Coordination control method based on photovoltaic energy storage SOC safety limit

Abstract

The invention discloses a coordination control method based on a photovoltaic energy storage SOC safety limit. The method comprises the following steps: acquiring key information such as photovoltaic maximum output power Ppvmax, energy storage battery input and output power Pbat, load power Pref, energy storage battery maximum capacity and SOC value in a photovoltaic power generation and energy storage unit; the SOC value of the energy storage battery is calculated in real time, and the relation between the maximum output power Ppvmax of the photovoltaic unit and the load power Pref is judged; according to different conditions of photovoltaic maximum output power Ppvmax, load power Pref and SOC, a strategy of combining MPPT control and power reduction control is adopted, and the system is divided into five operation modes. Through the coordination control strategy, the maximum photovoltaic power generation is ensured, the battery is prevented from being overcharged or overdischarged at the same time, the energy management of the photovoltaic energy storage system is optimized, and the stability and efficiency of the system are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of photovoltaic energy storage, and specifically is a coordinated control method based on the SOC safety limit of photovoltaic energy storage. Background Art

[0002] With the continuous growth of global energy demand and the enhancement of environmental protection awareness, photovoltaic power generation, as a green, clean and renewable energy, has been widely studied and applied. However, photovoltaic power generation is intermittent and volatile, and its output power is greatly affected by factors such as light intensity and weather conditions, making it difficult to directly meet load demand and stabilize the operation of the power grid. Therefore, introducing energy storage units in photovoltaic systems has become an important means to solve this problem.

[0003] Energy storage units (such as lithium batteries or other electrochemical energy storage devices) can store the surplus energy of photovoltaic power generation and provide supplementary energy to the load or grid when the photovoltaic output is insufficient, thereby improving the stability and energy utilization efficiency of the system. However, the state of charge of the energy storage battery directly affects its charging and discharging performance, safety and service life. When the SOC of the battery is too high or too low, it may cause overcharging or over-discharging of the battery, and even cause safety hazards.

[0004] The comparison with the existing technology is as follows:

[0005] Technical comparison with patent CN117913772A "A DC microgrid energy management control strategy based on energy storage battery SoC"

[0006] 1. Patent CN117913772A proposes an adaptive droop control strategy based on the state of charge (SoC) of the energy storage module-battery, which maintains the DC bus voltage and the SoC of the energy storage module within a safe operating range. This patent proposes a combination of the advantages of MPPT control and power reduction control, which solves the problem of battery overcharge or over-discharge that may be caused by MPPT control alone, and also avoids the occurrence of light abandonment under power reduction control alone, thus achieving an organic unity of power generation efficiency and energy storage safety. There are essential differences in the technical goals of the two.

[0007] 2. Patent CN117913772A proposes that when the DC bus voltage is too low or normal, the photovoltaic generator will seamlessly return to the MPPT mode to provide power support; if the DC bus voltage is too high, the photovoltaic generator will seamlessly return to the PL mode to avoid overcharging the battery. This patent proposes that in order to prevent the energy storage battery from being overcharged or over-discharged for a long time, the working mode of the photovoltaic system will be adaptively adjusted according to the state of charge (SOC) of the energy storage battery to ensure that the battery SOC is always within a safe range. There is an essential difference in the technical ideas of the two.

[0008] 3. Patent CN117913772A proposes that the battery adaptive droop control strategy based on SoC is realized through PID dual-loop control. This patent combines MPPT control with power reduction control to dynamically coordinate the working status of photovoltaic power generation and energy storage system through a coordinated control strategy. There is an essential difference between the two at the control level.

[0009] Technical comparison with patent CN116094085A "A method for protecting energy storage batteries for microgrid energy management systems"

[0010] 1. Patent CN116094085A proposes a method for protecting energy storage batteries in microgrid energy management systems, which protects load faults based on power data and disconnection priority. This patent provides a coordinated control strategy based on the safety limit of photovoltaic energy storage SOC, which dynamically coordinates the working status of photovoltaic power generation and energy storage systems through the combination of MPPT control and power reduction control. There is an essential difference between the technical goals of the two.

[0011] 2. Patent CN116094085A obtains the maximum charging power, maximum discharging power, and first real-time power of the energy storage battery through the management control unit, obtains the second real-time power of the power supply, and obtains the third real-time power of the load, and stores the power data including the maximum charging power, maximum discharging power, first real-time power, second real-time power, and third real-time power in the corresponding register. This patent divides the photovoltaic microgrid into 5 operating modes based on the comparison between the maximum output power Ppvmax of the photovoltaic unit and the load power Pref and the value of SOC. There is an essential difference in the technical ideas of the two.

