Photovoltaic and photovoltaic storage self-synchronous voltage source parallel system timing frequency coordination support control method and system

Abstract

This invention discloses a time-series frequency coordinated support control method and system for a photovoltaic and photovoltaic-storage self-synchronous voltage source parallel system. It comprises two main parts: transient power compensation control based on the fast response characteristics of the photovoltaic-storage units, and quasi-steady-state reserve power compensation control based on the active power reserve characteristics of the photovoltaic units. By introducing a high-pass filter and adaptive coefficients to correct the power reference value of the photovoltaic-storage units, rapid increase in transient power is achieved in the early stages of frequency drop. A four-layer logic judgment mechanism, including frequency deviation, DC voltage change rate, capacitor transient power, and voltage recovery, is constructed to identify the quasi-steady-state stage and trigger the photovoltaic units to engage integral compensation, fully releasing the reserved active power reserve. This invention can effectively reduce the maximum frequency change rate and increase the minimum transient frequency point during the inertial response stage, and significantly improve the quasi-steady-state frequency of the system during the primary frequency regulation stage, achieving full utilization of photovoltaic reserve resources and multi-source coordinated frequency support.

Description

Technical Field

[0001] This invention relates to the field of power system frequency control technology, and in particular to a time-series frequency coordinated support control method and system for a parallel system of active power reserve photovoltaic and photovoltaic-storage self-synchronizing voltage sources. Background Technology

[0002] Photovoltaic units are typically connected to the grid via power electronic converters. The large-scale replacement of traditional synchronous generator units has led to a significant decrease in the equivalent inertia of the power grid, resulting in a system exhibiting characteristics of low inertia and weak damping. Under power imbalance conditions such as sudden load increases or fluctuations in source-side output, the rate of change of grid frequency (RoCoF) increases significantly, and the frequency minimum (Nadir) continues to shift downward. In severe cases, this may trigger generator tripping or even system collapse, posing a significant challenge to the safe and stable operation of the power system.

[0003] To enhance system frequency support capabilities, existing technologies propose methods for converting grid-connected photovoltaic (PV) systems into self-synchronizing voltage sources (or grid-connected systems) for control, giving them inertia and damping characteristics similar to synchronous machines. Depending on the energy source, these technologies are mainly divided into two categories: PV-storage self-synchronizing voltage sources with energy storage and active power reserve PV self-synchronizing voltage sources utilizing PV load shedding. PV-storage types utilize the chemical energy reserves of batteries, offering fast response but are costly and have limited lifespan; active power reserve types utilize reserved power from the PV array, offering good economic efficiency but with inherent delays in the regulation process and slower response times.

[0004] However, existing research largely focuses on the control of single-type power sources or simple parallel operation, lacking collaborative control strategies tailored to the differences in response characteristics of different power sources. In multi-machine parallel systems, using only fixed droop control or virtual synchronous machine control cannot effectively distinguish the differences in transient inertial response and quasi-steady-state primary frequency regulation requirements. Specifically, active power backup photovoltaic systems without energy storage are limited by the dynamics of DC-side capacitor voltage and control delay, making it difficult to provide rapid support in the initial stage of frequency drop; while if the photovoltaic-energy storage unit bears too much power throughout the process, it will lead to redundant capacity configuration and poor economic efficiency. Existing technologies fail to fully utilize the complementary characteristics of "fast response of photovoltaic-energy storage unit" and "long-lasting photovoltaic backup power," making it difficult to achieve optimized support for the entire process of system frequency change rate, transient minimum point, and quasi-steady-state frequency while considering economic efficiency. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a time-frequency coordinated support control method and system for a photovoltaic and photovoltaic-storage self-synchronous voltage source parallel system, which effectively suppresses the grid frequency drop rate and improves the transient and quasi-steady-state frequency support capability of the system, in order to address the shortcomings of the existing technology.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a time-frequency coordinated support control method for a photovoltaic and photovoltaic-storage self-synchronizing voltage source parallel system, comprising the following steps:

[0007] S1, Collects the grid frequency at the grid connection point of the parallel system. DC bus voltage of active standby photovoltaic self-synchronizing voltage source Preamp output power and photovoltaic array power ;

[0008] S2, Based on the power grid frequency By using a high-pass filter to extract frequency change characteristics, a transient power compensation command is generated to control the photovoltaic storage self-synchronization voltage source to increase active power output during the frequency drop transient phase.

