Abstract
Modern power networks are becoming more complex and challenging to operate due to the increasing deployment of large-scale low-carbon technologies, expansion to supergrids, and the integration of High-Voltage Direct Current (HVDC) systems. Power system operators are constantly looking for new technologies and innovative approaches to improve power grid reliability, stability, and security. To address these challenges, the integration of HVDC grids within AC power networks potentially provides operators with more control over the power system. This integration also offers new and high-priority functions through controlling HVDC alongside AC power networks, such as enhanced control and optimization of the power system. Moreover, the integration of HVDC grids enables asynchronous power networks to interconnect at multiple contact points and achieve higher and more reliable power transfer capability.This approach can provide a more controllable network with an overall better performance than conventional high-voltage AC networks with point-to-point HVDC. However, with increased connectivity and interdependency between devices and subsystems, the risk of vulnerabilities and cyberattacks is also increased. Therefore, it is crucial to ensure secure system state information to ensure the integrity of power system operation. In addition, advanced cybersecurity measures and protocols must be implemented to protect the system against potential cyberattacks. These measures include developing and improving monitoring, threat detection, and response systems. Indeed, the integration of new technologies into power networks requires specialized monitoring tools with the Supervisory and Data Acquisition (SCADA) system and beyond to provide adequate observation of the system. In addition to conventional AC measurements, the SCADA system must also collect and process DC measurements. Moreover, the Energy Management System (EMS) needs to fully integrate the control functions of the multiterminal HVDC grid, such as the controls of the converter stations, and the control of the DC power flows into the state estimator and other functions. As HVDC technologies advance, this integration is in need of new development to integrate new monitoring and control tools that can provide a more comprehensive view of the system’s operation and ensure accurate decision-making. This thesis presents a unified two-stage Weighted Least Square (WLS) state estimation algorithm suitable for the Voltage Source Converter (VSC) and Line Commutated Converter (LCC) HVDC lines embedded into AC power systems. The mathematical formulas for the unified approach are derived for modeling the AC, DC, AC/DC conversion components, and control functions. The work aims to develop an enhanced paradigm of incorporating the HVDC systems into the AC network. It contains four aspects: (i) formulating a unified SE approach for multiple VSC-type converters embedded into the AC network that accounts for the power conversion losses and the VSC modulation control function; (ii) formulating a unified SE approach for an LCC-type HVDC link in an AC/DC grid that accounts for the firing control functions and the AC/DC power and voltage equality constraints; (iii) implementing a unified power system state estimator utilizing a hybrid two-stage state estimation approach that uses data from both SCADA and Phasor Measurement Units (PMUs) to be able to refine the results and bound several types of outliers; (iv) developing corresponding models for HVDC systems embedded into the AC power grid, particularly for LCC and VSC converters using commercial power flow software. This work starts by developing mathematical formulations of the power conversion losses and the modulation index for representing the characteristics of the VSC-based AC/DC power grid. Next, the LCC-type HVDC link embedded in the AC network is developed by accounting for the firing control functions, particularly the variation of LCC firing and extinction angles. Next, a two-stage WLS approach using both SCADA and PMU measurement is developed for the estimation solution. Network models for both an AC network with multiple VSC-type HVDC links and an AC network with LCC HVDC links are developed and tested. Comparative numerical results on multiple systems show the efficacy of the unified and operation approaches in achieving more accurate and reliable estimates of the AC/DC state, even in the presence of gross errors, incorrect control functions, outliers, and false data injection attacks.