Reseach On Impedance Matching And Parasitic Parameters Of The Induction Heating Power Supply

With the development of microelectronic technique, more and more new power semiconductor devices have being widely used in high power converters such as induction heating device and achieve good efficiency. Meanwhile, the adoption of new microprocessors greatly reduce the complexity of traditional analog control circuits that are composed of separation components, and provides comprehensive protection for the power converter topology, which makes a digitization and intelligent control process.However, compared to microelectronics, the inverter topologies and control algorithms of induction heating have suffered a slow development these years. The traditional inverter topology, e.g. voltage source full-bridge inverter, its switching devices are met with voltage spike problem because of stray inductance. The voltage spike leads to efficiency decline and electromagnetic interference. The widely used control algorithms such as Pulse Frequency Modulation can’t cover the whole power range for its efficiency drop when operated in high switching frequency. The others such as Phase Shift control and Pulse Density Modulation all have problems corresponding to control or usability.In order to analyze the problems of control algorithms existing in the voltage source inverter, several common power control algorithms of induction heating are listed in this thesis including Pulse Frequency Modulation, Phase Shift Modulation, Pulse Density Modulation and so on. This thesis focuses on some characteristics of the control algorithms, including power range, power resolution, zero voltage switching status of switches, output power efficiency, usability and so on. The specific analytical techniques contain the modeling, theoretical and statistical calculations, sequence analysis, graphics of important data. Through the analysis, their advantages and disadvantages are also indicated. Then, in order to analyze the problems caused by the parasitic parameters of the inverter, the thesis mainly focus on the calculation on stray inductance. In order to lessen the stray inductance, the commonly used laminated busbar are modeled and statistical calculated, and a optimization method is obtained.In order to solve the drawbacks of the traditional power control algorithms, this thesis presents the Asymmetrical Frequency Modulation(AFM) control algorithm, in which, the two legs of the bridge are driven by two different switching frequencies. This algorithm makes the output power of the inverter varies much. The switching frequency varies little within each piecewise ranges. Continuous output power and resonant current as well as high efficiency is therefore achieved. The implementation process is analyzed and the output power and efficiency is theoretical calculated, and is verified with a digital signal processor(DSP) based on induction heating prototype. The results turned out to be correct with the theoretical calculation, which means that AFM is a good choice to solve the problems met by the traditional control algorithms.