| Summary: | A new and improved stabilizer was developed for the variable speed
generation (VSG) system. The VSG system exhibits periodic oscillations which
sometimes leads to a loss of synchronism. After careful study, a simple but
effective strategy to stabilize the system was implemented with real time digital
feedback control.
The VSG system consists of an engine, which is the prime mover, driving
a doubly fed machine (DFM), which is the generator. The stator of the DFM is
directly connected to the grid while the rotor is connected to the grid through
a power electronic converter. The converter used in this study is a series
resonance converter (SRC), but the proposed method may also be applied to
other kinds of converters. The stabilizer senses the RPM of the engine, the
feedback signal, and controls the rotor current amplitude and frequency of the
doubly fed machine.
Control was implemented using the 80C196KB microcontroller. The
software consists of a mix of "C" and assembly language. Speed being an
important factor in the implementation, care was taken to minimize the control
loop times. The important features of the hardware and software developed for
the stabilizer are:
(1) 12 MHz controller board
(2) Real time digital band pass filter
(3) Instantaneous rotor speed measurement
(4) Interrupt driven measurement and control loops
(5) User defined setup parameters
(6) IBM PC based real time serial communication
The performance of the VSG system was studied with and without the
stabilizer. A significant improvement in the stability of the system was noticed
over the entire region of operation. === Graduation date: 1991
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