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The interconnection of microgrids to form a network known as the multi‐microgrid (MMG) brings higher resilience and support in providing power to the loads. The dynamic response during interconnection is usually bypassed with the addition of synchro‐checkers installed on all the microgrids and the exchange of critical setting points between the microgrids prior to interconnection via a low‐bandwidth communication. This paper introduces a novel decentralized framework for maintaining the voltage and frequency of the microgrids within permissible operating range during the interconnection. The proposed control strategy is triggered when the microgrids violate the defined states of operation and the fast control action from each type of Distributed Generation (DG) in the microgrid is designed to tackle the transients in the voltage and frequency in order to regulate them within the IEEE standards. Moreover, the study is extended to evaluate the performance of interconnecting single microgrids to form MMG using the decentralized proposed control strategy and then sectionalizing the MMG back into separate autonomous microgrids. The results have been verified using PSCAD/EMTDC. The proposed control strategy demonstrates superior performance and simplicity for carrying out the energy management for interconnecting and sectionalizing of MMG without any kind of communication and synchro‐check infrastructures. [ABSTRACT FROM AUTHOR]

This study proposes single-phase improved coupled-inductor (CL) Z-source (ZS) ac–ac converters with integrated high-frequency transformer (HFT) isolation. They can provide wide range of buck–boost voltage with same/reversed phase angle, similar to the existing ZS ac–ac converters. Meanwhile, integrating a HFT with CL in proposed converters benefit in two-fold: (i) the CL enhances the voltage gain, which in turn reduces the voltage stresses/ratings of active switches. Moreover, the turns ratio of CL add another degree of freedom to gain adjustment beside the duty ratio; (ii) the HFT (20 kHz) is integrated with CL by adding only one winding to the same magnetic core, which provides electrical isolation for applications such as dynamic voltage restore, saving extra bulky line frequency (60 Hz) transformer. In addition, the proposed converters provide both continuous input/output currents. The commutation strategy is also implemented to eliminate the switch voltage spikes. A proposed HFT isolated improved three-winding Δ-CL ZS (Δ-ZS) ac–ac converter is introduced at first, and its operation, circuit analysis and component design/selection are discussed in detail along with comparisons with counterpart converters. Various different CL structures based proposed HFT isolated ZS ac–ac converters are presented afterwards. Experimental results on 200 W prototype converter are provided finally to verify their merits. [ABSTRACT FROM AUTHOR]

In this study, a new self-balancing 7-level inverter (SB7LI) topology, suitable for interfacing the low voltage renewables with the power grid, is proposed that uses coupled inductors to generate additional levels in the output voltage. Owing to the presence of a self-balancing circuit, the voltage across the two-input DC capacitors is self-balanced by charging them in series and discharging them in parallel. The self-balancing feature of the proposed SB7LI also obviates the sensing of input DC capacitors’ voltages. The SB7LI is controlled using a novel multi-sine wave pulse width modulation strategy. A significant advantage of the proposed SB7LI topology is that it uses fewer power components in comparison with traditional multi-level inverter topologies, which ensures higher power density and compact circuits. This also improves the overall efficiency of the system and reduces the cost. Further, a modified version of the SB7LI is also presented with a reduced number of power components. An additional advantage of coupled inductors is their filtering action on the output voltage/current, which reduces the overall filter requirements. SB7LI can be easily extended to an n-level, 3-φ application. The proposed SB7LI and modified SB7LI are validated through simulations in MATLAB/SIMULINK and hardware experiments on 300 W laboratory prototypes. [ABSTRACT FROM AUTHOR]

In this study, an efficient multi‐orbital simulation model is presented for satellite Electrical Power Subsystem (EPS) which is integral to the success of the mission. The model integrates converter models, PV array model, DC bus model, and a numerical battery model according to a generalised EPS architecture to form one unified model of the entire EPS. The proposed model reduces simulation complexity, enhances speed, and enables multi‐orbit analysis capability. Dynamic interaction among the elements is modelled through a coordinated control containing maximum power point tracking (MPPT), voltage regulation, battery charge/discharge control and management. Practical concerns of digital control implementation for PI controllers and MPPT are also incorporated in the model. Anti‐windup is implemented to avoid latency in controller action after the eclipse. Additionally, a robust MPPT algorithm ensures fast immediate action after eclipse. Efficient component models and practical attention‐to‐detail enable the developed model to simulate multiple orbits with eclipse periods. The superior speed of the model, ability to simulate multiple orbits, and test different control strategies are demonstrated with a practical case study of Mysat‐1, an imaging satellite launched by the Khalifa University. The model can be used as a proof‐of‐concept tool for predicting the operational behaviour of EPS during the development of a satellite. [ABSTRACT FROM AUTHOR]

This study presents a H∞ mixed-sensitivity robust control design to improve the overall damping performance of lowfrequency oscillations for power systems with doubly fed induction generator-based (DFIG) wind power generation. The supplementary damping controller is designed in the linear matrix inequality framework which allows the placement of the closed-loop poles inside a pre-defined region for improved stability. The damping signal is implemented at the reactive power modulation of the rotor-side converter of the DFIG wind turbine (DFIG-WT). The damping contribution of the power oscillator damper is compared with that provided by the power system stabiliser (PSS) of the synchronous generator (SG). State-space system analysis and time-domain simulations show the capability of DFIG-WT to enhance the overall damping of the oscillatory modes even if PSSs are not installed at SG s. Also, the designed controller shows a robust performance to wind speed variations. The performance evaluation is based on the revised two-area four machines system and the revised New England 39-bus system. [ABSTRACT FROM AUTHOR]

