Optimal sizing and limitations of passive filters in the presence of background harmonic distortion

In this paper, the optimal sizing and limitations of shunt, passive, single-tuned harmonic filters for industrial loads are examined. The investigation takes into account not only harmonic current sources due to nonlinear loads, but also the presence of background voltage harmonic distortion. First, an analytical approach in simplified cases is developed, which leads to closed form expressions. These expressions help in gaining a deeper insight into the role of the filter branches and the influence of the various parameters of the system. They also show, both quantitatively and qualitatively, the limitations of passive filters with respect to harmonic control. Next, the general case of this constrained optimization problem is formulated and solved using genetic algorithms. The constraints ensure acceptable solutions in accordance with Standard recommendations, utility regulations and filter parameter variations. The proposed objective function to be maximized is a modified version of the power factor and ensures the optimal solution among acceptable ones. Through extensive simulations of an example system for a variety of voltage and current harmonic levels, potentialities and limitations of filter branches are thoroughly investigated. Practical conclusions drawn can be considered as guidance on engineering judgment for harmonic control in any specific application.