Search

In this article, a novel step-up transformerless inverter topology is presented for the grid-connected solar PV system. The proposed topology has the features of a dc–dc step-up converter and two-level inverter. First, it offers the transformerless grid connection of solar PV system with negligible leakage current and higher efficiency, and second, it provides inherent high gain step-up so that low-voltage solar PV modules can be directly connected. In addition, the proposed topology has low-voltage stress, less power losses, and requires fewer independent gate drive signals compared to the other existing transformerless inverter configurations with voltage boosting capability. The design, modes of operation, analysis, and developed PWM strategy, for the proposed inverter topology, are presented in detail. Furthermore, the system performance is validated experimentally through a 400 VA laboratory prototype. The experimental investigation demonstrates that the proposed topology results in transformerless voltage boosting while achieving improved system efficiency. [ABSTRACT FROM AUTHOR]

Single-phase matrix converters (MCs) are undergoing rapid developments due to their bipolar voltage gain (as required in dynamic voltage restorers) and step-changed frequency operation (used in high step-up ac–dc rectifiers, and to provide medium frequency isolation in traction and wind turbine converters, etc.). However, existing buck–boost MCs require high-voltage/current rating devices, and suffer from large component voltage/current stresses and ripples, significantly degrading their efficiency. This article proposes a highly efficient single-phase buck–boost MC; consisting of eight IGBTs (implemented using two full-bridge IGBT modules), second-order input and output filters, and a small value film capacitor. Efficient discrete inverting and noninverting buck and boost operations are proposed (same as that of sixteen-switch cascaded buck–boost MC) with significantly lower component voltage/current stresses and ripples. In addition, flexible inverting and noninverting buck–boost operations are proposed with independent control of buck and boost duty ratios. All of the proposed operations are free of commutation issues, compatible with reactive loads, and provide smooth input and output currents. Furthermore, all the switches have same voltage stresses, and all four switches in a full-bridge module experience the same current stresses. A comprehensive description of circuit operation is presented based on a number of proposed switch modulation strategies with a nonunity power factor load, followed by design guidelines, and comparative evaluations with existing topologies. Finally, experimental verification results are presented, using a 400-VA laboratory prototype converter. [ABSTRACT FROM AUTHOR]

In this article, a single-phase bipolar buck–boost direct pulsewidth-modulated ac–ac converter is proposed, comprised of six insulated-gate bipolar transistors, a small film capacitor, and input/output LC filters. The converter can provide discrete noninverting buck (NIBu) and boost (NIBo) operations with voltage gains of D and 1/(1 – D), respectively. Moreover, it provides symmetric noninverting buck–boost (NIBB) and inverting buck–boost (IBB) operations with voltage gains of D/(1 – D) and –D/(1 – D), respectively. It supplies both continuous input/output currents, and it is well suited for reactive loads. It is immune from the commutation problem, and thus, has enhanced the reliability. The various modes of operation of the proposed converter make it suitable for diverse applications, including the following: 1) application as a direct ac voltage regulator when operating in NIBu and NIBo modes; 2) IBB operation can be utilized along with NIBu/ NIBo or NIBB operation to compensate both voltage sag and swell, when used as dynamic voltage restorer; and 3) symmetric NIBB/IBB operations can provide step-changed frequency output, similar to the single-phase matrix converters, for applications as induction motor drive or high-gain ac–dc rectifier. Extensive circuit analysis, component design guidelines, and appropriate comparisons are provided, followed by experimental results obtained using a laboratory prototype. [ABSTRACT FROM AUTHOR]

This paper proposes a novel wide-area control strategy to enhance the transient stability of a large inter-connected power grid. The proposed control strategy achieves maximal damping of the inter-area oscillations by calculating the optimal number of cluster centers based on a novel online coherency grouping. To achieve this objective, the critical electro-mechanical mode is selected using localness index method during transient conditions. In addition, the online identification of the full model is performed to estimate the states to be controlled during the grid disturbances. Thereafter, a discrete linear quadratic regulator (DLQR) is directly applied to the estimated states, and the corresponding signals are channelized through the loop of most controllable and observable machines of each coherent group. The efficacy of the proposed method is tested on IEEE 39 bus and IEEE 68 bus standard benchmark model. The results demonstrate faster damping with minimal computation burden compared to existing solutions such as a classical slow coherency and a multi-input multi-output (MIMO) based wide area damping controllers. [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]

