An approximate analysis of a starting process of a current source parallel inverter with a high-Q induction heating load

An approximate analysis of the start-up process of a resonant loaded current source parallel inverter is presented. The proposed approach may be applied to inverters whose industrial applications are induction heating and metal melting installations. To estimate the eigenvalues of the third-order set of differential equations, the iteration method has been used. By using the arrived at formulas it is possible to select inverter thyristors that meet the inverter start-up characteristics. The approximate formula's accuracy was estimated by computer-aided analysis. It is shown that at the inverter starting process the turn-off angle changing may be of two kinds: monotonous or oscillating. Regions of inverter parameters that cause one or the other of these two processes are determined. When the changing of the turn-off angle is monotonous, the achieved approximate formulas can be used. The analysis of the oscillating process was performed by applying the experimental design theory statistical methods to the computer-simulation results and the approximate formulas for the oscillating region were also obtained. Two examples of the inverter design procedure and thyristor choosing techniques are given. Finally, an experimental verification of the calculation results is performed.