Research On Control Strategies And Digitizing Design Method Of Multilevel Current Source Inverters

Multilevel current-source inverters (CSI) have the merits of simple topology structure, good output waveform, high power-factor and reliable protection. But the questions are the low DC utilization, complicated modulations and difficult implement. This thesis lays emphasis on the research of the control strategies and the digitizing design methodology of CSI. The concrete content is as follows:Based on the topology structure of direct-type CSI, a new fresh digitizing design methodology using FPGA is put forward by analyzing modulation principles of carrier phase-shifted SPWM, the multi-carrier vertical distribution SPWM and the step wave.According to the dual principle, the thesis proposes a new kind of third harmonic injection method, which injecting one sixth third harmonic in modulating wave. As a result, the utilization ratio of direct current increases 15.5 percent and the third harmonic is eliminated. And this raised DC utilization rate.On account of the topology of combined CSI, a TPWM modulator approach of location reverse cross is given out, which can come true easily and have no breakage in direct current. This system has four triangle waves modulated by trapezoidal wave, both the two waves upside and the two underside are crossed reversely, and the first half and the second half of trapezoidal wave use carrier modulation respectively. And also mathematical model is built and concluded that this method can keep current continuously, which ensures each phase balance and the carrier wave ratio is 2n+1 multiple of 3. Simultaneously, the relationship of displacement angle and harmonic is provided in multi-level inverter composed by three-unit CSI in parallel. Moreover the results of simulation of frequency spectrum and theory both prove that the TPWM is feasible and excellent.After expanding the essential space vectors from 19 to 25, the thesis offers a 25 SVPWM control procedures that needs symmetrical three-phase loads in the CSI topology made up of parallel two units. Also the output harmonics is smaller than 19 SVPWM in low frequency modulation.Furthermore, the thesis presents the hardware system combined the Matlab with DSPbuilder to achieve the control method of multilevel SVPWM collectively and simulates all the projects. This device advances a new unified solution for CSI and raises the design efficiency.