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A novel approach for synthesising sinus waveforms at power level

Şedele, Serkan Paki
In variable speed motor drive and uninterruptible power supply (UPS) applications, taditional method is to employ some kind of a modulation technique at a high frequency typically 6 kHz to 20 kHz range. In these modulation techniques, the switches are hard switched. The result is application of a series of pulses to the load, and if the load is inductive, sine wave current flows into the load. Hard and rapid switching causes a voltage waveform with a very high dv/dt (rate of change in voltage) causing high EMI problems, reduced life expectancy of the motor and additional losses. So a power supply generating pure sinusoidal voltage waveform is very desirable. In industry some low pass filters called sinusoidal filters, are used at the output of the inverters but this comes with additional cost and bulky filter elements. In this study, a novel approach for generating power level sinusoidal waveforms is proposed. The basic structure is a DC-DC converter that produces a rectified DC-link at its output and an H-bridge inverter that inverts the rectified sinusoids to form a sinusoidal voltage. Main advantages of the circuit are that the H-bridge inverter switches have no switching stresses, they are switched at low frequency so the reliability is increased. Throughout the study different circuit topologies have been investigated and the analysis of the chosen topologies is supported with computer simulations. The system is then set up in the laboratory. In order to prove of the concept, only a single phase inverter has been investigated at steady state conditions. Efficiency, distortion level, magnitude error and device stresses have been obtained. The results indicate that the proposed configuration is very promising.