Pichai Aree

Efficient and Precise Dynamic Initialization of Induction Motors Using Unified Newton–Raphson Power-Flow Approach

An accurate initialization is very important for power-system dynamic simulations. Using conventional power-flow model to initialize induction motors is not straightforward because an unavoidable mismatch between pre-specified reactive powers from power-flow calculation and the ones, actually required by motors. To overcome this problem, this paper presents a unified method for incorporating a nonlinear model of induction motors into Newton-Raphson (NR) power-flow algorithm, allowing precise steady-state solutions of power networks with induction motors to be solved simultaneously. The power-flow results of the extended algorithm are then compared with benchmark results for model verification. The ability of the extended algorithm is also demonstrated using IEEE-30 bus and 118 bus test systems with large groups of induction motor loads. The studied results indicate that the presented algorithm not only gives exact steady-state initialization without existence of the reactive power mismatches but also preserves powerful Newton-Raphsons quadratic convergence characteristics.

Effects of Large Induction Motors on Voltage Sag

Voltage sags is a problem affecting the electrical qualities. In this paper, effects of large induction motors on voltage sag characteristic are discussed. Moreover, the influences of different mechanical loads of the motors on voltage recovery are investigated. The study results show that reactive power contribution owing to the motors trapped flux linkage prevents fast collapse of the voltage, resulting in non-rectangular shape of sag. The motors negative torque induced during fault interval causes speed loss. The constant torque of mechanical load gives rise to the most speed loss, leading to a longer reacceleration and a great delay in voltage recovery.

Transient performance of self-excited wind-turbine induction generator under induction motor load

Self-excited induction generators (SEIG) are increasingly employed in remote areas for electricity production from wind energy. Analyzing of a stand-alone SEIG dynamic performance is largely limited to static load. This paper presents dynamic simulation of small SEIG feeding induction motor (IM) load. Mathematical models of SEIG, IM, and wind turbine are at first clearly implemented into Matlab/Simulink environment. The IM load coupled with constant and speed-squared mechanical torque are mainly considered under sudden connection to the SEIG. The study results reveal that the IM load with particular constant torque mostly causes a greatest fall of SEIG voltage during the sudden connection or decreasing of wind speed. The constant toque load also results in deepest and longest duration of SEIG voltage sag when the IM load is initially connected to the SEIG due to insufficient reactive power from the excitation capacitor. By applying an extra starting capacitor, the sufficient reactive power support can be obtained for successful startup of the IM load to the SEIG.

A novel second-order model of induction motor loads

In power system dynamic studies, it is necessary to represent induction motor loads with a standard reduced order model in order to reduce computational requirements. A third-order model, neglecting the stator transients, is often used. In this paper, the third-order model is further simplified into two second-order models, called as slip-flux-magnitude and slip-flux-angle models. The model derivations are given in detail. The dynamic responses of both models are compared with the higher third-order model for the cases of small and large horse power induction motor loads. The study results show that the slip-flux-angle model gives better approximation of the third-order model.

ELECTRICAL MODELING AND SIMULATION OF INDUSTRIAL POWER SYSTEM WITH MATLAB/SIMULINK PROGRAM

Power system dynamic simulations have been traditionally constrained to commercial package tools. While these tools are mostly efficient for large scale simulation, their component models are often encapsulated, and not possible to be examined and modified. For educational use, it is more important that the component modeling is transparent and flexible. Hence, in this paper, an object-oriented simulation of an industrial power system is constructed in Matlab/Simulink environment. The step-by-step implementation of Simulink block diagram model describing power system devices is fully given in detail. This presented approach is well suited to educational purpose in a way that students are able to modify their models and get quick start their simulations. The dynamic simulations with result and discussion are given through illustrative case study of voltage sag.

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

Abstract A power flow solution using a static constant MVA load model is a straightforward approach to initialize power system dynamic simulations. Using this model to represent induction motor load, however, may not be suitable due to a natural mismatch between initial bus scheduled powers and actual input powers that are computed afterward using their converged bus voltages. To avoid this mismatch occurrence, the Newton–Raphson power flow algorithm has been newly extended to incorporate non-linear characteristics of a composite load model in order to get an exact operating point of each individual induction motor and static load. The power flow solution of the applied 13-bus industrial power system reveals that the extended algorithm is capable of giving an exact active and reactive power input of the motors in correlation with their converged slips, internal bus voltages, and mechanical load torque characteristics and of voltage-dependent loads in relation to their exponent indices. Moreover, the computational efficiencies of the algorithm have been investigated using IEEE 14-bus and 57-bus networks. The results show that embedding induction motor and static exponent load models directly into the power flow mismatch function and Jacobian can improve computational efficiency since the power flow solution is well converged in a satisfactory quadratic manner.

Power flow algorithm with induction motors

This paper proposes an extended method of Newton-Raphson power flow algorithm to incorporate nonlinear model of induction motor loads. The proposed method is used for finding correct power system operating conditions, which can be employed for solving the problem of initializing the dynamic models of induction motor in stability studies. The power flow solution with a group of induction motors is demonstrated. Moreover, the computational efficiency of the extended algorithm has been investigated using IEEE-30bus system. The results show that this algorithm gives exact active and reactive powers of induction motors that are related with their converged slips, terminal voltages, and mechanical torque profiles. Furthermore, the extended algorithm shows a good convergent characteristic in quadratic manner.