Droop coefficient and damping coefficient control method and system for energy storage photovoltaic power station

Abstract

The invention relates to a droop coefficient and damping coefficient control method and system for an energy storage photovoltaic power station, and the method comprises the following steps: calculating a corresponding frequency deviation and a corresponding frequency deviation in the operation process of an energy storage photovoltaic system; when the calculated frequency deviation and the frequency deviation are both larger than the corresponding starting threshold values, self-adaptive change regulation and control are carried out on a droop coefficient and a damping coefficient of a virtual synchronous generator of the energy storage photovoltaic system; in the self-adaptive change process of the droop coefficient and the damping coefficient, if the product of the frequency deviation and the frequency deviation is larger than zero, the larger droop coefficient and damping coefficient are adopted; and if the product of the frequency deviation and the frequency deviation is smaller than zero, a smaller droop coefficient and a smaller damping coefficient are adopted. Compared with the prior art, the VSG frequency and active dynamic response performance can be effectively improved, the inertia level of the system is improved, and meanwhile, the output of the energy storage photovoltaic system is smoothed.

Description

Technical Field

[0001] This invention relates to the field of energy storage photovoltaic power station control technology, and in particular to a method and system for controlling the droop coefficient and damping coefficient of energy storage photovoltaic power stations. Background Technology

[0002] In traditional power systems dominated by synchronous generators, the generator rotor provides significant system inertia due to its mass and rotational characteristics. This inertia allows the generator rotor to utilize its kinetic energy to regulate power imbalances within the power system, preventing drastic, instantaneous frequency changes. Solar photovoltaic (PV) power systems, typically coupled with energy storage on the DC side and connected to the grid via an inverter, lack rotating parts and therefore cannot provide inertia. This results in a decrease in overall system inertia. Consequently, when power imbalances occur, the system frequency changes more rapidly. Since primary frequency regulation in power systems relies mainly on the generator's speed governor, in low-inertia systems, the rapid frequency changes prevent the speed governor from responding promptly, reducing grid frequency stability.

[0003] The invention disclosed in CN115133554A presents a comprehensive control method for primary frequency regulation of energy storage based on dual-layer constraints. The method divides the energy storage participation in frequency regulation into two control stages, using the frequency regulation dead zone as a boundary. If the system frequency is outside the frequency regulation dead zone, adaptive VSG control is used. The damping coefficient is subject to dual-layer constraints of energy storage SOC and frequency deviation Δf, and the inertia coefficient is subject to dual-layer constraints of SOC and the rate of change of frequency deviation, thus adaptively adjusting energy storage output to accelerate frequency regulation and prevent energy storage SOC saturation or depletion. If the frequency is within the frequency regulation dead zone, frequency regulation recovery parallel control is used: when the SOC is within a threshold, adaptive frequency regulation control is used; when the SOC exceeds the threshold, adaptive SOC recovery control is used. The frequency regulation recovery parallel control consists of droop control and VSG cascaded, where the droop coefficient is subject to dual-layer constraints of SOC and Δf.

[0004] The above scheme determines the frequency modulation dead zone based on the system frequency. Outside the frequency modulation dead zone, the damping coefficient is constrained by both the energy storage SOC and the frequency deviation Δf. Inside the frequency modulation dead zone, the droop coefficient is constrained by both SOC and Δf. The above scheme relies on the accurate setting of the frequency modulation dead zone and cannot adaptively adjust the damping coefficient and droop coefficient accurately. It can only limit a dynamic range and cannot effectively improve the dynamic response performance of VSG frequency and active power. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method and system for controlling the droop coefficient and damping coefficient of energy storage photovoltaic power plants, so as to effectively improve the dynamic response performance of VSG frequency and active power.

[0006] The objective of this invention can be achieved through the following technical solutions: A method for controlling the droop and damping coefficients of a photovoltaic power station for energy storage includes the following steps: During the operation of the energy storage photovoltaic system, calculate the corresponding frequency deviation and frequency offset; When the calculated frequency deviation and frequency deviation are both greater than the corresponding start-up threshold, the droop coefficient and damping coefficient of the virtual synchronous generator of the energy storage photovoltaic system are adaptively adjusted. During the adaptive change of the droop coefficient and damping coefficient, if the product of the frequency deviations is greater than zero, a larger droop coefficient and damping coefficient are used; if the product of the frequency deviations is less than zero, a smaller droop coefficient and damping coefficient are used.

