Heat distribution control using current amplitude and phase angle in zone-control induction heating systems

This paper proposes a new control method to expand the controllable zone number in a zone-control induction heating (ZCIH) system. The ZCIH system consists of multiple working coils and multiple inverters to control the amplitude and phase angle of each coil current to obtain uniformity in the temperature profile across a workpiece. The ZCIH system makes it possible to control the heat distribution, resulting in a fast heating capability at high temperature conditions. This paper derives a relation between the coil currents and the heat generated on each zone, when the phase angle between coil currents are controlled. Based on the analysis, a new control method is proposed to control the generated heat across the workpiece by adjusting both amplitudes and phase angles of the coil currents. Experimental results clarified that the proposed method can control the heat generated on five zones using only three working coils. As a result, N working coils are possible to control the heat generated on 2N-1 zones, leading to a remarkable heat distribution improvement and/or a significant cost reduction in the ZCIH system.