Trilateral control for LCL filter-based system with single grid current sensor in weak grid

Abstract

A trilateral control for LCL filter-based system is introduced by the authors with a single grid current sensor in weak grid conditions. The LCL filter increases the complexity when the uncertain nature of the grid comes into the picture. Moreover, the traditional three-loop control technique requires three current sensors on the inverter side, three voltage sensors to sense voltage across the capacitor, and three current sensors on the grid side combined for sensing. A novel trilateral control technique utilising a single sensor is implemented to sense the grid current. This technique has reduced a considerable number of current sensors and voltage sensors. The α axis of grid current is proportional to sensed ‘a’ phase grid current. The β current in the utility grid is acquired by employing the controller reference quantities of the grid current. The computation of another variable, that is, the current in the inverter side inductor and the voltage across the capacitor, is executed by an estimation algorithm. The proposed technique provides the feature of reducing implementation financial value and weight that reduces the complexity and size of hardware. The synchronisation technique is executed by a modified dual second-order generalised integrator digital phase-locked loop for the grid-connected converter. The implemented system offers the advantage of ease of implementation, good performance, and high stability. The validity of the proposed scheme in the implemented system is demonstrated by the simulated waveform obtained on the MATLAB/Simulink platform. Finally, the effectiveness of the proposed system is further justified by the experimental waveform procured from a prototype developed in the laboratory.