Network-configuration type full-power wind turbine reactive power support method based on active disturbance rejection control

Abstract

The present application relates to wind turbine voltage control technical field, especially to the network type full power wind turbine reactive power support method based on active disturbance rejection control, the method of the present application can provide active voltage support, increase reactive power, thereby lifting the voltage of the grid connection point, maintaining the system voltage stability when the system fault occurs and the voltage of the grid connection point drops by adding a first order linear active disturbance rejection control on the side of the grid side converter, the method of the present application provides guarantee for the network type wind turbine low voltage ride through and improves the active support ability of the system, and can promote the popularization and application of the network type wind turbine.

Description

Technical Field

[0001] This invention relates to the field of wind turbine voltage control technology, and in particular to a reactive power support method for grid-type full-power wind turbines based on active disturbance rejection control. Background Technology

[0002] The penetration rate of new energy sources such as wind power and photovoltaic power generation in the power system is continuously increasing. The traditional power system, dominated by synchronous generators, is transforming into a power system dominated by converters with a high proportion of wind power interconnection. This power system exhibits the "dual high" characteristics of "high proportion of new energy" and "high proportion of power electronic devices." Wind power generation equipment relies on grid-connected converters to connect to the grid. Currently, the vast majority of wind turbine units use grid-connected converters for control. Grid-connected converters lack the inertial response and reactive power support capabilities of traditional synchronous generator units. Against this backdrop, by leveraging the flexible controllable output characteristics of power electronic converters, wind turbine units can simulate the operating characteristics of synchronous generators, achieving "voltage source" control of the wind turbine units. This can effectively solve the problems of weak inertia and low short-circuit ratio faced by the new power system, further improving the stability of the power system.

[0003] To date, control methods for grid-connected wind turbines have only addressed control during grid steady-state conditions, neglecting to address voltage support under transient grid faults. This has hindered the widespread application of grid-connected wind turbine control methods in industry. Therefore, researching active voltage support strategies applicable to grid-connected converters and enhancing the active support capabilities of grid-connected wind turbines is of profound significance. Under grid faults, wind turbine generators require active voltage support. Traditional proportional-integral controllers (PICs) struggle to achieve ideal control performance when encountering external disturbances. Active disturbance rejection (ADRF) is developed based on traditional control theory, possessing strong fast tracking response and robust anti-interference capabilities, and has been widely applied in converter control. In grid-connected wind turbine control systems, the active grid support strategy is determined by the additional control of the grid-side converter. The transient voltage support strategy of the converter needs to respond in real-time to external disturbances; therefore, ADRF has significant applicability in transient voltage support strategy control. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by proposing a reactive power support method for grid-connected full-power wind turbines based on active disturbance rejection control (ADRC). By adding first-order linear ADRC to the grid-side converter, this invention enables the wind turbines to actively provide voltage support. In the event of a system fault, it achieves a controllable short-term voltage support response and low-voltage ride-through protection, maintaining system voltage stability.

[0005] To achieve the aforementioned objectives, the present invention employs the following technical solution: a reactive power support method for grid-connected full-power wind turbine generators based on active disturbance rejection control, comprising the following steps:

[0006] S1. Collect the instantaneous voltage of the power grid based on the common coupling point. When the power grid voltage drops and exceeds the set dead zone range, start the first-order linear active disturbance rejection control.

[0007] S2. Calculate the grid voltage deviation Δu0 based on the collected grid voltage.

[0008] S3. Input the calculated voltage deviation Δu0 into the first-order linear active disturbance rejection controller, and output the voltage compensation amount Δu after compensation by the controller.

