A control method for a DC microgrid system based on digital energy storage

Abstract

The present invention discloses a control method for a DC microgrid system based on digital energy storage, including: when the system operates normally, the output power of PCS1 is a power setting value, and the output power of PCS2 is the difference between the system power imbalance and the power setting value; when the DC load suddenly changes, the output power of PCS1 is automatically adjusted, and the instantaneous output response power is used to compensate for the power imbalance caused by the sudden change of the DC load, so as to achieve instantaneous system power balance; EMS sends a control command to adjust the output power of PCS2, and the output power of PCS1 automatically returns to the power setting value, so as to achieve steady-state system power balance; it also includes dynamically controlling the charging and discharging process of the energy storage system according to relevant parameters such as battery SOC, so as to effectively suppress bus voltage fluctuations. The present invention realizes power stability and voltage stability of the microgrid system by setting a reasonable power response mechanism and charging and discharging control strategy, and ensures the stable operation of the microgrid.

Description

Technical Field

[0001] The present invention relates to the technical field of microgrid intelligent control, and in particular to a control method for a direct current microgrid system based on digital energy storage. Background Art

[0002] Microgrid is a system unit composed of micro power source, load, energy storage system and control device. Traditional microgrid usually includes AC microgrid and DC microgrid system. Compared with AC microgrid, DC microgrid has uniqueness, diversity, controllability and interactivity, and has relative advantages with simple connection form, no need to consider voltage frequency phase, low cost and loss, etc. However, DC microgrid involves DC load systems such as energy storage and power generation, and the intelligent control and stable operation of the system is a very serious issue.

[0003] When a DC microgrid is operating in an isolated manner, the power balance in the grid seriously affects the power supply quality of the system, and in severe cases even causes system instability. If the voltage fluctuates greatly, the control effect and stability of each system in the grid will be reduced, and the power supply to the load end will be greatly affected. How to coordinate and control the power stability and voltage stability of the DC microgrid system has become a top priority. Summary of the invention

[0004] The present invention proposes a control method for a DC microgrid system based on digital energy storage, the purpose of which is to achieve power stability and voltage stability of the microgrid system and ensure the stable operation of the microgrid by setting a reasonable power response mechanism and charge and discharge control strategy.

[0005] The technical solution of the present invention is as follows:

[0006] A control method for a DC microgrid system based on digital energy storage, the DC microgrid system includes an energy storage management platform, EMS, PCS, energy storage system, photovoltaic system and DC load, the PCS is connected between the AC transformer and the DC bus, the energy storage system, photovoltaic system and DC load are respectively connected to the DC bus, the energy storage management platform collects signals from the PCS, energy storage system, photovoltaic system and DC load through the EMS and issues control commands, the PCS includes parallel PCS1 and PCS2. When the system is operating normally, the output power of PCS1 is the power setting value, and the output power of PCS2 is the system power imbalance value P i When the DC load changes suddenly, the output power of PCS1 is automatically adjusted, and the instantaneous output response power is used to compensate for the power imbalance caused by the DC load mutation, so as to achieve instantaneous system power balance, and EMS calculates the power imbalance P i A control command is issued to adjust the output power of PCS2, and the output power of PCS1 is automatically restored to the power setting value to achieve steady-state system power balance.

[0007] Furthermore, the control method of the DC microgrid system also includes a charge and discharge control method of an energy storage system, and the charge and discharge control method of the energy storage system includes the following steps:

[0008] First, the ratio η of the SOC of the i-th battery cell to the average SOC of all battery cells is calculated using the following formula: i :

[0009]

[0010] Where n is the number of battery cells in the energy storage system, SOC i is the state of charge of the ith battery cell.

[0011] Second, calculate the corrected droop coefficient K' of the i-th battery cell using the following formula: Ai :

[0012]

[0013] Among them, K Ai is the initial droop coefficient of the i-th battery cell, I A (i) is the bus side current.

[0014] Third, calculate the output voltage U of the i-th battery cell using the following formula: dc (i)

[0015]

[0016] Among them, U H1 The voltage threshold for droop charging, I Amin is the voltage threshold when the system power is seriously over-surplus, U L1 is the voltage threshold of droop discharge, I Amax It is the current threshold when the system power is seriously insufficient.

