C. P. Diduch

Sensitivity of failure detection using generalized observers

Abstract The sensitivity-robustness problem in analytical redundancy based fault detection is considered. To overcome the limits on achievable sensitivity imposed by the structure of classical state space observers, a new General Observer structure is proposed, which provides additional degrees of freedom in shaping the observer sensitivity. This structure is particularly useful in applications where there exists uncertainty in the system dynamics and external disturbances. A parametrization of all stabilizing general observers is given and the design process is formulated as a minimum observer sensitivity problem which is the dual to the minimum sensitivity control problem. A synthesis procedure is formulated by applying the H ∞ optimization theory.

Smart grid: Challenges, research directions and possible solutions

Power system is migrating from the conventional grid to the smart grid creates many active research areas to realize the objectives and the expected requirements from it. Different challenges facing the transformation of the conventional grid into a smart grid exist and need to be addressed by future research. This paper identifies the challenges facing the development of the smart grid, future research directions and suggests possible solutions to these challenges therefore realizing the objectives and the expected requirements of the smart grid.

Passive method-based islanding detection of Renewable-based Distributed Generation: The issues

In response to the Clean Energy Act, the penetration of Renewable-based Distributed Generators (RDGs) into the electric power grid is expected to continue to increase, resulting in reduced system losses, reduced transmission congestion and improved system efficiency; however, the intermittent nature of RDGs introduces significant variability that complicates the development of islanding detection schemes compared to conventional or non-renewable-based distributed generators (DGs). This manifests in the form of degraded reliability and power quality. Active methods where disturbances are injected into the grid for detecting islanding operations are not suitable for RDGs because they lead to power quality degradation. On the other hand, passive methods using local measurements do not introduce disturbances into the grid and are inexpensive; however, their performance may be compromised when operating in distorted environments. This paper presents a comprehensive survey of passive-based islanding protection schemes that have been proposed in the literature. The paper investigates the performance of the islanding detection schemes in the context of degraded power quality that will occur with the increased penetration of RDGs into the electric grid.

A new islanding detection approach using wavelet packet transform for wind-based distributed generation

Methods for detecting island in an electric power system are classified as active, passive or hybrid. For certain applications, passive methods are sometimes favored over other detection methods because they are cheap, simple and do not affect the power quality of the electric power system. This paper introduces an islanding detection approach based on wavelet packet transform using only local measurements of voltage and current at the point of common coupling. A new index named node rate of change of power defined in the time-frequency domain is introduced to quantify the rate of change of output power of the distributed generation (DG). The new index has been evaluated in seven different case studies including island case. The presented results have shown that the new index is effectively capable of determining the island case from other types of disturbances.

Parameter identification of thermal models for domestic electric water heaters in a direct load control program

This paper investigates an approach for identification of physical models of domestic electric water heaters (DEWHs) that are used to provide aggregated regulation services. The model is used within a direct load control (DLC) algorithm to estimate and forecast the water usage and temperature of individual water heaters. Individual physical models are used instead of aggregated models to allow the DLC algorithm to minimize the impact on customers by customizing the control of each water heater to individual water usage patterns. A single-zone lumped-parameter thermal model was considered for a single element DEWH. Two scenarios are investigated: i) when measurements of water temperature and heater power consumption are available, and ii) when measurements of only heater power consumption are available. The problem is challenging because water usage patterns cannot be measured directly and are governed by the behaviour of individual customers.

Failure detection and isolation: a new paradigm

A new approach to the failure detection and isolation problem or FDI is presented that combines parametric and nonparametric methods. The system is modeled as an interconnection of components that are subject to parametric failures. The FDI scheme is implemented in three stages. A diagnostic model is first developed to characterize the evolution of a feature vector and influence matrix as parameters in each component are subject to failures. Next a residual is generated using a parity equation and it is shown that the residual is a linear function of the change in the diagnostic parameters. In the third stage, isolation of faults is accomplished by finding the maximum correlation between the residual and estimates of the residual generated using a number of failure hypotheses. The development of the diagnostic model, a technique for identifying the diagnostic model using input-output measurements and its application in FDI is a significant contribution of the paper.

A new impedance-based approach for passive islanding detection scheme

This paper presents a new approach for islanding detection that is based on monitoring measures of impedance at the point of common coupling (PCC). A frequency dependent model that characterizes the change in circuit topology when an island occurs is developed as a first step in systematically selecting impedance metrics and thresholds for islanding detection. To implement passive islanding detection, the monitoring operation exploits the presence of harmonic distortion in the current and voltage at the PCC as a basis for computing measures of impedance at frequencies where there is sufficient harmonic content. Unlike signals based schemes that rely on heuristics, the proposed approach is based on an analytic model that reflects the interconnection topology. The main contribution of the work is the development of an analytic model that reflects the interconnection topology of distributed generators (DGs) with the electric power system (EPS) for DGs that include power converters and DGs that do not include power converters.

Sensitivity-robustness in failure detection: a frequency domain approach

The sensitivity-robustness problem, with application in control systems failure detection, is considered. A structure called the general observer is introduced and shown to have additional degrees of freedom in shaping the observer sensitivity compared to conventional state-space estimators. A complete design procedure which ensures a robust estimation against noise and unmodelled dynamics is formulated using factorization theory and H infinity optimization.<<ETX>>

Performance evaluation for grid impedance based islanding detection method

This paper develops an approach for islanding detection based on measurements of the frequency dependent impedance at the point of common coupling (PCC) that exploits the presence of harmonics introduced by the electric power system (EPS) and harmonics introduced by the distributed generator (DG). The approach is new: i) an analytic model for the frequency dependent impedance is derived from the interconnection topology and this may be used as a basis for selecting features of the impedance that change when islanding occurs, and ii) the variation of a frequency dependent feature is used to characterize a non detection zone (NDZ) and iii) the load parameter space is used to compare the NDZ of the grid impedance based scheme with under/over frequency schemes. Although the focus is passive islanding detection, it also encompasses active schemes where certain harmonics are intentionally injected rather than inherent.

A passive islanding detection index based on variation of signal energy

A new index for passive islanding detection is proposed. The approach exploits the inherent harmonic distortion produced by grid-connected power converters as well as the frequency dependent changes in the grid impedance as seen by the distributed generator before and following islanding. The new index is computed from the variation of signal energy over a certain band of frequencies contained within a virtual power signal. The virtual power signal is obtained from measurements of voltage and current at the point of common coupling. The approach is validated via simulation and is demonstrated on a 7kW distributed generator system.