A control method for suppressing power system oscillation based on energy storage VSG

Abstract

The present invention belongs to the field of power system stability and control, and relates to a control method for suppressing power system oscillations based on energy storage VSG. The steps are: detecting the difference between the virtual angular frequency of the energy storage VSG system and the reference angular frequency of the power grid, and obtaining a damping power signal through an additional damping controller based on bandpass filtering; designing the bandpass filter parameters according to the low-frequency oscillation characteristics of the new power system; introducing the damping power signal output by the additional damping controller into the active control loop of the energy storage VSG system, and constructing a model of the energy storage VSG system connected to a single-machine infinite system; based on linearization analysis, deriving the damping torque provided by the energy storage VSG system for the single-machine infinite system; and using the damping torque method to analyze the main parameters of the additional damping controller. The present invention constructs an additional damping control based on a bandpass filter according to the characteristics of low-frequency oscillations, increases the damping during the low-frequency oscillation process, and thus suppresses the low-frequency oscillations of the power system.

Description

Technical Field

[0001] The present invention belongs to the field of power system stability and control, and specifically relates to a control method for suppressing power system oscillation based on energy storage VSG. Background Art

[0002] As the global environment and climate deteriorate rapidly, countries around the world are actively promoting the transformation of their energy systems toward low-carbon, clean, and sustainable ones. The use of clean and renewable energy sources such as wind power and photovoltaic power generation has become an effective way to address energy shortages and environmental issues, and has been vigorously developed by countries around the world. However, new energy sources such as wind power and photovoltaic power generation are characterized by intermittency, randomness, and volatility. By connecting them to the grid with the help of power electronic equipment, new power systems exhibit characteristics such as low inertia and weak damping. Low-frequency oscillation (LFOS) is the relative swing between the rotor of a generator and the rotors of other units in a power system that lose synchronization after a disturbance. This swing, reflected in the power transmission of transmission lines, is generally considered to be the result of a lack of damping in the system. In new power systems, LFOS is a more severe problem.

[0003] In the classic virtual synchronous generator control model, the frequency modulation coefficient is equivalent to virtual damping, which cannot provide sufficient damping. This can result in negative damping for a single-machine infinite system, which can reduce power system stability. Therefore, an additional damping control is implemented in the active power control loop of the energy storage VSG system to suppress low-frequency oscillations. However, the control parameters affect the additional damping controller's ability to suppress oscillations. Summary of the Invention

[0004] To address the shortcomings of existing VSG technology, this invention provides a control method for suppressing power system oscillations based on VSGs. Its purpose is to improve the transient damping of the VSG system, enabling it to provide positive damping for the power system. This improves power system stability and suppresses low-frequency oscillations.

[0005] The technical solution adopted by the present invention to achieve the above-mentioned purpose is:

[0006] A control method for suppressing power system oscillation based on energy storage VSG includes the following steps:

[0007] Step 1. Detect the virtual angular frequency of the energy storage VSG system and the reference angular frequency of the grid, and make the difference between them to form the input signal of the additional damping controller. The damping power output signal is obtained through the additional damping controller based on bandpass filtering.

[0008] Step 2. Design the bandpass filter parameters according to the low-frequency oscillation characteristics of the power system.

[0009] Step 3. Introduce the damping power signal output by the additional damping controller into the active power control loop of the energy storage VSG system to build a single-machine infinite system model of the energy storage VSG system.

[0010] Step 4. Based on linearization analysis, a small signal model of a single-machine infinite system connected to the energy storage VSG system is constructed, and a Phillips-Heffron model is obtained in which the energy storage VSG system with an additional damping controller provides electromagnetic torque for the single-machine infinite system. The damping torque provided by the energy storage VSG system for the single-machine infinite system is further derived.

[0011] Step 5. Use the damping torque method to analyze and design the main parameters of the additional damping controller to ensure that the energy storage VSG containing the additional damping controller provides positive damping torque to the system, so that the additional damping controller can effectively suppress low-frequency oscillations.