[0012] 3. Patent CN116094085A: When a power supply or load fails, the faulty power supply or load actively sends an alarm message to the management control unit through the alarm line. The management control unit urgently stops the faulty power supply or load through the emergency stop line, and disconnects the corresponding load or power supply based on the disconnection priority, thereby reducing the risk of discharge overload and charging overload of the energy storage battery. According to this patent, the photovoltaic system will switch the working mode according to the SOC of the energy storage battery. Under normal circumstances, the photovoltaic system preferentially operates in MPPT mode to maximize the utilization of light energy. When the photovoltaic power generation power Ppv is greater than the load power Pref and the SOC (Sbat) of the energy storage battery exceeds 20%, the photovoltaic system will switch to power limiting mode. Summary of the invention

[0013] In view of the above problems, the present invention proposes a coordinated control method based on the safety limit of photovoltaic energy storage SOC. Through the combination of MPPT control and power reduction control, the working status of photovoltaic power generation and energy storage system is dynamically coordinated, which not only improves the power generation efficiency of the photovoltaic system, but also ensures the safety and life of the energy storage battery, and at the same time enhances the adaptability of the photovoltaic system to complex operating conditions.

[0014] To achieve the above object, the technical solution adopted by the present invention is:

[0015] A coordinated control method based on photovoltaic energy storage SOC safety limit includes the following steps:

[0016] Step 1: Obtain key data of the photovoltaic and energy storage SOC control strategy from the photovoltaic and energy storage units, including the maximum output power P of the photovoltaic unit pvmax , energy storage battery input and output power P bat , load power P ref , the maximum capacity and SOC value of the energy storage battery itself;

[0017] Step 2: Calculate the SOC value of the energy storage battery and compare it with the measured maximum output power P of the photovoltaic unit. pvmax With load power P ref The size of the pass;

[0018] Step 3: According to the maximum output power P of the photovoltaic unit pvmax With load power P ref Based on the comparison of the size and SOC value, the photovoltaic and energy storage microgrid is divided into five operating modes.

[0019] As a further improvement of the present invention, in step 1, for the maximum output power P of the photovoltaic unit pvmax The measurement method is:

[0020] Through the perturbation observation method in the MPPT algorithm, the maximum power point is continuously tracked when the battery light and temperature are constantly changing, and the maximum output power P of the photovoltaic unit is obtained. pvmax .

[0021] As a further improvement of the present invention, the specific steps of step 2 are as follows:

[0022] Step 201:

[0023] Compare the maximum output power P of photovoltaic units pvmax With load power P ref The size relationship of

[0024] Compare the maximum output power P of photovoltaic units pvmax With load power P ref When P pvmaxGreater than or equal to P ref When P pvmax Less than P ref , it is necessary to supplement it through energy storage units to ensure that the load power is not affected and to avoid power outages or voltage fluctuations;

[0025] Step 202:

[0026] For the energy storage battery SOC value S bat The calculation method is:

[0027]

[0028] Where: SOC(0) is the initial state of charge of the energy storage unit; P bat is the output power of the energy storage unit; C e is the capacity of the energy storage unit;

[0029] Step 203:

[0030] The VSG control strategy is used to simulate the inertia and damping characteristics of synchronous generators to enhance the stability of the power system when a high proportion of renewable energy is connected;

[0031] The VSG controller equation is:

[0032]

[0033] Where: J——rotational inertia, kg·m 2 ;ω——system angular velocity, rad / s; P m ——Input mechanical power, kW; P e ——system output active power, kW; D——damping coefficient, N·m·s / rad; ω n ——system rated angular velocity, rad / s; θ——system power angle, (°); P ref ——active power reference value, kW; m——active power droop coefficient; E——VSG power loop output voltage, V; U n ——Rated voltage value, V; n——Reactive power droop coefficient; Q ref ——Reactive power reference value, kVar; Q e ——System output reactive power, kW; U m ——Actual voltage effective value, V; k u ——Integral coefficient.

