Synthetic loading of three phase induction machines using PWM inverter

Synthetic loading is a method for testing induction machines in full loading conditions, by this method, induction machines without any mechanical load connected to the shaft can behave as a full loaded machine. This method could be useful when it is difficult to connect a mechanical load to the shaft as in case of vertical induction machines. This can be done by supplying the machine through a mixed frequency voltage source to generate an additional torque against the main torque. Therefore, the machine will draw the full load current without coupling to a mechanical load. There are different methods to achieve this task such as using two alternators or using PWM inverter with different modulation techniques such as Constant Voltage Variable Frequency (CVVF) method Variable Voltage Constant Frequency (VVCF) method and Variable Voltage Variable Frequency (VVVF) method. This paper discusses the principle of the synthetic loading and compare between the above mentioned methods according to the motor performance, losses and efficiency.