Resonant Converter Fed PMDC Motor Drive for Low Voltage Applications

At zero stator frequency the stator quantities are not affected by the rotor speed and, therefore, the speed cannot be observed from measured stator voltages and currents. Further, the stator voltage provided by the inverter is difficult to measure and sometimes is assumed to be equal to the reference voltage or calculated from the DC link voltage and inverter switches conditions. The errors caused are often negligible in high speeds. However, they can be relatively high in low speeds, since the voltages are reduced to maintain the reference flux and the errors due to the voltage drops and dead times in the switching devices become more prominent in lower output voltage range. However, they need a high computational effort to be implemented and a kind of intervention in the machine is necessary Despite the many attempts to obtain accurate flux and speed estimation for wide speed range induction motor drives proposed recently, it seems that the solutions do not meet simultaneously the simplicity, accuracy and reliability requisites to be largely accepted and used in the industries. This instantaneous average voltage-measuring scheme was used to obtain the results in this paper. The scheme is simple and inexpensive