A diode-clamped multilevel inverter with voltage boost function

Multilevel inverters are mainly used in high power and medium voltage applications to reduce the required voltage rating of the power semiconductor switching devices. On the other hands, these multilevel inverters are attractive for various applications regardless of the power ratings because they can essentially realize lower harmonics with lower switching frequency and lower electromagnetic interference (EMI). In this context, the multilevel inverters with larger number of levels suitable for circuit integration are actively investigated. Diode-clamped multilevel inverters are regarded as the promising solution. In the diode-clamped multilevel inverters whose number of the levels exceeds three, voltage balancing circuits for the DC capacitors to maintain the proper voltage are indispensable. The authors have been investigated the application of a circuit topology of the voltage balancing circuits so called Resonant Switched Capacitor Converters (RSCC). In the present paper, the utilization of the voltage boost function of RSCC to enhance the allowable range of the input voltage of the inverter is investigated. The voltage boost function is useful in the applications in which the DC source voltage is limited such as batteries and fuel cells. From the computer simulation and the experimental results, the usefulness and the operating characteristics of the voltage boost operation have been demonstrated.