Research On High Power Control System For Mine Soft Starter Based On Discrete Variable Frequency Technique

The content of this thesis is an important part of the project “Scraper Conveyor Drive System”(NO: 110148032), which is the College Students’ Innovation and Entrepreneurship Project sponsored by Taiyuan Science and Technology Bureau. Three phase AC asynchronous motor is the main power source in the transmission engineering. Because of its simple structure, low cost, stable and reliable operation, it is widely used in underground coal mine production. Thyristor soft starter due to its good startup performance obtains the widespread application in the larger power mine three-phase asynchronous motor starting process. But it reduces the starting current of the motor by reducing the stator terminal voltage, so starting torque inevitably decreased, which makes thyristor soft starter can not with heavy load starting, severely restricting its use in underground coal mine. Aiming at the above problems, it is very important to research a kind of soft start can output larger starting torque while reducing motor starting current control mode. The main research contents of this paper are as follows:After consulting a large number of domestic and foreign literature, the current situation of the development of the thyristor soft starter are detailed analyzed, in order to solve the problem of the existence of the current soft starter, in-depth study of the discrete variable frequency soft start control method, and the realization technology of discrete variable frequency soft start control system for in-depth study.The thyristor regulating circuit working principle is analyzed.The problem of discrete variable frequency soft start technology of phase sequence is studied and the positive sequence symmetrical combined voltage frequency is obtained. By three-phase symmetrical component method and simulation that no optimal combinatorial symmetric positive sequence voltage frequency phase angle combinations is obtained and the thyristor conduction mode is determined.How to realize discrete variable frequency soft start control is studied. The discrete variable frequency soft start control of minimum frequency as well as the transition frequency section and the frequency time is determined. Constant voltage and frequency ratio control strategy is used in the frequency and by power factor angle closed loop control strategy for a voltage ramp control mode is used in power frequency.The discrete variable frequency soft start control system and the conventional soft start control system simulation model is built in MATLAB/Simulink. Simulation results show that the discrete variable frequency soft start control method with conventional soft start control method to reduce the advantages of motor starting current, and can output larger starting torque.The discrete variable frequency soft start control system hardware circuit is designed. Based on the hardware circuit the functions of the system software is developed to realize. The test results show that the system is stable and reliable in hardware performance and software program of high real-time, fast response time.The test of voltage reduction circuit with symmetrical resistive load was carried out by the control mode of each frequency band. The line voltage of each phase was measured and compared with the simulation results, which verified the correctness of the program of the two frequency division. Based on 3k W three-phase asynchronous motor of the motor direct starting, motor voltage ramp control start test. The test results show that the conventional soft start control method can reduce the starting current of the motor, but also can limit the starting torque of the motor.