Y-connected modular multilevel converter (Y-MMC) is a new topology of direct AC/AC power conversion, with broad application prospects in fractional-frequency transmission system. This study studies the mathematical model of Y-MMC and builds the port-controlled Hamiltonian model. Since vector control scheme can hardly ensure global stability, the interconnection and damping assignment passivity-based control (IDA-PBC) method is applied for controller design of Y-MMC. Three typical IDA-PBC strategies are then proposed, featuring the asymptotical stability of the desired equilibrium. To eliminate steady-state error, integrators are further added to the IDA-PB controller. Different from the previous research, the proposed method enables the decoupling of different-frequency components and the suppression of frequency leakage. Besides, the reactive power distribution coefficients are introduced to characterise the optimisation allocation of reactive power between arms. Finally, the effectiveness and superiority of the proposed control strategy are verified by both the simulation and experiment results.

The development of power networks encounters numerous problems. On one hand, they result from the high cost of land lots and difficulties in acquiring them from the proprietors. On the other hand, there are technical obstacles related to the constructing lines between new power sources (e.g. wind farms) and power systems. Wind farms are frequently localised in areas where the power network is poorly developed. These difficulties necessitate specific ways in which wind farms can be connected with the existing power systems. One of them lies in locating new lines within the existing line right of way. Owing to the electromagnetic impact between the lines such solutions are not frequent. Too long close-proximity sections are avoided to reduce the consequences this impact. This study is devoted to the influence of high-voltage transmission lines on other power lines. The localisation options in a 400 kV line right of way are analysed. The construction process and further exploitation of a 110 kV line in normal and short-circuit conditions of a 400 kV line are presented. The prospective touch voltages and body currents are determined for these conditions.

The frequency and voltage control of a standalone micro-grid with synchronous generator-based distributed generator and electronically interfaced generator is discussed. A centralised linear model predictive controller is employed. The controller design is based on the state space model of the micro-grid. To decrease the number of optimising variables and calculation time of optimal control trajectory, the design of the controller is realised with the help of orthonormal Laguerre polynomials. The numerical instabilities that arise during implementation and the possible ways to overcome them are discussed. The impact of different generator constraints on the controller operation is discussed. Formulation of the micro-grid model and identifying the appropriate inputs and outputs to the controller is discussed in detail with the help of an eight bus micro-grid.

Certain power system situations force protection schemes to mal-operate. Such mal-operations associated with back-up protection (BP) schemes might worsen the situation by initiating the cascading effect, damaging critical elements such as generation units, transformers etc. of the power system, or leading to complete collapse of the power system. To adapt to such a network structure, the relays which are going to participate in BP of transmission line have to evolve. Integration of protection systems, communication network, and computer technology has to be the approach for faster information sharing and decision making. Analysis of recent blackouts clearly shows the importance of advancement of wide-area measurement systems and adaptive nature of relaying. Synchro-phasors assisted BP scheme is proposed in this work, which helps the relays adapt according to the prevailing system situations and decisive action is taken considering security and dependability aspects of the relays.

In recent years, optimal sizing and location of reactive power resources are drawing much attention to help the operators of the utilities to enhance the power system operations. Therefore, this work presents a new version of grey wolf optimiser (GWO) to solve the problem of optimal reactive power resources sizing for power system operation enhancement. The proposed method which called improved grey wolf optimiser (IGWO) can be derived by modifying the exploration–exploitation balance in the conventional GWO to enhance its rate of convergence. Also, the weighted distance strategy is employed in the proposed IGWO to overcome the drawback of the conventional GWO. Optimal reactive power resources sizing problem is non-linear and non-convex optimisation problem. To solve this problem, different objective functions are used. These objective functions are minimisation of generating cost, minimisation of transmission power loss and voltage profile improvement. The validity and superiority of the proposed IGWO method are tested using three standard IEEE systems for normal and contingency conditions. Then the results are compared with those obtained from other recently published algorithms. The simulation results show that the proposed IGWO method is more accurate and efficient than other recently published algorithms.

In microgrid with distributed energy storage, the line reactance of each distributed energy resource (DER) is not same due to their different distance far from the loads. This will lead to the ageing rate of every battery to be not consistent. Some of the batteries first appear ageing, the rest of the battery also quickly ages if these ageing batteries are not replaced in time. This will eventually make the whole microgrid cannot work properly. To solve this problem, the idea is inspired by V-shape formation of a flock of birds. The equalisation of line reactance between each DER is achieved through adopting improved droop control based on virtual reactance, and the equalisation of the cycle life of batteries is achieved by weighted factor for power rating method based on hierarchical control. Compared with the method without virtual reactance control, the cycle life of batteries is extended by 80% after using the proposed method.

