Optical storage cooperative inertia control method and system based on storage battery SOC

Abstract

The invention relates to a storage battery SOC-based light storage cooperative inertia control method and system, which is applied to an energy storage system and a photovoltaic system, and comprises the following steps: for the photovoltaic system, on the basis of a photovoltaic battery output power curve, taking the right side of a maximum power point as a stable working area; the output power of the photovoltaic cell is adjusted to be close to a stable working point by applying input voltage disturbance, the stable working point is close to the maximum power point, and voltage-power has a negative feedback characteristic; for the energy storage system, the running state of the energy storage system is divided into a deep discharge area, a stable working area and an overcharge limiting area according to the SOC value of the storage battery; for an energy storage system, on the premise that the maximum power output of a photovoltaic cell is greater than the load demand, the virtual inertia is adjusted in real time according to the current SOC partition of a storage battery; and the photovoltaic system responds to the inertia demand of the energy storage system, adjusts the output power through variable power tracking, and cooperates with the output power of the storage battery to realize virtual inertia support.

Description

Technical Field

[0001] This invention relates to the field of virtual inertia compensation technology, and in particular to a method and system for photovoltaic-storage cooperative inertia control based on a battery SOC. Background Technology

[0002] Photovoltaic (PV) power generation, with its advantages of low cost and flexible deployment, has become one of the most promising renewable energy sources. In microgrids with a high proportion of renewable energy integration, PV systems are connected to the grid via power electronic converters, undertaking frequency and voltage regulation functions to maintain system stability. However, the coordinated operation of PV power generation with traditional synchronous generators poses a greater challenge to its reliability. In recent years, researchers have proposed the virtual synchronous generator (VSG) control method, which is widely regarded as an important means to improve the stability of high-penetration PV power generation systems. The virtual synchronous generator (VSG) provides virtual inertia support to the grid by simulating the rotor dynamic characteristics of a synchronous generator, effectively suppressing system frequency fluctuations.

[0003] In microgrids with a high proportion of photovoltaic (PV) grid connection, PV power generation units typically operate in derating mode rather than continuously maintaining maximum power output to ensure sufficient system regulation margin. Existing research has attempted to reserve regulation capacity using master-slave or sensor-based methods, but this forced deviation from the maximum power point (MPP) leads to power waste, reduced energy efficiency, and decreased decarbonization effectiveness. Some literature addresses PV volatility by maintaining the PV system's output power at a rated proportion of its maximum power point to ensure reserve capacity. However, these methods do not endow the PV system with frequency and voltage regulation capabilities. Other methods utilize energy storage devices to compensate for the insufficient dynamic regulation capabilities of PV systems, but relying solely on energy storage increases investment and maintenance costs, and the relatively independent nature of PV power generation and energy storage fails to achieve coordinated control between PV and energy storage.

[0004] In summary, there is currently a lack of a method and system for coordinating optical and energy storage inertia control to solve or partially solve the aforementioned problems. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the existing technology and provide a photovoltaic-storage coordinated inertia control method and system based on battery SOC, so as to solve or partially solve the technical problems in microgrids with a high proportion of photovoltaic grid connection, such as the failure of virtual inertia control due to excessively high or low battery SOC, the easy occurrence of power waste, increased investment and operation and maintenance costs, and lack of frequency and voltage regulation capabilities of photovoltaics.

[0006] The objective of this invention can be achieved through the following technical solutions: One aspect of the present invention provides a photovoltaic-storage coordinated inertia control method based on battery SOC, applicable to energy storage systems and photovoltaic systems, the method comprising the following steps: For the photovoltaic system, based on the output power curve of the photovoltaic cell, the right side of the maximum power point is taken as the stable operating region. The output power of the photovoltaic cell is adjusted to be closer to the stable operating point by applying an input voltage disturbance. The stable operating point is close to the maximum power point and the voltage-power has negative feedback characteristics. For the energy storage system, its operating state is divided into a deep discharge zone, a stable operating zone, and an overcharge restriction zone based on the battery's SOC value. For the energy storage system, under the premise that the maximum power output of the photovoltaic cell is greater than the load demand, the virtual inertia is adjusted in real time according to the current SOC partition of the battery to ensure that the energy storage system can provide effective inertia response under different SOC states. The photovoltaic system responds to the inertia requirements of the energy storage system by adjusting its output power through variable power tracking, and works in coordination with the output power of the battery to achieve virtual inertia support.

[0007] As a preferred technical solution, if the battery SOC value is in the range of (0, 20%), it is classified as a deep discharge zone; if the battery SOC value is in the range of (20%, 90%), it is classified as a stable operating zone; and if the battery SOC value is in the range of (90%, 100%), it is classified as an overcharge restriction zone.

[0008] As a preferred technical solution, a battery SOC recovery step is also included: When the battery's SOC is in the deep discharge or overcharge limit region, the backup power of the photovoltaic system is used to regulate the battery's SOC through the VPPT algorithm, so that the battery's SOC can be restored to the stable operating region.

