A cooperative control method and system for inhibiting overvoltage disturbance of a doubly-fed wind turbine generator

Abstract

The application discloses a kind of inhibiting overvoltage disturbance of double-fed wind turbine's collaborative control method belonging to wind power system control field.The rotor side converter control law of double-fed wind turbine is deduced by defining double-fed wind turbine machine side macro variable, the rotor side converter control law of double-fed wind turbine is deduced by defining double-fed wind turbine network side macro variable, and collaborative controller is constructed, above-mentioned control law replaces the current inner ring structure of classic double-loop control, parameter vector is selected using the parameter selection method of collaborative controller, and the collaborative control of inhibiting overvoltage disturbance of double-fed wind turbine is realized.The method disclosed by the application can reduce the influence of overvoltage impact on DFIG, reduce the reactive current output by DFIG, achieve the effect of inhibiting overvoltage, ensure the stable operation of DFIG, and has significant advantages in inhibiting overvoltage peak value and peak value duration and reducing electrical quantity overshoot, and has good control effect on high-dimensional nonlinear wind power system.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of wind power system control, and particularly relates to a cooperative control method and system for suppressing overvoltage disturbance of a doubly-fed wind turbine. BACKGROUND

[0002] During the operation of a power system, overvoltage phenomena often occur, such as power frequency overvoltage caused by long line capacitance effect, voltage rise caused by sudden load shedding, and resonance overvoltage generated by capacitive inductive elements. Due to the special structure of the stator of a doubly-fed wind turbine (DFIG) directly coupled with the power grid, the doubly-fed wind turbine has weak overvoltage tolerance, and sustained overvoltage impact can cause impact current in the rotor, endangering equipment safety, and even leading to large-scale wind turbine off-grid, which has a great impact on the safe and stable operation of a new energy power system.

[0003] In the prior art, overvoltage problems of a power system are mainly addressed from the following two aspects: using external auxiliary devices and improving wind turbine converter control strategies. For example, in Chinese Invention Patent CN 202010391299.3, a doubly-fed wind turbine low-voltage ride-through control method and system based on transient overvoltage suppression are proposed, in which a measurement device is used to obtain the terminal voltage value of the wind turbine, and by comparing the actual voltage value with the given value, if the actual voltage value is greater than the given value, the converter control mode is switched. This method needs to rely on the addition of external equipment, but considering the wide distribution range of wind turbines in a wind farm, individually adjusting the voltage of a certain bus has little effect on the overall improvement, and the addition of extra equipment is costly and complex to maintain, which is not suitable for new energy systems with high proportion and high penetration rate of wind power. For another example, in Chinese Invention Patent CN 201710880776.0, a method, device and system for suppressing overvoltage at the output end of an inverter are proposed, in which when power grid outage is detected, the energy at the output end of the inverter is transferred in the opposite direction to reduce the output voltage of the inverter, but the switching control strategy does not consider the problem of voltage critical point fluctuation.

[0004] In recent years, cooperative control theory has gradually been concerned, and due to its simple control law design, good dynamic and steady-state characteristics of the controller, and strong robustness, it has been widely applied in power system control. However, in the existing technology applying cooperative control theory, there is no effective method to suppress overvoltage problems.

[0005] Therefore, how to reduce the impact of overvoltage impact on DFIG and ensure stable operation of DFIG is an urgent problem to be solved. SUMMARY

[0006] The application aims to provide a cooperative control method and system for inhibiting overvoltage disturbance of a doubly-fed wind turbine generator set.

[0007]

[0008] wherein K i3 , K s3 , K i4 , K s4 are PI coefficients, S is an integral term in PI control, I gd , I gq is an outlet current of the grid-side converter, I gdref is a DFIG grid-side active current reference value, I gqref is a DFIG grid-side reactive current reference value.

[0009] The application further comprises the following steps:

[0010] S2: obtaining a terminal voltage of the wind turbine generator set by using a measuring device, taking providing reactive power support for the power grid by the doubly-fed wind turbine generator set rotor-side converter under overvoltage state as a control target, and defining a doubly-fed wind turbine generator set terminal-side macro variable as

[0011]

[0012] wherein I rd , I rq are d, q-axis components of the rotor current, I rdref is a DFIG rotor active current reference value, I rqref is a DFIG rotor reactive current reference value, U s is a terminal voltage of the doubly-fed wind turbine generator set, U sref is a terminal voltage reference value of the doubly-fed wind turbine generator set.

[0013] S3: according to a state equation of the doubly-fed wind turbine generator set in dq coordinate system, combining a first-order differential expression of the doubly-fed wind turbine generator set terminal-side macro variable evolution dynamic equation:

[0014]

[0015] wherein T is a parameter of the system self-organizing process to reach a stable state, f(x, d, t) is a first-order differential function of the state variable x, x is a state variable, d is a control variable, and t is time.

[0016] The control law U rd , U rq of the doubly-fed wind turbine generator set rotor-side converter is derived.

[0017] The application aims to provide a cooperative control method and system for inhibiting overvoltage disturbance of a doubly-fed wind turbine generator set.

