithm. Considering the frequency range of subsynchronous oscillation, the center frequency of the LPF is selected as 100Hz to filter out high-frequency noise. In addition, in order to filter out the fundamental frequency signal in the grid current, the center frequency of the BSF is set to the fundamental frequency of 50Hz.

[0082] In this embodiment, a Fourier transform algorithm (discrete Fourier transformer, DFT) based on a sliding time window is adopted. By selecting a suitable time window size, and the time window size should be able to balance the requirements of time resolution and frequency resolution; in each sliding window, the current signal is sampled and the DFT algorithm is applied to calculate the spectrum of the signal in the window; the obtained spectrum is analyzed to identify the main frequency components, which are usually the frequencies of system oscillations; as the time window slides, the above process is repeated to update the estimated value of the frequency in real time. By providing continuous and real-time frequency monitoring, the system can respond to frequency changes in a timely manner and adjust the control strategy accordingly to suppress oscillations. In addition, the use of sliding time windows makes the algorithm more sensitive to instantaneous changes in the signal, which helps to improve the accuracy and response speed of monitoring.

[0083] In this embodiment, the three-point phasor interpolation method is used as an oscillation frequency monitoring algorithm by selecting three consecutive phasor data points in the monitoring data of the new energy power system. These points can be the measured values ​​of voltage or current, usually expressed in complex form (i.e., containing amplitude and phase information).

[0084] Since common interpolation methods include linear interpolation, quadratic interpolation, and Lagrange interpolation, etc. For three-point interpolation, quadratic interpolation or Lagrange interpolation can usually be used, both of which can provide better accuracy and smoothness.

[0085] Assuming the three points are (x0, y0), (x1, y1) and (x2, y2), the quadratic interpolation polynomial p(x) can be expressed as:

[0086] p(x)=ax 2 +bx+c

[0087] Among them, the coefficient a, the coefficient b and the coefficient c can all be obtained by solving a linear equation system based on three known points (x0, y0), (x1, y1) and (x2, y2).

[0088] The Lagrange interpolation formula is:

[0089]

[0090] Use the selected interpolation formula to calculate the value L(x) or p(x) at the point x that needs to be estimated. This point can be any position between two known data points to generate more detailed waveform data. The interpolation results are applied to the new energy power system.

[0091] In order to prevent the estimated value of the system resonant frequency from changing with the increase of equivalent system damping after the introduction of adaptive coupling reshaping control, a logic module is set in the resonant frequency estimation algorithm to stop updating the resonant frequency after the adaptive coupling reshaping control is put into use. In addition, in order to prevent the resonant frequency estimation algorithm from being affected by noise after the system oscillation current disappears, the resonant frequency estimation algorithm updates the estimated value of the resonant frequency only when the amplitude of the system oscillation current is greater than 5% of the amplitude of the fundamental frequency current and the change of the system resonant frequency is greater than 0.1Hz.

[0092] Step S13, obtaining the grid equivalent resistance and grid equivalent capacitive reactance of the new energy power system at the resonant frequency according to the system resonant voltage, the system resonant current and the grid impedance online identification algorithm.

[0093] In this step, if Figure 4 As shown in the figure, in order to adapt to the black / gray box power grid with complex network topology and multiple operation modes, an online identification algorithm for power grid impedance is provided. The algorithm first filters out the high-frequency components and fundamental frequency components in the PCC point voltage and power grid current through LPF and BSF to obtain the resonant voltage u p (ω n ) and the resonant current i g (ω n ).

[0094] According to Kirchhoff's voltage law, the circuit equation of the system at the resonant frequency can be derived as follows:

[0095]

[0096] Among them, E(s n ) is the electromotive force of the resonant frequency component of the receiving-end grid voltage. The grid strength of the receiving-end large grid is relatively high. Even if the grid itself has a certain resonant electromotive force component, its amplitude is usually small, and has little effect on the impedance identification accuracy and the control performance of the proposed coupling reshaping control. Therefore, the resonant frequency component electromotive force of the grid is ignored, and the grid impedance at the resonant frequency is derived as follows:

[0097]

[0098] It should be noted that in order to avoid fluctuations in the estimated value of the grid impedance after the introduction of adaptive coupling reshaping control and the disappearance of the system oscillation component, a logic module is set here. The logic of this module is consistent with the resonant frequency estimation algorithm and will not be repeated here.

[0099] Step S2, input the resonant frequency, system resistance value and grid reactance value obtained based on the real-time acquisition parameters and the black-gray box parameter identification algorithm into the coupling coefficient calculator, so that the coupling coefficient calculator outputs the system coupling coefficient, and calculates the coupling amplitude and coupling phase angle corresponding to the system coupling coefficient based on the system coupling coefficient.

[0100] This step also includes steps S21 to S23.

[0101] Step S21, determining whether the system oscillation current amplitude is greater than 5% of the fundamental frequency current amplitude, and whether the system resonant frequency change is greater than 0.1 Hz.

[0102] Step S22: if the system oscillation current amplitude is greater than 5% of the fundamental frequency current amplitude, and the system resonant frequency change is greater than 0.1 Hz, then update the estimated value of the resonant frequency and the system resistance value and grid reactance value at the resonant frequency.

