Extended Order Generalised Integral Control based Circulating Current Mitigating Scheme in Modular Multilevel Converters—A Balancing Approach

Abstract In modular multilevel converters (MMCs), circulating currents consist of both DC and AC components. However, these currents are significantly affected by even harmonic distortions, which introduce ripples in the sub-module (SM) capacitor voltages. These ripples contribute to the circulating currents, increasing the voltage stress on the SM switches and adversely impacting overall system performance. This paper presents a systematic approach to mitigating circulating currents by employing an extended order generalised integrator (EOGI), which effectively removes even harmonic components from the converter’s legs. The proposed solution has been evaluated against existing methods and has been demonstrated to offer enhanced robustness in the face of parameter uncertainties and sudden load variations. The scheme was initially validated using MATLAB/Simulink, with further real-time performance verification conducted via OPAL-RT simulation and experiments, yielding promising results.