[0009] As a preferred technical solution, the stable operating point of the photovoltaic cell is set at 0.9 times the maximum power point, and its adjustable power range is determined by the DC capacitor voltage fluctuation range.

[0010] As a preferred technical solution, the real-time adjustment of virtual inertia based on the current SOC partition of the battery is achieved using the following formula: in, The virtual inertia of the virtual synchronous generator; The damping coefficient of the photovoltaic-storage VSG is given under different charge / discharge zones. When the battery's state of charge (SOC) is in the bidirectional charge / discharge zone... When the battery's SOC is in the unidirectional charging zone, When the battery's state of charge (SOC) is in the unidirectional discharge zone, ; This represents the system's maximum load power. This represents the current load power requirement. This is the maximum discharge current of the battery; , These are the maximum allowable port voltage and the minimum allowable port voltage, respectively. This represents the maximum load power change in the system. Indicates the state of charge (SOC) of the battery; The maximum acceptable virtual inertia value; k p This is the droop coefficient of the diesel generator governor. H g Let be the inertia constant of the diesel generator; This is the delay coefficient for the primary frequency regulation of the diesel generator.

[0011] As a preferred technical solution, the battery faces the following constraints during the adjustment of virtual inertia: in, This is the battery discharge current. This is the maximum power of the battery. , All are open-circuit voltages of the battery.

[0012] As a preferred technical solution, the open-circuit voltage model of the battery is as follows: .

[0013] As a preferred technical solution, the method of adjusting the output power through variable power tracking includes: When the maximum output power of the photovoltaic system exceeds the current load demand, the photovoltaic system is in power surplus mode. The system adjusts its operation to the stable operating point through the VPPT algorithm to reserve backup power. When the maximum output power of the photovoltaic system is less than the current load demand, the photovoltaic system switches to the maximum power point and the battery supplements the power deficit to maintain inertia support.

[0014] Another aspect of the present invention provides a photovoltaic-storage cooperative inertia control system based on a battery SOC, for implementing the aforementioned photovoltaic-storage cooperative inertia control method, comprising: Photovoltaic subsystem, including photovoltaic cells; Energy storage subsystem, including batteries; The photovoltaic cell operating point adjustment module is used to adjust the output power of the photovoltaic cell based on the output power curve of the photovoltaic cell, taking the right side of the maximum power point as the stable operating region, by applying input voltage perturbation to make the operating point close to the maximum power point and the voltage-power have negative feedback characteristics. The inertia response adjustment module is used to divide the operating state of the battery into a deep discharge zone, a stable operating zone, and an overcharge limit zone according to the battery's SOC value. Under the premise that the maximum power output of the photovoltaic cell is greater than the load demand, the virtual inertia is adjusted in real time according to the current SOC zone of the battery to ensure that the energy storage system can provide effective inertia response under different SOC states. The variable power tracking module is used by the photovoltaic system to respond to the inertia demand of the energy storage system. It adjusts the output power through variable power tracking and works in coordination with the output power of the battery to achieve virtual inertia support.

[0015] As a preferred technical solution, the battery is a lead-acid battery.

[0016] Compared with the prior art, the present invention has at least one of the following beneficial effects: (1) Ensuring optimal inertia frequency regulation: This invention divides the operating state of the battery into a deep discharge zone, a stable operating zone, and an overcharge limit zone based on the battery's SOC value. For the energy storage system, under the premise that the maximum power output of the photovoltaic cell is greater than the load demand, the virtual inertia is adjusted in real time according to the current SOC zone of the battery to ensure that the energy storage system can provide effective inertia response under different SOC states. By using the VPPT algorithm to reasonably regulate the battery SOC when the battery SOC is in the unidirectional charge and discharge zone, it is kept in the bidirectional charge and discharge zone to ensure that the system always works in the optimal inertia frequency regulation state when dealing with frequency drops or rises caused by load switching.

[0017] (2) Reduce waste and cost, and improve utilization rate: In this invention, the photovoltaic system dynamically adjusts the operating point based on load demand and energy storage inertia demand through the VPPT algorithm. When there is a power surplus, it operates at the stable operating point on the right (0.9 times the maximum power point) to reserve backup power. When there is a power deficit, it switches to the maximum power point and works in coordination with the battery output power to provide virtual inertia for the AC system. This avoids the energy waste caused by forced deviation from MPP, and gives the photovoltaic system frequency and voltage regulation capabilities. At the same time, it reduces the single dependence on energy storage equipment, reduces system investment and operation and maintenance costs, and improves the overall energy utilization efficiency and decarbonization effect.