[0007] Furthermore, the adaptive variation expression of the droop coefficient is as follows: In the formula, The droop coefficient is... Based on the droop coefficient, The first droop coefficient, This is the second droop coefficient. The third droop coefficient, The rate of change of frequency, This represents the frequency deviation.

[0008] Furthermore, the adaptive variation expression of the damping coefficient is as follows: In the formula, The damping coefficient is... Based on the basic damping coefficient, The first damping coefficient, This is the second damping coefficient. The third damping coefficient, The rate of change of frequency, This represents the frequency deviation.

[0009] Furthermore, both the frequency deviation and the frequency deviation are greater than the corresponding start-up threshold, specifically: In the formula, The rate of change of frequency, For frequency deviation, The threshold for the rate of change of frequency is set. This is the threshold for initiating frequency deviation.

[0010] Furthermore, the expression for calculating the rate of change of frequency is as follows: In the formula, The rate of change of frequency, The current system frequency, For time.

[0011] Furthermore, the expression for calculating the frequency deviation is as follows: In the formula, For frequency deviation, The current system frequency, This is the reference frequency.

[0012] Furthermore, the energy storage photovoltaic system includes a photovoltaic power generation unit and a battery energy storage unit, which are connected to the local load or the power grid through a DC-DC converter, an inverter, and an RC filter. The inverter is used to control the voltage and current of the photovoltaic power generation unit; The RC filter is used to filter the port voltage and current of the inverter to obtain the three-phase sinusoidal voltage and current at the output port.

[0013] Furthermore, the method also includes establishing a small-signal model of the virtual synchronous generator in the inverter and photovoltaic power generation unit, obtaining the second-order transfer function expressions of the output power response characteristics and virtual angular velocity response characteristics of the virtual synchronous generator, which are used to simulate and obtain the influence of the droop coefficient and damping coefficient on the dynamic response process of the virtual synchronous generator, and verify the effectiveness of the droop coefficient and damping coefficient.

[0014] Furthermore, the second-order transfer function expression of the output power response characteristic of the virtual synchronous generator is as follows: In the formula, This represents the change in output power of the virtual synchronous generator. This represents the change in the synchronous angular velocity of the power grid. The inertial time constant, The droop coefficient is... The damping coefficient is... The rated angular velocity, Synchronous power; The second-order transfer function expression of the virtual angular velocity response characteristic of the virtual synchronous generator is as follows: In the formula, The virtual angular velocity is for the virtual synchronous generator.

[0015] The present invention also provides a droop coefficient and damping coefficient control system for energy storage photovoltaic power plants, characterized in that it includes a memory and a processor, wherein the memory stores a computer program, and the processor calls the computer program to execute the steps of the method described above.

[0016] Compared with the prior art, the present invention has the following advantages: (1) This invention proposes an adaptive change method involving the droop coefficient K and the damping coefficient D, and proposes an adaptive control strategy for the VSG control parameters of the energy storage photovoltaic system. Based on the two system frequency stability indicators of frequency change rate and frequency deviation, the VSG droop coefficient K and the damping coefficient D are dynamically adjusted. During the adaptive change of the droop coefficient K, when the system frequency deviates rapidly, a strong control mode with dual-parameter fusion is used to simultaneously respond to the magnitude and rate of change of the frequency deviation, thereby achieving dual suppression of the frequency deterioration trend and improving the system's adjustment stiffness and damping during dynamic processes. When the system frequency recovers autonomously, only the frequency change rate is moderately adjusted to avoid causing excessive interference to the recovery process, which is conducive to the system returning to steady state smoothly and without overshoot. The same control principle is used during the adaptive change of the damping coefficient D. Overall, it can effectively improve the dynamic response performance of VSG frequency and active power, increase the system inertia level, and smooth the output of the energy storage photovoltaic system.

