An approach to the initialization of dynamic induction motor models

Abstract

This paper proposes a steady state method as a solution to the problem of initializing the dynamic models of induction motors in transient stability studies. The results of the proposed method are compared to those obtained by two conventional initialization methods that are used in current production grade simulation programs, in a test power system that includes an industrial subsystem with a significant amount of induction motor loads. It is also shown in this paper that using a correct initialization method for these dynamic devices is important, because the choice of the method can modify the results of the dynamic time-domain simulation, and therefore the assessment of power system stability.

Improved Power Flow Initialization of Dynamic Studies with Non-linear Composite Load Model

“…In this article, the motor's air-gap power is readjusted during power flow iteration. It is important to point out that readjusting the air-gap power is basically needed in order to find a correct steady-state power flow solution, because the input active powers of induction motors are not fully independent of the voltage, as described in [11][12][13][14][15][16], but rather change due to the voltage variation. Moreover, their input powers are greatly changed according to the mechanical load characteristics, being connected to them.…”

“…The most drawing reactive power is particularly associated with the constant torque. According to the presented results, representing the induction motor model as constant input active power or constant slip [11][12][13][14][15][16] during power flow study may not be suitable to get the exact operating points, because these assumptions do not cover all their actual behaviors under a great variety of the mechanical torque profiles. Hence, the active and reactive powers and slip should be readjusted during power flow calculation.…”

“…The motor slip is set to a constant value so that only the motor's active and reactive powers are dependent on the updated terminal voltages during power flow calculation. More solutions put forward to solve the problem consider the motor's active power independently of voltage variations by means of constant mechanical torque assumption [13][14][15][16]. The reactive power and slip of each motor are updated at every iteration during the power flow calculation.…”

“…It has been well argued [6,[13][14][15][16][17] that inclusion of the induction motor model in power flow analysis for the purpose of initializing dynamic simulations is imperative for the correct dynamic assessments. Nevertheless, shortcomings with the existing approaches remain, since they may not be efficiently used to compute the exact operating condition of induction motors under various profiles of their mechanical loads, as recommended in [6].…”

“…The composite load model describing the behaviors of both induction motor and static voltage-dependent loads is considered. To get an exact active and reactive power input of each individual motor and static load, their scheduled active and reactive powers as well as slip are not kept fixed, similar to the mentioned techniques in [13][14][15][16], but rather are automatically adjusted along with their non-linear characteristics during each iteration. industrial power system.…”