This paper proposes a control strategy for a bidirectional grid-forming converter, operating as a virtual synchronous generator, based on an improved voltage controller to enhance the dynamics of the active and reactive power loops. The theoretical analysis and real-time simulation results demonstrate the enhanced disturbance rejection of the proposed strategy, which is based on disturbance input decoupling. Furthermore, virtual impedance is used to limit the current injected by the converter during grid transitory situations.

Energy management systems for microgrids are tailored to meet specific application needs and consider technical, economic, environmental, and reliability requirements. Regardless of their centralized or distributed structure, these systems are designed to efficiently manage microgrid operations, including energy generation, storage, and consumption, to ensure a reliable energy supply. In addition to these functions, the Energy Management System is also responsible for dealing with protection devices and systematically reacting to them to minimize disruptions, guaranteeing operational security. This study presents the strategies of a centralized energy management system deployed in a critical microgrid in Maranhão, Brazil. The protection functions in the protection devices for the two operating modes (on-grid and off-grid) and the subsequent decisions implemented as rules in the Energy Management System are discussed. This coordination between protection devices and management systems ensures rapid and selective response to faults, enhancing microgrid security and facilitating problem detection and resolution.

This paper proposes a current control strategy for grid-following inverters interfaced into the grid through LCL filters. It is proposed to utilize a proportional+resonant controller with a lead compensation in series with the proportional gain which allows the inverter to achieve high bandwidth. Furthermore, an active damping scheme with capacitor current feedback is applied to mitigate the adverse effect of the LCL filter resonance frequency. Moreover, the concept of capacitor voltage decoupling is utilized to enhance the disturbance rejection capability of the grid-following inverter. Theoretical analysis and experimental results validate the proposed strategy.

Wave energy converters have been attracting attention of researchers and industries all over the world. Many approaches have been presented for the modeling of these devices, but the reader might have difficulties on linking them. In this article is presented a friendly guideline for the modeling of direct-drive point absorber wave energy converters. A popular and relatively complex design is used as a guiding example, namely, a point absorber converter with a heaving buoy as wave absorption device connected to a power take-off system based on a linear generator. Both frequency and time-domain hydrodynamic modeling approaches are considered, and the absorption device hydrodynamic parameters are obtained from a dedicated diffraction-radiation analysis tool. The motion dynamics involving ocean waves and the converter elements are based on ocean and mechanical engineering theory. The linear generator electromagnetic model is based on an equivalent rotating machine which facilitates the generator analysis and the control of the energy produced. This guideline is intended to be used and adapted by new developers to test and validate their own wave energy converters.

In this paper an analytical modeling of the BEM method (Blade Element Moment Theory) with complementary correction methods for the performance analysis of the horizontal axis propeller wind turbines is described. This modeling was built from comparative analyzes of several correction methods proposed in the literature, of which those that presented better results were chosen, considering both medium and large turbines. To validate the results obtained from this modeling, experimental data from four turbines (NASA MOD-X series) in the order of 100kW to 7.3MW were used. A critical and comparative analysis was carried out to discuss the coherence of the results when predicting the performance of these turbines, with the objective of enabling the use of this modeling in a generalized way for horizontal axis propeller wind turbines with wide power range.

The microgrids have been applied satisfactorily for the supply of energy to isolated places. In isolated microgrids, energy storage systems and dispatchable energy sources are fundamental for continuous operation, and for power balance. The dispatchable sources are useful as backup, for maintenance operations, and for battery bank equalization charges. Practical experiences in isolated microgrids that uses synchronous generator (driven by a prime mover) have a potential operation problem when working with rectifiers to charge the battery bank whenever the available renewable resources are not sufficient. This is due the generator reactance that causes voltage distortions at the generator terminals, power quality problems for the microgrid and, eventually, inhibition of rectifier operation whenever there is a thyristor switching. This paper proposes the design of a bidirectional DC-AC converter control loops for application in isolated microgrids, improving the power quality, efficiency and operation. In addition, the use of a bidirectional converter reduces energy conversion losses and reduces the costs of implementing the microgrid by replacing two pieces of equipment (AC-DC and DC-AC converters) for just a single one. The contributions of the paper are the design methodology of the control loops of a bidirectional converter, whose development and application in real environment allows it to perform as grid-forming converter in isolated microgrids.

In this article, results and indicators of the operation evolution of the solar-wind hybrid microgrid installed on the island of Lençóis, Maranhão, Brazil, after ten years of operation are reported. This microgrid is considered a national reference project due to the longevity and robustness in serving the marine islands. This analysis evaluates aspects such as load evolution, challenges identified and overcome, experience with the storage system, and improvements introduced. Indicators of efficiency and socio-economic impacts are also presented and discussed.

This paper proposes a control technique that allows inverters to work as if they were synchronous machines, assuming the characteristics and properties that these machines have. The development of each control block that composes the Virtual Synchronous Machine (VSM) is presented. The proposed VSM can operate isolated, in parallel with other VSM's, sharing the active and reactive demanded power and connected to the main grid, without the need of control switching between grid-connected and isolated modes. Simulated and experimental results prove the developed theory.

In this paper, a modified droop technique is described to perform the state of charge balancing of multiple battery storage systems in microgrids. Each of these systems is independent and maintained by its own grid-forming converter. In addition, this balancing is done without the use of logical communication between the different grid forming converters. In this way, it is possible to distribute them over the microgrid, helping to enhance the quality of energy delivered to the loads. The proposed parallelism technique is capable of balancing energy storage systems with different characteristics and connected to grid forming converters with different nominal powers. It is also noted that, unlike some techniques found in the literature, the technique proposed here is capable of operating without causing power limitations or reducing the power availability of the converters.

The performance of current and voltage regulators during transients and steady-state is of primary concern for power converters intended for stand-alone applications. Dynamics performance and command tracking capability are enhanced by actively decoupling the controlled states variables. To further widen the current loop bandwidth while still preserving a well-damped system a lead compensator structure on the forward loop is proposed. A 3 kHz bandwidth with 0.707 damping factor is achieved for the inner current controller. Accordingly, also the voltage regulator bandwidth can be widen, thus requiring even more a proper anti-wind up scheme to avoid saturation of the integral term during demanding transients. Lab-tests are performed in accordance with standards imposed to uninterruptible power supplies, verifying the theoretical analysis.

Voltage and current control loops play an important role in the performance of microgrids employing power electronics voltage source inverters. Correct design of feedback loops is essential for the proper operation of these systems. This paper analyzes the influence of state feedback cross-coupling in the design of resonant regulators for inner current loops in power converters operating in standalone microgrids. It is also demonstrated that the effect of state feedback cross-coupling degrades the performance of the control loops by increasing the steady-state error. Different resonant regulators structures are analyzed and compared, performing experimental tests to validate the results of the theoretical analysis.

This paper presents a new strategy to control the generated power that comes from the energy sources existing in autonomous and isolated Microgrids. In this particular study, the power system consists of a power electronic converter supplied by a battery bank, which is used to form the AC grid (grid former converter), an energy source based on a wind turbine with its respective power electronic converter (grid supplier converter), and the power consumers (loads). The main objective of this proposed strategy is to control the state of charge of the battery bank limiting the voltage on its terminals by controlling the power generated by the energy sources. This is done without using dump loads or any physical communication among the power electronic converters or the individual energy source controllers. The electrical frequency of the microgrid is used to inform to the power sources and their respective converters the amount of power they need to generate in order to maintain the battery-bank state of charge below or equal its maximum allowable limit. It is proposed a modified droop control to implement this task.