[0018] In the formula: ψ1, ψ2 are macro variables of the machine side of the doubly-fed wind turbine, T1, T2 are the derived coordinated control parameters, L m is the excitation reactance, L r is the rotor reactance, L s is the stator reactance, ω r is the rotor speed of the wind turbine, ω s is the synchronous angular velocity, ω s1 is the slip angular velocity, I rd , I rq are the d, q axis components of the rotor current of the wind turbine, I sd , I sq are the d, q axis components of the stator current of the DFIG, U sd , U sq are the d, q axis components of the stator voltage of the DFIG, is the stator voltage derivative of the DFIG;

[0019] S4: according to the dq coordinate state equation of the doubly-fed wind turbine, combined with the macro variables of the grid side of the doubly-fed wind turbine, the control law U gd , U gq :

[0020]

[0021] In the formula: ψ3, ψ4 are macro variables of the grid side of the doubly-fed wind turbine, U sd , U sq are the d, q axis components of the stator voltage of the DFIG, I gd , I gq are the outlet currents of the grid side converter, R g , L g are the outlet impedance values of the grid side converter, ω s is the synchronous angular velocity, T3, T4 are the derived coordinated control parameters, K s3 , K s4 are PI coefficients, I gdref is the active current reference value of the grid side of the DFIG, I gqref is the reactive of the grid side of the DFIG;

[0022] S5: a coordinated controller is constructed, the control law of the rotor side converter of the doubly-fed wind turbine and the control law of the grid side converter of the doubly-fed wind turbine are applied, the current inner loop structure of the classic double-loop control is replaced, the outer loop structure of the classic double-loop control is retained, and the overall structure of the coordinated control of the doubly-fed wind turbine is constituted;

[0023] S6: selecting the parameter vector of the cooperative controller by using the parameter selection method of the cooperative controller, so as to realize the cooperative control for suppressing the overvoltage disturbance of the doubly-fed wind power generator.

[0024] The parameter selection method of the cooperative controller comprises the following steps:

[0025] S61: constructing a nonlinear equation to describe the doubly-fed wind power generator:

[0026]

[0027] In the formula, x is a state variable, d is a control variable, and t represents time;

[0028] S62: constructing a function by using the Krasovskii method:

[0029]

[0030] In the formula, f(x, d) is an n-dimensional nonlinear function of the system, f T (x, d) is the transpose of f(x, d), F(x) is the Jacobian matrix of the system, F T (x) is the transpose of F(x),

[0031] S63: for the nonlinear system constructed by formula (6), the Lyapunov direct method is used to judge the stability of the system at a certain operating point and control parameter, and when V(x) > 0 and the system is asymptotically stable;

[0032] S64: the Monte Carlo method is used to bring the parameter vector of the cooperative controller into the state equation (6) of the system, and then formula (7) is used to judge whether the parameter vector satisfies the condition;

[0033] The parameter vector of the cooperative controller is defined as:

[0034] H = [K i1 , K i2 , K i3， K i4， K iudc , K s1 , K s2 , K s3， K s4， K sudc T1, T2, T3, T4] (8)

[0035] In the formula,

[0036] K i1 , K s1 , K i2 , K s2 , K i3, K s3 , K i4 , K s4 is PI coefficient, K iudc is DC voltage control proportion parameter, K sudc is DC voltage control integral parameter, T1, T2, T3, T4 are derived collaborative control parameters.

[0037] The value of the collaborative controller parameter vector is:

[0038] H = [5, 1, 1, 10, 1, 100, 100, 100, 100, 50, 0.02, 0.02, 0.02, 0.02] (9).

[0039] A collaborative control system applying the collaborative control method for inhibiting overvoltage disturbance of a doubly-fed wind turbine generator set, characterized in comprising: a wind turbine, a DFIG, an RSC, a GSC, a collaborative controller, and a power grid, wherein the DFIG comprises a stator end and a rotor end, the wind turbine is connected to the rotor end of the DFIG; the power grid is connected to the stator end of the DFIG; the RSC is connected to the rotor end of the DFIG; the GSC is connected to the power grid; the collaborative controller comprises an RSC collaborative controller and a GSC collaborative controller, the RSC is connected to the RSC collaborative controller, and the GSC is connected to the GSC collaborative controller.

[0040] The present application has the following beneficial effects:

[0041] The collaborative control method for inhibiting overvoltage disturbance of a doubly-fed wind turbine generator set can reduce the influence of overvoltage impact on the DFIG, inhibit the overvoltage at the machine end of the DFIG by introducing the machine end voltage of the DFIG into a flow field, reduce the reactive current output by the DFIG during overvoltage fault, perform dynamic reactive power compensation, achieve the effect of inhibiting overvoltage, and ensure stable operation of the DFIG. Based on the collaborative control theory, the rotor-side converter current and the machine end voltage are introduced into a macro variable, a DFIG rotor / grid-side converter control law is designed, good dynamic and steady-state characteristics are achieved, and strong robustness is achieved. After being connected to the power grid, compared with the classic PI control, the collaborative control method has significant advantages in inhibiting overvoltage peak value and peak duration and reducing electrical quantity overshoot, has good control effect on high-dimensional nonlinear wind power systems, and has strong practicality. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 It is a flow chart of a collaborative control method for inhibiting overvoltage disturbance of a doubly-fed wind turbine generator set;

[0043] Figure 2 It is a system structure diagram applying a collaborative control method for inhibiting overvoltage disturbance of a doubly-fed wind turbine generator set;

[0044] Figure 3 Topology diagram of DFIG coordinated control and stator voltage vector oriented control model;