[0017] (2) The present invention sets the start condition for VSG parameter adaptive control. The system determines the output state based on the deviation between the set value and the controlled variable. When the deviation reaches a certain threshold, the controller will output the maximum or minimum control value to prompt the system to quickly approach the set value. Once the controlled variable approaches or reaches the set value, the controller output state may reverse to continue to keep the system running stably near the set value. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating a method for controlling the droop coefficient and damping coefficient of a photovoltaic power station for energy storage, provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of a photovoltaic power station VSG grid connection provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the primary frequency modulation, inertia, and damping characteristics of a VSG provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of VSG output curves under different droop coefficients provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the VSG frequency response under different droop coefficients provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the VSG frequency response under different damping coefficients provided in an embodiment of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0021] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0022] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed during use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0023] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0024] Furthermore, terms such as "horizontal" and "vertical" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0025] Example 1 like Figure 1As shown, this embodiment provides a method for controlling the droop coefficient and damping coefficient of a photovoltaic power station for energy storage, including the following steps: S1: Calculate the corresponding frequency deviation and frequency offset during the operation of the energy storage photovoltaic system; S2: When the calculated frequency deviation and frequency deviation are both greater than the corresponding start-up threshold, the droop coefficient and damping coefficient of the virtual synchronous generator of the energy storage photovoltaic system are adaptively adjusted. S3: During the adaptive change of the droop coefficient and damping coefficient, if the product of the frequency deviations is greater than zero, a larger droop coefficient and damping coefficient are used; if the product of the frequency deviations is less than zero, a smaller droop coefficient and damping coefficient are used.

[0026] Specifically, in step S1, the frequency deviation and its indices are described as follows: During power system operation, once subjected to disturbance inputs, the system exhibits various response behaviors, which can be reflected by multiple time-domain metrics. Specifically, when the system encounters a given step disturbance such as a sudden increase in load or generation loss, a series of relevant frequency stability indices need to be defined based on the system model. These indices are crucial because they serve as key indicators for measuring system stability when the system is disturbed.

[0027] The rate of change of frequency (RoCoF) is the derivative of frequency from a mathematical perspective, and physically represents how fast the frequency changes. Therefore, the expression for the rate of change of frequency (RoCoF) is: In the formula, The rate of change of frequency, The current system frequency, For time.

[0028] Frequency deviation represents the difference between the current system frequency and the reference frequency. Physically, it represents the system frequency level. Therefore, the expression for the corresponding frequency deviation is: In the formula, For frequency deviation, The current system frequency, This is the reference frequency.

[0029] In step S2, the adaptive adjustment process for the droop coefficient and damping coefficient is as follows: By adaptively adjusting the sagging coefficient K and damping coefficient DTo achieve high-quality frequency modulation, this solution uses adaptive parameters. bang-bang Control. In bang-bang In this control system, the controller output has only two states. The system determines the output state based on the deviation between the setpoint and the controlled variable. When the deviation reaches a certain threshold, the controller outputs its maximum or minimum control value to encourage the system to quickly approach the setpoint. Once the controlled variable approaches or reaches the setpoint, the controller output state may reverse to maintain stable operation of the system around the setpoint.

[0030] To prevent frequent parameter changes due to small frequency disturbances, adaptive startup conditions for VSG parameters are set. When the frequency deviation and frequency change rate exceed the startup threshold, the droop coefficient... K and damping coefficient D Participating in adaptive change, i.e. .

[0031] And when When using a larger droop coefficient K and damping coefficient D ,when When using a smaller droop coefficient K and damping coefficient D The adaptive control law is designed as follows: In the formula, The droop coefficient is... Based on the droop coefficient, The first droop coefficient, This is the second droop coefficient. The third droop coefficient, The rate of change of frequency, This represents the frequency deviation. In the formula, The damping coefficient is... Based on the basic damping coefficient, The first damping coefficient, This is the second damping coefficient. The third damping coefficient, The rate of change of frequency, This represents the frequency deviation.

[0032] This proposal suggests an adaptive control strategy for the VSG control parameters of an energy storage photovoltaic system, dynamically adjusting the VSG droop coefficient based on two system frequency stability indices: the rate of frequency change and the frequency deviation. K and damping coefficient D It can effectively improve the dynamic response performance of VSG frequency and active power, increase the system inertia level, and at the same time, smooth the output of the energy storage photovoltaic system.

[0033] Preferably, the energy storage photovoltaic system includes a photovoltaic power generation unit and a battery energy storage unit, which are connected to the local load or the power grid through a DC-DC converter, an inverter, and an RC filter. Inverters are used to control the voltage and current of photovoltaic power generation units; RC filters are used to filter the port voltage and current of an inverter to obtain the three-phase sinusoidal voltage and current at the output port.

[0034] It also includes establishing a small-signal model of the virtual synchronous generator in the inverter and photovoltaic power generation unit, obtaining the second-order transfer function expressions of the output power response characteristics and virtual angular velocity response characteristics of the virtual synchronous generator, which are used to simulate and obtain the influence of the droop coefficient and damping coefficient on the dynamic response process of the virtual synchronous generator, and verify the effectiveness of the droop coefficient and damping coefficient.

