Abstract: The relay protection configuration of the photovoltaic energy storage integrated electric vehicle charging station needs to comprehensively consider the collaborative operation characteristics of photovoltaic power generation, energy storage charging and discharging, charging piles, and the power grid. Its core lies in solving the problems of difficult coordination of protection action logic and reliable and efficient operation and maintenance under multi power structure. Based on relevant technical literature and standards, an analysis will be conducted from the aspects of protection requirements, configuration principles, control requirements, and compliance.

Electrical design of integrated photovoltaic energy storage charging station

The electric vehicle charging station belongs to the third level load and can be powered by a 10kV mains power supply. It usually uses a box type substation, consisting of three independent compartments: a high-voltage room, a transformer room, and a low-voltage room. The electricity capacity is generally between 630kVA and 1250kVA. The capacity of distributed photovoltaic installations at charging stations is limited by the site and is generally installed on top of carports or nearby buildings. The capacity of energy storage cabinets is selected based on charging needs and investment budgets. Photovoltaic combiner cabinets, energy storage combiner cabinets, energy storage cabinets and other related equipment can be placed in prefabricated cabins. The electrical primary main line diagram is shown in the figure.

Figure 1.1 Schematic diagram of the electrical main line of the photovoltaic energy storage integrated charging station

2 Requirements for relay protection of charging stations

The relay protection of integrated photovoltaic and energy storage charging stations will be more complex compared to traditional power stations. The integration of photovoltaic and energy storage systems will change the power supply structure of charging stations from a single power source to multiple power sources, resulting in changes in the distribution and direction of short-circuit currents. Photovoltaic inverter, energy storage

PCS are all power electronic devices, and their response time to faults is much longer than the combination of traditional relay protection devices and circuit breakers.

For example, when the low voltage side of a transformer is short circuited, the power grid, photovoltaic, and energy storage may simultaneously inject current into the fault point. Improper protection logic settings may result in misoperation or inability to quickly isolate the fault. Secondly, traditional low-voltage circuit breaker overcurrent protection may not meet the requirements of selective protection at all levels. It is necessary to ensure that only the fault area is cut off when a fault occurs, in order to avoid the expansion of the fault range caused by protection misoperation, which may affect the reliability of charging station operation. Afterwards, the configuration of relay protection also needs to meet the relevant standards and specifications for the integration of distributed power sources into the power grid.

2.1 Pile level protection

The protection requirements for off board chargers (DC charging stations) in GBT51313-2018 "Technical Standards for Distributed Charging Facilities for Electric Vehicles" are as follows: "4.0.6 Off board chargers should have functions such as AC input overvoltage protection, AC input overcurrent protection, DC output overvoltage protection, DC output overcurrent protection, and internal over temperature protection." The DC charging station protection function is mainly implemented by the internal module of the DC charging station, which can be combined with GB51348-2019 "Electrical Design Standards for Civil Buildings". "13.5.5 The end circuit of storage warehouses, electric vehicle charging and other places should be equipped with current limiting electrical fire protection devices." Some DC charging stations can be equipped with current limiting protection devices.

Requirements for AC charging stations: 4.0.7 AC charging stations should have overload protection, short circuit protection, and leakage protection functions. Leakage protection of AC charging stations should comply with the relevant provisions of the current national standard "Electric Vehicle Conductive Charging System Part 1: General Requirements" GB/T18487.1. ”According to the requirements of the "Electrical Design Standards for Civil Buildings", AC charging piles are equipped with electrical fire protection and current limiting protectors to quickly achieve overload, short circuit protection, and leakage protection.

2.2 0.4kV circuit relay protection

Photovoltaic inverters and energy storage converters themselves have relatively complete protection functions and do not require additional protective devices. According to the requirements of GB/T 19964 "Technical Regulations for Connecting Photovoltaic Power Stations to Power Systems", anti islanding protection devices are installed at the grid connection point to trip the photovoltaic and energy storage grid connected circuit breakers during power outages, preventing islanding operation from supplying power to the grid. The grid connection point needs to monitor power quality data, including current/voltage/total harmonic distortion rate, voltage qualification rate, voltage fluctuation/flicker, etc., and configure the APView400 power quality online monitoring device. In addition, in order to meet the selective requirements of 0.4kV protection and narrow the fault range in the event of a fault, low-voltage protection devices can be configured in the main circuit to achieve quick break, overcurrent protection, overload protection, undervoltage/overvoltage protection, leakage protection, and so on.

