Research OnApplying FESS And SVC To Improve The Power Quality In Micro-grid

With the energy crisis and environmental issues have become increasinglyserious, Smart Grid has become the common goal of every country owing to itscleanliness, intelligence and flexibility. Micro-grid is an important part of the SmartGrid. In the Micro-grid, solar, wind and other new energy sources are intermittent andunstable, and a large number of power electronic equipments are used in the control,access and protection of the Micro-grid. All these bring power quality problems,which restricts a wide range of applications for Micro-grid.Against the frequency and voltage deviation caused by DG’s power fluctuations,a proposal of combining Flywheel Energy Storage System (FESS) and Static VarCompensator (SVC) to improve the power quality is raised. We use the permanentmagnet brushless DC motor (BLDCM) as the flywheel drive motor. Flywheel is inparallel with DG on the same DC bus. When DG’s energy is sufficient, the FESS ischarged, and the electrical energy is changed into mechanical energy. In order tomaintain steady increase of the flywheel speed, we use speed and current doubleclosed-loop control system. When DG supplies energy inadequately or DG is in ashort-term failure, FESS changes into the discharge mode. We take use of a Boostcircuit to stabilize the DC bus voltage, and then transform DC into AC power throughthe inverter. SVC (TCR+TSC) is installed on the load side. It compares the detectionvoltage with rated voltage to calculate the reactive power shortage, and then controlswitching of TSC and the TCR firing angle. In this way, FESS can stabilize thesystem power, regulate frequency, and supply uninterruptible power to the load. SVCcan balance system reactive power in real time and maintain the load voltage stable.Therefore, the power quality of Micro-grid can be advanced effectively.We establish a simulation model of Micro-grid system with FESS and SVC atMatlab/Simulink platform and analyze the charging and discharging process of FESSrespectively. Observing system frequency waveform, load-side power levels andvoltage quality, we prove that the proposal of FESS and SVC is an effective measureto improve the micro-grid power quality.