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The concept of microgrid has emerged as a feasible answer to cope with the increasing number of distributed renewable energy sources which are being introduced into the electrical grid. The microgrid communication network should guarantee a complete and bidirectional connectivity among the microgrid resources, a high reliability and a feasible interoperability. This is in a contrast to the current electrical grid structure which is characterized by the lack of connectivity, being a centralized-unidirectional system. In this paper a review of the microgrids information and communication technologies (ICT) is shown. In addition, a guideline for the transition from the current communication systems to the future generation of microgrid communications is provided. This paper contains a systematic review of the most suitable communication network topologies, technologies and protocols for smart microgrids. It is concluded that a new generation of peer-to-peer communication systems is required towards a dynamic smart microgrid. Potential future research about communications of the next microgrid generation is also identified.

This study presents a transformerless topology for a grid-tied single-phase inverter capable of performing the simultaneous maximum power point tracking of two independent and series connected photovoltaic sources. This topology is derived from the neutral point clamped multilevel inverter in half-bridge configuration. The use of a half-bridge topology reduces the leakage current to very low values, whereas the multilevel topology presents an output voltage quality similar to that of a full-bridge inverter. To simultaneously track the maximum power of both photovoltaic sources, a generation control circuit is used. With this topology, it is possible to improve the performance of the converter under partial shadowing conditions, very common in photovoltaic facilities operating in residential areas. A 5 kW prototype of this topology has been implemented and tested in the laboratory.

ElsevierCarranza Castillo, O.; Figueres Amorós, E.; Garcerá Sanfeliú, G.; González Medina, R. (2013). Analysis of the control structure of wind energy generation systems based on a permanent magnet synchronous generator. Applied Energy. 103:522-538. doi:10.1016Energy. 103:522-538. doi:10. /j.apenergy.2012 Analysis of the control structure of a wind generation system based on permanent magnet synchronous generator AbstractThis paper presents the analysis of the two control structures used in wind generation systems with permanent magnet synchronous generators, variable speed and fixed pitch, to determine which structure is most appropriate for implementation. These control structures are speed control and torque control. The analysis considers all the elements of wind power generation system, with greater emphasis on the model of the turbine where mechanical torque is considered as a system variable and not as in other studies where it is considered as internal disturbance in the system. The analysis is developed so that the control structure is independent of AC/DC converter that is used in the system. From the analysis is obtained that the speed control can be stable using classical control techniques because it is a nonminimum phase system and the torque control is unstable because it has poles and zeros in the right half plane, very low frequency and very close to each other, so it is very difficult to control using classical control theory. In the evaluation of the speed control structure, the AC/DC converter is Three-phase rectifier Boost in Discontinuous Conduction Mode with an input filter and a Peak Current Control and to avoid the need of mechanical sensors, a Linear Kalman Filter has been chosen to estimate the generator speed.

In photovoltaic (PV) double-stage grid-connected inverters a high frequency DC-DC isolation and voltage step-up stage is commonly used between the panel and the grid-connected inverter. This paper is focused on the modeling and control design of DC-DC converters with Peak Current mode Control (PCC) and an external control loop of the PV panel voltage, which works following a voltage reference provided by a maximum power point tracking (MPPT) algorithm. In the proposed overall control structure the output voltage of the DC-DC converter is regulated by the grid-connected inverter. Therefore, the inverter may be considered as a constant voltage load for the development of the small-signal model of the DC-DC converter, whereas the PV panel is considered as a negative resistance. The sensitivity of the control loops to variations of the power extracted from the PV panel and of its voltage is studied.The theoretical analysis is corroborated by frequency response measurements on a 230W experimental inverter working from a single PV panel. The inverter is based on a Flyback DC-DC converter operating in discontinuous conduction mode (DCM) followed by a PWM full-bridge single-phase inverter. The time response of the whole system (DC-DC + inverter) is also shown to validate the concept.

In testing maximum power point tracking (MPPT) algorithms running on electronic power converters for photovoltaic (PV) applications, either a PV energy source (PV module or PV array) or a PV emulator is required. With a PV emulator, it is possible to control the testing conditions with accuracy so that it is the preferred option. The PV source is modeled as a current source; thus, the emulator has to work as a current source dependent on its output voltage. The proposed emulator is a buck converter with an average current mode control loop, which allows testing the static and dynamic performance of PV facilities up to 3 kW. To validate the concept, the emulator is used to evaluate the MPPT algorithm of a 230-W experimental microinverter working from a single PV module.

SUMMARYBidirectional power flow is needed in many power conversion systems like energy storage systems, regeneration systems, power converters for improvement of the power quality and some DC-DC applications where bidirectional high power conversion and galvanic isolation are required. The Dual Active Bridge (DAB) is an isolated, high voltage ratio DC-DC converter suitable for high power density and high power applications, being a key interface between renewable energy sources and energy storage devices. This paper is focused on the modeling and control design of a DC-DC system with battery storage based on a DAB converter with average current mode control of the output current and output voltage control. The dynamic response of the output voltage to load steps is improved by means of an additional load-current feedforward control loop. An analytical study of the load-current feed-forward is presented and validated by means of both simulations and experimental results.

The study of the loop gains frequency response in a power converter is a powerful tool commonly used for the design of the controllers used in the control stage. As the control of medium and high power electronic converters is usually performed digitally, it is useful to find a method to measure the digital loop gains. The purpose of this paper is to present a method for properly measuring the loop gain frequency response of digitally controlled power converters by means of an analog Frequency Response Analyzer (FRA). An analog sinusoidal reference signal generated by the FRA is injected through an Analog to Digital Converter (ADC) into the digital controller, and added to the discrete feedback signal. To obtain the frequency response of the open loop gain, both feedback and disturbed feedback signals are sent back to the FRA by using the Pulse Width Modulation (PWM) peripherals of the controller.