Micro-grid refers to a small power generation and distribution system composed of distributed power sources, energy storage devices (100kWh – 2MWh energy storage systems), energy conversion devices, loads, monitoring and protection devices, etc., to supply power to the load, mainly to solve the problem of power supply reliability.
EGBATT Microgrid is an autonomous system that can realize self-control, protection and management. As a complete power system, it relies on its own control and management for energy supply to achieve power balance control, system operation optimization, fault detection and protection, power quality management, etc. function.
The proposal of microgrid aims to realize the flexible and efficient application of distributed power, and solve the problem of grid connection of distributed power with a large number and various forms. The development and extension of microgrids can fully promote the large-scale access of distributed power sources and renewable energy, and realize the highly reliable supply of various energy forms for loads. Smart grid transition.
The energy storage systems in the microgrid are mostly distributed power sources with small capacity, that is, small units with power electronic interfaces, including micro gas turbines, fuel cells, photovoltaic cells, small wind turbines, supercapacitors, flywheels and batteries, etc. device. They are connected to the user side and have the characteristics of low cost, low voltage and little pollution. The following introduces EGBATT 100kWh energy storage system solution for microgrid power generation.
EGBATT 100 kWh Energy Storage System Mainly Includes
The proposed technical solution includes the following components: a single off-grid bidirectional energy storage converter PCS with a capacity of 50kW, connected to the grid at 0.4KV AC bus to enable bidirectional energy flow. The energy storage system is comprised of a 100kWh Lithium iron phosphate battery pack, consisting of ten battery packs of 51.2V and 205Ah each, connected in series to achieve a total voltage of 512V and a capacity of 205Ah.
To complete the control functions of the energy storage system, an Energy Management System (EMS) and Battery Management System (BMS) are included. These systems enable charging and discharging control of the energy storage system, battery SOC information monitoring, and other functions based on the dispatch instructions from the superior authorities.
| Serial Number | Name | Specification | Quantity |
|---|---|---|---|
| 1 | Energy storage converter | PCS-50KW | 1 |
| 2 | 100KWh Energy storage battery system | 51.2V 205Ah LiFePO4 Battery Pack | 10 |
| BMS control box, battery management system BMS, energy management system EMS | |||
| 3 | AC distribution cabinet | 1 | |
| 4 | DC combiner box | 1 | |
Features of the 100 kWh Energy Storage System are as follows:
- The system is primarily designed for peak and valley power usage, and can serve as a backup power source to prevent power surges and enhance power quality.
- The energy storage system has an array of vital functions such as communication, monitoring, management, control, early warning, and protection. It can continue to operate safely for an extended period. The system’s operational status is detectable through the host computer, and it is equipped with a range of data analysis functionalities.
- The BMS system operates by collaborating with the EMS system to supply battery pack information, and it can also communicate directly with the PCS through the RS485 bus. This facilitates various battery pack monitoring and protection functions in coordination with the PCS.
- The system can support conventional 0.2C charge and discharge. Additionally, it can operate while disconnected from the grid, or connected to it through a grid-connected mode.
EGBATT 100 kWh Energy Storage System proposed technical solution is a highly functional system designed to meet the needs of peak and valley power usage. It is also an efficient backup to avoid power increases and to enhance power quality. The system is equipped with robust functionality such as communication, monitoring, management, control, early warning, and protection, which make it highly reliable and safe to operate for extended periods. The provision for direct communication between the BMS and PCS along with conventional charge and discharge support for grid and off-grid modes make it highly flexible for various applications.
The Operation Mode of the Whole Energy Storage System has been described as follows:
- The energy storage system operates while connected to the grid, and its active and reactive power can be dispatched using the PQ mode or droop mode of the energy storage converter to meet the connected grid’s charging and discharging requirements.
- The energy storage system releases the load during peak electricity prices or periods of peak load consumption. By doing so, it can not only achieve peak-shaving and valley-filling effects on the power grid but also supplement energy consumption during peak electricity periods.
- The energy storage converter accepts power dispatching from superior authorities and manages charging and discharging for the entire energy storage system based on intelligent peak, valley, and normal period control.
- If the energy storage system detects any mains abnormalities, the energy storage converter is controlled to switch from grid-connected operation mode to island (off-grid) operation mode.
- When the energy storage converter operates independently off-grid, it supplies stable voltage and frequency as the primary voltage source to ensure uninterrupted power supply for the local loads.
