An optimal selection of induction heater capacitance considering dissipation loss caused by ESR

In the design of a parallel resonant induction heating system, choosing a proper capacitance for the resonant circuit is quite important. The capacitance affects the resonant frequency, output power, Q-factor, heating efficiency and power factor. In this paper, the role of equivalent series resistance (ESR) in the choice of capacitance is significantly recognized. Without the effort of reducing temperature rise of the capacitor, the life time of capacitor tends to decrease rapidly. This paper, therefore, presents a method of finding an optimal value of the capacitor under voltage constraint for maximizing the output power of an induction heater, while minimizing the power loss of the capacitor at the same time. Based on the equivalent circuit model of an induction heating system, the output power, and the capacitor losses are calculated. The voltage constraint comes from the voltage ratings of the capacitor bank and the switching devices of the inverter. The effectiveness of the proposed method is verified by simulations and experiments.

I. Introduction

Induction heating is widely used in metal industry for melting or heating of thin slab in a continuous casting plant because of good heating efficiency, high production rate, and clean working environments. A typical parallel resonant inverter circuit for induction heater is shown in Fig. 1. The phase controlled rectifier provides a constant DC current source. The H-bridge inverter consists of four thyristors and a parallel resonant circuit comprised capacitor bank and heating coil. Thyristors are naturally commutated by the ac current flowing through the resonant circuit. Therefore, this type of inverter called as a load commutated inverter [1], [2], [3].