This study presents a H∞ mixed‐sensitivity robust control design to improve the overall damping performance of low‐frequency 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]

This letter introduces a unit delay compensation scheme for Type-2 phase locked loop (Type-2 PLL) to eliminate the steady state phase angle error during the frequency ramp. The proposed PLL (ZPLL) uses an adaptive delayed signal cancellation (DSC) filter, along with a compensation scheme, to ensure effective operation under unbalanced grid. The proposed compensation scheme acts as an open-loop compensator, hence, ZPLL functions as Type-3 PLL with Type-2 dynamics features while preserving its second order characteristics. The proposed scheme is mathematically and experimentally validated under different scenarios of grid disturbances. The obtained results demonstrate the capability of the proposed compensation scheme to obtain a zero steady state phase angle error during the frequency ramp while employing symmetrical and asymmetrical voltage dip. [ABSTRACT FROM AUTHOR]

The article focuses on the HVDC technology (high voltage direct current) is used to transmit electricity over long distances by overhead transmission lines or submarine cables. It mentions HVDC allows power transmission between unsynchronized AC transmission systems; and most HVDC links use voltages between 100 kV and 800 kV. A 1,100 kV link in China was completed in 2019 over a distance of 3,300 km with a power of 12 GW.

High concentrations of induction motor loads can impose stress on transmission and distribution systems, leading to voltage instability in some situations. Properly sized and coordinated reactive power sources will provide for improved operation. We present a strategy for finding an optimal mix (type, size, and location) of dynamic shunt reactive compensation devices. The planning strategy is subject to satisfying steady-state, dynamic and transient performance criteria such as fault-induced delayed voltage recovery limits, as well as criteria related to single ( N–1) contingency and load disturbance events. Shunt reactive power compensation devices considered include mechanically switched capacitor banks, static reactive power compensators and static synchronous compensators. The proposed strategy employs a large number of multitimescale time-domain simulations suitable for use with high performance computing clusters and a genetic algorithm to solve the mixed-integer nonlinear programming formulation using parallel computation capabilities. The method is applied to a New England IEEE 39-bus system with assumed high penetration of induction motors. A comprehensive study shows that performance enhancement and significant cost reduction can be achieved using an optimum combination of various shunt compensator technologies. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel configuration and transient management scheme for Voltage Source Converter-High Voltage Direct Current (VSC-HVDC) connecting Large Scale Wind Farm (LSWF). The proposed configuration aims to fully utilize the HVDC converters with shunt and series reconfiguration during steady state and fault conditions respectively. Thus, it targets the employment of the available converters controls capabilities to enhance the Fault Ride-Through (FRT) performance of the VSC-HVDC and achieve smooth power evacuation to the electric grid. The control strategy is built in such a way to guarantee three factors: 1) enhancing the voltage profile of the electrical grid during symmetrical and asymmetrical grid faults, 2) providing smooth power evacuation from the LSWF, and 3) mitigating the DC link oscillations caused by unbalanced faults. Hence, the proposed scheme demonstrates superior performance of the VSC-HVDC system during steady state and transient conditions. Comprehensive simulation studies are carried out to demonstrate the gorgeous performance of the proposed VSC-HVDC configuration using PSCAD/EMTDC. In addition to that, a lab-scaled experimental set up is constructed to validate the functioning of the proposed VSC-HVDC configuration. [ABSTRACT FROM PUBLISHER]

This paper proposes a new fault ride-through (FRT) configuration for a fixed-speed induction generator-based–wind turbine (FSIG–WT). It utilizes a nine-switch converter (NSC) to enable shunt and series compensation in response to the system dynamics and grid faults. The steady-state control strategy and transient-management scheme are developed to ensure proper performance in steady-state, dynamic operation as well as enhanced FRT capability of the FSIG–WT. In addition to that, the developed control strategy tackles the balanced and unbalanced operation of the electric grid with an enhanced positive- and negative-sequence compensation control scheme. The recently reported grid synchronization scheme, namely, the frequency-locked loop (FLL) is implemented to achieve fast phase detection and transient response. Consequently, the performance of the FLL has been compared with the multiple reference–frame–phase-locked loop (MRF–PLL) to demonstrate its superior performance for enhancing transient response. The proposed topology, FLL, and control strategies are verified through a comprehensive simulation study to demonstrate the enhancement of the transient response and FRT capability of FSIG-WT in adherence to grid-code requirements. [ABSTRACT FROM PUBLISHER]

