Double-fed wind power plant series compensation sending-out system subsynchronous oscillation suppression method for achieving negative damping full compensation design

Abstract

The invention discloses a double-fed wind power plant series compensation sending-out system subsynchronous oscillation suppression method for achieving negative damping full compensation design, and belongs to the technical field of impedance characteristic optimization, and the method comprises the steps: simplifying a double-fed wind power plant series compensation sending-out system, and obtaining the equivalent output impedance and series compensation line impedance of a double-fed fan; in the simplified system, the equivalent output impedance of the doubly-fed fan is further simplified, a negative damping factor index is introduced according to the simplified equivalent output impedance of the doubly-fed fan and series compensation line impedance, and whether subsynchronous oscillation exists in the system or not is judged; a positive feedback control branch for realizing negative damping full compensation is added in a simplified system, and positive feedback gain and a negative damping item are designed to realize positive and negative cancellation; and carrying out adaptive adjustment on the positive feedback gain under different working conditions. According to the invention, oscillation risk suppression can be realized, the drift of the oscillation mode under different working conditions can be suppressed, the subsynchronous frequency band impedance characteristic of the doubly-fed fan is effectively optimized, and the operation stability of the system is improved.

Description

Technical Field

[0001] The present application relates to the technical field of impedance characteristic optimization, and in particular to a method for suppressing subsynchronous oscillation of a doubly-fed wind farm series-compensated transmission system that realizes a negative damping full compensation design. Background Art

[0002] Studies have shown that high series compensation in the line and low rotor speed of the induction motor and large rotor-side current loop proportionality coefficient have adverse effects on the safe and stable operation of the system. This interaction between control and series compensation capacitors was first discovered in a doubly fed wind power plant in southern Texas, USA in 2009, causing a large number of wind turbines to be disconnected from the grid and damage to the crowbar circuit. In 2016, hundreds of similar subsynchronous oscillation accidents occurred in Guyuan, China, causing abnormal vibration of transformers and frequent disconnection of wind turbines.

[0003] At present, existing stability analysis methods and impedance control solutions generally perform damping compensation for specific application scenarios. However, changes in actual working conditions can easily cause the drift of oscillation modes and the increase and decrease of damping, thus affecting the impedance control effect and oscillation suppression effect.

[0004] Therefore, it is urgent to clarify the root cause of negative damping in the subsynchronous frequency band of the doubly fed wind farm series compensation transmission system, explore the impedance reshaping control scheme based on the negative damping full compensation design, and realize the adaptive control strategy of subsynchronous oscillation of the doubly fed wind farm series compensation transmission system. Summary of the invention

[0005] The present application aims to provide a method capable of realizing an adaptive control strategy for subsynchronous oscillation of a doubly-fed wind farm via series compensation transmission system.

[0006] In order to achieve the above-mentioned purpose, the technical solution of this application is:

[0007] A method for suppressing subsynchronous oscillation of a doubly-fed wind farm transmission system through series compensation with a negative damping full compensation design, comprising:

[0008] Simplify the double-fed wind farm through series compensation transmission system, and obtain the simplified double-fed wind turbine impedance and series compensation line impedance;

[0009] In the simplified double-fed wind farm series compensation transmission system, a negative damping factor index is introduced according to the simplified double-fed wind turbine impedance and the series compensation line impedance to determine whether there is subsynchronous oscillation in the double-fed wind farm series compensation transmission system;

[0010] A positive feedback control branch with full negative damping compensation is added to the simplified double-fed wind farm series compensation transmission system, and the positive feedback gain and negative damping term are designed to achieve positive and negative cancellation;

[0011] The negative damping full compensation parameters are adaptively adjusted under different working conditions.

[0012] Optionally, the simplified doubly-fed wind farm is transmitted through a series compensation system to obtain a simplified doubly-fed wind turbine impedance and a series compensation line impedance, including:

[0013] Establish the simplified admittance coefficient matrix of doubly-fed wind turbine;

[0014] By establishing the simplified admittance coefficient matrix of the doubly-fed wind turbine, the simplified doubly-fed wind turbine impedance and the series compensation line impedance are obtained.

[0015] Optionally, the introducing of a negative damping factor index to determine whether there is subsynchronous oscillation in the series-compensated transmission system of the doubly-fed wind farm includes:

[0016] Analyze the impedance of the phase-locked loop when the simplified doubly-fed wind farm is sent out of the system through series compensation, and obtain the simplified rotor-side control equivalent impedance, and obtain the doubly-fed wind turbine output impedance according to the simplified rotor-side control equivalent impedance;

[0017] By analyzing the overall impedance of the doubly-fed wind farm when the series compensation transmission system occurs, it is found that the real part of the doubly-fed wind farm when the series compensation transmission system occurs is negative, which is a necessary condition for the oscillation to occur;

[0018] The real resistance term in the series-compensated transmission system of the doubly-fed wind farm is characterized as a negative damping factor for determining whether subsynchronous oscillation exists in the series-compensated transmission system of the doubly-fed wind farm. When the negative damping factor is less than 0, the system lacks sufficient damping capacity, and subsynchronous oscillation is generated in the exciting line.