[0009] S4. Input the voltage compensation amount Δu into the grid-side converter and calculate the modulation voltage U. t The calculation formula is as follows:

[0010] U t =ΔU+U t0 +I t R v (1)

[0011] In formula (1), U t0 I is the initial value of the modulation voltage. t R is the converter current. v For virtual resistance;

[0012] As a further preferred embodiment of the present invention, the control strategy activation step S1 is as follows:

[0013] When a grid fault occurs, a fault signal is usually generated by detecting the effective value of the voltage at the grid connection point; the abnormal voltage event at the grid connection point after the fault occurs is used as a fault identification signal, and when the event occurs, the grid-side converter additional control module is activated;

[0014] The fault signal F1 serves as a voltage fault criterion. It is generated by detecting the effective value of the grid connection point voltage and passing it through a hysteresis unit. Its expression is as follows:

[0015]

[0016] When the fault signal is set to 1, the system is identified as being in a fault state. At this time, the modulation voltage after the GSC additional control is:

[0017]

[0018] In formula (3): Δu t This represents the change in modulation voltage.

[0019] Furthermore, as a preferred embodiment of the present invention, the specific steps of step S3 are as follows:

[0020] S3.1 Design the linear extended state observer (LESO) for a first-order linear active disturbance rejection controller. The specific steps are as follows:

[0021] S3.1.1 Considering the complexity of nonlinear system control design, a dynamic compensation linearization method is used to transform the original nonlinear control system into a linear control system:

[0022]

[0023] In formula (4): x1 is the state variable; y is the system output; a(t) is the total unknown disturbance of the system; b is the compensation coefficient of the system's comprehensive disturbance; u is the control input;

[0024] S3.1.2. Perform disturbance estimation on the system's formula (4), and expand the real-time action of a(t) into a new state variable x2. Then, the new linear control model expression is:

[0025]

[0026] S3.1.3 To achieve real-time observation of the state variable x1 of the linear control system, a state observer is established for its extended system. The voltage deviation Δu0 is selected as the state variable x1, and the unknown total disturbance a(t) of the system is selected as the state variable x2. The reactive power output of the grid-connected wind turbine is adjusted in real time to respond to changes in grid voltage. Its expression is as follows:

[0027]

[0028] In formula (6), z1 and z2 are the system's observations of state variables x1 and x2; e is the system's output error; β1 and β2 are the system's gain parameters used for adjustment. denoted as z1 and z2, respectively; b is the compensation coefficient for the overall system disturbance; u is the control input.

[0029] S3.2 Design a linear state feedback controller (LSEF) for a first-order linear active disturbance rejection controller (AID) to compensate for the total disturbance in real time and counteract its effects. The input should be the estimated system voltage deviation and the reference voltage deviation Δ monitored in real time by the observer. uref The error between them is expressed as follows:

[0030]

[0031] In formula (7): e2 is the estimated value of the system voltage deviation and the reference value of the voltage deviation Δ monitored in real time by the observer. uref The error between them; β3 is the LSEF proportional coefficient, u0 is the control law, Δ uref Set it to 0.

[0032] Furthermore, as a preferred embodiment of the present invention, in step S3, the control parameters β1, β2, and β3 of the linear active disturbance rejection controller need to be tuned based on the observer and controller bandwidth method, taking into account the constraints of robustness and performance indicators. The tuning method is as follows:

[0033] The parameters of the bandwidth-based first-order linear active disturbance rejection controller are as follows:

[0034]

[0035] In formula (8), ω o ω is the observer bandwidth. c For controller bandwidth;

[0036] In process control, the controlled object can often be approximated as a form of FOPDT:

[0037]

[0038] In formula (9): k, τ, and T are the static gain, delay time, and time constant, respectively;

[0039] Considering the constraints of robustness and performance indicators, the tuning formula for the reduced FOPDT is as follows:

[0040]

[0041] The tuning of a first-order linear active disturbance rejection controller is transformed into tuning b and ω. c ω o Tuning of three parameters;

[0042] Based on the degree of autonomous voltage support during the disturbance, multiple experiments were conducted to obtain the FOPDT model parameters K, T, and τ.