[0012] Furthermore, in step 1, in the additional damping controller, the relationship between the output damping power signal and the input angular frequency is as follows:

[0013]

[0014] Where H0 is the filter gain, defined as H0 = H / Q, H is the relative passband gain; Q is the quality factor, representing the selectivity of the filter; s is the complex variable used for Laplace transform. d K is the damping power signal output by the additional damping controller. d is the gain coefficient of the additional damping controller.

[0015] Bandpass filter ω n is the center frequency of the bandpass filter, at which the phase lag angle of the signal passing through the bandpass filter is zero; ω v is the virtual rotor angular frequency of the energy storage VSG system, and ω0 is the grid reference angular frequency.

[0016] Furthermore, in step 2, the bandpass filter parameters include the center oscillation frequency and the quality factor:

[0017] The frequency range of low-frequency oscillation in the power system is 0.1Hz-2.5Hz, so the center frequency ω n The selection range is 0.1Hz-2.5Hz.

[0018] The quality factor Q is expressed as follows:

[0019]

[0020] Among them, f1 is the lower cutoff frequency, f2 is the upper cutoff frequency, f nis the center frequency. Oscillating signals below the lower cutoff frequency and above the upper cutoff frequency are filtered out by the bandpass filter. Therefore, the quality factor Q is selected in the range of (0.05-1).

[0021] Furthermore, in step 3, the energy storage VSG system is connected to a single-machine infinite system model including a mathematical model of the energy storage VSG system, a mathematical model of the synchronous generator, and an output power expression.

[0022] The mathematical model of the energy storage VSG system with additional damping controller is as follows:

[0023]

[0024] Where, t is time; P ref P is the output active power given value of the energy storage VSG system, v The active electromagnetic power output by the energy storage VSG system, δ v is the output power angle of the energy storage VSG system, ω v is the virtual rotor angular frequency of the energy storage VSG system, ω0 is the grid reference angular frequency, J v and D v are the virtual moment of inertia and virtual damping coefficient of the energy storage VSG system, K p is the active primary frequency regulation droop coefficient of the energy storage VSG system.

[0025] The mathematical model of the synchronous generator is as follows:

[0026]

[0027] Where, P mt is the mechanical power of the synchronous generator, P t is the output active power of the synchronous generator, δ t is the synchronous generator power angle, ω t is the synchronous generator rotor angular frequency, ω0 is the grid reference angular frequency J, D t are the moment of inertia and damping coefficient of the synchronous generator.

[0028] The output active power expression of the synchronous generator and energy storage VSG system is as follows:

[0029]

[0030] Where U B is the grid connection point voltage; θ B is the phase angle of the grid connection point; X ij (i, j = t, v, B) is the impedance from node i to node j in the circuit. U t 、U v is the terminal voltage of the synchronous generator and energy storage VSG system.

[0031] Furthermore, in step 4, the energy storage VSG system without the additional damping controller is connected to the single-machine infinite system model obtained in step 3 and linearized at the steady-state operating point. The small signal model of the single-machine infinite system connected to the energy storage VSG system is as follows:

[0032]

[0033] The small signal models of the input and output of the additional damping controller are as follows:

[0034]

[0035] Where s is the complex variable used for Laplace transform.

[0036] The electromagnetic torque provided by the energy storage VSG system for a single-machine infinite system is as follows, namely the Phillips-Heffron model:

[0037]

[0038] Where ΔT is the electromagnetic torque provided by the energy storage VSG system without additional damping controller to the synchronous generator, T d Δω t It is a torque proportional to the rotor angular velocity, which reflects the obstruction effect on the angular displacement of the rotor motion and plays a role in damping the rotor motion. s Δδ t It is the torque that is proportional to the angular displacement of the rotor motion and determines the synchronization performance of the synchronous generator.

