Reactive power compensation method and system with static reactive power generator and double-fed wind turbine

Abstract

The application discloses a kind of static reactive generator and the reactive compensation method of double-fed fan cooperation, including obtaining the data information of target power system, static reactive generator and double-fed fan;It is determined and the power distribution of reactive compensation that target power system reactive compensation is carried out;According to the power distribution result, double-fed fan is preferentially mobilized, and the reactive compensation of double-fed fan is realized;According to the power distribution result, static reactive generator is called, and the reactive compensation of static reactive generator and double-fed fan cooperation is realized.The application also discloses a kind of system for realizing the reactive compensation method of static reactive generator and double-fed fan cooperation.The application sets up reactive compensation priority scheme according to the characteristics of static reactive generator and double-fed fan, and continues to correspond to the control of double-fed fan and static reactive generator, so the application not only can realize the reactive compensation of static reactive generator and double-fed fan cooperation, but also has higher reliability and better accuracy.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electrical automation, and particularly relates to a static var generator and a reactive power compensation method and system cooperating with a doubly-fed fan. BACKGROUND

[0002] With the development of economy and technology and the improvement of people's living standards, electric energy has become an essential secondary energy in people's production and life, bringing endless convenience to people's production and life. Therefore, guaranteeing the stable and reliable supply of electric energy has become one of the most important tasks of the power system.

[0003] Wind power has developed rapidly in recent years with its abundant resources, clean and environmentally friendly, and relatively low cost. In recent years, doubly-fed wind power generators (DFIG) have been widely used as variable-speed constant-frequency asynchronous generators due to their simple grid connection operation and reactive power compensation characteristics. However, after DFIG is integrated into the distribution network, the dependence and uncertainty of wind energy resources, combined with the operating characteristics of DFIG, can easily cause frequent voltage fluctuations and flicker in the distribution network nodes, thereby adversely affecting the safe and stable operation of the power system.

[0004] In order to maximize the active power transmission capacity of wind turbines and improve the operating performance of the unit, the power system usually provides reactive power compensation equipment for it. Static var generator (SVG) can well meet the reactive power configuration requirements in the technical regulations for wind farm access to the grid due to its flexible and adjustable output reactive power, rapid compensation, superior harmonic characteristics, and effective improvement of voltage stability. Therefore, static var generators have been widely used in the field of wind power grid connection.

[0005] In the existing SVG control strategy, the PI control method in the synchronous coordinate system is more common. However, the parameter design of the PI controller in this type of control scheme is fixed and cannot adapt to the dynamic characteristics of the grid conditions or load changes, which may lead to a decline in control performance. Moreover, the PI control of the existing scheme is based on linear control theory, and the nonlinear characteristics existing in the grid will also affect the stability and performance of the system. Finally, the reactive power output of DFIG is also complex and variable, and the existing SVG control scheme cannot meet the cooperative work with DFIG. SUMMARY

[0006] One of the purposes of the present application is to provide a static var generator and a reactive power compensation method cooperating with a doubly-fed fan with high reliability and good accuracy.

[0007] The second object of the present application is to provide a system for realizing the reactive power compensation method of the static var generator and the doubly-fed wind turbine.

[0008] The reactive power compensation method of the static var generator and the doubly-fed wind turbine provided by the present application comprises the following steps:

[0009] S1. obtaining data information of a target power system, a static var generator and a doubly-fed wind turbine;

[0010] S2. determining reactive power compensation of the target power system according to the data information obtained in step S1, and performing power distribution for the reactive power compensation;

[0011] S3. mobilizing the doubly-fed wind turbine preferentially according to the power distribution result of step S2, and realizing reactive power compensation of the doubly-fed wind turbine based on control of a stator-side converter and control of a rotor-side converter of the doubly-fed wind turbine;

[0012] S4. calling the static var generator according to the power distribution result of step S2, and realizing reactive power compensation of the static var generator and the doubly-fed wind turbine based on model reference adaptive control.

[0013] The step S2 of determining reactive power compensation of the target power system according to the data information obtained in step S1, and performing power distribution for the reactive power compensation comprises the following steps:

[0014] According to the data information obtained in step S1, calculating a voltage deviation value of a grid connection point, and determining whether to start reactive power compensation according to a size relationship between the voltage deviation value and a voltage deviation dead zone, and calculating a target value of the reactive power compensation;

[0015] After starting the reactive power compensation, starting the doubly-fed wind turbine preferentially to perform the reactive power compensation, and calculating a reactive power compensation capability of the doubly-fed wind turbine;

[0016] According to a size relationship between the target value of the reactive power compensation and the reactive power compensation capability of the doubly-fed wind turbine, performing power distribution for the reactive power compensation between the static var generator and the doubly-fed wind turbine.

[0017] The step S2 specifically comprises the following steps:

[0018] Setting a voltage deviation dead zone;

[0019] Detecting a grid connection point voltage, and calculating a deviation value of the grid connection point voltage from a reference voltage;

[0020] Determining the deviation value:

[0021] If the deviation value is within the set voltage deviation dead zone, no action is taken;

[0022] If the deviation value exceeds the set voltage deviation dead zone range, reactive power compensation is started, and the deviation value is taken as the reactive power compensation target value Q all ;

[0023] The doubly-fed wind turbine is preferentially started to perform reactive power compensation;

[0024] The reactive power compensation capacity of the doubly-fed wind turbine is calculated by the following steps:

[0025] The total active power output P of the doubly-fed wind turbine is expressed as P=P S +P c , P S is the output of the stator direct side, and P c is the output of the rotor grid-connected side;

[0026] Since the double-side active power output of the doubly-fed wind turbine satisfies P c =-sP S , s is the slip of the doubly-fed wind turbine, and thus P=P S =(1-s)P s ;

