Improved terminal sliding mode direct power control for master-slave scheme in microgrids

Abstract

Master-slave control is a practical control scheme for operating microgrids in both islanded and grid-connected modes. It offers a competitive alternative to droop control, particularly for small-scale microgrids and/or nanogrids, where all loads are connected to the same bus, namely the point of common coupling (PCC). This control scheme enables a precise voltage/frequency adjustment, as well as accurate power/current injection. This study presents an improved version of sliding mode control (SMC), specifically integral terminal sliding mode control (ITSMC), in a microgrid environment. This presented approach incorporates the tanh function in the input control law to reduce chattering in the injected power/current. This study demonstrates how the master inverter stabilises voltage/frequency at the PCC, while the slave inverter regulates power injection using direct power control. ITSMC operates both inverters across various modes. Additionally, the performance of the developed approach is compared with that of some widely used controllers for microgrid operation. The adopted controllers for comparison are the proportional-integral (PI) controller, fractional-order PI controller, and power rate-SMC, which serves as a benchmark for adaptive SMC. The stability analysis is also presented to confirm that the developed ITSMC ensures robust and stable operation across different operational modes. Furthermore, the experimental setup, which is built in the lab with a power rating of 2 kVA for each inverter, demonstrates the good performance of the designed ITSMC for the microgrid under various dynamic loads and operating modes.