[0045] Figure 4 Topology diagram of RSC coordinated controller;

[0046] Figure 5 Topology diagram of GSC coordinated controller;

[0047] Figure 6(a) is a comparison chart of simulation results of bus B1 under 30% loss of L1;

[0048] Figure 6(b) is a comparison chart of simulation results of bus B2 under 30% loss of L1;

[0049] Figure 6(c) is a comparison chart of simulation results of DFIG DC link under 30% loss of L1;

[0050] Figure 7(a) is a comparison chart of simulation results of bus B1 under 50% loss of L1;

[0051] Figure 7(b) is a comparison chart of simulation results of bus B2 under 50% loss of L1;

[0052] Figure 7(c) is a comparison chart of simulation results of DFIG DC link under 50% loss of L1;

[0053] Figure 8(a) is a comparison chart of simulation results of bus B1 under 70% loss of L1;

[0054] Figure 8(b) is a comparison chart of simulation results of bus B2 under 70% loss of L1;

[0055] Figure 8(c) is a comparison chart of simulation results of DFIG DC link under 70% loss of L1;

[0056] Figure 9(a) is a comparison chart of simulation results of bus B1 under 30% loss of L2;

[0057] Figure 9(b) is a comparison chart of simulation results of bus B2 under 30% loss of L2;

[0058] Figure 9(c) is a comparison chart of simulation results of DFIG DC link under 30% loss of L2;

[0059] Figure 10(a) is a comparison chart of simulation results of bus B1 under 50% loss of L2;

[0060] Figure 10(b) is a comparison chart of simulation results of bus B2 under 50% loss of L2;

[0061] Figure 10(c) is a comparison chart of simulation results of DFIG DC link under 50% loss of L2;

[0062] Fig. 11(a) is a comparison chart of simulation results of bus B1 under L2 loss of 70%;

[0063] Fig. 11(b) is a comparison chart of simulation results of bus B2 under L2 loss of 70%;

[0064] Fig. 11(c) is a comparison chart of simulation results of DFIG DC link under L2 loss of 70%. DETAILED DESCRIPTION

[0065] The application provides a cooperative control method for inhibiting overvoltage disturbance of a doubly-fed wind turbine.

[0066] The application discloses a cooperative control method for inhibiting overvoltage disturbance of a doubly-fed wind turbine.

[0067] The macro variable is a function composed of system state variables, is selected according to a control target of the system, and is similar to ψ(x, t); the flow field obtained according to the macro variable is ψ(x, t) = 0; the target of the cooperative control is to make the state variables converge to the flow field surface, and then converge to an equilibrium point from the flow field surface; the definition of the flow field is equivalent to adding a constraint condition to the original system, so that the original system is reduced in order, and the dynamic process is described by the following formula:

[0068]

[0069] In the formula, ψ is the macro variable, T is a cooperative control parameter representing time, and when T > 0, the time constant of the state variable moving to the flow field surface is represented.

[0070] Based on the above cooperative control theory, the flow of the cooperative control method for inhibiting overvoltage disturbance of the doubly-fed wind turbine disclosed by the application is as shown in Figure 1 The specific implementation steps are as follows:

[0071] S1: taking the control of constant DC voltage of the grid-side converter of the doubly-fed wind turbine as a control target, and defining a macro variable of the doubly-fed wind turbine on the grid side:

[0072]

[0073] In the formula, K i3 , K s3 , K i4 , and K s4 are PI coefficients, S is an integral term in PI control, I gd , I gq is the outlet current of the grid-side converter, I gdref is a DFIG grid-side active current reference value, and I gqref is a DFIG grid-side reactive current reference value.

[0074] With the control target of constant DC voltage, the macro variables ψ3 and ψ4 of the grid-side of the doubly-fed wind turbine are selected to maintain the current I flowing into the converter gd and I gq The outlet current of the grid-side converter is represented by the following formula:

[0075]

[0076] In the formula, R g is the outlet resistance of the grid-side converter, L g is the reactance U sd , U sq , U rd , U rq is the stator and rotor voltage, ω s is the synchronous angular velocity.

[0077] S2: Obtain the terminal voltage of the wind turbine using the measuring device, and define the macro variable of the doubly-fed wind turbine as:

[0078]

[0079] In the formula, I rd , I rq are the d and q axis components of the rotor current of the wind turbine, I rdref is the active current reference value of the DFIG rotor, I rqref is the reactive current reference value of the DFIG rotor, U s is the terminal voltage of the doubly-fed wind turbine, U sref is the terminal voltage reference value of the doubly-fed wind turbine;

[0080] The macro variable of the doubly-fed wind turbine is selected, with the control target of providing reactive support to the grid when the DFIG is in overvoltage, considering that under the d-axis orientation control of the grid voltage, I rq is the output reactive current, and the selection of the macro variable of the doubly-fed wind turbine is completed.