This paper presents a novel modulated series dynamic braking resistor (MSDBR) control strategy for enhancing the fault ride-through (FRT) of doubly fed induction generator-based wind turbines. The proposed cost-effective protection scheme introduces a voltage booster that offers series voltage compensation capability and provides a means of power evacuation to mitigate the power imbalance during grid faults. To attain flexible and robust control solution for handling both balanced and unbalanced grid faults, the proposed scheme employs a modulated pulse width modulation (PWM) switching technique to control the stator phase voltage individually. The proposed transient management scheme allows the MSDBR to mitigate the impact from different types of grid faults and to fulfill with the recent grid code requirement. Also, reactive current injection capability during faults is also investigated with the proposed voltage reference algorithm. For the controller design, small-signal modeling is utilized with consideration of measurement dynamics for the tuning of controller parameters in order to ensure the system robustness and stability. Finally, the simulation results demonstrate the satisfactory performance of the MSDBR with its preferred allocation for enhancing the FRT performance against both balanced and unbalanced faults. [ABSTRACT FROM AUTHOR]

This paper investigates a special class of dynamic power system problem, namely subsynchronous resonance (SSR) resulted from a series-compensated network connecting doubly-fed induction generator (DFIG) based wind farms. A novel two-degree-of-freedom (2DOF) control strategy combined with a damping control loop is designed and analyzed for enhancing the system stability and alleviates the SSR that may arise due to the induction generator effect (IGE). The proposed control strategy is tested at different operating conditions of series compensation levels and low wind speeds to ensure the system stability. The doubly-fed induction generator based wind farms without the proposed control strategy leads to overall system instability during high series compensation and low wind speeds. Hence, the mitigation of the SSR and damping enhancement are critical to the entire power system stability. A reliable way of analyzing the system and designing effective control strategies against SSR based on the eigenvalue analysis and impedance based stability criterion is deployed. Moreover, analytical explanations have been elaborated to verify the procedure of the controller design. Fault ride-though capability has also been investigated with the proposed control strategy that is flexible to be integrated with the FRT schemes so as to assist the wind farm in mitigating the SSR during the fault recovery stage. Finally, time domain simulations are carried out to demonstrate the effectiveness of the proposed control strategy for mitigating the SSR and damping power system oscillations. [ABSTRACT FROM PUBLISHER]

This paper presents a novel system configuration for voltage source converter (VSC)-based high-voltage direct current (HVDC) transmission connected to a large-scale offshore wind power plant (WPP). The proposed scheme is reconfigured at the onshore end to achieve shunt and series compensation, which is named as ‘Unified-VSC-HVDC’ (U-VSC-HVDC). A mathematical model of the proposed configuration is derived to determine the rating of the employed series and shunt converters. To achieve a flexible control strategy for balanced and unbalanced fault conditions, the proposed transient management scheme employs positive and negative sequence controllers for the series compensation. The negative sequence voltage components are determined in such a way as to minimize power oscillations caused by asymmetrical faults, and hence to reduce DC link voltage overshoots. A test system comprised of a detailed representation of the proposed configuration is simulated and evaluated using PSCAD/EMTDC. A comprehensive study validates the capability of the proposed configuration and transient management scheme for achieving smooth power transfer and superior transient performance of the electrical grid. Also, it minimizes the possibilities of electrical network propagations in response to symmetrical and asymmetrical grid faults. [ABSTRACT FROM PUBLISHER]

This paper introduces a novel coordinated voltage-control (CVC) scheme for distributed generations (DGs) that relies on adaptively changing the roles (master or slave) of the devices [inverter-based DG, diesel generator, and online tap changer (OLTC)] within the smart grid, depending on system conditions. In addition, the proposed scheme imposes different control response and bandwidth on the devices to coordinate the reactive power among distributed generations (DGs) and OLTC steps. The main objective of the proposed method is twofold: 1) to maximize the reactive power reserve of DGs and, hence, facilitate reaction during contingency situations and 2) to provide voltage regulation during normal operating conditions. The simulated distribution system includes inverter-based DGs (photovoltaic and wind turbine), diesel generator, and OLTC and the potential of the CVC scheme is evaluated and analyzed in view of improving voltage profile, maximizing the reactive power reserve, enhancing fault ride through and improving the transient stability margin. The control algorithm is examined under steady state, load excursion, and three-phase-to-ground fault conditions. The results demonstrate the ability of the proposed CVC scheme to satisfy the targeted objectives with significant improvement in the maximum critical clearing time. The proposed scheme is independent of real-time measurements and is widely adaptive to the dynamics of power systems, thus making it quite suitable for utility implementation. [ABSTRACT FROM AUTHOR]

