Power Balance And Power Match Modulation Strategies For Cascaded Multilevel Inverter

Cascaded multilevel inverter is easy to modularize, and it has been widely used in highvoltage transducer, static var compensator (STATCOM) and photovoltaic grid connectedsystem. This paper is dedicated to achieving power balance for cascaded multilevel inverterunder different input sources.A SVPWM strategy that can achieve power balance and has lower output voltageharmonic for voltage source input applications is proposed in this paper. The merit of powerbalance of CPS is firstly introduced into this strategy base on a simplified SVPWM, andthen PD is introduced to optimize the output voltage harmonics. At last, a method ofsolving the complex process of this strategy base on state machine is proposed.The disadvantage of CPS for power source input had been analyzed. It can’t keep themerit of low harmonics of multilevel inverter, and the difference of PV panels that it can fitis small. This paper puts out a circulating PD based on a two-stage topology. It can achievepower match and lower output voltage harmonics, and the difference of PV panels that itcan fit is bigger when compared to CPS.To validate the effectiveness of the two modulation strategies, a prototype ofthree-phase cascaded five-level inverter and a prototype of single-phase two-stage cascadedfive-level grid-connected inverter are built in the laboratory. The design of hardware andsoftware flow is presented. The experimental results prove that the two strategies canachieve power balance or power matching, and have lower output voltage harmonic.