[0039] Among them, K2, K3, and K4 are related to the parameters of the energy storage VSG system connected to the single-machine infinite system, and the expressions are as follows:

[0040]

[0041]

[0042]

[0043] The electromagnetic torque provided by the additional damping controller for the single-machine infinite system is as follows:

[0044]

[0045] Where, ΔT p is the electromagnetic torque provided by the additional damping controller to the synchronous generator, T pd Δω tIt is a torque proportional to the rotor angular velocity, which reflects the obstruction effect on the angular displacement of the rotor motion and plays a role in damping the rotor motion. ps Δδ t It is the torque that is proportional to the angular displacement of the rotor motion and determines the synchronization performance of the synchronous generator.

[0046] The damping torque T provided by the energy storage VSG system with additional damping controller for the single-machine infinite system is as follows:

[0047] T=T d +T pd

[0048] Where, T d is the damping torque provided by the energy storage VSG system without additional damping controller to the synchronous generator, T pd It is the damping torque provided by the additional damping controller to the synchronous generator.

[0049] Among them, T d With T pd The expression of is derived from the small signal model as follows:

[0050]

[0051]

[0052] Furthermore, in step 5, the energy storage VSG system with the additional damping controller is set to provide positive damping torque for the synchronous generator, that is, T d +T pd Greater than zero. Gives the gain coefficient K d The lower limit of the value is:

[0053]

[0054] The present invention has the following beneficial effects and advantages.

[0055] The present invention uses the virtual rotor angular frequency deviation of the energy storage VSG system as the input signal, outputs the damping power signal through the gain link and the bandpass filter link, and obtains the damping power signal. The damping power signal of the additional damping control is introduced into the active power control link of the energy storage VSG system, and an energy storage VSG system with additional control is constructed. Based on linearization analysis, a small signal model of the energy storage VSG system connected to a single-machine infinite system is constructed. The damping torque provided by the energy storage VSG system for the single-machine infinite system is derived. The main parameters of the additional damping controller are analyzed using the damping torque method, and the goal is to ensure that the energy storage VSG with the additional damping controller provides positive damping to the system, so that the additional damping controller can effectively suppress oscillations. The present invention solves the problem that when the energy storage VSG system is running, the virtual damping is equivalent to the primary frequency modulation coefficient, cannot provide sufficient damping, is difficult to suppress, and even aggravates the system oscillation. To a certain extent, it improves the superiority of the energy storage VSG system after adding the additional damping controller.

[0056] The present invention addresses the problem of insufficient virtual damping in the VSG energy storage system. By using a bandpass filter to construct an additional damping control structure for the negative damping torque of the system, the structure is introduced into the active power control loop of the VSG energy storage system, solving the problem that the VSG energy storage system cannot effectively suppress oscillations.

[0057] Aiming at the low-frequency oscillation phenomenon of the power system to which the energy storage VSG system is connected, the present invention adopts a bandpass filtering method and a damping torque method, with the goal of providing a better damping torque for the oscillation signal within the low-frequency oscillation frequency range. An additional damping control is designed so that the additional damping controller provides a positive damping torque during the low-frequency oscillation process of the energy storage VSG system, thereby achieving the goal of suppressing system oscillation. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 This is a block diagram of the active control link of the energy storage VSG with the additional damping controller connected according to an embodiment of the present invention;

[0059] Figure 2 Schematic diagram of a Phillips-Heffron model in which an energy storage VSG system including an additional damping controller according to an embodiment of the present invention provides damping torque for a single-machine infinite system;

[0060] Figure 3 When the VSG main circuit remains consistent, a comparison curve of the output active power of the synchronous generator is shown using the traditional energy storage VSG control and the energy storage VSG control including the additional damping control of the present invention. DETAILED DESCRIPTION

[0061] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0062] The present invention provides a control method for suppressing power system oscillation based on energy storage VSG, comprising the following steps:

[0063] Step 1: Detect the virtual angular frequency of the energy storage VSG system and the reference angular frequency of the grid, and make a difference between the two to form the input signal of the additional damping controller. The damping power output signal is obtained through the additional damping controller based on bandpass filtering.

[0064] The virtual angular frequency of the energy storage VSG system is detected and subtracted from the grid reference angular frequency. The damped power output signal is obtained through an additional damping controller based on a bandpass filter. The following expression exists.

