Research Of Soft Starter Based On IGBT

The starting current is 4-7 times bigger or more than the rate current when high-power asynchronous motor starting directly. The extremely big starting current generates a large amount of Joule heat causing the excess temperature, that makes the motor aging or even burned. The starting current has effect on other electric equipment, poses a threat to the safe operation of power grid. The conventional soft starters decrease the starting current, and simultaneously reduce the starting torque, that makes using occasions limited.This paper, under the auspices of the National Nature Science of China (NSFC), based on the space voltage vector theory, studied the new type of soft starter. On the basis of hexagonal space voltage vector, this paper research on the strategy of dodecagonal space voltage vector trajectory; used IGBT (Insulated Gate Bipolar Transistor) as soft starter controller to design the main circuit, realized flux trajectory control and motor starting by dividing frequency. The main work can be summarized as follows.(1) Strategy analysis of soft starter controlOn the basis of comparison of various conventional soft starting control methods, the space voltage vector theory is applied, IGBT is used to design the main circuit of soft starter, the dodecagon stator flux control is realized. Firstly, the dividing frequency is chosen; Then, the voltage waveform is analyzed to find the distribution of voltage vector, the moment when IGBT turn-on and turn-off is got; Finally, the dividing frequency combination strategy is formulated according to the calculation results; the harmonic analysis is carried out.(2) Simulation and verification of soft starting processUsing MATLAB/Simulink software to build the soft starter system, and simulate the strategy of dodecagonal flux control. Compared with the current, torque and other parameters of asynchronous motor under different control strategies. The simulation results show that dodecagonal space vector flux trajectory control strategy soft starter can reduce the starting current and improve the starting torque. It verified the feasibility of the control strategy.(3) The design of soft starter control systemBased on space voltage vector dodecagonal flux trajectory, soft starter control system is designed. The hardware of soft starter is consist of master chip STM32 and its peripheral circuit, the power supply circuit, CPLD and its peripheral circuit, the voltage detecting circuit, the current detecting circuit, the IGBT drive and protect circuit; the software of soft starter is consist of control system program, space voltage vector dodecagonal starting program, starting condition judgment program.(4) Harmonic analysis of soft starter control strategyFourier analysis is used to calculate the harmonic content of dodecagonal flux trajectory during motor starting. The harmonic content of dodecagonal and hexagon stator flux trace control is compared by simulation results. The simulation results prove that the dodecagon flux trajectory control strategy can reduce the motor starting process of harmonic content, starting starting current is reduced under the same load.This paper based on the theory of space voltage vector, researched on a kind of soft starter, which based on dodecagonal flux trajectory control strategy and used IGBT as control device. The new type of soft starter can reduce the starting current and improve the starting torque, has certain theoretical significance and application value.