[0018] (3) Reduce the risk of voltage collapse: In this invention, the right side of the photovoltaic output power curve is selected as the stable operating area to ensure the negative feedback characteristic of power increase when the voltage drops. By applying periodic small-amplitude voltage disturbances, the operating point is gradually corrected by detecting the power change trend, so that the operating point is close to MPP, thereby reducing the risk of voltage collapse. At the same time, the load response speed is improved by using a larger power-voltage slope, which enhances the operational stability and provides a reliable photovoltaic power basis for photovoltaic-storage collaborative inertia control. Attached Figure Description

[0019] Figure 1 This is a flowchart of the photovoltaic-storage cooperative inertia control method based on battery SOC in the embodiment; Figure 2 This is a schematic diagram of the PV output power curve in the embodiment; Figure 3 This is a schematic diagram of a simplified battery model in the embodiment; Figure 4 This is a schematic diagram illustrating the SOC operating characteristics of the battery in the embodiment; Figure 5 This is a schematic diagram of the battery Udc control in the embodiment; Figure 6 This is a schematic diagram of the photovoltaic-storage collaborative inertial control system based on a battery SOC in the embodiment. Figure 7 This is a diagram of the microgrid structure of the diesel-photovoltaic-storage system in the embodiment; Figure 8 This is a schematic diagram of a simplified frequency analysis model used in the embodiments. Figure 9 A schematic diagram of the feasible range of VSG inertia parameters; Figure 10 A schematic diagram showing the maximum active power output deviation of the VSG within the feasible range of inertia parameters; Figure 11 A schematic diagram of energy storage configuration and adaptive inertia control strategy. Detailed Implementation

[0020] 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, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0021] Example 1 To address the problems existing in the prior art, this embodiment provides a photovoltaic-storage coordinated inertia control method based on battery SOC. The method aims to adjust the virtual inertia control parameters of the battery in real time according to the battery SOC, so as to ensure that the energy storage can provide effective inertia response under different states of charge, and avoid control failure due to excessively high or low SOC. The photovoltaic system adjusts its output in accordance with the inertia requirements of the energy storage, thus complementing the energy storage.

[0022] 1. Mathematical model of diesel-photovoltaic-storage microgrid.

[0023] In a diesel-photovoltaic-storage microgrid, photovoltaic power generation units and energy storage batteries are connected in parallel on the DC side and connected to the AC bus via an inverter employing virtual synchronous generation control. Together with the diesel synchronous generators in the microgrid, they share the tasks of frequency support and AC load power supply. A typical topology is as follows: Figure 7 As shown, the photovoltaic power generation unit and energy storage battery are connected to the local load and synchronous generator through a boost circuit, inverter, RL filter, and line impedance. Together with the boost converter circuit, it can be considered equivalent to the prime mover section of the synchronous generator, not only providing power to meet load demands but also undertaking the function of inertial frequency modulation power output.

[0024] A virtual synchronous generator provides virtual inertia by simulating the rotor motion equations of a synchronous generator. Assuming the pole pair number is 1, its mathematical model can be expressed as: in, δ For VSG's offensive role, J For rotational inertia, w 0 represents the grid synchronization angular velocity. T m , T e , T d These represent mechanical torque, electromagnetic torque, and damping torque, respectively. P For VSG output power, D Let be the damping coefficient. In equation (1), the moment of inertia is... J Inertial time constant is a physical quantity closely related to the system size, and its magnitude typically increases with the increase of the rated power of the equipment. H The inertia level, which can be used to measure the system, is defined as: H=Jw 0 2 / S n ,in S n This refers to the rated capacity of the synchronous generator. Based on this, this paper combines... Figure 7Based on the characteristics of the diesel generator speed governor and the photovoltaic-storage VSG in the diesel-photovoltaic-storage microgrid structure shown, a generalized and simplified frequency analysis model was constructed to study the frequency response and power distribution characteristics of the diesel generator-VSG system under load fluctuation conditions. The overall model framework is as follows: Figure 8 As shown.

[0025] Depend on Figure 8 It can be deduced that from load disturbance P load to system angular frequency deviation w g and the active power output of the photovoltaic-storage VSG P vsg The transfer functions are as follows: in, This represents the delay factor for the primary frequency regulation of the diesel generator. H g Let be the inertia constant of the diesel generator. k p This is the droop coefficient of the diesel generator governor. H vsg The virtual inertia coefficient of the optical-storage VSG. D vsg denoted as the damping coefficient of the photovoltaic-storage VSG.

[0026] 2. Photovoltaic cell control strategy.

[0027] The output characteristics of photovoltaic cells directly affect the operating status of photovoltaic-virtual generators (PV-VSG), where the current load demand power... P laod The intersection points with the photovoltaic cell output curve are B and C. The photovoltaic cell power output curve is shown below. Figure 2 As shown.

[0028] To ensure system stability, photovoltaic output power must possess negative feedback characteristics, meaning that power increases when voltage decreases. For example... Figure 2 As shown, operation at point C may lead to voltage collapse, while point B not only avoids this problem but also has a larger power-voltage slope, providing a faster load response. Therefore, this embodiment selects the right side of the curve as the stable operating region. The control process is as follows: starting from the initial state, input voltage perturbations are repeatedly applied, and the voltage is excited by the photovoltaic cells. U pv Changes alter the output power of photovoltaic cells P out This makes the final operating point close to the maximum power point.

