Power compensator for high power fluctuating loads with a supercapacitor bank energy storage

This paper presents a power compensator for high power loads to reduce voltage fluctuations at the point of common-coupling (PCC) and to compensate the reactive power drawn from the utility grid. In addition, the device may also be used to compensate current harmonics of nonlinear loads. Since the maximum amplitude variations in the supply currents become minimized, the compensator provides a possibility for power rating reduction of the transmission system. The compensator consists of a shunt active filter and a supercapacitor (SC) bank energy storage coupled to the system DC link via a bidirectional 3-phase DC-DC converter. The purpose of the equipment is to draw steady average power from the mains and to compensate the power fluctuations demanded by the load with the energy stored in the SC bank. In basic steady state operation the SC is discharged when the load power is greater than the average power. Correspondingly, the SC is charged from the mains when the load power is smaller than the average power. The control of the system is based on the p-q theory and the functionality of the system is verified by computer simulations with Matlab Simulink in a 250 kW stone crusher application. The simulation results show that the power fluctuations of the load are effectively reduced and the harmful causes, such as voltage flicker at the PCC, are expected to decrease substantially.