[0019] Optionally, a positive feedback control branch with full negative damping compensation is added to the simplified double-fed wind farm series compensation transmission system, and the positive feedback gain and negative damping term are designed to achieve positive and negative cancellation, including designing the full negative damping compensation as R v ·H f (s)·K e Form, where R v is the virtual resistance coefficient, which represents the additional damping coefficient introduced into the double-fed wind turbine through the series compensation transmission system, H f (s) is a negative damping compensation filter.

[0020] Optionally, the negative damping compensation filter is designed to have a gain of 1 at the resonant frequency and a gain of 0 at the fundamental frequency.

[0021] Optionally, a positive feedback control branch with full compensation of negative damping is added to the simplified doubly fed wind farm series compensation transmission system, and the positive feedback gain and the negative damping term are designed to achieve positive and negative cancellation. It also includes that when the output impedance of the doubly fed wind turbine is equal to 0, the negative damping of the doubly fed wind farm series compensation transmission system is offset to obtain the minimum value of the virtual resistance.

[0022] Optionally, the adaptive adjustment of the positive feedback gain under different working conditions includes:

[0023] Grid connection point oscillation information is detected;

[0024] Reading the preset negative damping full compensation bandwidth of the negative damping full compensation design of the series compensation transmission system of the doubly-fed wind turbine electric field;

[0025] Set the oscillation frequency voltage harmonic content threshold and the oscillation frequency current harmonic content threshold;

[0026] Setting the center frequency of the negative damping compensation filter;

[0027] Calculating the minimum value of the virtual resistance coefficient of the negative damping full compensation design gain;

[0028] Real-time monitoring of the voltage harmonic content and current harmonic content at the grid connection point;

[0029] Determine whether the following conditions are simultaneously met: the grid connection point voltage harmonic content < the oscillation frequency voltage harmonic content threshold and the grid connection point current harmonic content < the oscillation frequency current harmonic content threshold; if not, increase the minimum value of the virtual resistance coefficient; if satisfied, determine the value of the virtual resistance coefficient;

[0030] The adaptive adjustment of the positive feedback gain under different working conditions is completed.

[0031] Optionally, the detecting grid connection point oscillation information includes:

[0032] According to the value of the negative damping factor, it is judged that the double-fed wind turbine electric field has subsynchronous oscillation through series compensation transmission system;

[0033] The resonant component is extracted from the grid connection point through the negative damping full compensation design.

[0034] Optionally, the reading of the preset negative damping full compensation bandwidth of the negative damping full compensation design of the series compensation transmission system of the doubly-fed wind turbine electric field includes confirming that the oscillation frequency is within the effective action bandwidth of the negative damping full compensation bandwidth.

[0035] Optionally, the adaptive adjustment of the negative damping full compensation parameters under different working conditions includes sending the detected oscillation frequency information into the negative damping full compensation design to adapt to the center frequency of the negative damping compensation filter.

[0036] The method for suppressing subsynchronous oscillations of a doubly-fed wind farm series-compensated transmission system that implements a negative damping full compensation design provided in the present application can adapt to different operating conditions, achieve oscillation risk suppression, help suppress the drift of oscillation modes under different operating conditions, effectively optimize the impedance characteristics of the doubly-fed wind turbine in the subsynchronous frequency band, and improve the stability of the operation of the doubly-fed wind turbine series-compensated transmission system.

[0037] In order to make the above features and advantages of the application more obvious and easy to understand, the following embodiments are specifically cited and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The present invention is a flow chart of a method for suppressing subsynchronous oscillation of a doubly-fed wind farm system through series compensation transmission that realizes a negative damping full compensation design according to the present invention.

[0039] Figure 2 This is the block diagram of the series compensation output system and fan control of the doubly fed wind turbine.

[0040] Figure 3 Figure (a) is the power flow diagram of the doubly fed wind turbine in sub-synchronous operation mode.

[0041] Figure 3 Figure (b) is the power flow diagram of the doubly fed wind turbine in the super synchronous operation mode.

[0042] Figure 4 This is a simplified circuit topology diagram of a doubly-fed wind turbine.

[0043] Figure 5 This is a simplified equivalent impedance circuit diagram of the series-compensated transmission system of a doubly-fed wind farm.

[0044] Figure 6 This is the control block diagram of the full compensation controller with additional negative damping.

[0045] Figure 7 The flowchart is for adaptively adjusting the positive feedback gain under different working conditions.

[0046] Figure 8 This is the impedance curve and frequency sweep verification result diagram of the simplified doubly-fed wind turbine series-compensated output system.

[0047] Fig. 9 This is the output impedance curve of the doubly fed wind turbine before and after the introduction of the phase-locked loop.

[0048] Fig.10This is the impedance curve of the doubly-fed wind turbine after series compensation before and after the introduction of the additional negative damping full compensation controller.

[0049] Fig.11 This is the voltage and current waveform diagram of the PCC point of the doubly fed wind turbine after series compensation before adding negative damping full compensation adaptive control.