The Operation Mode of the Whole Energy Storage System is a well-designed solution that ensures flexible and efficient energy management. By providing two modes of operation (grid-connected and off-grid), the system can adapt to various energy requirements during peak times and periods of high load demand. The energy storage converter’s intelligent peak, valley, and normal period control, coupled with the PQ or droop mode, supports effective grid management, providing active and reactive power to meet the connected grid’s charging and discharging requirements. In case of any mains abnormalities, the converter switches to an island operation mode to ensure seamless power supply, providing stable voltage and frequency to the local loads. Overall, the operation mode of the whole energy storage system provides robust and flexible functionality, meeting diverse energy requirements efficiently and effectively.
The Energy Storage Converter (PCS) proposed technical solution has several advanced features, which are as follows:
- The advanced non-communication line voltage source parallel technology used in the PCS enables unlimited parallel connection of multiple machines. The system supports multi-source parallel operation and can be directly networked with diesel generators.
- Advanced droop control methods have been adopted in the design of the PCS, and voltage source parallel connection power equalization can reach 99%. The system supports three-phase 100% unbalanced load operation.
- Advanced droop control methods have been adopted in the design of the PCS, and voltage source parallel connection power equalization can reach 99%. The system supports three-phase 100% unbalanced load operation.
- The PCS supports online seamless switching between on-grid and off-grid operation modes capable of providing short-circuit support and self-recovery function during off-grid operation.
- The system has real-time dispatchable active and reactive power and a low-voltage ride-through function during grid-connected operation. Dual power supply redundant power supply mode has been incorporated into the design to improve the system’s reliability.
- The PCS can support multiple types of loads connected individually or mixed (resistive load, inductive load, capacitive load). The system has a complete fault and operation log recording function, and it can record high-resolution voltage and current waveforms when a fault occurs.
- Optimised hardware and software design has enabled the system to achieve high conversion efficiency of up to 98.7%.
- The DC side of the PCS is suitable for photovoltaic module connection, and it also supports parallel connection of multi-machine voltage sources. The system can be used as a black start power supply for off-grid photovoltaic power stations that operate at low temperatures and without power storage.
- The L-series converters have been designed to support 0V start-up, making them suitable for lithium batteries. The system has a 20-year long-life design.
In conclusion, the Energy Storage Converter (PCS) proposed technical solution has an array of advanced features that make it highly reliable, efficient, and versatile for various energy storage requirements, whether on-grid or off-grid.
Communication Method of Energy storage Converter
Ethernet Communication Scheme:
For a single energy storage converter, the RJ45 port on the converter can be directly connected to the RJ45 port on the host computer using a network cable. The energy storage converter can be monitored using the host computer monitoring system.
RS485 Communication Scheme:
In addition to the standard Ethernet MODBUS TCP communication, the energy storage converter offers an optional RS485 communication solution, which utilises the MODBUS RTU protocol. A converter (RS485/RS232) is used to connect the energy storage converter to the host computer. The energy storage converter can be monitored remotely via the Energy Management System, which is designed to monitor the energy storage converter’s functionality.
Communication Program with BMS
The proposed technical solution includes communication capabilities between the energy storage converter and the battery management unit (BMS), and monitoring of the status information of the battery is possible through the host computer monitoring software. The system can also perform alarm and fault protection actions for the battery based on the status of the battery, improving the overall safety of the battery pack.
The BMS system continuously monitors the temperature, voltage, and current information of the battery. The system communicates with the Energy Management System (EMS) and directly communicates with the PCS through the RS485 bus to enable real-time battery pack protection actions.
The temperature alarm measures of the BMS system are categorised in three levels, introducing primary thermal management through temperature sampling and relay-controlled DC fans. When the temperature in the battery module exceeds the limit, the BMS slave control module integrated in the battery pack will activate the fan to dissipate heat.
After the second-level thermal management signal warning, the BMS system links decisively with the PCS system to restrict the charging and discharge current of the energy storage converter or stop the charge/discharge behaviour of the PCS. The specific protection protocols are open and can be updated based on customer requirements.
After the third-level thermal management signal warning, the BMS system will cut off the DC contactor of the battery group to protect the battery, and the corresponding PCS converter assigned to the battery group will cease operations.
Overall, the proposed technical solution has achieved integrated monitoring and reliable protection of battery packs, enhancing the safety and reliability of the system.