[0027] The reactive power output Q of the doubly-fed wind turbine is the algebraic sum of the stator-side reactive power output Q s and the rotor-side reactive power output Q c of the inverter grid-connected side, and is expressed as Q=Q s +Q c ;

[0028] According to the power balance relationship, the doubly-fed wind turbine grid-connected side satisfies

[0029]

[0030] In the formula, U S is the node voltage of the stator side of the doubly-fed wind turbine grid-connected side; I S is the current flowing through the stator winding;

[0031] According to the characteristics of the inverter, the output current of the stator side satisfies

[0032]

[0033] In the formula, X S is the equivalent leakage reactance of the stator; X m is the excitation reactance; I rmax is the maximum current limit value of the inverter grid-connected side;

[0034] Then, the range of the reactive power output of the stator side and the rotor side is obtained as

[0035]

[0036] In the formula, i rmax is the maximum current of the rotor side; Sc The maximum capacity of the grid-side converter;

[0037] The output power reference value of the doubly-fed wind turbine under different operating conditions is represented as

[0038]

[0039] P ref is the output power reference value of the doubly-fed wind turbine; k max is the maximum power tracking coefficient; ω0 is the initial wind speed at which the doubly-fed wind turbine enters the maximum power tracking zone; ω min is the minimum rotor speed at which the doubly-fed wind turbine can maintain normal operation; ω w is the rotor speed; ω1 is the initial rotor speed at which the doubly-fed wind turbine enters the constant speed zone; P max is the maximum active power that the doubly-fed wind turbine can generate; ω max is the initial rotor speed at which the doubly-fed wind turbine enters the constant power zone;

[0040] The reactive power output of the doubly-fed wind turbine is the maximum capacity Q dfigm , which is represented as

[0041] Q dfigm = Q cmax + Q Smax

[0042] Q cmax is the maximum capacity of the reactive power output of the rotor-side converter; Q Smax is the maximum capacity of the reactive power output of the stator-side converter;

[0043] When the doubly-fed wind turbine performs reactive power compensation, the reactive power capacity Q c of the rotor-side converter is preferentially called; when Q c does not meet the requirement, the reactive power capacity Q S of the stator-side converter is called.

[0044] When the target value Q all of the reactive power compensation is less than or equal to Q dfigm , the doubly-fed wind turbine performs reactive power compensation, and the static reactive power generator is not in action.

[0045] When the target value Q all of the reactive power compensation is greater than Q dfigm , the remaining reactive power capacity except Q dfigm is borne by the static reactive power generator, which is represented as Q SVG = Q all - Q dfigm , Q SVG is the reactive power output capacity of the static reactive power generator.

[0046] The rated capacity QSVGN represents Q SVGN = U SVG 2 / Z, U SVG is the line voltage of the grid-connected inverter of the static var generator on the AC side, and Z is the equivalent reactance value of the static var generator on the AC side.

[0047] According to the power distribution result of step S2, the double-fed wind turbine is preferentially mobilized to perform reactive power compensation, including the following steps:

[0048] According to the power distribution result of step S2, the double-fed wind turbine is preferentially mobilized to perform reactive power compensation;

[0049] When the double-fed wind turbine performs reactive power compensation, the stator-side converter control of the double-fed wind turbine is performed according to the simplified voltage equation and the simplified flux linkage equation of the double-fed wind turbine in the dq coordinate system; meanwhile, the rotor-side converter control of the double-fed wind turbine is performed by using the vector control mode according to the active power and the reactive power exchanged between the rotor-side converter of the double-fed wind turbine and the power grid.

[0050] Finally, the reactive power compensation of the double-fed wind turbine is realized through the stator-side converter control and the rotor-side converter control.

[0051] The step S3 specifically includes the following steps:

[0052] Stator-side converter control:

[0053] Neglecting the stator resistance voltage drop of the double-fed wind turbine, the simplified voltage equation of the double-fed wind turbine in the dq coordinate system is obtained as follows:

[0054]

[0055] In the formula, u sd is the component of the stator-side converter voltage on the d-axis in the dq synchronous rotating coordinate system; ω s is the stator speed; ψ sq is the q-axis component of the stator flux linkage; U s is the stator voltage; u sq is the component of the stator-side converter voltage on the q-axis in the dq synchronous rotating coordinate system; ψ sd is the d-axis component of the stator flux linkage; u rd is the d-axis component of the rotor voltage; ψ rd is the d-axis component of the rotor flux linkage; s is the Laplace coefficient; ψ rq is the q-axis component of the rotor flux linkage; R r is the rotor resistance; i rd is the component of the stator current on the d-axis; u rq is the q-axis component of the rotor voltage; irq is the component of stator current in q-axis;

[0056] The flux equation is simplified as

[0057]

[0058] where L s is the stator inductance; i sd is the component of stator current in d-axis; L m is the mutual inductance between stator and rotor; i rd is the component of rotor current in d-axis; i sq is the component of stator current in q-axis; i rq is the component of rotor current in q-axis; L r is the rotor inductance;

[0059] The active power P s and the reactive power Q s generated by the stator of the doubly-fed wind turbine are finally obtained as

[0060]

[0061] When the stator-side converter is controlled, the component of rotor current in q-axis i rq is adjusted to realize the control of the stator-side reactive power output Q s of the doubly-fed wind turbine;

[0062] The rotor-side converter control:

[0063] The active power P c and the reactive power Q c exchanged between the rotor-side converter of the doubly-fed wind turbine and the power grid are expressed as

[0064]

[0065] where u cd is the component of rotor-side converter voltage in d-axis in dq synchronous rotating coordinate system; i cd is the component of rotor converter current in d-axis in dq synchronous rotating coordinate system; u cq is the component of rotor-side converter voltage in q-axis in dq synchronous rotating coordinate system; i cq is the component of rotor converter current in q-axis in dq synchronous rotating coordinate system;

[0066] When the vector control is adopted, u cq = 0, so that

[0067] When the rotor-side converter is controlled, the component of rotor converter current in q-axis i cq is adjusted to realize the control of the rotor-side reactive power output Q cThe control of the static var generator.

