Construction And Control Of Energy Storage Systems Used In Renewable Energy And Micro Grid

In recent years, China has accelerated the development and utilization of renewable energy. However, the power output of intermittent renewable energy, represented by wind power, photovoltaic power stations, is unstable, low-density, changes with time and climate. With the proportion of these energy capacities increases, there will have negative effects in the power grid.Energy storage technology can be used in intermittent renewable energy systems to provide the energy buffer, the reserve balance and the means to improve the effectiveness of intermittent renewable energy, which is also very active around the world. In a variety of energy storage technology, lead-acid battery performance well, although not the best energy storage equipment, but the technology is mature, high reliability and lower cost. As a new energy storage technology, supercapacitor has a great power density, suitable for high current charging and discharging of the occasion, and long service life. Therefore, this article will focus on using lead-acid battery technology and supercapacitor energy storage technology in the intermittent renewable energy.In this paper, the basic principle of the lead-acid battery energy storage system (BESS) based on voltage source converter is analyzed. On this basis, the mathematical model of BESS is established. In order to achieve smoothing wind turbine generator output active power and to improve the stability of asynchronous generator, this paper presents a control strategy consideration of the threshold voltage. With the help of this control strategy, BESS not only can smooth the active power output of wind turbine but also can improve the stability of asynchronous generator. In order to protect the lead-acid batteries to prevent them from overcharge and overdischarge, a new control method for regulating State-of-Charge of a battery is presented in this paper. By using this control strategy, BESS can smooth the wind power output without overcharge and overdischarge.Asynchronous generator need to absorb reactive power when they are running. If the system is inadequate or non-reactive support capability, induction generator will lose stability soon. In this paper, using series-parallel supercapacitor energy storage system in wind power to reduce output power fluctuations and improve asynchronous wind turbine generator stability is presented. The basic principle of the series-parallel type supercapacitor energy storage system is analyzed. On this basis, the mathematical model of series-parallel supercapacitor energy storage system is established. It shows that the shunt converter can be controlled to smooth the wind power, whilest the series converter can be controlled to stabilize the voltage at the wind turbine generator side. With the help of this control strategy, series-parallel supercapacitor energy storage system not only can smooth the active power output of wind turbine but also can improve the stability of asynchronous generator.In view of the lack of optimization of energy storage system capacity and power used in renewable energy, in this paper, the variance and maximum power ramp rate are used as indicators to optimize energy storage system requirements and capacity used in wind power. The simulation results based on the actual data show that this evaluation method can effectively determine the required capacity and power of energy storage system used for smoothing wind power output.In order to improve power supply reliability, the battery energy storage (BES) installed in low DC side of Solid State Transformer (SST) is presented in this paper. The mathematical model of SST/BES is established. Two different control modes for charge and discharge are designed. The results show that the SST/BES can improve power quality and reliability.