The environmental and economic impact of photovoltaic (PV) systems is continuously growing, serving as an effective alternative energy source. Yet, failures and underperformance, e.g. due to soiling and deterioration, can significantly affect PV production and shrink the capacity available. This becomes an important issue, especially when the plant is not easily accessible for manual checking. Typical monitoring tools can help energy managers to deal with such issues. However, their diagnostics might be misleading as reduced performance could also be caused by low radiation and other relative factors, which are difficult to identify given the non‐linear and stochastic relation of energy production and weather variables. In addition, accurate component‐based models that use local weather measurements as inputs are not always applicable. In this regard, a methodological approach for tracking the performance of PV systems is proposed, which uses an artificial neural network, trained using reported system data and irradiation predictions. Possible abnormalities are identified through the model and alerts are generated to proceed with maintenance actions. The approach is implemented into a decision support system for smart cities, demonstrating encouraging results. [ABSTRACT FROM AUTHOR]

Power generation from renewable energy resources is on the increase in most countries, and this trend is expected to continue in the foreseeable future. In an effort to enhance the integration of renewable power generation from solar and wind into the traditional power network, there is need to address the vulnerabilities posed to the grid as a result of the intermittent nature of these resources. Variability and ramp events in power output are the key challenges to the system operators due to their impact on system balancing, reserves management, scheduling and commitment of generating units. This has drawn the interest of utilities and researchers towards developing state of the art forecasting techniques for forecasting wind speeds and solar irradiance over a wide range of temporal and spatial horizons. The main forecasting approaches employ physical, statistical, artificial intelligence and hybrid methodologies. This study provides the rationale for forecasting in power systems, a succinct review of forecasting techniques as well as an assessment of their performance as applied in the literature. Also, techniques for improving the accuracy of forecasts have been presented together with key forecasting issues and developing trends. [ABSTRACT FROM AUTHOR]

This study presents a new scheme for a continuously variable (CV) series braking resistor (SBR) with independent per phase controller. The CV-SBR is a CV and not stepwise. A novelty of the work presented is that the CV-SBR operates on the whole range of wind speeds. The proposed scheme is applicable to fault ride-through (FRT) of fixed speed wind turbines (FSWTs). The CV-SBR scheme is compared to the single-step (SS) and multi-steps (MS) SBRs. The CV-SBR scheme is modelled and simulated in PSCAD/EMTDC™. The performance of the wind turbine is studied for balanced and unbalanced fault scenarios. The CV-SBR scheme is advantageous over the other two candidates with its ability to limit the fault current and reduce the turbine speed deviation at any wind speed. The CVSBR is employed with a static synchronous compensator (STATCOM) to allow FRT of FSWT connected to weak grid during nearby faults and to deliver the reactive current required by some grid codes. The CV-SBR scheme is successful in reducing voltage disturbance's consequences on the generator's mechanical system. Simulation results show that the CV-SBR allows FRT of FSWT connected to weak grid where the STATCOM alone is not able to sufficiently enhance the FRT of FSWT during nearby faults. [ABSTRACT FROM AUTHOR]

This study presents a novel coordinated secondary voltage control (CSVC) and reactive power management scheme for efficient utilisation of distributed energy resources in a smart distribution network. The proposed controller is developed to achieve efficient voltage regulation and to maximise the dynamic reactive power reserve in a distribution network to react during system contingencies. The simulated distribution system, including an on‐load tap changer (OLTC) and distributed energy resources, is implemented using PSCAD/EMTDC. The CSVC is designed to provide slow and medium speed responses, using low‐pass filters for OLTC and diesel generators, respectively, and a fast response by utilising inverter‐based distributed energy resources. Therefore it applies a control strategy with different bandwidth dedicated by the decentralised voltage controllers and reactive power management scheme. The CSVC is used to enhance the bus voltage control by utilising the reactive power loading capabilities among distributed energy resources and on‐load tap changers of the substation transformer. A comprehensive simulation has verified the superior performance of the proposed coordinated secondary voltage control with the reactive power management scheme for enhancing the voltage profile and the fault ride‐through capability, ensuring higher dynamic reactive power reserves in a distribution network, and improving the transient stability margin. [ABSTRACT FROM AUTHOR]

Hybrid micro‐grids are one of the most viable solutions to the present day problem of integration of renewable energy into existing power systems. With various options available for implementation of hybrid micro‐grids, the stability of such systems has to be ensured before they can be implemented. Further, conventional micro‐grid operational studies do not take into consideration the constraints set by the grid codes. This study analyses three types of interconnections, possible for implementation of hybrid micro‐grids, taking into consideration the transient stability and grid code constraints. The hybrid micro‐grid considered comprises a synchronous diesel generator and an inverter‐based distributed generation. The results and analysis are conducted by time‐domain simulations using MATLAB/Simulink software. The results provide the actual operational limits of possible micro‐grid interconnections under the set of given constraints. [ABSTRACT FROM AUTHOR]

Integration of dynamic grid support is required for distributed power systems that are interconnected with medium voltage grids. This study proposes a comprehensive control solution to enhance fault ride through (FRT) capability for utility‐scale photovoltaic (PV) power plants. Based on positive and negative sequence control schemes and PV characteristics, the approach alleviates dc‐bus double‐line‐frequency ripples, reduces voltage stress on inverter power switches and DC‐link capacitors, and minimises undesirable low‐order voltage and current harmonics that are presented on the ac side. The study proposes a new feature to achieve superior FRT performance by using the overload capability of grid‐tied inverters. A weak electric grid is used for the test case including a wind turbine induction generator, diesel engine driven synchronous generators and various loads. A comprehensive simulation verified the capability of the proposed control schemes for mitigating the voltage dip, enhancing the voltage response and further improving the stability of interconnected distributed generation in reaction to severe unbalanced voltage conditions because of asymmetrical grid faults. [ABSTRACT FROM AUTHOR]