[0068] Step S4: According to the power distribution result of step S2, a static var generator is called to realize the coordinated reactive power compensation of the static var generator and the doubly-fed wind turbine based on model reference adaptive control, including the following steps:

[0069] Simplify the structure of the static var generator, build a corresponding mathematical model, and obtain the state space expression of the static var generator;

[0070] Design a reference model to specify the expected response of the static var generator;

[0071] Finally, design a model reference adaptive control law for the static var generator to realize the control of the static var generator;

[0072] Finally, realize the coordinated reactive power compensation of the static var generator and the doubly-fed wind turbine.

[0073] The step S4 specifically includes the following steps:

[0074] Simplify the structure of the static var generator, build a mathematical model, and obtain the state space expression:

[0075] According to the main circuit diagram of the static var generator, the single-phase equivalent circuit of the static var generator is obtained as follows: the positive pole of the first voltage source is connected to the positive pole of the second voltage source through a series connection of a first resistor, a first inductor, and the first voltage source negative pole and the second voltage source negative pole are directly connected; wherein the voltage of the first voltage source is the capacitor side voltage u c of the static var generator, the voltage of the second voltage source is the grid side voltage u v , the resistance value of the first resistor is the line resistance R v of the static var generator, and the inductance value of the first inductor is the inductance L v of the static var generator.

[0076] Using the relationship of circuit elements, the dynamic differential equation of the single-phase equivalent circuit of the static var generator is derived as

[0077]

[0078] In the formula, i v is the current value output by the second voltage source; C is the capacitance value;

[0079] Introducing the state variable, the state space expression of the static var generator is obtained as

[0080]

[0081] In the formula, x p is the system state variable, and is the time derivative of the system state variable, and A p is the system state matrix, and B p is the system input matrix, and u p is the system input variable, and u p = [u v ];

[0082] The reference model is designed as follows:

[0083] The expression of the reference model is as follows:

[0084]

[0085] where x m is the state variable of the reference model; is the derivative of the state variable of the reference model; A m is the state matrix of the reference model; B m is the input matrix of the reference model; y r is the input variable of the reference model;

[0086] The model reference adaptive control law of the static var generator is designed as follows:

[0087] The tracking error equation of the static var generator model and the reference model is designed as follows

[0088]

[0089] where e is the tracking error; is the derivative of the tracking error; F is the designed state feedback controller matrix; K is the designed feedforward controller matrix;

[0090] The adaptive law of K and F is adjusted by using the Lyapunov stability theory to reach the convergence state e(t) is the tracking error at time t;

[0091] When F(e, t) = F0 and K(e, t) = K0, the static var generator model and the reference model are completely matched, K and F are variables related to the tracking error and time, and can be expressed as F(e, t) and K(e, t); F0 and K0 are the equilibrium values when the complete matching is achieved.

[0092] To make the static var generator model completely matched with the reference model, the following condition must be met

[0093]

[0094] Thus, the tracking error equation is expressed as

[0095]

[0096] wherein is a state feedback control matrix error, and is a feedforward control matrix error, and

[0097]

[0098] Construct Lyapunov function V as

[0099]

[0100] wherein P is a first positive definite symmetric matrix; tr is a trace of a matrix; P F , P K is a symmetric positive definite matrix;

[0101] Derive the derivative of Lyapunov function V with respect to t to obtain

[0102]

[0103] wherein A m is a stable matrix, and satisfies P is a first positive definite matrix, Q is a second positive definite matrix, and Q = Q T > 0;

[0104] In order to ensure that the derivative of Lyapunov function is negative definite, let the last two terms in the formula of be 0, then the model reference adaptive control law is

[0105]

[0106] wherein R1 and R2 are parameter matrices to be determined;

[0107] Finally, the model reference adaptive control law is used to control the static var generator, so as to realize the coordinated reactive power compensation of the static var generator and the doubly-fed wind turbine.

[0108] The application further provides a system for realizing the reactive power compensation method of the static reactive power generator and the doubly-fed wind turbine, comprising a data acquisition module, a reactive power distribution module, a wind turbine control module and a cooperative control module; the data acquisition module, the reactive power distribution module, the wind turbine control module and the cooperative control module are connected in series; the data acquisition module is used for acquiring data information of a target power system, a static reactive power generator and a doubly-fed wind turbine, and uploading the data information to the reactive power distribution module; the reactive power distribution module is used for determining reactive power compensation of the target power system according to the received data information, performing power distribution of the reactive power compensation, and uploading the data information to the wind turbine control module; the wind turbine control module is used for preferentially mobilizing the doubly-fed wind turbine according to the received data information and the power distribution result, controlling the doubly-fed wind turbine based on stator measurement converter control and rotor side converter control, realizing reactive power compensation of the doubly-fed wind turbine, and uploading the data information to the cooperative control module; and the cooperative control module is used for calling the static reactive power generator according to the received data information and the power distribution result, realizing reactive power compensation of the static reactive power generator and the doubly-fed wind turbine based on model reference adaptive control.

