| The six-pulse double-variable frequency converter can output more frequency above 16.67 HZ,so as to improve the soft-start performance of the motor by utilizing these frequency bands.In addition,the frequency control and speed regulation can be realized in the high frequency range making the full range of soft start possible.In this paper,based on the six-pulse bivariate frequency converter,,the full range soft start control strategy of induction motor under light load condition is studied.According to the characteristics of AC frequency converter output frequency,the frequency range below 50 HZ is divided into low frequency(below 16.67HZ),intermediate frequency section(16.67Hz~25Hz),high frequency section(27.27Hz~37.5Hz)and industrial frequency section.In the low frequency section,the voltage frequency ratio control strategy based on the optimal shift interval is combined to find the optimum starting torque matching the load to start the motor.In the middle frequency section and the high frequency section,by correcting the symmetry of the voltage wave,selecting and adding the limited transition frequency to reduce the difference between the frequencys,and combining the optimal voltage frequency ratio control strategy,the power factor and the efficiency can be improved A closed loop voltage regulation strategy is adopted in the power frequency section to achieve the soft transition from frequency conversion to voltage regulation switching Through low frequency,middle frequency,high frequency and power frequency soft start control strategy's coordination,the whole range soft start control of motor is realized.In order to verify the effect of the full range of soft-start control strategy proposed in this paper,a simulation model of AC-AC soft-start is set up under the environment of MATLAB / Simulink,The experimental results show that,in the full range of soft-start control strategy,the starting process of the motor is stable and effective. |
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