The Research And Design Of Discrete Frequency Soft Starter Based On DSP

Electronic soft starter, a motor-assist tool with the development of power electronics device, the core component of which consists of AC voltage regulation device composed of six sets anti-parallel thyristors. By controlling the firing angle of thyristor, we can regulate the voltage so as to easily change the operating characteristics of asynchronous motor. Because of the development of modern control theory and computer control technology, the new strategy of thyristor trigger came into being. Now apart with AC voltage regulation's single function of voltage regulating, we can bring in dual-ramp which constitutes dual-ramp voltage soft starter. Current closed loop can be also introduced into the function and constitutes current-limiting soft starter. The technology of discrete frequency soft starter has incredible advantages that indirect starting method and traditional method of starting cannot even match. Therefore, discrete frequency soft starter is so vital to the research on starting of three-phase asynchronous motor.This thesis first gives a brief introduction of operating principle to thyristor regulator, based on which brings discrete frequency technology and describes principle of discrete frequency. By analyzing the voltage phase sequence of sub frequency band after it was divided, we can nail down the maximum phase combination under each phase sequence by using symmetrical components method. Besides, applying to project practice, I do the research on specific problems of motor starting in process. I summarize how to select the start frequency band among all frequencies and switch principle covered each frequency band. Secondly, in order to reduce a large number of harmonic wave generated by the division starting of motor and make the starting torque stable, I put forward the VVVF control strategy based on equivalent sine. And by detecting the follow current of motor, closed loop control of the power factor angle is achieved, which greatly reduces jitter under the circumstances of under loading.Based on theoretical research and by using MATLAB/Simulink software to set up simulation models, I introduce the main modules of simulation model. After the introduction, I do the simulation study on the starting process of soft starter of ramp voltage, limited current and discrete frequency. By comparing various simulation results, I verify the feasibility and correctness of the discrete frequency soft starter program.Last but not least, I work out a three-phase asynchronous motor based on highperformance digital signal processor TMS320F28335 made by TI company. This soft starter has numerous variety control method which includes discrete frequency soft starter technology mentioned in this thesis. To different load and starting requirements, this soft starter can switch start mode, adjust the starting parameters to achieve the best effect. The main task of design includes hardware and software design of this new soft starter. At the meantime, I regulate the hardware and make some relevant starting experiment of motor soft starter. It turns out that the experiment results are consistent with simulation results, which again verify the superiority of control technology of discrete frequency soft starter applying to heavy load even full load motor. I have to say that this is another expanding application range of thyristor soft starter.