State Estimation for Hybrid VSC Based HVDC/AC Transmission Networks

Abstract

As the integration of High Voltage Direct Current (HVDC) systems on modern power networks continues to expand, challenges have appeared in different fields of the network architecture. In the Supervisory, Control and Data Acquisition (SCADA) field, software and toolboxes are expected to be modified to meet the new network characteristics. Therefore, this paper presents a unified Weighted Least Squares (WLS) state estimation algorithm suitable for hybrid HVDC/AC transmission systems, based on Voltage Source Converter (VSC). The mathematical formulas of the unified approach are derived for modelling the AC, DC and converter coupling components. The method couples the AC and DC sides of the converter through power and voltage constraints and measurement functions. Two hybrid power system test cases have been studied to validate this work, a 4-AC/4-DC/4-AC network and Cigre B4 DC test case network. Furthermore, comparison between the fully decentralized state estimation and the unified method is provided, which indicated an accuracy improvement and error reduction.

State Estimation for Hybrid VSC Based HVDC/AC: Unified Bad Data Detection Integrated With Gaussian Mixture Model

“…The converter Power Coupling (hpc(x)) is presented as a zero-constraint function between the AC/DC power and the converter losses as shown in ( 7) [8], [34].…”

“…where P convloss is the converter losses and can be calculated using an experimental statistical approach available in [4], [8], [10]. In Fig.…”

“…The PMUs based state estimators are discussed in [21] and [22]. HAM and WLS algorithms are used in [23] and [8] respectively as a unified state estimator for VSC-HVDC/AC, both argued that a unified (centralized) approach increase the estimation accuracy due to the higher redundancy rate of measurements.…”

Communication Requirements for a Hybrid VSC Based HVDC/AC Transmission Networks State Estimation

“…Then a centralized decoupled AC/DC state estimator takes time equal to the max(t SE−AC , t SE−DC ). However, in a coupled centralized approach further measurements are added such as voltage and power coupling constraints (available in [67]). It can be presented as shown in equation below:…”

“…The simulations were run on Intel Core i7-8750H, 2.20 GHz, GTX 1070 8 GB, and 16 GB RAM. The processing (estimation) time of an unified WLS is estimated based on the algorithm of this work [67], and implemented on Julia Optimization programming language [77]. The time performance is calculated for a 100 simulations on the Cigre B4 test case and shown in Figure 15 and Table 15.…”