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Sensorless Operation of PMSM DTC and Investigation of Sensor Integration

Author: JiaHongPing
Tutor: HeYiKang
School: Zhejiang University
Course: Motor and electrical
Keywords: Permanent magnet synchronous motor (PMSM) Direct torque control (DTC) Finite element analysis (FEA) Initial rotor position High-frequency signal injection Stator flux observer Variable structure control Instantaneous torque angle inspection Sensorless operation Sensor integration
CLC: TM341
Type: PhD thesis
Year: 2006
Downloads: 1051
Quote: 16
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Recently, the development of power electronics technique has being in its crucial time. The techniques of power electronics system integration, standardization, and modularization are served to eliminate the impediments faced by the development of the power electronics technique, and are the most promising outlet to expand its application field. System integration technique has already becoming the new development direction of power electronics technique.Power electronics system integration has two levels of implications: the power electronics subsystem integration and the application system integration of power electronics.As one of the application system of power electronics, the integrated drive system with high performance should not only include the integrated power conversion modules and filter modules, but also include the integrated sensor module, which is used to integrate the function of all sensors that are used to measure the motor’s voltage and current, to estimate the rotor position and its speed, and to observe the flux linkage and torque. Although the voltage and current can be measured directly by Hall sensors, the rotor position and its speed, the torque and flux linkage must be estimated by certain estimation scheme.From point of view of system integration, sensorless operation of Direct Torque Controlled (DTC) Permanent Magnet Synchronous Motor (PMSM) and sensor integration technique are deeply investigated in this dissertation. The investigated theoretical problems include:(1) Inspection of initial rotor position of PMSM.(2) High precise PMSM stator flux observer.(3) The ripple reduction of torque, flux, and current during PMSM DTC operation.(4) Speed estimation method suitable for sensorless operation of PMSM DTC.(5) Conceptually integrated sensor module for drive system.The main points studied in the dissertation are introduced as follows:1. The operation mechanism of traditional PMSM DTC was studied. Mathematic model for PMSM was built and verified by simulation and experiment investigation for the purpose of concluding the problems needed to be solved during sensorless operation of PMSM DTC.2. Inspection of initial rotor position of PMSM was studied based on injecting vibrating high-frequency voltage signal by both of Finite Element Analysis (FEA) and experiment. The high-frequency impedance difference between the d and q axis of PMSM caused by magnetic saturation while injecting high-frequency signal was used to inspect initial rotor position of both non-saliency and saliency PMSM. Furthermore, the non-linear magnetization characteristics of the stator iron core was used to judge the polarity of permanent magnetic pole by injecting voltage pulse signal. Experimental results indicated that the error of the inspected initial rotor position is less than 5° electrical degrees, which is accurate enough for PMSM to start up and make field orientation. The proposed approach has set the basis for the realization of high performance control strategy for PMSM DTC.3. The flux observer with non-linear orthogonal feedback compensation, suitable for PMSM DTC application, was presented. Accurate estimation of flux linkage, including its amplitude and phase angle, is essential for PMSM DTC and its sensorless operation, the estimating accuracy of which can be judged by orthogonal degree of flux with back electromotive force (emf). If the back emf and the flux observed are not orthogonal, the flux must be compensated, which can be realized only if both the back emf and the flux are continuous functions. However, during PMSM DTC operation, back emf and stator flux linkage are discrete signals, which must be formed as continuous quantities to perform vector dot product. For this purpose, a smoothing processing circuit was designed and the flux compensated degree was determined by orthogonality judgment. Experimental results verified that the proposed flux observer could observe the stator flux accurately in a wide speed range, and the realized DTC operation by this approach could still preserve the merit of quick dynamic torque response.4. VSS-DTC was structured by introducing the variable structure sliding mode (VSS) control strategy into PMSM DTC system. The VSS controller, designed according to exponential reaching law, can improve the dynamic performance in normal operation range effectively. The system’s high frequency dithering can be reduced by using continuous function instead of switching function. Space voltage vector modulation with the inverter switching frequency kept constant can be realized by replacing the hysteresis controller in a traditional DTC system with variable structure controller. Experimental study verified that the proposed control scheme significantly reduces current, flux and torque ripple, suppresses high-frequency noise effectively, preserves quick dynamic torqueresponse merit, and shows robustness to motor parameter uncertainty, disturbance, measuring error and measuring noise, which improves dynamic and static operation performance effectively, and forms a novel modified control scheme for PMSM DTC.5. A new speed estimation method, based on inspecting the instantaneous torque angle, was proposed, which is convenient to estimate speed and has the merit of quick dynamic response. Simulation based on sensorless operation of both non-saliency PMSM and saliency PMSM indicated that the proposed speed estimation method is suitable for different types of PMSM. Experimental results showed that PMSM VSS-DTC sensorless system has a wide range of operation speed and is capable of providing large torque during low-speed operation and starting up, which demonstrates that high dynamic and steady state performance of the system has been achieved and system’s reliability has been improved.6. The hardware structure and software functions of a sensor integration module had been discussed in detail. Conceptual sensor integration module had been structured for the first time, which enriches the types of power electronics system integration modules. Besides, this sensor integration module had also been used in high performance control strategies such as DTC and FOC for a PMSM which is proved to be capable of accurately measuring the voltage and current of the motor, estimating the rotor position and its speed, and observing the flux linkage and torque effectively. Therefore, It should be a very important portion in a high performance power electronics integration drive system.

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