Control method for participation of optical storage combined system in primary frequency modulation

Abstract

The invention discloses a control method for a light storage combined system to participate in primary frequency modulation, and the method comprises the following steps: firstly, calculating the frequency deviation of a grid-connected point of a photovoltaic power station, and calculating the active power regulation quantity required by the light storage combined system to participate in the primary frequency modulation of a power grid; the CEEMDAN is utilized to decompose the active power regulation quantity into a high frequency part, a medium frequency part and a low frequency part, the medium frequency part is transmitted to the photovoltaic converter system, and the low frequency part and the high frequency part are transmitted to the energy storage system; calculating the maximum additional power of primary frequency modulation of each converter of the photovoltaic power station according to the illumination condition and the operation state, and determining an optimal target power instruction of each converter; calculating the maximum adjustable power of primary frequency modulation of the energy storage system according to the capacity limitation and the charge state of energy storage, and determining an optimal target power instruction; and finally, issuing the optimal target power instruction to a corresponding converter and an energy storage system, so that the converter and the energy storage system automatically adjust own active power to instruction power according to the instruction.

Description

Technical Field

[0001] The present invention relates to the technical field of primary frequency regulation of photovoltaic power stations, and in particular to a control method for a photovoltaic-storage combined system to participate in primary frequency regulation. Background Art

[0002] With the increasing penetration of renewable energy such as wind power and photovoltaic power and the continuous commissioning of large-capacity DC projects, the power grid faces a series of problems such as the decrease in the overall inertia time constant of the system, the increase in net active power fluctuations, and the insufficient frequency regulation capacity of traditional synchronous units. The frequency regulation capacity of the power grid system continues to decline, the problem of power grid frequency control is becoming increasingly prominent, and the problem of power grid frequency safety is becoming more and more prominent. However, due to its own characteristics, the frequency response of new energy power stations is slow, which increases the pressure of frequency regulation and peak regulation of conventional generator sets. Therefore, the primary frequency regulation demand of new energy power stations is a development trend. Energy storage systems using power electronic interfaces, such as battery energy storage, supercapacitor energy storage, and flywheel energy storage, have the advantages of fast response speed, strong climbing ability, and flexible control, making them an effective means of power grid frequency regulation. In order to improve the frequency regulation performance, most of the existing new energy sites cooperate with energy storage to participate in primary frequency regulation. Therefore, photovoltaic power stations and energy storage participate in primary frequency regulation as a coordinated and complementary whole, which is an effective measure to ensure the frequency safety of the power grid under the new form.

[0003] Domestic and foreign scholars have conducted a lot of research on the issue of new energy systems with energy storage participating in primary frequency regulation. At present, most of the research is based on the comprehensive inertia control strategy, and the focus is on the optimal value of the proportion and differential coefficient, or the use of adaptive methods to dynamically adjust the parameters of the comprehensive inertia control (in terms of the allocation of frequency regulation responsibility for the reserve capacity of the frequency modulation power source). However, there are few studies on frequency modulation strategies based on the frequency domain characteristics of the frequency modulation signal. According to their output characteristics, energy storage systems can be divided into energy-type energy storage represented by electrochemical energy storage and power-type energy storage represented by supercapacitors and flywheels. Since the fluctuation of photovoltaic power contains power components of different frequencies and amplitudes, different energy storage can be combined with each other to absorb different components, which can not only effectively smooth the fluctuation of photovoltaic power generation, but also assist in participating in the primary frequency regulation of the power grid. However, the energy storage system is expensive, the configured capacity is small, and there are also state of charge constraints. How to use the photovoltaic power generation system and the hybrid energy storage system as a coordinated and complementary whole to participate in the primary frequency regulation and give full play to their respective functions is of great significance to improving the frequency stability of the new power system.

