Development Of 7.5kW Switched Reluctance Drive System

The content of this thesis is an important part of the project "Scraper Conveyor Drive System" (serial number:110148032), which is the College Students’Innovation and Entrepreneurship Project sponsored by Taiyuan Science and Technology Bureau. The scraper conveyor, which has problems like large current in starting, serious impact to the grid and difficulties in starting, is one of the important equipment of coal production in coal mine and need heavy-load start frequently. However, there are several advantages with switched reluctance motor, which include simple structure, small starting current, great starting torque, frequent starting possibly and high operating efficiency in the entire speed range, etc. So it is extremely applicable to drive coal transporter including scraper conveyor in the coal. Therefore, there exists important practice significance in the development of the high-power switched reluctance motor which applies to the scraper conveyor drive. Due to the fact that the control of the high-power switched reluctance motor being quite complicate and the price of the high power full control type semiconductor device being too high, a 7.5kW switched reluctance motor is used for research in this thesis. The main focus committed to the switched reluctance motor includes the following factors: the control strategy, hardware structure of the control circuit, current waveform of the motor windings and the capacity to load. The investigation lays a solid foundation for the development of the high-power switched mining reluctance motor and it gains practical experience.The research target of this thesis is to develop a switched reluctance drive system in which the TMS320LF2407A is used as control core and a three-phase switched reluctance motor, with the stator and the rotor for 12/8 poles and the power for 7.5kW, is used as the experimental prototype. The no-load experiment and load experiment were executed. Plus, the operation efficiency curve and mechanical characteristic curve were drawed. The main research contents are as follows:Quasi-linear inductor model of the 7.5kW switched reluctance motor is founded according to the object of study. Relevant control strategy is formulated, the energy floating when different voltage is applied to the two sides of the motor windings is analyzed and the selection of the power converter main circuit of the experimental prototype is done. On the basis of accessing to extensive literature, three-phase asymmetric half-bridge circuit is chose as the main circuit structure of the power converter.The hardware circuit of the speed control system has been designed, which includes IGBT driver circuit, position signal detection circuit, current signal detection circuit, PWM signal conditioning circuit, DC bus overvoltage and undervoltage detection circuit, fan failure protection circuit, etc. The debugging results of the hardware circuit show that the above circuit can be reliable and the indictors of the technical performance can satisfy the design requirements.Based on the position signal detection circuits which have been well developed, the relationship between the switched reluctance motor phase winding inductance and the position signal has been measured, the logical change phase table of the model is figured out, and the commutation sequence at the forward and reverse of the motor is determined.Modular programming methods have been adopted. The switched reluctance drive system application program, which is programmed by assembly language, include uniformly accelerated starting subroutine, the speed calculation subroutine, the chopped current control mode subroutine, the voltage PWM control mode subroutine and overcurrent fault protection subroutine, the position signal error fault protection subroutine, IGBT driver fault protection subroutine, etc. The above programs have a short execution time, which guarantees the real-time of the system.The speed control system test platform of the switched reluctance motor is founded. The joint debugging of the designed hardware circuit and the developed application program has been done. Current signals of three-phase windings, three position signals, waveform of phase current and winding voltage, waveform of voltage signal across IGBT and its driving signal were measured in the no-load conditions. The results show that the hardware circuit has been reasonably designed and the system has strongly anti-interference ability. The sampling results, which have been obtained through speed waveform during starting process and the current waveform under chopped current control mode and the voltage PWM control mode, show that the motor runs uniformly acceleration basically during starting process and the DSP-sampled current waveforms and actual current waveforms are basically the same.The platform of the load test is founded. Different loads loading experiments have been carried out to the switched reluctance drive system in different speed. The experimental results show that the system has a small static error and good anti-interference ability. The operation efficiency curve and mechanical characteristic curve have been drawn. The efficiency of the system is greater than 80% under the rated load conditions when the speed is above 600r/min. In the normal operation mode, the AC side input current effective value is 16.8% of its value under rated operation and the output torque is of 1.21 times of the rated torque at the speed of 100r/min. In the overloading running mode, the AC side input current effective value is 21.68% of its value under rated operation and the output torque is of 1.4 times of the rated torque at the speed of 100r/min.