Research of Digital Control Strategy for Multi-Resonant LLC Converter

Digital control of distributed power system is the developing trend of power electronic system integration. The prominent merits of LLC resonant topology can be specified as follows, full range of ZVS for primary switches and ZCS for secondary diodes are achieved, integration of resonant inductor and transformer is easy, wide range operation is realized. This paper deals with investigation about application of digital technology in LLC topology. Combined with the operation analysis of LLC topology, strategy of increment mode digital PID variable frequency control, which is based on DSP, is adopted, and that the flexibility of digital control facilitates modulation process. Main topology with voltage-doubler output and control algorithm are given. Design consideration and flow chart of software are specified. A prototype is built to verify the theoretical analysis. Experimental waveforms of the prototype are illustrated. Feasibility of analysis is proved and digital control strategy is verified. Operating range of switching frequency is 100 K to 160 K when input is from 104 V to 250 V(amplitude).