Chen-Ching Liu

Steady-state voltage stability regions of power systems☆

Abstract This paper deals with the steady-state (small-disturbance) voltage stability of power systems. A simple example is proposed to interpret the real-world phenomena of voltage instability. For general interconnected power systems, the voltage stability is studied via linearized dynamical equations of on-load tap changers and steady-state decoupled reactive power flow equations. A set of conditions is derived for a hyperbox of tap settings and load bus voltages to satisfy the steady-state stability requirements. The results can be used to construct steady-state voltage stability regions for the security monitoring of power systems.

Analysis of tap-changer dynamics and construction of voltage stability regions

The destabilizing behavior of on-load tap-changers is an important mechanism responsible for the voltage collapse of power systems. The authors use a nonlinear dynamic model of the tap-changer, impedance loads, and decoupled reactive power-voltage relations to reconstruct the collapse. Based on the proposed M-bus network model, results presented include (1) a criterion for voltage stability, (2) a method to obtain a voltage region, and (3) qualitative characterizations of the equilibria.<<ETX>>

Steady-state voltage stability regions of power systems

The steady-state voltage stability of a power system is studied via linearized dynamical equations of on-load tap changers and steady-state decoupled reactive power flow equations. A set of conditions is derived for a hyperbox of tap settings and load bus voltages to satisfy the steady-state stability requirements. The results can be used to construct steady-state voltage stability regions for the security monitoring of power systems.

Analysis of dynamic voltage collapse mechanism for a three-bus power system

Abstract The phenomenon of voltage collapse is reconstructed based on a three-bus power system with dynamic on-load tap-changers (OLTC). Utilizing nonlinear stability techniques, the monotonic fall of bus voltages is derived from instability of the dynamic system. The exact stability region of the system is constructed which demonstrates the concept of voltage stability region as a tool for the prevention of voltage collapse.

Inductive learning in power system voltage control

The application of inductive learning to voltage control and contingency assessment of power systems is considered. The first application discussed is the identification of correct control amount for remedial actions. The inductive learning application is intended to obtain a decision tree which identifies a proper value of the low voltage limit. It is shown that learning capability can be incorporated into a voltage control expert system (VCES) by including a decision tree. The VCES obtains the appropriate low voltage limit from a precomputed decision tree. The software implementation of th VCES with learning capability is described. The VCES with a learning module is integrated into the dispatcher training modulator environment. The second application is an attempt to use inductive learning to identify critical operating conditions/outages which may cause voltage problems in a power system. The selected attributes, generation of the training and test sets, and the numerical results are summarized.<<ETX>>

Qualitative assessment of voltage problems due to contingencies in a power system

The results of applying decision trees to qualitative assessment of the impact due to contingencies in a power system are described. Two applications are considered: (1) the assessment of the voltage deviation at a target bus and (2) the selection of contingencies causing voltage limit violations. The results show that selection of relevant attributes is important in building effective decision trees. Also, the decision tree approach can acquire accurate classification rules for selecting contingencies when a system is somewhat structured and restricted, like the IEEE 30-bus system.<<ETX>>

An extended study of dynamic voltage collapse mechanisms

Voltage collapse is a dynamic phenomenon involving several mechanisms such as load dynamics, generation VAr limit, and on-load tap changer. These mechanisms have been analyzed for a simple power system by the authors (27th Conf. on Decision and Control, Dec. 1988). In the present study another mechanism, relay operation, is added, and the load model is generalized. Each mechanism is investigated separately using a phase-space approach. Their effects are then combined to explain how a voltage collapse arises.<<ETX>>

Bounding the processing time of forward-chaining rule-based systems

The authors propose an analytical method for evaluating the processing time of forward-chaining rule-based systems. An upper bound on the computations is presented. Numerical examples are presented which point out the importance of rule and data structures in the efficient implementation of rule-based systems. It is concluded that very similar rule-base implementations can have significantly different computational characteristics. Thus, careful analysis should be applied to an online rule-based system, such as the Voltage Control Expert System for which fast response is important.<<ETX>>