[0081] S3: According to the state equation of the doubly-fed wind turbine in the dq coordinate system, and combined with the first-order differential expression of the constructed macro variable evolution dynamic equation:

[0082]

[0083] In the formula, T is a parameter indicating the speed of the system self-organization process to reach a stable state, f(x, d, t) is the first-order differential function of the state variable x, x is the state variable, d is the control variable, and t is the time;

[0084] The control law Urd 、U rq :

[0085]

[0086] In the formula: ψ1, ψ2 are the machine side macro variable of DFIG, T1, T2 are the derived coordinated control parameters, L m is the excitation reactance, L r is the rotor reactance, L s is the stator reactance, ω r is the rotor speed of the fan, ω s is the synchronous angular velocity, ω s1 is the slip angular velocity, I rd , I rq are the d, q axis components of the rotor current of the fan, I sd , I sq are the d, q axis components of the stator current of the DFIG, U sd , U sq are the d, q axis components of the stator voltage of the DFIG, is the derivative of the stator voltage of the DFIG;

[0087] The machine side control variable of the DFIG is derived, that is, the control law of the rotor side converter of the DFIG is derived, and the control target of providing reactive power support for the power grid can be realized, and the specific derivation process is as follows:

[0088] S31: In the dq coordinate system, the mathematical model of the DFIG is constructed, and the flux linkage and voltage equations of the DFIG are established as follows:

[0089]

[0090] In the formula: U sd , U sq , U rd , U rq are the stator and rotor voltages, Ψ sd , Ψ sq , Ψ rd , Ψ rq are the stator and rotor flux linkage components, I sd , I sq , I rd , I rq are the stator and rotor current components, L m is the excitation reactance, L ls , L lr are the leakage reactances after being reduced to the stator side, L s =L m +L ls , L r =L m +L lr , and p is a differential operator.s , R r is the stator winding resistance, ω s is the synchronous angular velocity, ω r is the rotor angular velocity.

[0091] S32: Substitute the flux equation into the voltage equation:

[0092]

[0093] where the variable definitions are the same as in equation (11) and equation (12).

[0094] S33: Solve the state equation with the stator and rotor currents as state variables:

[0095]

[0096] where ω s is the synchronous angular velocity, and the other variable definitions are the same as in equation (11) and equation (12).

[0097] S34: According to the doubly-fed wind turbine machine-side macro variable defined in equation (2), and the nonlinear equation describing the doubly-fed wind turbine constructed in equation (6), define the manifold as: ψ(x, t) = 0, and the cooperative control equation as:

[0098]

[0099] where ψ is the macro variable, T is the cooperative control parameter representing time, x is the state variable, d is the control variable, and t is time.

[0100] S35: Substitute ψ1 into the cooperative control equation in equation (15):

[0101]

[0102] S36: Substitute the derivative of I rd into:

[0103]

[0104] S37: Neglect the stator and rotor resistances as 0, and solve the control law of U rd as shown in equation (4).

[0105] S38: Similarly, substitute ψ2 into the cooperative control equation in equation (15), substitute the derivative of I rq , and solve the control law of U rq as shown in equation (4).

[0106] Thus, the control variables of the doubly-fed wind turbine machine side U rd , U rqThe derivation of the rotor side converter control law of the doubly-fed wind turbine is applied to the coordinated controller of the rotor side converter (RSC) of the DFIG to achieve the control target of providing reactive power support for the power grid and to maintain the active and reactive power output of the DFIG stator. Thanks to the simple characteristics of the control law design of the coordinated control theory, the RSC described in the embodiment has good dynamic and steady-state characteristics and robustness.

[0107] S4: According to the dq coordinate state equation of the doubly-fed wind turbine, the grid side macro variable of the doubly-fed wind turbine is combined to derive the grid side converter control law U gd , U gq :

[0108]

[0109] In the formula, ψ3, ψ4 are the grid side macro variables of the doubly-fed wind turbine, U sd , U sq are the dq axis components of the DFIG stator voltage, I gd , I gq are the grid side converter outlet currents, R g , L g are the grid side converter outlet impedance values, ω s is the synchronous angular velocity, T3, T4 are the derived coordinated control parameters, K s3 , K s4 are PI coefficients, I gdref is the DFIG grid side active current reference value, I gqref is the DFIG grid side reactive power;

[0110] The grid side control variable of the doubly-fed wind turbine is derived, that is, the grid side converter control law of the doubly-fed wind turbine is derived, which can achieve the control target of controlling the constant DC voltage. The specific derivation process is similar to the derivation process of the above-mentioned grid side control variable of the doubly-fed wind turbine. The same part will not be repeated. Through the derivation of the grid side control variable U gd , U gq of the doubly-fed wind turbine, the grid side converter control law of the doubly-fed wind turbine is formed, which is applied to the coordinated controller of the grid side converter (GSC) of the DFIG to achieve the control target of controlling the constant DC voltage, maintain the stability of the DC voltage and modulate the power factor, and maintain the stability of the DC link voltage under the impact of the machine end overvoltage, which is of great significance to the stable operation of the DFIG.

