| Firstly of all,making a brief introduction of the technology of the frequency conversion,traditional AC/AC frequency converter uses the method of off-line to calculate the triggering time,and look up the table to set the trigger for thyristors.With the development of the theory of AC/AC frequency conversion,the online of calculating of the trigger time is realized,this method uses an approximate method to calculate the pulse triggering time,but the original use of the horizontal axis(time)to calculate the pulse trigger time belongs to the fixed point switching mode.Fixed point switching mode can not achieve any frequency of operating,but also can not achieve switching frequency directly.So this paper presents an improved method to calculate the pulse triggering moment,this mode can achieve any frequency,and the mode of switching frequency with switching method directtyl.Then the simulation and experimental verification are carried out.The traditional motor start with soft starter,This way only changes the voltage of the power,Although the current of start is reduced,its torque is also relatively reduced.The use of inverter starting its small starting current,it can also maintain high torque.Although the inverter performance is good,in the market it is relatively high,and control complex,so this limit the application of frequency converter.A simple closed loop strategy is proposed in this paper,based on the AC inverter,the oprimal torque is used to start the work.Secondly,the model is established in MATLAB/Simulink.The calculation and optimal torque of the improved pulse trigger time are simulated.Through a lot of simulation to verify the feasibility of the strategy,and the motor start steady.Finally,an experimental platform for the optimum torque characteristics of the AC AC converter is set up,Through experiments,the feasibility of improving the trigger strategy and the optimal torque of the improved AC-AC variable frequency pulse is verified,and the motor more stable. |
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