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This article proposes the weighted dynamic aggregated (WD agg) model of large-scale systems consisting of $ \boldsymbol{n}$ grid-forming inverters in white-box islanded microgrids. The proposed WD agg approach models the microgrids $ \boldsymbol{n}$ grid-forming inverters, which have a similar control structure, by a single equivalent inverter and a controller that has a similar order and structure to the inverters in the microgrid. The parameters of the equivalent inverter and controller are obtained by considering the contribution of each state to the corresponding equivalent state. Compared with the existing models, while the complexity and computational burden of the studied system is reduced, the proposed WD agg model can provide an accurate single equivalent unit for a microgrid consists of a large number of grid-forming inverters with different sizes, operating points, and parameters. It is shown for various cases that the proposed WD agg model can be used in the steady-state, transient, and stability analyses with superior accuracy. The model can also be used to design the controller and inverters' parameters to ensure a desirable performance of the microgrid. The proposed WD agg model is evaluated by time-domain simulations and experimental implementation of four inverters connected to a load and CIGRE MV/LV benchmark for renewable energies for various case studies.

This article proposes weighted dynamic aggregation (WD agg) model for grid-following inverters and their controllers in applications such as photovoltaic (PV) farms or any renewable distributed generation (DG) integrated microgrids. The order and structure of the proposed WD agg model is similar to one inverter of the large-scale system. For example, the WD agg model of a PV farm becomes an equivalent single PV array, single inverter, and a controller with weighted average parameters, which hugely reduces the computational burden of the system studies. The parameter weights of each inverter are obtained based on the contribution of each unit in the overall dynamic behavior of the system. The proposed model can be used to mimic the steady-state, transient, and dynamics behavior of the system, and it can also be used to design controller and inverters parameters to ensure desirable performance of the large-scale system. The performance of the proposed method is simulated and experimentally evaluated by a small-scale PV farm consisting of three paralleled inverters with equal or unequal parameters in various inputs and stability conditions for a comprehensive study. The proposed model is also applied to CIGRE HV/MV 14-bus benchmark for renewable energies to show the functionality of the proposed model in large-scale and practical systems.

In this article, a fully soft-switched expandable high step-down dc–dc converter is presented. In order to achieve a high step-down voltage conversion ratio and low component count, the synchronous buck and Cuk converters are integrated. Lower switches’ voltage stress is realized by splitting the input voltage, which can considerably decrease the switches’ conduction loss. Moreover, switching losses along with the reverse recovery problems are mitigated due to the soft-switching operation of all semiconductor devices. The switch utilized for soft-switching operation is also used to replace the output diode as a synchronous rectifier, which reduces the conduction loss. The mentioned features have considerably contributed to the converter efficiency. Furthermore, the converter shares a common ground between the input and the output, which is desirable in many applications, while the converter output current is continuous without adding current ripple cancellation methods. Finally, the number of converter cells can be expanded or reduced; therefore, the converter can be applied to a wide range of loads. The operating principles and analysis of the proposed converter are presented, and the results from the implemented prototype are provided to verify the converter operation and performance.