[0111] S5: Constructing a cooperative controller, applying the rotor-side converter control law of the doubly-fed wind turbine and the grid-side converter control law of the doubly-fed wind turbine, replacing the current inner loop structure of the classic double-loop control, retaining the outer loop structure of the classic double-loop control, and constituting the overall structure of the cooperative control of the doubly-fed wind turbine;

[0112] The outer loop structure of the classic double-loop control is as follows:

[0113]

[0114] In the formula:

[0115] I rdref is the active current reference value of the DFIG rotor, I rqref is the reactive current reference value of the DFIG rotor, I gdref is the active current reference value of the DFIG grid side, K i1 , K s1 , K i2 , K s2 is a PI coefficient, K iudc is a DC voltage control proportional parameter, K sudc is a DC voltage control integral parameter, S is an integral term in PI control, P ref is the active power reference value of the DFIG output, P is the actual active output of the DFIG, Q ref is the reactive power reference value of the DFIG output, Q is the actual reactive output of the DFIG, U dcref is the DC link voltage reference value of the DFIG, U dc is the actual DC link voltage of the DFIG;

[0116] In the classic PI control, the RSC controls the DFIG rotor current I rd , I rq and further controls the output active and reactive power, and its efficiency directly affects the output waveform quality of the DFIG. The embodiment uses a cooperative controller to replace the inner loop PI link, the cooperative controller includes an RSC cooperative controller and a GSC cooperative controller, the structure of the RSC cooperative controller is as shown in Figure 4 , and the structure of the GSC cooperative controller is as shown in Figure 5 The control law design is simple, has good control effect on high-dimensional nonlinear wind power systems, and has high practicability.

[0117] S6: Selecting the parameter vector of the cooperative controller using the parameter selection method of the cooperative controller to realize the cooperative control of suppressing the overvoltage disturbance of the doubly-fed wind turbine, and the specific selection steps are as follows:

[0118] S61: Constructing a nonlinear equation to describe the doubly-fed wind turbine:

[0119]

[0120] where x is a state variable, d is a control variable, and t represents time. Considering that the DFIG is a typical nonlinear system, its control parameters are crucial to system stability, and not only should the system be kept in stable operation, but after being disturbed, the system should also be restored to steady state as soon as possible. For high-dimensional nonlinear control parameters, according to engineering experience, it is very difficult to select them.

[0121] S62: using the Krasovskii method to construct a function:

[0122]

[0123] where f(x, d) is an n-dimensional nonlinear function of the system, f T (x, d) is the transpose of f(x, d), F(x) is a Jacobian matrix of the system, F T (x) is the transpose of F(x),

[0124] S63: for the nonlinear system constructed by formula (6), using the Lyapunov direct method to judge the stability of the system at a certain operating point and control parameters, when V(x) > 0 and the system is asymptotically stable;

[0125] By the Lyapunov direct method, using formula (15) to judge the stability of the nonlinear system constructed by formula (6) to describe the doubly-fed wind turbine at a certain operating point and control parameters.

[0126] S64: using the Monte Carlo method to bring the cooperative controller parameter vector into the state equation (6) of the system, and then using formula (7) to judge whether the parameter vector satisfies the condition;

[0127] The cooperative controller parameter vector is defined as:

[0128] H = [K i1 , K i2 , K i3， K i4， K iudc , K s1 , K s2 , K s3， K s4， K sudc T1, T2, T3, T4] (8).

[0129] where:

[0130] K i1 , K s1 , K i2 , K s2 , Ki3 , K s3 , K i4 , K s4 is PI coefficient, K iudc is DC voltage control proportion parameter, K sudc is DC voltage control integral parameter, T1, T2, T3, T4 are derived collaborative control parameters.

[0131] The state variables selected in the embodiment are: I d , I q , I f , I D , I Q , U f , I sq , I sd , I rd , I rq , U rd , U rq , U gd , U gq , I gd , I gq , U dc , I gdref . Considering that the system state variables in the embodiment are more, it is difficult to obtain the system control parameters through the conventional analytical calculation method, the Monte Carlo method is used to select points, and the control parameters are selected through the back-feeding type (7) verification, and finally a group of suitable collaborative controller parameter vectors are obtained as follows:

[0132] H = [5, 1, 1, 10, 1, 100, 100, 100, 100, 50, 0.02, 0.02, 0.02, 0.02] (9)

[0133] In the classical PI control, the speed of the controlled quantity reaching the steady state is generally realized by adjusting the PI parameters, and if the P parameter value is too small, the convergence speed will be slow, and if the value is too large, the overshoot will be large. The present application adjusts through the collaborative control parameter T representing time, and the smaller the T parameter value, the faster the controlled quantity reaches the steady state, and there is no problem of overshoot.

[0134] The complete process of the collaborative control method for suppressing overvoltage disturbance of the double-fed wind turbine in the embodiment is completed, the collaborative control method in the embodiment applies the collaborative control theory to suppress the overvoltage at the terminal of the DFIG, reduces the reactive current output by the DFIG during overvoltage fault, dynamically adjusts the reactive power, and achieves the effect of suppressing overvoltage. Thanks to the simple advantage of control law design of the collaborative control theory, the impact of overvoltage on the DFIG is reduced through the definition of macro variable and the solution of control variable, and the stable operation of the DFIG is ensured.

[0135] Based on the proposed control laws for the rotor-side converter and grid-side converter of the doubly-fed induction generator (DFIG) wind turbine, as well as the selected cooperative controller parameter vector, time-domain simulations were performed using electromagnetic transient simulation software (Power Systems Computer-Aided Design, PSCAD) to verify the effectiveness of the proposed control laws and cooperative controller parameter vector. The specific verification process is as follows:

[0136] Taking the grid connection of a doubly fed wind farm in a certain region as an example, such as Figure 3 As shown, DFIG collaborative control and stator voltage vector orientation control models were built in PSCAD to verify the control effect under bus overvoltage conditions after load shedding.

