Stability control method and device for grid-connected converter

Abstract

The present application discloses a stability control method and device for a grid-connected converter, the method comprising: obtaining the grid-side voltage or current of the grid-connected converter; extracting the frequency and amplitude of the dominant harmonic from the grid-side voltage or current; determining the oscillation mode of the grid-connected converter according to the frequency and amplitude of the dominant harmonic to select the corresponding grid-connected stability control strategy for execution. The present application automatically detects the frequency and amplitude of the dominant harmonic in the grid-side output current or voltage of the grid-connected converter without increasing the system cost, determines whether the grid-connected converter has resonance or sub- or super-synchronous oscillation, and automatically adjusts the control strategy according to the judgment result to make the grid-connected converter operate stably, thereby improving the stable operation capability of the grid-connected converter in dealing with complex and changeable grid environments.

Description

Technical Field

[0001] The present application relates to the field of new energy technology, and in particular to a stability control method and device for a grid-connected converter. Background Art

[0002] In order to filter out high-frequency harmonics at the switching frequency level, grid-connected converters often need to be equipped with high-order filters at the AC input or output end. The widely used LCL filter is one of them. Under the same filtering performance requirements, the use of high-order filtering can not only reduce the size of the filter and save system costs, but also help increase the power density of the system. However, the output characteristics of high-order filters not only bring resonance risks to the grid-connected operation of grid-connected converters, but also introduce sub- and super-synchronous oscillation problems in power generation systems with a high proportion of new energy and high grid penetration.

[0003] For the sub-synchronous and super-synchronous oscillation problems, the output impedance characteristics of the grid-connected converter can be reshaped (hereinafter referred to as the impedance reshaping method) by optimizing the parameters of the phase-locked loop and the current regulator [Reference "Zhou Shiying, Zou Xudong, Tong Li, et al. Parameter design of the current loop controller of the LCL type grid-connected converter considering the influence of the phase-locked loop [J]. Proceedings of the CSEE, 2016, 36(4): 1075-1089."] or optimizing the voltage feedforward link of the current control loop [Reference "Yang Dongsheng, Ruan Xinbo, Wu Heng, et al. Virtual impedance method for improving the adaptability of LCL type grid-connected inverter to weak power grid [J]. Proceedings of the CSEE, 2014, 34(15): 2327-2335."] and other methods to solve them. Enhancing the damping capacity of the grid-connected converter is the starting point for solving its grid-connected resonance problem.

[0004] Commonly used damping enhancement methods are divided into passive damping and active damping. Among them, the passive damping method is simple to implement, and it can be realized by simply connecting a resistor in series or in parallel in the high-order filter branch installed at the AC input or output end of the grid-connected converter. However, the use of resistors will reduce the power generation efficiency of the grid-connected converter and also bring additional heat dissipation problems; for this reason, the industry prefers to use active damping methods without additional power loss. Active damping methods can be divided into those based on state feedback [literature "SHEN Guoqiao, XU Dehong. Split capacitor current control for LCL filter grid-connected inverter [J]. Proceedings of the CSEE, 2008, 28(18): 36-41.", "ZHOU Leming, LUO An, CHEN Yandong, et al. Robust grid-connected current feedback active damping control method for LCL type grid-connected inverter [J]. Proceedings of the CSEE, 2016, 36(10): 2742-2752."] and those based on filter compensation [literature "ZHENG Kun, ZHOU Lin, LONG Guixin, et al. A notch filter lag compensation method for photovoltaic grid-connected inverter under digital control [J]. Proceedings of the CSEE, 2019, 39(6): 1749-1757.", literature "YAO Wenli, YANG Yongheng, ZHANG Xiaobin, et al. Design and analysis of robust active damping for LCL filters using digital notch filters [J]. IEEE Transactions on Power Electronics, 2017, 32(3): 2360-2375.”, “Pena-Alzolar, Liserre M, Blaabjerc F, et al. Systematic design of the lead-lag network method for active damping in LCL-filter based three phase converters[J]. IEEE Transactions on Industrial Informatics, 2014, 10(1): 43-52.”] However, no matter which type of digital control system is used in the grid-connected converter, its effective damping frequency band is often limited due to the existence of digital control delay, and the effective frequency band varies depending on the specific damping strategy. For the resonance that appears outside the effective damping frequency band, if the damping strategy has no damping characteristics in this frequency band, it can only fail to suppress the resonance; but if the damping strategy exhibits negative damping characteristics in this frequency band, it will aggravate the resonance.

[0005] In addition, grid-connected resonance may occur in both strong and weak grids, while subsynchronous or supersynchronous oscillations often occur in weak grids. Some specific strategies in the impedance reshaping methods used to deal with subsynchronous and supersynchronous oscillations, such as enhancing the regulation capability of the current control loop, may conflict with the need for resonance suppression.

