Optimum control of selective and total harmonic distortion in current and voltage under nonsinusoidal conditions

摘要

Active-filter-based power-quality improvement schemes, in general, focus on the reduction of total harmonic distortion (THD) and improvements in power factor (PF). This may not be adequate because standards, such as IEEE-519/IEC 61000, require that apart from PF and THD, selective (specific) harmonic distortion (SHD) too, should be controlled. The issue is further complicated due to the presence of nonsinusoidal current and voltage waveforms in the power system. Under such conditions, any attempt to achieve unity PF does not result in harmonic-free current (or voltage). Similarly, compensation for current (or voltage harmonics) does not yield unity PF. The best solution to this tradeoff is the optimization of PF, SHD, and THD. This paper presents an algorithm which restricts the THD and SHD within the specified limits, while optimizing the PF. The algorithm uses the Lagrange optimization technique to minimize the total apparent power. The average active power demanded by the load dictates the equality constraint, while the maximum limits on THD and SHD lead to inequality constraints for the optimization problem. All of the analytical, simulation, and experimental results of this work are presented.