Flywheel energy storage system design for distribution network

Abstract

It is necessary to install flywheel energy storage (FES) systems in distribution networks, which can improve the quality and supplying reliability of electric power. In this paper, a 10 MJ FES system is designed, the power of which can reach 10 kW. The FES system is composed of four parts: (1) flywheel; (2) bearing; (3) motor/generator; and (4) AC power converter. The AC power converter consists of two inverters, one for the motor/generator and the other for power systems, both of which are controlled through a microprocessor controller. The control method is discussed in detail. During the storage period, the AC power converter makes sine waveform currents to accelerate the flywheel. At the generating times, the flywheel decelerates and returns energy to the DC bus and in the meantime the AC power converter transform the DC energy into 50 Hz alternating currents for power systems. The amplitude and the phase of the AC voltage for distribution systems can be modulated respectively, so the voltage of distribution network could be controlled in any case. The microprocessor controller uses the SPWM method to control the AC power converter and a SPWM control waveform measured by oscilloscope is given. The FES system is superior to any other energy storage system in that it has high efficiency, high SED, long life and no pollution to the environment. The FES system can be installed at the customer's site and does not require any new transmission facilities.