[0050] Fig.12 This is the Fourier analysis diagram of the current at the PCC point of the doubly-fed wind turbine after series compensation before the negative damping full compensation adaptive control is added.

[0051] Fig.13 This is the voltage and current waveform diagram of the PCC point of the doubly fed wind turbine after adding negative damping full compensation adaptive control and sending it through series compensation.

[0052] In the drawings, like reference numerals refer to the same drawing elements. DETAILED DESCRIPTION

[0053] In order to make the purpose and technical solution of the embodiment of the present application clearer, the technical solution of the embodiment of the present application will be clearly and completely described in conjunction with the drawings of the embodiment of the present application. Obviously, the described embodiment is a part of the embodiment of the present application, not all of the embodiments. Based on the described embodiment of the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0054] In a specific embodiment of the present application, a method for suppressing subsynchronous oscillation of a doubly-fed wind farm transmission system through series compensation with a negative damping full compensation design is provided, comprising steps S10 to S40.

[0055] S10: Simplify the series compensation transmission system of the doubly fed wind farm to obtain the equivalent output impedance of the doubly fed wind turbine and the series compensation line impedance.

[0056] S20: In the simplified doubly-fed wind farm series-compensated transmission system, the equivalent output impedance of the doubly-fed wind turbine is further simplified, and a negative damping factor index is introduced according to the simplified equivalent output impedance of the doubly-fed wind turbine and the series-compensated line impedance to determine whether there is subsynchronous oscillation in the doubly-fed wind farm series-compensated transmission system.

[0057] S30: adding a positive feedback control branch for achieving full compensation of negative damping to the simplified doubly-fed wind farm series compensation transmission system, and designing the positive feedback gain and negative damping term to achieve positive and negative cancellation.

[0058] S40: Adaptively adjusting the positive feedback gain under different working conditions.

[0059] The method for suppressing subsynchronous oscillations of a doubly-fed wind farm series-compensated transmission system that implements a negative damping full compensation design provided in the present application can adapt to different operating conditions, achieve oscillation risk suppression, help suppress the drift of oscillation modes under different operating conditions, effectively optimize the impedance characteristics of the doubly-fed wind turbine in the subsynchronous frequency band, and improve the stability of the operation of the doubly-fed wind turbine series-compensated transmission system.

[0060] In step S10, refer to Figure 1 In step S10, the doubly-fed wind farm is simplified through the series compensation transmission system to obtain the doubly-fed wind turbine equivalent output impedance and the series compensation line impedance.

[0061] As an example, see Figure 2 , Figure 2 The control block diagram of the double-fed wind farm is connected to the grid through the common coupling point PCC. g is the series compensation capacitor in the circuit, L g , R g is the grid impedance.

[0062] As an example, when the iron loss and the mechanical loss of the doubly-fed wind turbine are ignored, the power flow of the doubly-fed wind turbine is as follows: Figure 3 As shown, Figure 3 Figure a in the figure is the sub-synchronous operation mode of the doubly fed wind turbine. Figure 3 Figure b in the figure is the super synchronous operation mode of the doubly fed wind turbine; where P s is the stator power, P r is the rotor power; P es is the stator electromagnetic power, P er is the rotor electromagnetic power; P cus is the stator copper loss, P cur is the rotor copper loss; P o is the mechanical power output of the fan. Figure 3 It can be seen that most of the power of the doubly fed wind turbine flows through the stator circuit, and the grid-side converter only passes through the slip power, which is equivalent to a greater restriction on the current flow. The influence of the grid-side converter impedance on the overall impedance depends on its rated power. Therefore, the equivalent impedance of the grid-side converter is greater than the impedance of the wind turbine side. When analyzing, the grid-side converter can be regarded as an open circuit. At the same time, to simplify the analysis, the line impedance on the wind farm side is converted to the wind turbine side according to the transformer ratio and the influence of the transformer leakage reactance is ignored. Therefore, the simplified line impedance becomes as follows: Figure 4 The RLC series form shown.

[0063] As an example, define Indicates the voltage from the motor rotor side to the stator side. Indicates the current from the motor rotor side to the stator side. represents the small signal harmonic vector of the rotor-side converter modulation signal, The frequencies corresponding to the elements in are:

[0064]

[0065] Among them, For example, element I rp±x Represents the amplitude of the current from the rotor side to the stator side at the corresponding frequency, α rp ±x represents the initial phase angle of the current from the rotor side to the stator side at the corresponding frequency.

[0066] For a doubly fed wind turbine, the frequency is f p The grid voltage disturbance signal will generate harmonic responses of the same frequency in the stator, and when they are respectively connected to the rotor side with the frequency xf1-f r When the harmonics (x=0,1,2) act in phase, a pair of harmonics with a frequency of f will be generated on the output voltage of the rotor-side converter bridge arm. p +xf1-f r (x=0,1,2) and f p -xf1+f r (x=0,1,2) new small signal harmonics. After passing through the control loop, the harmonic small signal of this frequency will make each variable in the power circuit of the rotor-side converter contain a frequency of Harmonics of (x=0,1,2).