[0103] Step S23, if the system oscillation current amplitude is greater than 5% of the fundamental frequency current amplitude, the resonant frequency, system resistance value and grid reactance value obtained based on the real-time acquisition parameters and the black-gray box parameter identification algorithm are input into the coupling coefficient calculator.

[0104] Step S24, the coupling coefficient calculator calculates the coupled grid impedance, the admittance of the parallel converter and the system coupling coefficient according to the resonant frequency, the system resistance value and the grid reactance value obtained based on the real-time acquisition parameters and the black-gray box parameter identification algorithm.

[0105] The expression for the system resistance value is:

[0106]

[0107] Among them, Z sys (s n ) represents the coupling impedance model at the resonant frequency, Z r (s n ) represents the equivalent impedance of the new energy station at the resonant frequency, Z g (s n ) represents the equivalent impedance of the power grid at the resonant frequency, k represents the system coupling coefficient, and Z ge (s n ) represents the equivalent coupled grid impedance after considering the coupling relationship, represents the operator for taking the real part, R sys (s n ) represents the system resistance value.

[0108] In this step, according to the negative resistance criterion, increasing the resistance of the system at the resonant frequency can improve the stability of the system. If the equivalent impedance Z of the power grid at the resonant frequency is known g (s n), the equivalent resistance of the grid can be increased by reshaping the coupling relationship between the parallel converter and the grid (which can be regarded as enhancing local damping). Therefore, the process of increasing the grid resistance (local damping) based on the oscillation suppression strategy based on coupling reshaping does not require obtaining the impedance model of the new energy station, and the calculation of its coupling coefficient is only related to the grid impedance Z g (s n ) and the desired coupled grid impedance Z ge (s n Under the black-gray box condition, the proposed oscillation suppression strategy can be applied to increase the system equivalent resistance through online resonant frequency estimation and online grid impedance identification.

[0109] The schematic diagram of the mechanism of the subsynchronous oscillation suppression strategy based on coupling reconstruction in black / gray box new energy systems is shown in Figure 4 As shown. This oscillation suppression strategy reshapes the dynamic coupling relationship between the parallel converter and the power grid, which is equivalent to connecting a virtual resistance ΔR in series in the power grid that is only effective at the resonant frequency. It should be noted that when the virtual resistance is greater than the absolute value of the negative resistance presented by the new energy power system at the resonance point, the system oscillation can be completely suppressed. When the virtual resistance ΔR is less than the absolute value of the negative resistance presented by the new energy power system at the resonance point, the amplitude of the system oscillation current can also be reduced. Considering that the negative resistance presented by the new energy station at the resonance point varies with the system operating conditions and operating modes, and there are difficulties in the online impedance evaluation of the new energy station. The present invention sets the newly added resistance ΔR of the power grid to a fixed value, which can be determined by offline evaluating the negative resistance presented when the damping of the new energy power system is the worst. It should be noted that even if the initial setting ΔR is small, the system oscillation current will be effectively reduced, and the resistance value can be continued to be increased.

[0110] In this step, the system coupling coefficient k is the core of the adaptive coupling reshaping control, which determines whether the proposed strategy can effectively improve the system stability. For the convenience of analysis, it is assumed that the impedance of the new energy station at the resonant frequency is inductive. The resistance and inductive reactance of the new energy station at the resonant frequency are defined as R r (s n ) and X r (s n ), define the grid resistance and capacitance as R g (s n ) and X g (s n ). At the resonant frequency, X r (s n )=X g (s n ). The coupling grid impedance Z is obtained by reverse calculation. ge (s n ), the admittance Y of the parallel converter c (sn ) and the coupling coefficient k. It should be noted that this assumption does not affect the applicability of the proposed control strategy. When the impedance of the new energy station is capacitive, the analysis of the proposed control strategy and the calculation of the coupling coefficient are no different from the assumption.

[0111] The equivalent coupling impedance of the power grid can be changed by reshaping the coupling coefficient. First, the coupling grid impedance Z that is expected to be achieved after introducing the parallel converter and the adaptive coupling reshaping control strategy should be determined. ge (s n ). In order to suppress subsynchronous oscillation, it is necessary to increase the equivalent resistance of the grid at the corresponding resonance point, so Z ge (s n ) can be designed as follows:

[0112]

[0113] in, Represents the operator taking the real part. It should be noted that, in theory, the larger the newly added resistance ΔR, the more stable the system. However, the larger the newly added resistance, the higher the requirements for the capacity of the parallel converter and the performance of the controller to achieve the corresponding coupling relationship. Since the proposed coupling reshaping control only requires the design of one parameter (i.e., the newly added resistance ΔR), it is relatively easy to understand. Technicians can design it through the system's minimum negative resistance evaluated in advance, and retain a certain margin, or adjust it according to engineering experience. It should be noted that even if the newly added resistance is small, the system oscillation phenomenon can still be alleviated. At this time, you only need to increase the resistance value and calculate the coupling coefficient. This process can be achieved by iterative increase through methods such as the ramp method.

