Practical engineering approach to natural voltage balancing analysis in multilevel converters with balance booster

Abstract

The paper suggests simple engineering approach for evaluation of a natural balancing rate in multilevel voltage source capacitive converters with a balance booster. Balance booster is a series RLC-circuit with a resonance frequency tuned to match converter switching frequency. Natural voltage balancing dynamics in the presence of balance booster placed in parallel to a converter load is aperiodic (non-oscillatory) similar to that of the same converter working with a pure resistive load. The equivalent load resistance is slightly increased that of the booster (roughly by up to 20-25%; natural voltage balancing rate is slowed down in the same proportion). Some basic Flying Capacitor Converter topologies are considered and approximate balancing time constant formulas are derived and confirmed by computer simulations.