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This paper compares two methods for obtaining a discrete-time mathematical model for digital control design of a power system. The usual approach has been to use the shift operator q, or its equivalent z-transform, but this gives numerical difficulties with the small sampling periods which are now becoming usual with modern control hardware. It is shown, by means of the example of the identification of a generator excitation control system, that these problems can be avoided by the use of the delta operator Delta instead. Calculations show that the Delta-operator formulation also reflects the frequency and dynamic response of the system more accurately and conveniently.

Direct measurement of electric machine losses using the principle of the calorimetric method is described in this paper. The design and construction of a double chamber calorimeter (DCC) that can be used for measurement of harmonic losses of a 7.5 kW cage induction motor is discussed. The advantages of this approach are highlighted as compared with a single chamber type calorimeter. Conducted heat leakage through the calorimeter walls is estimated accurately by developing a simple thermal model and compared with the experimental results. Accuracy and reliability is investigated by performing experimental tests using a known heater. Limits for the air flow rate and temperature rise inside and across calorimeter chambers are derived. The calorimeter is capable of measuring a heat loss up to 1 kW corresponding to the 7.5 kW machine with an overall accuracy of [+ or -] 15 W. This provides a high resolution required for measurement of motor harmonic losses caused by distorted waveforms. keywords: induction motor, calorimeter, harmonic losses, calorimetric method, heat transfer.

Presents a concise transient SPICE model to predict the static and the switching behavior of power transistors, with emphasis placed on quasi-saturation effects. Simulation of ohmic and non-ohmic quasi-saturation phenomena by automatically adjusting the hole injection ratio term; Comparison of the origical SPICE bipolar junction transistor and experimental data for direct current and turn-on conditions.

Describes a two-level circuit model for a gate turn-off thyristor in power electronic simulations. Basis of the semiconducting phenomena; Incorporation of additional charge control, anode-cathode and gate-cathode resistance modulation networks to simulate turn-off phenomena; Methods for determining the model parameters.