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Stability analysis of microgrids based on real distribution network models and analysis of their model interactions are rarely reported in the published literature. Findings of such study is essential when designing robust primary and secondary controllers for distributed energy resources in microgrids. In this paper, a linearised model of a microgrid based on real 11 kV distribution feeder is presented, and the fidelity of the linearised model is validated against a detailed simulation model. A detailed eigenvalue analysis is performed to identify the dynamics and the stability of the microgrid. Eigenvalue sensitivity for various parameters, such as controller gains and network parameters are studied to identify the system stability margins and interactions among different distributed generators.

Series compensation using capacitor banks is a common technique used in power transmission systems, to improve the power transferring capability. However, it may lead to the generation of some natural frequencies due to the combination of inductor and capacitor. These frequencies are called as sub-synchronous frequencies which are below the power frequency of the power systems. They can give rise to sub-synchronous resonance (SSR). The SSR can cause physical damages to the power system equipment unless it is detected and mitigated prudently. This paper presents a robust controller which can be used to damp undesirable sub-synchronous oscillations. The small signal model required to design the controller is constructed using dynamic phasor approach. The performance of the controller is demonstrated using IEEE first benchmark model (FBM) for SSR studies. It’s shown that the proposed robust controller satisfactorily work under different operating conditions.

This paper presents a comprehensive analysis on the operating performance of three-phase Induction Motors (IMs) driven by unbalanced supply voltages. It is a well known fact that three-phase IMs are adversely affected by the presence of unbalanced supply voltages and it is required to derate the output power wisely for efficient and safer operation of the motor. There is a certain guidance given in NEMA MG1-1993 to decide a suitable derating level, however limitations and drawbacks of such practices have been identified. Although voltage unbalance is a well-defined concept, existence of numerous voltage unbalance conditions have led to problematic prediction of IM performance in terms of temperature rise and motor derating. Thus, different study approaches, their findings, limitations and shortcomings are critically reviewed in this paper in order to develop a comprehensive derating mechanism for three-phase IMs.

Even though solar power generation has become an emerging trend in the world, its penetration into the utility grid as a distributed generation source is not a satisfactory measure due to the inherent issues related to solar photovoltaic systems (SPVSs). In addressing these issues, microgrids have been identified as suitable integrating platforms for distributed, clean energy resources such as SPV. Different SPV and microgrid architectures are available for different applications depending on the resource availability and controllability. Reconfigurability is a concept that makes a system adaptable to two or more different environments by effectively utilizing the available resources. The review explains the applications of reconfigurable approaches on solar PV systems such as reconfigurable PV arrays, power conditioning unit (DC/DC converter, DC/AC inverter), microgrid controller and topology of distribution network with relevant studies. An analysis is also presented considering the unique features of reconfigurable systems in comparison to the static systems., Electrical engineering; Energy; Electrical systems reliability; Renewable energy resources; Renewable energy; Micro-grid; Problems related to solar PV; Reconfigurable architecture; Solar PV.

This paper presents an open source, freely downloadable, user friendly, MATLAB-based Power System Analysis Software (PSAS) for educational and research purposes of engineering undergraduate students. Using this software, users can familiar with four main analyses in power systems; (i) load flow analysis including Flexible Alternating Current Transmission System (FACTS) devices, (ii) transient stability analysis including stability margin calculation, (iii) small signal stability analysis, and (iv) Prony analysis. The above features have been implemented using standard bus systems; Single Machine Infinite Bus (SMIB) system, three generator nine bus system and two area four generator test system, where the user can select a test system at the beginning. The results of the developed software are validated using commercially available PSSE software.

This paper presents a software-based tool to educate undergraduate students about real-time monitoring in power systems. Large-disturbance rotor angle stability (transient stability) is used as the application of the developed monitoring tool. Two algorithms based on transient energy and Artificial Neural Network (ANN) are used to predict the transient stability of the power system under contingencies. First, the suitability of the aforementioned two algorithms for transient stability identification is demonstrated using simulation results of the 3-generator 9-bus test system and the 10-generator 39-bus test system. Then, this paper shows how the proposed transient stability monitoring algorithm is implemented in actual hardware, demonstrating the key aspects of real-time monitoring applications such as measurement, communication, data processing and display. The hardware setup is developed in such a way that the user can compare the transient stability status given by the display unit against the time-domain simulation result of the power system under the given contingency. Therefore, the developed monitoring tool is helpful for engineering undergraduate students to get a basic idea about power system monitoring in the real-time environment.

The impact of supply voltage unbalance (VU) on three-phase induction motors (IMs) is well known in terms of extra losses and associated derating to ensure that the motors do not prematurely fail. Theoretical studies, experimental results and standards exist in this regard. However, the approaches taken in the past are not seen be exhaustive now considering the modern tools such as Finite Element Modelling (FEM) software. Also, the relevant documentation available to-date on the subject does not cover the level of variability in the outcomes such as extra losses that can arise when an IM is subjected to the same level of VU that can be produced in a range of different ways. This paper emphasises the importance of Positive Sequence Voltage and the Complex Voltage Unbalance Factor (CVUF) in analysing the losses of a motor under different VU scenarios. Statistical analysis of the losses of three-phase IMs operating under different supply voltage unbalance scenarios is presented in this paper giving special focus to the behaviour of the core loss and copper loss. Two dimensional (2D) FEM is used to model the electromagnetics of the motor and Bertotti core loss model is used to evaluate the core losses. The outcomes of this analysis will be useful in the process of developing improved and cost effective mechanism of derating for mains connected three-phase IMs as well as in their design optimisation.