[0017] Fourth, the energy storage system dynamically adjusts the droop coefficient according to the battery SOC, and sets U H1 , U H2 ,I Amin , U L1 , U L2 ,I Amax The corresponding threshold parameters control the charging DC voltage of each battery cell at U H1 and U H2 The discharge voltage is controlled between U L1 and U L2 Among them, U H2 is the voltage threshold at which the system enters severe overpower control, U L2The voltage threshold at which the system enters severe underpower control.

[0018] Furthermore, the power setting value is greater than 0 and less than the rated power of PCS1.

[0019] Furthermore, during the operation of the system, the discharge power of the energy storage system is set to the minimum value among: the set power value of PCS1, the maximum discharge value of the supporting microgrid system uploaded by the energy storage system BMS to the EMS, and the difference between the total exchange power limit of the DC microgrid system and the power generation value of the photovoltaic system.

[0020] Furthermore, the power setting value is a charging power setting value P xzc Or discharge power setting value P xzf .

[0021] EMS calculates the power imbalance P i The method is:

[0022] P i =P cn +P gf +P f

[0023] When the system is in charging state, EMS sends the charging power value P to PCS2 through control commands. out1 for:

[0024] P out1 =P i -P xzc

[0025] When the system is in the discharge state, the EMS sends the discharge power value P to PCS2 through the control command. out2 for:

[0026] P out2 =P i -P xzf

[0027] Among them, P cn is the output power of the energy storage system, P gf is the output power of the photovoltaic system, P f For DC load.

[0028] Furthermore, the 24 hours of a day are divided into several time periods, and the charging and discharging status of the energy storage system is controlled in different time periods. The EMS calculates the system power imbalance and determines whether the system is currently in a charging state or a discharging state.

[0029] When the system is in the discharging state, EMS sends the discharge power setting value P to PCS1. xzf , send the discharge power value P to PCS2out2 ; When the system is in charging state, EMS sends the charging power setting value P to PCS1 xzc , send the charging power value P to PCS2 out1 .

[0030] Furthermore, the control method of the DC microgrid system also includes an intelligent air conditioning control method, and the intelligent air conditioning control method includes:

[0031] When the maximum temperature of the battery cell is higher than the cooling start temperature, the air conditioner starts cooling.

[0032] When the maximum temperature of the battery cell is lower than the cooling stop temperature, the air conditioner stops cooling.

[0033] In the charging state, when the lowest temperature of the battery cell is lower than the first heating start temperature, the air conditioner starts heating, and when the lowest temperature of the battery cell is higher than the first heating stop temperature, the air conditioner stops heating.

[0034] In the standby or discharging state, when the lowest temperature of the battery cell is lower than the second heating start temperature, the air conditioner starts heating, and when the lowest temperature of the battery cell is higher than the second heating stop temperature, the air conditioner stops heating.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) A reasonable power response mechanism is adopted. When the DC load of the system changes suddenly, PCS1 can track the change of instantaneous power and automatically adjust the output power, thereby achieving power balance of the DC system. EMS calculates the power imbalance according to the power setting value and operating status of the system and adjusts the output power of PCS2 to achieve power balance of the DC system.

[0037] (2) The charging and discharging control strategy of the energy storage system utilizes the droop characteristics of the battery, dynamically adjusts the droop coefficient through the battery SOC, strictly controls the charging and discharging DC voltage of a single battery, and further suppresses bus voltage fluctuations, thereby ensuring the stability of the bus voltage of the entire DC microgrid system;

[0038] (3) The power setting value range of PCS1 ensures that when the DC load changes suddenly, the instantaneous output response power of PCS1 can effectively compensate for the power imbalance caused by the DC load change, avoid the occurrence of grid circulation, and ensure the stable operation of the microgrid system;

[0039] (4) Implementing a time-sharing charging and discharging control strategy for the energy storage system to achieve coordinated energy management of the system;

[0040] (5) The setting of the charging and discharging power value of the energy storage system ensures that the real-time exchange power of the system does not exceed the total exchange power limit of the system;

[0041] (6) Intelligent air conditioning control realizes unmanned management and reduces battery loss and increases battery life. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is the electrical connection diagram of the microgrid system;

[0043] Figure 2 It is the topological diagram of the microgrid system;

[0044] Figure 3 It is a flow chart of power calculation and control method;

[0045] Figure 4 It is a schematic diagram of the PCS power change process;

