Open-Loop Capacitor Voltage Balancing of a Nine-Level Packed U-Cell Converter

This article presents a natural capacitor voltage balancing technique of packed U-cell (PUC) inverter extended for nine level topology realized by three floating capacitors and one DC source. The floating capacitors are charged to the voltage levels that maintain asymmetrical relationship between themselves and the DC source. The maximum inverter output voltage can reach up to the available DC source magnitude. With the proposed modulation technique, successful capacitor voltage balancing is possible for a nine -level packed U-cell (PUC9) inverter with three units of floating capacitor in its topology. The proposed modulation strategy achieves zero energy exchange between each capacitor and the remaining circuit. Thus, the need for any additional sensing equipment or complicated close loop control to achieve capacitor voltage balancing is eliminated. The singular DC source is realized with solar and battery combinations that are connected to inverter through unidirectional and bidirectional DC/DC converter respectively. This further verifies the robustness of control strategy as it considers practical scenario of a certain degree of voltage ripple across dc link capacitor of the DC/DC converter. Furthermore, the water pumping system is realized with a single-phase induction motor (IM). Stable operation of the said motor is established by integrating a close-loop V/f strategy with the modulation technique of solar inverter. The pumping system is simulated in MATLAB to validate its performance. A laboratory prototype is also built and tested with a resistive-inductive (RL) load to show the capability of the proposed open loop voltage balancing control of the solar inverter.