The synchronization between power grid and distributed power sources is a crucial issue in the concept of smart grids. For tracking the real-time frequency and phase of three-phase grids, phase-locked loop (PLL) technology is commonly used. Many existing PLLs with enhanced disturbance/harmonic rejection capabilities, either fail to maintain the fast response or are not adaptive to grid frequency variations or have high computational complexity. This paper therefore proposes a low computational burden Repetitive Controller (RC) assisted PLL (RCA-PLL) that is not only effective on harmonic rejection, but also has remarkable steady-state performance while maintaining fast dynamic. Moreover, the proposed PLL is adaptive to variable frequency conditions and can self-learn the harmonics to be cancelled. The disturbance/harmonic rejection capabilities together with dynamic and steady-state performances of the RCA-PLL have been highlighted in the paper. The proposed approach is also experimentally compared to the synchronous rotation frame PLL (SRF-PLL) and the Steady-State Linear Kalman filter PLL (SSLKF-PLL), considering the effect of harmonics from the grid-connected converters, unbalances, sensor scaling errors, d.c. offsets, grid frequency variations and phase jumps. The computational burden of the RCA-PLL is also minimized, achieving an experimental execution time of only 12 µs.

In this paper, a novel matrix converter modulation which minimises the converter losses is proposed. This approach preserves the same voltage ratio of traditional modulations with a key concept to compute the duties cycle using only the two closest input voltages instead of all three-phase voltages. Compared with Alesina-Venturini modulation, this new strategy achieves higher efficiency due to lower switching losses, in addition to a reduced harmonic content on the output current. Hence, a detailed mathematical treatment based on the knowledge of the output power demand will be shown and discussed. In order to validate the novel modulation, extensive experimental results will be also produced and compared with Venturinis modulation.

In the past two decades much research and industry effort has been dedicated to transportation electrification. In particular aerospace industry, with the more electric aircraft (MEA) revolution, is shifting toward the usage of electrical in place of mechanical energy on board to save fossil fuel and reduce polluting emissions. For this reason, phase-looked loops (PLLs) systems have been well developed for synchronizing different power sources and loads within the aircraft electrical grid. Since one of the proposed solutions for MEA power grids is to operate at variable frequency from 360 Hz to 800 Hz, a third-order model based steady-state linear Kalman filter PLL (SSLKF-PLL) has been proposed in literature to achieve fast tracking performance during such grid frequency variations. To suppress the potential disturbances due to harmonics in the grid, sensor scaling errors/unbalances and d.c offsets while maintaining low computational burden, this paper aims to enhance the disturbance rejection ability of SSLKF-PLL by adding a repetitive observer (RO). Simulation and experimental tests show that RO allows stable and effective suppression of disturbances from all above-mentioned sources during variable frequency operation. The execution time of the proposed PLL is only 4.23 using a Xilinx Zynq-7000 based platform, where the added RO takes 2.664 to execute, the SSLKF-PLL alone takes 1.566.

Nowadays the interest in active networks is significantly growing as a result of the larger diffusion of renewable energy sources and distributed generation systems connected to the grid. The possibility of installing in key points of these modern smart networks devices capable of intelligent energy routing and power flow control, is highly desirable in this scenario. Multilevel power converters and, in particular, Cascaded H-Bridge converters allow the required flexibility, availability and reliability to be considered as a building block for active nodes for the future electrical grid. This paper proposes a 3-port multilevel power converter capable of behaving as a network active node and demonstrates all its capabilities of energy routing and control under different operative conditions.