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A European efficiency enhancement strategy for the grid-tied inverters with common dc bus and ac bus in parallel operation is proposed in this paper. Based on the inherent relationship between the dc bus voltage and the grid-feeding power, two dc bus voltage regulators with different output limits are employed in each grid-tied inverter. The operation of the dc bus voltage regulators depends on the grid-feeding power level. Therefore, the grid-tied inverter has priority up to the maximum efficiency operation point, and then, to operate at full load mode with the increase of the grid-feeding power. As a result, the European efficiency of the grid-tied system is improved without any communication link and extra hardware cost. The operation principle of the grid-tied inverter system is analyzed in detail with the implementation of the proposed control, and the design guidelines for key parameters are given and discussed. A prototype with three grid-tied inverters in parallel operation is built and experimental tests have been conducted on it in terms of steady-state performances and dynamic performances. The experimental results show that the operation modes of each grid-tied inverter depend on its sensing gain of the dc bus voltage. The European efficiency of the grid-tied inverter system with the conventional control and with the proposed control are 94.74% and 95.17%, respectively, which means the European efficiency has been enhanced by 0.43%. These results verify the feasibility and effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

In this paper, a multilayer control is proposed for inverters that are able to operate in parallel without intercommunications. The first control layer is an improved droop method that introduces power proportional terms into the conventional droop scheme, letting both active and reactive power to be shared among the inverters. The second layer is designed to compensate the voltage deviations caused by the aforementioned droop control, thus improving the load-voltage regulation of the system. The third layer is a quasi-synchronization control that roughly adjusts the angle of the inverter to be close to the common ac bus. This layer ensures that the phase difference of each inverter is inside a limited margin with the help of the phase signal sensed from the common ac bus. The principle of operation of the control scheme has been analyzed in detail. A small-signal model has been developed in order to study the system dynamics, which can be used for adjusting the main control parameters. A prototype consisting of a two 35-kVA-inverter system has been built and tested in order to verify the feasibility of the proposed approach. [ABSTRACT FROM AUTHOR]

This study proposes a decentralised robust fuzzy control strategy for islanded operation of an AC microgrid with voltage source inverters. The objective is to design a robust controller for regulating the load voltage and sharing power among distributed generators (DGs) in the presence of uncertainties in the system and non‐linear loads. The AC microgrid consists of parallel DGs connected to a main AC bus. A Takagi‐Sugeno fuzzy approach is developed in this article to achieve stability and desired performance in dealing with non‐linearities in the islanded microgrid and H∞ criterion is used to obtain a robust control strategy in presence of uncertainties raised by unmodelled and high frequency dynamics. Therefore, a non‐convex condition in H∞ optimisation problem is converted to a convex linear matrix inequality (LMI) condition and is solved by MATLAB LMI toolbox. In order to develop a decentralized system, P–f and Q–V droop controllers are used to specify set‐points for local inverter controllers in each DG. The effectiveness of the proposed control strategy in presence of constant power load and DG accidental outage is validated by the simulation of a microgrid test system in MATLAB SimPowerSystems toolbox. Comparison with cascaded proportional integral controller shows advantages of robust T‐S controller. [ABSTRACT FROM AUTHOR]

A hybrid NanoGrid (NG) can be considered as the power supply system, for future community houses. In this study, the operation and control of an NG are presented. The NG consists of an AC bus and a DC bus, interconnected through a tie‐converter (TC). All AC loads and distributed energy resources (DERs) of the community houses are connected to the AC bus while all their DC loads and DERs are connected to the DC bus. The NG has an adequate generation capacity to supply its loads in off‐grid status as well as the capability to exchange power with the grid. The TC exchanges the power between two buses and regulates the voltage in both buses, in the case of off‐grid operation. The NG dynamics, with the proposed structure and developed primary and secondary control algorithms are validated through extensive computer simulations in PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

This paper proposes an electric powertrain architecture for future hybrid electric aircrafts which structure is only composed of permanent magnet synchronous machines for both generators (PMSG) and motors (PMSM). The direct connection through an AC bus of a PMSG with one or several PMSMs involves the suppression of power electronics usually embedded in electric or hybrid electric powertrains. The idea is clearly to simplify the architecture and to significantly reduce the weight of propulsive device, “weight being the prime enemy in aeronautics”. However, the connection between power generation and propulsion devices through power electronics converters offers degrees of freedom allowing to control and stabilize the whole system. Contrarily, the direct connection between synchronous machines (PMSG-PMSM) sets a rigid link with non-linear behavior between both devices, causing complex stability issues that are analyzed. For that purpose, after having discussed the advantages and drawbacks of this powertrain by comparison with classical architectures, including power electronics, a set of models (analytic and simulation) and analysis tools (root locus, transient time simulation) is proposed. They are used in a theoretical approach to emphasize the stability issue and to assess parameter sensitivity. A reduced power scale test bench with a single-motor AC powertrain is presented: together with circuit simulation models, it is used to compare and validate the theoretical analysis results.

With the rapid increase in renewable energy sources (RES) and distributed generation (DG), the integration of hybrid storage energy systems (H-ESS) have a key role to ensure networks safe operation. Furthermore, they can enhance power systems stability while supplying the local loads, supporting RES integration and sustainable energy systems development. In this paper, a specific residential Micro-Grid (MG), composed by a photovoltaic plant coupled with a battery-flywheel H-ESS is presented. As an innovative contribution with respect to the literature, the study provides a quantitative comparison between dynamic performances of two possible MG electrical architectures (AC bus and DC bus) under different operating conditions. It results that, the AC architecture enables improved current evolution at the grid interface (peak current value is reduced by 58% and transient time is 30% shorter). Since different power electronic devices are implemented in the AC and DC bus architectures, the Total Harmonic Distortion is assessed to quantify their impact on current and voltage waves. These results indicate that the AC bus MG is the better option for the considered configuration. Moreover, AC bus MGs could be an excellent solution for developing DG networks, especially considering its integration and compatibility features with pre-existing power grids infrastructures. • AC and DC bus MG configurations are compared for integrating HESS coupled to RES. • Simulations are performed in representative conditions and MG dynamics is examined. • AC architecture proves to reestablish the balance towards the grid faster by 30%. • At the point grid monitoring point, the peak current is halved in the AC architecture. • AC bus configuration is compatible with pre-existing power grids infrastructures. [ABSTRACT FROM AUTHOR]

This study deals with the development of a proportional‐resonant (PR) control applied on voltage regulation and harmonics compensation of a standalone self‐excited induction generator (SEIG) for micro‐hydro power generation system. The generation system considers: (i) a three‐phase induction generator (IG) as SEIG, (ii) which is driven by an unregulated micro‐hydro turbine, (iii) a three‐phase three‐legs distribution static synchronous compensator (DSTATCOM) and (iv) linear and non‐linear loads connected to the AC bus. The voltage regulation is performed through the injection of reactive power to the AC bus through the DSTATCOM, providing excitation current to the IG. It is considered the employment of PR control techniques, which offers suitable voltage regulation through voltage harmonics compensation in the point of common coupling. Furthermore, frequency regulation is performed on the demand side by an electronic load control connected to the DC bus of the DSTATCOM. Experimental results were obtained to demonstrate the good performance of the voltage and frequency regulation, provided by the control system during transients of linear and non‐linear loads. [ABSTRACT FROM AUTHOR]