[0034] As a further improvement of the present invention, the specific steps of step 3 are as follows:

[0035] The step 3 comprises:

[0036] Step 301:

[0037] Since the maximum power point has a nonlinear relationship with the light intensity, the power P is used. pv For voltage U pv The derivative of dP determines the position of its operating point on the PU curve. pv / dU pv =0, the system is considered to work in MPP;

[0038] Step 302:

[0039] Photovoltaic MPPT is to automatically optimize the maximum power point of photovoltaics, while the power limit mode is to make photovoltaics work at a position deviating from the maximum power point. Since the photovoltaic cell output PU curve has only one MPP, any power corresponds to two voltages U at the position deviating from the MPP. 1 and U 2 , the voltage at two locations and the voltage at the maximum power point U mpp The relationship between them is:

[0040]

[0041] Where: ΔU 1 and ΔU 2 They are the two voltages U corresponding to any power in the photovoltaic PU characteristic curve 1 and U 2 with U mpp The absolute value of the difference;

[0042] Step 303:

[0043] Photovoltaic storage unit collaborative control strategy:

[0044] Photovoltaic systems usually operate in maximum power tracking mode MPPT or power limiting mode. To prevent the energy storage battery from being overcharged or over-discharged for a long time, the working mode of the photovoltaic system will be adaptively adjusted according to the state of charge SOC of the energy storage battery to ensure that the battery SOC is always within a safe range;

[0045] According to the SOC of the energy storage battery, the photovoltaic system will switch the working mode. Under normal circumstances, the photovoltaic system will operate in the MPPT mode first to maximize the utilization of light energy. pv Greater than the load power P ref And the SOC (S bat ) exceeds 20%, the PV system will switch to power limiting mode;

[0046] Step 304:

[0047] The maximum output power P of the photovoltaic unit pvmax With load power P refThe size comparison and energy storage battery SOC (S bat ) value, the photovoltaic and energy storage microgrid is divided into five operation modes.

[0048] As a further improvement of the present invention, the five operating modes of the three photovoltaic energy storage micro-grids in step 3 are specifically as follows:

[0049] 1) When P pv >P ref And S bat When the temperature is higher than 80, the power reduction control is adopted and the energy storage battery is discharged;

[0050] The photovoltaic power is sufficient and the battery charge is high. At this time, the surplus power of the photovoltaic output is used to provide energy to the grid inverter. At the same time, the power output is limited to maintain energy balance. The system will reduce the power generation of the photovoltaic unit to avoid overcharging of the energy storage battery.

[0051] 2) When P pv >P ref And 50<S bat When ≤80, MPPT control is adopted and the energy storage battery is charged;

[0052] The battery charge is at a medium level and the photovoltaic power is sufficient. At this time, the photovoltaic unit gives priority to meeting the load demand, and the remaining power is mainly used to charge the energy storage battery. The battery charging power is dynamically adjusted according to the SOC to avoid overcharging and achieve efficient use of light energy;

[0053] 3) When P pv <P ref And 30<S bat When ≤50, MPPT control is adopted and the energy storage battery is discharged;

[0054] The battery charge is low and the photovoltaic power is insufficient to fully meet the load demand. At this time, the energy storage battery discharges to the outside to supplement the insufficient photovoltaic power to meet the load demand. The discharge power is dynamically adjusted according to the SOC to prevent the SOC from further decreasing and extend the battery life.

[0055] 4) When 20<S bat When ≤30, MPPT control is adopted and the energy storage battery is discharged;

[0056] The battery charge is low and only acts as a regulator to buffer photovoltaic fluctuations. It does not supply energy to the load. The photovoltaic unit outputs full power to meet the load demand first, and the remaining power is used through the inverter power supply network;

[0057] 5) When S bat When ≤20, MPPT control is adopted and the energy storage battery is charged;

[0058] The battery power is extremely low or exhausted and is only used for charging maintenance. At this time, the photovoltaic unit is used to charge the battery at full power, stops supplying energy to the load, and provides emergency power guarantee through the inverter when necessary.

