A microgrid (MG) is a building block of future smart grid, it can be defined as a network of low voltage power generating units, storage devices and loads. System of systems (SoS) is another concept involving large scale integration of various systems. In this paper, we provide an overview of recent developments in modeling and control methods of microgrid as well as presenting the reason towards incorporating MG into the existing grid. Various SoS control strategies when applied to MG are discussed.

Modeling and control of microgrid: An overview

The integration of renewable energy sources into power systems has gathered significant momentum globally because of its unlimited supply and environmental benefits. Within the portfolio of renewable energy, wind power is expected to have a soaring growth rate in the coming years. Despite its well known benefits, wind power poses several challenges in grid integration. The inherent intermittent and non-dispatchable features of wind power not only inject additional fluctuations to the already variable nature of frequency deviation, they also decrease frequency stability by reducing the inertia and the regulation capability. This paper closely examines these effects as well as the effect on tie-line flows and area control error, which causes a larger and longer frequency deviation in the integrated system. Further, the effect of wind power on frequency regulation capability at different penetration levels is also examined. The analytical and simulation results presented here provide some guidance on determining maximum wind power penetration level given a frequency deviation limit.

An Analysis of the Effects and Dependency of Wind Power Penetration on System Frequency Regulation

Optimization of Power System Stabilizers using BAT search algorithm

The paper presents a supplementary VSC-HVDC Power Oscillation Damping (POD) controller based on wide area measurement signals (WAMS). The controller is designed as Multi Input Single Output (MISO) using a Modal Linear Quadratic Gaussian (MLQG) methodology in order to target critical inter-area electromechanical modes. The approach has been tested on a large (16 machine, 68 bus) test network incorporating parallel HVDC/AC transmission and has shown improved damping compared to a traditional Power System Stabilizer (PSS) based controller structure utilizing local signals. The design process has incorporated the effects of wide area signal transmission delays. Variation in these signal delays and the complete loss of signals has been also investigated to establish the robustness of the WAMS based controller and its sensitivity to loss of signals. Extension of the controller to incorporate reactive power modulation has been investigated, as has variation in available active power modulation capacity. The proposed controller performance has been assessed through small and large disturbance analysis.

Damping of inter-area oscillations in mixed AC/DC networks using WAMS based supplementary controller

The Maisotsenko Cycle (M-Cycle) is a thermodynamic conception which captures energy from the air by utilizing the psychrometric renewable energy available from the latent heat of water evaporating into the air. The cycle is well-known in the air-conditioning (AC) field due to its potential of dew-point evaporative cooling. However, its applicability has been recently expanded in several energy recovery applications. Therefore, the present study provides the overview of M-Cycle and its application in various heating, ventilation, and air-conditioning (HVAC) systems; cooling systems; and gas turbine power cycles. Principle and features of the M-Cycle are discussed in comparison with conventional evaporative cooling, and consequently the thermodynamic limitation of the cycle is highlighted. It is reported that the standalone M-Cycle AC (MAC) system can achieve the AC load efficiently when the ambient air humidity is not so high regardless of ambient air temperature. Various modifications in MAC system design have been reviewed in order to investigate the M-Cycle applicability in humid regions. It is found that the hybrid, ejector, and desiccant based MAC systems enable a huge energy saving potential to achieve the sensible and latent load of AC in humid regions. Similarly, the overall system performance is significantly improved when the M-Cycle is utilized in cooling towers and evaporative condensers. Furthermore, the M-Cycle conception in gas turbine cycles has been realized recently in which the M-Cycle recuperator provides not only hot and humidified air for combustion but also recovers the heat from the turbine exhaust gases. The M-Cycle nature helps to provide the cooled air for turbine inlet air cooling and to control the pollution by reducing NOx formation during combustion. The study reviews three distinguished Maisotsenko gas turbine power cycles and their comparison with the conventional cycles, which shows the M-Cycle significance in power industry.

Overview of the Maisotsenko cycle – A way towards dew point evaporative cooling

Gas turbines have become increasingly popular in the different power systems, due to their lower greenhouse emission as well as the higher efficiency, especially when connected in a combined cycle setup. With increasing installations of gas turbines scheduled in different countries, the dynamics of the gas turbines become increasingly more important. In order to study such dynamics, accurate models of gas turbines are needed. This paper presents a comparative analysis and an overview of various models of gas turbines published in different literature.

Overview and Comparative Analysis of Gas Turbine Models for System Stability Studies

Although fuzzy logic has been successfully implemented in many industries, the acceptance of fuzzy logic within the power industry has met with limited success due to the requirement for prior information about an extremely complex system. A decentralized fuzzy logic controller (FLC) proposed in this paper has been designed, however, using a systematic analytical method based on a performance index in order to bypass the need for prior knowledge about the system. The proposed FLC tracks speed deviations to zero in order to stabilize the power output of the generator, while, at the same time, it controls and stabilizes the terminal voltage of the generator. This paper introduces an analytical method for the design of an FLC that successfully stabilizes both voltage and power oscillations following small and large disturbances in a power system. Simulations are performed with a multimachine power system, which includes a four-machine and a ten-machine (New England) system. The results obtained clearly demonstrate the effectiveness of designed FLCs in stabilizing the system. The responses of the system with FLCs are also compared with those obtained using classical power system stabilizers (PSSs) tuned by a conventional linear sequential tuning method (LSM) and optimization-based method.

Fuzzy Logic Controller for Decentralized Stabilization of Multimachine Power Systems

Many different types of gas turbines (GTs) are currently in use in power systems worldwide. These gas turbines can be broadly classed as single shaft GT (heavy duty GT) or twin shaft GT (aero-derivative). Due to the different construction of the two types of GT, their responses to the same operational disturbances can differ widely. Modern electronic governors offer wide scope for utilizing the GT to provide a contribution to network support in terms of damping provision and post-fault recovery, features that currently are not included in governor control performance specifications. In order to assess such capability, models capable of yielding more detailed information about GT dynamic behavior than those presently available are needed. This paper presents validated GT models developed from first principles based on the underlying physical processes that dictate the dynamic responses of GTs. The models are validated against manufacturer factory test data and differences in the dynamic behavior of the two major types of GTs are explored. In addition, phase compensated governors are implemented to explore the feasibility of employing such devices in a realistic GT operational scenario.

Validated Models for Gas Turbines Based on Thermodynamic Relationships

Road map for tuning power system controllers

The system stability is becoming an increasingly important issue in the deregulated power systems. Locally tuned controllers however, may not be able to meet the demands for robust stability of the system with increased level of uncertainties and coordinated tuning of large number of controllers is becoming necessary. Various optimisation based methods for coordinated tuning of controllers had been reported in the literature in the past and discussed separately. This work compares three commonly used forms of the objective function for coordinated tuning of PSSs to determine the effectiveness of the optimisation procedure. In addition, the optimisation-based method (s) are compared with the linear sequential method (based on the residues of the open loop transfer function) for coordinated tuning of PSSs. Both methods are tested on a four-machine two-area system developed in Matlab/simulink environment. The methods are compared in terms of ease of tuning, effectiveness and duration of the tuning procedure.

S.K. Yee

Papers

Overview and Comparative Analysis of Gas Turbine Models for System Stability Studies

Fuzzy Logic Controller for Decentralized Stabilization of Multimachine Power Systems

Validated Models for Gas Turbines Based on Thermodynamic Relationships

Road map for tuning power system controllers

Comparison of the optimisation and linear sequential method for tuning of multiple PSSs