[0114] Furthermore, the resistance of the coupled grid impedance is constructed at the original resonance point. If the system resonance point changes significantly due to the introduction of the parallel converter and the adaptive coupling reshaping control strategy, the strategy may fail. Therefore, it is necessary to ensure that the introduction of the coupling reshaping control does not cause changes in the system equivalent reactance. At this time, the imaginary part of the coupled grid impedance can be designed as follows:

[0115]

[0116] According to the above formula, the expected coupled grid impedance after introducing adaptive coupling reshaping control can be derived as follows:

[0117] Z ge (s n )=R g (s n )+ΔR-jX g (s n )

[0118] in, represents the operator for taking the imaginary part, R g(s n ) represents the grid resistance, ΔR represents the newly added resistance in the new energy power system, represents the operator for taking the real part, Z ge (s n ) represents the coupled grid impedance, Z g (s n ) represents the grid impedance, ΔR represents the virtual resistance in series in the grid only at the resonant frequency, and X g (s n ) represents the grid capacitive reactance.

[0119] Please refer to Figure 5 , Figure 5 is the impedance / admittance phasor diagram of the subsystem at the resonant frequency. In the impedance plane, the resistance of the power grid at the resonant point is equivalently increased by adaptive coupling reshaping control without changing the system resonant point, and the desired coupled power grid impedance Z can be constructed. ge (s n ).

[0120] After designing the desired coupled grid impedance, the equivalent admittance Y of the parallel converter can be derived in the admittance plane: c (s n )as follows:

[0121]

[0122] In order to achieve the desired equivalent admittance of the parallel converter, the coupling coefficient k can be inferred from equation (3) as follows:

[0123] k=Y c (s n ) / Y g (s n )

[0124] According to the above formula, the grid impedance Z is known g (s n ) and the desired parallel converter impedance Z c (s n ), the magnitude of the coupling coefficient k d and phase angle θ d It can be deduced as follows:

[0125]

[0126] Step S3, using the coupling amplitude, coupling phase angle and system resonant frequency as design parameters of the proportional phase shift controller, obtaining the phase lag and time constant of the proportional phase shift controller, and correspondingly outputting the resonant frequency current signal of the proportional phase shift controller.

[0127] This step also includes steps S31 to S32.

[0128] Step S31, based on the system resonant frequency, the grid oscillation frequency and the control parameters of the PI controller, respectively construct the transfer functions of the band-stop filter, the band-pass filter and the current inner loop of the parallel converter.

[0129] In this step, a proportional phase shift controller is used to achieve the desired coupling relationship between the parallel converter and the grid. The controller consists of a band-stop filter (BSF), a bandpass filter (BPF), a gain link and a phase shifter. The input signal of the proportional phase shift controller is the grid current, and the output signal is the reference value of the desired parallel current. The parallel converter will track the desired parallel current reference value to achieve the desired current coupling relationship.

[0130] In order to avoid affecting the fundamental frequency dynamic performance of the system and the system damping of the non-interested frequency band, the proposed coupling control strategy only builds a specific coupling relationship between the parallel converter and the power grid at the resonant frequency. Therefore, the present invention sets the center frequency of the BSF to the power grid frequency ω0 to filter out the fundamental component, and sets the center frequency of the BPF to the resonant frequency ω n To extract the resonant component.

[0131] The expressions of band-stop filter and band-pass filter are:

[0132]

[0133] Among them, G BSF (s) represents the transfer function of the band-stop filter, s represents the Laplace operator, ω0 represents the grid oscillation frequency, ζ0 represents the damping coefficient of the band-stop filter, G BPF (s) represents the transfer function of the bandpass filter, ω n represents the system resonant frequency, ζ n Represents the damping coefficient of the bandpass filter. The larger the damping coefficient ζ0 of the BSF is, the smaller the influence of the proposed control strategy on the fundamental frequency performance of the system will be, but it will also cause greater distortion of the resonant component signal. Therefore, the damping coefficient ζ0 of the BSF needs to be selected in a compromise, so the damping coefficient ζ0 is set to 0.5. The damping coefficient ζ0 of the BPF is n The smaller the value, the lower the gain at the non-center frequency (theoretically the non-resonant frequency), which is more conducive to reducing the influence of the proposed control strategy on the damping of the non-resonant frequency band system. However, when there is a certain deviation between the resonant frequency and the center frequency of the bandpass filter, a smaller damping coefficient will cause serious distortion of the extracted resonant component, which will also put forward higher accuracy requirements for the resonant frequency estimation algorithm. Therefore, the damping coefficient of BPF should also be selected in a compromise, so ζ is selected n is 0.5.

[0134] The desired current coupling relationship can be achieved by adjusting the gain coefficient and the phase shift angle of the phase shifter. The present invention uses two lead-lag functions in series to form a phase shifter, and its transfer function is as follows:

[0135]

[0136] Wherein, T1 and T2 represent the time constants of the phase shift function, which are used for phase adjustment.

