Study On Virtual Resistive Active Power Filter

Harmonics pollution of the utility grids is becoming more and more serious, and the requirement of power consumers for power quality is increasing. Because of the excellent performance, active power filters(APFs) are widely used in the field of harmonic control. The traditional APF, which is based on current detection, is usually just able to compensate harmonic current caused by the local nonlinear loads, and cannot absorb the harmonic current injected by other nonlinear loads from the power grid. The main purpose of this paper is to study a virtual resistive active power filter which can absorb harmonic current from the grid without the detection of the load current, and to propose a new strategy of harmonic control based on the virtual resistive APF, which can define the controlling or polluting behavior easily and give a reward or punishment correspondingly. With this strategy, we can fully mobilize power consumers’ enthusiasm of controlling harmonic pollution, so that we can achieve the purpose of improving power quality.In this paper, the specific harmonic detection methods based on both the instantaneous reactive power theory and the fast fourier transform are analyzed. And the parameters of PI controller for current and voltage control are designed by setting up the mathematical model of APF.Aiming at the limitation of the traditional APF in multi-harmonic source area, a kind of virtual resistive APF based on voltage detection is proposed. The APF proposed in this paper works as active harmonic resistors to absorb individual harmonic current by only detecting individual harmonic voltage of power system, breaking through the limitation of the traditional APF. On the basis of the virtual resistive APF, a new strategy of harmonic controlling is proposed in this paper. The virtual resistive APF makes the individual harmonic power absorbed reach the maximum value by adjusting the equivalent individual harmonic resistors, and if we define the controlling or polluting behavior by the direction of harmonic power flow and give them a reward or punishment correspondingly, the additional cost of consumers caused by absorbing the harmonic current will be compensated. In this way, power consumers’ enthusiasm of controlling harmonic pollution will be fully mobilized.Based on the deep analysis and study on the conditions of the optimal resistance under different circumstances, a method of automatic adjustment for the optimal resistance is proposed, which is based on one-dimensional search. And for the circumstance when system resistance is much smaller than system reactance, another method based on system impedance calculation is proposed. The simulation results show that the virtual resistive APF with the mechanism of optimal resistance automatic adjustment can adjust individual harmonic resistance to the optimal one rapidly, and perform well in harmonic control.A virtual resistive APF experimental system is designed based on TMS320F2812 DSP and the design method is detailedly introduced in terms of the main circuits, the control circuits and the program. The experimental results further demonstrate the effectiveness of the virtual resistive APF in harmonic control.