Optimal linear control in stabilizer design

Abstract

E lectric power systems are highly nonlinear systems and constantly experience changes in generation, transmission, and load conditions, which causes power system analysis and especially control system synthesis to be extremely laborious. Various design methods and algorithms were developed that are based on different models of electric power systems (linear, non-linear, single machine, multiple machines). The most common method of improving stability of the power system is the synthesis of the turbine and generator control systems, because of the high effectiveness and relatively low cost of these elements. The synthesis and construction of the effective synchronous generator and turbine controller is a very difficult task due to following problems: I Large variation of the possible operating conditions I Large variety of disturbances that can occur in power systems I Variation of plant parameters as a result of power network configuration changes I Difficulty with working out mathematical models capable of adequately describing the generator under various operating conditions I State of the art of classical methods for designing the control systems, which usually turns out to be impractical and inefficient. This article proposes an approach to robust power system stabilizer (PSS) design. The following four groups of control are considered as the solution of these difficulties. Classical Control The synthesis method is based on a transfer function that describes a generator and turbine with constant parameters. The classical controllers allow achieving effective control and ensuring stability of the power system , but these controllers are optimal only for one operating condition, and they cannot modify their dynamic properties during operation. The following is a very short description of the considerations and procedures used for selection of the PSS parameters. The phase compensation block should provide the appropriate phase-lead characteristic to compensate for the phase lag between the exciter input and the generator electrical (air-gap) torque. The first step in determining the phase compensation is to compute the frequency response between the exciter input and the generator electrical input. Based on this characteristic, the phase-lead compensation parameters are chosen. The phase characteristic to be compensated varies to some extent with system conditions. Therefore, a characteristic acceptable for various system conditions is selected. The derivative block with inertia serves as a high-pass filter, with the time constants T 5 and T 6 high enough to allow signals associated with oscillations in ω r to pass unchanged (these parameters are not critical and …