[0043] Then, using the tuning formula of the first-order linear active disturbance rejection controller (10), the parameters b and ω of the first-order linear active disturbance rejection controller are obtained. c ω o Finally, the control parameters β1, β2, and β3 of the first-order linear active disturbance rejection controller are obtained.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] (1) By adding first-order linear active disturbance rejection control to the grid-side converter, the present invention can provide active voltage support when the grid connection point voltage drops due to system faults, increase reactive power, thereby raising the dropped grid connection point voltage and maintaining system voltage stability.

[0046] (2) This invention provides protection for low voltage ride-through of grid-type wind turbines and enhances the active support capability of the system; it can promote the application of grid-type wind turbines. Attached Figure Description

[0047] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0048] Figure 1 This is a schematic diagram of the method flow proposed in this invention;

[0049] Figure 2 This is a structural diagram of the first-order linear active disturbance rejection controller proposed in this invention;

[0050] Figure 3 This is a schematic diagram of the additional active disturbance rejection control for the grid-side converter of the present invention;

[0051] Figure 4 This is a schematic diagram of a grid-connected permanent magnet direct-drive wind power grid-connected simulation system according to an embodiment of the present invention;

[0052] Figure 5(a) is a converter modulation voltage curve diagram according to an embodiment of the present invention;

[0053] Figure 5(b) is a voltage curve at the grid connection point according to an embodiment of the present invention;

[0054] Figure 5(c) is a graph showing the reactive power output curve of the wind turbine in an embodiment of the present invention. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. Of course, the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0056] Example 1

[0057] like Figure 1 As shown, this embodiment provides a technical solution for reactive power support of grid-connected full-power wind turbines based on active disturbance rejection control, comprising the following steps:

[0058] S1: Collect the instantaneous voltage of the power grid based on the common coupling point. When the power grid voltage drops and exceeds the set dead zone range, start the first-order linear active disturbance rejection control.

[0059] When a power grid fault occurs, a fault signal is typically generated by detecting the effective value of the grid connection point voltage. This invention uses the abnormal grid connection point voltage event after a fault occurs as a fault identification signal. When the event occurs, the additional control module of the grid-side converter is activated.

[0060] The fault signal F1 serves as a voltage fault criterion. It is generated by detecting the effective value of the grid connection point voltage and passing it through a hysteresis unit. Its expression is as follows:

[0061]

[0062] When the fault signal is set to 1, the system is identified as being in a fault state. At this time, the modulation voltage after the GSC additional control is:

[0063]

[0064] In formula (3): Δu t This represents the change in modulation voltage.

[0065] S2: Calculate the grid voltage deviation Δu0 based on the collected grid voltage;

[0066] S3: Input the calculated voltage deviation Δu0 into the first-order linear active disturbance rejection controller, and output the voltage compensation amount Δu after compensation by the controller;

[0067] Active disturbance rejection controllers have the particular advantage of estimating and compensating for all uncertainties, primarily through timely and accurate estimation and compensation of disturbances. Figure 2 The first-order linear active disturbance rejection controller structure diagram shown is mainly composed of a Linear Extended State Observer (LESO) and a Linear State Error Feed-back Controller (LSEF). The specific steps of step S3 are as follows:

[0068] S3.1: Design a linear extended state observer (LESO) for a first-order linear active disturbance rejection controller. The specific steps are as follows:

[0069] S3.1.1: Considering the complexity of nonlinear system control design, this invention employs a dynamic compensation linearization method to transform the original nonlinear control system into a linear control system.

[0070]

[0071] In formula (4): x1 is the state variable; y is the system output; a(t) is the total unknown disturbance of the system; b is the compensation coefficient of the system's comprehensive disturbance; and u is the control input.