[0029] 3. Battery DC / DC model.

[0030] Lead-acid batteries are widely used in grid-connected virtual synchronous generator (VSRG) systems due to their high energy density and low cost. This embodiment uses a typical electrochemical model to analyze their charge-discharge characteristics and their impact mechanism on the dynamic response and control parameter optimization of the VSG system. During charge-discharge, the electrical characteristic parameters (terminal voltage, internal resistance) of the lead-acid battery exhibit dynamic characteristics with changes in state of charge (SOC).

[0031] The equivalent battery model block diagram of this embodiment is as follows: Figure 3 As shown, the battery is designed as a voltage source and an internal output resistor ( A series circuit is constructed where the voltage source voltage depends on the battery's state of charge (SOC), and its expression with respect to SOC is shown below: In the formula, Open circuit voltage, , These are the maximum operating port voltage and the minimum allowable port voltage, respectively. This indicates the battery is in SOC (State of Charge) state.

[0032] Battery internal resistance The voltage drop is usually small, and during battery operation, it is generally negligible. Therefore, the battery output voltage is... Based on the relationship curve between battery port voltage and SOC, the charging and discharging process under different SOC states can be divided into three regions.

[19] ,like Figure 4 As shown.

[0033] The SOC-voltage characteristics of lead-acid batteries can be divided into three characteristic regions: (1) Deep discharge region (SOC∈(0,20%)): The port voltage is lower than the discharge cutoff threshold, exhibiting exponential decay characteristics, and only supports charging operation.

[0034] (2) Stable operating range (SOC∈(20%,90%)): The port voltage is roughly linearly related to SOC, and the battery can perform bidirectional charging and discharging operations.

[0035] (3) Overcharge restriction zone (SOC∈(90%,100%)): The port voltage exceeds the charging cutoff voltage threshold and increases exponentially, the charging function is limited, and only the discharging operation is supported.

[0036] Under high current, the lifespan of a battery is often significantly shortened, and prolonged exposure can lead to overheating or even fire. Therefore, when a battery supplies power to a load, its discharge current should be carefully controlled. Less than the maximum allowable discharge current Battery DC / DC converter constant voltage control, such as... Figure 5 As shown.

[0037] By storage battery According to the control strategy, the following applies to the battery current: Therefore, the charging and discharging power limit of the battery is: in, This is the battery discharge current. This is the maximum power of the battery. This is the open-circuit voltage of the battery.

[0038] 4. System inertia frequency adjustment requirements.

[0039] This embodiment constructs a system based on the dynamic characteristics of diesel generators, microgrid frequency stability indicators, and VSG power-energy constraints. H vsg and D vsg The feasible region analytical model of the parameters. To reduce power overshoot, fully utilize the power transmission capacity boundary of energy storage, and avoid excessive oscillations, the system operating point is designed in the critical damping or overdamped region. The frequency stability of the microgrid is characterized by two key indicators during the transient process: the maximum frequency deviation and the maximum rate of frequency change, which are mathematically defined as follows: Inertia control of the diesel-photovoltaic-storage microgrid under extreme maximum power disturbance D P load.max In this case, for VSG inertia parameters ( H vsg and D vsg The tuning requirements are proposed. The control objective is to satisfy the frequency safety constraint under the most unfavorable disturbance, that is, to maintain the critical damping / overdamping of the frequency dynamic response and the maximum rate of frequency change. R oCoFmax Deviation from maximum frequency |D f nadir.max All remain within the preset threshold range.

[0040] As can be seen from the formula of the diesel-photovoltaic-storage microgrid mathematical model mentioned above, the rate of frequency change is at the initial instant of the disturbance application. Therefore, the maximum frequency change rate is: The time-domain analytical expression for the system's angular frequency is: in, From the time-domain analytical expression of the system's angular frequency, the system's maximum frequency deviation |D f nadir.max |and their corresponding times t nadir They are respectively: The maximum frequency change rate limit in the formula for the comprehensive maximum frequency change rate | R oCoF.max | lim Maximum frequency deviation limit |D f nadir.max | lim The required VSG inertia parameters can be obtained. H vsg and D vsg The constraints are: The maximum frequency change rate limit and the maximum frequency deviation limit can be determined according to the distributed power generation grid connection technical specifications and microgrid power quality standards.

[30] Determined. Therefore, the constraint is satisfied. H vsg and D vsg Feasible range of parameters, such as Figure 9 As shown.

[0041] 5. Battery configuration requirements.

[0042] For a photovoltaic-storage VSG system using VPPT control, the active power D output by the photovoltaic-storage VSG is... P vsg The time-domain analytical solution of the active power output of the VSG under load fluctuations can be derived from the transfer function formula, and its peak value is denoted as D. P vsg.max From the initial value theorem, we can obtain the result at the instant the load disturbance is applied. The active power output of the VSG is: The time-domain analytical expression for the active power output of the VSG is: From the formula for the active power output of VSG, it can be seen that the maximum active power output deviation of the photovoltaic-storage VSG system is |D P vsg.max |and their corresponding times t vsg.max They are respectively: By combining the feasible range of VSG inertia parameters with the relationship between the VSG maximum active power output deviation and inertia parameters, the maximum active power output deviation of the VSG within the feasible range of inertia parameters can be obtained, such as... Figure 10 As shown.