[0009] Based on the DC bus voltage Preamp output power and photovoltaic array power Calculate the transient power of the DC-side capacitor. And the DC bus voltage change rate, combined with the grid frequency deviation, to identify whether the parallel system has entered the quasi-steady state stage;

[0010] S3. Based on the quasi-steady-state determination results, calculate the reserve power deficit of the active power reserve photovoltaic self-synchronization voltage source, generate a reserve power compensation command through integral regulation, and control the photovoltaic unit to release all reserve power.

[0011] The process of generating the transient power compensation command includes: setting the rated frequency... With grid frequency The difference is calculated, and the difference is input into a high-pass filter to obtain the high-frequency component ΔP. This high-frequency component is then multiplied by an adaptive coefficient K to obtain the transient power compensation value.

[0012] The specific implementation process for identifying whether a parallel system has entered the quasi-steady-state stage includes: if the following four conditions are met, the parallel system enters the quasi-steady-state stage;

[0013] The four conditions are: DC bus voltage change rate Change from negative to positive; capacitor transient power It changes from a negative value to a positive value and tends towards 0; ; For the rated frequency, This is the rated value of the DC bus voltage.

[0014] capacitor transient power The calculation formula is:

[0015] .

[0016] The specific implementation process of generating a backup power compensation command and controlling the photovoltaic unit to release all backup power includes: calculating the difference between the increased power of the active backup photovoltaic self-synchronizing voltage source and the reserved backup power at the current moment; inputting the difference into the integral controller, and superimposing the output of the integral controller into the power reference value of the active backup photovoltaic self-synchronizing voltage source, driving the photovoltaic unit to continuously increase power until all backup power is released.

[0017] As an inventive concept, the present invention also provides a timing and frequency coordinated support control system for a photovoltaic and photovoltaic-storage self-synchronizing voltage source parallel system, including a memory, a processor, and a computer program stored in the memory; the processor executes the computer program to implement the steps of the above method.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: By introducing transient power compensation control based on high-pass filter and adaptive coefficient in the photoelectric energy storage unit, the present invention makes full use of the instantaneous energy storage unit's characteristics of fast response and rapid energy storage. In the inertial response stage (transient) of frequency drop, the maximum rate of change of system frequency (RoCoF) is significantly reduced, and the minimum transient frequency point (Nadir) is effectively improved, thereby improving the system's anti-disturbance capability in the early stage of load change. Attached Figure Description

[0019] Figure 1 This is an equivalent circuit topology diagram of the parallel system of active power standby photovoltaic and photovoltaic-storage self-synchronizing voltage source in an embodiment of the present invention;

[0020] Figure 2 This is a flow diagram of the transient power compensation control signal of the optical storage self-synchronization voltage source in an embodiment of the present invention;

[0021] Figure 3 This is a flowchart of the multi-layer logic judgment process for identifying the quasi-steady-state stage of the system in an embodiment of the present invention;

[0022] Figure 4 This is a block diagram of the improved active-frequency loop control principle of the active power reserve photovoltaic self-synchronizing voltage source in an embodiment of the present invention.

[0023] Figure 5 This is a comparison chart of the power grid frequency and frequency change rate response under load surge conditions between the method proposed in this embodiment and the prior art. Figure 5 (a) is a comparison of the experimental waveforms of the frequency response curves at the load using the control method proposed in the embodiments of the present invention, the traditional unimproved control method, and the photovoltaic unit with only energy storage for traditional frequency regulation control; Figure 5(b) is a comparison of the experimental waveforms of the frequency change rate response curves at the load using the control method proposed in the embodiments of the present invention, the conventional unimproved control method, and the conventional frequency regulation control of photovoltaic units with only energy storage. Detailed Implementation

[0024] 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, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1

[0026] refer to Figure 1 This is an equivalent circuit topology diagram of the parallel system of a photovoltaic and solar-storage self-synchronizing voltage source with active power reserve in this embodiment of the invention. This embodiment constructs a four-terminal system, including an active power reserve photovoltaic self-synchronizing voltage source, a solar-storage self-synchronizing voltage source, and a synchronous generator set simulating grid characteristics. Each unit is connected to a common junction point via line impedance.

[0027] refer to Figure 2 This is a flow diagram of the transient power compensation control signal of the self-synchronizing voltage source for optical storage in this embodiment of the invention. To address the initial stage of frequency drop caused by a sudden load increase, this embodiment of the invention introduces a transient power compensation stage into the control loop of the self-synchronizing voltage source for optical storage.

[0028] refer to Figure 3 This is a schematic diagram of the multi-layer logic judgment process for identifying the quasi-steady-state stage of the system in an embodiment of the present invention. Since the active power reserve photovoltaic self-synchronization voltage source is limited by the DC-side capacitor and control delay, it is more suitable to be put into operation when the frequency is close to stable. This embodiment of the present invention designs a four-layer sequential logic judgment structure to accurately identify the quasi-steady-state stage.