This study presents a simple approach to modify the Prony algorithm to extract dominant low-frequency modes present in ring-down oscillations in power systems. The proposed approach is based on the observation that true modes present in the ring-down oscillations appear consistently, irrespective of the order of the Prony model. It is shown that the consistently appearing modes can be extracted using a sorting method. The improved Prony algorithm which has the feature of extracting only the true modes present in the input signal is utilised to propose an oscillation monitoring algorithm in this study. The suitability of the proposed oscillation monitoring algorithm for real-time monitoring of low-frequency inter-area oscillations is demonstrated using synthetic signals and simulated signals of different test systems.

Fast Valving (FV) mechanism of steam turbines is considered to be one of the most effective actions for enhancing the security of a power system subsequent to disturbances. It plays a significant role in mitigating the impact of severe disturbances by instantly decreasing steam turbine power, thus ensuring the power system stability. There is a direct relationship between the settings of Over-Speed Protection Control (OPC) unit of steam turbines and the control functions of FV. This paper proposes a generalized simulation-based procedure to determine the optimum intermediate valve actuation timings of the FV control action. A coal-fired thermal power plant has been used as the case study and the accuracy of the settings made using the proposed approach has been demonstrated using actually happened contingencies in a real power system. Finally, it is concluded that the proper selection of actuation timings of intermediate valves for FV scheme has a significant effect on enhancing frequency stability under transient conditions.

Transient stability of an electrical power system refers to the ability of the system to settle at the stable equilibrium point in the post-fault system subsequent to a specific fault scenario. This stability problem can be studied either as a system stability or a structural stability problem. In this paper, the concept of Lyapunov Exponents (LEs) is used to analyze the transient stability of IEEE 3-generator 9-bus and IEEE 16 generator 69 bus benchmark systems. A spectrum of LEs is calculated from the mathematical models and the Largest Lyapunov Exponent (LLE) being negative implies the exponential stability of the post-fault power system. The system stability regions for specific fault scenarios are determined using the invariance property of the LEs from the initial conditions. Furthermore, the structural stability regions in terms of parameters of the pre-fault system dynamic equations are also determined. This study demonstrates that the concept of LEs can be used as a novel method to determine if the post-fault power system is within the stability region of attraction of the new stable equilibrium point, and hence to determine the stability region. It is also proposed that the largest average exponential rate calculated over a short time window is a sound approach for early prediction of the stability.

Matrix Pencil (MP) and Hankel Total Least Squares (HTLS) algorithms approximate an input signal as a sum of decaying sinusoidal oscillations. This paper presents a simple technique to improve these algorithms for extracting only the true oscillations present in the input signal. The rationale behind the improvement is the observation that the true modes present in the input signal appear consistently irrespective of the order of the linear approximation used in MP and HTLS algorithms. It is shown that the modes appearing consistently can be extracted using a sorting method. The improved MP and HTLS algorithms presented in this paper are used for monitoring the low-frequency oscillations in power system in an online environment. The performances of the proposed algorithms are demonstrated using synthetic signals and simulated signals of different test systems.

Transient rotor angle stability assessment and oscillatory rotor angle stability assessment subsequent to a contingency are integral components of dynamic security assessment (DSA) in power systems. This study proposes a hybrid algorithm to determine whether the post-fault power system is secure due to both transient rotor angle stability and oscillatory rotor angle stability subsequent to a set of known contingencies. The hybrid algorithm first uses a new security measure developed based on the concept of Lyapunov exponents (LEs) to determine the transient security of the post-fault power system. Later, the transient secure power swing curves are analysed using an improved Prony algorithm which extracts the dominant oscillatory modes and estimates their damping ratios. The damping ratio is a security measure about the oscillatory security of the post-fault power system subsequent to the contingency. The suitability of the proposed hybrid algorithm for DSA in power systems is illustrated using different contingencies of a 16-generator 68-bus test system and a 50-generator 470-bus test system. The accuracy of the stability conclusions and the acceptable computational burden indicate that the proposed hybrid algorithm is suitable for real-time security assessment with respect to both transient rotor angle stability and oscillatory rotor angle stability under multiple contingencies of the power system.

Lyapunov Exponents (LEs) measure the exponential rates of divergence or convergence of nearby trajectories in state-space models. The study presented in this paper investigates the applicability of this concept to power system transient stability analysis. It is shown that the Largest Lyapunov Exponent (LLE) of the post-fault system subsequent to a given fault scenario is independent of the fault clearing time up to the Critical Clearing Time (CCT). Furthermore, the set of exponentially stable equilibrium points of the post-fault system corresponding to different load-generation combinations of the pre-fault system can also be characterized by this LLE. The study compares the LEs with the conventional Time Domain Simulation (TDS), Extended Equal Area Criterion (EEAC) and Potential Energy Boundary Surface (PEBS) methods. It is shown that LEs give reliable results. Further, the power system stability regions can be determined using the invariance of LEs within the same stability region.