[0043] Depend on Figure 10 It can be seen that, under the condition that the maximum frequency change rate limit and the maximum frequency deviation limit both meet the power system frequency standard requirements during the maximum load step fluctuation, the maximum active power output deviation required by the VSG can be determined, as well as the corresponding value when the system is in a critical damping state. H vsg and D vsg Parameter values.

[0044] For photovoltaic-storage VSG systems, considering the operating characteristics of photovoltaic power generation units near their maximum power point, U MMP ~ U pv3 The voltage range is considered the operating domain. To characterize the boundary / relationship curves of this domain, several data points are given. p i =( x i, y i ()( i Construct curves using implicit curve fitting methods for (e.g., 1, 2, ..., n). in, a , b , c , d This corresponds one-to-one with the solar irradiance S and ambient temperature T of the photovoltaic power generation unit at this moment. For example... Figure 2 As shown, for the VPPT algorithm of a photovoltaic power generation unit, its maximum output power fluctuation is determined by the PV output power curve and the DC capacitor voltage fluctuation range. Regarding the DC capacitor voltage: Therefore, the maximum power fluctuation range of a photovoltaic power generation unit is: in, P pv For the PV output power fluctuation range, P load The DC capacitor voltage is U pv2 PV output power P mmpThe DC capacitor voltage is U MMP The PV output power at that time. And according to the maximum charge / discharge power limit formula, the maximum power fluctuation range of the battery is... Since the inertia frequency modulation time is short, this paper assumes that the change in battery SOC is negligible during a single inertia frequency modulation process. The maximum active power output deviation of the photovoltaic-storage VSG control system depends only on the maximum charge and discharge power of the battery and the maximum power fluctuation range of the photovoltaic cell. Therefore, the maximum active power output deviation of the photovoltaic-storage VSG control system is: Maximum active power output deviation of the integrated photovoltaic-storage VSG system |D P vsg.max |and their corresponding times t vsg.max Therefore, we can find the answer to the above equation. Based on the standard voltage state of the battery's operating range, the maximum current limit of the battery can be calculated as follows: Ultimately, the battery configuration can be completed in an integrated manner according to the following logic: First, based on the required VSG inertia parameters... H vsg and D vsg Constraints, in R oCoFmax With |D f nadir Determined under constraints H vsg and D vsg The feasible region; then, within this feasible region, the maximum active power output deviation |D of the photovoltaic-storage VSG system is utilized. P vsg.max |and their corresponding times t vsg.max Calculate the maximum active power output deviation |D of the VSG. P vsg.max | This yields the peak power demand that the energy storage needs to withstand under the most unfavorable disturbance; then, combining the battery open-circuit voltage-SOC characteristics and the allowable voltage fluctuation on the DC side, the maximum discharge / charge current limit of the battery is calculated based on the battery's maximum current limit. I batt.dischar.max , I batt.char.max And based on this, the maximum power that the energy storage side can provide / absorb is obtained. P batt.max ( SOC )=U oc ( SOC ) min{ I batt.dischar.max , I batt.char.max (While simultaneously satisfying the inverter's rated power / current constraints), the battery capacity is ultimately configured at 0.5C according to the frequency regulation condition, enabling it to operate continuously for 2 hours under maximum power output conditions, thereby achieving the required frequency stability performance while satisfying the power-energy boundary.

[0045] 4. Photovoltaic-storage co-inertia control based on battery SOC.

[0046] Based on the analysis of the "frequency-inertia parameter" relationship in the previous section, we know that: virtual inertia H vsg The larger, R oCoF The smaller the value; the damping coefficient D vsg The larger D is f nadir The smaller. (Combination) Figure 10 Furthermore, it can be seen that the maximum active power output deviation of the photovoltaic-storage VSG system is |D P vsg.max The larger the value, the more permissible it is. H vsg and D vsg The wider the range of values, the better. Therefore, the optimal match can be selected for different SOC conditions. H vsg and D vsg These parameters can effectively improve the frequency stability of microgrids while meeting power / energy constraints.

[0047] There are two typical operating modes for photovoltaic virtual synchronous generators: (1) When the maximum output power of photovoltaics is greater than the load demand, the photovoltaic power is in surplus mode. Given that high-penetration photovoltaic systems generally have sufficient power generation capacity, PV-VSGs usually do not need to maintain maximum power output and can flexibly adjust the operating point. (2) When the maximum output power of photovoltaics is less than the load demand, the photovoltaic power is in deficit mode. At this time, the photovoltaic system needs to operate at the maximum power point (MPP). However, in series-type high-penetration grid-connected systems, the multi-unit collaborative operation mechanism can effectively balance the power deficit, which significantly reduces the probability of a single unit operating above MPP.

