Developing an Induction Heating System Laboratory with DSP Microprocessors and Power Electronic Devices

摘要

This induction heating system laboratory will be integrated into our existing energy conversion labs for senior students. Students will not only understand how the high alternating current induces eddy current in the work piece to convert the resistive losses into thermal energy, but will also observe that the work piece gradually heats up and eventually starts to glow red. The principle of induction heating is to convert electricity to thermal energy inside a conductive work piece by using alternating magnetic fields. The energy conversion efficiency is up to 95% for magnetic materials, and contamination is minimized due to the non-contact heating mode. Therefore, induction heating has been widely used in steel industries for many years. Most engineering students are baffled by magnetic field theories since magnetic fields are not something that they can see, touch or feel except through mathematical equations. To assist students' understanding of this energy conversion process, we are developing an induction heating system laboratory to cover engineering topics in applied magnetic field theories, communication systems, computer networks, power systems, power electronics, sensors, embedded systems, and control systems. In order to generate high strength alternating electromagnetic fields, a switching mode power supply is utilized to feed high frequency current to the induction coils. The major components of the switching mode power supply are DC diode bridges, DC filters, DC-AC IGBT invertors, matching transformers, and capacitor banks. A DSP microprocessor development board is utilized to generate the Pulse Width Modulation signals to drive IGBT devices. Also, zero-voltage switching techniques and closed-loop controls are used to control the output power levels. Infinite impulse filters and fast Fourier transform are built into the DSP microprocessors to obtain real time frequency spectrum analysis of system harmonics. The temperature of the work piece can be observed by using an infrared temperature sensor and the measured temperature can also be fed back to the main DSP microprocessor. The proper output power level adjustment by the microprocessor creates better temperature profiles in the work piece. The students are exposed to the commercial finite-element magnetic field analysis software which provides a visual representation of the magnetic field in the form of flux line plots and scaled color maps. In our current energy propagation class, we introduce and utilize Infolytica MagNet to calculate the magnetic field strength at different frequencies. This software package can also generate animations of alternating current magnetic fluxes in the work piece.