System design and implementation of induction generators self-excited by capacitors for maritime diesel electric propulsion systems

The paper proposes a startup and operation method of stand-alone self-excited induction generators (SEIG) for maritime diesel electric propulsion systems. When an induction machine operates as a generator, it needs an excitation current such that the rotating magnetic field can be built up and maintained. The excitation current can often be obtained from either grid or shunt capacitors. The proposed excitation mothed of SEIG is to start up the SEIG by the shunt capacitors and continue to operate with an inverter that supplies both the excitation current to the SEIG and active power to DC bus. The shunt capacitors are selected based on the series L-C circuit oscillation theory. The control of the inverter is with a space vector motor control. The method is verified by a test setup built by using commercial frequency converters. The test results show that the proposed SEIG system can operate as required.