One of the most emphasized problems to be solved in power systems in recent years is the line-current harmonics problem. This is due to the use of diode rectifiers, PWM converters, nonlinear loads, and so on. To reduce or eliminate such current harmonics, an active power filter (APF), which is a sophisticated power electronic converter, has been studied and used in some practical applications.
In this paper, we propose and discuss two new control methods for three-phase shunt APFs: the sinusoidal linecurrent control method and the instantaneous-reactivepower compensation control method. They are based on pulsewidth prediction control, or a predictive-instantaneous-current PWM control. Neither any instantaneous power information nor coordinate transformation is necessary for control. In the sinusoidal line-current control scheme, the controller governs the switching devices of the APF by using the pulse width that is optimally predetermined at the beginning of every switching period with the sinusoidal current reference. The line currents flow sinusoidally and are in phase with the voltage accordingly. In the instantaneous-reactive-power compensation control, the control is performed so that the resultant circuit of the load and the APF is regarded as a time-variant conductance circuit model. The APF with this control scheme can cancel effectively the instantaneous reactive component produced by the load though the controller is simple.
This paper discusses the performance characteristics of the APFs when a three-phase diode rectifier and an unbalanced load are connected to the line. The practicability of the proposed methods is verified by experiment.