[0067] Further, the The frequencies corresponding to each element in are expressed as:

[0068] {f p -(2f1-f r ),f p -(f1-f r ),f p -f r ,f p +f1-f r ,f p +2f1-f r}

[0069] Among them, f p , f1 and f r They represent the disturbance frequency, fundamental frequency and electrical frequency of fan rotation respectively.

[0070] As an example, according to Figure 4 The simplified circuit topology of the doubly fed wind turbine shown in the figure can be used to obtain the power circuit small signal model:

[0071]

[0072] Among them, Zig is the diagonal matrix of the motor passive impedance, is the small signal harmonic vector of the grid-connected voltage, is the small signal harmonic vector of the stator current of the grid-side converter of the doubly-fed wind turbine, The frequencies corresponding to the elements in are:

[0073]

[0074] Among them, For example, element I sp±x Table 2 shows the amplitude of the current from the rotor side to the stator side at the corresponding frequency, α sp ±x represents the initial phase angle of the current from the rotor side to the stator side at the corresponding frequency.

[0075] Similarly, the frequency f p The grid voltage disturbance signal will generate harmonic responses of the same frequency in the stator, and when they interact with the harmonics of frequency xf1 (x = 0, 1, 2) in the grid-side converter, a harmonic response of frequency f will be generated on the output voltage of the bridge arm of the grid-side converter. p ±xf1 new small signal harmonics. After passing through the control loop, the harmonic small signal of this frequency will make each variable in the power circuit of the grid-side converter contain a frequency of f p ± Harmonics of xf1(x=0,1,2).

[0076] Further, the The frequencies corresponding to each element in are expressed as:

[0077] {f p -2f1,f p -f1,f p ,f p +f1,f p +2f1}

[0078] Please continue reading Figure 4 ,according to Figure 4 The simplified circuit topology diagram of the doubly fed wind turbine shown in the figure can be used to obtain the small signal control model of the doubly fed wind turbine rotor side converter:

[0079]

[0080] Among them, Q r is the gain matrix related to the output current, the matrix P r is the gain matrix related to the output voltage, and its corresponding expression is:

[0081]

[0082] P rThe remaining elements are all 0.

[0083] Where diag is the diagonal matrix symbol; is the initial phase angle of the grid voltage, α r1 is the initial phase angle of the rotor side current, γ r1 is the initial phase angle of the rotor side converter modulation signal; H ri (s-jω1) is the expression after the PI controller of the rotor side current loop generates frequency offset, and its offset is jω1, K rd is the decoupling coefficient; I r M is the current from the motor rotor side to the stator side. r is the rotor side converter modulation signal; N s is the number of stator turns, N r is the number of rotor turns; G PLL (s) is the closed-loop transfer function of the phase-locked loop, G PLL The expression of (s) is:

[0084]

[0085] Among them, H PLL (s-jω1) is the expression after the frequency offset generated by the pi controller of the phase-locked loop, V s is the stator voltage.

[0086] As an example, by combining the power circuit small signal model formula and the doubly fed wind turbine rotor side converter small signal control model, the standard form of the admittance coefficient matrix of the doubly fed wind turbine can be obtained as follows:

[0087] Y=(UP r )(Z ig +C i Q r ) -1

[0088] Among them, Z ig is the diagonal matrix of the motor passive impedance; C i is the conversion matrix from rotor side current to stator side current; U is a 5×5 unit matrix.

[0089] As an example, extract the simplified admittance coefficient matrix Y of the doubly fed wind turbine at position (3,3) Y(3,3) to obtain the equivalent output impedance Z of the doubly fed wind turbine wf (s):

[0090] Z wf (s)=1 / Y (3,3)

[0091] As an example, the series compensation K cIt can be defined by the ratio of capacitive reactance to inductive reactance in the grid impedance at the fundamental frequency f1, which is usually 20% to 50%. g is the equivalent inductance of the weak network line, R g is the equivalent resistance of the weak network line, and the series compensation capacitor C g It can be defined as:

[0092] C g =1 / ((2πf1) 2 L g ·K c )

[0093] Furthermore, the series compensation line impedance Z can be obtained g (s) is:

[0094] Z g (s)=sL g +R g +1 / (sC g )

[0095] Where s is the complex frequency domain variable in the Laplace transform.

[0096] In step S20, refer to Figure 1 In step S20, in the simplified doubly fed wind farm series compensation transmission system, the equivalent output impedance of the doubly fed wind turbine is further simplified, and a negative damping factor index is introduced according to the simplified equivalent output impedance of the doubly fed wind turbine and the series compensation line impedance to determine whether subsynchronous oscillation exists in the doubly fed wind farm series compensation transmission system.

