Abstract:The simulation precision of the classic load model (CLM) is affected by the increasing proportion of installed energy storage capacity in the grid. This paper studies the all-vanadium redox flow battery (VRB) and proposes an equivalent model based on the measurement-based load modeling method, which can simulate the maximum output of the VRB energy storage system and fit the external characteristic of the system precisely in the occurrence of large disturbance and continuous small disturbance. The equivalent model is connected to CLM to form a generalized synthesis load model (GSLM), which considers the parameters of distribution network and reactive power compensation. Compared with CLM, GSLM has better structures and can describe the load characteristics of distribution network with energy storage system more precisely. Simulation results validate the effectiveness and good parameter stability of GSLM, and show that the higher the proportion of energy storage in the grid is the better description ability GSLM has.

Abstract:This paper proposes a novel controllable crowbar based on fault type (CBFT) protection technique for doubly fed induction generator (DFIG) wind energy conversion system connected to grid. The studied system consists of six DFIG wind turbines with a capacity of 1.5 MW for each of them. The operation mechanism of proposed technique is used to connect a set of crowbar resistors in different connection ways via activation of controllable circuit breakers (CBs) depending on the detected fault type. For each phase of DFIG, a crowbar resistor is connected in parallel with a controllable CB and all of them are connected in series to grid terminals. The adaptive neuro-fuzzy inference system (ANFIS) networks are designed to detect the fault occurrence, classify the fault type, activate the CBs for crowbar resistors associated with faulted phases during fault period, and deactivate them after fault clearance. The effectiveness of proposed CBFT protection technique is investigated for different fault types such as symmetrical and unsymmetrical faults taking into account the single-phase to ground fault is the most frequently fault type that occurs in power systems. Also, a comparison between the behaviours of studied system in cases of using traditional parallel rotor crowbar, classical outer crowbar, and proposed CBFT protection techniques is studied. The fluctuations of DC-link voltage, active power, and reactive power for studied system equipped with different protection techniques are investigated. Moreover, the impacts of different crowbar resistance values on the accuracy of proposed technique are studied. The simulation results show that, the proposed technique enhances the stability of studied wind turbine generators and contributes in protection of their components during faults.

Abstract:High penetration of Converter Interfaced Generations (CIGs) presents challenges in both microgrid (μGrid) circuit and other system with CIG resources, such as wind farms and PV plants. Specifically, protection challenges are mainly brought by the insufficient separation between fault and load currents, especially for μGrids in islanded operation, and the short connection length in μGrids. In addition, CIG resources exhibit limited inertia and weak coupling to any rotating machinery, which can result in large transients during disturbances. To address the above challenges, this paper proposes a Dynamic State Estimation (DSE) based algorithm for protection and control of systems with substantial CIG resources such as a μGrid. It requires a high-fidelity dynamic model and time domain (sampled value) measurements. For μGrid circuit protection, the algorithm dependably and securely detects internal faults by checking the consistency between the circuit model and available measurements. For CIG control, the algorithm estimates the frequency at other parts of a μGrid using CIG local information only and then utilizes it to provide supplementary feedback control. Simulation results prove that DSE based protection algorithm detects internal faults faster, ignores external faults and has improved sensitivity towards high impedance faults when compared to conventional protection methods. DSE based CIG control scheme also minimizes output oscillation and transient during system disturbances.

Abstract:In this paper, a sensitivity matrix based approach is proposed to improve the minimum damping ratio. The proposed method also avoids burdensome deviation calculations of damping ratio of large-scale power grids when compared to the Small-Signal-Stability Constrained Optimal Power Flow (SSSC-OPF) approach. This is achieved using the Matrix Perturbation Theory (MPT) to deal with the 2nd order sensitivity matrices, and the establishment of an optimal corrective control model to regulate the output power of generating units to improve the minimum damping ratio of power grids. Finally, simulation results on the IEEE 9-bus, IEEE 39-bus and a China 634-bus systems show that the proposed approach can significantly reduce the burden of deviation calculation, while enhancing power system stability and ensuring calculation accuracy.

Abstract:Three-phase pulse width modulation converters using insulated gate bipolar transistors (IGBTs) have been widely used in industrial application. However, faults in IGBTs can severely affect the operation and safety of the power electronics equipment and loads. For ensuring system reliability, it is necessary to accurately detect IGBT faults accurately as soon as their occurrences. This paper proposes a diagnosis method based on data-driven theory. A novel randomized learning technology, namely extreme learning machine (ELM) is adopted into historical data learning. Ensemble classifier structure is used to improve diagnostic accuracy. Finally, time window is defined to illustrate the relevance between diagnostic accuracy and data sampling time. By this mean, an appropriate time window is achieved to guarantee a high accuracy with relatively short decision time. Compared to other traditional methods, ELM has a better classification performance. Simulation tests validate the proposed ELM ensemble diagnostic performance.

