Aiming at the voltage stability problem of wind power grid-connected systems, a cooperative control scheme of Thyristor Controlled Series Compensator (TCSC) and Static Synchronous Compensator (STATCOM) is proposed in this study. The proposed scheme is applied in the wind power grid-connected system, a combined control strategy based on STATCOM double closed-loop feedback control and TCSC device is used to ensure that the system has enough reactive power to maintain its normal work during operation. The corresponding simulation model of wind power grid-connected system is built in MATLAB/Simulink. By analysing and comparing the waveforms of the operating examples with only TCSC, only STATCOM and TCSC-STATCOM, it is shown that the cooperative control of TCSC and STATCOM can quickly and effectively recover the bus voltage at the point of grid-connected wind farms after fault, which has a good performance on improving the voltage stability of wind power grid-connected system and increasing the low-voltage ride-through capability, and the cooperative control effect of TCSC and STATCOM is better than only using the control of TCSC or STATCOM.

In order to diagnose the wind turbine rolling bearing faults with vibration signals effectively, a fault diagnosis method based on Hankel tensor decomposition is proposed. Firstly, IMF-SVD (intrinsic mode function, IMF; singular value decomposition, SVD) is used to estimate the number of sources in sensor observation signals. Secondary, a third-order Hankel tensor is formed by the observation matrix, and a set of low-rank tensor subterms are obtained by tensor rank- decomposition. The fault features of each source are contained in the first and second modes of the corresponding subterm. Then, the source signals are reconstructed by the subterms. Finally, the envelope spectra of the reconstructed source signals are analysed, and the fault characteristic frequencies are extracted. The results of simulation and practical case analysis show that this method can realise the fault diagnosis of wind turbine rolling bearings correctly and effectively.

As the share of wind power increases in the power system, also the share of uncertain generation increases. This, in turn, increases the total balancing energy, real-time balancing power requirements and ramping of the balancing generation. In this study, the impact of wind power forecast errors on the real-time balancing need was investigated for different shares of wind energy (4–30%) in Finland and the Nordic region (comprising Denmark, Finland, Norway and Sweden). The size of the aggregation area of the net imbalances has an impact on the net imbalance volumes. The larger the size of the area is, the smaller the normalised net imbalance volumes are. In Finland, the impact of wind forecast errors on the net imbalance volumes and the largest net imbalances is almost two times as large as the impact of wind power forecast errors in the Nordic region. A shorter forecast horizon has an impact of similar magnitude both on reducing the net imbalance volumes and the largest net imbalances and on aggregating imbalances from large spatial areas. When day-ahead forecasts are not corrected intraday (ID) the impact on the net imbalance volumes and the largest net imbalances is twice as large as when ID forecasts are used.

Due to a growing penetration of permanent magnet synchronous generator-based wind turbine generation (PMSG-WTG) systems into the modern power grid, there is a strong interest in leveraging the potential capabilities of PMSG-WTG system to participate in the system frequency regulation during the grid event. In this work, a novel comprehensive frequency regulation (CFR) scheme is proposed specifically for rotor-speed-control-oriented PMSG-WTG systems. The step-wise inertial power response enables PMSG to perform the temporary frequency support. The rotor speed and pitch angle controllers are coordinated to curtail the wind power output for the persistent de-loaded operation, which can facilitate the primary frequency regulation through the variable-slope droop control. Furthermore, this CFR control scheme is implemented into the controls advanced research turbine 2 (CART2)-PMSG model, so as to investigate its potential impact on the structural loads of wind turbine. Simulation results show CFR can dramatically enhance overall frequency regulation capability of the PMSG-WTG's system and mitigate the frequency oscillations over a full range of wind speeds without causing large mechanical damages to the wind turbine.

This article presents a study on an axial-flux permanent-magnet synchronous generator (AFPMSG) with a double-sided rotor, coreless armature. The armature winding consists of non-overlapping concentrated coils and has a non-integral coil–pole ratio. It is shown that, with an appropriate choice of armature coil number to pole number, the fundamental winding factor of the AFPMSG can be made close to that of a full-pitched integral slot winding. The field distribution and load performance are computed for a prototype machine based on a two-dimensional, time-stepping finite element method. A study of the armature reaction effect of the coreless armature winding and the origin of torque ripple is also carried out. The computed voltage and current waveforms, as well as the load characteristics, are verified by practical experiments.