[0072] S3.1.2: Perform disturbance estimation on system (4), expand the real-time action of a(t) into a new state variable x2, and then the expression of the new linear control model is:

[0073]

[0074] S3.1.3: To achieve real-time observation of the state variable x1 of the linear control system, a state observer is established for its extended system. This invention selects the voltage deviation Δu0 as the state variable x1 and the unknown total disturbance a(t) of the system as the state variable x2, and adjusts the reactive power output of the grid-connected wind turbine in real time in response to changes in grid voltage. Its expression is as follows:

[0075]

[0076] In formula (6), z1 and z2 are the system's observations of state variables x1 and x2; e is the system's output error; β1 and β2 are the system's gain parameters used for adjustment. denoted as z1 and z2, respectively; b is the compensation coefficient for the overall disturbance of the system; u is the control input.

[0077] S3.2: Design a linear state error feedback (LSEF) controller for a first-order linear active disturbance rejection controller to compensate for the total disturbance in real time and counteract its effects. The input should be the estimated system voltage deviation and the reference voltage deviation Δ monitored in real time by the observer. uref The error between them is expressed as follows:

[0078]

[0079] In formula (7): e2 is the estimated value of the system voltage deviation and the reference value of the voltage deviation Δ monitored in real time by the observer. uref The error between them; β3 is the LSEF proportional coefficient, u0 is the control law, Δ uref Set it to 0.

[0080] In step S3, the control parameters β1, β2, and β3 of the linear active disturbance rejection controller need to be tuned based on the observer and controller bandwidth method, taking into account robustness and performance constraints. The tuning method is as follows:

[0081] The parameters of the bandwidth-based first-order linear active disturbance rejection controller are as follows:

[0082]

[0083] In formula (8), ω o ω is the observer bandwidth. c This refers to the controller bandwidth.

[0084] In process control, the controlled object can often be approximated as a form of FOPDT:

[0085]

[0086] In formula (9): k, τ and T are the static gain, delay time and time constant, respectively.

[0087] Considering the constraints of robustness and performance indicators, the tuning formula for the reduced FOPDT is as follows:

[0088]

[0089] The tuning of a first-order linear active disturbance rejection controller can be transformed into tuning b and ω. c ω o Tuning of the three parameters.

[0090] Based on the degree of autonomous voltage support during disturbances, this invention conducts multiple experiments to obtain the FOPDT model parameters K, T, and τ; then, using the tuning formula of the first-order linear active disturbance rejection controller (10), the parameters b and ω of the first-order linear active disturbance rejection controller are obtained. c ω o Finally, the control parameters β1, β2, and β3 of the first-order linear active disturbance rejection controller are obtained.

[0091] S4: Adjust the voltage compensation amount Δ u The input is fed into the grid-side converter to calculate the modulation voltage U. t The calculation formula is as follows:

[0092] U t =ΔU+U t0 +I t R v (1)

[0093] In formula (1), U t0 I is the initial value of the modulation voltage. t R is the converter current. v This is a virtual resistor.

[0094] like Figure 3 The diagram shown is a schematic flow chart of the grid-side converter additional active disturbance rejection control method of the present invention. When a fault occurs, the grid-side converter receives the fault signal and starts up using a first-order linear active disturbance rejection control voltage support strategy. The introduction of first-order linear active disturbance rejection control makes the modulation voltage U... t The voltage rises rapidly at the moment a fault occurs, thereby providing active voltage support, increasing reactive power, and thus raising the dropped grid connection point voltage to maintain system voltage stability.

[0095] The application effects of this invention are described in detail below based on simulation results:

[0096] To verify the effectiveness of the reactive power support method for grid-connected full-power wind turbines based on active disturbance rejection control proposed in this invention, a grid-connected permanent magnet direct-drive wind power grid-connected system was built on the PSCAD / EMTDC electromagnetic transient simulation platform, such as... Figure 4 The installed capacity of the wind turbine shown is 2MW, and the fault occurrence device is represented by a circuit breaker and a fault resistor; in addition, the parameters of the simulation model are shown in Table 1:

[0097] Simulation model parameters

[0098]

[0099] Table 1

[0100] The simulations of this invention were conducted under a constant wind speed of 10 m / s, with a three-phase short circuit occurring at the common coupling point. The results for the following three scenarios were analyzed and compared:

[0101] (1) The grid-type direct-drive wind turbine adopts control with virtual resistance (the wind turbine does not provide voltage response);

[0102] (2) Grid-type direct-drive wind turbines use existing droop control methods to participate in system voltage support (constant droop coefficient, coefficient is 0.5).

