New connection constraints for the power network (grid codes) require more flexible and reliable systems, with robust solutions to cope with uncertainties and intermittence from renewable energy sources (renewables), such as photovoltaic (PV) arrays. The interconnection of such renewables with storage systems through a direct current (DC) MicroGrid can fulfill these requirements. A “Plug and Play” approach based on the “System of Systems” philosophy using distributed control methodologies is developed in this paper. This approach allows to interconnect a number of elements to a DC MicroGrid as power sources, such as PV arrays, storage systems in different time scales, such as batteries and supercapacitors, and loads, such as electric vehicles and the main ac grid. The proposed scheme can easily be scalable to a much larger number of elements.

A nonlinear control able to perform voltage and power stability in Direct Current (DC) MicroGrids for an efficient renewable energy integration that is capable of providing frequency support to an Alternate Current (AC) grid is introduced in this work. A generic DC MicroGrid modeling is developed, and the introduced controllers are shown to ensure grid stability, both by a theoretical analysis with a formal proof of stability using Lyapunov techniques, than by simulations performed in MATLAB. A comparison with classical Proportional Integral (PI) control techniques is described to show the performance improvements.

A low-level distributed nonlinear controller for a DC MicroGrid integrated in a Smart Railway Station capable to recover trains' braking energy is introduced in this paper. The DC MicroGrid is composed by a number of elements: two different types of renewable energy sources (regenerative braking energy recovery from the trains and photovoltaic panels), two kinds of storages acting at different time scales (a battery and a supercapacitor), a DC load representing an aggregation of all loads in the MicroGrid, and the connection with the main AC grid. The nonlinear model of the MicroGrid is introduced, and a complete stability analysis is investigated to the purpose to meet power balance and grid voltage stability requirements. An Input-to-State Stability (ISS)-like Lyapunov function is obtained with a System-of-Systems approach, and it is utilized to develop the control laws for the converters in order to fulfill the dedicated objective each of them has. Simulation results, showing the desired grid behavior using the proposed nonlinear control laws, are introduced and compared with classical Proportional Integral (PI) linear controllers, with respect to performances and parametric robustness. The DC MicroGrid is shown to be able to operate braking energy recovery while performing load feeding and renewable energy integration and guaranteeing a proper DC voltage profile.

The present paper describes an Electric Vehicle (EV) charging station that provides ancillary services to the main AC grid, as for example frequency support and synthetic inertia. Due to the Direct Current (DC) nature of these loads and the easier integration of renewable energies, a DC Microgrid is considered to power the charging station. Targeting both DC grid voltage stability and the capability to support the main AC grid, nonlinear control laws based on Lyapunov theory and backstepping are developed for local and primary control levels (droop control). The proposed controllers are validated via Matlab-Simulink simulations in a 25 kW DC Microgrid with PV production, Vehicle to Grid (V2G) mode of operation, fast and slow vehicle charge, ancillary services to the AC main grid and islanded mode operation.

The current massive integration of constant power loads (CPLs) requires better dynamic performance in direct current (DC) microgrids. This imposes the needs for more advanced controllers for DC/DC converters, and especially for boost ones because of their nonminimum phase property. This article contributes to this research line and proposes an advanced nonlinear (NL) control strategy for the output voltage stabilization of boost converters using singular perturbation and dynamic feedback linearization strategies. The proposed techniques manage to impose a desired stable dynamics for the variable with the nonminimum phase characteristics, thus avoiding the problem of possible selection of unstable equilibria. At first, a theoretical proof of the stability of the close loop system with the proposed controller is provided. Then, an experimental validation composed by four case studies is performed. The results show good adaptability to a wide range of operating conditions and better performance regarding voltage tracking and load disturbances rejection of the proposed NL method with respect to classical control techniques.

Recent developments in power electronics and renewable energy sources have brought the risen of Direct Current (DC) Microgrids. By power converters' utilization, a DC Microgrid is able to integrate renewables, storage systems, and other devices in a simpler topology, since the major part of the modern grid's compounds have DC nature. This paper proposes a control strategy aiming to regulate the voltage in the DC bus of a Microgrid by a supercapacitor. The control law is applied to a bidirectional boost converter that connects the supercapacitor to the DC grid. The control scheme is based on dynamical feedback linearization and consists in splitting the system in different time scale dynamics, creating consequently a simplified model. Simulations on Matlab/Simulink illustrate how the control strategy is able to regulate the DC voltage with good performance.