[0097] As an example, from step S10, the equivalent output impedance Z of the complete doubly-fed wind turbine can be obtained. wf (s) is expressed as:

[0098]

[0099] in, is the initial phase angle of the grid voltage, α r1 is the initial phase angle of the rotor side current, γ r1 is the initial phase angle of the modulation signal of the rotor side converter; R r ′ / slip is the rotor winding resistance calculated to the stator side through the winding and slip, L l ' r is the rotor leakage inductance converted to the stator side through the winding and slip; L ls is the stator side winding resistance, R s is the stator side leakage inductance; K e is the stator-rotor turns ratio of the motor. slip is the slip rate reduction function related to wind speed and frequency, slip=(s-jω e ) / s; Hri (s-jω1) is the expression after the PI controller of the rotor side current loop generates frequency offset, and its offset is jω1; I r M is the current from the motor rotor side to the stator side. r G is the modulation signal of the rotor side converter; PLL (s) is the closed-loop transfer function of the phase-locked loop.

[0100] As an example, after ignoring the influence of the phase-locked loop equivalent impedance, the expression of the rotor side control equivalent impedance calculated to the stator side through the winding and the slip can be simplified to:

[0101]

[0102] Among them, H ri (s-jω1) is the expression after the PI controller of the rotor side current loop generates a frequency offset, and the offset is jω1.

[0103] Furthermore, after ignoring the influence of the equivalent impedance of the phase-locked loop, the simplified equivalent output impedance Z of the doubly fed wind turbine is i The expression of (s) is:

[0104]

[0105] Furthermore, the simplified double-fed wind farm is transmitted through the series compensation system to simplify the equivalent impedance circuit as follows: Figure 5 shown.

[0106] As an example, it can be known from the Nyquist stability criterion that when the double-fed wind turbine generates a frequency f through series compensation, r The necessary and sufficient conditions for the system to oscillate are: r Lower series compensation line impedance Z g And Z ignoring the effect of the equivalent impedance of the phase-locked loop i (s) (equal in amplitude) and the impedance phase shift of the two is greater than 180°, the overall impedance of the doubly fed wind turbine satisfies:

[0107]

[0108] Furthermore, we can get the real part of the system Z g (j2πf r )+Z i (j2πf r ) is negative, which is a necessary condition for the occurrence of oscillation. Therefore, by analyzing the real resistance term in the system impedance alone, the frequency band in which subsynchronous oscillations may occur in the system can be predicted.

[0109] As an example, a negative damping factor indicator is introduced to determine whether there is a subsynchronous oscillation in the system. According to the real resistance term Re(Z g (j2πf r )+Z i (j2πf r )), the negative damping factor Z is obtained re (s):

[0110]

[0111] Among them, k prc is the rotor current loop proportional coefficient.

[0112] As an example, when the negative damping factor Z re (j2πf r ) is less than 0 (i.e., when the amplitude of the negative resistance component exceeds the positive resistance component), the double-fed wind farm lacks sufficient damping capacity through the series compensation transmission system, which may excite the frequency f in the line r subsynchronous oscillation.

[0113] In step S30, refer to Figure 1 In step S30, a positive feedback control branch for achieving full compensation of negative damping is added to the simplified double-fed wind farm series compensation transmission system, and the positive feedback gain and negative damping term are designed to achieve positive and negative cancellation.

[0114] As an example, a fully compensated controller with additional negative damping is designed, including the positive feedback control branch. re By achieving positive and negative cancellation of the negative damping term in (s), the negative damping factor of the system can be always non-negative, thereby ensuring the stable operation requirements of the double-fed wind farm through series compensation transmission system. Therefore, in order to fundamentally ensure the stable control requirements of the double-fed wind farm through series compensation transmission system and eliminate the oscillation risk in the line, an additional positive feedback control branch is added to the original control structure of the double-fed wind turbine.

[0115] As an example, see Figure 6 The additional negative damping full compensation link in the additional negative damping full compensation controller is designed as R v ·H f (s)·K e Form, where R v is the virtual resistance coefficient, which represents the additional damping coefficient introduced into the double-fed wind farm through the series compensation transmission system, H f (s) is a negative damping compensation filter, which is designed to have a gain of 1 at the resonant frequency and a gain of 0 at the fundamental frequency, so as to achieve negative damping suppression at the resonant frequency and avoid affecting the fundamental frequency working characteristics. f(s) is designed as a second-order bandpass filter link:

[0116]

[0117] Among them, ω b is the central angular frequency of the additional negative damping full compensation controller, BW is the negative damping full compensation bandwidth, and s is the complex frequency domain variable in the Laplace transform.

[0118] As an example, the negative damping full compensation bandwidth BW needs to be configured in advance. The series compensation transmission system of the doubly fed wind farm first obtains the effective action frequency band of the additional negative damping full compensation controller by giving the passive parameters of the induction motor, and presets the initial negative damping full compensation bandwidth BW of the additional negative damping full compensation controller, so as to limit the negative damping full compensation bandwidth BW of the additional negative damping full compensation controller to a smaller range without losing effectiveness.

[0119] Specifically, the negative damping full compensation bandwidth BW is preconfigured to be 5 Hz, and ω b Configured as a subsynchronous oscillator with a center angular frequency of 2πf r .

