I. Application of battery energy storage system in photovoltaic power station
1. Stable system
In the photovoltaic power generation system, the power curve and the photovoltaic power generation load curve are quite different, and both have unpredictable triggers. However, if the energy is stored in the energy storage system, or if the energy storage system is used to buffer the energy, the photovoltaic power generation system can achieve stable power output and stable operation even under severe fluctuations.
2. Energy Reserve
When the photovoltaic power generation system operates abnormally, the electric energy in the energy storage system can play an emergency and transition role. For example, when the battery array cannot generate electricity at night or in rainy weather, the battery energy storage system can play the role of backup and emergency transition, and its energy storage capacity depends on the demand of the load.
3. Reliable quality
When the charging voltage peaks, the voltage drops or the power grid fluctuates greatly due to external interference, the energy storage system can effectively prevent its impact on the photovoltaic power generation system and ensure the photovoltaic power generation system. Output reliability and quality
Second, the main structure of the battery energy storage system
The energy storage system consists of battery, electrical components, mechanical support, heating and cooling system (thermal management system), bidirectional energy storage converter (PCS), energy management system (EMS) ) and a battery management system (BMS). The batteries are arranged, connected and assembled into a battery module, and then fixed and assembled into the cabinet together with other components to form a battery cabinet. Below we introduce the important parts.
1. The energy type battery and power type battery used in the battery energy storage system are different. Taking professional athletes as an example, power batteries are like sprinters. They have good explosive power and can release high power in a short period of time. The energy-type battery is more like a marathon runner, with high energy density and can provide longer use time on a single charge. Another feature of energy-based batteries is long life, which is very important for energy storage systems. Eliminating the difference between day and night peaks and valleys is the main application scenario of the energy storage system, and the use time of the product directly affects the project income.
2. Thermal management
If the battery is likened to the body of the energy storage system, then the thermal management system is the "clothing" of the energy storage system. Like people, batteries also need to be in a comfortable temperature environment (23~25℃) in order to exert higher work efficiency. If the battery operating temperature exceeds 50°C, the battery life will decline rapidly. When the temperature is lower than -10°C, the battery will enter the "hibernation" mode and cannot work normally.
It can be seen from the different performances of the battery in the face of high temperature and low temperature that the life and safety of the energy storage system in the high temperature state will be greatly affected, while the energy storage system in the low temperature state will completely strike. The function of thermal management is to give the energy storage system a comfortable temperature according to the ambient temperature. So that the whole system can "extend the lifespan".
3. Battery Management System (BMS)
Battery management system can be regarded as the commander of the battery system. It is the link between the battery and the user, mainly to improve the The utilization rate of the battery prevents the battery from being overcharged and overdischarged. It can infer the SOC (state of charge) of the system, the start and stop of the thermal management system, the system insulation detection and the balance between the batteries. BMS should take safety as the original design intention, follow the principle of "prevention first, control guarantee", and systematically solve the safety management and control of energy storage battery system.
4. Bidirectional energy storage converter (PCS)
In fact, energy storage converters are very common in daily life. The function of the mobile phone charger is to convert the 220V AC in the household socket to Converted to 5V~10V DC power required by the battery in the mobile phone. This is consistent with the pattern in which the energy storage system converts the alternating current to the direct current required by the stack during charging.
The PCS in the energy storage system can be understood as an oversized charger, but the difference from the mobile phone charger is that it is bidirectional. The bidirectional PCS acts as a bridge between the battery stack and the grid. On the one hand, it converts the AC power at the grid end into DC power to charge the battery stack, and on the other hand, converts the DC power from the battery stack into AC power and feeds it back to the grid.
5. Energy Management System (EMS)
The existence of the energy management system is to summarize the information of each subsystem in the energy storage system, and to comprehensively control the operation of the entire system. And make relevant decisions to ensure the safe operation of the system. The EMS will upload the data to the cloud and provide operational tools for the operator's background managers. At the same time, EMS is also responsible for direct interaction with users. The user's operation and maintenance personnel can view the operation of the energy storage system in real time through the EMS, so as to implement supervision.
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