The Design And Simulation Of Soft Starter For Asynchronous Motor

Asynchronous motor is the main load in power grid, its starting process often accompanieslarge starting current, rushing and affecting the safe operation of power grid. Soft starter is anovel kind of motor control device. Compared with the traditional motor starting mode, motorthat uses soft starting mode can realize the continuous stepless regulation of starting voltage andthe restraint of starting current, which can effectively improve the starting performance of themotor.The application of soft starter is very extensive, and the market prospect is very broad. Atpresent, foreign brands have occupied the majority of market share in native market of softstarter, while the technical strength of the domestic independent brands are relatively weak. Theproducts of foreign brands have the advantages of high fame, great variety, advanced technologyand perfect service, but are often too expensive, not suitable for the large-scale popularizationand application. In view of that situation, this paper takes STM32as the control core, researchingon an affordable soft starter products for asynchronous motor with reliable quality and goodperformance.The main work of this paper include the following aspects:（1）Briefly introduces of the concept of soft starter, summaries the present researchsituation of soft starter at home and abroad, studies on the starting characteristics of inductionmotor, and expounds the principles of the common starting/braking modes of asynchronousmotor. The various starting modes are compared, and the detailed voltage regulating principleand advantages of soft starter is described.(2) A detailed hardware design of the soft starter is carried out, including the selection ofcore micro controller (MCU), and the design of MCU minimum system. The main circuit isdesigned, the choice of the key device of thyristor is made and the corresponding protection istaken. A voltage detection circuit which has the functions of synchronous signal detecting, phaselack protection, and over-voltage protection is proposed. The current detecting circuit, theauxiliary power supply system, the thyristor driven circuit and the display circuit are alsorealized.(3) Partial software design of the soft starter is carried out, including the main program, theinterrupt service subprogram for synchronization signal, the incremental PI subprogram, thecurrent-limited starting subprogram, the ramp voltage starting subprogram, and the trigger delay subprogram. The detail of the working principle of each subprogram and flow chart is described,and the attention that need to be paid to the process of program design is mentioned, too.(4) uses MATLAB software as the simulation tool of AC voltage regulation system of softstarter. The simulation results show that, the soft starter can promptly improve the startingperformance of induction motor, reduce the impact to power grid, and achieve stable and reliablestarting. The deficiencies and prospected of the work of this paper is summarized in the end.