An industrial microgrid can be an effective way to introduce a high percentage of renewable power in the electrical energy supply of an industrial park. An optimal sizing process can be employed in the design phase of such a newly developed hybrid power system to assure the power system's technical and economic efficiency. While optimal sizing algorithms have been developed for different types of hybrid power systems, these often treat stand-alone systems and do not consider the socio-organisational drivers for inter-firm energy supply facilities. Here, a techno-economic optimisation is carried out using a genetic algorithm to determine the optimal system configuration of a grid-connected power system. The current development of the project Eiland Zwijnaarde in Ghent provides the basis for a concrete case study. The main results suggest that the optimal configuration consists of a significant share of renewable sources. A cogeneration unit can compensate the renewables’ intermittent behaviour and lower the thermal energy cost. Large-scale electrical storage is found not to be profitable under the used control structure. A gradual ingress of firms in the park and the subsequent sloped annual energy demand have a negative effect on the power system's fraction of shared facilities.

Modular multilevel converters (MMCs) provide advantages to reach medium-voltage operation increasing the power level in industrial applications. In this study, a tundish induction heating power supply based MMC (MMC-TIHPS) is investigated for heating molten steel. The equivalent model of MMC-TIHPS is established and the energy in horizontal and vertical directions are analysed. The heating control for molten steel consists of temperature increasing and constant temperature processes (alternatively called transient-state and steady-state operation). The main contribution of this study is to propose a direct power feedforward control based load current feedforward strategy for TIHPS. With this strategy, TIHPS can be controlled operating with full power to heat molten steel in transient state and guarantee the insulation effectiveness in steady state. Proper parameters of controllers are designed. Experimental results are conducted to validate the feasibility of MMC-TIHPS and the effectiveness of the proposed control method.

This study proposes a capacitor voltage synchronising control-based virtual synchronous generator (CVS-VSG) scheme for the inertial and primary frequency responses of type-4 wind turbine generators (WTGs) in wind power-dominated power systems. The CVS-VSG scheme is realised on type-4 WTGs based on the equations of motion of capacitor voltages. The type-4 WTGs are controlled as VSGs to emulate the inertial and primary frequency responses of conventional SGs. Active load sharing between Type-4 WTGs is achieved by a governor with capacitor voltage droop characteristics. Modal analysis was carried out on a test system with 73.58% wind power penetration. Simulation studies were undertaken to evaluate the performance of the CVS-VSG scheme on the test system subject to large disturbances.

In deregulated market environments, transmission system expansion planning becomes a troublesome task as transmission system operators lose their direct control over plant investments. Moreover, the increase in the share of renewable sources in electricity generation creates an uncertainty about future generation investments in terms of location and size. Assessment of transmission connection capacities, which determines the boundaries of new generation amount that can safely be connected from a region, is a mechanism that facilitates economic and reliable transmission expansion. In this study, use of two novel indices, namely region-based evaluation index (REI) and line-based evaluation index (LEI), is proposed for this purpose. REI aims to indicate the suitability of a region for new generation investments from a holistic point of view. Its calculation is based on the loadings of the lines under N − 1 conditions, and their overloading probabilities. LEI, on the other hand, is usable to assess each variation of the considered line's loading. By tracking LEI of a line, one can follow if a line's loading exceeds limits during contingencies, and observe if the loading benefits from additional generation. It allows identifying the weak points of the analysed system. The proposed methodology was demonstrated on projected Turkish Transmission Network model of 2026.

A dc microgrid is a low inertia system dominated by power converters. As a result, the change rate of the dc voltage is very fast under power variation. In this study, a distributed virtual inertia control is proposed to enhance the inertia of the dc microgrid and decrease the change rate of the dc voltage. The inertia of the dc microgrid can be enhanced by the kinetic energy in the rotor of the permanent magnet synchronous generators (PMSG)-based wind turbine, the energy stored in batteries and the energy from the utility grid. By introducing a virtual inertia control coefficient, a general expression of the inertial power provided by each controllable power sources is defined. The proposed inertia control is simply a first-order inertia loop and is implemented in the grid-connected converter, the battery interfaced converter and the PMSG interfaced converter, respectively. The small-signal model of the dc microgrid with the proposed inertia control is established. The range of virtual inertia control coefficient is determined through stability analysis. Finally, a typical dc microgrid is built and simulated in Matlab/Simulink, and the effectiveness of the proposed control strategy and correctness of the stability analysis are verified.