This paper presents new series grid interface topologies for enhancing the low voltage ridethrough capability of self-excited induction generator-based wind turbines. Two proposed schemes: static synchronous series compensator (SSSC) and controllable series braking resistor (CSBR) have been designed and simulated. The test system simulated represents a wind turbine connected to an electric grid with alternatively employing SSSC and CSBR. The potential of the two schemes is evaluated and analyzed using positive and negative-sequence reference frames in response to balanced and unbalanced fault scenarios. The simulation results using PSCAD/EMTDC demonstrate the performance of the proposed schemes for improving the fault ridethrough capability and transient stability margin in response to severe symmetrical and asymmetrical grid faults. The schemes have shown successful and fast mitigation of voltage disturbance consequences on the mechanical system. The schemes helped the wind turbine to remain connected with considerable isolation from grid faults. [ABSTRACT FROM PUBLISHER]

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]

This paper proposed a novel fault ride-through (FRT) configuration and transient management scheme to enhance the FRT capability of doubly fed induction generator-based wind turbines. The new configuration of the grid-side converter introduces shunt and series compensation for normal operation and voltage dips, respectively. A braking resistor is added to smooth switching transients from shunt to series interfaces and dissipate excessive power from the grid-side converter. To attain a flexible control solution for balanced and unbalanced fault conditions, the proposed transient management scheme employs positive and negative sequence controllers. A small-signal linear model is developed and examined to analyze the system dynamics for the series compensation topology. Based on the mathematical model, the controller is tuned to balance both voltage regulation performance and transient stability margins with consideration of various operating conditions. The combination of shunt and series interfaces demonstrates a low component count, simple protection structure, and improved performance of FRT with effective compensation to the electric grid. A comprehensive simulation verified the capability of the new configuration and transient management scheme. [ABSTRACT FROM AUTHOR]

Fossil fuel power plants continue to contribute significantly to carbon emissions, necessitating a transition towards cleaner energy sources. Despite the growing presence of renewables within the power systems, the incorporation of carbon capture technologies into the traditional thermal power plants holds great potential in emissions reduction. In this paper, the integration of renewable energy sources (RES) and coal-fired power generation units outfitted with carbon capture schemes is addressed. Multiple demand response (DR) programs and hydropower plants are strategically utilized to increase the power system flexibility. To effectively plan the day-ahead (DA) operation of the power system, a presumed market-clearing framework is adopted and modelled as a risk-constrained two-objective stochastic mixed-integer linear programming problem. The proposed framework helps to tackle the uncertainties related to RES and demand variations by employing a hidden Markovian process (HMP) technique. To simultaneously minimize the system's operational costs and CO 2 emissions, an enhanced version of the augmented ɛ -constraint method is employed. To prove its value, the proposed framework is devoted to the 24-bus IEEE reliability test system (IEEE-RTS). The system features substantial penetration of RES (exceeding 87% of peak load) and standard DR options capacities (less than 25% of peak load). The results show a 24% reduction in load peaks, an over 63% decrease in emissions, and a 17% reduction in the overall operation costs. • Proposing a comprehensive linearized mathematical framework accelerating the energy transition. • Coordinating the responsive power systems with carbon capture and hybrid ESS (BESS, PHS, HES). • Enhancing an effective augmented ɛ -constraint technique to simultaneously optimize cost and CO 2. • Presenting robust decision-making with two-stage SP, hidden Markovian process, and CVaR strategy. • Integrated approach: 87% of RES, cost & CO 2 reductions, fewer load peaks, enhanced flexibility. [ABSTRACT FROM AUTHOR]

