Analysis and control of a three-phase dc/ac step-up converter

Many applications employ PWM Voltage Source Inverter fed by a front-end diode rectifier. In some circustances, such as in UPS, a boost of the voltage is required. The commonly available solution such as the use of ac step-up transformers, or the substitution of the front-end stage with an active rectifier, or the addition of a chopper in the dc link are either complicate or expensive. A well known alternative is the use of a Current Source Inverter (CSI) instead of the VSI. However, the CSI requires reverse blocking capabilities for the switching devices, then it is not practicable using standard IGBT packages. A possible and not yet studied solution is to combine three boost choppers, in order to obtain a VSI allowing both a voltage step-up and the ac output. In this paper, after the introduction of the mathematical model of the proposed converter, some design considerations are discussed and its behaviour using sliding mode control is analysed. Simulations confirm the effectiveness of the proposed solution.