Advanced Linear and Nonlinear Control Design精品.pdf

Chapter 2 Advanced Linear and Nonlinear Control Design Rotor angle stability of a power system, as introduced in Chapter 1, concerns the electromechanical dynamics of generator rotors [2-1,2-2]. The rotors of all connected AC generators must operate at the same synchronous speed. Small oscillations between generator rotors occur frequently. Changes in the rotor angle relationship between generators are a function of generator loading, the distribution of loads in the network and the topology of the electrical network. The rotor angles between generators normally change very slowly as the system changes operating point through daily, weekly and seasonal cycles. Short-term transients will occur following a disturbance to the power system, and oscillations may arise from slowly evolving operating conditions. As is the case with essentially all physical phenomena, power system rotor angle stability is inherently a nonlinear control problem. The control problem in power system angle stability has several additional complicating factors. These include: • An accurate mathematical representation of an interconnected power system is usually of very high order, often containing several thousand state variables; • The system is multivariable, often containing numerous generators each with their own controllers; • The system is continuously time varying, with daily and seasonal cycles as well sudden short term changes; • The system often contains significant levels of noise due partly to the constant changing of many loads; • The system contains numerous nonlinearities, including saturation of generators, exciters, nonlinear power transfer characteristics and nonlinear load characteristics; • An interconnected power system covers a large geographic area, which may make communication and monitoring of the system difficult and expensive. Despite all of these difficulties, m