A low-frequency oscillation damping method based on rotor flux control virtual synchronous control

Abstract

A low-frequency oscillation damping method based on rotor flux control type virtual synchronous control belongs to the field of power electronics technology and includes the following steps: Step 1, decomposing the grid-connected doubly-fed wind power system into an equivalent mechanical subsystem and an equivalent electrical subsystem, deriving the damping torque model of the equivalent subsystem, and calculating the system net damping at the torsional vibration frequency point. Step 2, adding an additional damping control branch to the rotor flux inner loop of the rotor flux control type VSG strategy, and calculating the control parameters of the low-frequency oscillation damping strategy based on the system net damping at the torsional vibration frequency point. The present invention is applicable to rotor flux control type grid-connected doubly-fed wind turbine generator sets, and only optimizes the system low-frequency damping characteristics at the torsional vibration frequency point, without affecting the system damping characteristics in other frequency bands. It can effectively improve the system net damping at the torsional vibration frequency point, thereby suppressing the low-frequency oscillation instability of the doubly-fed wind turbine in a weak power grid scenario and improving the small disturbance stability of the system.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and in particular relates to a low-frequency oscillation damping method based on rotor flux control type virtual synchronous control. Background Art

[0002] As global wind power capacity continues to climb, modern power systems are increasingly characterized by weak damping, low inertia, and poor interference immunity. Due to the inverse distribution of wind resources and power load centers in my country, wind turbines are often located at the periphery of the power system. Consequently, wind turbines are often presented with a low short circuit ratio (SCR) grid configuration.

[0003] To address the poor adaptability of traditional grid-connected doubly-fed induction generators (DFIGs) to weak grid conditions, grid-connected control technologies, such as virtual synchronous generator control (VSG), have been gradually applied to DFIGs. By embedding the VSG control strategy into the rotor-side converter (RSC) of the DFIG, simulating the synchronous generator's rotor motion equations, the DFIG can be made to behave like a voltage source, thereby improving the grid-connected stability of the DFIG system. However, in weak grid scenarios, the interaction between the grid-connected wind turbine control, the grid, and the induction generator shaft system can introduce negative electrical damping. In extreme cases, this can cause low-frequency oscillations in the DFIG, hindering stable system operation. Therefore, optimizing the low-frequency damping characteristics of grid-connected DFIGs and suppressing low-frequency oscillation instability in weak grid scenarios remains a pressing challenge. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a low-frequency oscillation damping method based on rotor flux control type virtual synchronous control. Based on the idea of compensating electrical negative damping, an additional damping control branch is introduced into the rotor flux inner loop of the flux control type VSG strategy, and the control parameters are designed according to the system net damping at the torsional vibration frequency point, thereby improving the low-frequency damping characteristics of the grid-type doubly fed wind turbine and improving the low-frequency small disturbance stability of the system.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A low-frequency oscillation damping method based on rotor flux control type virtual synchronous control, the steps are as follows:

[0007] Step 1: Decompose the grid-connected doubly-fed wind power system into an equivalent mechanical subsystem and an equivalent electrical subsystem, derive the damping torque model of the equivalent subsystem, and calculate the net damping of the system at the torsional vibration frequency point;

[0008] Step 2: Add an additional damping control branch to the rotor flux inner loop of the rotor flux control type VSG strategy, and calculate the control parameters of the low-frequency oscillation damping strategy based on the system net damping at the torsional vibration frequency point.

[0009] Preferably, the sub-steps of step 1 are:

[0010] Step 1.1: Decompose the grid-connected doubly-fed wind turbine system into an equivalent mechanical subsystem and an equivalent electrical subsystem. The equivalent mechanical subsystem consists of the VSG active synchronization link, and the equivalent electrical subsystem consists of the VSG reactive excitation link, the grid-side converter control link, the doubly-fed induction machine, and the dynamic equations of the weak grid.

[0011] Step 1.2: Convert the stator active disturbance As input, the virtual synchronization phase angle As output, the damping torque model of the equivalent mechanical subsystem is constructed, which is expressed as:

[0012] (1);

[0013] In formula (1), d / d t is the differential calculation term, is the equivalent mechanical subsystem state variable, is the virtual synchronization angular frequency, is the virtual synchronization phase angle; A m is the small signal state space matrix; B m and C m are the input and output matrices respectively;

[0014] Step 1.3: Set the virtual synchronization phase angle As input, the stator active disturbance As output, the damping torque model of the equivalent electrical subsystem is constructed, which is expressed as:

[0015] (2);

