DFIG and SVG collaborative reactive power support strategy adopting active disturbance rejection control

Abstract

The invention discloses a DFIG and SVG collaborative reactive power support strategy adopting active-disturbance-rejection control. A first-order linear active-disturbance-rejection controller is designed to replace traditional PI control of a voltage outer ring of a doubly-fed wind generating set grid side converter; if the voltage drop occurs at the grid-connected point of the wind power plant, designing a q-axis current instruction value of the grid-side converter during the fault period as q-axis input of current inner loop control of the grid-side converter of the doubly-fed wind generating set, so that the doubly-fed wind generating set emits reactive power; after compensation, if the power factor of the doubly-fed wind generating set is smaller than a preset threshold value, the SVG device is made to send out reactive power according to the designed q-axis current instruction value of the SVG during the fault period. And after the fault is cleared, the q-axis current instruction value of the SVG is redesigned, so that the SVG device absorbs reactive power, and the overvoltage risk of the grid-connected point is reduced. According to the invention, a DFIG and SVG cooperative reactive power support strategy of active disturbance rejection control is adopted to meet the reactive power demand in the low voltage ride through period, and the operation stability of the wind power plant is effectively improved.

Description

Technical Field

[0001] The invention relates to a DFIG and SVG coordinated reactive support strategy using self-disturbance rejection control, and belongs to the technical field of wind power generation system fault control. Background Art

[0002] With the proposal of the "carbon peak and carbon neutrality" goals and under the new situation of "building a new power system with new energy as the main body", new energy is showing a new trend of accelerated development. Among them, new energy power generation energy represented by wind power generation technology has received great attention. The doubly-fed induction generator has become the most widely used in wind farms because of its good operating characteristics, active and reactive decoupling control, and small converter capacity.

[0003] The increase in wind farm penetration makes it unacceptable to shield wind power equipment when a fault occurs on the grid side. According to the latest technical regulations for wind farm access to the power system, during low voltage ride-through, wind turbines must ensure that they will not be disconnected from the grid and continue to operate for at least 625 milliseconds, and provide necessary reactive power support during voltage drops. Therefore, how to design a reactive power support strategy to meet reactive power demand during low voltage ride-through has become a problem that needs to be solved. Summary of the invention

[0004] The present invention provides a DFIG and SVG collaborative reactive support strategy using self-disturbance rejection control. The method uses the DFIG and SVG collaborative reactive support strategy using self-disturbance rejection control to meet the reactive power demand during low voltage ride-through, and takes into account the situation that after the fault ends, the voltage at the grid connection point may increase to a level exceeding the allowable range of the new energy station due to response delay; the present invention effectively improves the stability of wind farm operation.

[0005] The technical solution of the present invention is:

[0006] A DFIG and SVG coordinated reactive power support strategy using active disturbance rejection control, including:

[0007] Design a first-order linear anti-disturbance controller to replace the traditional PI control of the voltage outer loop of the grid-side converter of the doubly-fed wind turbine generator; the control of the grid-side converter of the doubly-fed wind turbine generator includes voltage outer loop control and current inner loop control;

[0008] Determine whether there is a voltage drop at the wind farm grid connection point: If there is a voltage drop, design the q-axis current command value of the grid-side converter during the fault period as the q-axis input of the current inner loop control of the grid-side converter of the doubly fed wind turbine generator set, so that the doubly fed wind turbine generator set can generate reactive power to compensate for the reactive power at the grid connection point; consider the maximum current capacity of the grid-side converter, limit the d-axis current command value; otherwise, end;

[0009] After compensation, determine whether the power factor of the doubly-fed wind turbine generator set is less than the preset threshold value: if so, the SVG q-axis current command value during the fault period is designed through the static reactive generator SVG and combined with the latest wind farm dynamic reactive compensation device grid-connected performance test specification requirements, so that the SVG device emits reactive power to adjust the reactive power of the grid-connected point; if not, the process ends after the adjustment is completed;

[0010] A Crowbar circuit is added on the RSC side of the doubly-fed wind turbine generator set, and its switching is controlled by a bypass switch. The bypass switch is initially disconnected, and the switching of the Crowbar circuit is controlled by determining the conditions based on the rotor side current.

[0011] Furthermore, it also includes: after the fault is removed, if the overvoltage level of the grid connection point is greater than a threshold value, switching the SVG control strategy to switch the working state of the SVG from a reactive power generation mode to a reactive power absorption mode.

