Research On Voltage Control Methods Of Photovoltaic DC Microgrid Based On Flywheel Energy Storage System

With the decreasing of fossil fuel and the increasingly serious environmental pollution, the development of distributed generation is faster and faster. As a small controllable generating system, microgrid consists of distributed generators, loads, energy storage devices and control systems. Its appearance points out the way forward for the application of distributed generation technology. Photovoltaic power generation has become the hotspot in the world's renewable energy sector and been widely applied to microgrid because of the adventages of the solar energy, cleanness,non-polluting and renewable. As a relatively new kind of energy storage modes, flywheel energy storage system(FESS) is predominant. Compared with traditional chemical forms of energy storage, it has the advantages of long life, high density, easily to control, pollution-free. It can be a dynamic adjusting device of power quality with a broad application prospect. This article studied on the DC bus voltage control of independent photovoltaic microgrid based on flywheel energy storage system in order to realize the energy to full use, maintain the stability of bus voltage and ensure the reliability and quality of the power supply.First of all, the mathematical simulation model of PV cell, as the micro-source, was established based on its operating principle and output characteristics. And the maximum power point tracking(MPPT) control of photovoltaic cell was achieved through a variable step size Perturb &Observe Algorithms method. In Matlab/Simulink environment, a simulation model of PV cell was built and MPPT control module simulation model was constructed.Secondly, this paper introduced the structure and the working principle of flywheel energy storage device and chose the brushless DC motor as the flywheel driven generator. Based on this, the mathematical simulation model and the equivalent circuit of FESS were constructed. The charging link, for example, adopted traditional speed and current double closed-loop control strategy. In Matlab/Simulink environment, a simulation model of FESS was built.Finally, started from the topological structure of independent photovoltaic microgrid, the importance of the DC bus voltage control was elaborated and related control principle was formulated. Sliding mode control strategy has many advantages, such as simple structure, insensitivity to parameter variation and external disturbance. The composite control algorithm based on sliding variable structure(SVC) and PI was proposed. Two ways of the control strategy for flywheel driven generator were designed and the simulation verification was carried out in Matlab/Simulink environment. The effects of both control methods were compared. The results of simulation showed that in the case of the external environment changing a lot, the composite control method based on sliding variable structure(SVC) and PI was better than PI control only.