Research On Active Filter Technology For Harmonic Restraint Of MID-frequency Induction Heating Power Supply

Induction heating power supply is a kind of power electronic device which usethe principle of electromagnetic induction to heat metal workpieces with eddy current.It has lots of advantages such as rapid heating speed, low energy consumption and etc.so it is widely used in industrial production. Inductiong heating power supply is aAC-DC-AC system. It generates mid-frequency current by rectifying and invertingline frequency current gotten from the grid. In the rectification process, it generates alot of harmonic current, causing serious harmonic pollution to the grid. The issue ofharmonic suppression for induction heating power supply is drawing increasingattention to researhers. In this paper, the structure and the harmonic characteristics ofinduction heating power supply is analyzed, then active power filter is chosen forharmonic suppression. Since harmonic examination system is the key part of APF, sothe harmonic current examination system is designed in this paper.After comparing several common harmonic examination methods, this paperchooses the ip-iq algorithm based on instantaneous reactive power theory as theexamination algorithm. Then a harmonic examination system based on CPLD andPC/104embedded IPC is designed. The hardware circuits design includes phase Avoltage zero-crossing detection circuit, three phase current acquisition circuit, PLLfrequency multiplier circuit, CPLD logic processing circuit and PC/104bus interfacecircuit. The software design includes software running on the CPLD and PC/104embedded IPC. Finally a harmonic examination prototype system is built, andexperiments results are good, showing the correctness of the design.