Controllable series compensation sub-synchronous oscillation suppression method based on linear active disturbance rejection control strategy

Abstract

The application discloses a controllable series compensation sub-synchronous oscillation suppression method based on a linear active disturbance rejection control strategy, which comprises the following steps: adopting a dynamic phasor method to perform mathematical modeling on the controllable series compensation, using the principle and differential characteristics of the dynamic vector method, taking the capacitance voltage of the TCSC and the inductance current of the TCR branch as state variables to perform modeling, and obtaining a dynamic phasor model of the controllable series compensation; designing a linear active disturbance rejection TCSC controller: applying the linear active disturbance rejection control principle to the dynamic phasor model of the controllable series compensation to change the series compensation degree, taking the power on the power transmission line as an input quantity, and respectively designing a linear extended state observer and a linear state error feedback law of the linear active disturbance rejection TCSC controller to control the series compensation degree of the controllable series compensation; and in a doubly-fed wind power plant grid-connected system, the TCSC based on the linear active disturbance rejection control strategy is used to suppress oscillation. The application improves the stability of the doubly-fed wind power plant grid-connected system when small disturbance and large disturbance occur.

Description

Technical Field

[0001] This invention relates to the field of power system stability analysis and control technology, specifically to a method for suppressing controllable series-complementary subsynchronous oscillations based on a linear active disturbance rejection control strategy. Background Technology

[0002] In recent years, wind power, as an environmentally friendly renewable energy source, has seen its installed capacity increase year by year. However, while maximizing energy utilization and flexibly outputting power, wind power also poses a serious challenge to the stable operation of the power grid. Due to its more complex dynamic characteristics than traditional power generation systems, wind power integration into the grid causes severe subsynchronous oscillations. This affects the development of wind power grid connection and even threatens the stable operation of the power system. Therefore, it is urgent to study the impact of wind turbine grid connection on system stability and feasible measures to mitigate its negative impacts.

[0003] There are two traditional methods for suppressing subsynchronous oscillations by adjusting controllable series compensation: one is to adjust the conduction angle of the thyristor so that the TCSC becomes inductive at the subsynchronous frequency, which can fundamentally eliminate the problem of subsynchronous resonance. However, this will limit the adjustment range of the thyristor conduction angle, making it impossible to adjust the TCSC impedance normally at the power frequency, thus affecting its ability to improve the transmission capacity of the line; the other is to utilize the positive resistance characteristic of the TCSC at the subsynchronous frequency, which can only alleviate the problem of subsynchronous resonance, but cannot fundamentally eliminate it. Summary of the Invention

[0004] The purpose of this invention is to provide a controllable series-complementary subsynchronous oscillation suppression method based on a linear active disturbance rejection control strategy for grid-connected systems of doubly-fed wind farms.

[0005] The technical solution to achieve the purpose of this invention is: a controllable series complement subsynchronous oscillation suppression method based on a linear active disturbance rejection control strategy, comprising the following steps:

[0006] Step 1: A mathematical model of the controllable series compensation is constructed using the dynamic phasor method. Utilizing the principle and differential characteristics of the dynamic phasor method, the capacitor voltage u of the TCSC is used as an example. C and the inductor current i of the TCR branch L The dynamic phasor model of the controllable series compensation is obtained by modeling it as a state variable; where TCSC is the controllable series compensation device and TCR is the thyristor controllable reactor.

[0007] Step 2: Design a linear active disturbance rejection (TCSC) controller: Apply the principle of linear active disturbance rejection control to the dynamic phasor model of controllable series compensation to change the series compensation degree. Using the power on the transmission line as the input, design the linear extended state observer and the linear state error feedback law of the linear active disturbance rejection (TCSC) controller to control the series compensation degree of controllable series compensation.

[0008] Step 3: In the doubly fed wind farm grid-connected system, load fluctuations and short-circuit faults are set for the system, and the TCSC based on the linear active disturbance rejection control strategy obtained in Step 2 is used to suppress the oscillations.

