Thermal Loading and Analysis of Modular Multilevel Converters using Injection Control of Circulating Current and Common-mode Voltage

The circulating current (CC) is an undesirable phenomenon in a modular multilevel converter (MMC), as it increases the capacitor voltage ripple, power losses and current stress on power semiconductor devices. Prior research has mainly focused on various control methods as well as modulation schemes to minimize the CC. This paper presents a comprehensive analysis of an MMC under common-mode voltage (CMV) injection and CC control strategies in terms of thermal loading and failure rate of power semiconductor devices. To benchmark these control strategies, a generalized control structure for the MMC is presented. To study the thermal loading on power semiconductor devices, an electro-thermal model is developed. The effectiveness of the presented control approach is demonstrated through detailed simulations and experimental studies using hardware-in-the-loop (HIL) system. Finally, the loading on power semiconductor devices of the MMC is evaluated under injection control of CC and CMV for different modulation schemes.