[0004] Therefore, there is still room for improvement in the prior art. Summary of the invention

[0005] The purpose of the present invention is to provide a control method for a photovoltaic and energy storage combined system to participate in primary frequency regulation, aiming to solve the technical problems that the existing energy storage system is expensive, has a small configuration capacity, and is difficult to use the photovoltaic power generation system and the hybrid energy storage system as a coordinated and complementary whole to participate in primary frequency regulation and give full play to their respective functions.

[0006] To achieve the above-mentioned purpose, the technical solution of the present invention is: the photovoltaic power generation system and the hybrid energy storage system are used as a coordinated and complementary whole to participate in primary frequency modulation, giving full play to their respective functions, which includes the following steps: S1. Collect the real-time power of each inverter in the photovoltaic power station and the measured grid frequency at the grid connection point. Under the condition that the light conditions allow (the power generation power exceeds 20% of the rated power), calculate the frequency deviation between the grid frequency at the grid connection point and the rated frequency of the grid in real time. ; S2. Calculate the active power regulation required for the photovoltaic and storage combined system to participate in the primary frequency regulation of the power grid according to the capacity limitation of the photovoltaic and storage combined system; S3. The required active power regulation is decomposed into high frequency components using the fully adaptive noise ensemble empirical mode decomposition (CEEMDAN) method. , IF , low frequency Three parts; S4. Transmitted to the photovoltaic inverter system, the low frequency ,high frequency Delivered to energy storage system; S5. Calculate the maximum additional power that can be generated by primary frequency modulation of each converter of the photovoltaic power station according to the lighting conditions and operating status, and then determine the optimal target power command of each converter; S6. Calculate the maximum adjustable power of the energy storage system for primary frequency modulation according to the capacity limit and state of charge SOC of the energy storage, and then determine the optimal target power instructions for the first energy storage system and the second energy storage system; S7. Send the optimal target power instructions of the converter and energy storage system to the corresponding converter and energy storage system, so that they automatically adjust their own active power to the instruction power according to the instructions.

[0007] The photovoltaic energy storage system in step S2 includes a photovoltaic power generation system and an energy storage system; the energy storage system includes a first energy storage system and a second energy storage system, the first energy storage system includes an electrochemical energy storage system, and the second energy storage system includes a flywheel energy storage system.

[0008] The step S2 calculates the active power regulation amount required for the photovoltaic and energy storage system to participate in the primary frequency regulation of the power grid according to the capacity limitation of the photovoltaic and energy storage system, including: In order to prevent the frequent adjustment of the controller caused by the slight fluctuation of the frequency during normal operation and the unnecessary frequent charging and discharging of the energy storage system, which will reduce the energy storage life, the primary frequency regulation dead zone of the photovoltaic converter and the energy storage system is set respectively; When the frequency deviation does not exceed the grid frequency dead zone, the converter and the energy storage system do not participate in the primary frequency modulation, the active power reference value remains unchanged, and the active power adjustment amount required for the photovoltaic power station to participate in the grid primary frequency modulation is set to 0; If the frequency deviation exceeds the grid frequency dead zone, the power-frequency (Pf) virtual droop control algorithm is used to calculate the active power regulation required for the photovoltaic storage system to participate in the primary frequency regulation of the grid; the virtual droop control principle is: (1)

[0009] Where K is the droop coefficient, The power of the combined photovoltaic and energy storage system participating in primary frequency regulation.

[0010] In step S3, the fully adaptive noise ensemble empirical mode decomposition (CEEMDAN) method is used to decompose the required active power regulation into high frequency , IF , low frequency Three parts; the specific steps are: S30: decomposing the required active power regulation amount into a plurality of modal components and a residual component by using fully adaptive noise set empirical mode decomposition; S31: Reconstruct the decomposition results into high frequencies , IF and low frequency Three parts; S32: Calculate whether the intermediate frequency component under each decomposition layer number meets the grid connection requirement of the grid connection point. If the standard is met, stop the loop; otherwise, continue to increase the decomposition layer number until the optimal decomposition layer number is found.

