Investigation On Key Aspects In Large Capacity High Frequency Resonant Inverter

High frequency large capacity resonant inverters have been applied extensively in a lot of heat treating industry areas from diatherming, melting, casting, rolling steel to hardening, temper and anneal, welding, dryer, which gave an enormous impetus to the development of national economy.This paper refers to the investigation on key technologies, including the main topology of the large capacity high frequency resonant inverter,load matching,the improvement on the capacity,the design of the driving circuit,the design of phase locked loop circuit and the softing-switching technology in order to achieve high frequency and high efficiency. China is facing great pressure in this power supply due to the out-of-date technologies, as well as the studies ignore of the problems in the ultrasonic frequency and medium frequency, the details must not be overlooked in the large capacity and high frequency conditions.The research is supported by Natural Science Foundation of Hebei Province "Study of the soft-switching technology of Large capacity high frequency dc-ac inverter" (No.E2009000714). It analyses the key technologies of large capacity high frequency interver, designs and debugs integration power units.The main contents and results obtained are as follows:1. The power regulator process of soft-switching is analyzed in detail using the improved limited bipolar control strategy for high frequency voltage-source inverter power supply.In the whole large range of power adjustment, reducing the switching loss, realizing soft-switching, and the ouput current was continuous and lowest output ripple, almost a sine wave.2. A big inductance is used in the current-source inverter to eliminating harmonic, which contributes to connect in parallel. Load matching method was flexible, which is apt to power adjusting. The main topology structure is impovered with a mall inductance series and a small capacitor parallelled, solving the problems of over-current, current-rising-rate protection, effective miller capacitance, and also increasing the switching speed of the power MOSFET, make sure that the main circuit was stable.3. Third order CLC load matching circuit is designed, which takes the place of the high frequncy transform to accomplish the higher effects and lower cost. Changing of the reserved capacitance value is to adjust the output power and frequency, which can let the output power and frequency wider, reducing the the selected stander of the Power MOSFET. Changing the power devices switching frequency and matching the load capacitance parameters are analyzed in quantitative, the output current and the load branch current are considered to set the capacitive operation ranges and the maximum output active power.4. On the base of full considering of the impact switch performance factors of parallel power MOSFET their own parameters and external parameters, equivalent power MOSFET switch circuit model, spelt out the parameters conformance range which guarantees to dynamic balanced current and synchronism with ZCSON for the first time. It is a theory supported to the parallel Power MOSFET in in project application.Then a clamping circuit is proposed to restrain the over voltage and decrese the losses generated by turn-off. The parameters design formula of the improved parallel module is present, and applied to current-type resonant inverter. The experimental results verified that the modes and theoretical analysis is rational: the dissimilarity trace of the G-S voltage is less than 5ns under the frequency of 500kHz, and achieves soft-switching.5. The paper presentes a new discontinuous current source gate driver for Power MOSFET in the high frequency resonant inverter, the detailed description of the work processing of the new driver and then making the driver control digitalization,which has many advantages, such as significant reduction of the switching transition time and switching loss, decrease the conduction loss and et al.6. Based on the phase-locked loop performance requirements in the resonant inverter, the paper designes a new PLL circuit,which has the advantage of wide bandwidth of tracking range, high locking accuracy, quickly dynamic respond performance and realized us order tracking speed, overcoming the circuit environmental noise.Through analysing the working principle of CLC load high frequency current-type resonnant inverter, a all-Digital Phase-Locked Loop with adjusting the capacitive angle is desighed. which is usful and superiority.At last, the above principle and scheme are used in a large capacity high frequency current-type inverter experimental system with 400kW/400kHz, and do many experiments and tests, to prove that the all above contol methods and results are correct and reliable.