[0137] It should be noted that the PI controller of the grid-connected converter current inner loop has static error when tracking non-DC signals. c (s n ) and the actual parallel converter current i c (s n ) There will be an additional phase angle difference between the two. The transfer function of the current inner loop of the parallel converter is expressed as:

[0138]

[0139] Among them, s represents the Laplace operator, G c (s) represents the transfer function of the current inner loop of the parallel converter, k p represents the proportional parameter of the PI controller in the current inner loop of the parallel converter, k i represents the integral parameter of the PI controller in the current inner loop of the parallel converter, L s Represents the filter inductance of the grid-connected converter, T s represents the switching period. The larger k p With k i and smaller T s It can bring higher current loop bandwidth and also bring smaller control deviation to the proposed coupling reshaping control. However, higher current loop bandwidth will also bring higher performance requirements and costs to the grid-connected converter. Therefore, the above parameters should be selected in a compromise. In this study, T s is set to 0.0005s, the closed-loop bandwidth of the current inner loop is set to 200Hz, and L s is 5mH, the proportional parameter k of the inner current loop p is 4, the integral parameter k i is 800.

[0140] Step S32, using the coupling amplitude as the gain coefficient of the proportional phase-shift controller, and the coupling phase angle as the phase-shift angle of the proportional phase-shift controller, to obtain the phase lag and time constant of the proportional phase-shift controller.

[0141] Step S4, based on Park transformation, obtain the AC-DC axis reference current signal corresponding to the resonant frequency current signal to adjust the reference value of the current inner loop in the parallel converter, so that the parallel converter is coupled with the new energy power system to suppress subsynchronous oscillation.

[0142] In this step, the magnitude of the coupling coefficient k can be d and phase angle θ d As the gain coefficient and phase shift angle of the proportional phase shift controller, the desired current coupling relationship between the parallel converter and the power grid is achieved. However, the BSF and the current inner loop of the parallel converter may bring additional phase angle deviation to the desired coupling coefficient. Therefore, in order to ensure the reliability of the proposed coupling reshaping control strategy, the phase shift angle of the phase shifter needs to compensate for the additional phase angle deviation introduced by the BSF and the current inner loop of the parallel converter. After compensation, the phase shift angle of the phase shifter can be calculated as follows:

[0143] θ PS =θ d -Δθ=θ d -(θ BSF +θ c )=θ d -arctan(G BSF (s n ))-arctan(G c (s n ))

[0144]

[0145] Among them, θ PS represents the phase shift angle of the phase shifter after compensation, θ d represents the phase of the coupling coefficient k, θ BSF represents the phase difference caused by the band-stop filter, θ c represents the phase difference caused by the inner loop of the parallel converter current, T represents the time constant of the phase shifter, s n represents the Laplace operator at the resonant frequency.

[0146] The adaptive coupling reshaping control is composed of three parts: a black / gray box parameter identification algorithm, a coupling coefficient calculator and a proportional phase shift controller. The black / gray box parameter identification algorithm estimates the system resonant frequency and the grid impedance at the resonant frequency online according to the oscillating voltage and current signals appearing in the system. The coupling coefficient calculator updates the amplitude and phase angle of the coupling coefficient according to the real-time estimated system resonant frequency and grid impedance. The proportional phase shift controller updates the center frequency of the BPF according to the system resonant frequency, and updates the gain coefficient and the time constant of the phase shifter according to the amplitude and phase angle of the coupling coefficient. The generated resonant frequency current signal generates a reference current signal through Park transformation and is superimposed on the reference value of the current inner loop of the parallel converter to achieve the desired coupling relationship between the parallel converter and the grid, so that the system can evaluate the system resonant frequency and grid impedance online, and adjust the coupling relationship between the parallel converter and the grid in real time, so as to improve the system's adaptability and coordination to different time-varying working conditions and control strategies.

[0147] In one example, a modified IEEE subsynchronous oscillation first standard model is built on the controller hardware-in-the-loop platform. The modified IEEE subsynchronous resonance first standard model is as follows: Figure 6 As shown in the figure, STATCOM is connected in parallel with a wind farm consisting of 2,000 double-fed wind turbines, and then connected to the grid through a series compensation line. Limited by the experimental conditions, it is assumed that all wind turbine parameters and working conditions (wind speed) are the same, and a single-machine aggregation model is used for wind farm equivalence.

[0148] To meet the demand for oscillation suppression, the capacity of the additional suppression device is usually set to 0.5%-5% of the capacity of the new energy station. Due to space limitations. In this example, the existing STATCOM is used for suppression, and its capacity is set to 40% of the wind farm capacity based on engineering experience. In addition, the real part of the desired coupled grid impedance in the coupled reshaping control is set to 5*R g .

[0149] The hardware-in-the-loop experimental platform consists of an RTLAB real-time simulator and an actual physical controller. The power part of the wind power generation system and the parallel converter is simulated by RTLAB, while the proposed control algorithm runs in the actual controller. The controller and RTLAB communicate through an external I / O board. The relevant voltage, current signals and control signals can be observed through an oscilloscope. The accuracy and speed of black-gray box parameter identification are related to the calculation frequency of the DFT algorithm. Due to the performance limitations of the actual physical controller, the frequency of the DFT algorithm is set to 250Hz.

[0150] In order to verify the effectiveness of the proposed coupling reshaping control strategy and observe the impact of the coupling reshaping control on the wide-band impedance of the system, the low-bandwidth outer loop control is ignored in this example to establish the impedance model of the test system. In addition, this section sets the wind speed of the fan to 7m / s, the number of online fans to 500, and the series compensation degree of the series compensation line to 80%. It should be noted that the system impedance model is established in this example only to verify the effectiveness of the strategy, and the system model and parameters are not substituted into the operation of the proposed control strategy.

