Control Strategy of High-Performance Active Rectifier Using Modular Multilevel Converter Without DC-link Voltage Sensors

Modular multilevel converter (MMC) is a popular topology in the medium-/high-voltage power conversion due to its modular structure, equal voltage stress, small line-line filter and low-distortion current. It can be operated as an active rectifier and achieve controllable dc output voltage and adjustable active/reactive power. However, dc-link voltage sensors must be installed to realize the feedback control of the system. To reduce the costs and improve the performance of MMC-based rectifier, this paper presents a sensor-less control strategy, which removes the traditional dc-link voltage sensors. An accurate prediction model of dc-link voltage is developed as well as a complete implementing method. The value of the output DC voltage is obtained through the prediction algorithm. The pre-charging, active-power and reactive-power mode of the MMC-based rectifier is extensively studied to validate its effectiveness. The proposed method not only reduces the system device cost but presents excellent steady-state and dynamic performance.