This paper control the dc-link capacitance of single power-cell with closed loop for energy feedback and steady DC-link capacitance voltage by rebuilding the rectification of single power-cell based on the technology of three PWM rectifier.

To make the servo system have the expected functions,it s especially important for selection of DC bus voltage in servo driver.

The direct torque control(DTC) system fed by TSMC was proposed that to control the inverter to implement DTC,and to control the rectifier to correct input power factor,or improve the performance of the DTC system by controlling input current space vector or the scope of DC bus voltage.

The reason about weakly performance at low speed-lower ratio of voltage signal-to-noise (SNR) was analyzed,and proposed a novel method-adjustable DC bus voltage,to enhance the SNR as well as to improve the low speed performance.

On the basis of analyzing the developing history and present status of soft-switching technique, DC-rail zero voltage transition soft-switching inverter circuit and resonant pole inverter circuit are selected as the study object in this paper.

In order to improve the line-to-line voltage quality of three-phase three-level inverter with H bridges,the phenomenon of DC-link ripples and the neighboring layer overlapping of line-to-line voltage are analyzed theoretically.