Extended Reactive Power Exchange With Faulty Cells in Grid-Tied Cascaded H-Bridge Converter for Solar Photovoltaic Application

Fault-tolerant operation is a key feature of grid-tied photovoltaic fed Cascaded H-Bridge converter, where the converter operates continuously with faulty bypassed cells. After bypassing the faulty cells, the number of healthy cells decreases, the available dc-link voltage reduces and active power among the phases become unequal. As a result, the converter produces unbalanced and distorted grid currents. Moreover, the maximum reactive power exchanged with the grid gets reduced with the available dc-link voltage. This article proposes a novel zero-sequence voltage injection technique for balancing the grid currents and preventing overmodulation in each cell of the converter. The proposed technique extends the reactive power capability of the converter during a postfault condition. Additionally, it also helps in equal active and reactive power flow in each phase of the converter. A new PWM clamping strategy is proposed in this article to implement the zero-sequence voltage addition in the converter. The proposed concept is verified through computer simulation and experimental results.