The Cascade Speed Regulating System Of Inner-feeding Motor Based On DSP Control

Motor system is an application field which is large-scale and has enormous demand. Quite a few motor systems applied in industry in our nation are fans, pumps and other transmission systems, and such kind of loads accounts for nearly half of the total quantity of industrial electrical transmission systems. A lot of electrical power loss is caused by these loads whose flow regulation devices depend on plates or valves. The main reason for such a condition is as follows: A lot of fans and pumps, which are selected according to the limit loads they might encounter, runs for 24 hours a day at a constant speed, however, the actual power required during the general running state is often much less than the power rating. Furthermore, the traditional speed regulation of the fans and pumps, which controls the airflow and water flow, is based on the opening adjustment of the plates(or valves) at the input or the output. Thus too much power input causes serious power loss.The background of the development and current condition of cascade speed regulation is introduced at the beginning of the thesis. Advantages and disadvantages comparison of the variable frequency speed regulation with that of the cascade speed regulation are presented as well as analysis of three kinds of cascade speed regulation systems. According to the characteristics of the chopper inner feedback cascade speed regulation, a DSP-based chopper inner feedback cascade speed regulation system is designed with compensation for the low power factor defect of the traditional cascade speed regulation. The significance and primary work of this subject are presented as well.Then the principle of chopper inner feedback cascade speed regulation is introduced. To reduce reactive power that a cascade speed regulation device absorbs from the power grid and raise system power factor, the phase angle of the inverter should be kept to a minimum based on analysis, the duty cycle of the chopper is controlled by DSP to adjust the additional electric potential in the motor rotor circuit for speed regulation; the selection principle of the chopper components and the structure and principle of IGBT are elaborated upon; inverter failure that is often encountered in engineering and solutions are introduced in detail; the calculation of parameters of chopper components is deduced in detail.DSP TMS320F2812 is applied in hardware design, the calculation is more accurate with more precise data acquired from analog signals. The design of all hardware modules are elaborated upon as well as parameters of the components; double-close-loop is applied in software design. The combination of DSP and PLC is creatively adopted in the control strategy, which helps to decrease the calculation of DSP and has the advantage of good anti-interference performance of PLC, thus the system is more safe and reliable. Ordinary wires are prone to interference due to the long distance between motors and cascade speed regulation systems in practice, however, optic-fiber transmission can avoid this situation, so an optic-fiber transceiver HFBR-1414 and an optic-fiber receiver HFBR-2412 are applied in the design. Tests shows that the chopper inner feedback cascade speed regulation system is a great potential technique with excellent control performance, prominent power-saving effect and a better anti-inference ability.