Message from editors

Power electronics is a key technology that enables the revolution of electric power generation, transmission, and distribution in modern power systems for improved energy security, efficiency, and sustainability. In distribution systems, power electronic converters not only serve as the critical interfaces between the utility grid and distributed energy resources such as solar, wind, and energy storage, but also play a pivotal role in power quality control and management. In transmission systems, high voltage high power electronic converters are the ideal candidate for achieving flexible and efficient power flow in bulk interconnected power systems. On one hand, it is no doubt that more electronic apparatus will be integrated into future power systems to further reduce carbon emissions. On the other hand, power electronic converters exhibit significantly different characteristics with traditional power system components and may bring a number of challenging stability issues from both converter-level and system-level perspectives. The knowledge and theories for understanding and analysis of more electronics power systems are still lacking and deserve in-depth studies

A rapid tracking method of maximum power point for solar units in series under uneven solar irradiance

When several solar units are combined into one branch in series, the multi-peak phenomenon of the output power of the branch would appear because of the bypass diodes. Based on analyzing the operation principle of the circuit, it was found that the number of peak points was determined by short-circuit currents and maximum-power- point currents of all the units in series. By use of the number of peak points and the values of the maximum-power-point currents, the power values of all the peak points were compared, then the approximate location of the global maximum power point was found, and finally the accurate point of maximum power was searched by incremental conductance method. This method has a rapid searching speed and an accurate result as well by applying a little calculation and using local-searching to replace global-searching. The proposed method is verified by experiments. Furthermore, the advantage of the faster searching speed is more obvious when more units are in series

High-Accuracy and Fast-Speed MPPT Methods for PV String Under Partially Shaded Conditions

The photovoltaic (PV) string under partially shaded conditions exhibits complex output characteristics, i.e., the current-voltage (I-V ) curve presentsmultiple current stairs, whereas the power-voltage (P-V ) curve shows multiple power peaks. Thus, the conventional maximum power point tracking (MPPT) method is not acceptable either on tracking accuracy or on tracking speed. In this paper, two global MPPT methods, namely, the search-skip- judge global MPPT (SSJ-GMPPT) and rapid global MPPT (R-GMPPT) methods are proposed in terms of reducing the searching voltage range based on comprehensive study of I-V and P-V characteristics of PV string. The SSJGMPPT method can track the real maximum power point under any shading conditions and achieve high accuracy and fast tracking speed without additional circuits and sensors. The R-GMPPT method aims to enhance the tracking speed of long string with vast PV modules and reduces more than 90% of the tracking time that is consumed by the conventional global searching method. The improved performance of the two proposed methods has been validated by experimental results on a PV string. The comparison with other methods highlights the two proposed methods more powerful