G.N. Bathurst

Trading wind generation in short term energy markets

Even with state-ofthe-art forecasting methods, the short-term generation of wind farms cannot be predicted with a high degree of accuracy. In a market situation, these forecasting errors lead to commercial risk through imbalance costs when advance contracting. This situation is one that needs to be addressed due to the steady increase in the amount of grid-connected wind generation, combined with the rise of deregulated, market-orientated electricity systems. In the presence of imbalance prices and uncertain generation, a method is required to determine the optimum level of contract energy to be sold on the advance markets. Such a method is presented here using Markov probabilities for a wind farm and demonstrates substantial reductions in the imbalance costs. The effect of market closure delays and forecasting window lengths are also shown.

Modelling of HVDC transmission systems in the harmonic domain

This paper describes an HVDC link modelled within the harmonic domain using a full Newton method for solution. The solution is rapid and robust for a variety of cases and shows excellent agreement with time domain simulation. The HVDC link is also modelled with an extended control system for realistic specification of the steady-state operating point.

Modeling of bipolar HVDC links in the harmonic domain

A method for accurate calculation of the harmonics generated by a bipolar HVDC link is described. The method illustrates the importance of including detailed representation of the mutual coupling effects of DC transmission lines, even when smoothing reactors are included. The overall solution is achieved by means of a unified Newton algorithm in the harmonic domain.

A multifrequency power flow of general applicability

A widened harmonic power flow algorithm is described capable of determining the interaction between the fundamental, harmonic, and interharmonic frequency components. The algorithm is multiphase and can include any number of nonlinearities. The New Zealand power system is used to illustrate the ability of the algorithm to determine the harmonic interaction between an HVDC link and an aluminum smelter.

A modular approach to the solution of the three-phase harmonic power-flow

This paper describes a modular algorithm for solution of power systems containing active nonlinear devices such as power converters. The solution is a unified real-valued Newton method allowing simultaneous solution of electrical and nonelectrical variables. The algorithm is demonstrated using the reduced equivalent of a real power system which includes both load-flow busbars and a large uncontrolled rectifier. The solution process is fast, robust and exhibits excellent convergence.

A graphical interface for interactive AC/DC system harmonic analysis

Detailed modelling of the harmonic cross-modulation process performed by a power converter, especially under unbalanced operation, is a difficult task. Although it can be achieved using time domain analysis, it is too slow for interactive work using PCs, and does not represent the frequency response of the components accurately. A fast accurate harmonic domain solution is therefore the best option. This paper presents an interactive program that combines the harmonic domain solution with pre- and post-processing graphics to analyse and display AC/converter/DC system harmonic interactions.

A comparison of converter models for the derivation of the AC system harmonic impedances

The effect of converter impedance is mostly ignored when performing harmonic analysis, as it is complicated to calculate, and a common assumption is that it has minimal effect. This paper compares the use of simplified techniques against a rigorous calculation of the converter impedance and demonstrates their effect on the frequency response of the system.