Research On A New Type Of Active Power Filter

Active power filter is widely used in various industrial fields and the power systems for its advantages of compensating harmonic and reactive power at the same time, filter performance not affected by grid parameters, high reliability and good compensation effect. At present, traditional APF with harmonic detection is applied most. However, the system of traditional APF contains harmonic detection and harmonic tracking control modules, so its structure is complex. What’s more, the compensation performance is limited by various factors and it costs high.This paper studies a kind of APF based on non-harmonic detection and indirect current control method. The harmonic detection is not required and the grid current is extracted directly. Then, the gird current will be controlled by the controller to realize the harmonic compensation.It needs to detect the voltage phase angle when determining the instruction current. However, the imbalance of three-phase grid voltages is a common Phenomenon, this paper employs positive sequence fundamental wave voltage phase angle’s detection method based on sinusoidal amplitude integrator to solve the problem. Indirect current control method includes two control loops: grid current control inner loop and DC voltage control outer loop. PI-VPI controller is applied to adjust the grid current in grid current inner loop and DC voltage outer loop controller is designed to keep DC voltage of APF constant by using a simple PI regulator.The common structure of APF is three-phase six-switch topology and the three legs are all composed by power switches. Therefore, the cost and switching loss is high. If one of the three legs is replaced by two capacitors, the number of switches to be controlled will reduce from 6 to 4 and the new structure is called three-phase four-switch APF which has the merits of reducing the switching losses and decreasing the cost of power switches and heat radiation. For three-phase four-switch topology, the voltage of the two capacitors in the DC side need to be controlled at the same value or the compensation performance will be influenced. This paper proposes the equivalent SVPWM modulation method with the voltage deviation’s effect to control the voltage and reduce the effect of the voltage deviation. At last, the combination of three-phase four-switch topology and no harmonic detection technology is a very economical harmonic suppression scheme.Finally, the reliability and validity of the new APF is analyzed and verified in MATLAB/Simulink, and experimental platform is also set up to verify some of the theories.