A modulation algorithm for inter-phase balancing in CHB Converters

This paper presents a simple modulation algorithm which accomplishes the voltage balance across the capacitors of a Cascaded H-bridge (CHB) converter using zero voltage injection. CHB converters are widely used in renewable energy production, especially in solar plants due to their modularity. This advantage can also become a problem when the power generated by the solar cell or consumed by a load is not equal among the three phases, leading to an unbalanced situation. The inter-phase unbalance refers to the voltage differences among the capacitors of different phases, for which a well-known technique to solve it consists of injecting a zero sequence voltage according to the power distribution. A simple modulation algorithm, which uses it, is presented in this paper including a mathematical proof. The proposed algorithm has been tested by simulation with a five-level CHB converter. At the end of the paper, a modification is introduced to improve the converter efficiency.