[0006] In this way, grid-connected converters need to formulate different response strategies for grids of different strengths. Although this strategy-customized response method can solve the grid-connected stability problem in many current application scenarios, it is difficult to adaptively match the grid-connected control requirements of strong and weak grids, causing grid-connected converters to face great challenges in the increasingly complex and changeable grid environment in the future. Summary of the invention

[0007] In order to overcome the problem of limited capability of a single strategy of a grid-connected converter in dealing with resonance problems as described in the background art and the conflict between the strategy for dealing with sub-synchronous oscillation and super-synchronous oscillation and the strategy for suppressing resonance when used simultaneously.

[0008] In one aspect, the present application provides a stability control method for a grid-connected converter, the method comprising:

[0009] Obtaining the grid-side voltage or current of the grid-connected converter;

[0010] Extracting the frequency and amplitude of the dominant harmonics from the grid-side voltage or current;

[0011] The oscillation mode of the grid-connected converter is determined according to the frequency and amplitude of the dominant harmonic, so as to select a corresponding grid-connected stability control strategy for execution.

[0012] In another aspect of the present application, a stability control device for a grid-connected converter is provided, the device comprising an acquisition module, an extraction module, and a determination module;

[0013] The acquisition module is used to acquire the grid-side voltage or current of the grid-connected converter;

[0014] The extraction module is used to extract the frequency and amplitude of the dominant harmonics from the grid-side voltage or current;

[0015] The determination module is used to determine the oscillation mode of the grid-connected converter according to the frequency and amplitude of the dominant harmonic, so as to select a corresponding grid-connected stability control strategy for execution.

[0016] The stability control method and device for the grid-connected converter provided in the embodiment of the present application, without increasing the system cost, automatically detects the frequency and amplitude of the dominant harmonics in the grid-side output current or voltage of the grid-connected converter, determines whether the grid-connected converter has resonance or sub- or super-synchronous oscillation, and automatically adjusts the control strategy according to the judgment result to make the grid-connected converter operate stably, thereby improving the stable operation capability of the grid-connected converter in coping with complex and changeable grid environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A control principle block diagram of a grid-connected converter provided in an embodiment of the present application;

[0018] Figure 2 A schematic diagram of a stability control device for a grid-connected converter provided in an embodiment of the present application;

[0019] Figure 3 A schematic diagram of a first-order generalized integrator with a frequency-locked loop provided in an embodiment of the present application;

[0020] Figure 4 A schematic diagram of a dual second-order generalized integrator with a frequency-locked loop provided in an embodiment of the present application;

[0021] Figure 5 A schematic diagram of a stability control method for a grid-connected converter provided in an embodiment of the present application.

[0022] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0023] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application clearer and more understandable, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0024] In the description of the present application, it should be understood that the orientations or positional relationships indicated by the terms "center", "upper", "lower", "front", "back", "left", "right", etc. are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0025] Variables and their definitions involved in the embodiments of this application:

[0026] u gab 、u gbc、u gca : Grid voltage;

[0027] u gαβ =u gα +ju gβ : The vector of the grid voltage in the αβ coordinate system, where u gα 、u gβ are its α and β axis components respectively;

[0028] u gd 、u gq : d-axis and q-axis components of the grid voltage;

[0029] i ga 、i gb 、i gc : Grid-connected current of the grid-connected converter;

[0030] i gαβ =i gα +ji gβ : The vector of the grid-connected current in the αβ coordinate system, where i gα 、i gβ are its α and β axis components respectively;

[0031] i gd 、i gq : d-axis and q-axis components of grid-connected current;

[0032] i a 、i b 、i c : Bridge arm current of the grid-connected converter;

[0033] i αβ =i α +ji β : The vector of the bridge arm current in the αβ coordinate system, where i α 、i β are its α and β axis components respectively;

[0034] i αβh =i αh +ji βh : The vector of the bridge arm harmonic current in the αβ coordinate system, where i αh 、i βh are its α and β axis components respectively;

[0035] G fw :Current control loop voltage feedforward controller

[0036] u gd_ f w 、u gq_fw : d-axis and q-axis voltage feedforward of current control loop;

[0037] K damp : Damping coefficient of capacitor current feedforward control link;

[0038] u dq_ref =u d_re f+ju q_re f: The vector of PWM modulation voltage command in dq coordinate system, where u d_ref 、u q_ref are their d and q axis components respectively;

[0039] u αβref =u α_ref +ju β_ref : Vector of PWM modulation voltage command αβ coordinate system, where u α_ref 、u β_ref are its α and β axis components respectively;

[0040] f h : Dominant harmonic frequency

[0041] I mh : Dominant harmonic current amplitude

[0042] OscMode: Oscillation mode corresponding to variable value

[0043] G APF : All-pass filter

[0044] G 1st_notch :Baseband Notch Filter

[0045] G CR :Grid-connected converter current regulator

[0046] K p_CR : Proportional coefficient of current regulator of grid-connected converter

[0047] Figure 1 A block diagram of the control principle of a grid-connected converter provided in an embodiment of the present application.

