Power System Frequency Control and Stability Analysis With Increasing Renewable Energy Penetration Level

With the ever-increasing penetration level of renewable energy generation units and the replacement of traditional synchronous generators, the issues associated with the deteriorated performance of power system frequency regulation and potential grid frequency instability become more significant. In this dissertation, the inertial control algorithms are investigated and analyzed for power electronics converter in a renewable energy generation unit. The concept and design of Virtual Synchronous Generator are comprehensively discussed, such that the small-signal stability and frequency stability of power systems with high renewable energy penetration level can be enhanced. Moreover, both nonlinear dynamic model and small-signal linearization of Virtual Synchronous Generator controlled inverter system are derived, and key system parameters are identified. By imitating the mathematical model of a synchronous generator, some undesirable features are inevitably introduced in Virtual Synchronous Generator control. Therefore, the dynamic droop mechanism and Extremum Seeking based secondary control are proposed and implemented for Virtual Synchronous Generator to improve its stability margin as well as eliminating steady-state error after power system disturbances. Furthermore, since relatively large time constant is introduced in the active power loop of Virtual Synchronous Generator as system inertia, Virtual Synchronous Generator control becomes unsuitable for the direct application on the Type IV wind power system. The conflict between fast varying wind power input and slow dynamics of Virtual Synchronous Generator controlled inverter is further identified in this dissertation. Aiming to address the compromised ability of Virtual Synchronous Generator with a desirable inertial response to deal with fast-changing wind conditions, Virtual Synchronous Generator with multiple virtual rotating masses is proposed in order to improve the active power tracking performance as well as to boost inertial control of a wind power generator. The performance of proposed inertial control is verified in the modified 10MVA IEEE 14 bus power system. The assessment of the simulation results provides a deep insight into different inertial control methods while demonstrating the applicability of Virtual Synchronous Generator on wind power generation systems. The power system oscillation damping function initially provided by synchronous generators becomes unavailable with the increasing penetration level of renewable energy. Therefore, it is crucial to enable the oscillation damping capability of a wind or solar farm so that the stability and resiliency of a power system can be maintained. The power domain impedance, an effective measurement-based approach for the analysis of power system interarea oscillation, is investigated in this dissertation. Comparing to current prevalent analysis approaches for interarea oscillation, the power domain impedance method does not require model approximation or aggregation, where accurate system oscillation modes can be described. Several case studies have been conducted in this dissertation to validate the effectiveness of the power domain impedance approach to analyze system interarea oscillation. Finally, the power domain impedance analysis is carried out to design the oscillation damping controller for a 150MW wind farm