| DC motor is important production equipment; its startup problem is an important factor affecting their life. If DC motor directly started under the rated voltage, its starting current would be 10～20 times of rated current. Especially for the motor of tens of Kilowatts,when it direct starts, there will be a tremendous impact on Power System and other equipments because of the huge starting current, and starting torque of motor itself will be great, resulting in commutator and armature winding damaged. It is not allowed for DC motor to start directly, how to solve motor startup problem has always been the concern of the people.This article studies and designs a soft starter for DC motor, which power supply is battery system. The starter is controlled by a microcomputer and uses IGBT as power switching elements. Its principle is basing on PWM chopping to reduce voltage. The soft starter has many advantages, such as simple structure, easy maintenance. It also has the function of soft starting, messages displaying and system protecting. The article introduces the whole system and gives detailed information about main circuit, controlling circuit, protecting circuit and so on. According to the design, I made a prototype and did some experiments. The DC motor is 175/220/320V and 175A. The experiment results show that starting current was controlled 2 times of rated current, and starting time is less than 10 seconds, also the whole starting is stationary and no impacting. If there are faults occurring including over-current, over-temperature, short-circuit and so on, the system can do real-time protection automatic.This soft starter can not only start DC motor step-less but also modify startup parameters to adapt to different motors and loads. Compared with the traditional mechanical starter, It can achieve continuous and step-less starting, and has the advantages of less impacting torque impulse current and good start repeating. So its large-scale application is easier.
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