[0137] The doubly-fed induction generator (DFIG) wind farm is connected to bus B1, using a single-unit equivalent model. Meanwhile, G2 is assumed to have infinite capacity, and the voltage at bus B4 is constant. The load uses a constant impedance model, with per-unit values ​​L1 = 0.35 + j0.08pu and L2 = 1.5 + j0.53pu calculated based on the wind farm capacity. Other simulation parameters are as follows:

[0138] Doubly fed wind farm parameters: Number of wind turbines: 75; Rated power: 1MW; Rated stator voltage: 690V; Stator leakage reactance: 0.16pu; Rotor leakage reactance: 0.18pu; Magnetizing reactance: 2.9pu; Stator resistance: 0.02pu; Rotor resistance: 0.03pu; Power base value: 1MW; Voltage base value: 1000V; DC link voltage: 1050V; Speed ​​base value: 314.159rad / s

[0139] Synchronous motor parameters: Capacity 90MW; Power factor 0.9; Armature resistance 0.0025pu; Excitation winding resistance 0.00043pu; D-axis damping winding resistance 0.0051pu; Q-axis damping winding resistance 0.000842pu; Direct-axis reactance 1.66pu; Quadrature-axis reactance 1.52pu; Stator leakage reactance 0.14pu; Excitation winding reactance 1.7204pu; D-axis damping winding reactance 1.5637pu; Q-axis damping winding reactance 0.876pu; AVR excitation system KA=80; TA=0.02;

[0140] Line parameters: X1=X2=X3=0.08+j0.2puDFIG Classic PI control parameters: RSC side inner loop parameters: Ki=1; Ks=100; Network side inner loop parameters: Ki=1; Ks=100;

[0141] like Figures 6(a)-11(c) As shown, Algorithm 1 is the classic PI control method, and Algorithm 2 is the cooperative control method for suppressing overvoltage disturbances in doubly-fed wind turbines described in this invention. The control effects of the two algorithms under different conditions are compared through two scenarios, and the comparison results are as follows:

[0142] Scenario 1: Load L1 at the wind farm export side, at t = 10s, the load loss due to circuit breaker tripping, leading to system overvoltage, reclosing successfully at t = 10.5s.

[0143] Fig. 6(a), Fig. 6(b) are bus voltage curves of bus B1, B2, Fig. 6(c) is DFIG DC link voltage curve, as shown in Figures 6(a)-6(c) The control effect of the coordinated control is obviously better than that of the classic PI control under the condition of 30% load L1 sudden drop.

[0144] As shown in Fig. 6(a), the bus B1 voltage under the coordinated control can suppress the impulse voltage peak value below 1.08pu, while the bus B1 impulse voltage under the PI control exceeds 1.09pu, with higher voltage peak value and longer duration.

[0145] As shown in Fig. 6(b), the voltage impulse of the common bus B2 of the traditional power supply and the doubly-fed wind farm under the coordinated control is smaller, the transition process is more stable, the transient duration is shortened and the voltage fluctuation is effectively suppressed.

[0146] As shown in Fig. 6(c), the DFIG DC link voltage under the coordinated control has small overshoot and reaches steady state quickly, compared with the PI control impulse voltage exceeding 1.06pu, the coordinated control has great improvement on the stability of the DC link voltage.

[0147] Figures 7(a)-7(c) For L1 sudden drop of 50%, the simulation results of the voltage of each node of the system are shown in Figures 7(a)-7(c) The control effect of the coordinated control is still better than that of the PI control under the condition of 50% load loss.

[0148] As shown in Fig. 7(a), under the condition of 50% load loss of bus B1, the impulse voltage peak value of the wind farm bus voltage under the PI control reaches 1.15pu. While under the coordinated control, the impulse voltage peak value is suppressed to 1.1pu, reducing the adverse effects of the impulse voltage on the stator and rotor of the DFIG.

[0149] As shown in Fig. 7(b), the bus B2 voltage under the coordinated control has reduced overshoot and shortened transition process.

[0150] As shown in Fig. 7(c), the DFIG DC link voltage under the coordinated control has smooth transition process and reduced impulse value.

[0151] Figures 8(a)-8(c)The system bus voltages are shown in Figure 8(a) when L1 is 70% lost. Under PI control, the voltage surge value at the DFIG turbine terminal bus reaches 1.2 pu, and the voltage peak duration is relatively long, which has an adverse effect on the wind turbine. Under coordinated control, the overvoltage peak is still suppressed to below 1.15 pu, and the transition process is smooth with reduced voltage fluctuations.

[0152] As shown in Figure 8(b), when the load loss of L1 is large, the cooperative control strategy still has a suppressive effect on the voltage of bus B2 and can shorten the transient transition process.

[0153] As shown in Figure 8(c), after the L1 loss is large, the DC link voltage of the DFIG also experiences a large impact. Under coordinated control, the impact voltage can be suppressed to a large extent and the transient transition process can be accelerated.

[0154] In scenario 1 of this embodiment, when the load on bus B1 experiences varying degrees of loss, the coordinated control can suppress the DFIG terminal surge voltage and accelerate the transient transition process to reduce voltage fluctuations. It also effectively suppresses the voltage at bus B2 and the DC link voltage of the DFIG.

[0155] Scenario 2: Load L2 on the B2 side of the common busbar of a doubly-fed wind farm and a conventional power source experiences overvoltage due to load loss caused by circuit breaker tripping at t=10s. The line reclosing is successful at t=10.5s. Specific simulation results are as follows:

[0156] like Figures 9(a)-9(c) As shown, when the load L2 drops by 30%, the DFIG coordinated control has a good effect on suppressing system overvoltage.