[0012] Furthermore, the first-order linear active disturbance rejection controller is mainly composed of a linear extended state observer, a linear error feedback law and a disturbance estimation compensation;

[0013] For the controlled object, the current balance equation is rewritten as follows:

[0014]

[0015] in, Indicates the DC side voltage u dc The first-order derivative of , f(ω(t), t) is the uncertainty of internal and external disturbances such as model error; b is the unknown controller gain; b0 is the set approximate controller gain; Indicates the d-axis current command value of the grid-side converter control during normal operation;

[0016] f(ω(t),t) and As a sum disturbance, a second-order linear extended state observer is designed to observe the state variables and estimate the disturbance:

[0017]

[0018] Where z1 is the observed value of the state variable; z2 is the estimated value of the total disturbance; e is the state variable observation error; β1 and β2 are the observer gains of the extended state observer;

[0019] The disturbance estimation compensation and linear error feedback law are designed as:

[0020]

[0021] in, Indicates the given value of the DC side capacitor voltage; k prepresents the controller gain;

[0022] When the total disturbance estimate z2 can accurately estimate the total disturbance of the system, the first-order linear active disturbance rejection controller can achieve the ideal control effect, and then we can get:

[0023] Furthermore, the grid-side converter q-axis current command value during the designed fault period is expressed as follows:

[0024]

[0025] Where: I qref K represents the q-axis current command value of the grid-side converter control during the fault period. It can be divided into two stages. When the grid-connected point voltage drops to between 0.2 and 0.9, the q-axis current command value is set to a dynamic value according to the grid voltage drop degree; when the grid-connected point voltage drops below 0.2, the q-axis current command value is set to a fixed value; K DFIG Indicates the reactive current regulation ratio coefficient of the wind farm; U indicates the per unit value of the grid connection point voltage; I N Indicates the per-unit value of the rated current of the wind farm;

[0026] Considering the maximum current carrying capacity of the grid-side converter, the d-axis current command value is limited. At this time, the specific expression of the d-axis current command value of the grid-side converter is as follows:

[0027]

[0028] Where: I dref Indicates the d-axis current command value of the grid-side converter during the fault period; Indicates the d-axis current command value of the grid-side converter during normal operation; I max Indicates the maximum current value allowed to pass through the grid-side converter; I qref Indicates the q-axis current command value of the grid-side converter during a fault.

[0029] Furthermore, the q-axis current command value of the SVG during the designed fault period is expressed as:

[0030]

[0031] Among them, I svgqref represents the q-axis current command value of SVG during the fault period, k2 represents the transient reactive current regulation ratio coefficient, U represents the voltage per unit value of the wind farm grid connection point, and U N Indicates the rated voltage per unit value of the wind farm, I N Indicates the per-unit value of the rated current of the wind farm.

[0032] The beneficial effects of the present invention are:

[0033] Firstly, due to the limitations of traditional PI control, the present invention adopts first-order linear self-resistance control to replace it, thereby improving the low voltage ride-through capability of the wind farm.

[0034] Secondly, when the three-phase fault occurs in the power grid and the voltage at the grid connection point drops, the electric field designs the q-axis current command value of the grid-side converter according to the requirements for reactive current support in the latest technical regulations on wind farm access to the power system to compensate for the reactive power at the grid connection point. When the d-axis current command does not reach the limit, the d-axis current command value under normal operation is adopted, and when the limit is reached, the maximum d-axis current command value is adopted. After compensation, if the power factor of the wind farm is still less than 0.95, the SVG device will design the q-axis current command value of the SVG in combination with the requirements for reactive current in the latest wind farm dynamic reactive compensation device grid connection performance test specifications to perform reactive compensation on the grid connection point. At the same time, the Crowbar circuit on the RSC side of the wind turbine generator is put into operation after detecting that the rotor side current exceeds the threshold, short-circuiting the rotor circuit of the motor, blocking the pulse signal of the rotor side converter, and locking the rotor side converter.

[0035] Thirdly, after the fault is resolved, the q-axis current command value of the SVG control is designed to change the SVG operating state, absorb excess reactive power at the grid-connected point, and smooth out overvoltage at the grid-connected point. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A flow chart of wind farm station coordinated SVG reactive support provided by the present invention;

[0037] Figure 2 This is the equivalent topological structure diagram of the wind farm and SVG;

[0038] Figure 3 This is the control block diagram of the grid-side converter;

[0039] Figure 4 It is the structural block diagram of the first-order linear active disturbance rejection controller LADRC involved in the grid-side converter control block diagram;

[0040] Figure 5 It is the SVG control frame diagram;

[0041] Figure 6 It is the power waveform of wind farm;

[0042] Figure 7 It is the SVG power waveform diagram;

[0043] Figure 8 This is the power waveform of the grid-connected point. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. It should be noted that the embodiments in this application and the features in the embodiments can be combined with each other arbitrarily without conflict.