[0059] Compared with the prior art, the beneficial effects of the present invention include at least:

[0060] The present invention proposes a coordinated control method based on the SOC safety limit of photovoltaic energy storage. The present invention uses MPPT control to track the maximum power point of photovoltaic modules in real time to maximize power generation efficiency. Through power reduction control, the output power is dynamically adjusted according to the SOC of the energy storage battery to avoid overcharging or over-discharging of the battery, protect the safety of the battery and extend its life. At the same time, the two control strategies are combined to reduce the abandonment of light through power reduction control when the power generation is in excess, optimize the energy storage release and load response when the power generation is insufficient, balance the energy distribution between photovoltaic power generation, energy storage and the power grid, and significantly improve the operating safety, economy and stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 :Structure diagram of photovoltaic and energy storage microgrid system;

[0062] Figure 2 : Flowchart of five working modes;

[0063] Figure 3 : Perturbation and observation model;

[0064] Figure 4 : Power reduction control algorithm;

[0065] Figure 5 : System simulation results when the battery state of charge reaches the upper limit;

[0066] Figure 6 : System simulation results when the battery state of charge reaches the lower limit. DETAILED DESCRIPTION

[0067] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0068] like Figure 1 As shown in the figure, this is a system structure of a coordinated control strategy based on the safety limit of photovoltaic energy storage SOC, including the following components: photovoltaic array, energy storage battery, BOOST converter, bidirectional DC / DC converter, coordinated control module, inverter, VSG control strategy, etc.

[0069] Photovoltaic array: Photovoltaic array is usually the core part of photovoltaic power generation system, and its function is to convert solar energy into electrical energy and output it.

[0070] Energy storage batteries: Energy storage batteries play a role in balancing power supply and demand in photovoltaic power generation systems, storing excess electricity and releasing electricity when there is insufficient sunlight or peak demand, thereby improving the reliability, stability and self-sufficiency of photovoltaic systems.

[0071] BOOST converter: used to boost the lower voltage direct current (DC) output by the photovoltaic array to a higher voltage to meet the charging needs of the energy storage battery or other load requirements.

[0072] Bidirectional DC / DC converter: Bidirectional DC / DC converter can realize bidirectional energy flow between photovoltaic cells and energy storage batteries. It can not only store the electricity generated by photovoltaics in the battery, but also release the stored electricity back to the system when demand peaks, thereby improving energy utilization efficiency and system stability.

[0073] Coordination control module: responsible for coordinating and optimizing the operation between various subsystems, ensuring that photovoltaics, energy storage, converters and inverters can work together to maximize system efficiency, avoid overcharging or over-discharging, and cope with load fluctuations.

[0074] Inverter: Converts DC power stored in the system (such as power from a photovoltaic array or battery) into alternating current (AC) and outputs it to the grid or load.

[0075] VSG control strategy: VSG control strategy improves the frequency stability and grid adaptability of renewable energy systems and enhances the reliability of power systems by simulating the inertia and regulation characteristics of synchronous generators.

[0076] The core idea of ​​the present invention is to ensure the maximum utilization of the photovoltaic power generation system while combining the state of the energy storage system to dynamically optimize the photovoltaic output and the energy storage charging and discharging process. By real-time monitoring of the energy storage SOC state, when the SOC is close to the safety upper limit, photovoltaic power generation switches from maximum power point tracking (MPPT) to power reduction control to avoid overcharging of the energy storage system. At the same time, when the load fluctuates, the energy storage system is used to provide power support to stabilize the system frequency and power balance. This strategy effectively realizes the efficient utilization of photovoltaic power generation and the safe operation of the energy storage system, and improves the stability and reliability of the system operation.

[0077] like Figure 2 As shown, the implementation steps of this method are as follows:

[0078] Step 1: Obtain key data of the photovoltaic and energy storage SOC control strategy from the photovoltaic and energy storage units, including the maximum output power P of the photovoltaic unit pvmax , energy storage battery input and output power P bat , load power P ref , the maximum capacity of the energy storage battery itself and the SOC value.

[0079] Step 2: Calculate the SOC value of the energy storage battery and compare it with the measured maximum output power P of the photovoltaic unit. pvmax With load power P ref The size relationship.

[0080] Step 3: According to the maximum output power P of the photovoltaic unit pvmax With load power P ref Based on the comparison of the size and SOC value, the photovoltaic and energy storage microgrid is divided into five operating modes.

[0081] Specifically, in step 1:

[0082] The maximum output power P of the photovoltaic unit pvmax The measurement method is:

[0083] Through the perturbation observation method in the MPPT algorithm, the maximum power point is continuously tracked when the battery light and temperature are constantly changing, and the maximum output power P of the photovoltaic unit is obtained. pvmax .

[0084] Specifically, in step 2:

[0085] Compare the maximum output power P of photovoltaic units pvmax With load power P ref The size relationship.

