Research Of Discrete Frequency Soft Starter For Asynchronous Motors Based On DSP

Three-phase squirrel cage induction motor has been widely used in production and dailylife because of its simple structure, reliable operation, cheap, and easy maintenance and smallsize. Large starting current produced by directly starting had made a great impact on thetransmission system and grid,so usually the large capacity motor must started by auxiliarystarting device such as soft starter. With the constantly growing and renewing of productionmachinery in various fields, motor starting performance was becoming more and more high.Traditional soft starter used simple step-down start was not able to adapt to the requirementsof the development of production because of the torque is too small. In this article,a newmethod of discrete frequency soft-start control to improve the motor starting torque wasproposed through the analysis of the mathematical model of the motor. discrete frequencysoft-start control was achieved by thyristor chopper technology.With the method of step-downand frequency reduced, the starting current was reduced and at the same time starting torqueof the motor was improved,so the heavy load starting was realized.Thorough analysis of the theory of discrete frequency, determined the relationship of thephase angle in each sub-frequency and the original signal.And the relationship of the phaseangle between phases in each sub-frequency was further analysised. The best phasecombination and the optimal trigger angle of each sub-frequency for maximumelectromagnetic torque of the motor was identified through the analysis of theory andsimulation.On the basis above, the discrete frequency soft starter of three-phase asynchronousmotorwas achieved though the seclect of the sterile frequency of discrete frequency softstarting process.Control system simulation model was built with simulink module of matlab.Then the simulation experiment of discrete frequency soft starter was did. Through the comparison of the simulation experimental results with other starting mode,verified the thecorrectness of theory analysis and advantages of discrete frequency soft starter for heavy-dutystarting. Finally, according to the theoretical analysis, the discrete frequency soft starter wasstudied and designed. the relevant experimental study has been did.The results shows thatstarting current of heavy load starting with discrete frequency soft starter was reduced, and thetorque was improved. Control system worked well. Starting performance of discretefrequency soft starter met the requirements of heavy load start. Feasibility of discretefrequency soft starter was verified once again.