Fast and safe control of low-capacitance static compensators with enhanced inductive operation

• Main Author: Rodriguez Ramos, Ezequiel
• Other Authors: Josep Pou
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Electrical and electronic engineering::Power electronics
• Online Access: https://hdl.handle.net/10356/156241
• Institution: Nanyang Technological University

Operation and management of the electrical network are becoming increasingly challenging nowa- days due to the rising number of renewable energy sources and electric vehicle charging stations connected to the grid. Cascaded H-bridge (CHB) static compensators (StatComs) are an estab- lished solution to provide voltage regulation to the grid, and thus, help overcome the operational and management challenges of the electric network. As a consequence of the current transition towards sustainability and decarbonization in energy and transportation sectors, the grid needs to employ more StatComs with more demanding performances to ensure correct operation. To realize cheaper, smaller and faster performing StatComs, researchers studied reducing the dc-link capacitors, and consequently, the concept of Low-Capacitance StatCom (LC-StatCom) was intro- duced. When using the same capacitor technology, reducing their capacitance implies less volume and associated cost. In addition, reducing the capacitances implies faster time constants in the ca- pacitor voltages, and thus disturbances could be rejected quicker. Reducing the capacitance value in CHB StatComs to a level where the oscillation on its capacitor voltages cannot be neglected, fundamentally changes the operating premise of the CHB StatComs. The design of LC-StatCom implies new relationships amongst modeling variables and therefore a new design procedure. In the LC-StatComs, the benefit of reduced capacitance comes with the cost of limited operation in the inductive mode and control complications to achieve fast transient performance while guaranteeing state variables’ safe operating limits. This thesis develops a comprehensive model of the LC-StatCom and accurately establishes the underlying operating premise of the system. Based on the developed models, the thesis then demonstrates model-based control approaches to effectively overcome the mentioned control complexities of the LC-StatComs. Developing a model-based methodology to filter the large second-order ripple on the capacitor voltages that also act as an observer to monitor the capacitance variations is a notable contribution of this thesis. Finally, to deal with a limited inductive operation of the LC-StatComs, the thesis pro- poses the use of the circulating current, which is a purely control-based solution and hence, can be readily applied with no hardware modifications. The findings of this thesis not only apply to the LC-StatCom, but are also beneficial for the design of other power electronics applications where a dc-link capacitance reduction is desired.