| The energy storage system is an important part of the microgrid, its addition has a great effect on the uninterruptible power supply, electric peak shaving, the improvement of power quality and micropower performance improvements, and it is the key to the safe and reliable operation of the microgrid. In order to meet the requirements of microgrid stability and efficiency, hybrid energy storage system is established by supercapacitor and battery, and its role in the microgrid is studied.Firstly, the basic principle and mathematical model of the double-fed wind power and photovoltaic power generation are introduced in this paper, and the structure and operation of microgrid which contains distributed generation are also summarized. Focusing on the vector control method of doubly-fed motor, and a ideal photovoltaic grid-connected inverter model is established.Secondly, three order battery and supercapacitor RC mathematical models are established according to the principle of the lead-acid battery and supercapacitor. The charging and discharging characteristics are analysed basing on simulations. In order to improve the technical and economic performance of the hybrid energy storage system, three kinds of parallel structure of the hybrid energy storage are digged in deep. The work process of the battery optimized by the active structures is proved in simulation results.To move forward, Bi-directional DC/DC and bi-directional DC/AC converter are designed on the basis of building hybrid energy storage system.The charging and discharging process of battery is modified because of the hysteresis control strategy. Compared with the traditional PID control, the sliding mode variable structure control provides a fast response and a inductor current with smaller ripple. For the shortcomings of traditional voltage/frequency control strategy, a droop control strategy which is suitable to low voltage microgrid is described in detail. A hybrid energy storage system model is established in Matlab/simulink which proves the validity of the control strategy of hybrid energy storage system.Finally, a wind/solar/storage hybrid microgrid dynamic simulation model is built. According to the three conditions:change light intensity and wind speed; sudden increase and reduce the load, sudden increase impact load, the microgrid are simulated respectively under grid-connected and islanded operation. Simulations demonstrate that performance of distributed generation is enhanced because of employing of the hybrid energy storage system, at the same time, the power quality of microgrid is improved. |
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