Abstract
This paper gives a new insight into the concept of load compensation under distorted voltages. Achieving both unity power factor (UPF) and perfect compensation of current harmonics are not possible where competition will arise between these two important factors. Through evaluating the present control strategies, a generalized, optimal, and flexible control strategy (OFC) for harmonic compensation of utility lines is proposed. The proposed control strategy, which provides a unified and highly flexible compensation framework has the ability of programming for perfect current harmonics compensation, or (UPF) accomplishment, or other newly defined objectives such as maximizing the power-factor subject to some adjustable constraints on the level of current harmonics and unbalancing via an on-line optimization algorithm. The strategy can fulfill the IEEE-519 standards requirements, while guaranteeing the best achievable power factor and optimum required rating for the compensator. Theoretical concepts and practical features of the proposed control strategy have been shown through extensive simulation studies using MATLAB/SIMULINK programs.
I. INTRODUCTION
WIDESPREAD use of power electronic systems have increased harmonics in the utility power networks over the past three decades. Active power filters were developed for harmonic compensation and power factor correction [1], [2]. Fig. 1 shows the block diagram of a parallel active filter. In active filters, the compensation strategy is quite important and various strategies have been proposed to improve the performance of active filters [3]–[5], [7]–[12]. Regardless of compensating tools, decision about which components are undesirable is made based on the compensation strategy, especially where the voltages are nonsinusoidal [6], [13]–[15].
VIII. CONCLUSION
In this paper, a new concept for load compensation was introduced. It was shown that under distorted voltages conditions an active filter with programmable performance is required. A new optimal and flexible control strategy (OFC) for harmonic compensation in nonsinusoidal voltage conditions is proposed where simultaneous compensation of both power factor and current harmonics is not possible. The control algorithm was formulated using a nonlinear optimization problem. It can be programmed for different types of useful cost functions and desirable constraints, which might be selected based on the power quality and some implementation requirements. OFC is a suitable strategy for achieving the IEEE-519 standards with best power factor with no severe impact on the compensator. It can be adapted for various applications where both the power factor improvement and harmonic cancellation of the load is the goal. Further application of OFC and also realizing it using Neural Networks will be presented in a subsequent paper.