[0109] The static reactive power generator and the doubly-fed wind turbine cooperative reactive power compensation method and system provided by the application set a priority scheme for reactive power compensation according to the characteristics of the static reactive power generator and the doubly-fed wind turbine, realize control of the doubly-fed wind turbine according to stator measurement converter control and rotor side converter control, realize control of the static reactive power generator according to model reference adaptive control, so that the application can realize reactive power compensation of the static reactive power generator and the doubly-fed wind turbine, has higher reliability and better accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0110] Figure 1 It is a method flowchart of the method of the application.

[0111] Figure 2 It is a circuit model schematic diagram of the static reactive power generator of the method of the application.

[0112] Figure 3 It is a single-phase equivalent circuit schematic diagram of the static reactive power generator of the application.

[0113] Figure 4 It is a reactive power output curve schematic diagram of the doubly-fed wind turbine of the embodiment of the application.

[0114] Figure 5 It is a reactive power output curve schematic diagram of the static reactive power generator of the embodiment of the application.

[0115] Figure 6 It is a function module schematic diagram of the system of the application. DETAILED DESCRIPTION

[0116] As Figure 1 The method flowchart of the method of the application is shown in the figure: the reactive power compensation method of the static reactive power generator and the double-fed wind turbine disclosed by the application comprises the following steps:

[0117] S1. Obtain the data information of the target power system, the static reactive power generator and the double-fed wind turbine;

[0118] S2. According to the data information obtained in step S1, determine the reactive power compensation of the target power system, and perform power distribution for the reactive power compensation; comprising the following steps:

[0119] According to the data information obtained in step S1, calculate the voltage deviation value of the grid connection point, and according to the size relationship between the voltage deviation value and the voltage deviation dead zone, determine whether to start the reactive power compensation, and calculate the reactive power compensation target value;

[0120] After starting the reactive power compensation, the double-fed wind turbine is preferentially started to perform the reactive power compensation, and the reactive power compensation capacity of the double-fed wind turbine is calculated;

[0121] According to the size relationship between the reactive power compensation target value and the reactive power compensation capacity of the double-fed wind turbine, the power distribution for the reactive power compensation between the static reactive power generator and the double-fed wind turbine is performed;

[0122] In specific implementation, comprising the following steps:

[0123] Set the voltage deviation dead zone;

[0124] Detect the grid connection point voltage and calculate the deviation value of the grid connection point voltage and the reference voltage;

[0125] Determine the deviation value:

[0126] If the deviation value is within the set voltage deviation dead zone range, do not act;

[0127] If the deviation value exceeds the set voltage deviation dead zone range, start the reactive power compensation, and take the deviation value as the reactive power compensation target value Q all ;

[0128] Since the DFIG (double-fed wind turbine) itself has the ability to adjust the reactive power, no additional cost is introduced, the SVG (reactive power generator) is an additional reactive power compensation device, and the cost is relatively high. Frequent start and stop will increase its loss, and the converter of the DFIG has a faster response speed to the reactive power and a good adjustment capacity, so the reactive power capacity of the DFIG is preferentially called to perform the reactive power compensation, and when the reactive power capacity of the DFIG cannot meet the requirement of the reactive power compensation, the reactive power capacity of the SVG is started to perform the reactive power compensation;

[0129] Preferentially start the double-fed wind turbine to perform the reactive power compensation;

[0130] The reactive power compensation capability of the DFIG is calculated by the following steps:

[0131] When the DFIG is connected to the power distribution network, it is connected through direct grid connection of the stator side and grid connection of the rotor side through the inverter, so the total active power P of the DFIG is determined by the output P S of the stator direct side and the output P c of the rotor grid side; therefore, the total active power P of the DFIG is expressed as P=P S +P c , P S is the output of the stator direct side, and P c is the output of the rotor grid side.

[0132] Since the total active power of the DFIG satisfies P c =-sP S , s is the slip of the DFIG, so P=(1-s)P S exists.

[0133] The reactive power output Q of the DFIG is the algebraic sum of the stator side reactive power Q s and the rotor side reactive power Q c of the inverter grid, which is expressed as Q=Q s +Q c .

[0134] According to the power balance relationship, the DFIG grid satisfies

[0135]

[0136] In the formula, U S is the node voltage of the stator side of the DFIG grid point; I S is the current flowing through the stator winding.

[0137] According to the characteristics of the inverter itself, the AC side of the PWM inverter is limited by its maximum current value, and the output current of the stator side satisfies

[0138]

[0139] In the formula, X S is the equivalent leakage reactance of the stator; X m is the excitation reactance; I rmax is the maximum current limit value of the inverter grid, which is generally not more than 1.5 times the rated current of the DFIG.

[0140] Then, the range of the reactive power that can be output by the stator side and the rotor side is obtained as

[0141]

[0142] In the formula, irmax is the maximum current of the rotor side; S c is the maximum capacity of the grid side converter;

[0143] The output power reference value of the DFIG under different operating conditions is expressed as

[0144]

[0145] P ref is the output power reference value of the DFIG; k max is the maximum power tracking coefficient; ω0 is the initial rotational speed of the DFIG entering the maximum power tracking zone; ω min is the minimum rotor rotational speed at which the DFIG can maintain normal operation; ω w is the rotor rotational speed; ω1 is the initial rotational speed of the DFIG entering the constant rotational speed zone; P max is the maximum active power that the DFIG can generate; ω max is the initial rotational speed of the DFIG entering the constant power zone;

[0146] After obtaining the active output reference value of the DFIG under the current operating condition, the maximum capacity of the reactive output of the DFIG under this state can be obtained according to the P-Q characteristic of the DFIG; the reactive output of the DFIG is the maximum capacity Q dfigm is expressed as

[0147] Q dfigm = Q cmax + Q Smax

[0148] P cmax is the maximum capacity of the reactive output of the rotor side converter; Q Smax is the maximum capacity of the reactive output of the stator side;

