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The use of a magnetic model to analyze the load dependent behaviour of a power supply

University of British Columbia

It has been known since the first half of the 1990s that power supplies based on the ferroresonant transformer technology are incompatible with certain more recent types of loads such as actively power factor corrected devices. This is an issue that still remains today. The objective of this thesis is to analyze whether a specific ferroresonant uninterruptible power supply, operating in line mode, can be controlled by a linear time-invariant controller. This work shows that whether the ferroresonant-based circuit can be compatible with the aforementioned type of load is dependent on the characteristics of the same. The study includes a comprehensive nonlinear model of the controlled ferroresonant transformer also known as the controlled constant voltage transformer. Saturation is a normal mode of operation for this device. The level of detail includes winding resistances, core resistances, continuously nonlinear magnetizing inductances, tapped windings, and leakage inductances. A complete nonlinear state-space model of the power supply where the constant voltage transformer constitutes the major part is derived. The investigation encompasses stability evaluation of the device with several types of loads using a generalized approach. For the analysis, the nonlinear system is converted into a linearized periodically time-varying system, which in turn is sampled by means of Poincaré mapping to provide a discrete-time representation of the model. An analytical approach explains, in the discrete-time domain, why certain loads may be impossible to control by a linear time-invariant controller. The study emphasizes this type of controller since in general, with unknown loads, the assumption is that the controller should be relatively simple and less dependent on specific load parameters or specific type of loads. To complement the theory, this work also proposes an approximate procedure that leads to an implementation of a practical feedback controller that stabilizes a specific actively power factor corrected load. Laboratory experiments show that, for line mode operation, the power supply can indeed be compatible with the aforementioned load.

Text

2010-01-16

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http://hdl.handle.net/2429/18267

Electrical and Computer Engineering

University of British Columbia

UBCV

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