[0048] like Figure 1 As shown, the grid voltage u gab 、u gbc 、u gca After coordinate transformation, we get the component u of the grid voltage in the αβ coordinate system. gα 、u gβ ; Then after passing through PLL (Phase Locked Loop, phase-locked loop), the d and q axis components u of the grid voltage are obtained gd 、u gq .

[0049] The grid-connected current i of the grid-connected converter ga 、i gb 、i gcAfter coordinate transformation, we get the component i of the grid-connected current in the αβ coordinate system. gα 、i gβ , and then through coordinate transformation, we can get the grid-connected current d and q axis components i gd 、i gq .

[0050] Grid side capacitor current i ca 、i cb 、i cc After coordinate transformation, we can get the component i of the grid side capacitor current in the αβ coordinate system: cα 、i cβ , and then through coordinate transformation, we can get the grid side capacitor current d and q axis components i cd 、i cq .

[0051] The d-axis and q-axis components of the grid voltage u gd 、u gq , grid-connected current d, q axis components i gd 、i gq , grid side capacitor current d, q axis component i cd 、i cq , given the current d and q axis components i d_ref 、i q_ref , given voltage d, q axis component u d_ref 、u q_ref , through the current control loop voltage feedforward controller G fw , grid-connected converter current regulator G CR , the damping coefficient K of the capacitor current feedforward control link damp After adjustment, the PWM modulation voltage of the grid-connected converter is obtained through coordinate transformation to control the grid-connected converter.

[0052] Figure 2 Schematic diagram of a stability control device for a grid-connected converter provided in an embodiment of the present application.

[0053] like Figure 2 As shown, the stability control device of the grid-connected converter includes an acquisition module, an extraction module and a determination module.

[0054] The acquisition module is used to acquire the grid-side voltage or current of the grid-connected converter.

[0055] The grid-side voltage or current of the grid-connected converter includes at least one of a bridge arm current, a grid-connected current, a grid-side capacitor current, a grid-side capacitor voltage, and a grid-connected point voltage.

[0056] In this example, the input is the bridge arm current i a 、i b 、i c The α and β axis components iα , iβ, the output is the α and β axis components i of the bridge arm harmonic current αh 、i βh Specifically, it can be realized by the following transfer function from input to output characteristics:

[0057] In the formula, G 1st_notch is the baseband notch filter, ω g is the grid fundamental angular frequency, ω c is the bandwidth coefficient of the band-stop filter.

[0058] The extraction module is used to extract the frequency and amplitude of the dominant harmonics from the grid-side voltage or current.

[0059] In this example, the grid-side voltage or current is sampled at equal time intervals to obtain a sampling sequence; the sampling sequence is subjected to discrete Fourier transform, and the component with the largest amplitude other than the fundamental wave is selected from the transform result as the dominant harmonic.

[0060] In this example, the extraction module extracts the frequency f of the dominant harmonic from the grid-side voltage or current. h and the current amplitude I mh The extraction module removes the fundamental component of the grid-side voltage or current. The grid-side voltage or current after the fundamental component is removed can be Figure 3 FOGI-FLL (First Order Gneneralized Intergrator With Frequency Lock Loop) or Figure 4 The DSOGI-FLL (Dual Second Order Gneneralized Intergrator With Frequency Lock Loop) shown extracts the frequency and amplitude of the dominant harmonic.

[0061] In other examples, the frequency and amplitude of the dominant harmonic can be extracted by at least one of a plurality of first-order generalized integrators with frequency-locked loops connected in series, a plurality of first-order generalized integrators with frequency-locked loops connected in parallel, a plurality of second-order generalized integrators with frequency-locked loops connected in series, and a plurality of second-order generalized integrators with frequency-locked loops connected in parallel.

[0062] The determination module is used to determine the oscillation mode of the grid-connected converter according to the frequency and amplitude of the dominant harmonics, so as to select a corresponding grid-connected stability control strategy for execution.

[0063] In this example, the determination module receives the dominant harmonic frequency f output by the extraction module. h and the dominant harmonic current amplitude I mh, combining the two, the oscillation mode of the grid-connected converter is determined as follows, and the output oscillation mode corresponds to the variable value OscMode.

[0064]

[0065] In the formula,

[0066] f Resmin is the lower limit of the frequency of the first resonant frequency interval corresponding to the first oscillation mode. In this example, the value is taken as follows:

[0067] f ResLim is the resonance critical frequency of the grid-connected converter based on the active damping method of capacitor current feedforward. When the delay of the digital control system is 1.5 control cycles, its value is f ResLim =f s / 6(f s is the sampling and control frequency of the system, which is also the execution frequency of the current control loop in this example);

[0068] V ResLmt is the bandwidth of the grid-connected converter's resonant critical frequency;

[0069] I mh_resLmt1 ~I mh_resLmt3 The resonant frequency is at f ResLim The left side outside the range (defined as the first resonant frequency range in this example), f ResLim In this example, it is defined as the second resonant frequency range, f ResLim The harmonic current amplitude threshold value when it is outside the range to the right (defined as the third resonant frequency interval in this example);

[0070] I mh_oscLmt is the harmonic current amplitude threshold value of the 4th oscillation mode;

[0071] f OscLmt is the upper limit frequency of the frequency range corresponding to the fourth oscillation mode. In this example,

[0072] Furthermore, a response module is included for executing a corresponding grid-connected stability control strategy.

