Title:  Dynamic State Estimation based Protection of Power Electronics Systems

Committee:

Dr. Sakis Meliopoulos, ECE, Chair, Advisor

Dr. Maryam Saeedifard, ECE

Dr. Santiago Grijalva, ECE

Dr. Daniel Molzahn, ECE

Dr. Andy Sun, ISyE

Abstract: Power electronics systems play an important role in modern power systems to realize sustainable generation and flexible transmission. Reliable protection of the power electronics systems is a core issue in reliable power system operation. The complex structure and diverse fault characteristics make the power electronics system protection a very complex problem. This dissertation proposes to use a dynamic state estimation-based protection (EBP) to protect the converter systems. The first step of the conducted research is developing the converter system models in both the time domain and the quasi-dynamic domain. The time domain converter model is developed with detailed circuits of the semiconductor devices. The switching of the valve is simulated by generating switching sequences using pulse-width modulation methods. The quasi-dynamic domain converter model is built to accelerate the simulation speed. The key of building a model is to express the relationship between the AC and DC side averaged variables using mathematic functions of the controller outputs. In this dissertation, the accuracy of the quasi-dynamic domain converter model is improved by incorporating a loss function in the energy conversion equation between the AC and DC sides. The previous applications of the EBP establish the protection zone model in the time domain. This is not feasible for the converter system since it is difficult to utilize the time domain converter model due to the restrictions of the computational capability of the processor and the sampling rate of the merging units. These restrictions can be overcome by setting up the protection zone model in the quasi-dynamic domain. The measurements from the merging unit are casted into phasor form using discrete Fourier Transform and split into real and imaginary parts to be processed by the state estimation algorithm. A static synchronous compensator (STATCOM) is used for the simulation of the fault and the validation of the EBP. The fault events are simulated in the time domain and the EBP is set up based on the quasi-dynamic domain converter system models. Four different types of faults with distinct fault characteristics are simulated and EBP shows excellent dependability in protecting the converter system.