[0103] (3) The grid-type direct-drive wind turbine adopts the control method proposed in this invention to participate in system voltage support;

[0104] At 24.0s, a three-phase short-circuit fault lasting 0.625s occurred at the common coupling point, resulting in a drop in the grid connection point voltage; the changes in modulation voltage, grid connection point voltage, and wind turbine reactive power output under the three conditions described above are as follows: Figures 5(a) to 5(c) As shown.

[0105] Simulation results show that when a grid-connected direct-drive wind turbine uses virtual resistance control (the turbine does not provide voltage response), the modulation voltage of the grid-side converter is approximately a straight line, at 0.56 pu. At this point, the valley of the grid connection point voltage curve is 0.35 pu, and all reactive power support comes from the grid-connected direct-drive wind turbine, amounting to 0.25 pu. When the droop control of the grid-connected direct-drive wind turbine uses a constant coefficient, the modulation voltage of the grid-side converter increases during low-voltage ride-through, resulting in increased reactive power output and a rise in the grid connection point voltage, providing some voltage support to the power system. During short-circuit periods, the modulation voltage increases to 0.9 pu, with an additional 0.35 pu of reactive power generated, and the grid connection point voltage rises to 0.39 pu, representing increases of 0.34 pu, 0.1 pu, and 0.04 pu respectively compared to case one. When the grid-connected direct-drive wind turbine adopts the first-order linear active disturbance rejection control method proposed in this invention, the modulation voltage of the grid-side converter increases by 0.5 pu during the low voltage ride-through period compared to Case 2, reaching 1.4 pu; the increased reactive power increases by 0.05 pu compared to Case 2, reaching 0.4 pu; and the grid connection point voltage increases by 0.07 pu compared to Case 2, reaching 0.46 pu.

[0106] In summary, when a short-circuit fault occurs in the power grid, the reactive power support method for grid-connected full-power wind turbines based on active disturbance rejection control proposed in this invention can effectively provide active voltage support according to the voltage drop at the grid connection point, raise the voltage at the grid connection point, optimize the voltage stability of the power grid, and help the wind turbines cross the fault zone.

[0107] This invention enables the grid-side converter to receive a fault signal when a fault occurs, employing a first-order linear active disturbance rejection control (ADRC) voltage support strategy. Simulation results show that the first-order linear ADRC voltage support strategy has better active voltage support capability than a fixed-coefficient voltage droop strategy. It can further raise the grid connection point voltage during faults, generate higher reactive power, and is applicable to various transient voltage drop scenarios.

[0108] The specific implementation schemes described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific implementation schemes of the present invention and are not intended to limit the scope of the present invention. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principles of the present invention should fall within the scope of protection of the present invention.

Claims

1. A reactive power support method for grid-connected full-power wind turbines based on active disturbance rejection control, characterized in that, Includes the following steps: S1. Collect the instantaneous voltage of the power grid based on the common coupling point. When the power grid voltage drops and exceeds the set dead zone range, start the first-order linear active disturbance rejection control. The control strategy activation process for step S1 is as follows: When a grid fault occurs, a fault signal is usually generated by detecting the effective value of the voltage at the grid connection point; the abnormal voltage event at the grid connection point after the fault occurs is used as a fault identification signal, and when the event occurs, the grid-side converter additional control module is activated; The fault signal F1 serves as a voltage fault criterion. It is generated by detecting the effective value of the grid connection point voltage and passing it through a hysteresis unit. Its expression is as follows: （2） In formula (2): U pcc0 U is the reference value for the grid connection point voltage. pcc This is the actual voltage value at the grid connection point; When the fault signal is set to 1, the system is identified as being in a fault state. At this time, the modulation voltage after the GSC additional control is: （3） In formula (3): Δu t k represents the change in modulation voltage. p k is the proportional adjustment coefficient. i Q is the integral coefficient. gref Q is the reactive power reference value. g This represents the actual value of reactive power. S2. Calculate the grid voltage deviation ∆u0 based on the collected grid voltage. S3. Input the calculated voltage deviation ∆u0 into the first-order linear active disturbance rejection controller, and output the voltage compensation amount ∆u after compensation by the controller. S4. Input the voltage compensation amount ∆u into the grid-side converter and calculate the modulation voltage U. t The calculation formula is as follows: （1） In formula (1), U t0 I is the initial value of the modulation voltage. t R is the converter current. v This is a virtual resistor.

