The Research And Simulation Of Motor Soft-Starter Based On Fuzzy Control

Three-phase AC asynchronous motor is widely used in areas such as industrial production and daily life. Because it has simple structure, reliable performance and low price, etc. It will produce much large inrush current which is approximately7to8times of the rated current when the motor is directly starting. The inrush current will affect the life of equipment and impact on the power grid and drag system. Traditional motor starter belongs to machinery starting, such as the series reactance starter, Y-Δ way starter and extended delta starter. But this starting mode will generate secondary impact current and secondary impact torque which may impact on the system. In view of this situation, through researching the characteristic of motor starting, this article uses the algorithm of fuzzy control to develop a new type of smart soft-starter. Its core controller is Atmegal1280. This mode belongs to non-contact starting. By controlling the angle of thyristor, it achieves that the voltage of the motor is gradually increased and the motor works gently, without shock current.This article designs a intelligent soft-starter which uses the mode of limiting current of fuzzy control, based by the algorithm of fuzzy control. It controls the angle of thyristor that decided by fuzzy controller to limit the starting current and gradually increase the voltage of the motor, by detecting the current of the motor. The fuzzy controller is designed by two-dimension, using the current deviation and the rate of the change deviation of current as the input signal, the angle of thyristor as the output signal. The input signal and output signal are used the function of triangular membership. The fuzzy rules use the statement of "If E and EC then U". In accordance with the input signal, the system CPU can output control signal by looking up the table which established by the analysis of theory and filed experience.The system designs the hardware and software of the soft-starter. The hardware part includes the circuit of detecting the signal of synchronization, the circuit of sampling the current, the circuit of the auxiliary power, the circuit of A/D conversion, the circuit of driver, the circuit of the protection, the circuit of key input and liquid crystal display. The main function of the software is to calculate the deviation of current and the rate of the change deviation of current as input signal, then to export the angle of the thyistor based on the algorithm of fuzzy control. The input is based on comparing the current of sampling signal with the signal of input by the key. Finally it controls the voltage of the motor to make the motor starting smoothly. The soft-starter is the integrated control system which includes the function of soft-start, soft-stop, key input, the display of LCD and a variety of protection. For different loads, through input of key to set the parameters, such as the limit of current, starting voltage, starting time and so on, the system makes the starting characteristic of the motor matching the loads and the motor starting smoothly. The system has a liquid crystal display that displays the status parameters of system. It also has many protections like the protection of over-voltage, the protection of over-current, the protection of thermal, the protection of phase and so on. When the system is detected by fault, the relay works and the soft-starter disconnects the circuit.