A. R. Wallace

Centralized and Distributed Voltage Control: Impact on Distributed Generation Penetration

With the rapid increase in distributed generation (DG), the issue of voltage regulation in the distribution network becomes more significant, and centralized voltage control (or active network management) is one of the proposed methods. Alternative work on intelligent distributed voltage and reactive power control of DG has also demonstrated benefits in terms of the minimization of voltage variation and violations as well as the ability to connect larger generators to the distribution network. This paper uses optimal power flow to compare the two methods and shows that intelligent distributed voltage and reactive power control of the DG gives similar results to those obtained by centralized management in terms of the potential for connecting increased capacities within existing networks

Optimal power flow as a tool for fault level-constrained network capacity analysis

The aim of this paper is to present a new method for the allocation of new generation capacity, which takes into account fault level constraints imposed by protection equipment such as switchgear. It simulates new generation capacities and connections to other networks using generators with quadratic cost functions. The coefficients of the cost functions express allocation preferences over connection points. The relation between capacity and subtransient reactance of generators is used during the estimation of fault currents. An iterative process allocates new capacity using optimal power flow mechanisms and readjusts capacity to bring fault currents within the specifications of switchgear. The method was tested on a 12-bus LV meshed network with three connection points for new capacity and one connection to an HV network. It resulted in significantly higher new generation capacity than existing first-come-first-served policies.

Efficiency and Dynamic Performance of Digitally Displacement Hydraulic Transmission in Tidal Current Energy Converters

Abstract Tidal current turbines extract kinetic energy from tidal current in much the same way as wind turbines do with wind. Tidal current velocities are by nature slow and variable, whereas electricity generation typically requires fast and steady rotary motion. This article investigates the performance of a hydraulic transmission system based on Digital Displacement™ technology, which allows variable speed of the tidal current turbine rotor while maintaining constant generator shaft speed. The case study of a generic horizontal axis tidal turbine is considered. Control strategies based on rotor variable speed are derived to optimize yearly power generation and to cope with short-term variations in stream velocity.

Climate change impacts on financial risk in hydropower projects

Limiting the emissions of greenhouse gases from power generation will depend, among other things, on the continuing and increased use of hydroelectric power. However, climate change itself may alter rainfall patterns, adversely affecting the financial viability of existing and potential hydro schemes. Previous work developed a methodology for quantifying the potential impact of climate change on the economics of hydropower schemes. Here, the analysis is extended to examine the potential for changes in project risk. A case study is presented that indicates that the applied climate change scenarios alter not only the mean financial performance of the scheme but also the financial risk facing it. Given that investors must balance project risk and reward, this finding has implications for the future provision of hydropower.

Quantification of voltage fluctuations caused by a wave farm connected to weak, rural electricity networks

This paper describes a wave-to-wire model of an array of wave energy converters developed in MATLAB/Simulink. The effects of connecting a 1MW wave farm to a weak, rural electricity network are investigated. Impacts of the wave farm on voltage quality are examined and both conventional and more intelligent control methods by which these impacts can be mitigated are discussed. The control methods compared are: constant voltage operation, constant power factor operation, On Load Tap Changing Transformer (OLTC) operation, automatic voltage and power factor controller (AVPFC) operation and fuzzy logic power factor controller operation. The applicability of these control methods are compared using certain indices - flicker severity index, voltage fluctuation index and global voltage regulation. Drawbacks of power factor control, voltage control and control using the OLTC transformer and the advantages of using more intelligent control methods, like the AVPFC or the fuzzy logic power factor controller, are established.

Modelling arrays of wave energy converters connected to weak rural electricity networks

This paper describes a modelling framework developed in Matlab/Simulink that has been used to study, analyse and improve the network integration of Wave Energy Converters (WECs). It presents and discusses a generic, time domain, resource-to-wire model that can be used to explore the effects of: increased device numbers, array size and physical positioning; and the adjustment of control parameters. The three-dimensional wave field is modelled as non-stationary, with statistical characteristics that are extracted from measured wave elevation time series to simulate increasingly realistic sea conditions. Each heaving buoy has high-pressure oil power take off with on-board energy storage, driving Doubly Fed Induction Generators (DFIGs). The results obtained from simulations using this model are used to demonstrate the overall effects of storage on real power production, and the effects of imaginary power control on network voltage profile. The opportunities for improved network integration are identified and discussed.