Research On Parallel PFC Technology

Active power filter and power factor correction technology are both effective method for restraining harmonic contamination and increasing power factor. Refer to conventional PFC topology, the shunt PFC studied in this paper doesn’t need to deal with the full load current, so it is possible to improve the efficiency. Based on direct source current control scheme, while the magnitude of the source current is decided by the DC side voltage control loop and the phase of the reference is locked with source voltage, the power factor will be nearly to 1. Three circuit structures have been studied in the paper. The single full-bridge shunt PFC is the most common and simple structure. The double full-bridge structure can increase the compensation capacity, and the high equivalent switching frequency can be achieved with CPS-SPWM technique, but two DC side capacitors is needed. Another structure has been introduced, the same performance can be fulfilled and only one DC side capacitor is needed. Based on the analysis of shunt PFC, a prototype has been designed and developed. The experimental results show that the shunt PFC can compensate the harmonic current well and increase the power factor.The parallel PFC can also be controlled with indirect current control scheme. By control the inverter’s amplitude and the phase angle between the inverter and the source, the source current is controlled indirectly, so it is not necessary to detect the load current for extracting the harmonic and reactive current. Three control schemes have been analyzed in detail and the design of line impedance has been analyzed.To avoid the inrush current while two voltage sources are paralleled, the operation principle of phase lock loop is analyzed firstly, A digital phase lock loop is designed. The experimental results show that the phase lock loop is with good performance to track the phase angle reference.The virtual resistance is also analyzed. Three control schemes which adopt the filter inductance current feed-forward, filter capacitor current feed-forward and output current feed-forward are proposed to produce the virtual resistance. The analysis results show that only filter inductance current feed-forward and filter capacitor current feed-forward can increase the output resistance significantly. At last, by using MATLAB tools, the PFC with indirect current control scheme has been simulated. The simulation results show that this control scheme has good performance in restraining the harmonics and increasing the power factor.