[0065]

[0066] Where H0 is the filter gain, and H0 = H / Q is defined, where H is the passband gain and its relative value is set to 10. n P is the center frequency of the bandpass filter. The phase lag angle of the signal passing through the bandpass filter at this frequency is zero. Q is the quality factor, which represents the selectivity of the filter. d K is the damping power signal output by the additional damping controller. d is the gain coefficient of the additional damping controller.

[0067] Step 2: Design the bandpass filter parameters according to the low-frequency oscillation characteristics of the power system.

[0068] According to the low-frequency oscillation characteristics of the power system, the center oscillation frequency of the bandpass filter parameters is designed. The low-frequency oscillation frequency range of the new power system is 0.1Hz-2.5Hz, so the center frequency ω n The selection range is 0.1Hz-2.5Hz.

[0069] According to the low-frequency oscillation characteristics of the power system, the quality factor of the bandpass filter parameters is designed. The expression of the quality factor Q is as follows:

[0070]

[0071] Where f1 is the lower cutoff frequency (0.1Hz), and f2 is the upper cutoff frequency (2.5Hz). n is the center frequency. Oscillating signals below the lower cutoff frequency are filtered out by the bandpass filter. Oscillating signals above the upper cutoff frequency are also filtered out by the bandpass filter. Therefore, the quality factor Q is selected in the range of (0.05-1).

[0072] Step 3: Introduce the damping power signal output by the additional damping controller into the active power control loop of the energy storage VSG system to build a single-machine infinite system model connected to the energy storage VSG system.

[0073] Figure 1 This is a block diagram of the active control link of the energy storage VSG system with the additional damping controller connected in an embodiment of the present invention, which can intuitively show the connection position of the additional damping controller.

[0074] The active power control loop of the energy storage VSG system with additional damping controller is as follows.

[0075]

[0076] Where, P ref P is the output active power given value of the energy storage VSG system, v The active electromagnetic power output by the energy storage VSG system, δ v is the output power angle of the energy storage VSG system, ω v is the virtual rotor angular frequency of the energy storage VSG system, ω0 is the grid reference angular frequency J v 、D v is the virtual moment of inertia and virtual damping coefficient of the energy storage VSG system, K p is the active primary frequency regulation droop coefficient of the energy storage VSG system.

[0077] The mathematical model of the synchronous generator is as follows.

[0078]

[0079] Where P mt is the mechanical power of the synchronous generator, P t is the output active power of the synchronous generator, δ t is the synchronous generator power angle, ω t is the synchronous generator rotor angular frequency, ω0 is the grid reference angular frequency J, D t are the moment of inertia and damping coefficient of the synchronous generator.

[0080] The output active power expression of the synchronous generator and energy storage VSG system is as follows.

[0081]

[0082] Where U B is the grid connection point voltage; θ B is the phase angle of the grid connection point; X ij (i, j = t, v, B) is the impedance from node i to node j in the circuit.

[0083] The small signal model of the energy storage VSG system connected to a single-machine infinite system is as follows.

[0084]

[0085] Where s is the complex variable used for Laplace transform.

[0086] Step 4: Based on linearization analysis, a small-signal model of the VSG energy storage system connected to the single-machine infinite bus system is constructed. The damping torque provided by the VSG energy storage system to the single-machine infinite bus system is derived.

[0087] The electromagnetic torque provided by the energy storage VSG system for the single-machine infinite system is as follows.

[0088]

[0089] Where ΔT is the electromagnetic torque T provided by the energy storage VSG system for the single-machine infinite system d Δω t It is a torque proportional to the rotor angular velocity, which reflects the obstruction effect on the angular displacement of the rotor motion and plays a role in damping the rotor motion. s Δδ t It is the torque that is proportional to the angular displacement of the rotor motion and determines the synchronization performance of the synchronous generator.

[0090] Among them, K2, K3, and K4 are related to the parameters of the energy storage VSG system connected to a single-machine infinite system, and their expressions are as follows.

