DC-Bus Voltage Sensorless Control of an Active Rectifier with Modular Multilevel Converter

The modular multilevel converter (MMC) is recognized as one of the promising converters for the electrification of ships and railways. Among different energy conversion stages, the MMC-based rectifier should realize stable DC output voltage and accurate input current control. However, output DC-bus voltage sensors must be installed, which are costly and bulky. This paper presents a simple but effective control method for the MMC-based rectifier, removing the traditional output DC-bus voltage sensor. An accurate evaluation model of DC-bus voltage is developed as well as the implementing method. Meanwhile, a safe and fast pre-charging scheme is presented for the MMC-based rectifier without output voltage sensors. The fault-tolerant capability of the proposed method when the failure of the output DC-bus voltage sensor occurs is examined. Simulated and testing results demonstrate that the proposed method presents not only excellent steady-state and dynamic performance but also strong fault-tolerant capability. The proposed evaluation model for DC-bus voltage has a high accuracy with an error of less than 1%. Besides, the pre-charging time is less than 0.5 s using the proposed sensorless control.