[0011] In step S4, the low frequency ,high frequency to the energy storage system, including ,high frequency Delivered to the first energy storage system and the second energy storage system.

[0012] The step S5 is to calculate the maximum additional power that can be generated by each inverter of the photovoltaic power station in one frequency modulation according to the illumination conditions and the operating status, and the specific steps are: S50: considering the capacity limitation of the converter and the light intensity of the photovoltaic power station, calculating the maximum value of the active output of the converter of the photovoltaic power station under the current light intensity according to the converter capacity and reactive power; S51: Based on the active power at the converter collection point and the light intensity of the photovoltaic power station, and provided that the capacity does not exceed the limit, the maximum additional power that can be generated by the converter in one frequency modulation is calculated.

[0013] In step S6, the maximum adjustable power of the energy storage system is calculated according to the capacity limit of the energy storage and the state of charge SOC. The specific steps are: S60: First, a Logistic regression function is used to determine the actual maximum charge and discharge power of the energy storage according to the energy storage capacity limit and the SOC; S61: Determine the actual primary frequency modulation output of the first energy storage system and the second energy storage system according to the frequency deviation, the maximum chargeable and dischargeable power of the first energy storage system and the second energy storage system, the primary frequency modulation low and high frequency power reference value, the rated power, etc.

[0014] Beneficial effects: In view of the problems of the overall inertia time constant reduction, net active power fluctuation increase, and insufficient frequency regulation capacity of traditional synchronous units in the new power system with new energy as the main body, the present invention proposes a control method for the participation of the photovoltaic and energy storage combined system in the primary frequency regulation based on CEEMDAN decomposition. First, the frequency deviation of the photovoltaic power station grid connection point is calculated, and the active power adjustment required for the photovoltaic and energy storage combined system to participate in the primary frequency regulation of the power grid is calculated. Then, the CEEMDAN decomposition method is used to decompose the active power adjustment amount into three parts: high, medium, and low frequency, to capture the local variation characteristics and periodic characteristics of the primary frequency regulation power component, and at the same time reduce interference. Next, an optimal photovoltaic and energy storage output allocation method considering the illumination conditions, photovoltaic converter output constraints, and energy storage system capacity constraints is proposed to achieve accurate correspondence between photovoltaic and energy storage and medium, low, and high frequency components, enhance the photovoltaic power station's active support capability for the power grid frequency, and effectively improve the system frequency characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flow chart of the control method of the photovoltaic energy storage combined system participating in the primary frequency regulation of the power grid in the present invention. DETAILED DESCRIPTION

[0016] In order to make the objectives, technical solutions and advantages of the present invention more clear and explicit, the present invention is further described in detail below with reference to the accompanying drawings and examples.

[0017] like Figure 1 As shown, the present invention discloses that a photovoltaic power generation system and a hybrid energy storage system are used as a coordinated and complementary whole to participate in primary frequency modulation, giving full play to their respective functions, and is characterized by comprising the following steps: S1. Collect the real-time power of each inverter in the photovoltaic power station and the measured grid frequency at the grid connection point. Under the condition that the light conditions allow (the power generation power exceeds 20% of the rated power), calculate the frequency deviation between the grid frequency at the grid connection point and the rated frequency of the grid in real time. ; S2. Calculate the active power regulation required for the photovoltaic and storage combined system to participate in the primary frequency regulation of the power grid according to the capacity limitation of the photovoltaic and storage combined system; S3. The required active power regulation is decomposed into high frequency components using the fully adaptive noise ensemble empirical mode decomposition (CEEMDAN) method. , IF , low frequency Three parts; S4. Transmitted to the photovoltaic inverter system, the low frequency ,high frequency Transmitted to energy storage system; S5. Calculate the maximum additional power that can be generated by primary frequency modulation of each converter of the photovoltaic power station according to the lighting conditions and operating status, and then determine the optimal target power command of each converter; S6. Calculate the maximum adjustable power of the energy storage system for primary frequency modulation according to the capacity limit and state of charge SOC of the energy storage, and then determine the optimal target power instructions for the first energy storage system and the second energy storage system; S7. Send the optimal target power instructions of the converter and energy storage system to the corresponding converter and energy storage system, so that they automatically adjust their own active power to the instruction power according to the instructions.

