Methods to Create Equivalent Models for Power System Studies

• Author / Creator

  Moghimi Haji, Moosa

• Adequate modeling of all of the power system components including generators, transmission lines, loads, and neighboring power systems is essential for power system analysis. With nowadays large interconnected power systems, it is common practice to represent only the study system with high accuracy and use simplified equivalent models for the neighboring systems. The type of the required equivalent depends on the type of the study they are intended for. For example, power flow studies require equivalent models at fundamental frequency, whereas high-frequency transient studies require frequency dependent network equivalents (FDNEs). This thesis research investigates methods to construct three equivalent models for power system studies. They are (1) measurement-based equivalent external system model for online steady-state power system analysis, (2) single-port and multi-port frequency dependent external network model for electromagnetic transient analysis and (3) measurement-based equivalent π circuit parameters estimation of parallel transmission lines. For the first subject, this research has developed an online network equivalencing method based on synchronized phasor measurement data. The phasor data is used to estimate and update a multi-port Thevenin equivalent circuit continuously. An important issue in implementing this method is that the external network should remain constant during the identification process. Therefore, a disturbance detection method is utilized to determine if noticeable changes have happened in the external system. For the second subject, a heuristic optimization method is used to find a FDNE from the frequency response data of an external system. An equivalent circuit consisting parallel branches with positive elements is considered and the problem is formulated as an over-determined nonlinear problem. A proper coding scheme is used and different optimization methods are applied and compared to choose the best one. For the multi-port case, a model consisting of all-positive and all-negative stable branches is considered to be able to fit the non-diagonal elements of the admittance matrix. The non-diagonal elements are fitted one by one and then the diagonal elements are fitted similar to a single-port problem. For the third subject, synchronized phasor data are utilized to find the π-circuit parameters of a newly constructed transmission line in parallel with an existing transmission line. The method utilizes the induced voltages as the excitation source and uses measurement data collected at both ends of the two parallel lines to estimate the unknown parameters. Different connections of the conductors of the new line are considered for collecting the required data. The parameter estimation problem is divided into two linear sub-problems which are solved using the least-squares method.

• Subjects / Keywords

  • Phasor Measurement Unit
  • Power System Equivalent Models
  • Transmission Line Parameter Measurement
  • Frequency Dependent Network Equivalent

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3Q52FS8D

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.