[0086] In order to ensure the stability of the system and the reliability of power supply, it is necessary to compare the maximum output power P of the photovoltaic unit. pvmax With load power P ref When P pvmax Greater than or equal to P ref When P pvmax Less than P ref , it is necessary to supplement it through energy storage units to ensure that the load power is not affected and to avoid power outages or voltage fluctuations.

[0087] For the energy storage battery SOC value S bat The calculation method is:

[0088]

[0089] Where: SOC(0) is the initial state of charge of the energy storage unit; P bat is the output power of the energy storage unit; C e is the capacity of the energy storage unit.

[0090] The VSG control strategy is used to simulate the inertia and damping characteristics of the synchronous generator to enhance the stability of the power system when a high proportion of renewable energy is connected.

[0091] The VSG controller equation is:

[0092]

[0093] Where: J——rotational inertia, kg·m 2 ;ω——system angular velocity, rad / s; P m ——Input mechanical power, kW; P e ——system output active power, kW; D——damping coefficient, N·m·s / rad; ω n ——system rated angular velocity, rad / s; θ——system power angle, (°); P ref ——active power reference value, kW; m——active power droop coefficient; E——VSG power loop output voltage, V; U n ——Rated voltage value, V; n——Reactive power droop coefficient; Q ref ——Reactive power reference value, kVar; Q e ——System output reactive power, kW; U m ——Actual voltage effective value, V; k u ——Integral coefficient.

[0094] Specifically, in step 3:

[0095] Since the maximum power point has a nonlinear relationship with the light intensity, the power P is used. pv For voltage U pv The derivative of dP determines the position of its operating point on the PU curve. pv / dU pv =0, the system can be considered to work in MPP.

[0096] Photovoltaic MPPT is to automatically optimize the maximum power point of photovoltaics, while the power limit mode is to make photovoltaics work at a position deviating from the maximum power point. Since the photovoltaic cell output PU curve has only one MPP, any power corresponds to two voltages U at the position deviating from the MPP. 1 and U 2 ,, Voltage at two locations and voltage at maximum power point U mpp The relationship between them is:

[0097]

[0098] Where: ΔU 1 and ΔU 2 They are the two voltages U corresponding to any power in the photovoltaic PU characteristic curve 1 and U2 with U mpp The absolute value of the difference.

[0099] Photovoltaic storage unit collaborative control strategy:

[0100] Photovoltaic systems usually operate in maximum power point tracking (MPPT) mode or power limiting mode. To prevent the energy storage battery from being overcharged or over-discharged for a long time, the working mode of the photovoltaic system will be adaptively adjusted according to the state of charge (SOC) of the energy storage battery to ensure that the battery SOC is always within a safe range.

[0101] According to the SOC of the energy storage battery, the photovoltaic system will switch the working mode. Under normal circumstances, the photovoltaic system will operate in MPPT mode first to maximize the use of light energy. pv Greater than the load power P ref And the SOC (S bat ) exceeds 20%, the PV system will switch to power limiting mode.

[0102] The maximum output power P of the photovoltaic unit pvmax With load power P ref The size comparison and energy storage battery SOC (S bat ) value, the photovoltaic and energy storage microgrid is divided into five operation modes;

[0103] 1) When P pv >P ref And S bat When it is higher than 80, the power reduction control is adopted and the energy storage battery is discharged.

[0104] The photovoltaic power is sufficient and the battery charge is high. At this time, the surplus power of the photovoltaic output is used to provide energy to the grid inverter, while limiting the power output to maintain energy balance. The system will reduce the power generation of the photovoltaic unit to avoid overcharging the energy storage battery.

[0105] 2) When P pv >P ref And 50<S bat When ≤80, MPPT control is adopted and the energy storage battery is charged.

[0106] The battery charge is at a medium level and the photovoltaic power is sufficient. At this time, the photovoltaic unit gives priority to meeting the load demand, and the remaining power is mainly used to charge the energy storage battery. The battery charging power is dynamically adjusted according to the SOC to avoid overcharging and achieve efficient use of light energy.

[0107] 3) When P pv <P ref And 30<S bat When ≤50, MPPT control is adopted and the energy storage battery discharges.

[0108] The battery charge is low and the photovoltaic power is insufficient to fully meet the load demand. At this time, the energy storage battery discharges to the outside to supplement the photovoltaic power that is insufficient to meet the load demand. The discharge power is dynamically adjusted according to the SOC to prevent the SOC from further decreasing and to extend the battery life.

