Research And Design Based On The Hybrid-Clamped Five-Level Inverter

Multilevel-converter is one of the most active technologies in medium-high voltage and high power applications in the recent years. The diode-clamped topology and the cascaded H-bridge topology are more popular in industry. However, due to the unbalance of the DC-link capacitors, the diode-clamped topology has not been extended into the five-level or higher level converters.The hybrid-clamped topology is proposed to achieve the balance of the DC-link capacitors in high-level converters, by the parallel connections of the DC-link capacitors and the flying capacitors. What's more, the control scheme of the hybrid-clamped topology is very simple, and it can be operated under all load conditions.The Analysis, research and design based on the hybrid-clamped topology are discussed in this paper.The structure and the operation principle of the hybrid topology are introduced including the circuit combination, the balance theory and the control scheme.All operation modes and the transitions between them are listed and classified into 3 kinds. Each kind of the transitions is analyzed in detail and its characteristics are induced, which are confirmed by the experiment results. A few kinds of carrier modulations are analyzed and compared on the effects on the transitions and the output voltage harmonics.A method of capacitance selection on the DC-link capacitors and the flying capacitors is proposed. The operation of the system is divided into five transition modes with different effects over the balance among the capacitors, and the most influential one is taken as the referred extreme condition for the selection of capacitances. Furthermore, the capacitance ratio of the DC-link capacitor to the flying capacitor is induced. The method is confirmed by simulation with constant current load.Based on the hybrid-clamped topology, a new topology combining the switched-capacitor and the diode-clamped circuits is proposed. The structure and the operation principle of the new topology are discussed in detail. Both advantages of the switched-capacitor and the diode-clamped circuits are brought into the new topology. Not only balancing the DC-link capacitors, but also it can step up the output voltage with kinds of boosting modes, and less power devices are used. The validity is confirmed by simulations and experiments on a five-level inverter.A prototype of the hybrid-clamped five-level three-phase inverter is built up in the lab, and validates the feasibility in high power applications.