| When the induction motor with load operation, particularly light load, in order to keep the motor flux constant,in general,the voltage frequency coordination control mode is the constant V/F.But the control mode of the constant V/F to consider issues more from the motor itself,without considering specific work conditions, such as load, voltage level,it makes the AC-AC converter and the induction motor operating conditions cannot be a better match and the motor power index(include power factor and efficiency) is not optimal,cannot achieve the purpose of saving energy.Therefore,this paper puts forward the control strategy of the best voltage frequency ratio,and combine the control strategy of online realtime continuous frequency conversion of the AC-AC converter, make the motor power index running on the higher economic status all the time.Firstly,this paper puts forward the control strategy of online realtime continuous frequency conversion of the AC-AC converter on the basis of using the off-line calculation of the cosine wave crossing method to calculate the trigger time,in table look-up way to trigger the thyristor,and realizes the output frequency realtime continuous change of the AC-AC converter.Secondly, Using the matlab bulids a simulation model,and making a contrastive study on the same motor with different load under the different frequency and different motor with load.Through a large number of simulation,get a general law that the power factor and efficiency of the motor with voltage change,and get the best voltage frequency ratio value base on the best power index of the motor.Finally,through specific experiments to verify the simulation conclusion,and combine the control strategy of online realtime continuous frequency conversion of the AC-AC converter,realize the control strategy of the best voltage frequency ratio online continuous frequency conversion,make the motor power index running on the higher economic status all the time. |
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