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Abstract
The application of Cascaded H-Bridge (CHB) multilevel converter StatCom is well established in the industry. In a conventional CHB StatCom, low frequency ripple on the dc side is limited to 10% by utilizing large capacitance. Having a smaller capaci-tance is advantageous because the system will be smaller, cheaper, and more reliable. However, reducing the capacitors will increase the ripple’s magnitude and causes problems such as, control and filtering issues, and high voltage stress on the semicon-ductors. In this thesis, the next generation of CHB StatCom i.e. Low Capacitance StatCom (LC-StatCom) is developed which is able to operate with ripple magnitudes close to the theoretical limit (smallest capacitors’ size). A feed-forward filtering scheme is developed that is able to effectively filter out large ripples without imposing any delay to the control loop and facilitates design of higher bandwidth capacitors’ voltage controllers. A decoupling theory which outlines requirements for completely decoupling the individual capacitors’ voltage controller from the rest of the control system is introduced. The decoupled control system has a linear cluster capacitors’ voltage controller which is essential for operation of the LC-StatCom The proposed LC-StatCom utilizes this linearity to have a variable capacitors’ voltage reference in order to limit the maximum voltage stress on the semiconductors. The proposed LC-StatCom and innovative solutions are evaluated by simulation and experimental case studies. It is shown that the LC-StatCom can achieve 80% reduction in the capacitors’ size, improve current quality, and reduce the maximum voltage stress on the semiconductors com-pared to a conventional StatCom. The LC-StatCom has a reduced operating area in the inductive region compared to conventional StatComs. In this thesis, to overcome this drawback, a hybrid LC-StatCom that utilizes a series thyristor bypassed inductor is developed. The compensated LC-StatCom developed in this thesis, provides approxi-mately 75% reduction in overall energy storage capacity of passive components.