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Title: Sensorless control of dual three-phase permanent magnet synchronous machine drives
Author: Almarhoon, Ali
ISNI:       0000 0004 5989 3130
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2016
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This thesis focuses on sensorless control methods for single and dual three-phase (DTP) permanent magnet synchronous machine (PMSM) drives covering both low and high-speed ranges. The sensorless control strategies for the high speed region are established based on flux-linkage observer (FO) estimator and simplified extended Kalman filter (EKF), while high-frequency carrier voltage injection based sensorless control strategies are utilised for low speed regions including standstill operation. In the high-speed range, the influence of back-EMF and current harmonics on sensorless control performance of single and dual three-phase PMSMs is investigated by utilising FO and simplified EKF-based sensorless control strategies. The single three-phase PMSM is employed to investigate the influence of back-EMF harmonics on position estimation accuracy, while the influence of current harmonics on the accuracy of rotor position and speed estimation is studied in the case of the DTP-PMSM, which inherently exhibits harmonic currents in ST-DTC methods. By employing the simplified EKF, the sensorless control performance is significantly enhanced, since it is less sensitive to such harmonics and distortions. When the rotor speed is low, machine saliency-based sensorless control strategies should be applied. The most commonly used conventional pulsating and rotating carrier voltage injection methods are presented for single and dual three-phase PMSMs, including measurement of the machine saliency level and analysis of cross-saturation effects. For the DTP-PMSM, both methods are applied to different machine models, i.e. the double dq model and the vector space decomposition (VSD) model. Both methods show decent sensorless control performances when the VSD model is employed since the mutual coupling between the two winding sets is eliminated. The pulsating and rotating carrier voltage injections utilising zero-sequence carrier voltage for rotor position estimation are investigated for single and dual three-phase PMSMs, which differ from conventional high-frequency pulsating and rotating carrier voltage injection methods that use carrier current response to estimate the rotor position. However, for the single three-phase PMSM with both techniques, undesirable 6th harmonic estimation error occurs due to multiple saliency components in the zero-sequence carrier voltage. The existing compensation schemes require time-consuming offline measurements and complex structures to solve this problem. In the case of DTP-PMSM drives, two independent high frequency signals are proposed to be injected for the two separated winding sets thanks to the existence of additional degree of freedom. By applying the proposed optimum phase shift angle between the two injected signals, improved pulsating and rotating carrier signal injection employing zero-sequence voltage based sensorless control techniques are proposed to suppress these 6th harmonic on rotor position errors. In addition, a new simple technique to measure the zero-sequence carrier voltage is proposed, in which one voltage sensor is put between the two isolated neutral points of the two stator winding sets. In order to achieve high accuracy in terms of estimating the rotor position for a wide speed range, a combination of sensorless control strategies to achieve smooth transition between low and high speeds is introduced. The combined sensorless control methods include the flux-linkage observer method and four different high-frequency carrier signal injection techniques. Such methods are applied to the DTP-PMSM to investigate the sensorless control performance within different speed ranges. The estimation of the rotor position is obtained by using the high-frequency carrier voltage signal injection methods in the low-speed range, while the flux-linkage observer method is utilised to estimate the rotor position within the high-speed range. Furthermore, a function similar to hysteresis is applied for certain speed ranges, with optimum weighted gains for both estimated positions to achieve a smooth transition between the combined methods.
Supervisor: Zhu, Zi-Qiang Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available