Abstract:Current and voltage waveforms recorded by intelligent electronic devices (IEDs) are more useful than just performing post-fault analysis. The objective of this paper is to present techniques to estimate the zero-sequence line impedance of all sections of a three-terminal line and the Thevenin equivalent impedance of the transmission network upstream from the monitoring location using protective relay data collected during short-circuit ground fault events. Protective relaying data from all three terminals may not be always available. Furthermore, the data from each terminal may be unsynchronized and collected at different sampling rates with dissimilar fault time instants. Hence, this paper presents approaches which use unsynchronized measurement data from all the terminals as well as data from only two terminals to estimate the zero-sequence line impedance of all the sections of a three-terminal line. An algorithm to calculate positive-, negative- and zero-sequence Thevenin impedance of the upstream transmission network has also been presented in this paper. The efficacy of the proposed algorithms are demonstrated using a test case. The magnitude error percentage in determining the zero-sequence impedance was less than 1% in the test case presented.

Abstract:The present-day power system is a complex network that caters to the demands of several applications with diverse energy requirements. Such a complex network is susceptible to faults caused due to several reasons such as the failure of the equipment, hostile weather conditions, etc. These faults if not detected in the real-time may lead to cascading failures resulting in a blackout. These blackouts have catastrophic consequences which result in a huge loss of resources. For example, a blackout in 2004 caused an economic loss of 10 billion U.S dollars as per the report of the Electricity Consumers Resource Council. Subsequent investigation of the blackout revealed that the catastrophe could have been prevented if there was an early warning system. Similar other blackouts across the globe forced the power system engineers to devise an effective solution for real-time monitoring and control of the power system. The consequence of these efforts is the wide area measurement system (WAMS). The WAMS consists of several sensors known as the phasor measurement units (PMUs) that collect the real information pertaining to the health of the power grid. This information in the form time synchronized voltage and current phasors is communicated to the central control center or the phasor data concentrator (PDC) where the data is analyzed for detection of power system anomalies. The communication of the synchrophasor data from each PMU to the PDC constitutes the synchrophasor communication system (SPCS). Thus, the SPCS can be considered as the edifice of the WAMS and its reliable operation is essential for the effective monitoring and control of the power system. This paper presents a comprehensive review of the various synchrophasor communication technologies, communication standards and applications. It also identifies the existing knowledge gaps and the scope for future research work.

Abstract:For maximum utilization of solar energy, photovoltaic (PV) power systems should be operated at the maximum power point (MPP) which can be achieved using maximum power point tracking (MPPT) methods. However, the occurrence of multi-peak on P-V curve of a PV array due to the changing environmental conditions such as being partially shaded increases the complexity of the tracking process. The global MPP cannot always be achieved by the conventional MPPT methods. Therefore a novel MPPT method for PV systems using flower pollination (FP) algorithm is proposed in this paper and the Levy flight is used to improve the convergence of FP algorithm. MPPT model of the PV system is established in MATLAB to verify the effectiveness of the proposed method, and the proposed method is compared with two well established MPPT methods. The simulation results indicate that the proposed MPPT method can quickly track the changes in external environment and effectively handle the partially shaded condition.

Abstract:With rapidly growing of Renewable Energy Sources (RESs) in renewable power systems, several disturbances influence on the power systems such as; lack of system inertia that results from replacing the synchronous generators with RESs and frequency/voltage fluctuations that resulting from the intermittent nature of the RESs. Hence, the modern power systems become more susceptible to the system instability than conventional power systems. Therefore, in this study, a new application of Superconducting Magnetic Energy Storage (SMES) (i.e., auxiliary Load Frequency Control (LFC)) has been integrated with the secondary frequency control (i.e., LFC) for frequency stability enhancement of the Egyptian Power System (EPS) due to high RESs penetration. Where, the coordinated control strategy is based on the PI controller that is optimally designed by the Particle Swarm Optimization (PSO) algorithm to minimize the frequency deviations of the EPS. The EPS includes both conventional generation units (i.e., non-reheat, reheat and hydraulic power plants) with inherent nonlinearities, and RESs (i.e., wind and solar energy). System modelling and simulation results are carried out using Matlab/ Simulink® software. The simulation results reveal the robustness of the proposed coordinated control strategy to preserve the system stability of the EPS with high penetration of RESs for different contingencies.