In this work the design of a Line Following Robot which is commonly used to carry children through shopping malls entertainment place is discussed as a new commercial product in this field. The robot has five different speed levels, and is able to follow 4.8cm wide black line carrying nominally 400kg load. The robot can be operated in two control mode; Line Following Mode and Service Mode. In the Line-Following Mode it follows the path of the black line in a suitable ground, while in the Manual Mode, it can be moved manually forwards, backwards, left and right free from the black lined path by a remote controller. Robot is operated using two permanent magnet DC motors on left and right sides. Forward and backward movement, or left and right side motors are controlled by two H-Bridge circuits. The batteries can be charged by AC supply from an external source or by DC supply from a solar panel.
Under grid distortions, Modular Multilevel Converters (MMC) must adopt proper control strategies to fulfill the power system requirements and ensure a stable operation. An inappropriate control under such conditions may lead to energy unbalances between the MMC legs, inaccurate current injection, and failure in the synchronization process. In this context, sequence extraction methods play a critical role in enhancing the performance of the control, firstly, by aiding the Phase-Locked Loop (PLL) to maintain the synchronization with the AC grid by following the positive sequence fundamental component of the voltage, secondly, by allowing an accurate active and reactive currents injection via the decoupled Voltage Oriented Control (dVOC), thirdly, by properly managing the internal energy of the MMC through the circulating current control. In prior researches, some sequence extraction methods have been used for MMC STATCOM. However, the sequence extraction was not the core of the performed studies and their impact on the system behavior has not been highlighted or tested in several grid conditions. This work fills this gap by first assessing the performance of a Single Delta Bridge Cell MMC (SDBC-MMC) STATCOM with four well-known sequence extraction methods (i.e., Decoupled Double Synchronous Reference Frame (DDSRF), Dual Second Order Generalized Integrator (DSOGI), Improved DSOGI, and Fortescue matrix-based (FMB) filter) under normal and abnormal grid conditions, then, finding the most suitable one in terms of stability, dynamics, and functionalities.
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