[0009] Compared with the prior art, the present invention has the following significant advantages: (1) By adjusting the series compensation degree of the controllable series compensation, the stability of the doubly fed wind farm grid-connected system is improved when small and large disturbances occur; (2) It can estimate and compensate for the total disturbance composed of subsynchronous disturbance and external disturbance, and has strong robustness and adaptability; (3) By improving the TCSC self-control, the subsynchronous oscillation phenomenon is suppressed, and no additional device is required. Attached Figure Description

[0010] Figure 1 This is a control strategy diagram for the controllable series-complementary subsynchronous oscillation suppression method based on linear active disturbance rejection control of the present invention.

[0011] Figure 2 The diagram shows the structure of the simulation controller built based on the linear active disturbance rejection TCSC control strategy.

[0012] Figure 3 This is a structural diagram of an application system for suppressing subsynchronous oscillations according to an embodiment of the present invention.

[0013] Figure 4 This is a comparison chart showing the changes in the inter-machine power angle of the synchronous machine system under load fluctuations using traditional TCSC control and LADRC-TCSC control.

[0014] Figure 5 This is a comparison chart of voltage changes at grid node 6 when using traditional TCSC and LADRC-TCSC during load fluctuations.

[0015] Figure 6 A comparison chart showing the power changes on the series compensation line when using traditional TCSC and LADRC-TCSC during load fluctuations.

[0016] Figure 7 This is a comparison chart showing the change in the inter-machine power angle of the synchronous machine system under short-circuit conditions using traditional TCSC control and LADRC-TCSC control.

[0017] Figure 8 This is a comparison chart of voltage changes at grid node 6 when using traditional TCSC and LADRC-TCSC during a short circuit.

[0018] Figure 9 This is a comparison chart showing the power changes on the series compensation line when using a traditional TCSC and a LADRC-TCSC during a short circuit. Detailed Implementation

[0019] This invention relates to a method for suppressing controllable series complement subsynchronous oscillations based on a linear active disturbance rejection control strategy, comprising the following steps:

[0020] Step 1: A mathematical model of the controllable series compensation is constructed using the dynamic phasor method. Utilizing the principle and differential characteristics of the dynamic phasor method, the capacitor voltage u of the TCSC is used as an example. C and the inductor current i of the TCR branch L The dynamic phasor model of the controllable series compensation is obtained by modeling it as a state variable; where TCSC is the controllable series compensation device and TCR is the thyristor controllable reactor.

[0021] Step 2: Design a linear active disturbance rejection (TCSC) controller: Apply the principle of linear active disturbance rejection control to the dynamic phasor model of controllable series compensation to change the series compensation degree. Using the power on the transmission line as the input, design the linear extended state observer and the linear state error feedback law of the linear active disturbance rejection (TCSC) controller to control the series compensation degree of controllable series compensation.

[0022] Step 3: In the doubly fed wind farm grid-connected system, load fluctuations and short-circuit faults are set for the system, and the TCSC based on the linear active disturbance rejection control strategy obtained in Step 2 is used to suppress the oscillations.

[0023] As a specific example, in step 1, the dynamic phasor method is used to mathematically model the controllable series complement, specifically as follows:

[0024] The primary circuit of the TCSC consists of a fixed capacitor C connected in parallel with the TCR branch (a thyristor-controlled reactor, with reactance L connected in series with an anti-parallel thyristor). The current flowing through the TCSC is i. l The current flowing through the TCR branch is i L The voltage across capacitor C is u. C .

[0025] Mathematical modeling of controllable series complement using the dynamic phasor method includes the following three sub-steps:

[0026] Step 11, using capacitor voltage u c and the inductor current i of the TCR branch L As state variables, they determine the state equations;

[0027] Step 12: Based on the differential characteristics of dynamic phasors, the TCSC state equation in dynamic phasor form is obtained for the state equation, and the order of the TCSC state equation under dynamic phasor is reduced.

[0028] Step 13: Decompose the phasors in the reduced-order TCSC state equation into real and imaginary parts to obtain a controllable cascaded complement dynamic phasor model.

[0029] Furthermore, step 11 specifically includes:

[0030] With capacitor voltage u c and the inductor current i of the TCR branch L The state equation, with the state variable as the state, is written as:

[0031]

[0032] Where q is the state function of the thyristor. If the thyristor is turned on, q = 1, and if it is turned off, q = 0.