[0016] In formula (2), is the equivalent electrical subsystem state variable, 、 and are the output small disturbances of the integral links of the reactive PI controller and the rotor flux PI controller respectively; is the small disturbance of DC bus voltage; 、 and They are the small signal state variable matrices of the induction motor shaft transmission system, grid-side converter vector control system and phase-locked loop control system of the doubly-fed wind turbine; A e is the small signal state space matrix; B e and C e are the input and output matrices respectively;

[0017] Step 1.4: Calculate the complex torque coefficients of the equivalent mechanical subsystem and the equivalent electrical subsystem and , whose expression is:

[0018] (3);

[0019] (4);

[0020] In formula (4), K m and K e are the synchronous torque coefficients of the equivalent mechanical subsystem and the equivalent electrical subsystem respectively; D m and D e are the damping coefficients of the equivalent mechanical subsystem and the equivalent electrical subsystem, respectively;

[0021] Step 1.5: Calculate the system torsional vibration frequency point based on the complex torque coefficient of the equivalent subsystem , and calculate the corresponding system net damping D sys ; Among them, at the system torsional vibration frequency point Satisfaction:

[0022] (5);

[0023] The corresponding system net damping is:

[0024] (6);

[0025] Preferably, step 2 includes the following sub-steps:

[0026] Step 2.1: Add an additional damping control branch to the rotor flux inner loop of the rotor flux control VSG strategy. The corresponding rotor flux command value can be expressed as:

[0027] (7);

[0028] (8);

[0029] In formula (7) and formula (8), and The rotor flux is dq The command value of the axis component; is the additional damping signal; is the reactive outer loop transfer function; is the small disturbance of the stator reactive power of the doubly-fed wind turbine; K g Control open-loop gain for added damping; is the reset link transfer function, T Its time constant is mainly used for isolating DC components and low-pass filtering; It is the n-order lead-lag phase correction link, T 1 and T 2 are the leading and lagging time constants respectively;

[0030] Step 2.2: As input, the stator active small disturbance As output, the corresponding transfer function G Ps ( s )for:

[0031] (9);

[0032] (10);

[0033] In formula (9) and formula (10), is the state variable of the doubly-fed wind power grid-connected system; A g is the small signal state space matrix; B g and C g are the input and output matrices respectively;

[0034] Step 2.3: Calculate the torsional vibration frequency point Lower transfer function G Ps ( s ) is expressed as follows:

[0035] (11);

[0036] A single leading link can correct up to 30°-40°. G Ps ( s ) introduces a phase shift Determine the order n of the phase compensation link, then the compensation angle of a single leading link is , the calculation method of low-frequency oscillation damping control parameters is:

[0037] (12);

[0038] (13);

[0039] (14);

[0040] In formula (13), D g To compensate for the electrical positive damping.

[0041] A computer storage medium executes program instructions for a low-frequency oscillation damping method based on rotor flux control type virtual synchronous control.

[0042] An electronic device for realizing low-frequency oscillation damping includes a computer storage medium, wherein the program instructions executed by the computer storage medium are a low-frequency oscillation damping method based on rotor flux control type virtual synchronous control.

[0043] A system for realizing low-frequency oscillation damping comprises a computer storage medium and an electronic device. The computer storage medium adopts a low-frequency oscillation damping method based on rotor flux control type virtual synchronous control.

[0044] The present invention can achieve the following beneficial effects:

[0045] The present invention is applicable to rotor flux-controlled grid-connected doubly-fed wind turbines, and only optimizes the system's low-frequency damping characteristics at the torsional vibration frequency point, without affecting the system's damping characteristics in other frequency bands. It can effectively improve the system's net damping at the torsional vibration frequency point, thereby suppressing the low-frequency oscillation instability of the doubly-fed wind turbine in a weak power grid scenario and improving the system's small-disturbance stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0047] Figure 1 This is the main circuit topology of the system of the present invention;

[0048] Figure 2 This is a control block diagram of the grid-type doubly-fed wind turbine RSC in the system of the present invention;

[0049] Figure 3 This is a control block diagram of the low-frequency oscillation damping strategy of the present invention;

[0050] Figure 4The equivalent mathematical model of the grid-connected doubly-fed wind power system of the present invention;

[0051] Figure 5 The low-frequency damping characteristics of the system before and after the low-frequency oscillation damping strategy is introduced into the present invention;

[0052] Figure 6 This is a simulation result diagram of the double-fed wind power grid-connected system with small disturbance in weak power grid according to the present invention. DETAILED DESCRIPTION

[0053] The preferred solution is Figures 1 to 6 As shown in the figure, a low-frequency oscillation damping method based on rotor flux control type virtual synchronous control is proposed. The main circuit topology of the doubly fed wind power grid-connected system is shown in the figure. Figure 1 As shown; RSC adopts rotor flux control type VSG strategy, and its control block diagram is as follows Figure 2 As shown; the low-frequency oscillation damping strategy proposed in the present invention is as follows Figure 3 The present invention effectively improves the low-frequency damping characteristics of the grid-type doubly-fed wind turbine, reduces the risk of low-frequency oscillation instability of the grid-type doubly-fed wind turbine in weak power grid scenarios, and improves the low-frequency small disturbance stability of the system.

