Linear Feedback Control of a Parallel Active Harmonic Conditioner in Power Systems

Harmonics are one of the major quality concerns. The increasing use of power semiconductor devices (i.e., nonlinear loads) is keeping harmonic distortion in electrical installations on the rise. Harmonics generally cause the distortions of voltage and current waveforms, which result in many harmful effects on both utilities and customers. A parallel active harmonic conditioner can be used to compensate current harmonics demanded by nonlinear devices so that the supply current remains quasi-sinusoidal. In principle, this conditioner consists of a voltage-source inverter connected in parallel between the utility system and the customer. The control of such an inverter is an essential step in harmonic compensation. Most of the existing control methods are formulated as a classical tracking problem that requires reference generation. In a previous work, a parallel active harmonic conditioner was formulated as a perturbation rejection problem rather than a reference tracking one, and a linear state feedback $H_{\infty }$ controller was synthesized in order to drive the inverter. The objective of this paper is to reduce the number of measured outputs, and therefore to design a linear output feedback $H_{\infty }$ controller by noniterative means. The robustness of such a controller with respect to the system impedance uncertainties is investigated. Moreover, the validity of the synthesized output feedback control law is revealed through both simulation and experimental results.