Modelling of Bidirectional Three-Phase Four-Wire Three-Level NPC MLC under Single-Loop Current Sensorless Control

Single-loop current sensorless control allows for abolishing of the instantaneous current measurement in the control system using only a single control loop with voltage feedback to stabilise the DC-bus voltage. This approach eliminates current sensors in the control circuit, benefiting from saving space on the printed circuit board and minimising power dissipation in the current measurement circuitry. This paper focuses on the single-loop current sensorless control applied to bidirectional three-phase four-wire three-level NPC MLC by simulation analysis and demonstrates the performance of the proposed current control algorithm in the rectifier and inverter modes and the step response with power direction change and grid-voltage change. In capacitor voltage balancing, an additional controller is applied, which is capable of compensating for the voltage asymmetry caused by adding a 2.5 kOhm resistor in parallel to one of the DC-bus capacitors. Our results demonstrate good performance of the proposed control method both in the inverter and rectifier modes, showing stable current shape in the low power and full power modes with acceptable harmonics content, meeting the requirements of the IEC 61000-3-2 standard for Class A devices. The analysis showed that the proposed control approach is suitable for industrial application.