[0151] like Figure 7As shown in the figure, according to the system impedance model, the resistance-frequency and reactance-frequency characteristic curves of the system can be drawn. It can be found that in this scenario, when there is no damping control, the zero-crossing point of the system reactance is 12.1Hz, and the system resistance at this frequency is -0.087pu. Since the system resistance is less than 0 at the reactance zero-crossing point, the system will produce a subsynchronous oscillation phenomenon of 12.1Hz. After applying the proposed coupling reshaping control, the zero-crossing point of the system reactance is still 12.1Hz, which also means that the proposed control strategy does not change the resonance point of the system. In addition, after applying the coupling reshaping control, the system resistance increment is about 0.0293pu, which is consistent with the designed resistance increment of 0.0296pu. Since the system at 12.1Hz is increased from -0.087pu to 0.206pu, the system resistance becomes positive. Therefore, the proposed coupling reshaping control can effectively suppress the subsynchronous oscillation in the frequency band of interest. In addition, since the proposed adaptive coupling reshaping controller can update the controller parameters in real time according to the real-time detected grid impedance and oscillation frequency, this strategy can increase the system equivalent resistance under different working conditions and different resonant frequencies. The relevant impedance characteristic curve and theoretical analysis are Figure 7 Similar, no further description is given here.

[0152] It should be noted that since the bandpass filter and the bandstop filter can effectively extract the resonant frequency component and filter out the component signals of other frequency bands, after applying the proposed adaptive coupling reshaping control, only the impedance characteristics near the resonant frequency are significantly different from the original impedance characteristics. It can be found that after applying the proposed coupling reshaping control, the system resistance is improved in the 4-20Hz frequency band and reduced in the 1-4Hz frequency band. However, there is no new reactance zero crossing point in the 1-4Hz frequency band, so the reduction in resistance in this frequency band does not affect the stability of the system. In addition, when the damping coefficient of the bandpass filter is further reduced, the influence of the damping controller on the surrounding frequency bands can also be reduced.

[0153] The wind speed of the wind power transmission system is set to 7m / s, the number of online wind turbines is 500, and the series compensation degree of the series compensation line is set to 40% and 80%. The test results of adaptive coupling reshaping control under different series compensation degrees are shown in Figure 2. Figure 8 shown.

[0154] When the series compensation is not put into use, the wind power transmission system operates stably. After 40% of the series compensation is put into use, the wind farm interacts with the series compensation line, the line current begins to oscillate, and the peak value of the line current is about 5.7kA. When the black-gray box parameter identification algorithm is applied, the estimated values ​​of the system oscillation frequency, the grid resistance and reactance at the resonant frequency reach stable values ​​after about 300ms, which are 8.6Hz, 0.072 (pu), and -0.0145 (pu), respectively. After the proposed adaptive coupling reshaping control is put into use, the controller reshapes the coupling relationship between the parallel converter and the grid by identifying parameters. The amplitude and phase angle of the coupling coefficient are updated to 0.74 and 159°, respectively, which is equivalent to increasing the grid impedance. Therefore, the system oscillation current disappears, and the peak value of the line current is stabilized at 4.1kA.

[0155] After 80% series compensation was put into use, the line current oscillation amplitude increased further, and the peak value of the line current was about 7.4kA. When the black-gray box parameter identification algorithm was applied, the estimated values ​​of the system oscillation frequency, grid resistance and reactance at the resonant frequency reached stable values ​​after about 120ms, which were 12.1Hz, 0.074(pu), and -0.208(pu), respectively. Subsequently, the adaptive coupling reshaping control updated the amplitude and phase angle of the coupling coefficient according to the parameter identification results to 0.70 and 151°, respectively. It should be noted that a higher series compensation degree brings a larger system oscillation frequency and smaller system damping, so the oscillation suppression time of the proposed strategy is slightly longer than that of the case of 40% series compensation. Finally, the line oscillation current disappeared and the line current peak dropped to 4.1kA. Under this condition, the controller hardware-in-the-loop experiment is consistent with the impedance stability analysis results in Section 3.1, which further verifies the effectiveness and correctness of the proposed control strategy.

[0156] The series compensation degree of the series compensation line is set to 80%, and the number of online wind turbines is 1000. The test results of adaptive coupling reshaping control at different wind speeds are shown in Figure 2. Fig. 9 The test results when the wind speed is 5m / s and 8m / s are as follows Fig. 9 (a) and Fig. 9 (b) As shown. After the series compensation is put into operation, the steady-state oscillation amplitudes of the line current under the two working conditions are 6.6kA and 2.2kA respectively. Obviously, the oscillation phenomenon of the system is alleviated after the wind speed is increased. The parameter identification results of the system under the two wind speeds are relatively similar, and the system resonant frequencies are estimated to be 14Hz and 14.3Hz respectively. Under both wind speeds, the adaptive coupling reshaping control can effectively suppress the system oscillation phenomenon. Finally, the line current peaks are reduced to 2.6kA and 12.5kA respectively.