[0054] In a weak power grid scenario, a grid-type doubly-fed wind turbine may exhibit negative damping characteristics due to the interaction between the induction motor shaft transmission system, the converter control system, and the weak power grid, ultimately causing the system to generate low-frequency power oscillations, seriously endangering the safe and stable operation of the system. To address this problem, the present invention proposes a low-frequency oscillation damping strategy based on rotor flux control type virtual synchronous control. This control strategy is based on the idea of compensating for electrical negative damping, introduces an additional damping control branch into the rotor flux inner loop of the flux control type VSG strategy, and designs control parameters based on the system net damping at the torsional vibration frequency point, thereby improving the low-frequency damping characteristics of the grid-type doubly-fed wind turbine and improving the low-frequency small disturbance stability of the system.

[0055] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings.

[0056] The first step is to decompose the grid-connected doubly-fed wind power system into an equivalent mechanical subsystem and an equivalent electrical subsystem, derive the damping torque model of the equivalent subsystem, and calculate the net damping of the system at the torsional vibration frequency point.

[0057] Step 1.1: Decompose the grid-connected doubly-fed wind power system into Figure 4 The equivalent mechanical subsystem and equivalent electrical subsystem are shown in Figure 1. The equivalent mechanical subsystem consists of the VSG active synchronization link, and the equivalent electrical subsystem consists of other converter control links, the doubly-fed induction machine, and the dynamic equations of the weak grid.

[0058] The detailed model parameters of the system are shown in Table 1, where: P nom and P mec are the rated powers of the system induction motor and wind turbine respectively, V nom is the system rated voltage, V dcnom is the rated DC capacitor voltage, H WT 、 K sh and D mutual Wind turbine shafting parameters, H and F is the induction motor shaft parameter, p n is the number of pole pairs of the induction motor, L s 、 L r and R s 、 R r are the inductance and resistance of the stator and rotor windings of the induction motor respectively, L m is the leakage inductance of the induction motor, D p and J eq It is the control parameter of VSG active synchronization link. K pQ 、 K i Q and K pF 、 K iF is the control parameter of VSG reactive excitation link, K p1 、 K i1 、 K p2 、 K i2 and K p3 、 K i3 are the grid-side converter control parameters.

[0059] Table 1 Simulation parameters of flux-link controlled grid-connected doubly fed wind turbine

[0060]

[0061] Step 1.2: Convert the stator active disturbance As input, the virtual synchronization phase angle As output, the damping torque model of the equivalent mechanical subsystem is constructed, which is expressed as:

[0062] (1);

[0063] (1) In the formula, is the equivalent mechanical subsystem state variable, is the virtual synchronization angular frequency, is the virtual synchronization phase angle; A m is the small signal state space matrix; B m and C m are the input and output matrices respectively.

[0064] Step 1.3: Set the virtual synchronization phase angle As input, the stator active disturbance As output, the damping torque model of the equivalent electrical subsystem is constructed, which is expressed as:

[0065] (2);

[0066] In formula (2), is the equivalent electrical subsystem state variable, 、 and are the output small disturbances of the integral links of the reactive PI controller and the rotor flux PI controller respectively; is the small disturbance of DC bus voltage; 、 and They are the small signal state variable matrices of the induction motor shaft transmission system, grid-side converter vector control system and phase-locked loop control system of the doubly-fed wind turbine; A e is the small signal state space matrix; B e and C e are the input and output matrices respectively.

[0067] Step 1.4: Calculate the complex torque coefficients of the equivalent mechanical subsystem and the equivalent electrical subsystem and , whose expression is:

[0068] (3);

[0069] (4);

[0070] In formula (4), Km and K e are the synchronous torque coefficients of the equivalent mechanical subsystem and the equivalent electrical subsystem respectively; D m and D e are the damping coefficients of the equivalent mechanical subsystem and the equivalent electrical subsystem, respectively.