[0045] The PI control of the voltage outer loop of the grid-side converter of the traditional double-fed wind turbine has problems such as large overshoot of the DC side voltage, long adjustment time and large voltage fluctuation during the fault. It is difficult to effectively track the command value during the fault. After a three-phase fault occurs in the grid of the wind farm grid-connected system, the voltage at the grid-connected point drops. At this time, the rotor-side converter of the wind farm may have an overcurrent phenomenon, affecting the stability of the unit. Long-term voltage drop may even cause the wind farm to be disconnected from the grid. And after the fault is removed, the delayed response of the equipment may also cause overvoltage at the grid-connected point, causing damage to the equipment. Therefore, it is necessary to improve the traditional PI control and improve the dynamic response performance of the converter. When a fault occurs in the power grid, the wind farm and SVG equipment will promptly provide reactive support to the grid-connected point and suppress the overvoltage phenomenon at the grid-connected point after the fault ends. Based on this, the present invention proposes a DFIG and SVG collaborative reactive support strategy using self-anti-disturbance control.

[0046] Example 1: Figure 1-Figure 5 As shown, the DFIG and SVG coordinated reactive power support strategy using active disturbance rejection control proposed in the present invention is described. The DFIG and SVG coordinated reactive power support strategy using active disturbance rejection control specifically includes:

[0047] Step 1: Design a first-order linear active disturbance rejection control to replace the traditional PI control of the voltage outer loop of the grid-side converter of the doubly fed wind turbine generator to improve the low voltage ride-through capability of the wind turbine;

[0048] Step 2: Determine whether there is a voltage drop at the wind farm grid connection point. If so, in combination with the relevant technical regulations for the wind farm to be connected to the power system, design the q-axis current command value of the grid-side converter during the fault period as the q-axis input of the current inner loop control of the grid-side converter of the doubly fed wind turbine generator set, so that the doubly fed wind turbine generator set can generate reactive power to compensate for the reactive power at the grid connection point and adjust the voltage at the grid connection point; limit the d-axis current command value under the consideration of the maximum current carrying capacity of the grid-side converter; if not, end;

[0049] Step 3: Determine the power factor of the doubly-fed wind turbine generator If it is less than the preset threshold, then jump to step 4; if not, then end after the adjustment is completed;

[0050] Step 4: Through the static reactive power generator SVG and in combination with the latest wind farm dynamic reactive power compensation device grid-connected performance test specification requirements, the SVG device generates reactive power to compensate for the reactive power of the grid-connected point and adjust the voltage of the grid-connected point;

[0051] Step 5: Add a Crowbar circuit on the RSC side of the doubly-fed wind turbine generator set, whose switching is controlled by a bypass switch. The bypass switch is initially disconnected, and the switching of the Crowbar circuit is controlled by determining the judgment condition based on the rotor side current;

[0052] Step 6: After the fault is cleared, the overvoltage level at the grid connection point is greater than the threshold value, and the SVG control strategy is switched to a reactive power absorption working state to smooth the overvoltage at the grid connection point.

[0053] Furthermore, the control of the grid-side converter of the doubly-fed wind turbine generator includes voltage outer loop control and current inner loop control. Considering that the voltage outer loop of the grid-side converter adopts traditional PI control, there are problems such as large DC side voltage overshoot, long adjustment time and large voltage fluctuation during faults. In order to better improve the low-power wear-through capability of the wind farm, the present invention adopts a first-order linear active disturbance rejection controller LADRC to replace the traditional PI control to improve the response performance of the DC bus voltage of the converter during faults. The control block diagram of the grid-side converter after the introduction of LADRC is shown as follows: Figure 3 shown.

[0054] According to the mathematical model of the doubly-fed wind turbine generator set, the power equation on the grid side is obtained, which is expressed as follows:

[0055]

[0056] Among them, u dc Indicates the DC side voltage, i c Indicates the DC side current, u gd 、u gq are the dq axis components of the grid-side voltage, i gd 、i gq They are the dq axis components of the grid-side current respectively.

[0057] Since the grid voltage-oriented vector control strategy directs the grid-side voltage to the d-axis, the d-axis coincides with the grid electromotive force, so u gq = 0. Combining the power equation on the grid side, the current balance equation can be obtained, that is, the d-axis component i of the grid-side current gd and DC side voltage u dc The relationship is as follows:

[0058]

[0059] Where i1 represents the output current of the machine-side converter, C dRepresents DC capacitance.