[0149] When the DFIG performs reactive power compensation, the rotor side converter has a faster response speed, and thus the reactive capacity Q c of the rotor side converter is preferentially called upon; when Q c does not meet the requirement, the reactive capacity Q S of the stator side is called upon;

[0150] When the target value Q all of the reactive power compensation is less than or equal to Q dfigm , the DFIG performs reactive power compensation, and the static var generator is not activated;

[0151] When the target value Q all of the reactive power compensation is greater than Q dfigm , the remaining reactive capacity except Q dfigm is borne by the static var generator, which is expressed as Q SVG = Qall -Q dfigm Q SVG The reactive power output of the static var generator;

[0152] Rated capacity Q of static var generator SVGN It means that Q was thought to be Q SVGN =U SVG 2 / Z, U SVG Z is the AC line voltage of the inverter at the grid connection point of the static var generator, and Z is the equivalent reactance value of the AC side of the static var generator.

[0153] S3. Based on the power allocation result of step S2, prioritize the activation of the doubly-fed induction generator (DFIG) wind turbine. Based on the control of the stator-side converter and the rotor-side converter of the DFIG wind turbine, achieve reactive power compensation for the DFIG wind turbine; including the following steps:

[0154] Based on the power allocation result of step S2, the doubly fed wind turbine is prioritized for reactive power compensation.

[0155] When the doubly fed wind turbine performs reactive power compensation, the stator-side converter of the doubly fed wind turbine is controlled according to the simplified voltage equation and simplified flux linkage equation of the doubly fed wind turbine in the dq coordinate system; at the same time, the rotor-side converter of the doubly fed wind turbine is controlled according to the active power and reactive power exchanged between the rotor-side converter of the doubly fed wind turbine and the grid.

[0156] Ultimately, reactive power compensation for the doubly-fed wind turbine is achieved through the control of the stator-side converter and the rotor-side converter.

[0157] The specific implementation includes the following steps:

[0158] Stator-side converter control:

[0159] Neglecting the stator resistance voltage drop of the doubly-fed induction generator (DFIG), the simplified voltage equation of the DFIG in the dq coordinate system is obtained as follows:

[0160]

[0161] In the formula u sd ω represents the component of the stator-side converter voltage on the d-axis in the dq synchronous rotating coordinate system. s ψ is the stator rotational speed; sq U represents the q-axis component of the stator flux linkage. s Stator voltage; u sq ψ represents the component of the stator-side converter voltage on the q-axis in the dq synchronous rotating coordinate system. sd The d-axis component of the stator flux linkage; u rd ψ is the d-axis component of the rotor voltage; rd ψ is the d-axis component of the rotor flux linkage; s is the Laplace coefficient;rq Rotor flux q-axis component; R r R is the rotor resistance; i rd is the component of stator current in d-axis; u rq is the rotor voltage q-axis component; i rq is the component of stator current in q-axis;

[0162] The flux equation is simplified as

[0163]

[0164] Where L s is the stator inductance; i sd is the component of stator current in d-axis; L m is the mutual inductance between stator and rotor; i rd is the component of rotor current in d-axis; i sq is the component of stator current in q-axis; i rq is the component of rotor current in q-axis; L r is the rotor inductance;

[0165] The active power P s and the reactive power Q s generated by the stator of the doubly-fed wind turbine are finally obtained as

[0166]

[0167] As can be seen from the above equations, the value of Q s is related to i rq ; since the d-axis and the q-axis are perpendicular in the dq synchronous rotating coordinate system, i rd is perpendicular to i rq , and the quantities perpendicular to each other have no coupling relationship, so the decoupling control of the active power and the reactive power at the stator side can be realized;

[0168] When the stator-side converter is controlled, the rotor current q-axis component i rq is adjusted to realize the control of the stator-side reactive power Q s of the doubly-fed wind turbine;

[0169] Rotor-side converter control:

[0170] The active power P c and the reactive power Q c exchanged between the rotor-side converter of the doubly-fed wind turbine and the power grid are expressed as

[0171]

[0172] Where u cd is the component of the rotor-side converter voltage in the d-axis of the dq synchronous rotating coordinate system; i cdis the component of the rotor-side converter voltage on the q-axis in the dq synchronous rotating coordinate system; i cq is the component of the rotor-side converter voltage on the q-axis in the dq synchronous rotating coordinate system; i cq is the component of the rotor-side converter voltage on the q-axis in the dq synchronous rotating coordinate system; i

[0173] When the vector control is adopted, u cq = 0, so that

[0174] When the rotor-side converter control is adopted, the component i cq of the rotor-side converter current on the q-axis is adjusted to realize the control of the rotor-side reactive power output Q c of the doubly-fed wind turbine;

[0175] S4. According to the power distribution result of step S2, the static reactive power generator is called to realize the coordinated reactive power compensation of the static reactive power generator and the doubly-fed wind turbine based on the model reference adaptive control; including the following steps:

[0176] The structure of the static reactive power generator is simplified, and the corresponding mathematical model is constructed to obtain the state space expression of the static reactive power generator;

[0177] The reference model is designed to specify the expected response of the static reactive power generator;

[0178] Finally, the model reference adaptive control law of the static reactive power generator is designed to realize the control of the static reactive power generator;

[0179] Finally, the coordinated reactive power compensation of the static reactive power generator and the doubly-fed wind turbine is realized;

[0180] In specific implementation, the following steps are included:

[0181] The structure of the static reactive power generator is simplified, a mathematical model is established, and a state space expression is obtained:

