Research And Development Of Speed Sensorless System Based On Stator Flux Orientation

This dissertation focused on the speed sensorless vector control of induction motor (IM) based on stator flux orientation (SFO). The profound theoretical analysis and study have been made against some critical questions. In this dissertation, the hardware platform with the structure of DSP(TMS320LF2407A)+CPLD has been constructed, and the speed sensorless AC variable speed drive experiments of IM based on stator flux orientation have been performed. The preferable variable speed performance and wider speed range of the system have been proved by experiments.The flux estimation is the most important question in speed sensorless control. Much less parameters in stator flux estimation are required than in rotor flux estimation. So the speed sensorless vector control of IM based on SFO is more robustness to parameters than it based on rotor flux orientation (RFO). In this dissertation, the start point and principle of the SFO have been represented in detail, the decoupling methods between flux and torque have been profound discussed, the control structure of the speed sensorless vector control based on SFO has been constructed, and the influences on the system performance by the inductances are also analyzed theoretically.The stator flux estimation is effected directly by stator current and voltage. In this dissertation, the theory of nonlinear morphological filter (NML) has been represented, and the NML is introduced into current filtering. It can be seen that the positive or negative plus disturbance is effectively eliminated in current signal and the primary characteristic of current signal is well preserved from experiment results. The production principle of dead-time, the effect of dead-time on fundamental voltage, harmonic voltage and current wave are discussed. A new method of dead-time compensation and phase-voltage measurement based on detecting the actual turn-on time of power tubes is presented in this dissertation. The harmonic is inhibited and the quality of wave is improved by using detected dead-time to compensation. At the same time, the measurement phase-voltage is high precision.In stator flux estimation, the saturation and DC drift will be easily produced by the pure integrator. The previous questions can be silenced by the one-order low pass filter (LPF), but the errors in magnitude and phase angle will be introduced inevitably. In this dissertation, the profound research on the theory, characteristic of the integrator with feedback compensation and the principle of parameter selection has been made. The limiting level fixed dual integrator can silence the saturation and DC drift questions, and can compensate completely the errors in magnitude and phase angle under the low frequency and saturation condition. The well stator flux observation result has been achieved by applying the limiting level fixed dual integrator to the stator flux observation.The computer simulation under the environment which approaches the actual work condition can supply the powerful guidance for research work. In this dissertation, the speed sensorless variable speed drive based on FO simulation platform of IM has been constructed on SaberDesigner which is a semi-physical simulation software. On the platform, the profound investigation and comparison between the speed sensorless system based on RFO and SFO has been performed, and the influences of IM parameter on the previous speed sensorless system has also been investigated.The parameter dependence of speed sensorless system can be indicated by means of theoretical analysis and simulation study. In this dissertation, based on the other scholars'research production, a modified off-line identification method of IM parameters has been presented. In this method, the SVPWM has been used. The identification procedure has been accelerated and the safety of system has been enhanced by applying the current regulator. The system anti-interference ability has been improved by utilizing the discrete fast fourier transform (DFFT) to calculate the effective value of voltage, current and the power factor. The existing conditions are utilized, the identification can be completed automatically, and no manual connection of electric wires action is required in the proposed method. This method is suitable to the speed sensorless scheme. The high uniformity and precision are presented from the experiment results.The parameters of IM will vary with the change of operating condition. The stator flux estimation nearly correlates with stator resistance in the speed sensorless system based on SFO. In this dissertation, a close loop on-line estimating method of stator resistance is presented. This method is easily realized and its theory is simple. The simulation results show that the stator resistance variation can be well traced and the system performance is improved by using this method. The slip frequency estimation will be effected by the rotor parameters and inductances when the dynamic speed estimation has been employed. The PI adaptive speed estimation method is introduced into the speed sensorless system based on SFO in this dissertation. So the influences of rotor parameters and inductances on speed estimation under the load condition have been avoided. It is showed that the speed sensorless system based on SFO used the previous speed estimation method is more robust to parameters from simulation results.