[0060] The first-order linear active disturbance rejection controller of the grid-side converter voltage outer loop is designed according to the current balance equation. The first-order linear active disturbance rejection controller is mainly composed of a linear extended state observer, a linear error feedback law and a disturbance estimation compensation. The current balance equation is rewritten as follows:

[0061]

[0062] in, Indicates the DC side voltage u dc The first-order derivative of , f(ω(t), t) is the uncertainty of internal and external disturbances such as model error; b is the unknown controller gain; b0 is the set approximate controller gain; represents the d-axis current command value of the grid-side converter control during normal operation; y represents the system output; f(ω(t), t) and As the total disturbance g, a second-order linear extended state observer is designed to observe the state variables and estimate the disturbance as follows:

[0063]

[0064] Among them, z1 is the state variable observation value; z2 is the total disturbance estimate; e is the state variable observation error; β1 and β2 are the observer gains of the extended state observer. According to the pole placement method, the observer gain of the second-order linear extended state observer is set to: β1 = 2ω0; Where ω0 is the observation bandwidth of the observer.

[0065] The disturbance estimation compensation and linear error feedback law are designed as:

[0066]

[0067] in, Indicates the d-axis current command value of the grid-side converter control during normal operation; Indicates the given value of the DC side capacitor voltage; k p Represents the controller gain. When the total disturbance estimate z2 can accurately estimate the total disturbance of the system, the first-order linear active disturbance rejection controller can achieve the ideal control effect. Substituting equation (5) into equation (3), we can get:

[0068]

[0069] Through the above analysis, it can be seen that for the DC bus voltage controlled object, the first-order linear active disturbance rejection controller introduced according to the present invention replaces the traditional PI control of the voltage outer loop of the grid-side converter of the doubly fed wind turbine generator. The specific LADRC structure block diagram is as follows: Figure 4 shown.

[0070] Furthermore, when a three-phase fault occurs in the power grid and the voltage at the grid connection point drops, the wind farm combines the requirements for reactive current support in the latest technical regulations related to wind farm access to the power system, and designs the specific expression of the q-axis current command value of the grid-side converter control of the doubly-fed wind turbine during the fault period as follows:

[0071]

[0072] Where: I qref Indicates the q-axis current command value of the grid-side converter control during the fault period. It can be divided into two stages. When the grid-connected point voltage drops to between 0.2 and 0.9, the q-axis current command value is set to a dynamic value according to the grid voltage drop degree. When the grid-connected point voltage drops below 0.2, the q-axis current command value is set to a fixed value. K DFIG Indicates the reactive current regulation ratio coefficient of the wind farm; U indicates the per unit value of the grid connection point voltage; I N Indicates the per-unit value of the rated current of the wind farm.

[0073] Furthermore, considering the maximum current carrying capacity of the grid-side converter, it is necessary to limit the d-axis current command value. At this time, the specific expression of the d-axis current command value of the grid-side converter is as follows:

[0074]

[0075] Where: I dref Indicates the d-axis current command value of the grid-side converter during the fault period; Indicates the d-axis current command value of the grid-side converter during normal operation; I max Indicates the maximum current value allowed to pass through the grid-side converter; I qref Indicates the q-axis current command value of the grid-side converter during a fault.

[0076] By applying the above technical solution, it can be known that if a voltage drop occurs at the wind farm grid connection point, the q-axis current command value of the grid-side converter during the fault period is calculated according to formula (7), and the q-axis current command value of the grid-side converter during the fault period is used as the q-axis input of the current inner loop control of the grid-side converter of the doubly fed wind turbine generator set, thereby enabling the doubly fed wind turbine generator set to generate reactive power and adjust the reactive power of the grid connection point; at the same time, the d-axis current command value of the grid-side converter during the fault period calculated by formula (8) prevents the d-axis current from being too large and causing damage to the converter.

[0077] Further: After the double-fed wind turbine generator set generates reactive power to achieve regulation, the power factor of the wind farm is calculated at this time The expression is as follows:

[0078]

[0079] Where: P DFIG Indicates the active power generated by the doubly-fed wind turbine generator set; Q DFIG Represents the reactive power generated by the doubly-fed wind turbine generator.

[0080] Determine the power factor of the wind farm at this time If it is greater than or equal to 0.95, it indicates that the reactive power generated by the doubly-fed wind turbine generator meets the design specifications. If it is less than 0.95, the SVG equipment is started for coordination.

[0081] Further: When the double-fed wind turbine generator generates reactive power to achieve regulation, the power factor of the wind farm When it is still less than 0.95, the SVG device will design the q-axis command value in combination with the requirements for reactive current in the latest wind farm dynamic reactive compensation device grid-connected performance test specification. The specific expression is as follows:

[0082]

[0083] Among them, I svgqref represents the q-axis current command value of SVG during the fault period, k2 represents the transient reactive current regulation ratio coefficient, U represents the per unit voltage of the wind farm grid connection point, and U N Indicates the rated voltage per unit value of the wind farm, I N Indicates the per-unit value of the rated current of the wind farm.

