| High-voltage and high-power variable frequency drive technology is an effective method to resolve the waste of energy of traditional AC drive system. With the advantages of the fewer power devices and simple circuit, the three-level NPC structure has been successfully applied to drive the induction motor under 4.16kV. Due to the problems among the withstand voltage level, control and protection technolongy, the application of three-level NPC structure in 6kV and higher voltage situation has been limited. Foucs on those issues, the research is carried out through such aspects as the improvement of main circuit structure, optimize of control strategy and perfection of protect function, software and hardware development and device experiment.The defrcts of traditional three-level circuit have been maked up by using phase independent di/dt restraint circuit and IGCT series inverters. The problem of partial over-current phenomena and voltage level increase has been analyzed emphatically. Based on theoretical analysis, modeling and simulation, and experimental research, the parameter and performance of those new designs have been analyzed in details. With this new type of main circuit structure, the harmonic content of the output voltage has been reduced, the highly active and stable of series connect of power devices have been realized, the output voltage level has been increased, and the over currents Phenomenon of local circuit has been solved.The key technology of SPWM Digital theory, the primary algorithm and the main problems have been analyzed meticulously and completely. The digital theory of triangular carrier and sinusoidal modulation wave generation, PWM duty cycle calculation, switching states configuration and gating signals fault diagnosis were studied with the combination of characteristics of high-voltage high-power three-level neutral point clamped (NPC) inverter. By using FPGA, the on-off time calculation the simplified calculation method, all round dead state configuration and universal over-modulation principle has been realized well. The simulation and experimental results are given to verify the correctness, feasibility of the digitization assumption.The nonlinear unified discrete time domain modeling method is introduced in asynchronous motors variable frequency drives system simulation. In this way, the motor control strategy, modulation algorithm and primary circuits are combined together and it provides an excellent analysis platform for algorithm and main circuit performance analysis. Based on the unified model, the high-performance constant U/f control principle has been put forward. The slip following self adaptive startup method, magnetic flux compensator, the current limiter and DC bus voltage compensator has been used in this improved control principle.Based on the characteristics of high voltage asynchronous motors variable frequency drive system, the various fault types of drive system have been analyed. According to the results, a series protectiong method such as an voltage deviation protection,, combined charging protection and one point earthing protection of DC bus has been put forward. The protection configuration can reflect the fault of 24-pulse rectifier, DC bus, three-level inverter and load accurate and timely.The high reliability hardware and software based on layer organization structure and coordination mechanism has been put forward and relasized. In the control system, the DSP+FPGA+CPLD based new digital implementation circuit has been used and the safty interlock function has been realized. The equipment has finish the 6kV resistance load experiment and high-voltage motor industry operation. The high performance of control system, reliability and operation stability of protection system, accuracy of nonlinear unified discrete time domain model are proved by the experiments. And the result shows that all various parameter reach the design request.
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