Based on the detailed analysis of operation principle of a single phase three-level AC chopper, its control strategy was studied. Clock-interleaved constant frequency integration control scheme was proposed to achieve the closed-loop control of single phase three-level AC chopper. The hardware implemen- tation method of this control scheme was presented,which was validated by simulation and experiment. Simulation and experiment results prove that clock-interleaved constant frequency integration control scheme is of many advantages such as simple control structure,easy hardware implementation,fast dynamic response,perfect harmonic performance and high power factor. Due to its no duty cycle limits, clock-interleaved constant frequency integration controlled single phase three-level AC chopper can achieve full-range regulation of output voltage. Clock-interleaved constant frequency integration control can be also extended to more level AC chopper flexibly.

Multilevel converter has been widely used in DC / DC converter, inverter and rectifier, but it is rarely used in AC chopper. In the very few reports of multilevel AC chopper, the attention stress is limited on the study of the circuit topology and working principle. The report about the closed-loop control of multilevel AC chopper has not been seen yet. In this paper, on the basis of a three-level AC chopper principle of an in-depth analysis, the closed-loop controls of multilevel AC chopper are primary studied. Compare with common PI control, unified frequency integration control have fast dynamic response, good tracing ability, good regulating capacity and simple structure. Clock-interleaved unified frequency integration control is proposed to implement the closed-loop control of three-level AC chopper. The proposed control method not only can be applied to the mentioned three-level circuit, but also used in others three-level AC chopper. Even for the high number of circuit topology, it is easy to expand. The simulation experiment result proves the feasibility and validity of the proposed control method.

Ac choppers have been widely used in industry applications such as lighting dimmers, industrial heater, soft-starting of induction motors and speed control of pumps, and their control method often adopt voltage instantaneous value PI control. This method has the fault of bad dynamic response and the distortion of output voltage at zero-crossing. One-cycle control technique can solve this problem. One-cycle control is a nonlinear control method which has fast transient response and good tracking performance. A single phase ac chopper with one-cycle control method is presented; the basic operational theory and control method are discussed in this paper. Finally, simulation waveforms and experimental results are given. The experimental results demonstrate the effectiveness of this control technique.