[0048] Therefore, this paper improves the control algorithm based on the first, more common operating state. Typically, point B in the photovoltaic VPPT algorithm operates at 0.9. The system load represents the power demand of the photovoltaic cells. The adjustable power range of the photovoltaic cells, determined by the DC capacitor voltage fluctuation range, and the adjustable power range of the storage battery, determined by its capacity and SOC, are considered. Based on the characteristics of the photovoltaic cells and storage batteries within the photovoltaic-storage co-located VSG system, their maximum inertia supply capabilities are studied to rationally configure the storage battery capacity to meet the system's inertia requirements. For different battery SOC states, a battery SOC self-recovery strategy is developed. When the battery SOC is in the unidirectional charge / discharge zone, the VPPT algorithm is used to rationally regulate the battery SOC, maintaining it in the bidirectional charge / discharge zone. This ensures that the system operates in the optimal inertia frequency regulation state when the frequency drops or rises due to load switching.

[0049] The inertia of the VSG is adaptively controlled by the State of Charge (SOC) according to the following formula: When the maximum power output of the photovoltaic cell exceeds the load demand and the battery's state of charge (SOC) is in the bidirectional charge / discharge region... When the maximum power output of the photovoltaic cell exceeds the load demand and the battery's state of charge (SOC) is in the unidirectional charging zone, When the maximum power output of the photovoltaic cell exceeds the load demand and the battery's state of charge (SOC) is in the unidirectional discharge region, Among them are: in, This represents the system's maximum load power. The current load demand power, This represents the maximum load power change of the system. 6. Overall control method flow: See Figure 1 This method is applied to energy storage systems and photovoltaic systems, and includes the following steps: Step S1: For the photovoltaic system, based on the output power curve of the photovoltaic cell, the right side of the maximum power point is taken as the stable operating region. The output power of the photovoltaic cell is adjusted to be closer to the stable operating point by applying an input voltage disturbance. The stable operating point is close to the maximum power point and the voltage-power has negative feedback characteristics.

[0050] Specifically, the stable operating point of the photovoltaic cell is set at 0.9 times the maximum power point, and its adjustable power range is determined by the DC capacitor voltage fluctuation range. Step S2: For the energy storage system, the operating state is divided into a deep discharge zone, a stable operating zone, and an overcharge restriction zone based on the battery's SOC value.

[0051] Specifically, the division method is described in section 2, Battery DC / DC Model.

[0052] Preferably, when the battery's SOC is in the deep discharge region or the overcharge limit region, the backup power of the photovoltaic system is used to regulate the battery's SOC through the VPPT algorithm, so that the battery's SOC can be restored to the stable operating region.

[0053] Step S3: For the energy storage system, under the premise that the maximum power output of the photovoltaic cells is greater than the load demand, the virtual inertia is adjusted in real time according to the current SOC partition of the battery.

[0054] Specifically, the virtual inertia adjustment is described in section 3 above, "Photovoltaic-storage collaborative inertia control based on battery SOC." During the virtual inertia adjustment process, the battery is limited by battery current and charging / discharging power.

[0055] In step S4, the photovoltaic system responds to the inertia demand of the energy storage system by adjusting its output power through variable power tracking, and works in coordination with the output power of the battery to achieve virtual inertia support.

[0056] When the maximum output power of the photovoltaic system exceeds the current load demand, the photovoltaic system is in power surplus mode. The system adjusts its operation to the stable operating point through the VPPT algorithm to reserve backup power. When the maximum output power of the photovoltaic system is less than the current load demand, the photovoltaic system switches to the maximum power point and the battery supplements the power deficit to maintain inertia support.

[0057] Preferably, an energy storage configuration and adaptive inertia control strategy are as follows: Figure 11 As shown. Based on the existing traditional synchronous generators in microgrids, the inertia frequency regulation requirements of the system are first clarified according to the two key constraints of the system's maximum power fluctuation and frequency performance requirements. This leads to the following... Figure 9 The feasible range of VSG inertia parameters shown, and Figure 10 The maximum active power output deviation of the VSG within the corresponding interval is determined. Next, considering the installed capacity of the photovoltaic cells and the DC bus voltage variation range, the adjustable power range of the photovoltaic system under the VPPT algorithm is determined. Taking into account the system's inertia frequency regulation requirements and the adjustable power range of the photovoltaic system, the battery capacity configuration scheme is determined. Finally, an inertia adaptive control strategy is proposed: this strategy simultaneously considers the battery's SOC state and the photovoltaic-storage power output limitations imposed by the photovoltaic VPPT algorithm, ensuring that the diesel-photovoltaic-storage system always remains in a critical damping state, thereby achieving optimal frequency regulation performance.

[0058] 7. Simulation verification.