[0157] The series compensation degree of the series compensation line is set to 80% and the wind speed is 5m / s. The test results of adaptive coupling reshaping control under different numbers of online wind turbines are shown in the figure. Fig.10The test results of adaptive coupling remodeling control when the number of online fans is 500 and 1500 are shown in Fig.10 (a) and Fig.10 (b) As shown. After the series compensation is put into use under both working conditions, the line current begins to oscillate, and the line current peak values ​​are 4.8kA and 12.2kA respectively in the steady state of oscillation. With the increase of the number of online fans, the system oscillation frequency also increases from 12Hz to 14.9Hz. Fig.10 As shown in the figure, the proposed control strategy can still accurately identify the system parameters when different numbers of wind turbines are online and effectively suppress them.

[0158] In order to verify the effectiveness and superiority of adaptive coupling reshaping control in suppressing oscillations in black-gray box systems, this paper compares the suppression performance of traditional voltage feedforward-based adaptive damping control under different numbers of online fans. Test results of traditional voltage feedforward-based adaptive damping control under different numbers of online fans Fig.11 shown.

[0159] like Fig.11 As shown in the figure, when 500 wind turbines are online, the use of traditional adaptive damping control even increases the system current peak from 4.8kA to 6.2kA, and the system oscillation intensifies. When 1500 wind turbines are online, the use of traditional adaptive damping control reduces the system current peak from 12.2kA to 9.7kA, and the degree of system oscillation is reduced, but the system oscillation current still exists. It can be found that because traditional analysis methods are difficult to reveal the dynamic interaction mechanism between parallel converters and power systems, the oscillation suppression performance of adaptive damping control in different systems and different working conditions is not the same, and the effectiveness is difficult to guarantee.

[0160] Based on the above method, the embodiment of the present application discloses an oscillation suppression system suitable for a black-gray box power system, referring to Fig.12 The oscillation suppression system 1 includes a black-gray box system parameter identification module 11, a coupling processing module 12 and an oscillation suppression module 13 connected in sequence, wherein:

[0161] The black-gray box system parameter identification module 11 is used to obtain the real-time acquisition parameters of the new energy power system, and obtain the resonant frequency of the new energy power system current based on the real-time acquisition parameters and the black-gray box parameter identification algorithm, and calculate the system resistance value and the grid reactance value at the resonant frequency;

[0162] The coupling processing module 12 is used to input the resonant frequency, system resistance value and grid reactance value obtained based on the real-time acquisition parameters and the black-gray box parameter identification algorithm into the coupling coefficient calculator, so that the coupling coefficient calculator outputs the system coupling coefficient, and calculates the coupling amplitude and coupling phase angle corresponding to the system coupling coefficient based on the system coupling coefficient, and uses the coupling amplitude, coupling phase angle and system resonant frequency as design parameters of the proportional phase-shift controller, obtains the phase lag and time constant of the proportional phase-shift controller, and outputs the resonant frequency current signal of the proportional phase-shift controller accordingly;

[0163] The oscillation suppression module 13 is used to obtain the AC-DC axis reference current signal corresponding to the resonant frequency current signal based on the Park transformation to adjust the reference value of the current inner loop in the parallel converter, so as to couple the parallel converter with the new energy power system to suppress subsynchronous oscillation.

[0164] In one example, the black-gray box system parameter identification module 11 is used to obtain the system resonant voltage and system resonant current of the new energy power system; obtain the system resonant frequency of the new energy power system at the resonant frequency according to the system resonant current, the Fourier transform algorithm based on the sliding time window and the three-point phasor interpolation method; identify the resonant frequency of the new energy power system current according to the system resonant voltage, the system resonant current and the grid impedance online identification algorithm, and calculate the system grid resistance and grid reactance values ​​at the resonant frequency.

[0165] In one example, the coupling processing module 12 is used to determine whether the amplitude of the system oscillating current is greater than 5% of the fundamental frequency current amplitude and whether the change in the system resonant frequency is greater than 0.1 Hz; if the amplitude of the system oscillating current is greater than 5% of the fundamental frequency current amplitude and the change in the system resonant frequency is greater than 0.1 Hz, the estimated value of the resonant frequency and the grid resistance and grid reactance values ​​at the resonant frequency are updated; if the amplitude of the system oscillating current is greater than 5% of the fundamental frequency current amplitude, the system current resonant frequency, the grid resistance and the grid reactance at the resonant frequency obtained based on the real-time acquisition parameters and the black-gray box parameter identification algorithm are input into the coupling coefficient calculator; the coupling coefficient calculator calculates the coupled grid impedance, the admittance of the parallel converter and the system coupling coefficient according to the system current resonant frequency, the grid resistance and the grid reactance at the resonant frequency obtained based on the real-time acquisition parameters and the black-gray box parameter identification algorithm.

[0166] In one example, the expression for the coupled grid impedance is:

[0167]

[0168] Z ge (s n )=R g (s n )+ΔR-jX g(s n )

[0169] in, represents the operator for taking the imaginary part, R g (s n ) represents the grid resistance, ΔR represents the newly added resistance in the new energy power system, represents the operator for taking the real part, Z ge (s n ) represents the coupled grid impedance, Z g (s n ) represents the grid impedance, ΔR represents the virtual resistance in series in the grid only at the resonant frequency, and X g (s n ) represents the grid capacitive reactance.

