A Fault Toleration Strategy for DC Voltage Sensors in Cascaded Photovoltaic Systems Based on Active-coupling Power Units

Cascaded H-bridge (CHB) is a promising topology for utility-scale photovoltaic generation due to its advantages like modularity, scalability, and capability of direct access to medium voltage grids. However, owing to the large quantity of components in the circuit, CHB is less reliable. As one common fault, the DC-link voltage sensor fault will cause the current/voltage mistracking and power mismatch, which will further lead to unbalanced DC-link voltages and even system instability. To address this issue, in this paper, a coupling-dc strategy is proposed to improve the system reliability from the sensor perspective. By deriving the DC voltage self-balancing mode, and selecting the optimal mode combination, a DC-link voltage sensor fault ride-through modulation strategy based on coupled-dc power units is proposed. Finally, an experimental hardware platform is built to verify the proposed techniques.