[0033] Furthermore, step 12 specifically includes:

[0034] Applying the differential properties of dynamic phasors to equation (1), the TCSC state equation expressed in dynamic phasor form is obtained as follows:

[0035]

[0036] Among them, U c1 and I L1 These represent the fundamental frequency dynamic phasors of the capacitor voltage and the inductor current in the TCR branch, respectively; I l ω and ω represent the current flowing into the TCSC and the corresponding current frequency, respectively;

[0037] Due to U c1 Compared to I L1 The dynamic process is long, meaning it takes a relatively long time to reach a quasi-steady state. L1 Slow, so I L1 The dynamic process is regarded as Therefore:

[0038]

[0039] Among them, L eff (σ) is the equivalent inductance of the thyristor in the TCR branch when the conduction angle is σ;

[0040] The order of the state equations under dynamic phasors is reduced as shown in the following equation:

[0041]

[0042] Among them, C eff (σ) is the equivalent capacitance of TCSC.

[0043] Furthermore, step 13 specifically includes:

[0044] The phasors in the reduced-order state equation are decomposed into real and imaginary parts, i.e., U c =U cR +jU cI I l =I lR +jIlI The controllable series complement dynamic phasor model is obtained as follows:

[0045]

[0046] Express the capacitance in terms of reactance, and write the above equation as:

[0047]

[0048] in,

[0049] As a specific example, step 2 involves designing a linear active disturbance rejection (TCSC) controller, as detailed below:

[0050] like Figure 1 As shown, the control quantity u of the linear active disturbance rejection TCSC controller is X. Ceff The controller consists of three parts: a tracking differentiator (TD), a linear extended state observer (LESO), and a linear state error feedback control law (LSEF). The design steps are as follows:

[0051] Step 21: Design the controller input to be the active power P flowing through the line where the TCSC is located. TCSC Because the subsynchronous oscillation phenomenon of the system changes rapidly, in order to compensate for the subsynchronous disturbance in real time and in a suitable manner, the tracking differentiator is omitted here, and the given value is set to...

[0052] Step 22: The design of the extended state observer in linear active disturbance rejection control utilizes the system's output P TCSC The system tracks the state information of the system and estimates the total disturbance of the system by using the input u of the controlled object.

[0053] like Figure 1 As shown in the LESO module, the actual measured active power P of the line where the TCSC is located will be displayed. TCSC Feedback is sent to LESO for state observation, and the observer control equation is equation (7):

[0054]

[0055] In the formula, the observer's output signal z1 tracks the command signal, z2 tracks the derivative of the command signal, z3 is the LESO estimate of the total disturbance caused by the subsynchronous disturbance and the external disturbance; β1, β2, and β3 are linear parameters, and b0 is a given non-zero constant.

[0056] Step 23: As Figure 1In the LSEF loop shown, the active power setpoint of the line where the TCSC is located is subtracted from z1 and then input together with z2 into the LSEF to obtain the output u0. The feedback control quantity u0 is then compensated according to the total disturbance estimated by LESO to obtain the compensated control quantity u, which suppresses the subsynchronous oscillation of the system. The control of LSEF is given by equation (8):

[0057]

[0058] In the formula, v1 is the input signal, e1 and e2 are the error and the differential of the error, respectively; k p k d1 The gain coefficient of the PD circuit. This is the given value for the input power.

[0059] Step 24: Based on the mathematical model of the controller, build the controller in the simulation software as follows: Figure 2 As shown.

[0060] As a specific example, step 3 applies a linear active disturbance rejection (TCSC) controller to suppress subsynchronous oscillations, specifically as follows:

[0061] In a doubly fed wind farm grid-connected system, load fluctuations and short-circuit faults are set for the system. The TCSC based on the linear active disturbance rejection control strategy obtained in step 2 is used. The active power on the TCSC line is used as the controller input and the output is the equivalent capacitive reactance of the TCSC. The change of the equivalent capacitive reactance is achieved by changing the magnitude of the injected current at the two nodes of the TCSC, and finally the oscillation is suppressed.

[0062] In such Figure 2 The doubly fed wind farm grid-connected system shown is configured with load fluctuations and short-circuit faults. The linear active disturbance rejection controller (TCSC) designed in step 2 is applied to the series compensation device of the wind farm grid-connected line to suppress subsynchronous oscillations.

[0063] The present invention will now be described in further detail with reference to specific embodiments.

