The Design And Practical Application Of Flux Observer

The accuracy of stator flux observation influences the system performance in stator flux oriented control system. Using hardware to measure the flux does not only add the cost, but also cannot get high accuracy. The common method is to indirectly obtain the flux by calculating it with the information of motor voltage, current, speed and so on that can be directly measured. The flux observer can be divided into open loop observer and closed loop observer. The open loop observer is widely used for its simple algorithm.U-I model depending only on the stator resistance is selected as the research target in this thesis. Several improving methods to overcome the initial value and integration saturation problems of pure integrator are compared. The theoretical deduction for the value of important parameter in each method is done, and the range that can be chosen is listed. Meanwhile, motor voltage and current impact the estimation of flux. In this thesis, the method of calculating the motor voltage by the duration time of power tube is presented, which is based on the dead time compensation of correcting the pulse width in stator flux oriented direction. The morphological filter is introduced into the filtration of motor current, and is compared with the traditional hardware filtration methods. The conclusion that morphological filter has the best filtration result is drawn. The flux observer helps the common V/f improve the performance in low frequency range. Controlling the flux amplitude in close loop manner makes the motor flux constant in low speed and so the performance with heavy load is improved. Simulation results show that the flux obtained by the flux observer coincides with the motor actual flux.