Estimation of Load Characteristics in Power System by Using Normal Operating Data

Abstract

It is important to include the behavior of load in studies of loss of generation and consequent load shedding and also in studies of long-term dynamics of a power system. This paper proposes a method which estimates load-frequency and load-voltage characteristic constants separately at the same time, by using normal operating data.
The power system can be represented as an equivalent model which is composed of a major bus load, an equivalent impedance and a voltage source behind it. When the load capacity is small enough compared with the total system capacity, variations of active power of the load have little effect on frequency changes in the total system. Voltage changes behind the equivalent impedance are caused by variations of the operating condition in the external system, so voltage changes are independent to variations of active and reactive power of the major bus load under the state of nominal frequency and voltage. So coherences between them decreases to zero according to the increase of data in number and it is possible to estimate the load-frequency and load-voltage characteristic constants. Necessary measuring periods and accuracies of estimation are clarified and the effectiveness of the proposed method is verified by simulation results.