Squirrel cage induction machines in distributed generation and microgrids

The focus of this work is to study the modeling and control issues related to active control of reactive power for plug-and-play operation of a squirrel cage induction generator in a microgrid. Coordinated design and control system for an integral induction generator and active excitation system (IGAES) in a microgrid is presented.;Frequency droop control is utilized for real power sharing and is realized either through a constant rotor frequency control or alternatively using an inversely proportional relationship between machine torque and slip frequency. Voltage droop control is utilized for reactive power sharing and is realized through an inversely proportional relationship between reactive power and terminal voltage.;A phase locked loop utilizing the induction generator d-axis terminal voltage to drive the frequency droop controls is presented as a novel means for controlling the induction generator in microgrid applications.;The voltage droop characteristic is enhanced through the addition of a feedforward term representing the nominal reactive power required of the induction generator as a function of output power.;State variable control utilizing local measurements is developed for system level analysis. The response of the proposed system to control setpoints, load changes and grid connection and disconnection is presented using analysis, simulation and experimentation.;The use of eigenvalue migration as a function of time is presented as a measure of small-signal stability and is especially useful for evaluating self-excitation of the induction generator.;The scaling of the controller scheme with power level and issues related to modeling different power levels of IGAES is discussed as well as providing reactive power compensation in the presence of significant non-linear auxiliary loads.;Development and analysis of a series harmonic filter with integral power factor correction capacitance as part of a passive excitation control scheme for the induction generator is presented as a lower cost alternative to the active system for grid-tied applications. The use of sequence analysis for this filter under voltage unbalance conditions is presented. Such a filter was also shown to prevent single phasing operation of ambient rectifier loads under voltage unbalance conditions.