CURRENT OVERSAMPLING ANALYSIS FOR ADVANCED CONTROL OF ELECTRIC AC DRIVES

Abstract: The main purpose of this thesis is to develop a sensorless control for a synchronous reluctance motor by using the slope measurement of the current ripple introduced by the Space Vector Modulation.The position estimation is performed at each Space Vector Pulse Width Modulation period and it relies on the estimation of current derivatives. The current derivative estimation was carried out using a recursive least squares regression (RLS), which was implemented on an FPGA, on the currents oversampled at 10 MHz.Two  different  position  observers  were  developed:  the  first  is  based  on the  calculation  of  current  derivatives  during  the  longest  application time of a single SVPWM voltage vector. The second, instead, is an ob- server independent of the electrical resistance of the motor, but which requires the current derivatives estimation during two different voltage vectors.The  RLS  regression  algorithm  and  position  observers  performances were analysed both in simulation and by experimental tests at different speeds, during speed variations and with applied load torque.The  main  source  of  position  estimation  errors  are  the  high-frequency current  oscillations,  which  prevent  an  accurate  estimation  of  current derivatives.  These  oscillations  are  due  to  IGBT  switching  and  to  the presence  of  parasitic  elements  in  the  cable,  in  the  inverter  and  in  the motor.Since  these  oscillations  are  present  just  after  a  switch  commutation, the  estimation  of  current  derivatives  has  been  delayed  by  some  µs  in order to reduce the estimation error. However, this technique reduces the time window during which the linear regression is performed, thus reducing its precision.Therefore, a more in-depth study was carried out on the causes and ef- fects of high frequency oscillations, and a model of the drive, in which the parasitic elements were also considered, was realized using MatlabSimscape.