Induction generator has several benefits to offer for the micro, mini power systems under consideration. These benefits relate to the generator design as follows:

i) Cost of Materials: Use of electromagnets rather than permanent magnets means lower

cost of materials for the induction generator. Rare earth permanent magnets are substantially more expensive than the electrical steel used in electromagnets. They also must be contained using additional supporting rings.

ii) Cost of Labor: PM’s require special machining operations and must be retained on the

rotor structure by installation of the containment structure. Handling of permanent magnets that are pre-charged is generally difficult in production shops. These requirements increase the cost of labor for the PM generator.

iii) Generator Power Quality: The PM generator produces raw ac power with unregulated

voltage. Depending upon the changes in load and speed, the voltage variation can be wide. This is all the more true for generators exceeding about 75 kW power rating. On the other hand with SR generator, the output waveforms are non-sinusoidal and peaky as shown in Figure 8. These waveforms must be filtered in order to get reasonably constant voltage output.



produce a constant dc voltage. Additionally, the ac voltage can be stepped up or down using a transformer to provide multiple levels of voltages if required.

iv) Fault Conditions: When an internal failure occurs in a PM generator, the failed winding

will continue to draw energy until the generator is stopped. For high-speed generators, this may mean a long enough duration during which further damage to electrical and mechanical components would occur. It could also mean a safety hazard for the individuals working in the vicinity. The induction generator on the other hand is safely shut down by de-excitation within a few milliseconds, preventing the hazardous situations.

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