[0046] Figure 5 It is a schematic diagram of the time-sharing control strategy;

[0047] Figure 6 This is a schematic diagram of the battery charge and discharge control droop characteristics;

[0048] Figure 7 This is a schematic diagram of intelligent air conditioning control. DETAILED DESCRIPTION

[0049] The technical solution of the present invention is described in detail below with reference to the accompanying drawings:

[0050] like Figure 1 and Figure 2 As shown, the DC microgrid system includes an energy storage management platform, EMS, PCS, energy storage system, photovoltaic system and DC load. The PCS is connected between the AC transformer and the DC bus. The energy storage system, photovoltaic system and DC load are respectively connected to the DC bus. The PCS, energy storage system, photovoltaic system and DC load all interact with the energy management system EMS through a serial port server and a switch in a specific protocol. The energy storage management platform collects signals from the PCS, energy storage system, photovoltaic system and DC load through the EMS and issues control commands. The PCS includes parallel PCS1 and PCS2. In this embodiment, the DC load includes three 60kW DC charging piles and a 5G base station system. The energy storage system is a distributed digital energy storage system that adopts the principle of cascade utilization of retired power batteries, and reads the battery health status SOH and state of charge SOC of the battery in real time to monitor the availability of retired batteries.

[0051] The energy storage converter PCS plays a role of bidirectional conversion in the DC microgrid system. Its operating status affects the operation of the entire system. It is the link between the power grid and the electric energy storage device. It shoulders the role of charging and electric energy feedback. It is one of the key devices of the energy storage system and provides a prerequisite for the vigorous development of distributed power generation systems. At the same time, as a controllable energy storage power source in the microgrid, PCS solves the contradiction between the large power grid and the distributed power source, so that the microgrid can be connected to the large power grid and can also be disconnected from the main grid and run independently when the power grid fails or when needed, which improves the safety, stability and economy of the power system.

[0052] The energy management system EMS is the control center of the entire system. The system operates according to the established strategy, while protecting the microgrid and adopting the charging and discharging control strategy to control the charging and discharging operation of the overall system.

[0053] like Figure 3 , a control method for a DC microgrid system based on digital energy storage, when the system operates normally, the output power of PCS1 is the power setting value, and the output power of PCS2 is the difference between the system power imbalance and the power setting value.

[0054] The power setting value is set according to the overall system configuration capacity and field test experience, and the parameter setting range is mainly determined based on the change range of the system load. When the system is in the charging state, the power setting value is the charging power setting value P xzc When the system is in the discharge state, the power setting value is the discharge power setting value P xzf .

[0055] When the DC load suddenly changes, PCS1 automatically adjusts according to its own power value and the state of the entire DC system, and instantly outputs response power to compensate for the power imbalance caused by the sudden change in DC load, thereby achieving instantaneous system power balance.

[0056] EMS collects photovoltaic power, energy storage power, and DC load charging power in real time and calculates the power imbalance P i And send control commands (rectification / inversion) and corresponding power values ​​to adjust the output power of PCS2 to achieve the purpose of compensating for the power imbalance caused by sudden changes in DC load.

[0057] P i =P cn +P gf +P f

[0058] Among them, P cn is the output power of the energy storage system, P gf is the output power of the photovoltaic system, P f For DC load.

[0059] When the system is in charging state, EMS sends the charging power value P to PCS2 through control commands. out1 for:

[0060] P out1 =P i -P xzc

[0061] When the system is in the discharge state, the EMS sends the discharge power value P to PCS2 through the control command. out2 for:

[0062] P out2 =P i -P xzf

[0063] At this time, the output power of PCS1 automatically returns to the power setting value, thereby achieving steady-state system power balance.

[0064] Furthermore, the power setting value of PCS1 is greater than 0 and less than the rated power of PCS1.

[0065] The power setting value is not 0. Take the system in the discharge state as an example for explanation: assuming that the power setting value is 0, all discharge power is output by PCS2. When the system discharge increases, PCS1 can adapt to the instantaneous changes. After the calculation cycle, because PCS1 is not controlled and PCS2 is controlled, EMS will still control PCS2 to increase the discharge power and continue to output. However, when the system discharge decreases or the instantaneous load increases, causing the total system power to become smaller, PCS2 is not adapted to the instantaneous changes and still performs high-power discharge output. At this time, PCS1 will output reverse power and change to charging operation. In this way, the reverse power output by PCS1 and PCS2 will form a circulation between PCS1 and PCS2.