[0059] To verify the effectiveness of this method, a simulation model of a diesel-photovoltaic-storage system was built based on a simulation platform. The photovoltaic array is connected to the grid via a 50kVA inverter with a switching frequency of 20kHz. The inertia time constant of the diesel generator in the system is taken as 1.5s, and the governor droop coefficient is set to 60. The maximum fluctuation amplitude of the AC load is 40kW. For this diesel-photovoltaic-storage microgrid, the minimum allowable frequency ( f nadir ) and maximum frequency change rate ( R oCoF.max The constraints are 49.5Hz and 7Hz / s, respectively. Meanwhile, the battery port voltage varies from 200 to 300V within the bidirectional charge / discharge region. Based on the above system modeling and parameter settings, further analysis of frequency stability and inertia support characteristics was conducted. Combining frequency constraints and battery voltage operating ranges, the impact of energy storage capacity configuration and control strategies on system dynamic performance was explored to verify the effectiveness of the proposed method in improving the inertia frequency regulation capability of microgrids and ensuring frequency security. Simulations were performed under two conditions: (1) Considering the transient operating condition of a battery SOC of 20% and a maximum load disturbance of 40kW. The simulation results of the frequency and active power output of each module of the diesel-photovoltaic-storage system are as follows: Figure 9 As shown. Under given operating parameters, based on the SOC adaptive control formula, the VSG virtual inertia time constant and damping coefficient are set to 1.36s and 23.86, respectively. Based on the maximum current limit formula for the battery, the maximum current limit of the energy storage unit is 90A, and the maximum power output of the battery energy storage is 17.5kW. System simulation under a maximum load disturbance condition of 40kW.

[0060] The simulation results show that the maximum frequency change rate of the diesel-photovoltaic-storage system is... R oCoF.max With the lowest frequency point f nadir All system frequency requirements were met. Furthermore, the operating characteristics of the photovoltaic power generation unit under VPPT control and the maximum output power of the energy storage battery were fully utilized, as shown in Table 1. Therefore, it can be concluded that under a maximum load fluctuation of 40kW, all system frequency indicators met the requirements for safe operation.

[0061] (2) When the battery SOC is 50%. Considering the transient condition of a maximum load disturbance of 40kW, the maximum power output of the battery energy storage is 22.5kW, which can provide a large virtual inertia for the VSG. At this time, the VSG inertia damping parameters are 2.4s and 85.

[0062] Table 1 lists the values ​​of various indicators obtained from the simulation results. As can be seen from the table, when the system faces a 40kW load cutoff, all frequency indicators have reached the safety threshold, and the working characteristics of the photovoltaic-storage system are fully coordinated, giving full play to the system's inertial frequency modulation potential.

[0063] Table 1 Simulation conditions and results Simulation results verify the effectiveness of the VSG inertia and damping parameter configuration method and energy storage configuration strategy based on system frequency variation requirements in this embodiment. Furthermore, considering the different SOCs of the battery and the operating characteristics of the photovoltaic power generation units, the inertia frequency regulation capabilities of both are fully coordinated to maximize the system's optimal inertia frequency regulation capability.

[0064] In summary, this method studies the maximum inertia supply capacity of both photovoltaic cells and batteries within the photovoltaic-storage co-located VSG system based on their characteristics, and then rationally configures the battery capacity to meet the system's inertia requirements. For different battery SOC states, a battery SOC self-recovery strategy is developed. When the battery SOC is in the unidirectional charge / discharge region, the photovoltaic cells utilize the VPPT algorithm to rationally regulate the battery SOC, maintaining it in the bidirectional charge / discharge region. This ensures that the system always operates in the optimal inertia frequency regulation state when the frequency drops or rises caused by load switching.

[0065] Example 2 Based on Example 1, this example provides a photovoltaic-storage cooperative inertial control system based on a battery SOC. See [link to example]. Figure 6 ,include: (1) Photovoltaic subsystem, including photovoltaic cells.

[0066] (2) Energy storage subsystem, including batteries, which may be lead-acid batteries.

[0067] (3) Photovoltaic cell operating point adjustment module, which is used to adjust the output power of photovoltaic cell by applying input voltage disturbance based on the output power curve of photovoltaic cell, taking the right side of the maximum power point as the stable operating area, so that the operating point is close to the maximum power point and the voltage-power has negative feedback characteristics. (4) Inertia response adjustment module, which is used to divide the operating state of the battery into deep discharge zone, stable working zone and overcharge limit zone according to the SOC value of the battery. Under the premise that the maximum power output of the photovoltaic cell is greater than the load demand, the virtual inertia is adjusted in real time according to the current SOC zone of the battery. (5) Variable power tracking module, used to realize the photovoltaic system responds to the inertia demand of the energy storage system, adjusts the output power through variable power tracking, and works in coordination with the output power of the battery, and realizes virtual inertia support through limited operation or reserved backup.

