H-bridge Cascaded Multi-level Inverter

Because of small switch stress, high quality load wave and easy packaging, cascaded inverter will be more and more widely used in flexible AC transmission system (FACTS), high voltage DC transmission and Variable-Frequency Speed Regulation System. Using the method of carrier phase shifted SPWM (CPS-SPWM), the high equivalent switching frequency can be obtained with low switching frequency devices. This technique improves the equivalent switching frequency through the counteraction of lower order harmonics. So it is with a perfect performance on harmonic feature. Among the various multilevel PWM methods used in cascaded multilevel inverter, carrier phase-shifted SPWM (CPS-SPWM) has been widely used in the control of multilevel inverter for its principle relatively simple and easy to control. In this paper, the basic principles of cascaded inverter and CPS-SPWM are studied, and some relative simulations and experiments will be done to prove some principles.This paper first briefly introduced in the cascaded inverter and its modulation strategy based on the state of development, in-depth analysis of multi-level cascaded inverter and carrier phase-shifting SPWM (CPS-SPWM) modulation strategy principles. It will provide the basic of theory for the following simulation and systems experiment studies.Secondly, based on the MATLAB7.1 / Simulink simulation platform, single-phase five-level and three-phase five-level cascaded inverters based on carrier-based phase shift modulation will be simulated. In-depth studies the waveforms work in different carrier frequencies, as well as under different modulations, and the system harmonic analysis will be done. The carrier phase-shifting modulation (CPS-SPWM) strategy and the related principles of cascaded inverter are clarified.Finally, the experimental platform of three-phase double H-bridge cascaded five-level inverter is established with the controller based on DSP and FPGA. And the system experimental studies are completed, the relative experimental results are obtained and analysed, so the operation of the cascaded H-bridge multilevel inverter system is carried out.