[0073] Specifically:

[0074] When OscMode = 0, the grid-connected converter is in non-oscillation mode, and the response module maintains the grid-connected stability control strategy unchanged;

[0075] When OscMode=1, the grid-connected converter resonates and the resonant frequency is located in the first resonant frequency interval, and the response module adjusts the grid-connected control strategy in a direction that is conducive to suppressing the resonance in the first resonant frequency interval.

[0076] The specific adjustment steps include:

[0077] a1) Calculate the upper limit of the damping coefficient of the capacitor current feedforward control link according to the following formula:

[0078]

[0079] In the formula, ω h is the angular frequency corresponding to the dominant harmonic frequency, f s is the sampling and control frequency of the system, which is also the execution frequency of the current control loop in this example, L pfc is the inductance of the bridge arm of the grid-connected converter, k damp_max It is the upper limit of the damping coefficient of the capacitor current feedforward control link;

[0080] b1) The damping coefficient k of the current capacitor current feedforward control link damp With k damp_lim Compare, if k damp ≥k damp_max , then first k damp =k damp_max , then k damp Decrease with a certain step size, k damp During the process of reducing, the amplitude of the dominant harmonic current I mh If the dominant harmonic current I mh If k decreases, then continue to decrease damp , until k damp Reduce to the lower limit setting value k damp_min or I mh Below I mh_resLmt1 ; If the dominant harmonic current I mh If it drops to a certain level and no longer changes significantly, then maintain k damp The current value remains unchanged; if the dominant harmonic current I mh If it does not decrease but increases significantly, then k damp callback;

[0081] c1) If the current capacitor current feedforward damping coefficient is reduced to the lower limit k damp_min Post-harmonic current amplitude I mh Still higher than I mh_resLmt1 , then the grid-connected converter current regulator G CR The proportionality factor K p_CR Decrease in steps of a certain length. K p_CRDuring the process of reducing, the amplitude of the dominant harmonic current I mh If the dominant harmonic current amplitude I mh If it decreases, then continue to reduce K p_CR , until K p_CR Reduce to the lower limit setting value K p_CRmin or I mh Below I mh_resLmt1 ; If the dominant harmonic current amplitude I mh If it drops to a certain level and no longer changes significantly, K p_CR The current value remains unchanged; if the dominant harmonic current amplitude I mh If it does not decrease but increases significantly, then K p_CR Callback.

[0082] When OscMode=2, the grid-connected converter resonates and the resonant frequency is in the second resonant frequency interval. The response module adjusts the grid-connected control strategy in a direction that is conducive to suppressing the resonance in the second resonant frequency interval. The specific approach includes:

[0083] a2) If the damping coefficient k of the current capacitor current feedforward control link is damp ≠0, then k damp Set to 0;

[0084] b2) The voltage control value u output by the current control loop αβ_ori After all-pass filter G APF The u obtained later αβ_apf Then it is used as the grid-connected converter PWM modulation voltage vector u αβref .

[0085] The transfer function of the input-output characteristic of the fully synchronous filter used is

[0086]

[0087] In the formula, ω n It is the angular frequency corresponding to the all-pass filter output lagging 90° relative to the input signal.

[0088] c2) If k damp = 0 and the all-pass filter G APF The dominant harmonic current amplitude I after being connected in series to the control loop of the grid-connected converter mh Still higher than I mh_resLmt3 , then the grid-connected converter current regulator G CR The proportionality factor K p_CR Decrease in steps of a certain length. K p_CR During the reduction process, the dominant harmonic current amplitude I mh If the dominant harmonic current amplitude I mhIf it decreases, then continue to reduce K p_CR , until K p_CR Reduce to the lower limit setting value K p_CRmin or I mh Below I mh_resLmt3 ; If the dominant harmonic current amplitude I mh If it drops to a certain level and no longer changes significantly, K p_CR The current value remains unchanged; if the dominant harmonic current amplitude I mh If it does not decrease but increases significantly, then K p_CR Callback.