[0029] refer to Figure 4 This is a block diagram illustrating the improved active-frequency loop control principle of the active-reserve photovoltaic self-synchronizing voltage source in an embodiment of the present invention. When the above... Figure 3 After the logic judgment outputs the enable signal as shown, this embodiment automatically engages the backup power compensation control.

[0030] The present invention provides a time-frequency coordinated support control method for a parallel system of active power reserve photovoltaic and photovoltaic-storage self-synchronizing voltage sources, comprising the following steps:

[0031] Collect grid frequency at the grid connection point of the parallel system And the DC bus voltage of the active standby photovoltaic self-synchronizing voltage source Preamp output power and photovoltaic array power ;

[0032] Based on power grid frequency A high-pass filter is used to extract frequency variation characteristics, generating transient power compensation commands to control the photovoltaic-storage self-synchronizing voltage source to increase active power output during frequency drop transient phases. The generation of transient power compensation commands includes: adjusting the rated frequency... With grid frequency The difference is calculated, and the high-frequency component is obtained by inputting it into the high-pass filter. This component is then multiplied by an adaptive coefficient to obtain the transient power compensation value. The sign of the adaptive coefficient is determined by the sign of the high-pass filter output value to ensure that the transient power compensation value is positive during frequency drop and recovery, preventing the power command from decreasing in the opposite direction during frequency recovery.

[0033] Based on DC bus voltage Preamp output power and photovoltaic array power Calculate the transient power of the DC-side capacitor. The system uses DC bus voltage change rate and grid frequency deviation as inputs to determine whether it has entered a quasi-steady-state phase through multi-layer logic. The criteria for determining whether the system has entered a quasi-steady-state phase include calculating capacitor transient power. The system consists of two parts: transient power of the capacitor and logic determination. Defined by the following formula:

[0034] ;

[0035] The required logical judgment must satisfy the following four conditions in sequence:

[0036] 1) Frequency determination: Rated frequency With grid frequency The following relationship must be satisfied:

[0037] ;

[0038] 2) Voltage change rate determination: DC bus voltage change rate Change from a negative value to a positive value;

[0039] 3) Capacitor power determination: the transient power of the capacitor It changes from a negative value to a positive value and tends towards 0;

[0040] 4) Voltage recovery determination: DC bus voltage With the rated value The deviation must satisfy the following relationship:

[0041] ;

[0042] Based on the quasi-steady-state determination results, the reserve power deficit of the active power reserve photovoltaic self-synchronizing voltage source is calculated. A reserve power compensation command is generated through integral regulation to control the photovoltaic unit to release all reserve power. The generation process of the reserve power compensation command is as follows: the difference between the increased power output of the active power reserve photovoltaic self-synchronizing voltage source and the reserved reserve power at the current moment is calculated; the difference is input to the integral controller, and the output of the integral controller is superimposed on the power reference value of the active power reserve photovoltaic self-synchronizing voltage source, driving the photovoltaic unit to continuously increase power output until all reserve power is released.

[0043] Table 1 Simulation data for Example 1

[0044]

[0045] Figure 5 (a) and Figure 5 (b) The graphs show a comparison of the grid frequency and frequency change rate response under a sudden load surge condition, comparing the method proposed in this invention with existing technologies. The condition is a sudden load surge of 6 kW at 2 seconds. The purple curve corresponds to Scheme 5, i.e., the method proposed in this invention; the blue curve corresponds to Scheme 1, where the photovoltaic units do not participate in frequency regulation, and only the photovoltaic-storage units participate in frequency regulation with unmodified control; the brown curve corresponds to Scheme 2, where the photovoltaic units are modified without active power reserve control and participate in frequency regulation together with the photovoltaic-storage units. Figure 5 It can be known that:

[0046] Regarding transient frequency: the lowest transient frequency achieved using the method of this embodiment (Scheme 5) is 49.87 Hz, which is an improvement over the unimproved Scheme 3. Simultaneously, the absolute value of the extreme value of the frequency change rate is reduced to 0.74 Hz / s, a significant improvement compared to Scheme 2 (0.87 Hz / s) which only uses backup photovoltaic frequency regulation. This indicates... Figure 2 The transient power compensation control shown effectively leverages the rapid response capability of the photovoltaic storage unit and suppresses sharp frequency drops.