The standard alternative-arm converters (AAC) with the sweet spot or short overlap operation have faced a challenge of balancing submodule (SM) capacitor voltages, where this issue has not been paid much attention so far. In this paper, a new control strategy for the SM-capacitor voltage balancing of the AAC applied in high-voltage dc transmission systems is proposed. The suggested control technique is composed of three regulators, where a control for the average voltage of all SM capacitors, the voltage balancing among the converter arms, and the voltage balancing of the individual SM capacitor are performed. Based on the operation principle of the standard AAC, which activates only three of six converter arms simultaneously, the energy balancing of the three activated arms is performed every one sixth of the fundamental cycle by the converter common offset voltage. Band-stop filters with the central frequencies at the fundamental, second-, and third-order components of the line frequency are applied to obtain the average values of the SM capacitor voltages for the feedback controllers. The simple proportional and integral controllers are employed for this scheme and the voltages of SM capacitors are mostly balanced during the steady states and kept closely to the rating with overshoot of less than 7% under the transient conditions. The proposed control method is verified by simulation results for a 33-level AAC under both normal and fault conditions. [ABSTRACT FROM AUTHOR]

Leading wind turbine manufacturers are running life extension programs for their installed wind farms which include fixed speed induction generator-based wind turbines (FSIG-WT). To accommodate the requirement of recent grid codes in these upgrades, this paper presents a new topological configuration to enhance the fault ride through (FRT) operation of FSIG-WT. The topology comprises ten semiconductor switches in total and performs shunt and series compensation concurrently in response to the dynamic grid conditions. A coordinated control strategy is developed for the proposed topology to ensure smooth steady state operation, enhanced transient response, and most importantly, FRT capability in adherence to the recent grid code requirements. In addition, the control strategy maintains the linear modulation range and uniform switching frequency across all the switches participating in series and shunt compensation. The validity of the proposed topology and the coordinated control strategy is verified through extensive simulation study under different operating conditions. [ABSTRACT FROM AUTHOR]

This paper introduces a new technique to characterize the ac grids stability connected to multiterminal high-voltage direct current networks. The proposed method identifies the maximum active powers that converters can exchange with an ac network without losing the transient stability using trajectory sensitivity analysis. Therefore, the generators' rotor angles variations due to various converters active powers exchange are measured and normalized. Consequently, the norm of each trajectory vector is used as an indicator of the system proximity to instability. To enhance the accuracy of the method for online stability assessment applications, the steady-state initial conditions of the sensitivity network variables are precisely obtained using the Newton shooting method. For this purpose, the detailed differential and algebraic models representing the dynamics of the ac and dc networks have been formulated and analytically solved simultaneously with the sensitivity network. Comprehensive simulation studies on the IEEE 68-bus benchmark system are carried out using PSCAD/EMTDC for validation purposes. Results show that the modified approach provides more accurate results compared to the normal trajectory sensitivity analysis with less time compared to multiple time-domain simulations. [ABSTRACT FROM PUBLISHER]

This paper introduces an efficient algorithm to adaptively determine the droop coefficients of generating units in hybrid ac–dc networks. These generating units include conventional synchronous generators and multiterminal high-voltage direct-current (MTDC) converters. The proposed algorithm relies mainly on trajectory sensitivity to reschedule power generation according to the new calculated droop coefficients to ensure and/or system stability margin for set of credible contingencies with different load conditions. The Newton shooting method is used to find the new steady-state values for the systems when load is changed. MTDC converters are modeled in such a way to emulate the inertia behavior of the synchronous generators. This virtual emulation is achieved by providing two additional control layers that link and control the converter powers through inertia constants similar to synchronous generators. Also, an expression for generated powers controlled by the droop coefficients is developed to be utilized in the algorithm. Finally, comprehensive simulation studies on the IEEE 68-bus benchmark system are carried out using PSCAD/EMTDC interfaced with MATLAB to validate the proposed algorithm. [ABSTRACT FROM AUTHOR]

The low cost of diesel generators have led to their increased presence in hybrid microgrids. The presence of low-inertia devices in such microgrids makes the stability of hybrid microgrids a pressing concern. This paper analyzes the impact of equal and unequal active power sharing conditions on the dynamic stability of a hybrid microgrid. The sensitivity of low-frequency eigenvalues to changes in active power droop gains is studied and a “domain of stability” region is proposed to assess the stability of hybrid microgrids under different power sharing conditions. The different operating regions within the domain of stability are defined. Based on the sensitivity analysis and the domain of stability, the optimal droop gain for the diesel generator to improve the stability of the microgrid is determined. Time-domain simulations are carried out in the MATLAB/Simulink software environment and are used to validate the small-signal stability analysis results. [ABSTRACT FROM AUTHOR]

