Efficiency Investigation of an Induction Motor drive system with Three Different Types of Frequency Converters with focus on HVAC applications

This paper discusses the efficiency of induction motor drives for HVAC applications, basedon measurements made on three 4kW induction motor drives. Both converter efficiency aswell as induction motor efficiency is studied and in particular the total system efficiency isdetermined. Measurements have been performed on a 4kW induction motor fed by threedifferent types of frequency converters. Converters A and B use an open loop, constant fluxcontrol, where B has a L-C filter on its output. Converter C uses an open loop, fieldweakening algorithm but also a special pulse width modulation (PWM) technique in order toreduce the switching losses in the converter. Simulations and measurements have shown thatan efficiency improvement of the system can be achieved using a field weakening algorithmwhich improves the efficiency at light load with 18% at 30Hz which in particular is ofimportance in HVAC applications. At full load the difference in efficiency is negligiblebetween system A and C but 3% lower using system B due to the sinus filter. Efficiencyimprovements were also accomplished by using the special PWM technique. It was alsofound that it is important to make a complete optimization of the energy efficiency. Usingsystem B, with L-C filter, gives higher machine efficiency but a low overall efficiency due tohigh converter losses. As a general conclusion, it has been shown that system C was the bestsolution from an efficiency point of view for a typical HVAC application.