[0182] According to the main circuit diagram of the static reactive power generator (as shown in Figure 2 , the single-phase equivalent circuit (as shown in Figure 3 ) of the static reactive power generator is obtained as follows: the positive pole of the first voltage source is connected to the positive pole of the second voltage source through a series connection of a first resistor, a first inductor, and the negative pole of the second voltage source; the negative pole of the first voltage source and the negative pole of the second voltage source are directly connected; wherein the voltage of the first voltage source is the capacitor-side voltage u c of the static reactive power generator, the voltage of the second voltage source is the grid-side voltage u v , the resistance value of the first resistor is the line resistance R v of the static reactive power generator, and the inductance value of the first inductor is the inductance L v of the static reactive power generator;

[0183] With the circuit element relationship, the dynamic differential equation of the single-phase equivalent circuit of the SVG is derived as

[0184]

[0185] where i v is the current value output by the second voltage source; C is the capacitance value;

[0186] The state variable is introduced, and the state space expression of the SVG is obtained as

[0187]

[0188] where x p is the system state variable, and is the time derivative of the system state variable, and A p is the system state matrix, and B p is the system input matrix, and u p is the system input variable, and u p = [u v ];

[0189] The reference model is designed as follows:

[0190] In order to obtain the output results meeting the expected response of the system, the reference model is designed to specify the expected response of the SVG, and the MRAC (model reference adaptive control law) system adjusts the controller parameters in real time according to the error between the actual model and the reference model, drives the system to track the output of the reference model, and achieves the ideal output results.

[0191] The following formula is used as the expression of the reference model:

[0192]

[0193] where x m is the state variable of the reference model; is the derivative of the state variable of the reference model; A m is the state matrix of the reference model; B m is the input matrix of the reference model; y r is the input variable of the reference model;

[0194] The model reference adaptive control law of the SVG is designed as follows:

[0195] The tracking error equation of the SVG model and the reference model is obtained by design as

[0196]

[0197] where e is the tracking error; is the derivative of the tracking error; F is the designed state feedback controller matrix; K is the designed feedforward controller matrix;

[0198] The adaptive laws of K and F are adjusted by using Lyapunov stability theory to achieve the convergence state e(t) is the tracking error at time t;

[0199] When F(e, t) = F0 and K(e, t) = K0, the static var generator model is completely matched with the reference model, K and F are variables related to the tracking error and time, which can be expressed as F(e, t) and K(e, t); F0 and K0 are the equilibrium values when the static var generator model is completely matched with the reference model; to make the static var generator model completely matched with the reference model, the following condition must be satisfied

[0200]

[0201] Thus, the tracking error equation is expressed as

[0202]

[0203] where is the error of the state feedback control matrix, and is the error of the feedforward control matrix, and

[0204]

[0205] The Lyapunov function V is constructed as

[0206]

[0207] where P is the first positive definite symmetric matrix; tr is the trace of the matrix; P F , P K is a symmetric positive definite matrix;

[0208] The derivative of the Lyapunov function V with respect to t is obtained as

[0209]

[0210] where A m is a stable matrix, and satisfies P is the first positive definite matrix, Q is the second positive definite matrix, and Q = Q T > 0;

[0211] In order to ensure that the derivative of the Lyapunov function is negative definite, the last two terms in the expression of are set to 0, and the model reference adaptive control law is

[0212]

[0213] wherein R1, R2 are parameter matrices to be determined;

[0214] Finally, the static var generator is controlled by using the model reference adaptive control law to realize the coordinated reactive power compensation of the static var generator and the doubly-fed wind turbine.

[0215] The effects of the method are further described below in combination with an embodiment:

[0216] Simulation is performed by using Matlab / Simulink, reactive load is put into the system at 4s to make the system voltage drop, the DFIG preferentially outputs and quickly reaches the upper limit of reactive power (as shown in FIG. 2), and is maintained near the maximum reactive power output with fluctuation, then the SVG based on MRAC control is started to compensate, and the reactive power is quickly and accurately supplemented according to the reactive power shortage of the system. Figure 4 It can be seen that the reactive power output of the SVG is fast in response, small in overshoot, and accurate in tracking, and the simulation results verify the effectiveness of the method and the excellent performance of the MRAC control method. Figure 5 As shown in FIG. 1, the system of the application comprises a data acquisition module, a reactive power distribution module, a wind turbine control module and a coordinated control module.

[0217] As shown in FIG. 1, the system of the application comprises a data acquisition module, a reactive power distribution module, a wind turbine control module and a coordinated control module. Figure 6 As shown in FIG. 1, the system of the application comprises a data acquisition module, a reactive power distribution module, a wind turbine control module and a coordinated control module. The data acquisition module is used for acquiring data information of a target power system, a static var generator and a doubly-fed wind turbine, and uploading the data information to the reactive power distribution module. The reactive power distribution module is used for determining reactive power compensation of the target power system according to the received data information, performing power distribution for the reactive power compensation, and uploading the data information to the wind turbine control module. The wind turbine control module is used for preferentially mobilizing the doubly-fed wind turbine according to the received data information and the power distribution result, controlling the stator side converter and the rotor side converter based on the doubly-fed wind turbine, and realizing reactive power compensation of the doubly-fed wind turbine, and uploading the data information to the coordinated control module. The coordinated control module is used for calling the static var generator according to the received data information and the power distribution result, realizing coordinated reactive power compensation of the static var generator and the doubly-fed wind turbine based on model reference adaptive control.

