Ohmic heating of food by means of high frequency power inverters

In this paper, an ohmic heater circuit is proposed using low cost, low volume, high power factor, high efficiency, and high frequency power inverters. In order to reduce switching losses while keeping operation frequency high, the well-known techniques of zero-voltage switching (ZVS) and phase shifting control are described and used. A low frequency control loop is proposed as a way of getting low harmonic input current distortion and thus high power factor. The power stage and the control loop are shown and discussed. Experimental results are given for a single-phase, 3-kW, 60 kHz-switched full bridge ZVS inverter with efficiency higher than 90% and power factor 0.99.