[0064] Example

[0065] To verify the effectiveness of the present invention, a system was constructed as follows: Figure 3The wind turbine grid-connected model shown depicts generators connected to buses 1-4 as synchronous generators (1-4 in total). Generators 1 and 2 are located in region I, and generators 3 and 4 are located in region II, forming a four-generator, two-region system. The generator connected to bus 12 is a doubly-fed induction generator (DFIG) connected to region I. The model consists of 100 1.5MV DFIGs, equivalent to a single-unit model, with a total capacity of 150MW. The voltage is increased to 230kV via the wind turbine's transformer and main transformer, and then connected to the two-region, four-generator system consisting of four synchronous generators via a 200km series-compensated transmission line. The following simulation experiments were conducted.

[0066] 1) Load disturbance

[0067] After setting the load on bus 7 to fluctuate upwards by 1% during the period of 1 to 1.1 seconds, the controller parameters are adjusted using the bandwidth method and set to: K P =100,K d1 =20, b0=10, β1=150, β2=7500, β3=125000, perform transient calculations in the time domain simulation. Figure 4 This section compares the changes in the inter-machine power angle of the synchronous machine system under load fluctuations using traditional TCSC control and LADRC-TCSC control. Figure 5 This section compares the voltage changes at grid node 6 when using traditional TCSC and LADRC-TCSC under load fluctuations. Figure 6 This section compares the power changes on the series compensation line when using a traditional TCSC and a LADRC-TCSC during load fluctuations. It shows that when small load fluctuations occur, the linear self-rejecting TCSC has a better oscillation suppression effect.

[0068] 2) Short circuit fault

[0069] A three-phase short-circuit fault was set on the grid-connected transmission line of the doubly fed wind turbine at 5s and disappeared after 0.1s. Time-domain simulation transient calculations were performed. Figure 7 This section compares the changes in the inter-machine power angle of the synchronous machine system under short-circuit conditions using traditional TCSC control and LADRC-TCSC control. Figure 8 This section compares the voltage changes at grid node 6 under short-circuit conditions using both traditional TCSC and LADRC-TCSC. Figure 9 This section compares the power changes on the series compensation line when using a traditional TCSC and a LADRC-TCSC during a short circuit. It shows that under large short-circuit disturbances, the linear active disturbance rejection TCSC has a better oscillation suppression effect than the traditional control strategy.

Claims

1. A method for suppressing controllable series-complementary subsynchronous oscillations based on a linear active disturbance rejection control strategy, characterized in that, Includes the following steps: Step 1: A mathematical model of the controllable series compensation is constructed using the dynamic phasor method. Utilizing the principle and differential characteristics of the dynamic phasor method, the capacitor voltage u of the TCSC is used as an example. C and the inductor current i of the TCR branch L The dynamic phasor model of the controllable series compensation is obtained by modeling it as a state variable; where TCSC is the controllable series compensation device and TCR is the thyristor controllable reactor. Step 2: Design a linear active disturbance rejection (TCSC) controller: Apply the principle of linear active disturbance rejection control to the dynamic phasor model of controllable series compensation to change the series compensation degree. Using the power on the transmission line as the input, design the linear extended state observer and the linear state error feedback law of the linear active disturbance rejection (TCSC) controller to control the series compensation degree of controllable series compensation. Step 3: In the doubly fed wind farm grid-connected system, load fluctuations and short-circuit faults are set for the system, and the TCSC based on the linear active disturbance rejection control strategy obtained in Step 2 is used to suppress the oscillations.

2. The controllable series-complementary subsynchronous oscillation suppression method based on linear active disturbance rejection control strategy according to claim 1, characterized in that, In step 1, the dynamic phasor method is used to mathematically model the controllable series complement, as detailed below: The primary circuit of the TCSC consists of a fixed capacitor C connected in parallel with the TCR branch, and the reactance L in the TCR is connected in series with an anti-parallel thyristor; the current flowing through the TCSC is i. l The current flowing through the TCR branch is i L The voltage across capacitor C is u. C ; Mathematical modeling of controllable series complement using the dynamic phasor method includes the following three sub-steps: Step 11, using capacitor voltage u c and the inductor current i of the TCR branch L As state variables, they determine the state equations; Step 12: Based on the differential characteristics of dynamic phasors, the TCSC state equation in dynamic phasor form is obtained for the state equation, and the order of the TCSC state equation under dynamic phasors is reduced. Step 13: Decompose the phasors in the reduced-order TCSC state equation into real and imaginary parts to obtain a controllable cascaded complement dynamic phasor model.