Integrating renewable energy resources (RES) is a challenge for power system operators due to their fluctuations and unpredictability. At the same time, the water shortage problem and the needs to desalinate more freshwater increase the prominence of sufficient energy resources for sustainable operation. Therefore, this paper presents a market-clearing mechanism in a co-optimization model that coordinates the operation of grid-connected reverse osmosis water desalination plants (RO-WDPs) and the operation of renewable-rich power systems. It is assumed that electric demands can participate in the provision of demand response (DR) to the market via multiple DR options. The DR options related to the general loads are demand shifting, load curtailment, distributed generation, and hybrid energy storage systems (HESS). These HESS includes battery storage and hydrogen storage systems. Pertaining to their special characteristics, a new DR option is proposed as a customized option for RO-WDPs. The market clearing mechanism is assumed to be based on the security-constrained unit commitment (SCUC) and formulated as a stochastic mixed-integer linear programming problem (MILP) to optimally schedule the day-ahead operation of the power system. The presented model is applied on 6-bus and IEEE 24-bus reliability test system (RTS) test power systems with significant penetration of RES to demonstrate its merits. The simulation results show that the system efficiency is enhanced by adding the energy flexibility of RO-WDP without endangering the water demand-supply when using the proposed coordinated model. Hence, the total operation cost is minimized, the RES integration is facilitated, and the hourly electricity prices are smoothened. • We propose coordination model of grid-connected RO desalination and responsive power system. • The power system in our model considers five DR options including hybrid ESS. • We avoid the generic DR model to reschedule the RO desalination flexibility. • The day-ahead operation of our energy–water nexus incorporates system uncertainties. • The incorporated approach minimizes cost and CO2 and enhances the system flexibility. [ABSTRACT FROM AUTHOR]

This paper proposes the notion of “critical cluster” in inverter based droop controlled microgrids, thus representing the neighborhood of the distributed generation units that determines the small signal stability margin of the entire system. The clustering starts from the lowest impedance electrical connection between distributed generators, termed as “critical line”. At first, the systematic study of few similar microgrids by means of the eigenvalue analysis of their small signal models reveals the correlation between the location of their dominant low frequency modes and the individual connections between neighboring inverters. Second, the sensitivity analysis of active power droop gain with respect to network parameters confirms the previous findings and shows the dominating effect of the critical line's impedance. Simulations and small signal analysis studies assess the impact of the choice of various interconnection points when two individual droop controlled islanded microgrids are connected to form a single microgrid. At the same time, simplified models on the basis of critical clusters allow the effective approximation of the stability margin corresponding to the original systems. The results reveal that different interconnection points lead to strong variations in the performance of the coupled microgrid both in terms of transient response and small signal stability. [ABSTRACT FROM PUBLISHER]

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]

Solar photovoltaic power generation accurate prediction is crucial for optimizing the efficiency and reliability of solar power plants. This research work focuses on predicting photovoltaic power using various machine learning algorithms, including ensemble of regression trees, support vector machine, Gaussian process regression, and artificial neural networks. Performance of these algorithms is further improved through hyperparameter optimization using Bayesian optimization and random search optimizers. Hourly data with a 30-min temporal resolution for an entire year is collected from a 10 MW Masdar solar photovoltaic project based in the United Arab Emirates. Photovoltaic historical power curve is generated using the System Advisor Model software, and to ensure data consistency, the collected dataset is normalized, with the interrelationships among variables computed using the Pearson relation coefficient. The results substantiate that Gaussian process regression demonstrates the best performance (lowest prediction errors) in terms of computing predicted solar photovoltaic generation power, followed by artificial neural networks, ensemble of regression trees, and the support vector machine across both optimizers. Concerning hyperparameter optimization, Bayesian optimization -based model outperformed support vector machine, Gaussian process regression, and artificial neural networks algorithms, except for the ensemble of regression trees. The proposed work contributes to the advancement of solar photovoltaic power prediction by combining the power of machine learning algorithms with hyperparameter optimization techniques. Additionally, the results emphasize the importance of hyperparameter optimization in enhancing machine learning model performance, providing valuable insights into adaptability and accuracy across varying seasonal conditions. Proposed methodology for solar PV power prediction using machine learning algorithms with different optimizers. [Display omitted] • The study employs machine learning techniques to predict solar photovoltaic power. • It utilizes UAE's Masdar PV project data with 30-min resolution for entire year. • Bayesian and random search are used to enhance machine learning models performance. • Performance evaluation of these models is computed by error, speed and size metrics. • Gaussian process regression shows superior predictive accuracy than other models. [ABSTRACT FROM AUTHOR]