[0170] In one example, the expression for the system resistance value is:

[0171]

[0172]

[0173] Among them, Z sys (s n ) represents the system coupling impedance model at the resonant frequency, Z r (s n ) represents the equivalent impedance of the new energy station at the resonant frequency, Z g (s n ) represents the equivalent impedance of the power grid at the resonant frequency, k represents the system coupling coefficient, and Z ge (s n ) represents the equivalent coupled grid impedance after considering the coupling relationship, represents the real part operator.

[0174] In one example, the coupling processing module 12 is used to construct a band-stop filter, a band-pass filter and a transfer function of the current inner loop of the parallel converter based on the system resonant frequency, the grid oscillation frequency and the control parameters of the PI controller; the coupling amplitude is used as the gain coefficient of the proportional phase-shift controller, and the coupling phase angle is used as the phase shift angle of the proportional phase-shift controller to obtain the phase lag and time constant of the proportional phase-shift controller.

[0175] In one example, the expressions for the band-stop filter and the band-pass filter are:

[0176]

[0177]

[0178] Among them, G BSF(s) represents the transfer function of the band-stop filter, s represents the Laplace operator, ω0 represents the grid oscillation frequency, ζ0 represents the damping coefficient of the band-stop filter, G BPF (s) represents the transfer function of the bandpass filter, ω n represents the system resonant frequency, ζ n Represents the damping coefficient of the bandpass filter.

[0179] In one example, the transfer function of the current inner loop of the shunt converter is expressed as:

[0180]

[0181] Among them, s represents the Laplace operator, G c (s) represents the transfer function of the current inner loop of the parallel converter, k p represents the proportional parameter of the PI controller in the current inner loop of the parallel converter, k i represents the integral parameter of the PI controller in the current inner loop of the parallel converter, L s Represents the filter inductance of the grid-connected converter, T s Represents the switching cycle.

[0182] In one example, the expression for the time constant is:

[0183] θ PS =θ d -(θ BSF +θ c )

[0184]

[0185] Among them, θ PS represents the phase shift angle of the phase shifter after compensation, θ d represents the phase of the coupling coefficient k, θ BSF represents the phase difference caused by the band-stop filter, θ c represents the phase difference caused by the inner loop of the parallel converter current, T represents the time constant of the phase shifter, s n represents the Laplace operator at the resonant frequency.

[0186] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An oscillation suppression method applicable to a black-gray box power system, characterized in that: The method comprises: Acquire the real-time acquisition parameters of the new energy power system, and acquire the resonant frequency of the new energy power system current based on the real-time acquisition parameters and the black-gray box parameter identification algorithm, and calculate the system resistance value and the grid reactance value at the resonant frequency; The resonant frequency, the system resistance value and the grid reactance value obtained based on the real-time acquisition parameters and the black-gray box parameter identification algorithm are input into a coupling coefficient calculator, so that the coupling coefficient calculator outputs a system coupling coefficient, and calculates a coupling amplitude and a coupling phase angle corresponding to the system coupling coefficient based on the system coupling coefficient; The coupling amplitude, the coupling phase angle and the system resonant frequency are used as design parameters of a proportional phase-shift controller, a phase lag and a time constant of the proportional phase-shift controller are obtained, and a resonant frequency current signal of the proportional phase-shift controller is output accordingly; Based on the Park transformation, an AC-DC axis reference current signal corresponding to the resonant frequency current signal is obtained to adjust the reference value of the current inner loop in the parallel converter, so that the parallel converter is coupled with the new energy power system to suppress subsynchronous oscillation.

2. The method according to claim 1, characterized in that The method of acquiring the real-time acquisition parameters of the new energy power system, acquiring the resonant frequency of the current of the new energy power system based on the real-time acquisition parameters and the black-gray box parameter identification algorithm, and calculating the system resistance value and the grid reactance value at the resonant frequency specifically includes: Obtaining a system resonant voltage and a system resonant current of the new energy power system; According to the system resonant current, a Fourier transform algorithm based on a sliding time window and a three-point phasor interpolation method, a system resonant frequency of the new energy power system current at the resonant frequency is obtained; According to the system resonant voltage, system resonant current and grid impedance online identification algorithm, obtaining the grid equivalent resistance and grid equivalent capacitive reactance of the new energy power system at the resonant frequency; The grid impedance online identification algorithm is used to filter out the high-frequency components and fundamental frequency components in the PCC point voltage and grid current through LPF and BSF to obtain the resonant voltage u p (ω n ) and the resonant current i g (ω n ), according to Kirchhoff's voltage law, the circuit equation of the system at the resonant frequency can be derived as follows: The resonant frequency component electromotive force of the power grid is ignored, and the power grid impedance at the resonant frequency is derived as follows: Among them, E(s n ) represents the electromotive force of the resonant frequency component of the receiving-end grid voltage, s n represents the Laplace operator at the resonant frequency, that is, s n =jω n , Z g (s n ) represents the grid impedance.

