SiC-VSI with sinusoidal voltages for an enhanced sensorless control of the induction machine

In the last few years, intensive research within the field of advance control schemes for AC drives has been conducted worldwide. With the currently available control schemes, power electronic converters and signal processing the realization of motor drives featuring excellent properties in a wide speed and torque range is possible. An operation of the motor drives without restrictions demand the measurement of the angular position of the shaft. As optical high resolution encoders are sensitive to environmental influences, like dust, vibration and temperature, they are prone to failure. They also demand additional cables and interfaces. Therefore, in the last decades a worldwide extensive research in industry and academia has led to several tech-niques pertaining the operation of a drive without the utilization of mechanical encoders. The so called ‘sensorless’ or "encoderless" control schemes have been en-hanced in multiple research works to achieve a high dynamic performance for stand-ard electrical AC- machines.
The present work deals with the sensorless control of the asynchronous machines by using the so-called fundamental wave models of the machine. It is well-known that a sensorless control can be achieved with good performance that can be developed based on the terminal voltages and currents of the machine without any measurement of the rotor position. Unfortunately, this method fails at low stator frequencies, and therefore the sensorless operation is only possible at medium or high speed. In addi-tion the model utilized for the control is not fed with the stator voltages since they are usually not measured. Moreover the terminal voltages are reconstructed out of their reference values which are calculated by the controller. For this reason the con-trol task becomes more complex because the imperfections and nonlinearity of the inverter have to be considered.
Power electronics inverters equipped with SiC switches for feeding the AC machines can be operated at higher switching frequencies, many research groups have been working with such system aiming better performance, a higher efficiency and some featuring sinusoidal output voltages. Nevertheless the objective of the current research is a different one, namely to obtain smooth terminal voltages that can be easily measured in order to enhance the classical fundamental-wave, sensorless control schemes as well as of other methods like the natural field orientation (NFO) and the control with an model reference adaptive system (MRAS).