[0091]

[0092]

[0093]

[0094] The electromagnetic torque provided by the additional damping controller for the single-machine infinite system is as follows.

[0095]

[0096] Where, T pd Δω t It is a torque proportional to the rotor angular velocity, which reflects the obstruction effect on the angular displacement of the rotor motion and plays a role in damping the rotor motion. ps Δδ t It is the torque that is proportional to the angular displacement of the rotor motion and determines the synchronization performance of the synchronous generator.

[0097] Figure 2 It is a schematic diagram of a Phillips-Heffron model in which an energy storage VSG system with an additional damping controller connected thereto according to an embodiment of the present invention provides damping torque for a single-machine infinite system.

[0098] Step 5: Use the damping torque method to analyze the main parameters of the additional damping controller, and ensure that the energy storage VSG containing the additional damping controller provides positive damping to the system, so that the additional damping controller can effectively suppress oscillation.

[0099] The damping torque provided by the energy storage VSG system with additional damping controller for the single-machine infinite system is as follows.

[0100] T=T d +T pd

[0101] Where, T d is the damping torque provided by the energy storage VSG system without additional damping controller to the synchronous generator, T pd is the damping torque provided by the additional damping controller to the synchronous generator

[0102] Among them, T d With T pd The expression of is derived from the small signal model as follows:

[0103]

[0104]

[0105] The energy storage VSG system with additional damping controller provides positive damping torque for the synchronous generator, that is, T d +T pd Greater than zero. Gives the gain coefficient K d The lower limit of the value is:

[0106]

[0107] Figure 3 The figure shows a comparison curve of the output active power of the synchronous generator when the traditional energy storage VSG control and the energy storage VSG control including the additional damping control of the present invention are adopted when the VSG main circuit remains consistent.

[0108] Figure 3 It is obtained by designing simulation experiments based on MATLAB / Simulink platform. In the simulation experiments, the synchronous generator output active power is set to 75kW and the energy storage VSG system output active power is set to 100kW. v 5.5 kg·m 2 , D v 3000,K p is 7000, J is 7.5 kg·m 2 , D t It is 140,000.

[0109] Depend on Figure 3It can be seen that when using traditional energy storage VSG control, the oscillation suppression process of the synchronous generator is slow. When using energy storage VSG control with the additional damping control of the present invention, the oscillation can be suppressed in time, so that the oscillation amplitude of the synchronous generator is reduced and the convergence time is shortened.

[0110] The simulation experiment verifies that the additional damping control of the present invention can effectively suppress the low-frequency oscillation of the power system, and provides certain theoretical support and technical guarantee for the grid-connected operation control of the energy storage VSG system.