[0071] Step 1.5: Calculate the system torsional vibration frequency point based on the complex torque coefficient of the equivalent subsystem , and calculate the corresponding system net damping D sys Among them, at the system torsional vibration frequency point Satisfaction:

[0072] (5);

[0073] The corresponding system net damping is:

[0074] (6);

[0075] Step 2: Add an additional damping control branch to the rotor flux inner loop of the rotor flux control type VSG strategy, and calculate the control parameters of the low-frequency oscillation damping strategy based on the system net damping at the torsional vibration frequency point.

[0076] Step 2.1: Add an additional damping control branch to the rotor flux inner loop of the rotor flux control VSG strategy. The corresponding rotor flux command value can be expressed as:

[0077] (7);

[0078] (8);

[0079] In formula (7) and formula (8), and The rotor flux is dq The command value of the axis component; is the additional damping signal; is the reactive outer loop transfer function; is the small disturbance of the stator reactive power of the doubly-fed wind turbine; K g Control open-loop gain for added damping; is the reset link transfer function, T Its time constant is mainly used for isolating DC components and low-pass filtering; It is the n-order lead-lag phase correction link, T 1 and T 2 are the leading and lagging time constants respectively.

[0080] Step 2: As input, the stator active small disturbance As output, the corresponding transfer function G Ps ( s )for:

[0081] (9);

[0082] (10);

[0083] In formula (9) and formula (10), is the state variable of the doubly-fed wind power grid-connected system; A g is the small signal state space matrix; B g and C g are the input and output matrices respectively.

[0084] Step 3: Calculate the torsional vibration frequency point Lower transfer function G Ps ( s ) is expressed as follows:

[0085] (11);

[0086] A single leading link can correct up to 30°-40°. G Ps ( s ) introduces a phase shift Determine the order n of the phase compensation link, then the compensation angle of a single leading link is , the calculation method of low-frequency oscillation damping control parameters is:

[0087] (12);

[0088] (13);

[0089] (14);

[0090] In formula (13), D g To compensate for the electrical positive damping.

[0091] In specific implementation, the system torsional vibration frequency point , the net damping of the system Torsional vibration frequency point The amplitude and phase are 0.61 and , the phase compensation link uses 3 leading links, each link compensates , reset link time constant T =3s, the time constants of the phase compensation link are T 1=0.1358 and T 2=0.0543. Select the desired compensation electrical positive damping D g =0.1, then the additional damping controls the open-loop gain K g =0.047. The low-frequency damping characteristics of the system before and after the introduction of the low-frequency oscillation damping strategy are as follows: Figure 5 As shown in the figure, it can be seen that the low-frequency torsional vibration frequency point is maintained f i =1.854Hz remains unchanged, and the net damping of the system is given by When the value increases to 0.0098, the system stability under small disturbance is significantly improved. Under small disturbance of weak power grid, the simulation results of the grid-connected double-fed wind power system are as follows: Figure 6 As shown in the figure, when the gain coefficient Kg = 0, the additional damping control branch stops running, the system is disturbed by SCR, and the doubly fed wind turbine generates low-frequency power oscillation divergence, and the system becomes unstable. K g = 0.05, the low-frequency oscillation additional damping strategy is put into operation, and the wind turbine active power response curve converges quickly after the system is disturbed, effectively improving the small disturbance stability of the system. K g When the value reaches 0.1, the additional positive damping provided by the additional damping control will increase, and the convergence speed of the wind turbine active power will be accelerated after the system is disturbed.

[0092] A computer storage medium executes program instructions for a low-frequency oscillation damping method based on rotor flux control type virtual synchronous control.

[0093] An electronic device for realizing low-frequency oscillation damping includes a computer storage medium, wherein the program instructions executed by the computer storage medium are a low-frequency oscillation damping method based on rotor flux control type virtual synchronous control.

[0094] A system for realizing low-frequency oscillation damping comprises a computer storage medium and an electronic device. The computer storage medium adopts a low-frequency oscillation damping method based on rotor flux control type virtual synchronous control.