[0157] As shown in Figure 9(a), after L2 sheds the load, the peak impulse voltage of bus B1 reaches 1.12 pu under PI control. Under coordinated control, the peak impulse voltage is suppressed to below 1.1 pu, and the voltage fluctuation is reduced, allowing the voltage to reach steady state quickly.

[0158] As shown in Figure 9(b), the voltage surge value of bus B2 is suppressed under coordinated control, effectively reducing the peak voltage of the surge.

[0159] As shown in Figure 9(c), under coordinated control, the oscillation frequency of the DFIG DC link voltage is reduced and the voltage peak value is lowered.

[0160] Figures 10(a)-10(c) Voltage curves of each node in the system when the load loss of the common bus is 50%.

[0161] As shown in Figure 10(a), due to the heavy load at the common point, after a 50% loss, the impulse voltage of bus B1 exceeds 1.16 pu under PI control, while under coordinated control, the peak impulse voltage is suppressed to around 1.12 pu.

[0162] As shown in Figure 10(b), the bus B2 voltage still has a good control effect under coordinated control, which accelerates the transient transition process and reduces the overshoot.

[0163] As shown in Figure 10(c), the DC link voltage of the DFIG is greatly reduced under coordinated control and quickly reaches a steady state value.

[0164] Figures 11(a)-11(c) The system bus voltages after a 70% load loss (L2) are shown in Figure 11(a). Under PI control, when the load loss is 70%, the impulse voltage at the DFIG turbine terminal bus exceeds 1.2 pu, which adversely affects the normal operation of the wind turbine. Under coordinated control, the overvoltage peak does not exceed 1.15 pu, and the transition process is smooth with reduced oscillation frequency.

[0165] In scenario 2 described in this embodiment, the DFIG collaborative control strategy is effective in suppressing system overvoltage under sudden load drops at the point of common point. Compared to traditional PI control, collaborative control has advantages in both transient response time and overshoot. This significantly contributes to the safe and stable operation of the system and the voltage stability of the wind farm.

[0166] The second embodiment of the present invention, as follows: Figure 2 As shown, a cooperative control system applying the cooperative control method for suppressing overvoltage disturbances in a doubly-fed induction generator (DFIG) wind turbine is disclosed. The system includes: a wind turbine 100, a DFIG 200, an RSC 300, a GSC 400, a cooperative controller 500, and a power grid 600. The DFIG includes a stator end 210 and a rotor end 220. The wind turbine 100 is connected to the rotor end 220 of the DFIG 200. The power grid 600 is connected to the stator end 210 of the DFIG 200. The RSC 300 is connected to the rotor end 220 of the DFIG 200. The GSC 400 is connected to the power grid 600. The cooperative controller 500 includes an RSC cooperative controller 510 and a GSC cooperative controller 520. The RSC 300 is connected to the RSC cooperative controller 510, and the GSC 400 is connected to the GSC cooperative controller 520.

[0167] In this embodiment, the voltage DQ-axis component of the rotor end 220 of the DFIG200 is U. rd U rq The voltage DQ-axis component of the stator terminal 210 of DFIG200 is U. sd U sq Since the stator terminal 210 of the DFIG200 is directly connected to the power grid 600, it can be approximated that the voltage at the power grid 600 is still U. sd U sq The output voltage of GSC400 is U. gd U gqThe GSC cooperative controller 520 is connected with the GSC 400 to realize the control law of the grid-side converter of the doubly-fed wind turbine generator set, and maintain the DC link voltage U dc and the constant power factor; the RSC cooperative controller 510 is connected with the RSC 300 to realize the control law of the rotor-side converter of the doubly-fed wind turbine generator set, and maintain the active and reactive power output by the stator end 210 of the DFIG 200.

[0168] The application can reduce the influence of overvoltage impact on the DFIG, inhibit the overvoltage at the DFIG end by introducing the DFIG end voltage into the flow field, reduce the reactive current output by the DFIG during overvoltage fault, perform dynamic reactive power compensation, achieve the effect of inhibiting overvoltage, ensure the stable operation of the DFIG, has significant advantages in inhibiting the overvoltage peak value and the peak value duration and reducing the overshoot of electrical quantity, has good control effect on the high-dimensional nonlinear wind power system, and has strong practicability.

