Neutral Point Voltage Control Method for Three-Level Diode-Clamped Converter Based on Fourth Harmonic Current Injection

DC-link neutral point voltage balancing for three level neutral point clamped converters has been extensively investigated. Many effective methods have been reported with desirable performances under high power factor conditions. However, most of the reported methods tend to be weakened when the converter operates at lower power factor, and very few methods can function under no-load or light-load condition. This paper proposes an alternative DC-link neutral point voltage control method based on injection of fourth order harmonic current. The proposed method works in full power factor range and no-load condition, where most other methods become less effective. A detailed description of the formulation, control of the method followed by simulation results are presented to confirm the performance of the method.