The Research On High Starting Torque Soft Starter Based On Fuzzy Control Theory

Soft starting technology have been widely used in industrial production at home and abroad, accompany with the development of power electronics technology and intelligent control technology. Traditional electronics soft starters have used the method of gradually increase stator voltage to rated voltage. This method can start AC asynchronous motor smoothly and can also reduce starting current and decrease the impact to electric network by starting motor. Because of three-phase asynchronous motor electromagnetic torque is directly proportional to stator voltage, and if stator voltage being decreased,electromagnetic torque will be largely decreased,so the applied range of electronics soft start technology has been limited by the characteristic that electromagnetic torque is small.Because of such deficiency of traditional electronics soft starters, this thesis has researched a kind of discrete frequency high torque soft starter based on current fuzzy control.This project can make traditional electronics soft starter reduce stator voltage frequency when it reduce stator voltage value. And it can make electronics soft starter start according to synchronous speed and start from low speed to high speed discretely. It can also reduce energy waste during starting process, and conquer default of small torque of traditional electronics soft starter, and can make induction motor start smoothly in full load situation with high starting torque and low starting current.This thesis puts AC/AC frequency convert theory in induction motor soft starting control, and it researches a induction motor high torque soft start method which is based on discrete frequency control. This thesis deeply analyzes discrete frequency convert theory, and advances a kind of discrete frequency starting fire angle optimum choice principle,and simulate to the discrete frequency starting process with the tool box of MATLAB/SIMULINK, and proves the discrete frequency start method precedes traditional directly start method,current-limiting start method and ramp voltage start method.For increase current control robustness, in aspect of soft starter current control, this thesis researches method of fuzzy control to motor start current after analyses basic theory of fuzzy control self-adaption PID. By taking advantage of worker usual experience or other experience this method can make controlled target running in high efficiency control and regulate in a situation of being unaware of math model of the controlled target. During the process of motor voltage increasing fuzzy control self-adaption PID can send motor current and voltage signal to trigger after detects and operates these two signals and make the thyristor breakover and can also adjust turn-on angle to achieve optimum control result in motor start process. This thesis make further analysis that fuzzy control technology is a effective method to solve the problem of control motor current in motor starting process, and this method has a high level robustness that traditional method can not surpass.At last, based on 16bit signal chip this thesis developed a AC asynchronous motor digital soft starter, completed control system hardware and software desire,and gave experimental result of current fuzzy controlled discrete frequency high torque soft starter, and this thesis gave its own suggestion to some problem relating to further research.The research of this thesis have indicated that current fuzzy controlled discrete frequency high torque soft starter have excellent performance, simulate result and experiment result have proved the correctness and effectiveness of discrete frequency theory.