| Large-capacity converters,especially the ultra-large-capacity converter equipment with rated voltage of 3-10 k V and capacity of 10-200 MW occupy an important position in national defense construction and industrial production,including large-scale wind tunnels drivers,ship electric propulsion,steel rolling,Mine upgrading,railway traction,oil and gas transportation and others.Even now,these key equipment still rely on imports.In this paper,the key technical of the ultra-large capacity IGCT five-level NPC/H synchronous motor speed control system are studied,including the pulse width modulation strategy,the energy process analysis of the converter,synchronous motor speed control strategy,control system design and other key issues.The primary works and achievements of this dissertation are summarized as follows:A fast modulation strategy with switching frequency of 500 Hz and applicable to IGCT five-level NPC/H topology is proposed.The minimum pulse width and overmodulation problems are also considered.From the point of voltage vector design,switch sequence decoding and switch sequence,this paper solves the problem of voltage mutation in traditional seven-segment modulation algorithm under NPC/H topology with low switching frequency,and considers the power consumption equalization,the equivalent switching frequency is increased by 50%.Aiming at the narrow pulse width under low modulation,its generation mechanism is analyzed and a switching sequence solution with step-wave output is designed.A fast over-modulation strategy is proposed for NPC/H topology,without storing data and complex calculation formula,with the output voltage linear gain characteristics.Aiming at the secondary pulsation problem of energy storage in five-level NPC/H converter,an energy conversion process analysis and suppression method with full-cycle operation range is proposed.The energy fluctuation mechanism of five-level NPC/H is analyzed,its energy storage has quadratic ripple characteristics.During the transient PWM control period,the relationship between DC energy storage and switching vector is analyzed.The method of energy fluctuation suppression is proposed from the PWM switching sequence design.Experiments in the PWM cycle show the effectiveness of the proposed suppression strategy.During the process control cycle of the converter,the energy transfer characteristics of the speed-regulating unit during acceleration and deceleration are analyzed.The control parameters are designed,the effectiveness of the proposed method is verified by control process experiment.Aiming at the DC drift problem of the traditional synchronous motor flux observer voltage model,a new hybrid flux observation model based on the improved voltage model is proposed.The improved voltage model uses the second-order generalized integrator to replace the pure integral component in the traditional voltage model,which can eliminate the DC deviation of the back EMF and make the output flux circle clear.A hardware and software hierarchical design of synchronous motor control system is proposed and a digital control system for synchronous motor based on VME bus was developed.The experimental platform verified the control performance and reliability of its software and hardware.The experiment of high voltage motor shows that its speed regulation performance meets the static speed error <0.01%,the current dynamic response time <10ms and the speed dynamic response time <100ms.A convert based IGCT five-level NPC/H for synchronous motor speed control system was developed,and the engineering experiment was carried out on the 6.9k V / 20 MW wind tunnel drive system.The experimental results show that the developed converter stabilizes in the full speed range,the voltage of the upper and lower arms is balanced,and the DC bus has no obvious impact,verify the effectiveness of the theoretical method and device developed in this paper. |
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