[0095] The above embodiments are merely preferred technical solutions of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention shall be the technical solutions set forth in the claims, including equivalent alternatives to the technical features of the technical solutions set forth in the claims. In other words, equivalent alternatives and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A low-frequency oscillation damping method based on rotor flux control type virtual synchronous control, characterized in that The following steps are involved: The grid-connected doubly-fed wind power system is decomposed into an equivalent mechanical subsystem and an equivalent electrical subsystem, the damping torque model of the equivalent subsystem is derived, and the net damping of the system at the torsional vibration frequency point is calculated. An additional damping control branch is added to the inner loop of the rotor flux control type VSG strategy, and the control parameters of the low-frequency oscillation damping strategy are calculated based on the system net damping at the torsional vibration frequency point. The equivalent mechanical subsystem consists of the VSG active synchronization link; The equivalent electrical subsystem consists of the VSG reactive excitation link, the grid-side converter control link, the doubly-fed induction motor, and the dynamic equations of the weak grid; The construction process of the damping torque model of the derived equivalent subsystem includes: 1) The stator active disturbance As input, the virtual synchronization phase angle As output, the damping torque model of the equivalent mechanical subsystem is constructed, which is expressed as: （1）； In formula (1), d / d t is the differential calculation term, is the equivalent mechanical subsystem state variable, is the virtual synchronization angular frequency, is the virtual synchronization phase angle; A m is the small signal state space matrix; B m and C m are the input and output matrices respectively; 2) Set the virtual synchronization phase angle As input, the stator active disturbance As output, the damping torque model of the equivalent electrical subsystem is constructed, which is expressed as: （2）； In formula (2), is the equivalent electrical subsystem state variable, 、 and are the output small disturbances of the integral links of the reactive PI controller and the rotor flux PI controller respectively; is the small disturbance of DC bus voltage; 、 and They are the small signal state variable matrices of the induction motor shaft transmission system, grid-side converter vector control system and phase-locked loop control system of the doubly-fed wind turbine; A e is the small signal state space matrix; B e and C e are the input and output matrices respectively.

2. The low-frequency oscillation damping method based on rotor flux control type virtual synchronous control according to claim 1, characterized in that: The construction process of the damping torque model of the derived equivalent subsystem further includes: 3) Complex torque coefficients of equivalent mechanical subsystem and equivalent electrical subsystem and The calculation process is as follows, and the expression is: （3）； （4）； In formula (4), K m and K e are the synchronous torque coefficients of the equivalent mechanical subsystem and the equivalent electrical subsystem respectively; D m and D e are the damping coefficients of the equivalent mechanical subsystem and the equivalent electrical subsystem, respectively.

3. The low-frequency oscillation damping method based on rotor flux control type virtual synchronous control according to claim 2, characterized in that: The construction process of the damping torque model of the derived equivalent subsystem further includes: 4) Calculate the system torsional vibration frequency point based on the complex torque coefficient of the equivalent subsystem , and calculate the corresponding system net damping D sys ; Among them, at the system torsional vibration frequency point Satisfaction: （5）； The corresponding system net damping is: （6）。 4. The low-frequency oscillation damping method based on rotor flux control type virtual synchronous control according to claim 3, characterized in that: The process of adding an additional damping control branch to the rotor flux inner loop of the rotor flux control type VSG strategy is as follows: 1) The corresponding rotor flux command value is expressed as: （7）； （8）； In formula (7) and formula (8), and The rotor flux is dq The command value of the axis component; is the additional damping signal; is the reactive outer loop transfer function; is the small disturbance of the stator reactive power of the doubly-fed wind turbine; K g Control open-loop gain for added damping; is the reset link transfer function, T Its time constant is mainly used for isolating DC components and low-pass filtering; It is the n-order lead-lag phase correction link, T 1 and T 2 are the leading and lagging time constants respectively.

5. The low-frequency oscillation damping method based on rotor flux control type virtual synchronous control according to claim 4, characterized in that: The process of calculating the control parameters of the low-frequency oscillation damping strategy based on the system net damping at the torsional vibration frequency point is as follows: Will As input, the stator active small disturbance As output, the corresponding transfer function G Ps ( s )for: （9）； （10）； In formula (9) and formula (10), is the state variable of the doubly-fed wind power grid-connected system; A g is the small signal state space matrix; B g and C g are the input and output matrices respectively; Step 2.3: Calculate the torsional vibration frequency point Lower transfer function G Ps ( s ) is expressed as （11）； The maximum correction of a single leading link is 30°-40°. G Ps ( s ) introduces a phase shift Determine the order n of the phase compensation link, then the compensation angle of a single leading link is , the calculation method of low-frequency oscillation damping control parameters is: （12）； （13）； （14）； In formula (13), D g To compensate for the electrical positive damping.

6. A computer storage medium, characterized in that: The executed program instructions are a low-frequency oscillation damping method based on rotor flux control type virtual synchronous control according to any one of claims 1 to 5.

7. An electronic device for achieving low-frequency oscillation damping, comprising a computer storage medium, characterized in that: The program instructions executed by the computer storage medium are a low-frequency oscillation damping method based on rotor flux control type virtual synchronous control according to any one of claims 1 to 5.

8. A system for achieving low-frequency oscillation damping, comprising a computer storage medium and an electronic device, characterized in that: The computer storage medium adopts a low-frequency oscillation damping method based on rotor flux control type virtual synchronous control according to any one of claims 1 to 5.

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