Capacitor Voltage Balancing Control Strategy For Single-phase Five-Level ANPC Photovoltaic Inverter

Abstract

Single-phase five-level active neutral point clamped (ANPC) topology is attractive for photovoltaic system. However, it has capacitor voltage unbalancing problems for both dc-link capacitors and flying capacitors. Due to the coupling effect, capacitor voltages are usually indirectly controlled or even uncontrolled, which may influence the quality of output waveform. This paper investigates phase shift PWM (PS-PWM) based capacitor voltage balancing rules and proposes capacitor voltage balancing decoupling control strategy. By injecting the compensation voltage to modulation wave and adjusting the operation time of redundant switching states in each switching period, both the voltages of dc-link capacitors and flying capacitors can be directly controlled. Because the proposed method uses two different degrees of freedom of the topology, decoupling control is realized naturally. Moreover, the dc-link capacitor voltage balancing strategy can be used in other single-phase inverter topologies by simply change the coefficient of the compensation voltage formula. The effectiveness of the proposed method is verified by simulation and experiment results.