Claims

1. A static var generator and doubly-fed wind turbine cooperative reactive power compensation method, comprising the following steps: S1. Obtain data information of a target power system, a static var generator and a doubly-fed wind turbine; S2. According to the data information obtained in step S1, determine the reactive power compensation of the target power system, and perform power distribution for the reactive power compensation; S3. According to the power distribution result of step S2, preferentially mobilize the doubly-fed wind turbine, control the stator side converter and the rotor side converter of the doubly-fed wind turbine, and realize the reactive power compensation of the doubly-fed wind turbine; S4. According to the power distribution result of step S2, call the static var generator, realize the reactive power compensation of the static var generator and the doubly-fed wind turbine based on model reference adaptive control; specifically comprising the following steps: Simplify the structure of static var generator, establish mathematical model and get state space expression ; Design reference model According to the state space expression and the reference model, a tracking error equation of the static reactive power generator model and the reference model is obtained wherein is the tracking error; is the derivative of the tracking error; is the derivative of the reference model state variable; is the state matrix of the reference model; is the system state matrix; is the system input matrix; is the designed state feedback controller matrix; is the input matrix of the reference model; is the system input matrix; is the set feedforward controller matrix; is the input variable of the reference model; Using Lyapunov stability theory, the adaptive law of and is adjusted to achieve a convergent state; to make the static var generator model completely match the reference model, it is necessary to satisfy In the formula , is the equilibrium value for a perfect match; Thus the tracking error equation is expressed as wherein is a state feedback control matrix error, and ; is a feedforward control matrix error, and ; Constructing lyapunov functions To wherein is a first positive definite symmetric matrix; is a trace of a matrix; , is a symmetric positive definite matrix; Taking the derivative of the Lyapunov function with respect to t, we obtain In the formula is a stable matrix, and satisfies , is a first positive definite matrix, is a second positive definite matrix, ; To ensure that the derivative of the Lyapunov function is negative definite, let If the last two terms in the formula are 0, then the model reference adaptive control law is: In the formula , is the parameter matrix to be determined.

2. The method of reactive power compensation of a static var generator and a doubly-fed wind generator in cooperation according to claim 1, characterized in that According to the data information obtained in step S1, determine the reactive power compensation of the target power system, and perform power distribution for the reactive power compensation, comprising the following steps: According to the data information obtained in step S1, calculate the voltage deviation value of the grid-connected point, and determine whether to start the reactive power compensation according to the size relationship between the voltage deviation value and the voltage deviation dead zone, and calculate the target value of the reactive power compensation; After starting the reactive power compensation, preferentially start the doubly-fed wind turbine to perform the reactive power compensation, and calculate the reactive power compensation capability of the doubly-fed wind turbine; According to the size relationship between the target value of the reactive power compensation and the reactive power compensation capability of the doubly-fed wind turbine, perform the power distribution for the reactive power compensation between the static var generator and the doubly-fed wind turbine.

3. The method of reactive power compensation of a static var generator and doubly-fed wind generator in cooperation according to claim 2, characterized in that The step S2 specifically comprises the following steps: Set the voltage deviation dead zone; Detect the grid-connected point voltage, and calculate the deviation value of the grid-connected point voltage and the reference voltage; Determine the deviation value: If the deviation value is within the set voltage deviation dead zone, do not act; If the deviation value exceeds the set voltage deviation dead band range, reactive power compensation is started, and the deviation value is taken as the reactive power compensation target value ; Preferentially start the doubly-fed wind turbine to perform the reactive power compensation; The reactive power compensation capability of the doubly-fed wind turbine is calculated by the following steps: The total active power output P of the doubly-fed wind turbine is expressed as , Pd is the output on the stator direct side, Pr is the output on the rotor grid side; Since the double-sided active power output of the doubly-fed wind turbine meets , the slip of the doubly-fed wind turbine, there exists ; Reactive power output of doubly-fed wind turbine For stator-side reactive power output And rotor-side reactive power output for inverter grid connection The algebraic sum of ; According to the power balance relationship, when the doubly-fed wind turbine is connected to the grid, it satisfies In the formula is the node voltage at the stator side of the point of grid connection of the doubly-fed wind turbine; is the current flowing through the stator winding According to the characteristics of the inverter itself, the output current of the stator side satisfies In the formula is the equivalent leakage reactance of the stator; is the excitation reactance; is the maximum current limit value when the inverter is grid-connected; Then, the range of the reactive power that can be output by the stator side and the rotor side is In the formula is the maximum current on the rotor side; is the maximum capacity of the grid-side converter; The output power reference value of the doubly-fed wind turbine under different operating conditions is expressed as wherein is the output power reference value of the doubly-fed wind turbine; is the maximum power tracking coefficient; is the initial wind speed at which the doubly-fed wind turbine enters the maximum power tracking region; is the minimum rotor speed at which the doubly-fed wind turbine can maintain normal operation; is the rotor speed; is the initial rotor speed at which the doubly-fed wind turbine enters the constant speed region; is the maximum active power that the doubly-fed wind turbine can deliver; is the initial rotor speed at which the doubly-fed wind turbine enters the constant power region; The reactive power output of a doubly-fed wind turbine is at maximum capacity is represented as In the formula is the maximum capacity of the reactive power output of the rotor-side converter; is the maximum capacity of the reactive power output of the stator-side converter When the doubly-fed wind turbine is to perform reactive power compensation, the reactive power capacity of the rotor-side converter is called first ; when the requirements are not met, the reactive power capacity of the stator-side converter is called ; When the reactive power compensation target value is less than or equal to , the double-fed wind turbine carries out reactive power compensation, and the static reactive power generator is inactivated. When the reactive power compensation target value is greater than , the remaining reactive power capacity other than is borne by the static reactive power generator, denoted as , is the reactive power capacity output by the static reactive power generator; Rated capacity of static var generator Indicates that , Is the line voltage of the grid-connected point inverter AC side of static var generator, Is the equivalent reactance value of the AC side of static var generator.