[0089] When OscMode=3, the grid-connected converter resonates and the resonant frequency is located in the third resonant frequency interval (a frequency band located outside the bandwidth range of the grid-connected converter resonant critical frequency and on the right side and lower than the Nyquist frequency), and the response module adjusts the grid-connected control strategy in a direction that is conducive to suppressing the resonance in the third resonant frequency interval. The specific methods include:

[0090] a3) If the damping coefficient k of the current capacitor current feedforward control link is damp > 0, then k damp Set to 0;

[0091] b3) If k damp After setting to 0, the dominant harmonic current amplitude I mh Still higher than I mh_resLmt3 , then the grid-connected converter current regulator G CR The proportionality factor K p_CR Decrease in steps of a certain length. K p_CR During the process of reducing, the amplitude of the dominant harmonic current I mh If the dominant harmonic current amplitude I mh If it decreases, then continue to reduce K p_CR , until K p_CR Reduce to the lower limit setting value K p_CRmin or I mh Below I mh_resLmt3 ; If the dominant harmonic current amplitude I mh If it drops to a certain level and no longer changes significantly, K p_CR The current value remains unchanged; if the dominant harmonic current amplitude I mh If it does not decrease but increases significantly, then K p_CR Callback.

[0092] When OscMode=4, the grid-connected converter has subsynchronous or supersynchronous oscillation, and the response module adjusts the grid-connected control strategy in a direction that is conducive to suppressing subsynchronous or supersynchronous oscillation, such as reducing the bandwidth of the phase-locked loop, adjusting the proportional coefficient of the grid-connected converter current regulator, etc.

[0093] Figure 5 A schematic diagram of a stability control method for a grid-connected converter provided in an embodiment of the present application.

[0094] like Figure 5 As shown, the method includes:

[0095] Step S11, obtaining the grid-side voltage or current of the grid-connected converter;

[0096] Step S12, extracting the frequency and amplitude of the dominant harmonic from the grid-side voltage or current;

[0097] Step S13: determining the oscillation mode of the grid-connected converter according to the frequency and amplitude of the dominant harmonic, so as to select a corresponding grid-connected stability control strategy for execution.

[0098] In one example, extracting the frequency and amplitude of the dominant harmonic from the grid-side voltage or current includes:

[0099] Sampling the grid-side voltage or current at equal time intervals to obtain a sampling sequence;

[0100] Perform discrete Fourier transform on the sampling sequence, and select the component with the largest amplitude other than the fundamental wave from the transform result as the dominant harmonic.

[0101] In one example, extracting the frequency and amplitude of the dominant harmonic from the grid-side voltage or current includes:

[0102] Eliminating the fundamental component of the voltage or current on the grid side;

[0103] For the grid-side voltage or current after the fundamental component is eliminated, the frequency and amplitude of the dominant harmonic are extracted through at least one of a first-order generalized integrator with a frequency-locked loop, a dual second-order generalized integrator with a frequency-locked loop, at least two first-order generalized integrators with frequency-locked loops connected in series, at least two first-order generalized integrators with frequency-locked loops connected in parallel, at least two second-order generalized integrators with frequency-locked loops connected in series, and at least two second-order generalized integrators with frequency-locked loops connected in parallel.

[0104] In one example, determining the oscillation mode of the grid-connected converter according to the frequency and amplitude of the dominant harmonic includes:

[0105] Comparing the frequency and amplitude of the dominant harmonic with the frequency threshold value and the amplitude threshold value one by one;

[0106] If the amplitude of the dominant harmonic is lower than the minimum value of all amplitude threshold values, determining that the oscillation mode of the grid-connected converter is a non-oscillation mode;

[0107] If the frequency of the dominant harmonic is in the kth resonant frequency interval, and the amplitude of the dominant harmonic exceeds the amplitude threshold value corresponding to the kth resonant frequency interval, then the oscillation mode of the grid-connected converter is determined to be the kth oscillation mode; wherein k∈[1,3];

[0108] If the frequency of the dominant harmonic is within the resonant frequency interval corresponding to subsynchronous or supersynchronous oscillation, and the amplitude of the dominant harmonic is higher than the amplitude threshold corresponding to subsynchronous or supersynchronous oscillation, the oscillation mode of the grid-connected converter is determined to be the fourth oscillation mode.

[0109] In one example, the resonant frequency interval corresponding to the subsynchronous or supersynchronous oscillation refers to a frequency band above 0 Hz and below the LC resonant frequency formed by the grid-side inductance and capacitance of the grid-connected converter;

[0110] The first resonant frequency interval refers to a frequency band located outside the bandwidth range of the grid-connected converter resonance critical frequency and located on the left side and above the LC resonant frequency formed by the grid-side inductance and capacitance of the grid-connected converter;

[0111] The second resonant frequency interval refers to a frequency band within the bandwidth of the critical resonant frequency of the grid-connected converter;

[0112] The third resonant frequency interval refers to a frequency band located outside the bandwidth range of the grid-connected converter resonant critical frequency to the right and lower than the Nyquist frequency.

[0113] In one example, determining the oscillation mode of the grid-connected converter according to the frequency and amplitude of the dominant harmonic includes:

[0114] The output oscillation pattern corresponds to the variable value.

[0115] In one example, the selecting a corresponding grid-connected stability control strategy to execute includes:

[0116] According to the variable value corresponding to the oscillation mode, a grid-connected stability control strategy corresponding to the variable value corresponding to the oscillation mode is obtained.