[0066] If the power setting value is the rated power, if the discharge or charge suddenly increases, PCS1 cannot make additional adjustments because it is already running at full load and loses the ability to adapt to instantaneous changes, so it cannot be set to the rated power value.

[0067] The maximum power value that PCS1 can exchange instantly is the difference between the rated power of PCS1 and the power setting value, and this difference is not less than the change amplitude of the DC load. When the system load suddenly changes, PCS1 instantly outputs the response power (i.e. the DC load sudden change amount). When the EMS calculation cycle is reached, this output amount will be transferred to PCS2 in milliseconds, and power exchange will be carried out through PCS2. Figure 4In this embodiment, before the load suddenly changes, the system power imbalance is 65kW, and the power setting value of PCS1 is 15kW. When the load suddenly increases by 30kW, PCS1 is not controlled by EMS, and the output power increases by 30kW instantly. After reaching the EMS calculation cycle, the total power demand of the system is calculated to be 95kW. At this time, the power value sent by EMS to PCS2 is 80kW, and the output power of PCS1 is restored to the power setting value of 15kW, that is, the power supply when the system load suddenly changes is transferred from PCS1 to PCS2. Continue to operate under this working condition. When the system power imbalance suddenly decreases by 10kW, PCS2 cannot respond to the instantaneous change. At this time, the output power of PCS1 will instantly decrease by 10kW and become 5kW output. After the calculation cycle, EMS calculates that the system power demand is 85kW. At this time, the power value sent to PC2 is 70kW, and the output power of PCS1 is still stable at 15kW.

[0068] During the entire regulation process, EMS does not control PCS1, but only frequently controls PCS2. The purpose of not controlling PCS1 is to prevent instantaneous fluctuations in the microgrid system caused by instantaneous changes in system energy: when the load suddenly changes, the current suddenly changes, and the power electronic devices inside PCS1 are activated. Under the premise of not being controlled by EMS, it can timely track the changes in system load to replenish power to ensure the instantaneous stability of the microgrid system.

[0069] The response time of PCS1 can reach milliseconds, while the calculation cycle of EMS is in the second range, so the response time of PCS is faster than that of the energy management system EMS. After completing the power calculation, EMS sends a control command to change the output power of PCS2. At this time, the power exchange caused by the sudden change of load is transferred from PCS1 to PCS2, thereby realizing the stable power regulation of the microgrid system.

[0070] When the energy storage system or photovoltaic system is in the discharge / generation state, the output power of the energy storage system or photovoltaic system is negative, but the grid-side power may not be negative, which depends on the coordination between the system DC load and power generation. When the system is in the discharge state, EMS sends the discharge power setting value P to PCS1. xzf , send the discharge power value P to PCS2 out2 ; When the system is in charging state, EMS sends the charging power setting value P to PCS1 xzc , send the charging power value P to PCS2 out1 .

[0071] This method implements a time-sharing charging and discharging control strategy for the energy storage system and the photovoltaic system to achieve coordinated system energy management and control. Figure 5The charging and discharging system of the energy storage system is connected to the DC 750V bus, and the following control strategy is implemented for charging and discharging, which is cycled twice a day. The first cycle is: charging at low electricity prices (23:00-7:00) and discharging at the peak of the electricity price in the morning (10:00-15:00). The second cycle is: charging at the normal electricity price in the afternoon (15:00-18:00) and discharging at the peak of the electricity price in the evening (18:00-21:00). For economic reasons, the charging and discharging of energy storage is not performed from 21:00 to 23:00.

[0072] During the morning normal electricity price period (7:00-10:00) and the morning peak electricity price period (10:00-15:00), distributed photovoltaic power generation gives priority to charging electric vehicles, and the surplus power is connected to the grid. Charging of distributed energy storage systems is prohibited during this period. During the afternoon normal electricity price period (15:00-18:00), charging of electric vehicles is given priority. If the electric vehicle cannot be fully consumed, the energy storage system will be charged and the surplus power will be connected to the grid.