4. The method of reactive power compensation of a static var generator and doubly-fed wind generator in cooperation according to claim 3, characterized in that According to the power distribution result of step S2, preferentially mobilize the doubly-fed wind turbine, control the stator side converter and the rotor side converter of the doubly-fed wind turbine, and realize the reactive power compensation of the doubly-fed wind turbine, comprising the following steps: According to the power distribution result of step S2, preferentially mobilize the doubly-fed wind turbine to perform the reactive power compensation; When the doubly-fed wind turbine performs the reactive power compensation, according to the simplified voltage equation and the simplified flux linkage equation of the doubly-fed wind turbine in the dq coordinate system, perform the stator side converter control of the doubly-fed wind turbine; at the same time, according to the active power and the reactive power exchanged between the rotor side converter of the doubly-fed wind turbine and the grid, adopt the vector control mode to perform the rotor side converter control of the doubly-fed wind turbine; Finally, through the stator side converter control and the rotor side converter control, realize the reactive power compensation of the doubly-fed wind turbine.

5. The method of reactive power compensation of a static var generator and doubly-fed wind generator in cooperation according to claim 4, characterized in that The step S3 specifically comprises the following steps: Stator side converter control: Neglect the stator resistance voltage drop of the doubly-fed wind turbine, and obtain the simplified voltage equation of the doubly-fed wind turbine in the dq coordinate system as follows: wherein is the stator-side inverter voltage component on the d-axis in the dq synchronous rotating coordinate system; is the stator speed; is the stator flux q-axis component; is the stator voltage; is the stator-side inverter voltage component on the q-axis in the dq synchronous rotating coordinate system; is the stator flux d-axis component; is the rotor voltage d-axis component; is the rotor flux d-axis component; is the Laplace coefficient; is the rotor flux q-axis component; is the rotor resistance; is the stator current component on the d-axis; is the rotor voltage q-axis component; is the stator current component on the q-axis; Simplify the flux linkage equation as wherein is the stator inductance; is the stator current d-axis component; is the stator-rotor mutual inductance; is the rotor current d-axis component; is the stator current q-axis component; is the rotor current q-axis component; is the rotor inductance; The final active power emitted by the stator of the doubly-fed wind turbine and the reactive power is ； Adjusting the rotor current q-axis component when the stator side converter is controlled , to realize the control of stator side reactive power output of the doubly-fed wind turbine . Rotor side converter control: Active power exchanged between the rotor side converter of a doubly-fed wind turbine and the grid and reactive power is represented as wherein is the component of the rotor-side converter voltage on the d-axis in the dq synchronous rotating coordinate system; is the component of the rotor converter current on the d-axis in the dq synchronous rotating coordinate system; is the component of the rotor-side converter voltage on the q-axis in the dq synchronous rotating coordinate system; is the component of the rotor converter current on the q-axis in the dq synchronous rotating coordinate system; When vector control is adopted, Thus, we obtain ; When the rotor-side converter is controlled, the component of the rotor-converter current on the q-axis is adjusted , to achieve control of the rotor-side reactive power output of the doubly-fed wind turbine .

6. The method of reactive power compensation of a static var generator and doubly-fed wind generator in cooperation according to claim 5, characterized in that The step S4 further comprises the following steps: According to the main circuit diagram of the static var generator, a single-phase equivalent circuit of the static var generator is obtained: a positive electrode of a first voltage source is connected to a negative electrode of a second voltage source through a first resistor, a first inductor and a connection of a positive electrode of the second voltage source; a negative electrode of the first voltage source is directly connected to a negative electrode of the second voltage source; wherein a voltage of the first voltage source is a capacitor-side voltage of the static var generator , a voltage of the second voltage source is a grid-side voltage , a resistance of the first resistor is a line resistance of the static var generator , and an inductance of the first inductor is an inductance of the static var generator . Using the circuit element relationship, the dynamic differential equation of the single-phase equivalent circuit of the static var generator is derived as In the formula is the current value output by the second voltage source; is the capacitance value; Introducing the state variable, the state space expression of the static var generator is obtained as wherein is a system state variable, and ; is a time derivative of a system state variable, and ; is a system state matrix, and ; is a system input matrix, and ; is a system input variable, and ; Design reference model: The following formula is used as the expression of the reference model: wherein is a state variable of the reference model; is a derivative of the state variable of the reference model; is a state matrix of the reference model; is an input matrix of the reference model; is an input variable of the reference model; Adaptive law of Lyapunov stability theory is used to adjust and to achieve convergence state , is the tracking error at time t. Set and when the static reactive generator model is perfectly matched with the reference model, and are variables related to the tracking error, the time; 、 are equilibrium values when perfectly matched. Finally, the static var generator is controlled by using the model reference adaptive control law to realize the coordinated reactive power compensation of the static var generator and the doubly-fed wind turbine.

7. A system for realizing the reactive power compensation method of the static var generator and the doubly-fed wind turbine in cooperation according to any one of claims 1 to 6, characterized by The data acquisition module, the reactive power distribution module, the wind turbine control module and the coordinated control module are connected in series; the data acquisition module is used for acquiring data information of the target power system, the static var generator and the doubly-fed wind turbine, and uploading the data information to the reactive power distribution module; the reactive power distribution module is used for determining the reactive power compensation of the target power system according to the received data information, performing power distribution of the reactive power compensation according to the acquired data information, and uploading the data information to the wind turbine control module; The wind turbine control module is used for preferentially mobilizing the doubly-fed wind turbine according to the received data information and the power distribution result, realizing the reactive power compensation of the doubly-fed wind turbine based on the stator measurement converter control and the rotor side converter control, and uploading the data information to the coordinated control module; The coordinated control module is used for calling the static var generator according to the received data information and the power distribution result, realizing the coordinated reactive power compensation of the static var generator and the doubly-fed wind turbine based on the model reference adaptive control.

Images