According to the present scenario, as demand for electricity has increased both in terms of base load energy and peak availability, it is vital to emphasise on the concept of demand side management (DSM). DSM assures efficient utilisation of facilities by managing the energy resources of the customers and optimally modifying their energy demand profiles. It is extremely useful for the power industry to integrate the smart grids with a DSM framework for achieving a sustainable energy goal. This study focuses on modelling of DSM using a day-ahead load shifting approach as a minimisation problem. For optimisation purpose, symbiotic organisms search (SOS) algorithm has been used. A platform independent of the control parameter is unique and exhibits paramount features of this algorithm. The formulated work has been tested on different areas of smart grid applications viz. residential, commercial and industrial types of customers. A comparison of outcomes, obtained from several algorithms with the proposed SOS algorithm, has been carried out on the basis of peak load reduction leading to lessening of a utility bill. Finally, it is proven that demand management, while using the SOS approach, exhibits better accuracy than the other algorithms compared in the present framework.

This study addresses the robust stability analysis for an islanded microgrid with droop-controlled inverter-based distributed generators (DGs). Owing to large load changes, microgrid structure reconfiguration, and higher-power demands, the low-frequency (LF) dominant modes of a microgrid stir toward unstable zone and make the system more oscillatory or even unstable. In this study, a robust two-degree-of-freedom (2DOF) decentralised droop controller, which is the combination of the conventional droop with a robust transient droop function, is utilised for each inverter-based DG unit. Unlike conventional tuning of 2DOF droop controllers, a new design procedure is proposed to robustly determine the transient droop gains to effectively damp the LF oscillatory modes of the islanded microgrid irrespective of disturbances, equilibrium point variations, and uncertain parameters of a microgrid. To mitigate the LF power oscillations at different microgrid conditions, inspired by Kharitonov's stability theorem, a robust D-stability analysis is performed to determine the specific ranges of the transient droop gains to provide a robustness margin for the disturbances, equilibrium point variations, and uncertain parameters of the islanded microgrid. Finally, digital time-domain simulation studies are performed in MATLAB/SimPowerSystems software environment to verify the effectiveness of the proposed method.

In this study, a comprehensive online multi-period power dispatch formulation that takes AC constraints, renewable energy, and ramping constraints into account is proposed. The AC power flow equations, voltage limits, and thermal limits are respected to ensure the obtained solution causes no static violation while guaranteeing transfer capability. A four-stage solution methodology is proposed to solve the non-linear constrained optimisation problem in which the thermal limit constraints are equivalently represented by active-set-based constraints in the third stage, and an adaptive homotopy-enhanced primal-dual interior point method (PDIPM) in solving power dispatch problem is presented in the fourth stage to reliably and efficiently obtain the solution. This solution methodology enhances both the robustness and speed of the PDIPM. The proposed four-stage solution methodology has been evaluated on several testing systems, ranging from a 30-bus system to a 3012-bus system with four time periods, with promising results.

Support vector machine (SVM) is very efficacious in pattern recognition and function estimation problems. However, its application to design efficient automatic generation control (AGC) scheme has not been investigated till date by the researchers and power engineers worldwide. Hence, in this study an early attempt has been made to present a combined design of optimal control and optimisation problem of least-squares SVM (LS-SVM)-based AGC of multi-area energy systems. The radial basis function (RBF) kernel is used to train the LS-SVM. To validate the efficacy of the approach, the proposed control method is implemented on various 2-area system models such as non-reheat thermal, reheat thermal and hydro-thermal energy systems. The trained LS-SVM RBF-kernel-based AGC is realised with 1% load perturbation in one of the control area and the obtained results are compared with multi-layer perceptron artificial neural network and the conventional integral based controller in order to show the supremacy of the proposed control design. Furthermore, the performance of the AGC design is examined considering the system non-linearities such as governor dead-band and generation rate constraint.

The demand response (DR) resources provided by modern industrial users tend to be diversified because of the popularisation of renewable energy. In this context, for the problem of satisfaction and uncertainty in the DR, a load-scheduling model considering load aggregators (LAs) is presented. In the multi-level DR scheduling system, the users and aggregator simultaneously participate in the decision; thus, the proposed methodology is a two-stage optimisation process. The first-stage optimisation considers the load interruption strategies of complex industrial processes, where a multi-objective optimisation model is established to coordinate the user benefits and satisfaction. This model is solved by non-dominated sorting genetic algorithm-II (NSGA-II) and the entropy weight double-base point method to obtain the optional interruptible load (IL) contracts for production processes. The second-stage optimisation maximises the economic returns of the LA considering the uncertainty of the resource's response, where chance-constraint programming is applied to solve the problem and select the appropriate IL contract. The effectiveness of the proposed methodology is examined according to the actual industrial production process. The multi-objective coordination effect of production load-scheduling is shown in an example. Finally, the effects of joint resource scheduling and different confidence levels on the profit of the aggregator are analysed.

