This article presents a power management strategy (PMS) to control the power flow in a dc microgrid operating in the grid-connected mode. The microgrid model is composed of the ac utility grid interfaced with a voltage source inverter operating as a grid-forming converter (VSC), an energy storage system (ESS) formed by a battery bank and a bidirectional dc-dc converter operating as a grid-supporting unit, a distributed generation acting as a grid-feeding unit, and the customer loads with strict voltage regulation. The power management technique applies a virtual inertia concept together with a state of charge-based management function to regulate the charging and discharging process of the battery bank according to the dc microgrid power flow. Thus, high-rate peaks of power are avoided, which improves the ESS life cycle. With the proposed PMS, an autonomous power flow is achieved inside the dc microgrid, while the ac utility grid focuses exclusively upon forming the dc bus and processing the surplus or shortage of power. In addition, the proposed strategy simplifies the communication link between the grid inverter and the ESS, since the VSC power is the sole information exchanged. The experimental results show that the proposed PMS is reliable, leading to high ESS performance and power flow control within the dc microgrid, without degrading the dc bus voltage.

This article presents as a new contribution a proposal to optimize the performance of switched reluctance generator (SRG) in a variable wind energy conversion system (WECS). An approach based on design of computational experiment (DCE) is applied to determinate the optimal firing angles and the optimal DC link voltage that guarantee the best system behavior for each rotor speed. Third order response surface model (RSM) based on space-filling designs is applied to build a multiobjective function considering efficiency improvement and torque ripple reduction. Interior point method (IPM) is applied to find the minimum of the surface, optimizing the process. Direct power control (DPC) is used to obtain the maximum power as function of the rotor speed, employing the optimal parameters. Hysteresis and single pulse current control are applied for low and high speed operation, respectively. Simulation and experimental results have shown that the proposed approach returned a good compromise between SRG high efficiency and low torque ripple. Moreover, the presented technique reduces the computational effort and provides a clear massive data simulation framework.

This paper presents an interfaced wind energy conversion system (WECS) using the switched reluctance generator (SRG). A bidirectional DC-DC converter is adopted as an interface stage to achieve optimal excitation voltage at the SRG side, while a voltage source converter regulates the DC-bus voltage. The SRG works with superior performance, which is characterized by a compromise between efficiency and torque ripple, using the optimal excitation parameters. In addition, the interface stage adds a filtering behavior, mitigating the voltage ripple produced by the SRG, thus improving the power quality reflected in the grid current. A comparison of optimized SRG systems, with direct connection and with interfaced connection, is conducted. Experimental results show that the interface converter improves the performance of the SRG in WECS. Although the extra converter efficiency is approximately 88%, the overall system efficiency is only reduced by up to 2.5% due to the SRG optimal parameters. Nonetheless, as advantages of the method, the torque oscillations are reduced by up to 9.5% in high speeds. Moreover, due to the converter filtering behavior, the grid current harmonic content is reduced by up to 6% in the comparison. Therefore, this research indicates that the proposed approach is a viable option for SRG in WECS, especially for scenarios where the DC-DC converter is already necessary, such as in a microgrid application.

A fault current limiter (FCL) based on an arrangement of parallel connected high temperature superconducting tapes constituting a limiter element was designed and tested in 220 V line for a fault current peak between 1 kA to 2 kA. The limiter employed second generation (2G) HTS tapes of YBCO coated conductor reinforced with stainless steel. Four tapes were electrically connected in parallel with 0.4 m effective length per element wherein 16 elements connected in series constitutes a single-phase unit. The FCL performance was evaluated through over-current and current fault tests. Its recovery characteristics were used to design the shunt protection. The designed limiting ratio is 4 for 16 elements and the experimental result for one element showed a 20% limiting ratio. For the fault current test one element can withstand five cycles of fault without degradation. It was observed recovery times below 0.5 s under nominal load using a shunt resistance of 173 mOmega.

The control of the input voltage of DC-DC converters is frequently required in photovoltaic applications. In this special situation, unlike conventional converters, the output voltage is constant and the input voltage is controlled. This paper deals with the analysis and the control of the buck converter with constant output voltage and variable input.

This paper presents a proposal to control active and reactive power of small wind turbines employing permanent magnet synchronous generator (PMSG) in distributed generation systems. A three-phase AC-DC-AC electric power converter is employed to process the energy generated by the PMSG. Direct power control is applied to generate the PWM signals at the DC-DC converter, which allows controlling the active power through an adaptive PI controller by means of a gain scheduling adaptation mechanism. A voltage source inverter (VSI) is utilized to connect the machine to the electrical grid following stability and low harmonic distortion requirements. In addition, VSI has the role of controlling the reactive power exchanged with the grid. Simulation results have shown that the proposed system is reliable, leading to good results for a small-scale wind turbine. Moreover, direct power control is a strong and low-cost alternative for maximum power point tracking application. The reactive power control, in turns, adds a suitable extra degree of freedom to the system, which can be used to reduce the impact of voltage fluctuations and short-circuit on the grid.