2. The reactive power support method for grid-type full-power wind turbines based on active disturbance rejection control according to claim 1, characterized in that, The specific steps of step S3 are as follows: S3.1 Design the linear extended state observer (LESO) for a first-order linear active disturbance rejection controller. The specific steps are as follows: S3.1.1 Considering the complexity of nonlinear system control design, a dynamic compensation linearization method is used to transform the original nonlinear control system into a linear control system: （4） In formula (4): x1 is the state variable; y is the system output; a(t) is the total unknown disturbance of the system; b is the compensation coefficient of the comprehensive disturbance of the system; u is the control input; S3.1.

2. Perform disturbance estimation on the system's formula (4), expand the real-time action of a(t) into a new state variable x2, and then the new linear control model expression is: （5） S3.1.3 To achieve real-time observation of the state variable x1 of the linear control system, a state observer is established for its extended system. The voltage deviation ∆u0 is selected as the state variable x1, and the unknown total disturbance a(t) of the system is selected as the state variable x2. The reactive power output of the grid-connected wind turbine is adjusted in real time to respond to changes in grid voltage. Its expression is as follows: （6） In formula (6), z1 and z2 are the system's observations of state variables x1 and x2; e is the system's output error; β1 and β2 are the system's gain parameters used for adjustment. denoted as z1 and z2, respectively; b is the compensation coefficient for the overall system disturbance; u is the control input. S3.2 Design a linear state feedback controller (LSEF) for a first-order linear active disturbance rejection controller (AID) to compensate for the total disturbance in real time and counteract its effects. Design its inputs to be the estimated system voltage deviation and the reference voltage deviation Δ, both monitored in real time by the observer. uref The error between them is expressed as follows: （7） In formula (7): e2 is the estimated value of the system voltage deviation and the reference value of the voltage deviation ∆ monitored in real time by the observer. uref The error between them; β3 is the LSEF proportional coefficient, u0 is the control law, ∆ uref Set it to 0.

3. The reactive power support method for grid-type full-power wind turbines based on active disturbance rejection control according to claim 1, characterized in that, In step S3, the control parameters β1, β2, and β3 of the linear active disturbance rejection controller need to be tuned based on the observer and controller bandwidth method, considering the constraints of robustness and performance indicators. The tuning method is as follows: The parameters of the bandwidth-based first-order linear active disturbance rejection controller are as follows: （8） In formula (8), ω o ω is the observer bandwidth. c For controller bandwidth; In process control, the controlled object can often be approximated as a form of FOPDT: （9） In formula (9): k, τ, and T are the static gain, delay time, and time constant, respectively; Considering the constraints of robustness and performance indicators, the tuning formula for the reduced FOPDT is as follows: (10) The tuning of a first-order linear active disturbance rejection controller is transformed into tuning b and ω. c ω o Tuning of three parameters; Based on the degree of autonomous voltage support during the disturbance, multiple experiments were conducted to obtain the FOPDT model parameters K, T, and τ. Then, using the tuning formula of the first-order linear active disturbance rejection controller (10), the parameters b and ω of the first-order linear active disturbance rejection controller are obtained. c ω o Finally, the control parameters β1, β2, and β3 of the first-order linear active disturbance rejection controller are obtained.

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