3. The method according to claim 2, characterized in that The step of inputting the resonant frequency, the system resistance value, and the grid reactance value obtained based on the real-time acquisition parameters and the black-gray box parameter identification algorithm into a coupling coefficient calculator specifically includes: Determine whether the system oscillation current amplitude is greater than 5% of the fundamental frequency current amplitude, and whether the system resonant frequency change is greater than 0.1 Hz; If the system oscillating current amplitude is greater than 5% of the fundamental frequency current amplitude, and the system resonant frequency change is greater than 0.1 Hz, then updating the estimated value of the resonant frequency and the system resistance value and grid reactance value at the resonant frequency; If the system oscillation current amplitude is greater than 5% of the fundamental frequency current amplitude, the resonant frequency, the system resistance value and the grid reactance value obtained based on the real-time acquisition parameters and the black-gray box parameter identification algorithm are input into the coupling coefficient calculator; The coupling coefficient calculator calculates the coupled grid impedance, the admittance of the parallel converter and the system coupling coefficient according to the resonant frequency, the system resistance value and the grid reactance value obtained based on the real-time acquisition parameters and the black-gray box parameter identification algorithm.

4. The method according to claim 3, characterized in that The expression of the coupling grid impedance is: Z ge (s n )=R g (s n )+ΔR-jX g (s n ) in, represents the operator for taking the imaginary part, R g (s n ) represents the grid resistance, represents the operator for taking the real part, Z ge (s n ) represents the coupled grid impedance, Z g (s n ) represents the grid impedance, ΔR represents the virtual resistance in series in the grid only at the resonant frequency, and X g (s n ) represents the grid capacitive reactance.

5. The method according to claim 1, characterized in that The expression of the system resistance value is: Among them, Z sys (s n ) represents the system coupling impedance model at the resonant frequency, Z r (s n ) represents the equivalent impedance of the new energy station at the resonant frequency, Z g (s n ) represents the equivalent impedance of the power grid at the resonant frequency, k represents the system coupling coefficient, and Z ge (s n ) represents the equivalent coupled grid impedance after considering the coupling relationship, represents the operator for taking the real part, R sys (s n ) represents the system resistance value.

6. The method according to claim 1, characterized in that The coupling amplitude, the coupling phase angle and the system resonant frequency are used as design parameters of the proportional phase shift controller to obtain the phase lag and the time constant of the proportional phase shift controller, specifically including: Based on the system resonant frequency, the grid oscillation frequency and the control parameters of the PI controller, a band-stop filter, a band-pass filter and a transfer function of the current inner loop of the parallel converter are respectively constructed; The coupling amplitude is used as the gain coefficient of the proportional phase-shift controller, and the coupling phase angle is used as the phase-shift angle of the proportional phase-shift controller to obtain the phase lag and time constant of the proportional phase-shift controller.

7. The method according to claim 6, characterized in that The expressions of the band-stop filter and the band-pass filter are respectively: Among them, G BSF (s) represents the transfer function of the band-stop filter, s represents the Laplace operator, ω0 represents the grid oscillation frequency, ζ0 represents the damping coefficient of the band-stop filter, G BPF (s) represents the transfer function of the bandpass filter, ω n represents the system resonant frequency, ζ n Represents the damping coefficient of the bandpass filter.

8. The method according to claim 6, characterized in that The transfer function of the current inner loop of the parallel converter is expressed as: Among them, s represents the Laplace operator, G c (s) represents the transfer function of the current inner loop of the parallel converter, k p represents the proportional parameter of the PI controller in the current inner loop of the parallel converter, k i represents the integral parameter of the PI controller in the current inner loop of the parallel converter, L s Represents the filter inductance of the grid-connected converter, T s Represents the switching cycle.

9. The method according to claim 1, characterized in that The expression of the time constant is: i PS =θ d -(θ BSF +θ c ) Among them, θ PS represents the phase shift angle of the phase shifter after compensation, θ d represents the phase of the coupling coefficient k, θ BSF represents the phase difference caused by the band-stop filter, θ c represents the phase difference caused by the inner loop of the parallel converter current, T represents the time constant of the phase shifter, s n represents the Laplace operator at the resonant frequency.

10. An oscillation suppression system suitable for a black-grey box power system, characterized in that: The oscillation suppression system (1) comprises a black-gray box system parameter identification module (11), a coupling processing module (12) and an oscillation suppression module (13) which are connected in sequence, wherein: The black-grey box system parameter identification module (11) is used to obtain real-time acquisition parameters of the new energy power system, and based on the real-time acquisition parameters and the black-grey box parameter identification algorithm, obtain the resonant frequency of the new energy power system current, and calculate the system resistance value and the grid reactance value at the resonant frequency; The coupling processing module (12) is used to input the resonant frequency, the system resistance value and the grid reactance value obtained based on the real-time acquisition parameters and the black-gray box parameter identification algorithm into a coupling coefficient calculator, so that the coupling coefficient calculator outputs the system coupling coefficient, and respectively calculates the coupling amplitude and coupling phase angle corresponding to the system coupling coefficient based on the system coupling coefficient, uses the coupling amplitude, the coupling phase angle and the system resonant frequency as design parameters of the proportional phase shift controller, obtains the phase lag and time constant of the proportional phase shift controller, and correspondingly outputs the resonant frequency current signal of the proportional phase shift controller; The oscillation suppression module (13) is used to obtain an AC-DC axis reference current signal corresponding to the resonant frequency current signal based on Park transformation, so as to adjust the reference value of the current inner loop in the parallel converter, so as to couple the parallel converter with the new energy power system to suppress subsynchronous oscillation.

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