DTC driven single phase fed voltage source inverter with small dc-link capacitor

In voltage source inverters (VSI) relatively large de-link capacitors are used to provide stable dc-link voltage and energy storage. However electrolytic capacitors are large, heavy and expensive. In many cases the lifetime of the electrolytic capacitor is the main factor that limits the lifetime of the frequency converter. Large de-link capacitor causes high line current peaks during dc-link capacitor load. Power factor correction circuits are traditionally used to correct line current quality in single phase supplied VSI. To overcome the problem of the line current quality and big electrolytic capacitor, a relatively small film capacitor (MPPF, metallized polypropylene film capacitor) is selected. While overcoming the problem of the line current waveform and the life time of the electrolytic capacitor the new problem is arisen in the form of the heavily fluctuating dc-link voltage. This leads to heavily fluctuating torque. Many industrial dynamically low performance applications, such as pumps and fans, are high inertia loads. Thus even heavily fluctuating torque can be tolerated. DTC motor control is used to maintain as smooth torque behavior as possible.