Search

SUMMARY Motors are widely utilized in industry. When the mechanical load oscillates, a motor injects interharmonic currents to the grid and becomes an interharmonic source. The interharmonic currents have an important impact on power quality. This paper, respectively, presents the spectrum of the stator interharmonic currents of the induction and synchronous motors. The mathematical models of both motors, which are nonlinear when the load torque oscillates, are linearized. Then, the spectrum expressions of the interharmonic currents of the two types of motors are derived, respectively. On this basis, the relationship between load torque oscillations and the spectrum of the stator interharmonic currents is analyzed. The effect of the various induction motor steady output powers on the spectrum of the interharmonics is investigated. Simulation results validate the theoretical analysis. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Summary: An improved dynamic power flow (DPF) model considering governor nonlinearity is presented. The proposed DPF model is intended for the analysis of post‐contingency power flow after primary frequency regulation. During the regulation process, the governors play an important role while it is difficult to involve the nonlinear segments in the static method. So in this paper, the governor model with amplitude‐limit and deadband is simplified and included in DPF model. Using the describing function method, the effect of deadband is equivalent to an increment of regulation coefficient. The amplitude‐limit is handled by iterative correction. Applying the algorithm to a three‐node system, a case study of load variation proves the effectiveness of the algorithm. Simulations on a practical grid in southern China further demonstrates the practicability and applicability. The algorithm enhances the accuracy of post‐contingency power flow analysis and provides effective analysis for the static security of power system. [ABSTRACT FROM AUTHOR]

Summary: The frequency stability of power system is usually jeopardized by the active power deficit for major disturbances. To deal with these events, adaptive load shedding schemes are effective, and the steady frequency prediction is considered as the prerequisite. However, none of previous predictive methods has taken into consideration the nonlinear segment that may distort system frequency response. This paper investigates the effect of speed governor deadband and presents a method to evaluate its effect on the steady frequency. Based on the wide area measurement system measurements, a predictive algorithm of steady frequency is studied. It utilizes the modified regulation coefficient to consider the governor deadband effect and employs instantaneous measurements of postdisturbance to calculate the steady frequency directly. Simulations on the IEEE‐9 system and a practical system of China have solidified the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]