[0120] As an example, after adding the additional negative damping full compensation link, the negative damping factor Z can be obtained. re (s) In the negative damping compensation filter H f (s) center frequency f b Expressions near Z r ' e (s):

[0121]

[0122] Among them, R v Minimum in Z r ' e (s) = 0, at which time the negative damping of the series-compensated transmission system of the doubly-fed wind farm is just offset and is in a critical stable state. v The expression for the minimum value is:

[0123]

[0124] In step S40, refer to Figure 1 In step S40, the positive feedback gain is adaptively adjusted under different working conditions.

[0125] As an example, since the impedance of the doubly fed wind turbine is greatly affected by wind speed and wind turbine output, the oscillation mode will also drift with different working conditions. Due to the existence of errors, it is necessary to v(min)On this basis, adaptive adjustment is performed until the voltage V and current I information of the grid-connected point meet the grid-connected requirements, thereby enabling the doubly fed wind turbine to operate stably under different working conditions.

[0126] Therefore, in order to achieve safe and stable operation of the wind farm under all operating conditions, it is necessary to adaptively adjust the parameters of the positive feedback gain designed for the additional negative damping full compensation controller according to different operating conditions, so as to achieve the safe and stable operation requirements of the doubly fed wind farm series compensation transmission system under all operating conditions.

[0127] As an example, see Figure 7 , the adaptive adjustment of the parameters of the additional negative damping full compensation controller also includes: S401 to S408.

[0128] Step S401: Detecting grid connection point oscillation information.

[0129] Step S402: reading a preset negative damping full compensation bandwidth BW of an additional negative damping full compensation controller of a series compensation transmission system of a doubly-fed wind farm.

[0130] Step S403: Setting the oscillation frequency voltage harmonic content threshold V th The current harmonic content threshold I th .

[0131] Step S404: Setting the negative damping compensation filter H f (s) center frequency f b .

[0132] Step S405: Calculate the virtual resistance coefficient R of the additional negative damping full compensation controller gain at this time v The minimum value R v(min) .

[0133] Step S406: Real-time monitoring of the grid connection point voltage harmonic content V and grid connection point current harmonic content I information.

[0134] Step S407: Determine whether the following conditions are met at the same time: the grid connection point voltage harmonic content V < the oscillation frequency voltage harmonic content threshold V th And the grid-connected point current harmonic content I< oscillation frequency current harmonic content threshold I th If not satisfied, increase R v , if satisfied, determine R v The value of .

[0135] Step S408: the adaptive adjustment of the positive feedback gain under different working conditions is completed.

[0136] As an example, the step S401 further includes:

[0137] According to the negative damping factor Zre The value of (s) determines that the double-fed wind farm has subsynchronous oscillation in the series compensation transmission system;

[0138] The resonant component is extracted from the grid connection point by the additional negative damping full compensation controller.

[0139] As an example, the step S402 further includes: confirming that the oscillation frequency is within the effective action bandwidth of the negative damping full compensation bandwidth BW.

[0140] As an example, the step S404 further includes: sending the detected oscillation frequency information to the additional negative damping full compensation controller and the negative damping compensation filter H f (s) center frequency f b Suitable.

[0141] The present application provides a method for suppressing subsynchronous oscillations of a series-compensated transmission system of a doubly-fed wind farm that can realize a negative damping full compensation design, simplifies the impedance model of a doubly-fed wind turbine, introduces a negative damping factor indicator, explores the formation cause of the negative damping characteristics of the system, utilizes the basic idea of ​​damping cancellation, solves the parameter boundary of an additional negative damping full compensation controller, performs parameter design on the additional negative damping full compensation controller, and realizes oscillation risk suppression through an adaptive negative damping full compensation control method that adapts to different working conditions, which helps to suppress the drift of oscillation modes under different working conditions, effectively optimizes the impedance characteristics of the subsynchronous frequency band of the doubly-fed wind turbine, and improves the stability of system operation.

[0142] As an example, in order to verify the feasibility and effectiveness of the method for suppressing subsynchronous oscillations of a doubly-fed wind farm through series compensation transmission system with full compensation design of negative damping, the present application provides a verification method for the method for suppressing subsynchronous oscillations of a doubly-fed wind farm through series compensation transmission system with full compensation design of negative damping, and gives the following example: Figure 2 The main parameters and values ​​of the series-compensated output system of the doubly-fed wind farm shown in Table 1 are shown in Table 1. The rated output power of the doubly-fed wind turbine is 1.5MW.

[0143] Table 1 Main parameters of the double-fed wind farm series transmission system

[0144]

[0145]

[0146] As an example, in step S10, the equivalent output impedance Z of the doubly-fed wind turbine is obtained. wf (s) and the impedance model Z of the series compensation line g(s) After that, a complete simulation model of the double-fed wind farm with series compensation transmission system is established, and the test impedances of the wind turbine and the series compensation line of the complete simulation model are obtained by frequency sweeping (the test points are marked with blue and red triangles respectively). Figure 8 The simplified impedance curve and frequency sweep verification results of the series-compensated output system of the doubly-fed wind farm are given, where the blue and red solid line curves represent the theoretical impedance Z of the doubly-fed wind turbine, respectively. wf (s) and the series compensation line impedance Z g (s). At the same time, Figure 8 It can be seen that the frequency sweep result of the complete wind turbine model is well consistent with the simplified theoretical impedance curve within 1kHz, especially in the sub-supersynchronous frequency band. Therefore, when analyzing the sub-synchronous oscillation of the double-fed wind farm through series compensation, the equivalent output impedance Z of the double-fed wind turbine can be used. wf (s) to simplify the analysis.