[0117] In one example, the selecting a corresponding grid-connected stability control strategy to execute includes:

[0118] If the oscillation mode of the grid-connected converter is a non-oscillation mode, maintaining the grid-connected stability control strategy unchanged;

[0119] If the oscillation mode of the grid-connected converter is the first oscillation mode, adjusting the grid-connected control strategy to suppress the resonance in the first resonant frequency interval;

[0120] If the oscillation mode of the grid-connected converter is the second oscillation mode, adjusting the grid-connected control strategy to suppress the resonance in the second resonant frequency interval;

[0121] If the oscillation mode of the grid-connected converter is the third oscillation mode, the grid-connected control strategy is adjusted to suppress the resonance in the third resonant frequency interval.

[0122] If the oscillation mode of the grid-connected converter is the fourth oscillation mode, the grid-connected control strategy is adjusted to suppress subsynchronous or supersynchronous oscillation.

[0123] In one example, the grid-side voltage or current of the grid-connected converter includes at least one of a bridge arm current, a grid-connected current, a grid-side capacitor current, a grid-side capacitor voltage, and a grid-connected point voltage.

[0124] The preferred embodiments of the present application are described above with reference to the accompanying drawings, but the scope of the present application is not limited thereby. Any modification, equivalent substitution and improvement made by a person skilled in the art without departing from the scope and essence of the present application shall be within the scope of the present application.

Claims

1. A stability control method for a grid-connected converter, characterized in that: The method comprises: Obtaining the grid-side voltage or current of the grid-connected converter; Extracting the frequency and amplitude of the dominant harmonics from the grid-side voltage or current; Determining the oscillation mode of the grid-connected converter according to the frequency and amplitude of the dominant harmonic, so as to select a corresponding grid-connected stability control strategy for execution; The extracting the frequency and amplitude of the dominant harmonic from the grid-side voltage or current comprises: Sampling the grid-side voltage or current at equal time intervals to obtain a sampling sequence; Perform discrete Fourier transform on the sampling sequence, and select the component with the largest amplitude other than the fundamental wave from the transform result as the dominant harmonic; Determining the oscillation mode of the grid-connected converter according to the frequency and amplitude of the dominant harmonic includes: Comparing the frequency and amplitude of the dominant harmonic with the frequency threshold value and the amplitude threshold value one by one; If the amplitude of the dominant harmonic is lower than the minimum value of all amplitude threshold values, determining that the oscillation mode of the grid-connected converter is a non-oscillation mode; If the frequency of the dominant harmonic is in the kth resonant frequency interval, and the amplitude of the dominant harmonic exceeds the amplitude threshold value corresponding to the kth resonant frequency interval, then the oscillation mode of the grid-connected converter is determined to be the kth oscillation mode; wherein k∈[1,3]; If the frequency of the dominant harmonic is within the resonant frequency interval corresponding to the subsynchronous or supersynchronous oscillation, and the amplitude of the dominant harmonic is higher than the amplitude threshold value corresponding to the subsynchronous or supersynchronous oscillation, then the oscillation mode of the grid-connected converter is determined to be the fourth oscillation mode; The resonant frequency interval corresponding to the subsynchronous or supersynchronous oscillation refers to a frequency band above 0 Hz and below the LC resonant frequency formed by the grid-side inductance and capacitance of the grid-connected converter.

2. A stability control method for a grid-connected converter, characterized in that: The method comprises: Obtaining the grid-side voltage or current of the grid-connected converter; Extracting the frequency and amplitude of the dominant harmonics from the grid-side voltage or current; Determining the oscillation mode of the grid-connected converter according to the frequency and amplitude of the dominant harmonic, so as to select a corresponding grid-connected stability control strategy for execution; The extracting the frequency and amplitude of the dominant harmonic from the grid-side voltage or current comprises: Eliminating the fundamental component of the voltage or current on the grid side; For the grid-side voltage or current after the fundamental wave component is removed, the frequency and amplitude of the dominant harmonic are extracted through a first-order generalized integrator with a frequency-locked loop, a dual second-order generalized integrator with a frequency-locked loop, at least two second-order generalized integrators with frequency-locked loops connected in series, or at least two second-order generalized integrators with frequency-locked loops connected in parallel; Determining the oscillation mode of the grid-connected converter according to the frequency and amplitude of the dominant harmonic includes: Comparing the frequency and amplitude of the dominant harmonic with the frequency threshold value and the amplitude threshold value one by one; If the amplitude of the dominant harmonic is lower than the minimum value of all amplitude threshold values, determining that the oscillation mode of the grid-connected converter is a non-oscillation mode; If the frequency of the dominant harmonic is in the kth resonant frequency interval, and the amplitude of the dominant harmonic exceeds the amplitude threshold value corresponding to the kth resonant frequency interval, then the oscillation mode of the grid-connected converter is determined to be the kth oscillation mode; wherein k∈[1,3]; If the frequency of the dominant harmonic is within the resonant frequency interval corresponding to the subsynchronous or supersynchronous oscillation, and the amplitude of the dominant harmonic is higher than the amplitude threshold value corresponding to the subsynchronous or supersynchronous oscillation, then the oscillation mode of the grid-connected converter is determined to be the fourth oscillation mode; The resonant frequency interval corresponding to the subsynchronous or supersynchronous oscillation refers to a frequency band above 0 Hz and below the LC resonant frequency formed by the grid-side inductance and capacitance of the grid-connected converter.