[0109] 4) When 20<S bat When ≤30, MPPT control is adopted and the energy storage battery discharges.

[0110] The battery charge is low and only acts as a regulator to buffer photovoltaic fluctuations, but does not supply energy to the load. The photovoltaic unit outputs full power, giving priority to meeting the load demand, and the remaining power is used by the inverter power grid.

[0111] 5) When S bat When ≤20, MPPT control is adopted and the energy storage battery is charged.

[0112] The battery power is extremely low or exhausted and is only used for charging maintenance. At this time, the photovoltaic unit uses full power to charge the battery, stops supplying energy to the load, and provides emergency power guarantee through the inverter when necessary.

[0113] In the coordinated control strategy based on the SOC safety limit of photovoltaic energy storage proposed by the present invention, the MPPT control and power reduction control adopted are respectively as follows: Figure 3 and Figure 4 As shown. The MPPT control strategy is used to maximize the efficiency of photovoltaic power generation. By adjusting the working point of the photovoltaic system in real time, it ensures that the system always operates at the optimal power point to maximize the acquisition of solar energy. Power reduction control is used to ensure that the battery state does not exceed the safe SOC limit. When the battery SOC approaches the upper limit, the power reduction control automatically starts to reduce the photovoltaic power generation output, avoid battery overcharging, and ensure the safety of the energy storage battery and the long-term stable operation of the system. The coordinated work of the two realizes the optimized management of photovoltaic power generation and energy storage systems by real-time monitoring of battery SOC and photovoltaic power generation, maximizing system efficiency while ensuring the life of the battery and the stability of the power grid.

[0114] S bat When the upper limit is reached, the system response waveform is as follows Figure 5 As shown, at 1.5s, the system switches to working mode 2, and the battery output is approximately 0 power. bat Maintain around 80%.

[0115] S bat When the lower limit is reached, the system response waveform is as follows Figure 6 As shown, at 1.5s, the system switches to working mode 3, the base power of the converter system tracks the output power of the photovoltaic panel, and the battery outputs approximately 0 power. batMaintained at around 20%; at 2.5s, the photovoltaic output power decreases, and the converter system can still track the photovoltaic output.

[0116] The above description is only a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any modification or equivalent change made based on the technical essence of the present invention still falls within the scope of protection required by the present invention.

Claims

1. A coordinated control method based on the SOC safety limit of photovoltaic energy storage, characterized by: The following steps are involved: Step 1: Obtain key data of the photovoltaic and energy storage SOC control strategy from the photovoltaic and energy storage units, including the maximum output power P of the photovoltaic unit pvmax , energy storage battery input and output power P bat , load power P ref , the maximum capacity and SOC value of the energy storage battery itself; Step 2: Calculate the SOC value of the energy storage battery and compare it with the measured maximum output power P of the photovoltaic unit. pvmax With load power P ref The size of the pass; Step 3: According to the maximum output power P of the photovoltaic unit pvmax With load power P ref Based on the comparison of the size and SOC value, the photovoltaic and energy storage microgrid is divided into five operating modes.

2. The coordinated control method based on the photovoltaic energy storage SOC safety limit according to claim 1 is characterized in that: In step 1, for the maximum output power P of the photovoltaic unit pvmax The measurement method is: Through the perturbation observation method in the MPPT algorithm, the maximum power point is continuously tracked when the battery light and temperature are constantly changing, and the maximum output power P of the photovoltaic unit is obtained. pvmax .

3. The coordinated control method based on the photovoltaic energy storage SOC safety limit according to claim 1 is characterized in that: The specific steps of step 2 are as follows: Step 201: Compare the maximum output power P of photovoltaic units pvmax With load power P ref The size relationship of Compare the maximum output power P of photovoltaic units pvmax With load power P ref When P pvmax Greater than or equal to P ref When P pvmax Less than P ref , it is necessary to supplement it through energy storage units to ensure that the load power is not affected and to avoid power outages or voltage fluctuations; Step 202: For the energy storage battery SOC value S bat The calculation method is: Where: SOC(0) is the initial state of charge of the energy storage unit; P bat is the output power of the energy storage unit; C e is the capacity of the energy storage unit; Step 203: The VSG control strategy is used to simulate the inertia and damping characteristics of synchronous generators to enhance the stability of the power system when a high proportion of renewable energy is connected; The VSG controller equation is: Where: J——rotational inertia, kg·m 2 ;ω——system angular velocity, rad / s; P m ——Input mechanical power, kW; P e ——system output active power, kW; D——damping coefficient, N·m·s / rad; ω n ——system rated angular velocity, rad / s; θ——system power angle, (°); P ref ——active power reference value, kW; m——active power droop coefficient; E——VSG power loop output voltage, V; U n ——Rated voltage value, V; n——Reactive power droop coefficient; Q ref ——Reactive power reference value, kVar; Q e ——System output reactive power, kW; U m ——Actual voltage effective value, V; k u ——Integral coefficient.

