Study For Interface Modeling And Control Method Of The Micro-grid Hybrid Energy Storage System

Currently, large centralized power plants occupied a pivotal position in the industrial production. However, most of the existing power generation technology is based on non-renewable energy sources, such as fossil fuels and nuclear energy. With the continuous development of new energy technologies and power electronics technology, distributed generation technology matures. Micro-grid is an effective way to achieve access to large distributed power grid. Energy storage technology has a very important significance in the micro-grid. Traditional storage system is an energy storage technology used alone. However, use of this single method is often difficult to meet the requirements of energy storage system performance for micro-grid. Due to a variety of energy storage technologies each have advantages, especially super capacitors and batteries are highly complementary in terms of performance. Super-capacitors have rapid charge and discharge capacity, highly reversible functional process, high power density and a lower energy density compared to the battery characteristics. Therefore, the super-capacitor connected to the energy storage system, can play a positive role in maintaining the stable operation of the system and improve the performance of the system.This paper aims to study the super-capacitors with lithium-ion batteries used in combination to improve the performance of the energy storage system. Firstly the super capacitor is directly connected with a battery in parallel.that is called passive connection mode. Then, established the Thevenin equivalent circuit of the energy storage system, and analyzed the performance of the system based on Matlab simulation. Compared to a single battery storage, this system has some benefits, such as reducing the cell voltage and current ripple; reducing peak output current of the battery; enhancing the output power capability of the system; saving energy such that efficiency of the system higher; extending system run time. The super-capacitor is connected to the DC bus via power converter, and a lithium-ion battery is connected directly to the DC bus, that is called semi-active mode. The bidirectional DC-DC converter is interface of the system. That controls energy flow of the storage units. Its precise model is the basic of control strategy design. This paper established the bi-directional DC/DC converter average model, based on state-space averaging method. And designed a control strategy, the power smoothing strategies based on the moving average method effectively smooth output power of the battery. Super-capacitor under/over voltage protection strategies effectively avoid the high or low voltage of the end of the super-capacitor, and thus achieve effective protection for the super-capacitor. Semi-active topology hybrid energy storage system not only has advantages above, but also brought a series of other possibilities and advantages, such as the expansion of the scope of work to run a super-capacitor; power system performance has been further improved; system can be applied a series of control and management strategies, which can ensure the stability of the system. Performance and capacity of the super-capacitor can be optimized, thereby reducing the cost of the system.