3. A stability control method for a grid-connected converter, characterized in that: The method comprises: Obtaining the grid-side voltage or current of the grid-connected converter; Extracting the frequency and amplitude of the dominant harmonics from the grid-side voltage or current; Determining the oscillation mode of the grid-connected converter according to the frequency and amplitude of the dominant harmonic to select a corresponding grid-connected stability control strategy for execution; The extracting the frequency and amplitude of the dominant harmonic from the grid-side voltage or current comprises: Sampling the grid-side voltage or current at equal time intervals to obtain a sampling sequence; Perform discrete Fourier transform on the sampling sequence, and select the component with the largest amplitude other than the fundamental wave from the transform result as the dominant harmonic; Determining the oscillation mode of the grid-connected converter according to the frequency and amplitude of the dominant harmonic includes: Output oscillation mode corresponding to variable value; The selecting a corresponding grid-connected stability control strategy to execute includes: According to the variable value corresponding to the oscillation mode, a grid-connected stability control strategy corresponding to the variable value corresponding to the oscillation mode is obtained; The selecting a corresponding grid-connected stability control strategy to execute includes: If the oscillation mode of the grid-connected converter is a non-oscillation mode, maintaining the grid-connected stability control strategy unchanged; If the oscillation mode of the grid-connected converter is the first oscillation mode, adjusting the grid-connected control strategy to suppress the resonance in the first resonant frequency interval; If the oscillation mode of the grid-connected converter is the second oscillation mode, adjusting the grid-connected control strategy to suppress the resonance in the second resonant frequency interval; If the oscillation mode of the grid-connected converter is the third oscillation mode, adjusting the grid-connected control strategy to suppress the resonance in the third resonant frequency interval; If the oscillation mode of the grid-connected converter is the fourth oscillation mode, adjusting the grid-connected control strategy to suppress subsynchronous or supersynchronous oscillation; The first resonant frequency interval refers to a frequency band located outside the bandwidth range of the grid-connected converter resonance critical frequency and located on the left side and above the LC resonant frequency formed by the grid-side inductance and capacitance of the grid-connected converter; The second resonant frequency interval refers to a frequency band within the bandwidth of the critical resonant frequency of the grid-connected converter; The third resonant frequency interval refers to a frequency band located outside the bandwidth range of the grid-connected converter resonant critical frequency to the right and lower than the Nyquist frequency.

4. The stability control method of a grid-connected converter according to any one of claims 1 to 3, characterized in that: The grid-side voltage or current of the grid-connected converter includes at least one of a bridge arm current, a grid-connected current, a grid-side capacitor current, a grid-side capacitor voltage or a grid-connected point voltage.

5. A stability control device for a grid-connected converter, characterized in that: The device comprises an acquisition module, an extraction module and a determination module; The acquisition module is used to acquire the grid-side voltage or current of the grid-connected converter; The extraction module is used to extract the frequency and amplitude of the dominant harmonic from the grid-side voltage or current; the extraction module is also used to sample the grid-side voltage or current at equal time intervals to obtain a sampling sequence; Perform discrete Fourier transform on the sampling sequence, and select the component with the largest amplitude other than the fundamental wave from the transform result as the dominant harmonic; The determination module is used to determine the oscillation mode of the grid-connected converter according to the frequency and amplitude of the dominant harmonic, so as to select the corresponding grid-connected stability control strategy for execution; the determination module is also used to compare the frequency and amplitude of the dominant harmonic with the frequency threshold value and the amplitude threshold value one by one; if the amplitude of the dominant harmonic is lower than the minimum value of all amplitude threshold values, the oscillation mode of the grid-connected converter is determined to be a non-oscillation mode; if the frequency of the dominant harmonic is in the kth resonant frequency interval, and the amplitude of the dominant harmonic exceeds the kth resonant frequency interval, the oscillation mode of the grid-connected converter is determined to be a non-oscillation mode. When the amplitude threshold value corresponding to the subsynchronous or supersynchronous oscillation is reached, the oscillation mode of the grid-connected converter is determined to be the kth oscillation mode; wherein, k∈[1,3]; if the frequency of the dominant harmonic is located in the resonant frequency interval corresponding to the subsynchronous or supersynchronous oscillation, and the amplitude of the dominant harmonic is higher than the amplitude threshold value corresponding to the subsynchronous or supersynchronous oscillation, the oscillation mode of the grid-connected converter is determined to be the fourth oscillation mode; the resonant frequency interval corresponding to the subsynchronous or supersynchronous oscillation refers to a frequency band above 0 Hz and below the LC resonant frequency formed by the grid-side inductance and capacitance of the grid-connected converter.