[0018] The present invention proposes to utilize a photovoltaic power generation system and a hybrid energy storage system composed of electrochemical energy storage and flywheel energy storage, integrate the respective advantages and available capacity of the photovoltaic and storage combined system, and improve the economic efficiency of the photovoltaic and storage combined system participating in the primary frequency regulation of the power grid while ensuring the primary frequency regulation effect, and enhance the transient frequency support capacity of the grid-type photovoltaic and storage system. When the power system experiences a long period of random load fluctuation, the CEEMDAN decomposition method proposed in the present invention is used to decompose the grid frequency deviation / power deviation into three parts: medium, low, and high in the frequency domain, and the photovoltaic power generation system, electrochemical energy storage system, and flywheel energy storage system respond to the corresponding components, giving full play to the rapid response capabilities of the different characteristics of the photovoltaic power station and the hybrid energy storage, reducing the number of charge and discharge times of the electrochemical energy storage, and extending its service life.

[0019] The photovoltaic energy storage system in step S2 includes a photovoltaic power generation system and an energy storage system; the energy storage system includes a first energy storage system and a second energy storage system, the first energy storage system includes an electrochemical energy storage system, and the second energy storage system includes a flywheel energy storage system.

[0020] The step S2 calculates the active power regulation amount required for the photovoltaic and energy storage system to participate in the primary frequency regulation of the power grid according to the capacity limitation of the photovoltaic and energy storage system, including: In order to prevent the frequent adjustment of the controller caused by the slight fluctuation of the frequency during normal operation and the unnecessary frequent charging and discharging of the energy storage system, which will reduce the energy storage life, the primary frequency regulation dead zone of the photovoltaic converter and the energy storage system is set respectively; When the frequency deviation does not exceed the grid frequency dead zone, the converter and the energy storage system do not participate in the primary frequency modulation, the active power reference value remains unchanged, and the active power adjustment amount required for the photovoltaic power station to participate in the grid primary frequency modulation is set to 0; If the frequency deviation exceeds the grid frequency dead zone, the power-frequency (Pf) virtual droop control algorithm is used to calculate the active power regulation required for the photovoltaic storage system to participate in the primary frequency regulation of the grid; the virtual droop control principle is: (1)

[0021] Where K is the droop coefficient, The power of the combined photovoltaic and energy storage system participating in primary frequency regulation.

[0022] The photovoltaic power station implements a fast frequency response function according to the active power-frequency (Pf) characteristic curve function: (2)

[0023] in, is the total active power target value of the photovoltaic power station after primary frequency regulation, is the actual frequency of the power grid, The frequency modulation dead zone, i.e. the frequency fast response action threshold, is in Hz; is the rated frequency of the system in Hz; is the rated power of the photovoltaic power station, in MW, is the system modulation rate, It is the initial value of active power before adjustment of the PV power station, in MW.

[0024] In step S3, the fully adaptive noise ensemble empirical mode decomposition (CEEMDAN) method is used to decompose the required active power regulation into high frequency , IF , low frequency Three parts; the specific steps are: S30: decomposing the required active power regulation amount into a plurality of modal components and a residual component by using fully adaptive noise set empirical mode decomposition; S31: Reconstruct the decomposition results into high frequencies , IF and low frequency Three parts; S32: Calculate whether the intermediate frequency component under each decomposition layer number meets the grid connection requirement of the grid connection point. If the standard is met, stop the loop; otherwise, continue to increase the decomposition layer number until the optimal decomposition layer number is found.

[0025] In step S4, the low frequency ,high frequency to the energy storage system, including ,high frequency Delivered to the first energy storage system and the second energy storage system.