Claims

1. A method for cooperative control of overvoltage disturbance of a doubly-fed wind turbine, the method comprising the following steps: S1: obtaining a terminal voltage of the wind turbine by using a measuring device, and taking control of a DC voltage of a grid-side converter of the doubly-fed wind turbine as a control target; defining a grid-side macro variable of the doubly-fed wind turbine; S2: obtaining a terminal voltage of the wind turbine by using a measuring device, and taking providing reactive power support for the grid by a rotor-side converter of the doubly-fed wind turbine in an overvoltage state as a control target, and defining a machine-side macro variable of the doubly-fed wind turbine; S3: according to a state equation of the doubly-fed wind turbine in a dq coordinate system, and combining a first-order differential expression of an evolution dynamic equation of the machine-side macro variable: wherein ψ is the macro variable, T is a parameter of a self-organizing process of the system to reach a stable state, f(x, d, t) is a first-order differential function of a state variable x, x is the state variable, d is a control variable, and t is time; S5: constructing a cooperative controller, and applying a control law of the rotor-side converter of the doubly-fed wind turbine and a control law of the grid-side converter of the doubly-fed wind turbine to replace a current inner loop structure of a classical double-loop control, and retaining an outer loop structure of the classical double-loop control to form an overall structure of the cooperative control of the doubly-fed wind turbine; and S6: selecting a parameter vector of the cooperative controller by using a parameter selection method of the cooperative controller to realize the cooperative control of the overvoltage disturbance of the doubly-fed wind turbine. 2.The method according to claim 1, wherein the parameter selection method of the cooperative controller comprises the following steps: S61: constructing a nonlinear equation to describe the doubly-fed wind turbine: wherein x is a state variable, d is a control variable, and t represents time; S62: constructing a function by using a Krasovskii method: S64: bringing the parameter vector of the cooperative controller into a state equation (6) of the system by using a Monte Carlo method, and judging whether the parameter vector satisfies a condition by using equation (7); wherein the parameter vector of the cooperative controller is defined as: wherein the parameter vector of the cooperative controller has a value of: including: a wind turbine (100), a doubly-fed induction generator (200), a rotor-side converter (300), a grid-side converter (400), a cooperative controller (500), and a grid (600), wherein the doubly-fed induction generator (200) comprises a stator end (210) and a rotor end (220), the wind turbine (100) is connected to the rotor end (220) of the doubly-fed induction generator (200), the grid (600) is connected to the stator end (210) of the doubly-fed induction generator (200), the rotor-side converter (300) is connected to the rotor end (220) of the doubly-fed induction generator (200), the grid-side converter (400) is connected to the grid (600), and the cooperative controller (500) comprises a rotor-side converter cooperative controller (510) and a grid-side converter cooperative controller (520), the rotor-side converter (300) is connected to the rotor-side converter cooperative controller (510), and the grid-side converter (400) is connected to the grid-side converter cooperative controller (520). wherein: K i3 , K s3 , K i4 , K s4 is a PI coefficient, S is an integral term in PI control, I gd , I gq is a grid-side converter outlet current, I gdref is a DFIG grid-side active current reference value, I gqref is a DFIG grid-side reactive current reference value; characterized in that ​ ​ wherein I rd , I rq are the d, q axis components of the rotor current of the wind turbine, I rdref is the active current reference value of the rotor of the DFIG, I rqref is the reactive current reference value of the rotor of the DFIG, U s is the terminal voltage of the doubly-fed wind turbine, U sref is the terminal voltage reference value of the doubly-fed wind turbine; ​ ​ Derivation of rotor-side converter control law U for doubly-fed wind turbines rd , U rq : In the formula: ψ1, ψ2 are the machine side macro variables of the doubly-fed wind turbine, T1, T2 are the derived coordinated control parameters, L m is the excitation reactance, L r is the rotor reactance, L s is the stator reactance, ω r is the wind turbine rotor speed, ω s is the synchronous angular velocity, ω s1 is the slip angular velocity, I rd , I rq are the wind turbine rotor current d, q axis components, I sd , I sq are the DFIG stator current dq axis components, U sd , U sq are the DFIG stator voltage dq axis components, is the DFIG stator voltage derivative quantity; S4: According to the dq coordinate state equation of the doubly-fed wind turbine, combined with the macro-variable of the grid-side of the doubly-fed wind turbine, the control law U of the grid-side converter of the doubly-fed wind turbine is derived gd , gq : In the formula: ψ 3, ψ 4 are double-fed wind turbine grid-side macro variable, U sd , U sq It is DFIG stator voltage dq axis component, gd , I gq It is grid-side converter outlet current, R g , L g It is grid-side converter outlet impedance value, ω s It is synchronous angular velocity, T 3, T 4 are derived collaborative control parameters, K s3 , K s4 It is PI coefficient, I gdref It is DFIG grid-side active current reference value, I gqref It is DFIG grid-side reactive; ​ ​ ​ ​ ​ ​ where: f(x,d) is an n-dimensional nonlinear function of the system, f T (x,d) is the transpose of f(x,d), F(x) is the Jacobian matrix of the system, F T (x) is the transpose of F(x), S63: For the nonlinear system constructed by equation (6), use Lyapunov direct method to judge the stability of the system at a certain operating point and control parameters, when V(x) > 0 and the system is asymptotically stable; ​ characterized in that ​ H = [K i1 , K i2 , K i3 , K i4 , K iudc , K s1 , K s2 , K s3 , K s4 , K sudc T1, T2, T3, T4] (8) ​ K i1 , K s1 , K i2 , K s2 , K i3 , K s3 , K i4 , K s4 is a PI coefficient, K iudc is a direct current voltage control proportional parameter, K sudc is a direct current voltage control integral parameter, T1, T2, T3, T4 are derived cooperative control parameters.

3. The cooperative control method for inhibiting overvoltage disturbance of a doubly-fed wind generator set according to claim 2, characterized in that, ​ H＝[5,1,1,10,1,100,100,100,100,50,0.02,0.02,0.02,0.02] (9)。 4. A coordinated control system applying the coordinated control method for inhibiting overvoltage disturbance of a doubly-fed wind power generator set according to claim 1, characterized in that, ​ ​

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