[0035] The process of establishing the small-signal model of the virtual synchronous generator in the inverter and photovoltaic power generation unit is described below: Photovoltaic power plant topology with energy storage, such as Figure 2 As shown in the diagram, in this system, the photovoltaic (PV) power generation unit and energy storage are connected to the local load or grid through a DC-DC converter, an inverter, and an RC filter. The PV power generation unit and the battery energy storage are coupled on the DC side, utilizing the charging and discharging levels of the battery energy storage to suppress fluctuations in the PV power station's output. The inverter controls the voltage and current of the PV power station; the inverter port voltage and current are filtered by the RC filter to obtain the three-phase sinusoidal voltage and current at the output port.

[0036] The inverter uses VSG control to simulate the rotor characteristics of a synchronous generator, incorporating the classic second-order equations of a synchronous generator into the control strategy. Its per-unit rotor motion equations are expressed as follows: In the formula: δ For VSG's offensive role, H The inertial time constant, ω g The synchronous angular velocity of the power grid. ω For VSG virtual angular velocity, ω n The rated angular velocity, P m , P e These are mechanical power and electromagnetic power, respectively. D is the damping coefficient.

[0037] Its small-signal model is: In the formula: "Δ" represents a small signal quantity.

[0038] VSG Mechanical Power P m The following is obtained from the primary frequency modulation characteristics of the VSG: In the formula: K The droop coefficient is... P ref This is the reference power.

[0039] Its small-signal model is: VSG primary frequency modulation and inertia, damping characteristics, such as Figure 3 As shown.

[0040] The expression for the active power output of the VSG is: In the formula: E This refers to the inverter port voltage; U g This refers to the grid voltage. S n VSG rated capacity; Z Line impedance; α It is the impedance angle.

[0041] The small-signal relationship between active power and power angle can be obtained: In the formula: S E = EU g sin( α - δ ) / ( S n Z The synchronous power is obtained by solving the static operating point.

[0042] VSG control responds to the grid synchronization angular velocity, using it as input to regulate the virtual angular velocity of the VSG, thereby controlling its output. The grid synchronization angular velocity and VSG output power response characteristics are typical second-order transfer functions. The response characteristics of the power grid synchronous angular velocity and the VSG virtual angular velocity are typical second-order transfer functions: The VSG control structure contains two transfer functions. The transfer function, represented by the grid synchronization angular velocity and the VSG output power response characteristics, can be used to analyze the changes in the VSG's active power and the system's response when the VSG is subjected to frequency disturbances from the external system. The transfer function, presented by the grid synchronization angular velocity and the VSG's virtual angular velocity response characteristics, can be used to analyze the VSG's virtual frequency response when the VSG is subjected to frequency disturbances from the external system.

[0043] The following is a detailed description of the impact of simulation-obtained droop and damping coefficients on the dynamic response of a virtual synchronous generator: 1) Influence of grid synchronous angular velocity - VSG output power parameters Using grid frequency disturbance as input: In the formula: τ The duration of the pulse. α This represents the pulse amplitude.

[0044] The time-domain response model of the grid synchronization angular velocity minus the VSG output power is obtained, yielding indices regarding the power regulation process, with the peak time being: In the formula: λ = ω n S E .

[0045] The trough time is: Adjustment time is: This yields a set of VSG electromagnetic power time-domain curves under specific parameters. Different droop coefficients... of VSG electromagnetic power dynamic characteristics such as Figure 4 As shown.

[0046] 2) Using grid frequency disturbance as input: Analyze the influence of parameters on the dynamic characteristics of the VSG virtual angular velocity. Different droop coefficients... K and damping coefficient D The effects on the dynamic process of grid synchronous angular velocity - VSG virtual angular velocity are as follows: Figure 4 , 5 As shown.

[0047] Because the transfer function of the grid synchronous angular velocity - VSG virtual angular velocity contains a zero, the droop coefficient... K Too small or damping coefficient D An excessively large droop coefficient will cause the zero point to approach the imaginary axis, resulting in poor dynamic performance. Therefore, a larger droop coefficient should be selected. K and a smaller damping coefficient D Moving the zero point away from the imaginary axis can effectively improve the dynamic characteristics of the VSG frequency.

