| The asynchronous machine always works in the under-load and the idling working conditions, due to the load changing frequently sometimes. However, in order to satisfy the heavy load, we need to choose an asynchronous machine with a comparatively bigger power. So, when the machine is running in the under-load or the idling working circumstance, its power factor will be very low. As a result, the efficiency of the system is low and the electric energy is wasted greatly.Firstly, this paper discusses the reason of the low efficiency, analysis the energy consumption, and find the relationship of efficiency and power factor and the load. This paper also analysis the possibility of the theory: reducing voltage to increase the power factor according to the changing rules of the power factor. The power factor is very low when the load of the motor is very low, especially the idling load, the motor's running efficiency is very low, so we can decrease the input voltage to increase the power factor.Secondly, based on the theories above and the basic theory of fuzzy control, this paper used a kind of integral fuzzy control with adjustable factor to control the triggle angle of thyristor to reduce the input voltage of the motor, in order to increase the power factor. From this we can get a good result of energy saving.At last, this paper make a design of the hardware and the software of the control system. The main arithmetic circuit is made up of three phase anti-parallel connection of thyristor booster circuit, power factor dectect circuit, the thyristor trigger circuit as well as the serial storage circuit. The central control unit is single chip processor of PIC16F877A. In the software design, each main function module detail flowchart is given. This article also introduces the subsystem's anti-interruption design measures of the software and hardware. Then this paper gives the experimental result of the syetem, proposes the direction of further improment.
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