Research On DSP-based Control For Power Factor Correction

Reducing harmonic pollution especially generated by conventional AC/DC rectifier and improving the power factor are hotspot in power electronics fields, so PFC (Power Factor Correction) is used in many applications. With the development of digital technique, more and more PFC control algorithms can be implemented in power electronics by the digital signal processors (DSP). Nowadays it is popular to use digital control in power supply design.In this thesis, a PFC project based on DSP is presented firstly. Multiple-loop control strategy with the instantaneous outer voltage loop and inner current loop is used in the PFC converter. How to design the two loops, hardware and software of the control system are analyzed in details. The simulation results of MATLAB confirm that the circuit parameters are appropriate. In the end, a laboratory prototype based on TMS320LF2407A is presented. The test results validate a good performance of the digital implementation under the ac line voltage variation, with the switching frequency 50 KHz.It is one of the directions about control strategy's development to simplify the control algorithm, reduce the control cost, and increase the switching frequency. In this thesis, a method in which the duty ratio is directly calculated without current sensor is deduced. Most calculations can be accomplished in several switching cycles. This strategy doesn't need detecting the current and calculations of inner current loop are replaced by the direct duty ratio calculation. The MATLAB simulation results verify the feasibility of this control strategy. The control algorithm is simple and computing time is minished, so the switching frequency can be improved up to 100 KHz with TMS320LF2407A DSP.A kind of PFC control strategy without voltage loop is also put forward in this thesis via improving the control algorithm. A good dc voltage regulation can be obtained by adjusting gainαunder ac line voltage variations. By detecting the load current to adjust the control coefficient, the output voltage is steady under load variations. The control characteristics of this circuit are investigated by simulation analysis with MATLAB. This control strategy is very simple in algorithm, so the computing amount is decreased greatly. Finally the digital control of PFC with switching frequency 150 KHz is realized by TMS320LF2407A DSP. When switching frequency is lower, because of fewer calculations, more resource of DSP can be used in latter DC/DC converter, where the input current shaping and output voltage regulation can be realized with one piece of DSP.