Co-firing coal and biomass has been applied in existing coal-fired power stations recently. Online blend-type identification was investigated by support vector machine (SVM) using flame emission spectrum for combustion optimisation. A spectrometer was used to capture the flame emission spectrum during co-combustion in a 0.3 MW furnace. A total of 22 flame features were defined and extracted from the flame emission spectrum for blend-type identification. ReliefF was applied to calculate the important weights of the extracted fame features. Alkali metals atomic excitation spectral intensities and the means of spectral signals show obviously higher important weights than the other flame features. Ultraviolet signal is more important than visible and infrared signals for blend-type identification. SVM was adopted to identify the blend types. The method of ‘ReliefF + SVM’ was proposed to obtain the optimum feature vector. The number of optimum features can be reduced from 22 to 17 if only the prediction accuracy is considered. The optimum sampling number is 12. At the optimum feature vector (17 features) and the optimum sampling number (12), the average prediction accuracy of the five fuels is 99.67%. The results demonstrate that combining SVM and flame emission spectrum is suitable for online blend-type identification during co-combustion.

As renewable energy sources (RESs) penetration increases in the power system, the transmission system operators face new challenges to ensure system reliability and flexibility while ensuring high utilisation of uncertain RES generation. Controllable transformers with on-load tap changers and phase shifting capability are the promising flexibility tools to keep the system acceptable security and flexibility levels by controlling the voltage levels and energy flow. The AC optimal power flow (AC OPF) with detailed modelling considerations such as the bus voltage magnitude by including these devices is challenging. This study develops the AC OPF model to propose a robust flexibility optimisation framework for daily scheduling problem with uncertain wind energy sources. Nevertheless, the proposed formulation representation is an intractable mixed integer nonlinear programming (MINLP) while it includes AC grid constraints and the augmented modelling of the mentioned transformers. Accordingly, the proposed MINLP problem has been converted into a mixed-integer linear program where a certain level of solution accuracy can be achieved for the available time budget. The effectiveness of the proposed method is demonstrated using a modified 6-bus and IEEE 118-bus test systems.

This paper presents a novel robust model reference adaptive system (MRAS) technique for rotor speed estimation of direct torque control (DTC) of an induction motor drive used for solar PV powered water pumping. The maximum power point tracking (MPPT) of PV array is assured by a proposed P&O algorithm, which has improved tracking time without deviation during insolation change. Moreover, an additional loop is incorporated in the MPPT control, which provides an additional feature of derating the panel, which consequently controls the flow rate. The effect of parameter variation e.g. change in rotor resistance, stator resistance and the rotor time constant on the stability of overall system, is analysed and tested. The MRAS involves fluxes estimation and uses the same machine parameters which are involved in DTC. The elimination of speed sensor and parameters adaptation make the overall induction motor drive (IMD) suitable for such application. The stability of the system is assured by Lyapunov's stability criterion and the stability of parameters adaptation is shown by Bode plot and well-known Popov's stability criterion. Therefore, the reduced sensors (voltage and current sensors) based proposed system with deviation-free MPPT technique and with flow rate controller, is modeled, simulated, and experimentally verified.

Recently, subsynchronous interaction (SSI), a type of stability issue caused by interactions between power electronic converters and weak grids, has attracted great concerns. Many efforts have been made to use impedance/admittance-based methods for its modelling and analysis. However, most impedance/admittance models (IM/AMs) are aimed at higher-frequency dynamics and do not reflect the coupling effects between sub- and super-synchronous frequencies or the outer control loops, which, as indicated in this work, have significant impacts on the characteristics of SSI. To fill the gap, this study derives the explicit frequency-coupled AM for a typical grid-tied voltage-sourced converter by taking the coupling effects and outer-loop controls into full account and further investigates their impacts on the subsynchronous stability. The model itself and its effectiveness in predicting the stability of SSI have been validated with detailed electromagnetic transient simulations.

Microgrids (MGs) are regarded as the best solution for optimal integration of the renewable energy sources into power systems. However, novel control strategies should be developed because of the distinct inherent feature of MG components in comparison to conventional power systems. Although the droop-based control method is adopted in the MG to share power among distributed generation units, its dependency to grid parameters makes its implementation not as convenient as that in conventional power systems. Virtual impedance has been proposed as the complementary part of droop control in MGs. In this study, adaptive virtual impedance is designed considering its effects on the system performance in the MG including: (i) decoupling active and reactive power control by making the grid X/R ratio high, (ii) maximum transferable power through the feeder, (iii) stability concern and (iv) precise reactive power sharing in different operating modes as well as smooth transition from connected mode to islanded mode (IM). To this end, a novel method is proposed to determine the reactive power reference of distributed generation (DG) units according to their contribution in reactive power sharing in IM. In addition, simulation in MATLAB/Simulink environment is conducted to assess the performance of the control system.