The backlash, which is always present in the gears of drive-trains to enable smooth operation, may increase with time due to the wear and tear during mechanical power transmission. Accurate knowledge of the amount of backlash non-linearity is required in such systems for monitoring control applications as well as developing maintenance strategies. In this study, the modelling and online estimation of the backlash existing in the gear train of wind turbine driven doubly fed induction generator (DFIG) systems is presented. The estimation has been performed using the unscented Kalman filter considering the backlash as a parameter and augmenting it as a state into the dynamics. Local measurements of the DFIG system have been used to estimate the backlash. The performance and efficacy of the method have been investigated in different scenarios viz. system parameters, noise levels of the measurements and operating points of the DFIG system. The estimation has also been performed in an environment of the time-varying wind, modelled by Van der Hoven's spectral model. The estimation has been enabled by the bad-data detection and examined in the presence of unknown mechanical parameters of the shaft.

Operation flexibility is a prerequisite to ensure the success of a power market operation. Due to the variable generation mix, generation units that are flexible to meet the challenge of ramping and provide operation reserve are important in today's system operations. Generators participating in frequency regulation and other ancillary services might lose energy market revenue due to reserved margins, thus regulation performance should be evaluated and paid for. The actual value of operation flexibility is dependent on the system characteristics and the market mechanism. Using the information available in energy management system and combined cycle power plants, this study proposes a simple and practical method to estimate the variant fuel cost increase of combined cycle units to provide frequency regulation service in an island power system. Based on actual operation data, analysis results testify the fact that the efficiency of the combined cycle units is reduced at lower loads and the units are subjected to different fuel cost increases at distinct operation configurations. The proposed method is justifiable and applicable for assessing variant costs incurred in providing energy system flexibility.

Power systems are prone to cascading outages leading to large-area blackouts with significant social and economic consequences. Intentional controlled islanding (i.e. the separation of the system into sustainable islands) is an effective strategy to mitigate these catastrophic events. To ensure a correct separation, nonetheless, it is crucial to define a suitable time to split the system (i.e. to answer the when to island question). To consider the probability of the event, the reliability of the system components, the reliability of the information and communication technologies, and the potential economic costs of the event, answering the above question within a risk-based framework becomes critical. To date, however, this has not been done. This study proposes a risk-based methodology to define, in an adaptive manner, a suitable time to split the system following an event. This methodology complements the well-studied where to island question, resulting in an integral solution of the islanding problem. To illustrate the approach, the IEEE 118-bus dynamic system is adopted considering realistic security criteria. Simulation results demonstrate the effectiveness and flexibility of the methodology in identifying a suitable time for the creation of islands, which, in turn, results in the prevention of blackouts that would otherwise be obtained.

The primary aim of load frequency control (LFC) is to provide a good quality of electrical power to the consumers within a prescribed limit of frequency and scheduled tie-line power deviation. To achieve this objective, LFC needs highly efficient and intelligent control mechanism. Subsequently, here, a novel integral-tilt-derivative (I-TD) controller, fine-tuned by a powerful heuristic optimisation technique [called as water cycle algorithm (WCA)], is proposed for the LFC study of a two-area interconnected thermal-hydro-nuclear generating units. The studied system involves non-linearities like generation rate constraints, governor dead band, and boiler dynamics. To explore the effectiveness of the proposed controller, dynamic responses of the studied system, as obtained using I-TD controller, are compared to those yielded by other controllers such as tilt-integral-derivative and conventional proportional–integral–derivative controllers. The investigation demonstrates that the proposed I-TD controller delivers better performance in comparison to the other counterparts. Furthermore, sensitivity analysis is carried out to show robustness of the WCA tuned proposed I-TD controller by varying system parameters and loading condition. It is perceived that the proposed I-TD controller is robust and offers better transient response under varying operating conditions.

