| The mine hoist is an important transport equipment during coal mine producing. Its electric driving and control devices are always the research focus in the electric driving field. At present, in our country the electric driving schemes applied to the mine hoist are rotor in series with resistor adjustable speed system, DC motor V-M reversible adjustable speed system, vector control system with thyristor AC-AC frequency conversion, etc. This paper proposes a research issue which applies dual-PWM AC-DC-AC frequency conversion scheme to the mine hoist regarding that the hoist requires high reliability, four-phase operation and wide range of adjustable speed. This research issue can be divided into rectification , which using PWM rectifier, and inverter, which using AC motor vector control.Firstly, the paper gives the mathematical model of asynchronous machine under arbitrary reference frames and the per-unit model is generalized. An improved indirect vector control scheme based on SVPWM has been proposed by combining direct and indirect vector control, whose merits and defects have been analyzed in details.Secondly, the analysis of working principle of three-phase voltage source PWM rectifier (VSR) system is given. The mathematical model of three-phase VSR is established in three-phase static and synchronous rotational reference frame. The control strategy of three-phase VSR is voltage-oriented vector control method based on dual-close-loop control using current inner loop and voltage outer loop. The independent control of active power and reactive power is obtained through the feed-forward decoupling method.Thirdly, the overall structure of the dual-PWM system is given. Each part of the system is designed. The main circuit includes choosing the inductance, capacitance and power switching device. The control device uses TMS320F2812 DSP, which is powerful enough to fulfill the requirements of the system. Sample and conditon circuit is designed, which is used to detect AC and DC voltages, AC currents and the machine rotor speed. The optical fiber isolated driving circuit is built, which chooses 2SD315A as the driving chip. The hardware protection circuit is also got designed. The system control program is composed, which includes rotor speed test, the digital PI regulator, A/D, SVPWM algorithm.Lastly, the dual-PWM frequency conversion system is simulated based on Matlab/Simulink, which verifies that the control system is correct and effective. The prototype of the experimental system has been built, power rating of which is 15KW. The system is proved to be capable of running in unity power factor, bi-direction powerflow and four-phase operation according to the experimental result. The system has the features of very small harmonic current, good system dynamic performance and wide speed range, which meets the design requirements. This research issue has some reference value to the improvement of mine hoister for our country. |
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