[0073] The working status of PCS is different in different time periods, as follows:

[0074] The first time period: 23:00-7:00. During this time period, the energy storage system is allowed to charge. The energy storage system and the electric vehicle DC charging pile are combined into a DC load. The photovoltaic system power generation power must be 0, and the unbalanced power at this time must be greater than or equal to 0. At this time, the charging power needs to be sent to PCS2 to obtain electricity from the power grid.

[0075] The second time period: 7:00-10:00. During this time period, the photovoltaic system is generally in a power generation state. At this time, the energy storage system is prohibited from charging and discharging, and priority is given to charging electric vehicles and load power consumption. If the photovoltaic system has surplus power generation, the surplus power can be connected to the grid. At this time, the power imbalance is a negative value, and the PCS needs to discharge to the grid. The system sends the discharge power, and the PCS2 performs the discharge operation; if the photovoltaic system power generation does not meet the load power consumption, refer to the operation of the first time period, and send the charging power to the PCS to meet the load power consumption.

[0076] The third time period: 10:00-15:00. This time period is the peak period of electricity consumption. The electricity price is high and the energy storage system is allowed to discharge. During this time period, the energy storage system discharges and the photovoltaic system generates electricity at the same time. According to the calculation method of the power imbalance, if the power imbalance is negative, it means that the load power consumption is less than the overall discharge. The system needs to send the discharge power control to PCS2 to achieve the surplus power access to the grid; if the power imbalance is positive, it means that the discharge of the photovoltaic system and the energy storage system cannot meet the load power consumption. Charging power needs to be sent to PCS2 to meet the load power consumption.

[0077] The fourth time period: 15:00-18:00, this stage is not the peak period of electricity consumption, it is the parity period, during this time, the photovoltaic system will generally generate electricity, and the photovoltaic system can be used to generate electricity to meet the charging needs of electric vehicles and energy storage systems. If the power imbalance is negative, it means that the photovoltaic system can generate electricity to meet the energy storage system and electric vehicle charging, and the surplus power can be connected to the grid. At this time, the discharge power is sent to PCS; if the power imbalance is positive, it means that the photovoltaic system cannot generate electricity to meet the load power consumption, and it is necessary to take electricity from the grid to meet the power consumption of the energy storage system and electric vehicles. At this time, the charging power needs to be sent to PCS2.

[0078] The fifth time period: 18:00-21:00, this stage is the peak period of electricity consumption and the peak electricity price period. At this time, there is no photovoltaic system power generation in the general area, and the energy storage system is allowed to discharge. The system power consumption is basically supplied by the energy storage system discharge. If the power imbalance is positive, it means that the energy storage system discharge and photovoltaic system power generation cannot meet the power consumption of electric vehicles, and it is necessary to take power from the large power grid side and send charging power to PCS2; if the power imbalance is negative, it means that the energy storage system discharge and photovoltaic system power generation can not only meet the power consumption of electric vehicles, but also provide surplus power to the grid. At this time, the discharge power is sent to PCS2.

[0079] The sixth time period: 21:00-23:00. During this stage, the energy storage system neither charges nor discharges, and the photovoltaic system does not generate electricity. The power imbalance is definitely greater than or equal to 0. During this stage, only charging power is sent to the PCS, and electricity is taken from the grid.

[0080] In this embodiment, the maximum value of the sum of the output power of PCS1 and PCS2 during system operation is 200kW, so the total exchange power of the system is not greater than 200kW. This function is achieved by sending instructions from the EMS to the battery management system BMS of the energy storage system to set the discharge power of the energy storage system. The discharge power of the energy storage system is set to the minimum value of the power setting value of PCS1, the maximum discharge value of the supporting microgrid system uploaded to the EMS by the energy storage system BMS, and the difference between the total exchange power limit of the DC microgrid system and the power generation value of the photovoltaic system.

[0081] The battery pack and battery pack management system are the most important parts of the system, focusing on the consistency of the battery, the voltage difference of the single cell, the temperature and temperature difference of the single cell, the protection and control of the battery energy network card and the battery temperature. The system sends voltage and current threshold parameters through the EMS to dynamically control the charging and discharging process according to relevant parameters such as the battery SOC, effectively suppressing bus voltage fluctuations.

