DSP-BASED DRIVE FOR SENSORLESS VECTOR CONTROL OF PMSM STANISLAV TAIROV, LUIZ C. STEVANATTO Exact Science and Technology Center University of Caxias do Sul P.O. Box 1352, Caxias do Sul., Brazil E-mails: vtairov@ucs.br, luiz.carlos@ucs.br Abstract  Methods for adjustment of drive parameters during the change of control modes are presented. The methods are ap- plied to Permanent Magnet Synchronous Motor (PMSM) sensorless control with Sliding Mode Observer (SMO) to estimate the rotor position. The phase compensation was proposed to optimize rotor position in the speed control mode. This technique is based on the measurement of control current with constant load torque. The validity of the proposed methods is verified experimentally. The proposed control algorithm was implemented in the DSP software. Keywords Permanent Magnet Synchronous Motor (PMSM), Slide Mode Observer (SMO), Digital Signal Processor (SMO). Resumo  Os métodos de ajuste dos parâmetros do inversor de freqüência durante a mudança dos modos de controle foram representados. Os métodos foram aplicados para Motores Síncronos de Ímã Permanente (MSIP) sem sensores com utilização do Observador de Modo Deslizante (OMD) para estimar a posição do rotor. Compensação da fase foi proposta para otimizar a posição do rotor para controle de velocidade. Esta técnica se baseia na medição de corrente para torque constante em rotor. A validade dos métodos propostos foi verificada experimentalmente. O algoritmo de controle proposto foi implementado em software de Processador Digital de Sinais. Palavras-chave Motor Síncrono de Ímã Permanente (MSIP), Observador de Modo Deslizante (OMD), Processador Digital de Sinais (PDS). 1 Introduction Permanent Magnet Synchronous Motors (PMSM) with Field Oriented Control drives are widely used in various industrial applications due to their high-power factor, high-torque density, high efficiency and small size. For effective application of vector-control algo- rithms, it is necessary to know the rotor position. Encoders or revolvers have been used for sensing the rotor position. However, the position sensor increases the cost and decreases reliability and noise immunity of the PMSM drive system. Therefore, vector-control methods, in the absence of any shaft sensors, have been investigated by many researchers. Sensorless control in field-oriented PMSM relies on dependency of the rotor position upon the back electromotive force (back-EMF) induced in the stator windings (Jufer, et. al, 1987; Utkin, et. al, 1999). The estimation of the rotor position and speed (state variables) requires the use of a relatively accurate motor model, the knowledge of the feeding voltages (system input) and the measurement of motor currents (system output) with waveforms proportional to back-EMF. Several estimated methods were covered in literature, which base on state observers (Jones, 1989 et. al; Ciccarella, 1993, et. al; Solsona, 1996, et. al; Hamada, 1999, et. al], extended Kalman filters (Parasiliti, et. al, 1999;Terzic, et. al, 2001) and sliding mode observer (Vittek, et. al, 2000; Elbuluk, et. al, 2003). Among the various approaches, the Sliding Mode Observer (SMO) represents an attractive proposal because it is robust to measurement noise, parameter deviations and the inherent high gain structure (Utkin, et. al, 1999). This method doesn't require high computational charge (as in the case of Kalman Filter) and may be effectively implemented in low-cost controllers. However, SMO introduces time-delay in the rotor position estimation due to the use of the low-pass filter to extract rotor position angle from back-EMF signal. Meanwhile, this low-pass filter leads to unavoidable and unwanted phase lag in the rotor-angle estimation. Various sensorless control schemes were proposed to improve the accuracy of the rotor position estimation (Elbuluk, et. al, 2003; Cascella, et. al, 2003; Salvatore, et. al, 2002). For variable speed drive, the speed and frequency of back-EMF are not constant. Thus, a compensation method that can accommodate this situation is needed. Theoretically, the compensation angle can be obtained directly by the phase/frequency response of the adopted low-pass filter. In fact, a further correction is needed due to various deviations of motor parameters, measurement errors, calculation delay, etc. This research presents one method to compensate phase lag in SMO for the PMSM drive with close-loop velocity control. Practical recommendations were made to change control mode in real time from starting open-loop to close-loop speed control.