Research On Counter-rotating Fan's Control Strategies Of Soft-starting

With the development of electric power technique,the AC induction motors are widely used in various fields.However,there are many problems for the asynchronous motors' direct starting,such as large starting current,low starting torque,great impact on the power grid,great impact on the mechanical equipment.As a result,direct starting will make a greater impact on the power grid.Softstarting of AC induction motor can reduce starting current to avoid damaging the motor.On the same time,it can also reduce voltage of power grid to avoid the influence on other electrical equipment of the same power grid.Besides,the soft-starting of AC induction motor can also be controlled easily to raise working efficiency and energy efficiency.In this thesis,the starting characteristics of the induction motor are firstly analyzed and the necessity of soft-starting is determined.Then the principles of SCRs adjusting voltage and controlling the induction motor are analyzed.on the basis of analysis above,a control scheme based on thyristors in anti-parallel and a control strategy based on current control are proposed.The control scheme in this thesis is designed with TMS320F2812 for the key controller.The fiber-optic is used for transmitting signals between high-pressure manifold and the low power.The application on a 10 k V fan showed that the trigger ensures high pressure series thyristor valve group working reliability.Besides,thyri stors type selection and voltage equalizing problem are analyzed.Specifically speaking,power factor angle are taken as the feedback,and the adjustment of trigger angle for SCRs are ensured to tracked in a timely manner freewheeling angle changes that av oid the oscillation of motor.The results showed that the starting current of large asynchronous motors can be limited to less than 3 times the rated current with this control strategy.Finally,on the basis of the control strategy and the designed scheme,the experiment platform is constructed and experiments on different starting current and different presetting time are conducted.Results showed that the proposed control scheme can achieve the soft-starting of medium-voltage induction motor.