[0084] By applying the above technical solution, it can be seen that when the double-fed wind turbine generator set generates reactive power to achieve regulation, the power factor of the wind farm When it is still less than 0.95, the q-axis current command value of the SVG during the fault period is calculated by formula (10), and the q-axis current command value of the SVG during the fault period is used as the q-axis input of the current inner loop control of the SVG device, so that the SVG device generates reactive power, thereby adjusting the reactive power of the grid connection point.

[0085] Furthermore: when the power grid fails, the stator and rotor windings of the doubly-fed wind turbine generator set induce transient impact currents. In order to protect the rotor-side converter from damage, a Crowbar circuit is connected in series in the rotor-side circuit of the doubly-fed wind turbine generator set to suppress the overcurrent on the rotor side during the fault period. Its switching is controlled by the bypass switch, and the initial state is disconnected.

[0086] When it is detected that the rotor side current of the wind turbine generator satisfies the following formula:

[0087]

[0088] Where: i dr and i qr Represents the dq axis component of the rotor current; i rlinmIndicates the maximum allowable current on the rotor side.

[0089] When equation (11) holds true, the rotor side Crowbar protection circuit is activated to short-circuit the rotor circuit of the motor, block the rotor side converter pulse signal, and lock the rotor side converter to prevent the rotor side overcurrent protection device from being damaged.

[0090] The resistance R in the Crowbar circuit C The value of R is very important. C If the resistance is too large, the rotor current will decay quickly, the power switch devices in the grid-side converter and the AC side overvoltage of the rotor-side converter will be damaged, while if the resistance is too small, it will not be able to limit the rotor overcurrent. C The minimum and maximum values ​​of the optimal range of resistance are expressed as follows:

[0091] The minimum value of Rc in the setting range:

[0092]

[0093] Where: U s Represents the stator voltage amplitude; ω s Indicates the angular velocity of the synchronous motor; L σ =L σs +L σr Indicates the total magnetic leakage of stator and rotor; I safe Indicates the converter safety current threshold, which is generally 1.2 times the rated rotor current.

[0094] The maximum value of Rc in the setting range:

[0095]

[0096] Where: U s Indicates the stator voltage amplitude; U dcmax Indicates the maximum value that the DC bus voltage can withstand.

[0097] In summary, the resistance R C Reasonable value range, in order to better suppress the short-circuit current, R C Generally, a larger value is taken within the optimal selection range, that is, R c =λR cmax , where λ is the safety margin factor, which is generally taken as 0.9~0.95.

[0098] Furthermore: after the fault is cleared, the delayed response of the SVG device and the doubly-fed wind turbine may cause excess reactive power at the grid connection point, causing the voltage at the grid connection point to rise to a level exceeding the allowable range of the new energy station, causing equipment damage. At this time, the SVG device needs to change its operating state to absorb the excess reactive power at the grid connection point and smooth out the overvoltage at the grid connection point. Based on this, the q-axis current command value of the SVG control after the fault is cleared is designed to switch the working state of the SVG from the reactive power emission mode to the reactive power absorption mode.

[0099]

[0100] in: It represents the q-axis current command value of SVG control after fault removal; I svgqref0 Indicates the q-axis current command value of SVG control during normal operation; I svgqref1 Indicates the q-axis current command value of SVG control in reactive absorption mode;

[0101] I svgqref1 =K svg (U-1)

[0102] Where: K svg represents the proportionality coefficient; U represents the per unit voltage of the wind farm grid connection point.

[0103] From the above, it can be seen that the present invention adopts first-order linear anti-disturbance control to replace the PI control of the grid-side converter voltage loop, improves the dynamic response performance of the converter, and when the grid voltage drops due to a three-phase fault in the grid, the q-axis command value of the wind turbine grid-side converter is redesigned according to the latest technical regulations related to the access of wind farms to the power system to provide reactive support for the grid. After considering the current carrying capacity of the converter, the d-axis current amplitude is limited to avoid the output current being greater than the inverter tolerance current due to an excessively large command value, which damages the power electronic devices in the inverter and causes economic losses. At the same time, the rotor-side Crowbar circuit is activated to short-circuit the rotor circuit of the motor, block the rotor-side converter pulse signal, and lock the rotor-side converter to suppress rotor-side overcurrent and protect the equipment from damage. When the power factor of the wind turbine is still less than 0.95 after adjustment, the SVG device redesigns the q-axis command value in combination with the grid-connected performance test specification of the dynamic reactive power compensation device of the wind farm to meet the grid's demand for reactive power during the fault. After the fault is cleared, the SVG operating state is changed to absorb excess reactive power at the grid-connected point to avoid damage to the equipment caused by voltage rise at the grid-connected point.