[0026] The step S5 is to calculate the maximum additional power that can be generated by each inverter of the photovoltaic power station in one frequency modulation according to the illumination conditions and the operating status, and the specific steps are: S50: considering the capacity limitation of the converter and the light intensity of the photovoltaic power station, calculating the maximum value of the active output of the converter of the photovoltaic power station under the current light intensity according to the converter capacity and reactive power; S51: Based on the active power at the converter collection point and the light intensity of the photovoltaic power station, and provided that the capacity does not exceed the limit, the maximum additional power that can be generated by the converter in one frequency modulation is calculated.

[0027] In step S6, the maximum adjustable power of the energy storage system is calculated according to the capacity limit of the energy storage and the state of charge SOC. The specific steps are: S60: First, a Logistic regression function is used to determine the actual maximum charge and discharge power of the energy storage according to the energy storage capacity limit and the SOC; S61: Determine the actual primary frequency modulation output of the first energy storage system and the second energy storage system according to the frequency deviation, the maximum chargeable and dischargeable power of the first energy storage system and the second energy storage system, the primary frequency modulation low and high frequency power reference value, the rated power, etc.

[0028] In view of the problems of the overall inertia time constant reduction, net active power fluctuation increase, and insufficient frequency regulation capacity of traditional synchronous units in the new power system with new energy as the main body, the present invention proposes a control method for the participation of the photovoltaic and energy storage combined system in the primary frequency regulation based on CEEMDAN decomposition. First, the frequency deviation of the photovoltaic power station grid connection point is calculated, and the active power regulation required for the photovoltaic and energy storage combined system to participate in the primary frequency regulation of the power grid is calculated. Then, the active power regulation amount is decomposed into three parts of high, medium and low frequency using the CEEMDAN decomposition method to capture the local variation characteristics and periodic characteristics of the primary frequency regulation power component, while reducing interference. Next, an optimal photovoltaic and energy storage output allocation method considering the illumination conditions, photovoltaic converter output constraints and energy storage system capacity constraints is proposed to achieve accurate correspondence between photovoltaic and energy storage and medium, low and high frequency components, enhance the photovoltaic power station's active support capability for the power grid frequency, and effectively improve the system frequency characteristics.

[0029] The above are only preferred implementation modes of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. It should be pointed out that for technicians in this technical field, any modification or equivalent replacement of the technical solution of the present invention without creative work does not depart from the protection scope of the technical solution of the present invention.

Claims

1. A control method for a photovoltaic energy storage system participating in primary frequency modulation, characterized in that: The following steps are involved: S1. Collect the real-time power of each inverter in the photovoltaic power station and the measured grid frequency at the grid connection point. Under the condition that the light conditions permit, calculate the frequency deviation between the grid frequency at the grid connection point and the rated frequency of the grid in real time. , the condition that the light conditions allow is that the power generation exceeds 20% of the rated power; S2. Calculate the active power regulation required for the photovoltaic and storage combined system to participate in the primary frequency regulation of the power grid according to the capacity limitation of the photovoltaic and storage combined system; S3. Use the fully adaptive noise ensemble empirical mode decomposition method to decompose the required active power regulation into high-frequency , IF , low frequency Three parts; S4. Transmitted to the photovoltaic inverter system, the low frequency ,high frequency Delivered to energy storage system; S5. Calculate the maximum additional power that can be generated by primary frequency modulation of each converter of the photovoltaic power station according to the lighting conditions and operating status, and then determine the optimal target power command of each converter; S6. Calculate the maximum adjustable power of the energy storage system for primary frequency modulation according to the capacity limit and state of charge SOC of the energy storage, and then determine the optimal target power instructions for the first energy storage system and the second energy storage system; S7. Send the optimal target power instructions of the converter and energy storage system to the corresponding converter and energy storage system, so that they automatically adjust their own active power to the instruction power according to the instructions.