Claims

1. A control method for suppressing power system oscillation based on energy storage VSG, characterized in that: The following steps are involved: Step 1. Detect the virtual angular frequency of the energy storage VSG system and the grid reference angular frequency, and take the difference between the two to form the input signal of the additional damping controller. The damping power output signal is obtained through the additional damping controller based on bandpass filtering; Step 2. Design the bandpass filter parameters based on the low-frequency oscillation characteristics of the power system; Step 3. Introduce the damping power signal output by the additional damping controller into the active power control loop of the energy storage VSG system to build a single-machine infinite system model for the energy storage VSG system. Step 4. Based on linearization analysis, a small-signal model of a single-machine infinite system connected to the energy storage VSG system is constructed. The Phillips-Heffron model of the electromagnetic torque provided by the energy storage VSG system with the additional damping controller for the single-machine infinite system is derived. The damping torque provided by the energy storage VSG system for the single-machine infinite system is further derived. Step 5. Use the damping torque method to analyze and design the main parameters of the additional damping controller to ensure that the energy storage VSG with the additional damping controller provides positive damping torque to the system, so that the additional damping controller can effectively suppress low-frequency oscillations; Furthermore, in step 1, in the additional damping controller, the relationship between the output damping power signal and the input angular frequency is as follows: Where H0 is the filter gain, defined as H0 = H / Q, where H is the relative passband gain; Q is the quality factor, representing the selectivity of the filter; s is the complex variable used for Laplace transform; P d K is the damping power signal output by the additional damping controller. d is the gain coefficient of the additional damping controller; Bandpass filter ω n is the center frequency of the bandpass filter, at which the phase lag angle of the signal passing through the bandpass filter is zero; ω v is the virtual rotor angular frequency of the energy storage VSG system, ω0 is the grid reference angular frequency; Furthermore, in step 2, the bandpass filter parameters include the center oscillation frequency and the quality factor: The frequency range of low-frequency oscillation in the power system is 0.1Hz-2.5Hz, so the center frequency ω n The selection range is 0.1Hz-2.5Hz; The quality factor Q is expressed as follows: Among them, f1 is the lower cutoff frequency, f2 is the upper cutoff frequency, f n is the center frequency; oscillation signals below the lower cutoff frequency and above the upper cutoff frequency will be filtered out by the bandpass filter; therefore, the selection range of the quality factor Q is (0.05-1); Furthermore, in step 3, the energy storage VSG system is connected to the single-machine infinite system model including the energy storage VSG system mathematical model, the synchronous generator mathematical model and the output power expression; The mathematical model of the energy storage VSG system with additional damping controller is as follows: Where, t is time; P ref P is the output active power given value of the energy storage VSG system, v The active electromagnetic power output by the energy storage VSG system, δ v is the output power angle of the energy storage VSG system, ω v is the virtual rotor angular frequency of the energy storage VSG system, ω0 is the grid reference angular frequency, J v and D v are the virtual moment of inertia and virtual damping coefficient of the energy storage VSG system, K p is the active primary frequency regulation droop coefficient of the energy storage VSG system; The mathematical model of the synchronous generator is as follows: Where, P mt is the mechanical power of the synchronous generator, P t is the output active power of the synchronous generator, δ t is the synchronous generator power angle, ω t is the synchronous generator rotor angular frequency, ω0 is the grid reference angular frequency J, D t is the moment of inertia and damping coefficient of the synchronous generator; The output active power expression of the synchronous generator and energy storage VSG system is as follows: Where U B is the grid connection point voltage; θ B is the phase angle of the grid connection point; X ij (i, j = t, v, B) is the impedance from node i to node j in the circuit; U t 、U v is the terminal voltage of synchronous generator and energy storage VSG system; Furthermore, in step 4, the energy storage VSG system without the additional damping controller is connected to the single-machine infinite system model obtained in step 3 and linearized at the steady-state operating point. The small signal model of the single-machine infinite system connected to the energy storage VSG system is as follows: The small signal models of the input and output of the additional damping controller are as follows: Where s is the complex variable used for Laplace transform; The electromagnetic torque provided by the energy storage VSG system for a single-machine infinite system is as follows, namely the Phillips-Heffron model: Where ΔT is the electromagnetic torque provided by the energy storage VSG system without additional damping controller to the synchronous generator, T d Δω t It is the torque proportional to the rotor angular velocity; Among them, K2, K3, and K4 are related to the parameters of the energy storage VSG system connected to the single-machine infinite system, and the expressions are as follows: The electromagnetic torque provided by the additional damping controller for the single-machine infinite system is as follows: Where, ΔT p is the electromagnetic torque provided by the additional damping controller to the synchronous generator, T pd Δω t It is the torque proportional to the rotor angular velocity; The damping torque T provided by the energy storage VSG system with additional damping controller for the single-machine infinite system is as follows: T=T d +T pd Where, T d is the damping torque provided by the energy storage VSG system without additional damping controller to the synchronous generator, T pd is the damping torque provided by the additional damping controller to the synchronous generator; Among them, T d With T pd The expression of is derived from the small signal model as follows: Furthermore, in step 5, the energy storage VSG system with the additional damping controller is set to provide positive damping torque for the synchronous generator, that is, T d +T pd greater than zero; Gain coefficient K d The lower limit of the value is:

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