Influence of converter capacitance in resonance-based sensorless switched reluctance drives

By observation of electrical resonances, switched reluctance drives can be controlled without position sensor. The range of resonance frequencies is defined by the position-dependent phase inductance and a parasitic capacitance, mainly associated with the converter switches. In this paper, an analytical model is used to predict the aligned resonance frequency, taking into account material and geometry factors, as well as dynamic effects such as eddy current losses. The range of resonance frequencies can be influenced by mounting external capacitors over the power semiconductor devices. It is shown that an optimal aligned frequency is associated with a trade-off between a high position resolution and a high pulse-width modulation frequency. Good correspondence is obtained between the model-predicted results and measurements on a switched reluctance drive.