6. A stability control device for a grid-connected converter, characterized in that: The device comprises an acquisition module, an extraction module and a determination module; The acquisition module is used to acquire the grid-side voltage or current of the grid-connected converter; The extraction module is used to extract the frequency and amplitude of the dominant harmonics from the grid-side voltage or current; the extraction module is also used to remove the fundamental component of the grid-side voltage or current; for the grid-side voltage or current after removing the fundamental component, the frequency and amplitude of the dominant harmonics are extracted through a first-order generalized integrator with a frequency-locked loop, a dual second-order generalized integrator with a frequency-locked loop, at least two second-order generalized integrators with frequency-locked loops connected in series, or at least two second-order generalized integrators with frequency-locked loops connected in parallel; The determination module is used to determine the oscillation mode of the grid-connected converter according to the frequency and amplitude of the dominant harmonic, so as to select the corresponding grid-connected stability control strategy for execution; the determination module is also used to compare the frequency and amplitude of the dominant harmonic with the frequency threshold value and the amplitude threshold value one by one; if the amplitude of the dominant harmonic is lower than the minimum value of all amplitude threshold values, the oscillation mode of the grid-connected converter is determined to be a non-oscillation mode; if the frequency of the dominant harmonic is in the kth resonant frequency interval, and the amplitude of the dominant harmonic exceeds the kth resonant frequency interval, the oscillation mode of the grid-connected converter is determined to be a non-oscillation mode. When the amplitude threshold value corresponding to the subsynchronous or supersynchronous oscillation is reached, the oscillation mode of the grid-connected converter is determined to be the kth oscillation mode; wherein, k∈[1,3]; if the frequency of the dominant harmonic is located in the resonant frequency interval corresponding to the subsynchronous or supersynchronous oscillation, and the amplitude of the dominant harmonic is higher than the amplitude threshold value corresponding to the subsynchronous or supersynchronous oscillation, the oscillation mode of the grid-connected converter is determined to be the fourth oscillation mode; the resonant frequency interval corresponding to the subsynchronous or supersynchronous oscillation refers to a frequency band above 0 Hz and below the LC resonant frequency formed by the grid-side inductance and capacitance of the grid-connected converter.

7. A stability control device for a grid-connected converter, characterized in that: The device comprises an acquisition module, an extraction module and a determination module; The acquisition module is used to acquire the grid-side voltage or current of the grid-connected converter; The extraction module is used to extract the frequency and amplitude of the dominant harmonic from the grid-side voltage or current; the extraction module is also used to sample the grid-side voltage or current at equal time intervals to obtain a sampling sequence; Perform discrete Fourier transform on the sampling sequence, and select the component with the largest amplitude other than the fundamental wave from the transform result as the dominant harmonic; The determination module is used to determine the oscillation mode of the grid-connected converter according to the frequency and amplitude of the dominant harmonic, so as to select the corresponding grid-connected stability control strategy for execution; the determination module is also used to obtain the grid-connected stability control strategy corresponding to the variable value corresponding to the oscillation mode according to the variable value corresponding to the oscillation mode; if the oscillation mode of the grid-connected converter is a non-oscillation mode, the grid-connected stability control strategy is maintained unchanged; if the oscillation mode of the grid-connected converter is the first oscillation mode, the grid-connected control strategy is adjusted to suppress the resonance in the first resonant frequency interval; if the oscillation mode of the grid-connected converter is the second oscillation mode, the grid-connected control strategy is adjusted to suppress the resonance in the second resonant frequency interval; if the The oscillation mode of the grid-connected converter is the third oscillation mode, and the grid-connected control strategy is adjusted to suppress the resonance in the third resonant frequency interval; if the oscillation mode of the grid-connected converter is the fourth oscillation mode, the grid-connected control strategy is adjusted to suppress subsynchronous or supersynchronous oscillation; the first resonant frequency interval refers to a frequency band located on the left side outside the bandwidth range of the critical frequency of the resonance of the grid-connected converter and above the LC resonant frequency formed by the grid-side inductance and capacitance of the grid-connected converter; the second resonant frequency interval refers to a frequency band within the bandwidth range of the critical frequency of the resonance of the grid-connected converter; the third resonant frequency interval refers to a frequency band located on the right side outside the bandwidth range of the critical frequency of the resonance of the grid-connected converter and below the Nyquist frequency.

8. The stability control device for a grid-connected converter according to any one of claims 5 to 7, characterized in that: The grid-side voltage or current of the grid-connected converter includes at least one of a bridge arm current, a grid-connected current, a grid-side capacitor current, a grid-side capacitor voltage or a grid-connected point voltage.

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