This paper proposes a new robust controller in a stationary reference frame for doubly fed induction generators (DFIGs) of grid-connected wind turbines. Initially, a DFIG dynamic model is derived from the voltage and flux equations in αβ coordinates, where uncertainties and disturbances intrinsic to the system are accounted for as perturbation terms are added to the nominal model. Then, a controller design procedure that guarantees the DFIG stability under uncertainties and disturbances at the grid side is presented in detail. It is demonstrated that a very fast dynamic behavior can be obtained with the proposed controller, which improves the transient response of the grid-connected DFIG, particularly under conditions of unbalanced voltage dips resulting from asymmetrical network faults. In order to conform with the fault ride-through capability requirements, this paper proposes a new reference strategy, which is divided into normal and fault operation modes. Experimental results are given to support the theoretical analysis and to illustrate the performance of the grid-connected DFIG with the proposed controller.

Energy Storage Systems (ESS) and Distributed Generation (DG) are topics in a large number of recent research works. Moreover, given the increasing adoption of EVs, high capacity EV batteries can be used as ESS, as most vehicles remain idle for long periods during work or home parking. However, the high EV penetration introduces some issues related to the charging power requirements, thereby increasing the peak demand for microgrids where EV chargers are installed. In addition, photovoltaic distributed generation is becoming another issue to deal with in EV charging microgrids. Therefore, this new scenario requires an Energy Management System (EMS) able to deal with charging demand, as well as with generation intermittency. This paper presents an EMS strategy for Microgrids that contain an EV parking lot (EVM), Photovoltaic (PV) arrays, and dynamic loads connected to the grid considering a Point of Common Coupling (PCC). The EVM-EMS utilizes the projections of future PV generation and future demand to accomplish a dynamic programming technique that optimizes the EVs’ charging (G2V) or discharging (V2G) profiles. This algorithm attends to user preferences while reducing the demand grid dependences and improves the microgrid efficiency.

When the wind power accounts for a large portion of the islanded microgrid power, it may need to support the ac bus frequency regulation. The increasing penetration of variable speed wind turbines (WT) in microgrids leads to a lower inertia, as the rotational speed of the turbine and the grid are decoupled by power electronic converters. Lower system inertia results in a larger and faster frequency deviation after occurrence of abrupt variations on generation and load. It is possible to implement control loops in the WT converters to provide a virtual inertia and support frequency regulation in the microgrid. This paper investigates the variables related to the frequency compensation capability of WT, such as kinetic energy, dc-link capacitance, turbine size, wind penetration, number of turbines, operating region along the power curve, power reserve and droop control gain, etc. The analysis is structured as a Design of experiment (DOE) to have a clear and organized comparison of multiple system configurations. An optimal control technique is applied to provide fair comparison among the system variables. A flowchart explaining how the DOE and controllers gains were defined is provided.

This paper presents an improved control scheme for operation of grid-tied inverters in order to attain IEEE 1547.2-2008 harmonic limit standard even with a wide range of grid parameters. This control structure includes an active damping with a new current estimator and a proportional resonant (PR) controller with harmonic compensation (HC). In order to guarantees the inverter operation with a wide range of grid parameters the damping and the controller gains are designed considering robustness characteristics. Moreover, it proposes a new estimator for the current filter capacitor for operation with a wide range filter resonance frequency. The grid synchronization mechanism uses the MSOGI-FLL technique. Experimental results are carried out and presented to validate the control structure design and the proposed current estimation.

This paper presents an auxiliary circuit for the current-fed half-bridge (CFHB) converter, aiming to clamp the high voltage spikes across the main switches caused by the energy stored in the leakage inductance of the transformer. This circuit also provides zero-current switching (ZCS) to the main switches at turn-off. Moreover, the rectifier diodes and the auxiliary switch operates under ZCS at turn-on and turn-off. Another feature of the proposed circuit is that it is composed of just one active switch, reducing the number of auxiliary sources and drivers compared to the conventional active-clamped current-fed half-bridge (ACCFHB) converter. In addition, the inclusion of the clamping circuit increases the voltage ratio of the converter. A 300 W prototype was built to validate the analysis and design proposed in this paper. The converter was tested for various load conditions at 100 kHz, and a peak efficiency of 96.2% was obtained. Also, a comparison of efficiency for the CFHB employing other conventional clamping circuits is presented.

This paper proposes a dispatchable photovoltaic (PV) hybrid inverter for output power tracking without any dependency on the converter’s efficiency and with no power closed loop. The system uses an extra-low-voltage battery energy storage system (BEES) based on a Li-ion battery pack to be applicable for use inside homes and other installations close to the end-user. A bidirectional isolated current-fed dual-active bridge (CF-DAB) converter associated with the batteries provides a wide conversion voltage ratio and ensures safety for the users. The proposed control system shares the DC bus voltage controller between the ac grid interfacing converter (AC-DC) and CF-DAB (DC-DC), eliminating the converter’s efficiency in the reference equations. When dispatchable power is not required, or according to the user’s request, the battery’s charge/discharge current can be specified. A disturbance rejection technique avoids low-frequency current ripple on the battery side. It contributes to the battery’s lifespan. Experimental results presenting the dc bus voltage control, current disturbance rejection, and power dispatching are included to validate the proposal.