A novel technique for optimising harmonics and reactive power with load balancing under nonsinusoidal supply and unbalanced load conditions

Abstract

Generally, conventional power factor corrections techniques assume ideal conditions, viz. sinusoidal supply voltage and balanced load. But vast majority of the domestic and industrial loads present in the power distribution system are nonlinear and unbalanced. Under such conditions, attempt to make the power factor unity result into a nonsinusoidal source current, which increases total harmonic distortion (THD) in the system. On the other hand attempt to make harmonic free current may not result in unity power factor because of the harmonics present in the supply voltage. Thus, there is a trade-off between improvement in power factor and reduction in THD. With the introduction of power quality norms by various utilities, it has become unavoidable to optimize power factor while satisfying harmonics limits. In this paper, a novel technique for optimisation of THD and power factor subject to power quality constraints is presented. The algorithm uses Lagrange multiplier technique to optimise the nonlinear equations. The algorithm calculates the control coefficients by Newton Raphson method and is used to compute the desired source current that balances the system besides optimising power factor satisfying the load power while meeting the THD limits. Knowing the load current, the compensating current to be supplied by the shunt active power filter to the power system is calculated. This technique, besides satisfying the power quality norms, also balances the imbalance in the system. It is applicable for single-phase and multiphase system under sinusoidal and nonsinusoidal supply conditions. The proposed scheme does not use the widely used p-q theory and use simple computational techniques. Simulation using MATLAB has shown encouraging results. The scheme is being implemented in hardware using DSP.