The Engineering Design Of Control System For HR-IFS1 Thyristor Medium Frequency Power Supply

Induction heating power supply can non-contact heat metal components based on electromagnetic induction principle. It is now widely used in industrial heating with the characteristics of clean and high efficient. As the emerge of more and more kinds of induction heating power supply load, the heating mode and the environment are become more and more complicated. Thyristor Medium Frequency Power Supply(TMFPS) have to improve its properties for engineering application. In this paper, based on the load voltage zero point at a specific time in ahead for inverse transformation the Silicon Controlled Rectifier(SCR) intermediate frequency power supply is regard as the research object. It analyzed the factors that influence the signal detection and thyristor trigger to solve the problem such as phase sequence detection in the work of engineering, amplitude range compatible, test parameters of the linear range, thyristor drive anti-interference. The paper completed the following work.In order to solve phase sequence matching problem in engineering application, the paper designed optical coupling high voltage measurement circuit, it can detects signal that include the positive and negative work sequence, shortage of supply and supply phase and cycle, makes the system automatically match the change of the supply phase sequence. Also it simplified the circuit structure and eliminated synchronous transformer.In different working situations especially overload, the load voltage is smaller than usually when it starts, which makes frequency tracking more difficult. The paper designed a circuit that based on the coupling constant current tube and the light coupling with high and low voltage conduction threshold. It has good fault-tolerant capability and less leaping voltage at the zero cross moment. TMFPS load frequency is varied, analog filter network can reduce the noise amplitude, but it brings phase shift that limited the performance of frequency detection circuit. On the basis of using high input voltage comparison circuit, the paper also uses dithering middle value and the digital filter circuit that had the Schmidt properties to approximate the real zero-cross moment, which can identify the load frequency and supply phase more accurate.In the whole amplitude range of frequency voltage and current supply, detection parameters are difficult to linearization, it is incompatible between high and low range. Therefore, a dual channel amplitude detection circuit is designed for overcoming this problem, the amplitude detection is processed by a piecewise linearization.In consideration of SCR trigger requirements and anti-interference requirements in engineering application, this paper designed a powerful triggering and anti-interference thyristor driving circuit, on one hand it eliminate the pulse transformer and has feature on powerful triggering and low holding current ability, on the other hand, the circuit with push-pull structure can effectively filter out interference pulse. The paper also designed a phase shifting control circuit that based on FPGA, it make debugging and reuse more easily and flexible.In the paper,signal detection circuit and SCR drive circuit were tested. The results show that signal detection circuit and SCR driving circuit can match the change of phase sequence in TMFPS engineering application. The linearization of amplitude detection parameters is improved. Load voltage frequency can be identified between high and low amplitude range under complex working conditions. It can also effectively filter out the engineering application of electromagnetic interference when driving SCR.