Cooperation of Wide Area Control with Renewable Energy Sources for Robust Power Oscillation Damping

In this paper, a Wide Area Control (WAC) scheme cooperates with Renewable Energy Sources (RESs) to achieve a robust power oscillation damping. The WAC signals are synthesized by a two-level hierarchical controller which utilizes global measurements from all the installed synchronous generators to maximize the performance of the generators’ local controllers. In the proposed WAC scheme, the dynamic operation of RES is also taken into consideration for the implementation of WAC signals, in order to make the generators “aware” of the RES oscillations. Further, the local controller of the RES is modified in order to utilize the available reactive power for compensating any local voltage oscillations, leading that way to a controller which does not require any WAC signals. The performance of the proposed scheme has been tested and validated in the IEEE 9-bus test system where it is indicated that the proposed scheme improves the power system’s dynamic stability

Dynamic Load Modelling Using Real Time Estimated States

Dynamic load models are necessary for accurate monitoring and control of the system during various events as well as for better understanding the behavior and the characteristics of the system. In this paper, a realistic approach of load modelling using real time estimated states is studied. Since Phasor Measurement Units (PMUs) are not installed yet at every bus, a linear state estimator is used to provide the state of the buses without PMUs. The overall impact of the real time estimated states and the inaccurate load model parameters are studied on the IEEE 39-bus dynamic test system. In addition, the realistic approach of load modelling is enhanced by using various load types while errors that affect the estimated states, such as line parameter errors and measurement gross errors are also considered. Furthermore, a sensitivity analysis with inaccurate load model parameters is performed to show their effect on the results of load modelling

Performance Enhancement of MAF based PLL with Phase Error Compensation in the Pre-Filtering Stage

The large scale integration of Renewable Energy Sources (RES) requires sophisticated control techniques for efficient power transfer under faults and/or off-nominal grid conditions. A RES is efficiently integrated to the grid via proper control of the Grid Side Converter (GSC) by accurately estimating the grid voltage phase angle. Moving Average Filter (MAF) based Phase Lock Loop (PLL) techniques provide reduced complexity, however, they present disadvantages under specific grid fault conditions. The most recent MAF based technique is the EPMAFPLL, which provides improved dynamic response and reduces the phase error under off-nominal grid frequencies. However, the EPMAFPLL presents high phase and frequency overshoot at the time of fault. Furthermore, inaccurate harmonic mitigation under off-nominal grid frequencies was not investigated in EPMAFPLL. A modified EPMAFPLL (EPMAFPLL Type 2) is proposed in this paper. The modified EPMAFPLL accurately compensates the offset errors under off-nominal grid frequencies, offers lower frequency overshoot and faster dynamics under faults. In addition, it provides accurate compensation of grid voltage harmonics under off-nominal grid frequencies

Semantically-enhanced Configurability in State Estimation Structures of Power Systems

The estimation of the states of an electric power system, that is, the magnitude and angle of the voltage at all buses, is a very critical input to many monitoring and control functions of power systems. The recently witnessed rapid deployment of synchronized measurement technology (SMT) in power systems, has led to research advancements in the state estimation technology that introduce the notion of hybrid state estimation. These techniques incorporate the synchrophasors provided by the Phasor Measurement Units (PMUs) in the state estimation process, thus improving the state estimation accuracy. However, both the traditional as well as the hybrid techniques, assume a pre-defined configuration and characteristics of the measurement devices. This work explores how semantic modelling and reasoning techniques may contribute to the online configuration of the state estimation architectures given the available measurement capabilities at each moment

Intentional Controlled Islanding and Risk Assessment: A Unified Framework

Power systems are prone to cascading outages leading to large-area blackouts, and intentional controlled islanding (ICI) can mitigate these catastrophic events by splitting the system into sustainable islands. ICI schemes are used as the last resort to prevent cascading events; thus, it is critical to evaluate the corresponding system risks to ensure their correct operation. This paper proposes a unified framework to assess the risk of ICI schemes. First, a novel ICI method to create islands with minimum power imbalance is presented. Further, a risk assessment methodology is used to assess the probability and impact of the main operational modes of the ICI scheme. The unified framework provides insights on the benefits of implementing ICI, considering the uncertainties related to its reliability. The ICI scheme is demonstrated using the IEEE 9-bus system. The proposed unified framework is then fully deployed on the actual power system of Cyprus. Multiple case studies on the real network are created to demonstrate the adaptability and robustness of the proposed scheme to different system conditions. The adoption of the unified framework highlights that the system risk significantly reduces with the ICI in service, even when the reliability uncertainties associated with the scheme are considered.J. Quirós-Tortós, P. Demetriou, M. Panteli, E. Kyriakides and V. Terzija, "Intentional Controlled Islanding and Risk Assessment: A Unified Framework," IEEE Systems Journal., pp. 1-11, Oct. 2017. © 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works

Three-phase phase-locked loop synchronization algorithms for grid-connected renewable energy systems:A review

The increasing penetration of distributed renewable energy sources (RES) requires appropriate control techniques in order to remain interconnected and contribute in a proper way to the overall grid stability, whenever disturbances occur. In addition, the disconnection of RES due to synchronization problems must be avoided as this may result in penalties and loss of energy generation to RES operators. The control of RES mainly depends on the synchronization algorithm, which should be fast and accurately detect the grid voltage status (e.g., phase, amplitude, and frequency). Typically, phase-locked loop (PLL) synchronization techniques are used for the grid voltage monitoring. The design and performance of PLL directly affect the dynamics of the RES grid side converter (GSC). This paper presents the characteristics, design guidelines and features of advanced state-of-the-art PLL-based synchronization algorithms under normal, abnormal and harmonically-distorted grid conditions. Experimental tests on the selected PLL methods under different grid conditions are presented, followed by a comparative benchmarking and selection guide. Finally, corresponding PLL tuning procedures are discussed.This work was supported by the supported by the Research Promotion Foundation (RPF) of Cyprus under Project KOINA/SOLAR-ERA.NET/1215/06