The ever increasing power demand and stress on reducing carbon footprint have paved the way for widespread use of photovoltaic (PV) integrated microgrid. However, the development of a reliable protection scheme for PV integrated microgrid is challenging because of the similar voltage-current profile of PV array faults and symmetrical line faults. Conventional protection schemes based on pre-defined threshold setting are not able to distinguish between PV array and symmetrical faults, and hence fail to provide separate controlling actions for the two cases. In this regard, a protection scheme based on sparse autoencoder (SAE) and deep neural network has been proposed to discriminate between array faults and symmetrical line faults in addition to perform mode detection, fault detection, classification and section identification. The voltage-current signals retrieved from relaying buses are converted into grey-scale images and further fed as input to the SAE to perform unsupervised feature learning. The performance of the proposed scheme has been evaluated through reliability analysis and compared with artificial neural network, support vector machine and decision tree based techniques under both islanding and grid-connected mode of the microgrid. The scheme has been also validated for field applications by performing real-time simulations on OPAL-RT digital simulator.

The geographic suitability brings the offshore wind farm (OWF) and marine current farm (MCF) together with their aggregated power fed to grid simultaneously in most relevant energy harnessing infrastructures. However, stability assessment of the integrated system is a major concern due to the integration of stochastic and intermittent sources with parametric uncertainty. Bridge-type fault current limiter (BFCL) has consolidated their application for a suitable enhancement of stability margin for most modern supply systems. In this article, a detailed modelling of the integrated system is carried out in the presence of BFCL along with consideration of uncertainty as well. A robust H∞ controller design strategy for stability assessment of grid-connected OWF and MCF in the presence of parametric uncertainties is presented in this article. Linear matrix inequality (LMI) conditions are derived in the context of evaluating the robust controller gain with respect to desired robust stability margin. The efficacy of the controller design is compared with that of H∞ loop shaping and conventional P-I control through different case studies with simulation followed by real-time digital simulator (RTDS) validation.

The power output from the wind turbine in distributed generation (DG) resources is intermittent in nature, which adversely affects the system frequency in an interconnected system. Hence, it is important to study the system dynamic performance when DG resources are connected to the existing power system. This study presents the load frequency control of the three-area thermal–thermal–hydro system with DG resources in area 1. Proportional integral fractional derivative (PID ^μ ) controller is proposed as a secondary controller. System dynamics are compared among integral, proportional integral (PI), PI derivative (PID), fractional order PID (PI ^λ D ^µ ) and PID ^μ controllers whose parameters are optimised simultaneously using nature inspired ant lion optimiser (ALO) technique. The analysis shows the competitive performance of PI ^λ D ^µ and PID ^μ controllers. Furthermore, the PID ^μ controller parameters are optimised using hybrid ALO-pattern search technique, which outperforms the ALO optimised PID ^μ controller. A flexible AC transmission system device called gate controlled series capacitor performs better than an interline power flow controller. The studies show that the gate controlled series capacitor placed in all lines is its optimal location. The system dynamics are improved considerably with the incorporation of high voltage direct current link, the transient droop of the hydro governor. The PID ^µ controller effectively handles the parametric variations, random load and wind power profiles.

Recently, the electromechanical oscillations are becoming the primary concerns in power grids due to the integration of renewable energy generations (REGs). The inherent characteristics of REGs, e.g. low or no inertia, stochastic generation, could lead to the lower damping margin in power systems. A supplemental control such as power system stabiliser or power oscillation damping (POD) controller is widely applied to augment the damping margin in power systems. However, the PSS or POD using local signal is not adequate to damp the oscillation contributed from different sources. Hence, a wide-area damping controller can be employed in this context. Nonetheless, the wide-area controller suffers from communication failure. Therefore, the wide-area controller with resilient to communication failures is inevitable. This study proposed a wide-area POD design method considering resiliency. A modified differential evolution algorithm is employed to synthesise the wide-area damping control. The two-area and Java-Indonesian (three-area) power systems are used to evaluate the performance of the proposed controller for oscillation damping. From the results, it is evident that the critical mode(s) of the system successfully damped by employing the proposed controller. It is also found that the proposed controller is robust against communication failures.

To meet the increase in peak electricity demand, reduce fossil fuel emissions in Oman, and as an initiative taken by the government, by 2030 15% (3000 MW) of the total energy mix (20,000 MW) should be generated from renewable energy resources. It is crucial for the stakeholders and photovoltaic (PV) enthusiast to predict the return on investments and its performance in the local climatic conditions. In this study, a case study has been presented where different factors under local climatic conditions are studied. The results showed that the output power degradation for all modules is around 1.96%/year, which is almost double compared with European countries. Electrical analysis of different PV technologies showed that multi-crystalline silicon technology installed in hot-and-dry climate is degrading (around 2.54%/year) faster, while thin-film technology (CdTe) has shown lowest degradation (average of 0.8%/year) compared with any other PV technology. Furthermore, infrared image analysis showed that the presence of hot cells in PV modules is also a significant contributing factor in PV degradation rates. Severity of interconnect breakage tests confirm the increase of the series resistance of PV modules, which further contributes to the reduction of short-circuit current and thus PV maximum output. power.