Analytical research on unified power quality conditioner based on super capacitors energy storage system

To extend the compensation ability of unified power quality conditioner (UPQC) and suppress the grid current fluctuation at the time of power regulation, a kind of improved UPQC topological structure is proposed. With advantages of high power density, large electrostatic capacity and long cycle life, super capacitors are combined with bidirectional DC/DC converter to compose the energy storage system in parallel with DC-link to keep DC voltage constant and to be used also as a spare UPS. Low frequency mathematical model of the conditioner under dq coordinates based on state-space method is built and non-PLL compensation detecting method is applied. In addition, both the control strategy of voltage and current compensation and energy management schemes of super capacitors are given. This structure provides a new fitting way for UPQC and simulation results show clearly the feasibility.