An AC TO AC converter improved in input current harmonics and power factor

This paper is on an AC/AC converter which converts a three phase line frequency power to a single phase of a higher frequency for induction heating. It is a single conversion system in contrast to a widely known double conversion system; AC/DC/AC. But the latter system has two disadvantages; (1) Input line harmonics are so large (especially under power control by DC voltage regulation) that it is difficult to incorporate an effective harmonic filter network. (2) It has a power factor of lag and decreases in the further lagging direction in power control. In contrast, the AC/AC converter system presented here in Figure 1 or 2 has some good features, without reducing conversion efficiency. The commutation scheme is shown in Figures 3 and 5, and is similar to those presented in papers [1] — [3]. But the new method is further improved especially in the above-mentioned features.