[0082] Specifically, Figure 6 , the method also includes a charge and discharge control method for an energy storage system, comprising the following steps:

[0083] First, during the charging and discharging process, the battery SOC (state of charge represents the percentage of remaining battery power) changes continuously, so real-time adjustment of the charging and discharging capacity of each unit is essential. By balancing the charging and discharging between units, the SOC of each battery can be effectively balanced. The ratio of the SOC of the i-th battery unit to the average SOC of all battery units is η i for:

[0084]

[0085] Where n is the number of battery cells in the energy storage system, SOC i is the state of charge of the ith battery cell.

[0086] Second, calculate the corrected droop coefficient of the i-th battery cell using the following formula:

[0087]

[0088] K' Ai is the corrected droop coefficient of the i-th battery cell. The change of the droop coefficient is closely related to the battery SOC. During the discharge process, the SOC decreases continuously, the droop coefficient increases accordingly, and the discharge current gradually decreases. On the contrary, during the charging process, the SOC increases continuously, the droop coefficient increases accordingly, and the charging current gradually decreases. K Ai is the initial droop coefficient of the i-th battery cell, I A (i) is the bus side current.

[0089] Third, calculate the output voltage U of the i-th battery cell using the following formula: dc (i)

[0090]

[0091] Among them, U H1 The voltage threshold for droop charging, I Amin is the voltage threshold when the system power is seriously over-surplus, U L1 is the voltage threshold of droop discharge, I Amax It is the current threshold when the system power is seriously insufficient. When the battery unit is charging, I A (i)<0, the larger the bus voltage I A (i) The larger the absolute value, the more current and voltage will droop. When the battery cell is discharging, I A (i)>0, the smaller the bus voltage I A (i) As the absolute value increases, the current and voltage show droop characteristics opposite to those during charging.

[0092] According to the change of droop coefficient due to SOC, U dc The maximum value of (i) is U H2 , when discharging Udc The minimum value of (i) is U L2 , that is: U H2 is the voltage threshold at which the system enters severe overpower control, U L2 The voltage threshold at which the system enters severe underpower control.

[0093] Fourth, the droop characteristics of the battery cell are used for charge and discharge control. The energy storage system dynamically adjusts the droop coefficient according to the battery SOC and sets U H1 , U H2 ,I Amin , U L1 , U L2 ,I Amax The corresponding threshold parameters strictly control the charging DC voltage of each battery cell within U H1 and U H2 The discharge voltage is controlled between U L1 and U L2 between.

[0094] When the bus voltage enters the preset voltage range of the droop characteristic control strategy, the power buffering capacity of the battery unit is utilized, and the battery unit is used as the internal network balancing point. The battery unit converter autonomously switches to the droop charging control and droop discharging control states according to the bus voltage change, so that the power in the network is balanced again, thereby achieving stable control of the bus voltage.

[0095] Furthermore, the microgrid system also includes an air-conditioning intelligent control system, which collects ambient temperature and performs intelligent temperature control to achieve intelligent start and stop of the air-conditioning. Figure 7 , the method also includes intelligent control of the air conditioner, including:

[0096] When the maximum temperature of the battery cell is higher than the cooling start temperature, the air conditioner starts cooling.

[0097] When the maximum temperature of the battery cell is lower than the cooling stop temperature, the air conditioner stops cooling.

[0098] In the charging state, when the lowest temperature of the battery cell is lower than the first heating start temperature, the air conditioner starts heating, and when the lowest temperature of the battery cell is higher than the first heating stop temperature, the air conditioner stops heating.

[0099] In the standby or discharging state, when the lowest temperature of the battery cell is lower than the second heating start temperature, the air conditioner starts heating, and when the lowest temperature of the battery cell is higher than the second heating stop temperature, the air conditioner stops heating.

[0100] This method responds to the national call for green, low-carbon, energy-saving and consumption-reducing, and coordinates the operation of distributed energy, electric vehicle charging and distributed digital energy storage systems based on retired batteries through DC microgrid control, giving full play to the advantages of large power supply capacity and low loss of DC microgrid systems.

