Averaged-Model-Based Nonlinear Control of a PWM Three-Phase Four-Leg Shunt Active Power Filter

Current harmonics caused by nonlinear loads yield major power quality related problems in the utility. Such harmonics are commonly reduced by employing static compensators known as Active Power Filters (APF). APF topologies are of various types, depending on technical and economical requirements. In this paper, a new constant-frequency nonlinear control scheme for a shunt three-phase four-leg APF is proposed. The APF is used to compensate the current distortion and the reactive power created by a typical industrial load. The elaboration of the control law is based on the state-space averaged model of the converter, computed in the (d,q,0) synchronous frame. The multiple-loop control scheme consists, first, of inner controllers that ensures current shaping and reactive power compensation, and second, an outer loop to allow voltage regulation at the DC side of the filter. In addition, a nonlinearity compensation block is integrated in the inner sub-controller in order to ensure perfect cross-decoupling and linearity between the inner inputs and outputs. The control system is implemented numerically using Matlab/Simulink tool. The performance of the proposed control approach is finally discussed through the obtained simulation results.