Constraint Harmonic Compensation Strategy for Extending Power Routing Capability in CHB Converter

Power routing or uneven power distribution in modular systems based on a cascaded H-bridge (CHB) converter is sometimes desired or even required, such as in hybrid battery energy storage applications. For series-connected cells, such as in CHB, the power among the energy sources can be unbalanced by controlling the modulation indices of the original sinusoidal modulation (SM) signals. However, the capability of enlarging power unbalance is limited with SM because of the limited modulation range. For increasing the power routing capability, a constraint harmonic compensation strategy (CHCS) is proposed. The CHCS utilizes discontinuous modulation (DM) for increasing the linear modulation range of the additionally loaded cells and a compensating modulation (CM) for removing the harmonics introduced by DM. To ensure that the CM cells are free from overmodulation, the CHCS is equipped with modification stages that optimally distribute the harmonic signal among the CM cells and limit the modulation indices of the DM cells when necessary. The advantage of the CHCS is that it resolves key limitations of existing DM methods based on first harmonic DM (FHDM) and harmonic compensation strategy (HCS), which either unnecessarily restrict the power routing capability or suffer from potential overmodulation. The validity of the CHCS is verified by simulation and experiment in comparison with different power routing methods in terms of the impact on power quality and power routing capability. Compared to SM, the CHCS enable 19.5 % increase in power routing capability.