[0048] Example 2 This embodiment provides a droop coefficient and damping coefficient control system for energy storage photovoltaic power plants, including a memory and a processor. The memory stores a computer program, and the processor calls the computer program to execute the steps of the droop coefficient and damping coefficient control method for energy storage photovoltaic power plants as described in Embodiment 1.

[0049] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for controlling the droop coefficient and damping coefficient of a photovoltaic power station for energy storage, characterized in that, Includes the following steps: During the operation of the energy storage photovoltaic system, calculate the corresponding frequency deviation and frequency offset; When the calculated frequency deviation and frequency deviation are both greater than the corresponding start-up threshold, the droop coefficient and damping coefficient of the virtual synchronous generator of the energy storage photovoltaic system are adaptively adjusted. During the adaptive change of the droop coefficient and damping coefficient, if the product of the frequency deviations is greater than zero, a larger droop coefficient and damping coefficient are used; if the product of the frequency deviations is less than zero, a smaller droop coefficient and damping coefficient are used.

2. The method for controlling the droop coefficient and damping coefficient of a photovoltaic power station for energy storage according to claim 1, characterized in that, The adaptive variation expression of the droop coefficient is: In the formula, The droop coefficient is... Based on the droop coefficient, The first droop coefficient, This is the second droop coefficient. The third droop coefficient, The rate of change of frequency, This represents the frequency deviation.

3. The method for controlling the droop coefficient and damping coefficient of a photovoltaic power station for energy storage according to claim 1, characterized in that, The adaptive variation expression of the damping coefficient is as follows: In the formula, The damping coefficient is... Based on the basic damping coefficient, The first damping coefficient, This is the second damping coefficient. The third damping coefficient, The rate of change of frequency, This represents the frequency deviation.

4. The method for controlling the droop coefficient and damping coefficient of a photovoltaic power station for energy storage according to claim 1, characterized in that, Both the frequency deviation and the frequency deviation are greater than the corresponding start-up threshold, specifically: In the formula, The rate of change of frequency, For frequency deviation, The threshold for the rate of change of frequency is set. This is the threshold for initiating frequency deviation.

5. The method for controlling the droop coefficient and damping coefficient of a photovoltaic power station for energy storage according to claim 1, characterized in that, The expression for calculating the rate of change of frequency is: In the formula, The rate of change of frequency, The current system frequency, For time.

6. The method for controlling the droop coefficient and damping coefficient of a photovoltaic power station for energy storage according to claim 1, characterized in that, The expression for calculating the frequency deviation is: In the formula, For frequency deviation, The current system frequency, This is the reference frequency.

7. The method for controlling the droop coefficient and damping coefficient of a photovoltaic power station for energy storage according to claim 1, characterized in that, The energy storage photovoltaic system includes a photovoltaic power generation unit and a battery energy storage unit. The photovoltaic power generation unit and the battery energy storage unit are connected to the local load or the power grid through a DC-DC converter, an inverter and an RC filter. The inverter is used to control the voltage and current of the photovoltaic power generation unit; The RC filter is used to filter the port voltage and current of the inverter to obtain the three-phase sinusoidal voltage and current at the output port.

8. The method for controlling the droop coefficient and damping coefficient of a photovoltaic power station for energy storage according to claim 7, characterized in that, The method also includes establishing a small-signal model of the virtual synchronous generator in the inverter and photovoltaic power generation unit, obtaining the second-order transfer function expressions of the output power response characteristics and virtual angular velocity response characteristics of the virtual synchronous generator, which are used to simulate and obtain the influence of the droop coefficient and damping coefficient on the dynamic response process of the virtual synchronous generator, and verify the effectiveness of the droop coefficient and damping coefficient.

9. The method for controlling the droop coefficient and damping coefficient of a photovoltaic power station for energy storage according to claim 8, characterized in that, The second-order transfer function expression of the output power response characteristic of the virtual synchronous generator is as follows: In the formula, This represents the change in output power of the virtual synchronous generator. This represents the change in the synchronous angular velocity of the power grid. The inertial time constant, The droop coefficient is... The damping coefficient is... The rated angular velocity, Synchronous power; The second-order transfer function expression of the virtual angular velocity response characteristic of the virtual synchronous generator is as follows: In the formula, The virtual angular velocity is for the virtual synchronous generator.

10. A droop coefficient and damping coefficient control system for energy storage photovoltaic power plants, characterized in that, It includes a memory and a processor, the memory storing a computer program, and the processor calling the computer program to perform the steps of the method as described in any one of claims 1 to 9.

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