H∞ voltage control of a direct high-frequency converter

Providing a secure power network is a demanding task but as network complexity is expected to grow with the connection of large amounts of distributed generation so the problem of integration, not just connection, of each additional generator becomes more protracted. A fundamental change to contemporary network architectures may eventually become necessary and this will provide new opportunities for power electronic converters to deliver advanced management and new power flow control features. Direct resonant converters (Dang 2005), could be used in novel devices such as the Active Transformers (Garlick 2008). The key to the successful exploitation of these devices will be their versatility, controllability and cost efficiency

A model-based approach to wind turbine condition monitoring using SCADA data

Modern wind turbines are complex aerodynamic, mechanical and electrical machines incorporating sophisticated control systems. Their design continues to increase in size and they are increasingly being positioned offshore where the environment is hostile and where there are limited windows of opportunity for repair and maintenance activities. Condition monitoring is essential offshore if Wind Turbines (WTs) are to achieve the high reliability necessary for sustained operation. Contemporary WT monitoring systems already provide vast amounts of data, the essential basis of condition monitoring, much of which is ignored until a fault or breakdown occurs. This paper presents a model-based approach to condition monitoring of WT bearings. The backbone of the approach is the use of a least squares algorithm for estimating the parameters of a discrete time transfer function (TF) model relating WT generator temperature to bearing temperature. The model is first fitted to data where it is known no problems exist. It is then used in predictive mode and the estimates of the bearing temperature are compared with the real measurements. The authors propose that significant discrepancies between the two are indicative of a developing problem with the bearings. The promising experimental results achieved so far indicate that the approach is viable

The architecture and control of large power networks with distributed generation

This paper briefly summarises the evolution of transmission and distribution networks since the late 19th century, and explains that the introduction of significant amounts of distributed generation may bring about a future fundamental change to the network architecture. Providing a secure power network is a demanding task, but as network complexity is expected to grow with the connection of large amounts of distributed generation, so the problem of integration, not just connection, of each successive generator becomes more protracted. A fundamental change to the network architecture may eventually become necessary and a new architecture, perhaps based on power cells, containing generation, energy storage and loads has been proposed by some researchers. This paper describes a novel power cell interface. It makes the case for the conventional power transformer to be replaced by an Active Transformer, the objective being to provide a more controllable, flexible and robust connection that will facilitate greater network management and business opportunities, and new power flow control features. The Active Transformer design is based on an a.c. link system described by Thomas Lipo in 1986 and an a.c.-a.c. high-frequency direct converter design demonstrated by Dang in 2006. It consists of a resonant, supply-side converter, a high frequency transformer and a resonant, load-side converter. This paper describes a model of the Active Transformer, built in Simulink®, and presents the results of simulations that demonstrate its action to control current in a resistive load

Architecture and control of large power networks with distributed generation

The architecture of the UK's passive power network has taken over one hundred years to evolve through a process of demand and technology led development. In the early years of electrical power, distribution systems were islands of distributed generation, often of different voltages and frequencies. Increasing demand for electrical power and the need to reduce distribution costs eventually led to the standardisation of frequency and voltages and to the connection of the island systems into a large network. Today's power networks are characterised by their rigid hierarchical structure and unidirectional power flows. The threat of climate change is driving the demand for the use of more renewable energy. For electricity production, this is achieved through generation using more wind, biomass, tidal and solar energy. This type of generation is often referred to as Distributed Generation (DG) because it is not a centralised facility connected to the high voltage transmission grid but a distributed source connected to the lower voltage distribution network. The connection of DG to the distribution network significantly alters the power flow throughout the network, and costly network reinforcement is often necessary. The advancement in the control of electrical power has largely been facilitated by the development of semiconductor power electronic devices and has led to the application of "Flexible Alternating Current Transmission Systems (FACTS), which include such devices as "Static Var Compensators" (SVC) and Static Compensators (STATCOM), for the control of network voltages and power flows. Providing a secure power network is a demanding task, but as network complexity is expected to grow with the connection of high levels of DG, so the problem of integration, not just connection, of each successive generator becomes more protracted. A fundamental change to the network architecture may eventually become necessary, and a new, more active network architecture, perhaps based on power cells containing local generation, energy storage and loads, has been proposed by some researchers. The results of an historic review of the growth of power networks, largely in the UK, forms the basis of a case to replace the conventional power transformer with an Active Transformer that will provide a more controllable, flexible and robust DG connection and (i) will facilitate greater network management and business opportunities, and new power flow control features. The Active Transformer design is based on an a.c. link system and an a.c.-a.c. highfrequency direct resonant converter. This thesis describes a model of the converter, built in MATLAB and Simulink®, and used to explore control of the converters. The converter model was then used to construct a model of the Active Transformer, consisting of a resonant, supply-side converter, a high frequency transformer and a resonant, load-side converter. This was then used to demonstrate control of bi-directional power flow and power factor control at the Grid and Distribution Network connections. Issues of robustness and sensitivity to parameter change are discussed, both for the uncompensated and compensated converters used in the Active Transformer. The application of robust H∞ control scheme proposed and compared to a current PI control scheme to prove its efficacy