Globally stable control of three-phase three-wire shunt active power filters

This paper proposes a new control strategy for three-phase three-wire shunt active power filters. The idea in this strategy is to form an energy-like Lyapunov function in terms of the active filter states and then determine the control law that makes the time derivative of the Lyapunov function always negative for all values of the states. It is shown analytically that a globally stable control is possible. The references for the active filter currents are obtained by subtracting the measured load currents from the generated source current references. The amplitude of the source currents is adjusted by employing a proportional-integral regulator in the voltage control loop. Matlab simulations are performed for a nonlinear load drawing quasi-square-wave currents from the mains. Simulation results show that the Lyapunov function-based control strategy not only eliminates the load current harmonics successfully, but also exhibits excellent transient response during large load variations.