[0104] According to a second aspect of an embodiment of the present invention, a processor is provided, wherein the processor is used to execute operations, wherein the operations include executing any one of the above-mentioned DFIG and SVG collaborative reactive support strategies using active disturbance rejection control.

[0105] Embodiment 2: The optional implementation mode of the present invention is described below in conjunction with the accompanying drawings:

[0106] Taking the equivalent topological structure of a wind farm as an example, its equivalent topological diagram is as follows: Figure 2 As shown, it is assumed that a three-phase ABC short circuit fault occurs in the system, and the wind farm parameters are shown in Table 1. The present invention provides a wind power low-power penetration strategy that takes into account reactive support and active anti-disturbance technology and SVG control, which is carried out in the following steps:

[0107] Table 1 Specific parameters of double-fed wind turbine

[0108]

[0109] like Figure 2 A three-phase ABC short circuit fault occurs at point F, and the voltage amplitude drops to 0.7pu after the fault.

[0110] 1. Considering the problems of large DC side voltage overshoot, long adjustment time and large voltage fluctuation during fault in the traditional PI control of the voltage outer loop of the grid-side converter of the doubly fed wind turbine, in order to better improve the low-voltage ride-through capability of the wind farm, the design adopts first-order linear active disturbance rejection control to replace the traditional PI control to improve the system's fault ride-through capability and improve the response performance of the DC bus voltage during faults.

[0111] According to the mathematical model of the doubly-fed wind turbine generator set, the power equation on the grid side can be written as:

[0112]

[0113] Since the grid voltage-oriented vector control strategy directs the grid-side voltage to the d-axis, the d-axis coincides with the grid electromotive force, so u gq = 0. Combined with the power equation on the grid side, the current balance equation can be obtained, that is, the d-axis component i of the grid side current gd and DC side voltage u dc The relationship is as follows:

[0114]

[0115] The first-order linear active disturbance rejection controller of the grid-side converter voltage outer loop is designed according to the current balance equation. The first-order linear active disturbance rejection controller is mainly composed of a linear extended state observer, a linear error feedback law and a disturbance estimation compensation. The current balance equation is rewritten as follows:

[0116]

[0117] In the above, b0 is the set approximate controller gain, which is 35. Assuming the total disturbance g, a second-order linear extended state observer is designed to observe the state variables and estimate the disturbance as follows:

[0118]

[0119] According to the pole placement method, the observer gain of the extended state observer is set to: β1 = 2ω0; Where ω0 is the observation bandwidth of the observer and its value is 150; so β1=300; β2=22500;

[0120] The disturbance estimation compensation and linear error feedback law are designed as:

[0121]

[0122] k p =ω c

[0123] Among them, the DC side capacitor voltage given value The value is 1500; controller bandwidth ω c The value is 100. When the total disturbance estimate z2 can accurately estimate the total disturbance of the system, the first-order linear active disturbance rejection controller can achieve the ideal control effect. The above formula can be rearranged to obtain:

[0124]

[0125] In summary, the control parameters of the first-order linear ADRC are:

[0126] β1=300

[0127] β2=22500

[0128] k p =100

[0129] b0=35

[0130] 1. When a three-phase fault voltage drop occurs at the grid connection point, the wind farm should transmit reactive power during the fault period to stabilize the grid voltage in accordance with the requirements for reactive current support in the latest technical regulations on wind farm access to the power system. The specific expression for the q-axis current command value of the grid-side converter of the doubly-fed wind turbine during the fault period is as follows:

[0131]

[0132] Among them: Wind farm reactive current regulation proportional coefficient K DFIG The value is 3; the per-unit value U of the grid connection point voltage during the fault period is 0.7pu; the per-unit value I of the wind farm rated current N The value is 0.32pu.

[0133] According to the wind farm data in Table 1 and the voltage drop at the grid connection point, the q-axis current command value of the grid-side converter of the doubly-fed wind turbine generator is as follows:

[0134] I qref =0.192pu

[0135] Considering the maximum current carrying capacity of the grid-side converter, it is necessary to limit the d-axis current command value. At this time, the specific expression of the d-axis current command value of the grid-side converter is as follows:

[0136]

[0137] Where: The maximum current value I allowed to pass through the grid-side converter max The value is 0.31pu.