The increased penetration levels of renewable energy resources (RESs) transform the power generation schema into one that is more susceptible to changes due to weather conditions, complicated load profiles, and reduced inertia levels. One of the main challenges that power grids can encounter under varying and low system inertia (SI) is poor frequency response (FR). Therefore, this paper proposes a novel online tool for assessing, predicting, and enhancing the frequency stability (FS) of power systems with renewable power generation and energy storage systems (ESS). Firstly, the tool provides accurate tracking of the SI in real-time settings using recursive least square identification and Kalman filtering to provide accurate and computationally efficient results. Secondly, the tool estimates the FR of the whole system in a virtual environment for different contingencies and inertia levels. The accuracy of the FR is improved by classifying the frequency response models (FRMs) based on the SI levels. Lastly, the proposed tool computes the optimal additional estimated reserve power (ERP) required from PV and battery energy storage systems (BESS) to provide inertial and primary frequency support to the power grid at the onset of a contingency. In addition, a reserve power allocation and load-shedding strategies are proposed and implemented to dynamically adjust the reserve power of PV power plants. This dynamic control of the PV power plant reserve capacity guarantees the availability of adequate reserves for addressing unforeseen systems contingencies. Moreover, dedicated FR controllers for PV and BESS are employed to emulate the synchronous machine's inertial response (IR) and primary frequency control (PFC). The performance of the proposed tool and the FR controllers are tested and validated on a generic power grid and the IEEE 39 bus system using MATLAB Simulink and the OPAL-RT real-time simulation software. • Power system inertia estimation in a real-time environment with minimum data. • Frequency nadir estimation using multi-regressed models based on the system inertia. • Estimation of optimal reserve power for PV and BESS for frequency stability. • Dynamic adjustment of PV sub-optimal operation. • Frequency response controllers for PV and BESS, and optimal load shedding strategy. [ABSTRACT FROM AUTHOR]

Deferrable power-driven demands such as water and thermal ones possess a capability of energy storage which can be exploited to further optimize electric systems. This paper proposes a new optimized scheduling framework for electric grids by simultaneously exploiting the high-inertia thermal dynamics and lossless water storage. Unlike previous ideas in the literature, both water and thermal demands are managed to realize the long-term and short-term load-shifting strategies, respectively. First, distributed water/thermal loads are aggregated where the virtual storage can be represented by battery models. Then, a further optimized scheduling framework is proposed with a mixed-integer nonlinear programing problem. Comparative studies show that the water storage offers outstanding flexibility for electric system via pumps scheduling, especially for the electric load-shifting strategy in a long time-horizon thanks to the lossless water-storage process. Meanwhile, the thermal storage can directly support short-term electric load-shifting to avoid price spikes of electricity. Numerical results show that the proposed method can reduce the total cost of micro-grids by maximizing the usage of renewable energy sources, avoiding price spikes, and reducing dependence on high-cost centralized energy-storage facilities provided that the critical water-energy demands are preserved. [ABSTRACT FROM AUTHOR]

Direct power control (DPC) has gained much attention for medium-voltage applications due to its fast power control capability. However, a conventional static switching table based DPC can lead to unsatisfactory response when the converter is connected to an electric grid because it is commonly designed assuming ideal and constant voltages of the grid and the dc link. Therefore, the actual grid voltage and the actual converter dc-link voltage should be considered while designing the switching table. This paper proposes a novel dynamic switching table for the DPC, considering actual grid and dc-link voltages variation. The proposed dynamic switching table incorporates a new definition of power influence crossover angles of each converter space vector. The proposed scheme dynamically adapts the switching table by feeding forward the actual grid and dc-link voltages, and hence the converter's power is precisely controlled. The proposed technique is verified for the three-level neutral point clamped converters connected to a standard IEEE 9-bus test system. Moreover, the real-time simulations are performed in a real-time digital simulator, OPAL-RT. The obtained results verified the effectiveness of the proposed DPC strategy under different grid fault scenarios. [ABSTRACT FROM AUTHOR]

