2008 IEEE Region 10 Colloquium and the Third International Conference on Industrial and Information Systems, Kharagpur, INDIA December 8 -10, 2008. >497 < 978-1-4244-2806-9/08/$25.00© 2008 IEEE 1 UNIVERSAL PLL STRATEGY FOR SENSORLESS SPEED AND POSITION ESTIMATION OF PMSM Georges el Murr,Damian Giaouris, and J.W. Finch School of Electrical, Electronic and Computer Engineering Newcastle University Newcastle upon Tyne, United Kingdom Damian.Giaouris@ncl.ac.uk Abstract— the implementation of the Phase Locked Loop (PLL) structured observer in high frequency signal injection schemes requires tuning of the PI controller to lock on the rotor position. The PI controller is tuned depending on the Signal to Noise Ratio (SNR) which is related to the amount of saliency/anisotropy presented in the machine, the amplitude and phase of the incoming modulated carrier signal. Thus, in case any of the mentioned factors changes then the PI has to be retuned again, otherwise it will loose track. In this paper a new PLL structure is suggested to avoid any disturbance that affects the demodulation and detection process. The new PLL scheme is totally independent of any machine parameters except the saliency/anisotropy, which is essential to obtain the rotor speed and position information. Keywords-component; High-frequency signal injection, Phase- Locked Loop, Sensorless control, Surface-Mounted Permanent Magnet Synchronous Motor I. INTRODUCTION The main objective of sensorless control is to achieve the same control performance as vector control without using speed or position sensor [1]. Such a sensor can be the most expensive and fragile component in the whole electric drive. Sensorless techniques Fig.1 are divided into two classes, those using the fundamental properties or model of the machine [2-5] and those exploiting subsidiary features often called anisotropies based model [6-9]. Fig.1: Categories of sensorless control techniques Sensorless control of a PMSM has become more and more acceptable in industrial applications due to the large amount of research effort that has been spent in developing reliable, low- cost PMSM drives. The simplest fundamental model methods are based on rotor flux position estimation, by integrating the back-EMF [10]. Such an approach is very simple but fails at low and zero speed. In general, low speed operation is critical for such fundamental based methods, since the estimated rotor flux can be very sensitive to stator resistance variations, and measurement noises. In addition, sensorless schemes that are based on the application of sophisticated identification procedures (such as flux observers, Kalman filter [1-3] etc.) allow, with some limitations very low speed operation, but can be too complex and expensive to be used in practical systems. Other estimation techniques can be based on stator phase voltage third harmonics or spatial phenomena inherent within the machine, such as slot harmonics, rotor/stator eccentricities, and winding asymmetries. However, all these approaches can fail at zero speed for lack of useful information. Signal injection schemes [11-15] can be more efficient, at low and zero speed, than any other sensorless estimation scheme. Such methods have the capability to provide accurate position and speed estimation without requiring information about the motor parameters. This is due to the presence of saliency/anisotropy in the machine. The saliency/anisotropy is the inductance difference between direct-inductance l d and quadrature-inductance l q and it is due to either the asymmetric structure of the machine or the flux induced magnetic saturation due to the fundamental excitation. The interaction between the injected high frequency signal and the spatial variations in the machine inductances produces an amplitude- modulated signal containing useful information attached to the carrier frequency. The demodulation and extraction of this information constitute the main interest of this paper, which is presented as follows: In section II a theoretical background of the conventional modulation, heterodyning demodulation, and the PLL observers implemented in rotating and alternating signal injection schemes. Section III covers the proposed demodulation as well as the speed and position estimation method. Finally, results of the estimated and actual rotor speed and position are presented in section IV to validate the proposed method and compare it with the conventional schemes. IEEE Kharagpur Section & IEEE Sri Lanka Section Authorized licensed use limited to: Newcastle University. Downloaded on March 16,2010 at 10:17:08 EDT from IEEE Xplore. Restrictions apply.