2.3 10kV Circuit Relay Protection

The 10kV incoming circuit and transformer are respectively equipped with line protection device AM5SE-F and transformer protection device AM5SE-T. If no circuit breaker is installed on the high-voltage side of the transformer, a transformer protection device shall be installed at the incoming line. Both incoming line protection and transformer protection should be equipped with directional current quick break, overcurrent, and overload protection. Transformer protection also needs to be equipped with non electrical protection, including temperature protection and door opening protection. Oil immersed transformers also need to be equipped with gas protection.

According to the "Interim Measures for the Management of Power Quality" and the "Technical Regulations for the Integration of Photovoltaic Power Stations into the Power System", the public connection points of distributed power generation users also need to monitor power quality data and configure power quality online monitoring devices; For users who self use and do not have surplus electricity connected to the internet, anti backflow protection or anti backflow regulation devices need to be installed.

2.4 Coordination Controller

In addition to intelligent gateway data collection, protocol conversion, storage and other functions, the coordination controller ACCU-100 also has the function of controlling the usage strategy of new energy. It can control photovoltaic output, energy storage charging/discharging, charging control of charging piles, and load regulation according to preset logic, and interact with cloud platforms to respond to cloud strategy configuration.

3 Charging Station Equipment

The Ankerui AEV200-DC240M split type DC charging cabinet adopts a design of one cabinet with four piles, with a single pile high charging power of 240kW, charging voltage of 150V-1000V, and single pile high current of 250A, meeting the fast charging needs of users. Equipped with functions such as AC input overvoltage protection, AC input overcurrent protection, DC output overvoltage protection, DC output overcurrent protection, and internal over temperature protection

Figure 3.1 AEV200-DC240M Charging Cabinet and AEV200-DC250AS DC Charging Station

In addition to split type charging stations, the company also provides 160kW, 120kW, 80kW, 60kW, 30kW DC charging stations and 7kW AC charging stations to meet the charging requirements of various occasions.

4 Smart Energy Management Platform

The AcrelEMS smart energy management platform integrates functions such as power monitoring, power quality analysis and governance, charging pile operation management, distributed photovoltaic monitoring, and energy storage management. It can help improve the reliability of power supply for integrated charging stations, optimize energy use strategies, locally consume new energy generation, and reduce charging costs.

4.1 Charging Operation Management

Ankerui Charging Operation Management Platform is a charging facility management system based on the Internet of Things and big data technology. It can monitor, schedule, and manage charging stations, improve their utilization and efficiency, and enhance users' charging experience and service quality. Users can make advance appointments for charging through apps or mini programs, avoiding waiting in line at charging stations, and providing more accurate charging demand data for charging stations, facilitating subsequent scheduling and management. The platform supports functions such as scanning/swiping cards for charging, navigation for finding piles, order management, monitoring of charging piles, and revenue analysis.

Figure 4.1 Charging Operation Management

4.2 Photovoltaic energy storage energy management

The energy management strategy realizes the interactive integration and flexible allocation of energy between the power grid, photovoltaic power generation, energy storage devices, and charging facilities. The system optimizes and regulates under the premise of ensuring the safe operation of transformers, effectively eliminating peak valley differences, smoothing loads, short-term flexible expansion, improving the operational efficiency of power equipment, and compensating for load fluctuations. At the same time, in situations where power transmission to the grid is not allowed, reverse power can be effectively prevented by adjusting photovoltaic power generation, energy storage charging, and adjusting charging piles.

4.3 Orderly Charging Management

The system monitors the load rate of transformers in real-time, calculates the remaining capacity of transformers, and dynamically controls charging based on charging demand and energy storage system discharge capacity, including user permission recognition, charging behavior statistics, charging power control, allowing/prohibiting new charging, adjusting charging prices, and other methods to guide user charging demand and improve the friendliness and capacity of the power grid for charging.

5 Conclusion

The photovoltaic energy storage integrated charging station adopts layered and graded protection and monitoring to improve power supply reliability and compliance of distributed power station operation, and cooperates with smart energy management platform and reasonable new energy control strategy to achieve efficient charging and economic balance. The AcrelEMS smart energy management platform, combined with various relay protection and automatic control devices from Ankerui, can simultaneously manage a large number of various charging stations scattered in different regions. Control strategies can be formulated based on the charging stations to make them operate cleaner and more efficiently.