Study Of Active Power Factor Correction Technology

Power-Factor-Correction (PFC) is a state-of-art technique for reducing harmonic distortion and increasing the power supply network efficiency. Power-Factor (PF) is one of the quality indices of electric equipment, and the Active-Power-Factor-Correction (APFC) technique is the fundamental way to improve it. In recent years, with the stricter quality requirement of electric equipment, this technique has become the focus in the power electronics research field and has been widely applied.The essence of PFC technology is to shape the input current of electrical equipment, and to take power from the supply network but not to give any back. In other words, the input impedance should present to the AC source a resistive load, and the input current should be proportionate to the AC voltage instantaneously. Using power electrical converter, the APFC technology achieves this by controlling energy transportation. In today's APFC research field, the remaining challenges include the appropriate topologic structure of power converter, the optimization of control mode and even the performance improvement of power switch.In this thesis, the main task is to simplify and optimize the APFC control mode, which is undertaken by the basic topologic structure analysis and the mathematic relationship analysis of power converter, and the following new control modes are proposed:1. A PFC circuit within a Half-Bridge output stage is proposed based on the working principle of Buck-Boost converter. This circuit works as a voltage follower to achieve near unit power-factor, and the output waveform also is symmetrical (duty cycle is 50%). Since this circuit can reduce the output voltage, the requirement of the voltage sustaining capability of all power switches can be reduced accordingly.2. A simple way to realize frequency variable controlled Boost type PFC circuit is proposed. The basic principle of this new control mode is that the capacitance and the inductor are both linear components, and the inductor current can be simulated by the voltage of a capacitance, hence both the multiplier and the current detecting loop which are indispensable in traditional control mode can be eliminated. The whole...