BMS Function
The BMS or Battery Management System is an electronic circuit equipment that monitors the real-time status of the battery. It effectively keeps track of the battery voltage, battery current, insulation status, electrical SOC, individual battery module and monomer status, safety management during charging and discharging, and emergency protection for any faults that may arise. The BMS also ensures optimal control of the battery modules and battery clusters to guarantee the safe, reliable, and stable operation of the batteries.
Battery Management System Composition and Function Description
The battery management system is composed of several units such as the battery management unit ESBMM, battery cluster management unit ESBCM, battery stack management unit ESMU, and their respective current and leakage current detection units. The BMS system provides the functions of high-precision detection and reporting of analog signals, fault alarm, upload and storage, battery protection, parameter setting, active equalization, battery pack SOC calibration, and information interaction with other devices
Energy Management System (EMS)
The energy management system is the primary control system for managing the energy storage system. Its main function is to monitor both the energy storage system and the load, and then analyze the data collected. Based on the analysis results, it will generate real-time operation scheduling curves. This real-time data is used to formulate a suitable power allocation plan in accordance with the forecast dispatch curve.
Device Monitoring
The device monitoring module is used to view the real-time data of the devices in the system. It presents the data in both list and configuration formats, through which the devices can be controlled and configured dynamically.
Energy Management
The energy management module formulates an energy storage/load co-optimized control strategy by combining the forecast results of system analysis module and the measured data from the operational control module. This module mainly encompasses areas such as energy management, energy storage scheduling, and load forecasting.
The energy management system operates in both grid-connected and off-grid modes. It can carry out 24-hour long-term forecast dispatch, short-term forecast dispatch, and real-time economic dispatch. The system ensures the reliability of power supply for users while also improving the overall economy of the system.
Event Alarm
The system is required to support multi-level alarms, such as general alarms, important alarms, and emergency alarms. The system should allow the setting of different alarm threshold parameters and thresholds. The system should automatically adjust the color of the alarm indicators at all levels and the frequency and volume of the sound alarms based on the alarm level.
Whenever an alarm is triggered, it should be automatically notified in a timely manner. The alarm information shall be displayed and the system should also provide a printing function for the alarm information. The system should have an alarm delay processing function with user-settable alarm delay and alarm recovery delay. The user can set the alarm delay time. If an alarm is eliminated within the alarm delay range, the alarm will not be sent. If the alarm is generated again within the alarm recovery delay range, there will be no alarm recovery information generated.
Report Management
The report management module provides query, statistical, sorting, and printing statistics of relevant equipment data. It also facilitates the management of basic report software. The monitoring and management system should have the capability of storing various historical monitoring data, alarm data, and operation records, which are collectively referred to as performance data, in the system database or external memory.
The monitoring and management system should exhibit the ability to display performance data in an intuitive form, analyze the collected data, and detect any abnormal conditions. The statistics and analysis results shall be displayed in the form of reports, graphs, histograms, and pie charts.
The monitoring and management system must also generate regular performance data reports for monitored objects. The system should generate various statistical data, charts, and logs, and be able to print them.
Safety Management
The energy management module formulates an energy storage/load co-optimized control strategy by combining the forecast results of system analysis module and the measured data from the operational control module. This module mainly encompasses areas such as energy management, energy storage scheduling, and load forecasting.
The energy management system operates in both grid-connected and off-grid modes. It can carry out 24-hour long-term forecast dispatch, short-term forecast dispatch, and real-time economic dispatch. The system ensures the reliability of power supply for users while also improving the overall economy of the system.
Monitoring System
The energy management module formulates an energy storage/load co-optimized control strategy by combining the forecast results of system analysis module and the measured data from the operational control module. This module mainly encompasses areas such as energy management, energy storage scheduling, and load forecasting.
The energy management system operates in both grid-connected and off-grid modes. It can carry out 24-hour long-term forecast dispatch, short-term forecast dispatch, and real-time economic dispatch. The system ensures the reliability of power supply for users while also improving the overall economy of the system.
Fire Protection and Air Conditioning System
The container cabinet comprises two compartments: the equipment compartment and the battery compartment. The battery compartment is cooled by air conditioning and equipped with a heptafluoropropane automatic fire-extinguishing system. The system is designed without a pipe network.
The equipment compartment is cooled through forced air-cooling and equipped with standard dry powder fire extinguishers. Heptafluoropropane is an ideal solution for fire suppression as it is a colorless and odorless gas that is non-polluting, non-conductive and does not contain water. Moreover, it does not cause damage to electrical equipment and has a high efficiency and speed for extinguishing fires.
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