[0068] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A photovoltaic-storage cooperative inertia control method based on battery SOC, characterized in that, Applied to energy storage systems and photovoltaic systems, the method includes the following steps: For the photovoltaic system, based on the output power curve of the photovoltaic cell, the right side of the maximum power point is taken as the stable operating region. The output power of the photovoltaic cell is adjusted to be closer to the stable operating point by applying an input voltage disturbance. The stable operating point is close to the maximum power point and the voltage-power has negative feedback characteristics. For the energy storage system, its operating state is divided into a deep discharge zone, a stable operating zone, and an overcharge restriction zone based on the battery's SOC value. For the energy storage system, under the premise that the maximum power output of the photovoltaic cells is greater than the load demand, the virtual inertia is adjusted in real time according to the current SOC partition of the battery. The photovoltaic system responds to the inertia requirements of the energy storage system by adjusting its output power through variable power tracking, and works in coordination with the output power of the battery to achieve virtual inertia support.

2. The photovoltaic-storage cooperative inertia control method based on battery SOC according to claim 1, characterized in that, If the battery's SOC value is in the range of (0, 20%), it is classified as the deep discharge zone; if the battery's SOC value is in the range of (20%, 90%), it is classified as the stable operating zone; if the battery's SOC value is in the range of (90%, 100%), it is classified as the overcharge restriction zone.

3. The photovoltaic-storage cooperative inertia control method based on battery SOC according to claim 2, characterized in that, It also includes battery SOC recovery steps: When the battery's SOC is in the deep discharge or overcharge limit region, the backup power of the photovoltaic system is used to regulate the battery's SOC through the VPPT algorithm, so that the battery's SOC can be restored to the stable operating region.

4. The photovoltaic-storage cooperative inertia control method based on battery SOC according to claim 1, characterized in that, The stable operating point of the photovoltaic cell is set at 0.9 times the maximum power point, and its adjustable power range is determined by the DC capacitor voltage fluctuation range.

5. The photovoltaic-storage cooperative inertia control method based on battery SOC according to claim 1, characterized in that, The real-time adjustment of virtual inertia based on the current SOC partition of the battery is achieved using the following formula: in, The virtual inertia of the virtual synchronous generator; The damping coefficient of the photovoltaic-storage VSG is given under different charge / discharge zones. When the battery's state of charge (SOC) is in the bidirectional charge / discharge zone... When the battery's SOC is in the unidirectional charging zone, When the battery's state of charge (SOC) is in the unidirectional discharge zone, ; This represents the system's maximum load power. This represents the current load power requirement. This is the maximum discharge current of the battery; , These are the maximum allowable port voltage and the minimum allowable port voltage, respectively. This represents the maximum load power change in the system. Indicates the state of charge (SOC) of the battery; The maximum acceptable virtual inertia value; k p This is the droop coefficient of the diesel generator governor. H g Let be the inertia constant of the diesel generator; This is the delay coefficient for the primary frequency regulation of the diesel generator.

6. The photovoltaic-storage cooperative inertia control method based on battery SOC according to claim 5, characterized in that, During the adjustment of virtual inertia, the battery is subject to the following constraints: in, This is the battery discharge current. This is the maximum power of the battery. , All are open-circuit voltages of the battery.

7. The photovoltaic-storage cooperative inertia control method based on battery SOC according to claim 6, characterized in that, The open-circuit voltage of the battery is modeled as follows: 。 8. The photovoltaic-storage cooperative inertia control method based on battery SOC according to claim 1, characterized in that, The aforementioned adjustment of output power via variable power tracking includes: When the maximum output power of the photovoltaic system exceeds the current load demand, the photovoltaic system is in power surplus mode. The system adjusts its operation to the stable operating point through the VPPT algorithm to reserve backup power. When the maximum output power of the photovoltaic system is less than the current load demand, the photovoltaic system switches to the maximum power point and the battery supplements the power deficit to maintain inertia support.

9. A photovoltaic-storage cooperative inertial control system based on a battery-powered system-on-a-chip (SOC), characterized in that, To implement the optical-storage cooperative inertia control method as described in any one of claims 1-8, the method includes: Photovoltaic subsystem, including photovoltaic cells; Energy storage subsystem, including batteries; The photovoltaic cell operating point adjustment module is used to adjust the output power of the photovoltaic cell based on the output power curve of the photovoltaic cell, taking the right side of the maximum power point as the stable operating region, by applying input voltage perturbation to make the operating point close to the maximum power point and the voltage-power have negative feedback characteristics. The inertia response adjustment module is used to divide the battery's operating state into a deep discharge zone, a stable operating zone, and an overcharge limit zone based on the battery's SOC value. Under the premise that the maximum power output of the photovoltaic cell is greater than the load demand, the virtual inertia is adjusted in real time according to the current SOC zone of the battery. The variable power tracking module is used by the photovoltaic system to respond to the inertia demand of the energy storage system. It adjusts the output power through variable power tracking and works in coordination with the output power of the battery to achieve virtual inertia support.

10. A photovoltaic-storage cooperative inertial control system based on a battery SOC according to claim 9, characterized in that, The battery in question is a lead-acid battery.

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