| Because of un-controlled rectifier, general inverter has some drawbacks, such as low ac-side power factor, big current ripple and un-revisable power flow. By replacing the un-controlled rectifier of general inverter with PWM rectifier, dual-PWM variable-frequency system is realized. This kind of device can actively eliminate ac-side harmonic pollution of inverter, raise ac-side power factor, economize energy resources, and promote performance of inverter.In this paper, dual-PWM variable-frequency system has been divided into two parts: PWM rectifier and PWM inverter, structurally and functionally. The author lays a strong emphasis on study of PWM rectifier and its control method. Under steady state, the four-quadrant working principle of PWM rectifier has been explained here, the key for which has been found to be ac-side current control. Based on the mathematical model under reference frame (a, b, c), the mathematical model under reference frame dq is deduced by introducing the idea of rotating reference frame. After analyzing and comparing two kinds of current control methods of three-phase VSR: indirect current control and direct current control, the author employs the latter as main control scheme, which is to control the phase and amplitude of ac-side current directly, by using dual closed-loop control scheme, through sampling currents of phase a and b and converting them by 3s/2r to get active component and reactive component of ac-side current.Based on the above-all study, experimental device has been designed, including power circuit, control circuit, sampling in-phase circuit and protecting driving circuit. Its controller is DSP TMS320F240. Control firmware has been realized with assembly language of DSP. At last experimental results are presented, as well as the analysis of them.
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