It is being increasingly recognised that the decentralised secondary frequency regulation (SFR) is more suitable for the expanding power systems. Decentralised SFR can more rapidly restore system frequency and damp generator rotor oscillations, as well as relieve the information-exchange stress between the control centre and widespread generators. Compared to other previously proposed methods, rotor angle droop (RAD) control is simpler and more straightforward. Similar to primary frequency control, the RAD controllers mainly distribute load variance among generators based on their rated capacity. However, they can rapidly and autonomously restore the system frequency without the intervention of a dispatching centre, which makes it more convenient for distributed generation (such as photovoltaic) to participate in frequency regulation. This study shows that the unbalance value between load forecast and real demand can be calculated through absolute rotor angle deviation. This calculated amount can then be reallocated to achieve more economical results. By calculating the area control error and changing the generation in different areas, the tie-line power flow (PF) can be controlled similarly. However, the fluctuation on the tie-line PF can be decreased since generators near the loads bear slightly more burden. This is helpful for tie-line control in large interconnected power systems.

A short-term planning model for restructuring distribution network based on heat maps is proposed here. A heat map, as the analytical tool of population density in a geographical map, is used to estimate the maximum air-conditioning load. Furthermore, the maximum load of each distribution transformer can be obtained. Two criteria for evaluating distribution network planning schemes are suggested. The first criterion is reflecting on the adequacy of the total transforming capacity of substations in a region. The second criterion is reflecting on the qualification of the structure of a 10 kV distribution network. A short-term planning model of the 10 kV restructuring distribution network is established when the first criterion is satisfied, whereas the second criterion is unsatisfied. The objective function is the minimum restructuring cost, and the constraints are the total and self-capacity requirements and the connectivity and radial structure of the 10 kV distribution network. Ultimately, a practical 10 kV distribution network is used to verify the effectiveness of the model.

This study presents a method for discriminative detection of direct current (DC) faults on voltage source converter-powered multi-terminal high-voltage direct current transmission systems using two fundamental guiding principles, namely instantaneous current-differential and travelling waves. The proposed algorithm utilises local voltage and current measurements from all transmission lines connected to a DC busbar, and current measurement from the DC side of the converter. The scheme operates at a sampling frequency of 96 kHz, which conforms with IEC 61869-9. No long distance communication is involved while measurements and signal exchange within DC substations are enabled by the utilisation of IEC 61850. Performance is assessed firstly through detailed transient simulation, using verified models of modular multi-level converters, hybrid DC circuit breakers and inductive DC-line terminations. Furthermore, practical performance and feasibility of the scheme are evaluated through laboratory testing, using the real-time Opal-RT hardware prototyping platform. Simulation and experimental results demonstrate that the proposed protection algorithm can effectively, and within a very short period of time (i.e. <1 ms), discriminate between busbar and line faults (internal faults), while remaining stable during external faults. Additionally, it has been demonstrated that IEC 61869-9 is suitable for enabling fast DC protection schemes incorporating travelling waves.

This study presents a new power transformer protection scheme based on extraction of positive and negative sequence components of superimposed differential currents. Different types of internal faults, magnetising inrush, and over-excitation conditions have been generated by modelling in service power transformer of power transmission system of India using PSCAD/EMTDC software package. The simulation results clearly indicate the efficacy of the proposed scheme in detecting different types of internal faults like turn-to-turn, inter-winding, line-to-ground, line-to-line, and line-to-line-to-ground. Together, the proposed scheme is competent to achieve effective discrimination between various external events (over-excitation condition and various magnetising inrushes) and internal faults. Moreover, it provides equally promising results during current transformer (CT) saturation condition as well as for different connection and rating of the power transformer. Further, it remains stable during errors in the CT and tap change condition. Additionally, authenticity of the proposed scheme has been evaluated using internal fault and magnetising inrush data recorded in the real field. At the end, comparative assessment of the proposed scheme with the existing and conventional techniques clearly indicate its superiority in terms of better sensitivity for internal faults and higher stability during external events.

A conformal array sensor suitable for partial discharge (PD) detection of electrical equipment was designed which displays multiple characteristics including compatibility with the surface of any carrier without affecting the performance of the carrier. Taking a cylindrical conformal array as an example, the simulation model was given and the array flow pattern of the cylindrical conformal array sensor was determined. Based on the Euler transform, the algorithm of multiple signal classification (MUSIC) was improved. An algorithm of array signal direction finding suitable for conformal array sensors was proposed and its performance under different signal-to-noise ratios and different array elements was simulated. The improved algorithm and conformal array sensor were used to simulate and test the PD signal. The results show that the algorithm and the conformal array sensor are suitable for PD detection of electrical equipment.