Stability of converter systems supplied by non-constant voltage source

In this study, the instability modes and effects of a non-constant voltage supply on power-electronic drives with different configurations are analyzed. The systems with constant-voltage sources are also investigated. In order to analyze converter drives with non-constant voltage sources, models are derived for the components together with system interfacing. The bifurcation-theory oriented method is used in this study to examine the dependence of the stability on system parameters. The bifurcation analyses are verified by detailed computer simulations using the Electromagnetic Transient Program.; The analysis is emphasized on effects of the non-constant voltage supply on the power-electronic drive systems. A variable frequency control is derived to apply to the induction-motor drive systems supplied by PV arrays to improve the efficiency. With this method, the optimum slip of the motor is maintained as the levels of insolation and temperature vary. Therefore, the highest efficiency can be achieved at different insolation and temperature levels. This method also offers an improvement in stability for the current-fed inverter drive system with linear-torque type loads.; An adjustable field-flux control approach to maximize the gross mechanical output and improve the operating condition of dc-motor drive systems supplied by PV arrays is also derived. With this method, the motor can always operate at the corresponding optimal state for any insolation and ambient temperature levels. The controller adjusts the motor flux in a self-adaptive manner, and therefore an instantaneous maximum efficiency can also be achieved as environmental and load conditions vary. Because the power losses are reduced, the safe rating range of the motor can be extended to all possible input power levels without overheating the motor, and the variation of the motor current and voltage can be kept in much narrower ranges.