3. The controllable series-complementary subsynchronous oscillation suppression method based on a linear active disturbance rejection control strategy according to claim 2, characterized in that, Step 11 specifically involves: With capacitor voltage u c and the inductor current i of the TCR branch L The state equation, with the state variable as the state, is written as: Where q is the state function of the thyristor. If the thyristor is on, q = 1; if it is off, q = 0.

4. The controllable series-complementary subsynchronous oscillation suppression method based on a linear active disturbance rejection control strategy according to claim 3, characterized in that, Step 12 specifically involves: Applying the differential properties of dynamic phasors to the state equations, we obtain the TCSC state equations expressed in dynamic phasor form: Among them, U c1 and I L1 These represent the fundamental frequency dynamic phasors of the capacitor voltage and the inductor current in the TCR branch, respectively; I l ω and ω represent the current flowing into the TCSC and the corresponding current frequency, respectively; Due to U c1 Compared to I L1 The dynamic process is long, meaning it takes a relatively long time to reach a quasi-steady state. L1 Slow, so I L1 The dynamic process is regarded as Therefore: Among them, L eff (σ) is the equivalent inductance of the thyristor in the TCR branch when the conduction angle is σ; The order of the state equations under dynamic phasors is reduced as shown in the following equation: Among them, C eff (σ) is the equivalent capacitance of TCSC.

5. The controllable series-complementary subsynchronous oscillation suppression method based on a linear active disturbance rejection control strategy according to claim 4, characterized in that, Step 13 specifically involves: The phasors in the reduced-order state equation are decomposed into real and imaginary parts, i.e., U c =U cR +jU cI I l =I lR +jI lI The controllable series complement dynamic phasor model is obtained as follows: Express the capacitance in terms of reactance, and write the above equation as: in, 6. The controllable series-complementary subsynchronous oscillation suppression method based on a linear active disturbance rejection control strategy according to claim 4, characterized in that, In step 2, the control quantity u of the linear active disturbance rejection TCSC controller is X. Ceff The controller consists of three parts: a tracking differentiator TD, a linear extended state observer LESO, and a linear state error feedback control law LSEF. The steps are as follows: Step 21: The controller input is the active power P flowing through the line where the TCSC is located. TCSC Eliminating the tracking differentiator stage, let the given value Step 22: Utilize the system output P TCSC The system tracks the state information of the controlled object's input u and estimates the total disturbance of the system; the active power of the line where the TCSC is located is fed back to LESO for state observation. The observer control equation is as follows: In the formula, the observer's output signal z1 tracks the command signal, z2 tracks the derivative of the command signal, z3 is the LESO estimate of the total disturbance caused by the subsynchronous disturbance and the external disturbance; β1, β2, and β3 are linear parameters, and b0 is a given non-zero constant. Step 23: In the LSEF stage, the active power setpoint of the line where the TCSC is located is subtracted from z1 and then input together with z2 into the LSEF to obtain the output u0; then, the feedback control quantity u0 is compensated according to the total disturbance estimated by LESO to obtain the compensated control quantity u, which suppresses the subsynchronous oscillation of the system. The control of LSEF is as follows: In the formula, v1 is the input signal, e1 and e2 are the error and the differential of the error, respectively; k p k d1 The gain coefficient of the PD circuit. This is the given value for the input power.

7. The controllable series-complementary subsynchronous oscillation suppression method based on a linear active disturbance rejection control strategy according to claim 4, characterized in that, Step 3 is as follows: In a doubly fed wind farm grid-connected system, load fluctuations and short-circuit faults are set for the system. The TCSC based on the linear active disturbance rejection control strategy obtained in step 2 is used. The active power on the TCSC line is used as the controller input and the output is the equivalent capacitive reactance of the TCSC. The change of the equivalent capacitive reactance is achieved by changing the magnitude of the injected current at the two nodes of the TCSC, and finally the oscillation is suppressed.

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