[0138] Through the above formula, the d-axis current command value of the grid-side converter is obtained as follows:

[0139] I dref =0.243pu

[0140] At this time, the wind farm status changes from absorbing 7.26MVA reactive power from the grid to emitting 0.4MVA reactive power to the grid. The power conversion of the wind farm is as follows: Figure 6 Shown to support grid voltage.

[0141] 2. After the wind farm transmits reactive power, calculate the power factor of the wind farm at this time The specific expression is as follows:

[0142]

[0143] Among them: The active power generated by the fan P DFIG The value is -0.8MW; the reactive power generated by the wind turbine is Q DFIG The value is 0.4MVA. The power factor calculated by the above formula is 0.89.

[0144] 3. Because the power factor is less than the set threshold value of 0.95, the SVG device transmits reactive current to the grid connection point in accordance with the latest wind farm dynamic reactive compensation device grid connection performance test specification. The specific expression of the SVG's q-axis current command value is as follows:

[0145]

[0146] Among them, the transient reactive current regulation ratio coefficient k2 is 1.5. Combined with the capacity of SVG itself, the q-axis current command value of SVG is -816.5A. At this time, SVG generates reactive power, and the power conversion between SVG and the grid connection point is as follows: Figure 7 , Figure 8 shown.

[0147] 4. During a fault, when it is detected that the rotor side current of the wind turbine is greater than or equal to the maximum allowable current, the rotor side Croebar circuit is activated to protect the stability of the rotor side converter. The resistor R C The value of R is very important. C If the resistance is too large, the rotor current will decay quickly, the power switch devices in the grid-side converter and the AC side of the rotor-side converter will be overvoltage, thus damaging the converter. If the resistance is too small, it will not be able to limit the rotor overcurrent. C The minimum and maximum values ​​of the optimal range of resistance are expressed as follows:

[0148] The minimum value of Rc in the setting range:

[0149]

[0150] The maximum value of Rc in the setting range:

[0151]

[0152] Where: stator voltage amplitude U s The value is 563V; the DC bus voltage can withstand the maximum value U dcmax Take the value of 1950V; thus we get R cmax =0.0029Ω.

[0153] In summary, the resistance R C Reasonable value range, in order to better suppress the short-circuit current, R C Generally, a larger value is taken within the reasonable value range, that is, R c =λR cmax , where λ is the safety margin factor, which is generally taken as 0.9~0.95.

[0154] Let λ be 0.9, so Rc=0.00261Ω is selected.

[0155] 6. After the fault is cleared, the delayed response of the SVG device and the doubly-fed wind turbine may cause excess reactive power at the grid connection point, causing the voltage at the grid connection point to rise to a level exceeding the allowable range of the new energy station, causing equipment damage. At this time, the SVG device needs to change its operating state to absorb the excess reactive power at the grid connection point and smooth out the overvoltage at the grid connection point. Based on this, the q-axis current command value of the SVG control after the fault is cleared is designed to switch the working state of the SVG from the reactive power emission mode to the reactive power absorption mode.

[0156]

[0157] I svgqref1 =Ksvg (U-1)

[0158] Where: SVG scale factor K svg The value is 2.

[0159] After the fault is cleared, the per-unit value of the grid-connected point voltage will be greater than that during the fault period. In the embodiment of the present invention, it is greater than 1.1U N Considering the capacity of SVG, set At this time, SVG absorbs reactive power, and the power conversion is as follows: Figure 7 shown.

[0160] The principle of the present invention is as follows:

[0161] The traditional wind farm station converter side control often adopts PI control, which has the problem of large DC side voltage overshoot, long adjustment time and inability to quickly adjust the operating state for compensation during faults. This causes the voltage drop to last too long, increasing the risk of system instability, and during faults, traditional wind turbines often rely on external reactive power compensation equipment or the power grid itself to provide reactive power support. Therefore, when a low voltage fault occurs in the power grid, the traditional wind farm may fail to provide sufficient reactive power support in time, resulting in further deterioration of the voltage at the grid connection point. The present invention adopts the first-order self-disturbance rejection control technology to replace the PI control of the traditional converter to improve the dynamic response performance of the converter. In the event of a fault, the wind farm combines the relevant technical regulations for the access of the wind farm to the power system with the SVG control to jointly perform reactive compensation on the grid connection point and stabilize the voltage at the grid connection point. The Crowbar circuit on the RSC side is also put into operation to suppress the overcurrent on the rotor side. After the fault is removed, the surplus reactive power of the grid connection point is absorbed by changing the SVG operating state, the overvoltage at the grid connection point is suppressed, and the equipment is protected from damage. The present invention can enable the wind farm to provide a specified dynamic reactive current support capability and suppress overvoltage phenomena when a fault ends, thus providing a reference for low voltage ride-through control of the wind farm.