2. A control method for a photovoltaic energy storage system participating in primary frequency modulation according to claim 1, characterized in that: The photovoltaic energy storage system in step S2 includes a photovoltaic power generation system and an energy storage system; the energy storage system includes a first energy storage system and a second energy storage system, the first energy storage system includes an electrochemical energy storage system, and the second energy storage system includes a flywheel energy storage system.

3. The control method for the photovoltaic and energy storage system participating in primary frequency modulation based on CEEMDAN decomposition according to claim 1 is characterized in that: The step S2 calculates the active power regulation amount required for the photovoltaic and energy storage system to participate in the primary frequency regulation of the power grid according to the capacity limitation of the photovoltaic and energy storage system, including: In order to prevent the frequent adjustment of the controller caused by the slight fluctuation of the frequency during normal operation and the unnecessary frequent charging and discharging of the energy storage system, which will reduce the energy storage life, the primary frequency regulation dead zone of the photovoltaic converter and the energy storage system is set respectively; When the frequency deviation does not exceed the grid frequency dead zone, the converter and the energy storage system do not participate in the primary frequency modulation, the active power reference value remains unchanged, and the active power adjustment amount required for the photovoltaic power station to participate in the grid primary frequency modulation is set to 0; If the frequency deviation exceeds the grid frequency dead zone, the power-frequency virtual droop control algorithm is used to calculate the active power regulation required for the photovoltaic storage system to participate in the primary frequency regulation of the grid; the virtual droop control principle is: （1） Where K is the droop coefficient, The power of the combined photovoltaic and energy storage system participating in primary frequency regulation.

4. The control method for a photovoltaic energy storage system participating in primary frequency modulation according to claim 1, characterized in that: In step S3, the fully adaptive noise set empirical mode decomposition method is used to decompose the required active power regulation amount into high frequency , IF , low frequency Three parts; the specific steps are: S30: decomposing the required active power regulation amount into a plurality of modal components and a residual component by using fully adaptive noise set empirical mode decomposition; S31: Reconstruct the decomposition results into high frequencies , IF and low frequency Three parts; S32: Calculate whether the intermediate frequency component under each decomposition layer number meets the grid connection requirement of the grid connection point. If the standard is met, stop the loop; otherwise, continue to increase the decomposition layer number until the optimal decomposition layer number is found.

5. The control method for the photovoltaic and energy storage system participating in primary frequency modulation based on CEEMDAN decomposition according to claim 1 is characterized in that: In step S4, the low frequency ,high frequency to the energy storage system, including ,high frequency Delivered to the first energy storage system and the second energy storage system.

6. The control method of the photovoltaic energy storage system participating in primary frequency modulation based on CEEMDAN decomposition according to claim 1 is characterized in that: The step S5 is to calculate the maximum additional power that can be generated by each inverter of the photovoltaic power station in one frequency modulation according to the illumination conditions and the operating status, and the specific steps are: S50: considering the capacity limitation of the converter and the light intensity of the photovoltaic power station, calculating the maximum value of the active output of the converter of the photovoltaic power station under the current light intensity according to the converter capacity and reactive power; S51: Based on the active power at the converter collection point and the light intensity of the photovoltaic power station, and provided that the capacity does not exceed the limit, the maximum additional power that can be generated by the converter in one frequency modulation is calculated.

7. The control method for a photovoltaic energy storage system participating in primary frequency modulation according to claim 1, characterized in that: In step S6, the maximum adjustable power of the energy storage system is calculated according to the capacity limit of the energy storage and the state of charge SOC. The specific steps are: S60: First, a Logistic regression function is used to determine the actual maximum charge and discharge power of the energy storage according to the energy storage capacity limit and the SOC; S61: Determine the actual primary frequency modulation output of the first energy storage system and the second energy storage system according to the frequency deviation, the maximum chargeable and dischargeable power of the first energy storage system and the second energy storage system, the primary frequency modulation low and high frequency power reference value, the rated power, etc.

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