[0147] As an example, in step S20, see Fig. 9 According to the output impedance curve of the doubly fed wind turbine before and after the introduction of the phase-locked loop, Z wf (s) is the output impedance of the doubly fed wind turbine before the phase-locked loop, Z i (s) is the output impedance of the doubly fed wind turbine after the phase-locked loop. It can be seen that as the frequency gradually approaches the fundamental frequency, the equivalent impedance Z of the phase-locked loop pll (s) decreases rapidly until it is close to the output impedance of the doubly fed wind turbine without considering the phase-locked loop. At this time, the output impedance of the doubly fed wind turbine will be determined by these two factors. The impedance of the doubly fed wind turbine in other frequency bands is basically dominated by the output impedance of the doubly fed wind turbine without considering the phase-locked loop. Considering that the doubly fed wind turbine has inductive negative damping in the super-synchronous operation state, which interacts with the capacitive impedance characteristics of the series-compensated line to form oscillation, it can be determined that the frequency band where sub-synchronous oscillation occurs must be located in In this risk frequency range, the effect of the phase-locked loop on the impedance of the doubly-fed wind turbine can be ignored, so it can be ignored in the simplified analysis of the output impedance of the doubly-fed wind turbine.

[0148] As an example, in step S30, the negative damping of the double-fed wind farm transmitted through the series compensation system is just offset and offset to be in a critical stable state. v(min) , under the working conditions in Table 1, use the rotor side parameters in the table to perform R v Design, calculate R from the above formula v The minimum value is 0.0652, the center frequency f b Set to f b =25Hz, the current working condition will be adapted to the R v(min) After the additional negative damping full compensation controller is connected, the impedance curve of the doubly fed wind turbine is as follows: Fig.10It can be seen that the margin of the doubly-fed wind turbine is increased from -12.39° to -1.77°, and the damping capacity of the doubly-fed wind farm through series compensation transmission system is improved.

[0149] The error compared with the theoretical analysis is due to the frequency deviation caused by the simplification of the impedance model of the doubly fed wind turbine in the control process and the introduction of an additional negative damping full compensation controller.

[0150] As an example, in step S40, under the working conditions in Table 1, the calculated R v(min) is 0.0652, then in R v(min) See Fig.11 , the voltage and current waveforms of the PCC point of the double-fed wind farm after series compensation are given under the working conditions shown in Table 1, and the corresponding Fourier analysis results are as follows Fig.12 As shown, this shows that the doubly fed wind turbine is connected to a capacitive series compensation line so that the doubly fed wind farm meets the resonance condition through the series compensation transmission system. At this time, the voltage and current distortion at the PCC point is serious, and the central oscillation frequency is 25Hz, which is basically consistent with the theoretical analysis. Fig.13 The voltage and current waveforms of the PCC point during the adaptive negative damping compensation process when the double-fed wind turbine is switched into the series compensation line are given. Fig.11 Comparative analysis shows that when the line is cut in, the doubly fed wind farm gradually oscillates through the series compensation transmission system. However, as the current and voltage harmonics generated by the PCC point are detected, the additional negative damping full compensation controller is put into control, and the doubly fed wind farm gradually enters a stable state through the series compensation transmission system.

[0151] Although the present application has been disclosed as above with the embodiments, it is not intended to limit the present application. Any person with ordinary knowledge in the technical field can make some changes and modifications without departing from the spirit and scope of the present application. Therefore, the scope of protection of the present application shall be determined by the scope of the attached patent application.

Claims

1. A method for suppressing subsynchronous oscillation of a doubly-fed wind farm transmission system through series compensation with full compensation design for negative damping, characterized in that: include, Simplify the double-fed wind farm series compensation transmission system to obtain the double-fed wind turbine equivalent output impedance and series compensation line impedance; In the simplified doubly-fed wind farm series-compensated transmission system, the doubly-fed wind turbine equivalent output impedance is further simplified, and a negative damping factor index is introduced according to the simplified doubly-fed wind turbine equivalent output impedance and the series-compensated line impedance to determine whether subsynchronous oscillation exists in the doubly-fed wind farm series-compensated transmission system; A positive feedback control branch for achieving full compensation of negative damping is added to the simplified double-fed wind farm series compensation transmission system, and the positive feedback gain and negative damping term are designed to achieve positive and negative cancellation; The positive feedback gain is adaptively adjusted under different working conditions.

2. The method for suppressing subsynchronous oscillation of a doubly-fed wind turbine electric field through series compensation transmission system realizing negative damping full compensation design as claimed in claim 1 is characterized in that: The simplified doubly-fed wind farm is transmitted through the series compensation system to obtain a simplified doubly-fed wind turbine impedance and a series compensation line impedance, including: Establish the simplified admittance coefficient matrix of doubly-fed wind turbine; By establishing the simplified admittance coefficient matrix of the doubly-fed wind turbine, the simplified doubly-fed wind turbine impedance and the series compensation line impedance are obtained.

