Reseach On Full Digital Controlled High-power Induction Heating Power Supply

Because of its environmental protection, energy saving and high efficieny, induction heating power supply(IHPS) is widely used in industrial production and modern life. By taking half/full bridges which commonly used in IHPS as the research object, the working principles and characteristics of LC series resonance are analysed, the advantages and disadvantages of different power-control scheme such as variable frequency, pulse desity and DC chopper modulation are summarized. Combining of different power-control can improve the efficiency in the whole power range effectively.Aiming at high frequency high power applications, a novel multiple-frequency IHPS based on center tap transformer is proposed. Its output frequency is as twice as the device switching frequency by combining symmetrical two half bridges and sharing two equal resonant capacitances. The specific operation modes and the corresponding relationship between parameters are analyzed. The characteristics of soft switching, power losses and modulation are studied.To avoid the shortcomings such as narrow frequency, poor reliability, slow dynamic response, of traditional analog control, a full digital controlled method is designed. Based on DSP chip TMS320F28335, a new digital phase difference detection method between the voltage and current, the finite impulse response digital filter and software phase-locked loop(SPLL) program are designed. Experimental tests show that it can detect phase difference accurately, the SPLL can tracking the load resonant frequency accurately. A DC chopper power control algorithm is developed. The PI control method was adopted to realize it. The control software including state machine transition, interrupt service routine, system fault response is designed in detail.A 500 w multi-frequency supply is made and the results verify the effectiveness of the proposed topology, the correctness of the theoretical analysis. Further more, a 100kw/6.2kHz IHPS prototype which is fully digital controled is fabricated. The test result verify the feasibility of the digital DC chopper power control, the software phase-locked loop frequency tracking algorithm and the control system software.