Comparative Study of Synchronous Generator Harmonic Models

In order to predict voltage distortion in stand-alone synchronous generator supplied systems, accurate harmonic models of the machine are required. In an industrial context, often simplified models based on the inverse sequence and subtransient reactance are used. However, if the full machine is considered, a process known as frequency conversion occurs. In this paper, the deviation between the voltage distortion predicted through simplified models and frequency conversion is derived. Using these expressions, the error made through the simplified models is calculated for commercial machines with varying power ratings. Finally, the error calculation is applied to a 250kVA machine and evaluated through simulation. Based on the results, the negative sequence reactance yields the most reliable results, with an important reduction in the error for high power machines. However, for machines with a high subtransient saliency, the use of simplified models will result in significant errors.