3. The method for suppressing subsynchronous oscillation of a doubly-fed wind farm transmission system through series compensation with full negative damping compensation design as claimed in claim 2, characterized in that: The negative damping factor index is introduced to determine whether the double-fed wind farm has subsynchronous oscillation through series compensation transmission system, including: Analyze the impedance of the phase-locked loop when the simplified doubly-fed wind farm is sent out of the system through series compensation, and obtain the simplified rotor-side control equivalent impedance, and obtain the doubly-fed wind turbine output impedance according to the simplified rotor-side control equivalent impedance; By analyzing the overall impedance of the doubly-fed wind farm when the series compensation transmission system occurs, it is found that the real part of the doubly-fed wind farm when the series compensation transmission system occurs is negative, which is a necessary condition for the oscillation to occur; The real resistance term in the series compensation transmission system of the doubly fed wind farm is characterized as a negative damping factor for determining whether there is subsynchronous oscillation in the series compensation transmission system of the doubly fed wind farm. When the negative damping factor is less than 0, the system lacks sufficient damping capacity, which stimulates the doubly fed wind farm to generate subsynchronous oscillation in the series compensation transmission system.

4. The method for suppressing subsynchronous oscillation of a doubly-fed wind farm system through series compensation transmission with full negative damping compensation design as claimed in claim 3, characterized in that: The method adds a positive feedback control branch with full negative damping compensation to the simplified double-fed wind farm series compensation transmission system, designs the positive feedback gain and the negative damping term to achieve positive and negative cancellation, including designing the full negative damping compensation as R v ·H f (s)·K e Form, where R v is the virtual resistance coefficient, which represents the additional damping coefficient introduced into the double-fed wind turbine through the series compensation transmission system, H f (s) is a negative damping compensation filter.

5. The method for suppressing subsynchronous oscillation of a doubly-fed wind farm transmission system through series compensation with a negative damping full compensation design as claimed in claim 4, characterized in that: The negative damping compensation filter is designed to have a gain of 1 at the resonant frequency and a gain of 0 at the fundamental frequency.

6. The method for suppressing subsynchronous oscillation of a doubly-fed wind farm transmission system through series compensation with a negative damping full compensation design as claimed in claim 4, characterized in that: The method further includes adding a positive feedback control branch with full negative damping compensation to the simplified doubly-fed wind farm series compensation transmission system, designing the positive feedback gain and the negative damping term to achieve positive and negative cancellation, and also including that when the output impedance of the doubly-fed wind turbine is equal to 0, the negative damping of the doubly-fed wind farm series compensation transmission system is offset to obtain the minimum value of the virtual resistance.

7. The method for suppressing subsynchronous oscillation of a doubly-fed wind farm transmission system through series compensation with a negative damping full compensation design as claimed in claim 6, characterized in that: The adaptive adjustment of the positive feedback gain under different working conditions includes: Grid connection point oscillation information is detected; Reading the preset negative damping full compensation bandwidth of the negative damping full compensation design of the series compensation transmission system of the doubly-fed wind turbine electric field; Set the oscillation frequency voltage harmonic content threshold and the oscillation frequency current harmonic content threshold; Setting the center frequency of the negative damping compensation filter; Calculating the minimum value of the virtual resistance coefficient of the negative damping full compensation design gain; Real-time monitoring of the voltage harmonic content and current harmonic content at the grid connection point; Determine whether the following conditions are simultaneously met: the grid connection point voltage harmonic content < the oscillation frequency voltage harmonic content threshold and the grid connection point current harmonic content < the oscillation frequency current harmonic content threshold; if not, increase the minimum value of the virtual resistance coefficient; if satisfied, determine the value of the virtual resistance coefficient; The adaptive adjustment of the positive feedback gain under different working conditions is completed.

8. The method for suppressing subsynchronous oscillation of a doubly-fed wind farm transmission system through series compensation with full negative damping compensation design as claimed in claim 7, characterized in that: The detected grid connection point oscillation information includes: According to the value of the negative damping factor, it is judged that the double-fed wind turbine electric field has subsynchronous oscillation through series compensation transmission system; The resonant component is extracted from the grid connection point through the negative damping full compensation design.

9. The method for suppressing subsynchronous oscillation of a doubly-fed wind farm transmission system through series compensation with full negative damping compensation design as claimed in claim 7, characterized in that: The reading of the preset negative damping full compensation bandwidth of the negative damping full compensation design of the series compensation transmission system of the double-fed wind turbine electric field, This includes confirming that the oscillation frequency is within the effective action bandwidth of the negative damping full compensation bandwidth.

10. The method for suppressing subsynchronous oscillation of a doubly-fed wind farm transmission system through series compensation with full negative damping compensation design as claimed in claim 7, characterized in that: The adaptive adjustment of the negative damping full compensation parameters under different working conditions includes sending the detected oscillation frequency information into the negative damping full compensation design to adapt to the center frequency of the negative damping compensation filter.

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