Control strategies for series and shunt active filters

Designs of shunt and series active filter controllers are presented in systems that have voltage and current with unbalances and/or harmonics. The control strategy considers the presence of harmonics and unbalances simultaneously in the system voltage and load current. Although fundaments of the instantaneous active and reactive power theory (the pq theory) are used to design the controller, it is not directly used, since the Clarke transformation (abc to αβ θ transformation) is avoided. These fundaments and a method of minimization, together with a robust synchronizing circuit (PLL control circuit), are combined to form a concise control strategy. The shunt control strategy provides current compensation, such that the compensated current drawn from the network is sinusoidal, balanced and minimized. In other words, the compensated current corresponds to the active component (that component in phase with the system voltage) of the fundamental positive-sequence current of the load. The series control strategy provides compensated voltages in such a way that the voltage delivered to the critical load is sinusoidal and balanced (it comprises only the fundamental positive-sequence component). Simulation results are presented to validate the proposed control strategies.