| AC voltage controller has been widely used in industry applications such as lighting dimmers, industrial heater, soft-starting of induction motors and speed control of pumps. Phase controlled mode with thyristor is always used in AC voltage controller at present, which has some drawbacks, such as high harmonic distortion for voltage and low line power factor in deep control. AC chopper can solve these problems, and this is also the focus of this paper.The present situation of single-phase AC chopper at home and abroad has been analyzed in this paper, the working principle of the Buck-type AC chopper has been studied deeply. RC commutation mode is proposed to solve the commutation problem of AC chopper. On the basis of the study of traditional closed-loop control methods, especially PI control for the Buck-type AC chopper, one-cycle control scheme which is of good waveform quality, fast transient response and good tracking performance is adopted. It can solve the problems, such as static error and the distortion of output voltage at zero-crossing in PI control. On the basis of theory analysis and simulation studies, the sample machine which has power of 200W is developed. The theory analysis is verified by the final experimental results.Besides, because the voltage level of power electronics can't satisfy the requirements of equipment in high power applications, the technology of multilevel can solve this problem. The work principle of a three-level AC chopper has been analyzed. Clock-interleaved unified frequency integration control is proposed to implement the closed-loop control of three-level AC chopper. The theory analysis is verified by the simulation experimental results. |
