Research On Harmonic Suppression Strategy Of Induction Motor Based On Adaptive Morphological Filter

Because of its advantages such as simple structure,reliable operation,and low operation and maintenance costs,three-phase induction motors have been widely used in industrial control field.With the development of pulse width modulation technology,the frequency conversion speed regulation system of three-phase induction motors mainly uses voltage-type pulse width modulation inverters.However,due to the nonlinearity of the inverter,there are a lot of harmonics in the current input to the motor.Current harmonics will cause torque fluctuations,leading to increased motor losses and severely affecting the smooth operation of motor.In order to solve these problems,this paper makes a thorough research on the current harmonics of three-phase induction motors.Firstly,this paper discusses the vector control principle of induction motors.Based on the structure and operating principles of three-phase induction motors,a mathematical model of induction motors is established,and the dynamic model of induction motors in a two-phase stationary coordinate system is derived.When the vector direction of the flux linkage of the rotor overlaps the d-axis direction,the dynamic mathematical model of the induction motor at this time is analyzed,and the relationship between the current of dq axis and the electromagnetic torque is obtained.By studying the characteristics of harmonic current caused by dead time effect of inverter,the model of harmonic current is derived.Combining the current harmonic model of the motor with the vector control method of the motor,the influence of current harmonics on the control system is analyzed to provide ideas for the design of the subsequent control structure.Secondly,study the basic principles of mathematical morphology and analyze the characteristics of the basic operations of mathematical morphology.The method of selecting the shape of the mathematical morphological structure element and the general rules of the size selection are summarized by simulation experiments.Based on the basic rules of morphology,a hybrid morphological filter combining the advantages of mathematical morphology open and closed operations is designed.At the same time,an adaptive morphological filter is designed in combination with the minimum variance algorithm to solve the problem of selecting structural elements of the morphological filter.Thirdly,according to the characteristics of the harmonic current in the induction motor system,a filter is added to the feedback channel of the vector control system to eliminate current harmonics and prevent harmonic interference signals from flowing into the controller.In this paper,a traditional hybrid morphological filter is added to the control structure to implement a morphological filter-based harmonic suppression strategy.By using this harmonic suppression strategy and Butterworth filter-based harmonic suppression strategy as a comparison method at different speeds,and the comparison of current waveforms proves that the proposed control strategy has good harmonic suppression characteristics.Because the structural elements of the morphological filter are difficult to select under variable speed conditions,the harmonic suppression effect is not good when the speed step changes.In order to better suppress the harmonic current of the motor,a current harmonic suppression strategy based on adaptive morphological filter is proposed.It is verified through simulation that the proposed control strategy can dynamically adjust the size of the structural elements of the morphological filter,so that it can still have a good harmonic suppression effect under variable speed conditions.Finally,Combining simulation analysis and theoretical calculation,a hardware experimental platform for three-phase induction motor based on cSPACE hardware-in-the-loop simulation system is designed,and the hardware implementation steps of the experiment are given.Through the above experimental platform,the proposed harmonic suppression strategy was tested separately,and the results proved the effectiveness and feasibility of the method.