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ADVANCED ELECTRIC GENERATOR & CONTROL FOR
HIGH SPEED MICRO/MINI TURBINE BASED POWER SYSTEMS

INTRODUCTION

High-speed micro-turbines and mini-turbines play a significant role in the Distributed
Power Systems that provide dependable electric power close to the user. Several high-speed
turbo-generators manufactured by various corporations are now available in the 30 kW to 90 kW
range. These systems operate at speeds from 50000 RPM to 120000 RPM. The generator is
directly coupled to the turbine shaft. This obviates the need for a gearbox, helps reduce the size
of the generator, and lowers the cost of the overall system. The output power is electronically
processed and conditioned to provide constant voltage dc or multi-phase ac power at constant
frequency.
Technology of micro-turbines is moving forward to address ratings above 100 kW due to
the growing demand for larger units. There is a tendency to use multiple units of the existing 30
to 90 kW packages to satisfy this demand for higher power capacity. However, use of turbogenerators
of higher ratings is likely to be beneficial to the user for the following reasons:
a) lower cost of investment per kW for purchase and installation
b) lower cost of maintenance because of reduced parts count
c) higher efficiency
d) safer operation.
At the present time most generators used with micro-turbines are based on permanent
magnet technology. It is the objective of this paper to compare alternatives to the PM generator
technology, and introduce induction generator technology as a more viable alternative in the
power range exceeding 100 kW. The approach in this paper is to present the concept in all its
dimensions including the issues of generator and controller design. The authors are currently
engaged in the development of the high-speed induction generator systems. Their experience in
the field of the technology forms the basis supporting the discussions in this paper.