Microgrids are becoming popular because of the rise of distributed energy resources (DERs). The quest for efficient utilization of DERs resulted in the development of hybrid dc/ac microgrids, which consist of independent dc and ac subgrids. Controlling the power exchange across hybrid microgrids is an important aspect in maximizing the benefits. There are numerous techniques proposed in the literature to control the power flow; however, most of these techniques use proportional-integral controllers which are difficult to tune and exhibit slow response. To eliminate the drawback of existing control solutions, this letter proposes a novel strategy to exchange active power among dc and ac microgrids. The proposed control strategy is based on the hill climbing algorithm that uses perturbations of power angle δ and observes the corresponding changes in the active power. An average model of the hybrid microgrid is first developed for the evaluation of the proposed algorithm. The proposed algorithm is then applied to verify its effectiveness for achieving sufficient power exchange and enhancing the dynamic response. The model is implemented and tested using MATLAB/Simulink. Moreover, the proposed control strategy is experimentally validated using a real-time simulator, OPAL-RT. [ABSTRACT FROM PUBLISHER]

Being more actively involved in the electricity market and power systems, wind farms are urgently expected to have similar controllable behavior to conventional generations so that demand assigned by the system operator can be met. However, determining the method of dispatching the reference among the widely spread and low-rating wind turbines is difficult. This paper provides a cooperation-driven distributed control scheme for wind farm active power regulation. Instead of competing with neighboring controllers completely, the control strategy evaluates system-wide impacts of local control actions, and aims to achieve coordinated control effect. In addition, the kinetic energy storage potential in a wind turbine is tapped to provide a buffer for power dispatch. Case studies demonstrate that a large wind farm can be effectively controlled to accurately track the demand power through the proposed control scheme. [ABSTRACT FROM PUBLISHER]

• The KDE-UCV is introduced for the first time for long-term power system planning. • The nonparametric model is applied to both of wind speed and solar irradiance datasets. • KDE-UCV produces accurate probability densities than conventional approaches. • Assessments reveal robust performance with high R2 and low error metrics. • K-S test results indicate a clear evidence of a good fit for the KDE-UCV estimator. Uncertainties associated with power generation from wind energy systems and Photovoltaic (PV) power systems present a major challenge for power system planners and operators. To account for such uncertainties, probabilistic models and probability density estimations for wind speed and solar irradiance, and their corresponding wind and PV power are highly required for long-term (multi-year) power system planning, expansion, and dispatching tools. In this article, a novel Kernel Density Estimator (KDE) model using unbiased cross-validation method for bandwidth selection is proposed for the estimation of both wind speed and solar irradiance probability densities. The estimation performance of the proposed model is assessed against the traditional parametric models (Weibull and Rayleigh distributions for wind speed, and Beta distribution for solar irradiance), and the traditional nonparametric KDE approach employing a rule-of-thumb method for bandwidth selection. The performance accuracy of all models is tested using the coefficient of determination R 2 , two error metrics (Mean Absolute Error (MAE) and Root Mean Squared Error (RMSE)), in addition to the Kolmogorov–Smirnov (K–S) test that was used to assess the goodness-of-fit. The proposed approach achieved the highest percentage improvements for R 2 (24% and 23%), and the lowest MAE (66% and 36%) and RMSE (63% and 25%) metrics over the popular parametric distributions for wind speed and solar irradiance, respectively, in addition to the K–S test p-values indicating a clear evidence of a good fit. Results confirm the accuracy and robustness of the probability density estimates for wind speed and solar irradiance produced by the proposed model. [ABSTRACT FROM AUTHOR]

A variable frequency transformer (VFT) is being considered as a new alternative to the classical back-to-back high voltage direct current (HVDC) link for interconnection of two asynchronous networks. The VFT is a retrospective form of frequency converter using the wound rotor induction machine (WRIM), which converts the constant frequency input into a variable frequency output. The prime objective of VFT is to achieve controlled bidirectional power transfer between the two asynchronous networks. This paper presents a detailed working principle of VFT technology and proposes a new hierarchical control strategy for establishing the VFT connection with two power systems to achieve bidirectional power transfer between them. Also, to restrict the grid fault propagation from one side of the VFT to the other side, a series dynamic braking resistor based fault ride-through (FRT) scheme is proposed. The performance of the VFT during the synchronization process, steady-state, dynamic, and the grid fault conditions is evaluated using the real-time hardware in-loop (HIL) system. The plant is simulated in real time using OPAL-RT real-time simulator while the control algorithm is implemented in digital signal processor to carry out HIL study. All the important results supporting the effectiveness of the proposed control strategy and FRT scheme are discussed. [ABSTRACT FROM AUTHOR]