[0047] Regarding the quasi-steady-state frequency: the quasi-steady-state frequency restored using the method of this embodiment is 49.94Hz, which is an improvement compared to Scheme 1 (49.91Hz) where photovoltaics do not participate in frequency modulation and Scheme 2 (49.92Hz) as a conventional backup. This indicates that... Figure 4 The backup power compensation control shown successfully utilizes the photovoltaic backup power, achieving better frequency recovery. In summary, the timing-coordinated control strategy proposed in this embodiment of the invention does not require inter-unit communication, and leverages the respective advantages of photovoltaic and energy storage and photovoltaic power in the inertial response stage and the primary frequency regulation stage of the frequency response, respectively, achieving frequency coordination support throughout the entire process.

[0048] Example 2

[0049] Embodiment 2 of the present invention provides a system corresponding to Embodiment 1 above, including a memory, a processor, and a computer program stored in the memory; the processor executes the computer program in the memory to implement the steps of the method of Embodiment 1 above.

[0050] In some implementations, the memory may be high-speed random access memory (RAM), and may also include non-volatile memory, such as at least one disk storage device.

[0051] In other implementations, the processor can be any type of general-purpose processor, such as a central processing unit (CPU) or a digital signal processor (DSP), and there is no limitation here.

[0052] Example 3

[0053] Embodiment 3 of the present invention provides a computer-readable storage medium corresponding to Embodiment 1 above, on which a computer program / instructions are stored. When the computer program / instructions are executed by a processor, they implement the steps of the method of Embodiment 1 above.

[0054] A computer-readable storage medium can be a tangible device that holds and stores instructions for use by an instruction execution device. A computer-readable storage medium can be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any combination thereof.

[0055] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of this application can be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0056] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0057] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0058] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0059] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A time-frequency coordinated support control method for a photovoltaic and photovoltaic-storage self-synchronizing voltage source parallel system, characterized in that, Includes the following steps: S1, Collects the grid frequency at the grid connection point of the parallel system. DC bus voltage of active standby photovoltaic self-synchronizing voltage source Preamp output power and photovoltaic array power ; S2, Based on the power grid frequency By using a high-pass filter to extract frequency change characteristics, a transient power compensation command is generated to control the photovoltaic storage self-synchronization voltage source to increase active power output during the frequency drop transient phase. Based on the DC bus voltage Preamp output power and photovoltaic array power Calculate the transient power of the DC-side capacitor. And the DC bus voltage change rate, combined with the grid frequency deviation, to identify whether the parallel system has entered the quasi-steady state stage; S3. Based on the quasi-steady-state determination results, calculate the reserve power deficit of the active power reserve photovoltaic self-synchronization voltage source, generate a reserve power compensation command through integral regulation, and control the photovoltaic unit to release all reserve power.

2. The time-frequency coordinated support control method for a photovoltaic and photovoltaic-storage self-synchronizing voltage source parallel system according to claim 1, characterized in that, The process of generating the transient power compensation command includes: setting the rated frequency... With grid frequency The difference is calculated, and the difference is input into a high-pass filter to obtain the high-frequency component. This high-frequency component is then multiplied by an adaptive coefficient to obtain the transient power compensation value.

3. The time-frequency coordinated support control method for a photovoltaic and photovoltaic-storage self-synchronizing voltage source parallel system according to claim 1, characterized in that, The specific implementation process for identifying whether a parallel system has entered the quasi-steady-state stage includes: if the following four conditions are met, the parallel system enters the quasi-steady-state stage; The four conditions are: DC bus voltage change rate Change from negative to positive; capacitor transient power It changes from a negative value to a positive value and tends towards 0; ; For the rated frequency, This is the rated value of the DC bus voltage.

4. The time-frequency coordinated support control method for a photovoltaic and photovoltaic-storage self-synchronizing voltage source parallel system according to claim 3, characterized in that, capacitor transient power The calculation formula is: 。 5. The time-frequency coordinated support control method for a photovoltaic and photovoltaic-storage self-synchronizing voltage source parallel system according to claim 1, characterized in that, The specific implementation process of generating a backup power compensation command and controlling the photovoltaic unit to release all backup power includes: calculating the difference between the increased power of the active backup photovoltaic self-synchronizing voltage source and the reserved backup power at the current moment; inputting the difference into the integral controller, and superimposing the output of the integral controller into the power reference value of the active backup photovoltaic self-synchronizing voltage source, driving the photovoltaic unit to continuously increase power until all backup power is released.

6. A timing-frequency coordinated support control system for a photovoltaic and photovoltaic-storage self-synchronizing voltage source parallel system, comprising a memory, a processor, and a computer program stored in the memory; characterized in that, The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 5.

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