A novel machineless dynamometer for load testing three-phase induction motors

This paper describes a novel method for rapid full load efficiency evaluation of three phase induction motors using a synthetic loading technique, without the need to connect a load to the machine's drive shaft. The new method uses a digital signal processor (DSP) controlled high switching frequency power electronic inverter to synthetically load the induction machine, while using a new real-time data acquisition system to accurately determine and record the machine's performance. The method proposed considerably reduces the testing time compared with conventional methods of efficiency measurement and the accuracy of the result is maintained. Moreover the use of the power electronic inverter allows a comprehensive control over all the quantities which determine the rate at which the power is dissipated inside the induction machine. This method can also directly quantify rotational losses of the induction motor under test.