The Measure And Control System For Cascaded Multilevel Inverters

In multi-level inverters, the voltage stress of each power device is relatively lower, that is suitable to realize the high voltage and large capacity inverters with the low voltage resistant power devices. And it is possible to enhance the quality of inverter's output voltage obviously by using multi-level inverters. Therefore, with the development of power devices, the multi-level converter technology has been an effective approach for inverters to achieve high voltage and large power. In this paper, selected one of the strong competitive advantage topology—cascaded multi-level inverters as the research object. Completed its topology, control strategy and the measure and control system design.First of all, this paper analysed the research signification, domestic and foreign research status of multi-level inverters. Compared the characteristics of three mature types of topology, acquired the advantage of cascaded multi-level inverters and, consequently, taked it as the research object. Comparative analysis of the four modulation strategy, chosed carrier Phase-Shifted SPWM(PS SPWM )'s modulation method and Constant Proportion of Voltage to Frequency's control strategy. Through mathematical analysis and theoretical simulation, we can confirm that our choice is correct and feasible. Pointed out the relation of cascade units' number and carrier phase-shifted angle, and the modulation ratio (M)'s impact on the output voltage. Complete the mathematical model of cascade inverter and the dead-time effection.In the next part, accomplished the hardware's design, include the type selection of Digital Signal Processor (DSP), Complex Programable Logic Device(CPLD), and Intelligent Power Module(IPM); The circuits' design of system power, measurement(speed,current,voltage,fault) circuits and communication. Using Labwindows / CVI to achieve a upper computer interface, the realization of the inverter's turn and off, set the speed, communication configured, voltage, current and speed measured, current software filtering, harmonic analysis. Compiled the lower computer(DSP)'s Serial Communication Interface(SCI), AD converter,speed measuring (QEP) and some control program.At last, the hardware and software have been debugged on the experiment platform, successfully achieved the carrier Phase-Shifted SPWM multi-level output of inverter, and no-load test of asynchronous motor driven by the inverter is performed. Measure and control interface can accurately communicate with the lower computer, quickly set the various control commands, and can display real-time inverter output frequency, output voltage and output current. All of these work increased experimental convenience, improved work efficiency.