Claims

1. A control method for a DC microgrid system based on digital energy storage, wherein the DC microgrid system comprises an energy storage management platform, an EMS, a PCS, an energy storage system, a photovoltaic system and a DC load, wherein the PCS is connected between an AC transformer and a DC bus, and the energy storage system, the photovoltaic system and the DC load are respectively connected to the DC bus, and the energy storage management platform collects signals from the PCS, the energy storage system, the photovoltaic system and the DC load through the EMS and issues control commands. Features: The PCS includes PCS1 and PCS2 in parallel. When the system is operating normally, the output power of PCS1 is the power setting value, and the output power of PCS2 is the system power imbalance value P i The difference between the power setting value; when the DC load changes suddenly, the output power of PCS1 is automatically adjusted, and the instantaneous output response power is used to compensate for the power imbalance caused by the DC load mutation, so as to achieve instantaneous system power balance; EMS calculates the power imbalance amount P i A control command is issued to adjust the output power of PCS2, and the output power of PCS1 is automatically restored to the power setting value to achieve steady-state system power balance; The power setting value is the charging power setting value P xzc Or discharge power setting value P xzf ; EMS calculates the power imbalance P i The method is: P i =P cn +P gf +P f When the system is in charging state, EMS sends the charging power value P to PCS2 through control commands. out1 for: P out1 =P i -P xzc When the system is in the discharge state, the EMS sends the discharge power value P to PCS2 through the control command. out2 for: P out2 =P i -P xzf Among them, P cn is the output power of the energy storage system, P gf is the output power of the photovoltaic system, P f For DC load.

2. The control method of the DC microgrid system based on digital energy storage according to claim 1, Features: The invention also includes a charge and discharge control method of an energy storage system, wherein the charge and discharge control method of the energy storage system comprises the following steps: First, the ratio η of the SOC of the i-th battery cell to the average SOC of all battery cells is calculated using the following formula: i : Where n is the number of battery cells in the energy storage system, SOC i is the state of charge of the i-th battery cell; Second, calculate the corrected droop coefficient K' of the i-th battery cell using the following formula: Ai : Among them, K Ai is the initial droop coefficient of the i-th battery cell, I A (i) is the busbar current; Third, calculate the output voltage U of the i-th battery cell using the following formula: dc (i) Among them, U H1 The voltage threshold for droop charging, I Amin is the voltage threshold when the system power is seriously over-surplus, U L1 is the voltage threshold of droop discharge, I Amax It is the current threshold when the system power is seriously insufficient; Fourth, the energy storage system dynamically adjusts the droop coefficient according to the battery SOC, and sets U H1 , U H2 ,I Amin , U L1 , U L2 ,I Amax The corresponding threshold parameters control the charging DC voltage of each battery cell at U H1 and U H2 The discharge voltage is controlled between U L1 and U L2 between; Among them, U H2 is the voltage threshold at which the system enters severe overpower control, U L2 The voltage threshold at which the system enters severe underpower control.

3. The control method of the DC microgrid system based on digital energy storage according to claim 1, Features: The power setting value is greater than 0 and less than the rated power of PCS1.

4. The control method of the DC microgrid system based on digital energy storage according to claim 1, Features: During system operation, the discharge power of the energy storage system is set to the minimum value among the set power value of PCS1, the maximum discharge value of the supporting microgrid system uploaded by the energy storage system BMS to the EMS, and the difference between the total exchange power limit of the DC microgrid system and the power generation value of the photovoltaic system.

5. The control method of the DC microgrid system based on digital energy storage according to claim 1, Features: Divide the 24 hours of a day into several time periods, and control the charging and discharging status of the energy storage system in different time periods. The EMS calculates the system power imbalance and determines whether the system is currently in a charging or discharging state. When the system is in the discharging state, EMS sends the discharge power setting value P to PCS1. xzf , send the discharge power value P to PCS2 out2 ; When the system is in charging state, EMS sends the charging power setting value P to PCS1 xzc , send the charging power value P to PCS2 out1 .

6. The control method of the DC microgrid system based on digital energy storage according to any one of claims 1 to 5, Features: It also includes an air conditioner intelligent control method, the air conditioner intelligent control method comprising: When the maximum temperature of the battery cell is higher than the cooling start temperature, the air conditioner starts cooling; When the maximum temperature of the battery cell is lower than the cooling stop temperature, the air conditioner stops cooling; in the charging state, when the minimum temperature of the battery cell is lower than the first heating start temperature, the air conditioner starts heating, and when the minimum temperature of the battery cell is higher than the first heating stop temperature, the air conditioner stops heating; In the standby or discharging state, when the lowest temperature of the battery cell is lower than the second heating start temperature, the air conditioner starts heating, and when the lowest temperature of the battery cell is higher than the second heating stop temperature, the air conditioner stops heating.

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