[0162] The specific implementation modes of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A DFIG and SVG collaborative reactive support strategy using active disturbance rejection control, characterized in that: include: Design a first-order linear anti-disturbance controller to replace the traditional PI control of the voltage outer loop of the grid-side converter of the doubly-fed wind turbine generator; the control of the grid-side converter of the doubly-fed wind turbine generator includes voltage outer loop control and current inner loop control; Determine whether there is a voltage drop at the wind farm grid connection point: If there is a voltage drop, design the q-axis current command value of the grid-side converter during the fault period as the q-axis input of the current inner loop control of the grid-side converter of the doubly fed wind turbine generator set, so that the doubly fed wind turbine generator set can generate reactive power to compensate for the reactive power at the grid connection point; consider the maximum current capacity of the grid-side converter, limit the d-axis current command value; otherwise, end; After compensation, determine whether the power factor of the doubly-fed wind turbine generator set is less than the preset threshold value: if so, the SVG q-axis current command value during the fault period is designed through the static reactive generator SVG and combined with the latest wind farm dynamic reactive compensation device grid-connected performance test specification requirements, so that the SVG device emits reactive power to adjust the reactive power of the grid-connected point; if not, the process ends after the adjustment is completed; A Crowbar circuit is added on the RSC side of the doubly-fed wind turbine generator set, and its switching is controlled by a bypass switch. The bypass switch is initially disconnected, and the switching of the Crowbar circuit is controlled by determining the conditions based on the rotor side current.

2. The DFIG and SVG coordinated reactive power support strategy using active disturbance rejection control according to claim 1 is characterized in that: After the fault is cleared, the overvoltage level at the grid connection point is greater than the threshold value, and the SVG control strategy is switched to switch the working state of the SVG from the reactive power generation mode to the reactive power absorption mode.

3. The DFIG and SVG coordinated reactive power support strategy using active disturbance rejection control according to claim 1 is characterized in that: The first-order linear active disturbance rejection controller is mainly composed of a linear extended state observer, a linear error feedback law and a disturbance estimation compensation; For the controlled object, the current balance equation is rewritten as follows: in, Indicates the DC side voltage u dc The first-order derivative of , f(ω(t), t) is the uncertainty of internal and external disturbances such as model error; b is the unknown controller gain; b0 is the set approximate controller gain; Indicates the d-axis current command value of the grid-side converter control during normal operation; f(ω(t),t) and As a sum disturbance, a second-order linear extended state observer is designed to observe the state variables and estimate the disturbance: Where z1 is the observed value of the state variable; z2 is the estimated value of the total disturbance; e is the state variable observation error; β1 and β2 are the observer gains of the extended state observer; The disturbance estimation compensation and linear error feedback law are designed as: in, Indicates the given value of the DC side capacitor voltage; k p represents the controller gain; When the total disturbance estimate z2 can accurately estimate the total disturbance of the system, the first-order linear active disturbance rejection controller can achieve the ideal control effect, and then we can get:

4. The DFIG and SVG coordinated reactive power support strategy using active disturbance rejection control according to claim 1 is characterized in that: The q-axis current command value of the grid-side converter during the design fault period is expressed as follows: Where: I qref It represents the q-axis current command value of the grid-side converter control during the fault period. It can be divided into two stages. When the grid-connected point voltage drops to between 0.2 and 0.9, the q-axis current command value is set to a dynamic value according to the grid voltage drop degree; when the grid-connected point voltage drops below 0.2, the q-axis current command value is set to a fixed value; K DFIG It indicates the reactive current regulation ratio coefficient of the wind farm; U indicates the per unit value of the grid connection point voltage; I N Indicates the per-unit value of the rated current of the wind farm; Considering the maximum current carrying capacity of the grid-side converter, the d-axis current command value is limited. At this time, the specific expression of the d-axis current command value of the grid-side converter is as follows: Where: I dref Indicates the d-axis current command value of the grid-side converter during the fault period; Indicates the d-axis current command value of the grid-side converter during normal operation; I max Indicates the maximum current value allowed to pass through the grid-side converter; I qref Indicates the q-axis current command value of the grid-side converter during a fault.

5. The DFIG and SVG coordinated reactive power support strategy using active disturbance rejection control according to claim 1 is characterized in that: The q-axis current command value of the SVG during the designed fault period is expressed as: Among them, I svgqref represents the q-axis current command value of SVG during the fault period, k2 represents the transient reactive current regulation ratio coefficient, U represents the per unit voltage of the wind farm grid connection point, and U N Indicates the rated voltage per unit value of the wind farm, I N Indicates the per-unit value of the rated current of the wind farm.

Images