| This study is a part of the Doctoral Program of Higher Education of the Ministry of Education (NO.20101402120004). It is proposed on the issue of high-voltage great-power frequency control. Widely used high-pressure great-power pump and fan motor, making the frequency control evident day by day. The traditional low-voltage inverter technologies have become incompetent for modern industry. Multi-level inverters are more widely used in the high-voltage great-power frequency control due to its advantages of small harmonic content, the output voltage closer to the sine wave, low demand of power devices and so on.The topology structure and operating principle of the diode clamped three-level inverter is analyzed in this article. on this basis, the control algorithm and the neutral-point balancing control method of the three-level inverter is studied.The experimental platform of the three-level inverter is built, and the experimental research of space vector PWM (SVPWM) control method for three-level inverter is completed. The ideal experimental waveforms are received. the main contents of this article are as follows:The research situation, development prospects and topology structure of the multi-level inverter are introduced. The work principle and topology structure of the diode-clamped three-level inverter is analyzed. The two commonly used control algorithm(SPWM and SVPWM) for three-level inverter are researched. The solution to the problem of the midpoint potential unbalance is given.On the basis of theoretical studies, the simulation model of the SPWM control algorithm is established in PSPICE, and the simulation model of the SVPWM control algorithm is established in MATLAB. These two control algorithms are simulated under different modulation. The simulation results show that the output voltage and current waveforms based on the latter algorithm have less distortion and better quality.The cause for neutral-point unbalance is studied. Based on the theoretical analysis of injected zero-sequence component, the SPWM control strategy, which is through injecting zero sequence component to balance the midpoint is improved by introducing the feedback structure. Thus a SPWM control method which restraining midpoint potential fluctuation is received. In addition, the balance control method for midpoint based on the space voltage vector is also simulated.The simulation results show that these two control methods are able to inhibit the midpoint fluctuations.Based on theoretical analysis and simulation studies, the hardware circuit, including main circuit, driver circuit, voltage sampling circuit, current polarity detection circuit and protection circuit, are designed. Make these circuits debugged and the results show that the hardware circuit meets the requirements.The software implementation method of SVPWM for three-level inverter is derived.The program of control system for three-level inverter is written using C language based on DSP2812, including the main program and interrupt service routines.Among them, the former is used to complete the calculation of reference voltage amplitude.The latter mainly realize SVPWM generation, AD sampling as well as current polarity checking function. Make these programs debugged and the results show that the software design is correct and effective.The hardware and software experimental platform for three-level inverter is established, and consider the former one as carrier to mke program debugged to get the experimental waveforms.The experimental results show that all parts of the experimental device can work properly and can receive phase voltage and line voltage waveforms accurately.The experimental results verify that the design of hardware and software are rational and the control method of SVPWM is correct, all these lay a foundation for further debugging of the system. |
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