4. The coordinated control method based on the photovoltaic energy storage SOC safety limit according to claim 1 is characterized in that: The specific steps of step 3 are as follows: The step 3 comprises: Step 301: Since the maximum power point has a nonlinear relationship with the light intensity, the power P is used. pv For voltage U pv The derivative of dP determines the position of its operating point on the PU curve. pv / dU pv =0, the system is considered to work in MPP; Step 302: Photovoltaic MPPT is to automatically optimize the maximum power point of photovoltaics, while the power limit mode is to make photovoltaics work at a position deviating from the maximum power point. Since the photovoltaic cell output PU curve has only one MPP, any power at the position deviating from the MPP corresponds to two voltages U1 and U2. The voltages at the two positions are proportional to the maximum power point voltage U1. mpp The relationship between them is: Where: ΔU1 and ΔU2 are the two voltages U1 and U2 corresponding to any power in the photovoltaic PU characteristic curve and U mpp The absolute value of the difference; Step 303: Photovoltaic storage unit collaborative control strategy: Photovoltaic systems usually operate in maximum power tracking mode MPPT or power limiting mode. To prevent the energy storage battery from being overcharged or over-discharged for a long time, the working mode of the photovoltaic system will be adaptively adjusted according to the state of charge SOC of the energy storage battery to ensure that the battery SOC is always within a safe range; According to the SOC of the energy storage battery, the photovoltaic system will switch the working mode. Under normal circumstances, the photovoltaic system will operate in the MPPT mode first to maximize the utilization of light energy. pv Greater than the load power P ref And the SOC (S bat ) exceeds 20%, the PV system will switch to power limiting mode; Step 304: The maximum output power P of the photovoltaic unit pvmax With load power P ref The size comparison and energy storage battery SOC (S bat ) value, the photovoltaic and energy storage microgrid is divided into five operation modes.

5. A coordinated control method based on photovoltaic energy storage SOC safety limit according to claim 4, characterized in that: The five operating modes of the three photovoltaic energy storage micro-grid plans in the steps are as follows: 1) When P pv >P ref And S bat When the temperature is higher than 80, the power reduction control is adopted and the energy storage battery is discharged; The photovoltaic power is sufficient and the battery charge is high. At this time, the surplus power of the photovoltaic output is used to provide energy to the grid inverter. At the same time, the power output is limited to maintain energy balance. The system will reduce the power generation of the photovoltaic unit to avoid overcharging of the energy storage battery; 2) When P pv >P ref And 50<S bat When ≤80, MPPT control is adopted and the energy storage battery is charged; The battery charge is at a medium level and the photovoltaic power is sufficient. At this time, the photovoltaic unit gives priority to meeting the load demand, and the remaining power is mainly used to charge the energy storage battery. The battery charging power is dynamically adjusted according to the SOC to avoid overcharging and achieve efficient use of light energy; 3) When P pv <P ref And 30<S bat When ≤50, MPPT control is adopted and the energy storage battery is discharged; The battery charge is low and the photovoltaic power is insufficient to fully meet the load demand. At this time, the energy storage battery discharges to the outside to supplement the insufficient photovoltaic power to meet the load demand. The discharge power is dynamically adjusted according to the SOC to prevent the SOC from further decreasing and extend the battery life. 4) When 20<S bat When ≤30, MPPT control is adopted and the energy storage battery is discharged; The battery charge is low and only acts as a regulator to buffer photovoltaic fluctuations. It does not supply energy to the load. The photovoltaic unit outputs full power to meet the load demand first, and the remaining power is used through the inverter power supply network; 5) When S bat When ≤20, MPPT control is adopted and the energy storage battery is charged; The battery power is extremely low or exhausted and is only used for charging maintenance. At this time, the photovoltaic unit is used to charge the battery at full power, stops supplying energy to the load, and provides emergency power guarantee through the inverter when necessary.

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