Supervisor:
Huai wang

Co-Supervisor:

Assessment Committee:
Yajuan Guan(Chair)
Liuchen Chang, University of New Brunswick, Canada
Alon Kuperman, Ben Gurion University of the Negev, Israel

Moderator:
Yajuan Guan

Abstract:

In power electronics applications, capacitors, and inductors, as fundamental components, are used for harmonic filtering, power balancing, energy buffering, and transmission. However, passive components are generally designed and manufactured with fixed impedance types and values, making them unable to adjust according to circuit requirements. Different applications may require components with various specifications, which increases the complexity of design and manufacturing, thus raising costs. Active impedance elements, as one solution for variable impedance, offer the advantage of continuous adjustment across a wide range of impedance values. Existing implementation methods for active impedance elements face issues of inaccurate impedance realization due to a lack of robustness against system parameter variations and changing conditions. Additionally, they suffer from either complex control requirements or the need for high-precision signal acquisition. To address these issues, this study investigates a series of active impedance elements with plug-and-play capability and their variable and robust control solutions.

Firstly, this study introduces robust impedance control methods for the active capacitor and inductor. Compared to existing impedance control methods, the proposed control methods enable the active impedance elements to maintain their impedance at a given reference, even under variations in operating conditions and system parameters. The uniqueness of these methods lies in the closed-loop control of the output impedance of the active impedance elements. By accumulating impedance errors through an iterative learning controller to update control coefficients, the equivalent impedance of the active impedance elements can be adjusted accordingly. The feasibility and effectiveness of the proposed impedance control methods are demonstrated through case studies on the active capacitor and inductor.

Secondly, a concept of a plug-and-play unified active impedance module with variable impedance is proposed. Based on the suggested topology and corresponding impedance control strategy, the active impedance module can instantly adjust its impedance value and type, allowing it to flexibly function as a variable positive or negative capacitor or inductor. The proposed unified impedance control method requires only internal capacitor voltage and inductor current signals from within the module, simplifying the controller. Moreover, the absence of external electrical signals enables plug-and-play operation.

Lastly, based on the proposed active impedance module with variable impedance, a solution for a hybrid LC resonant circuit composed of an active impedance module and passive components is introduced. The hybrid LC resonant circuit, utilizing the active impedance module, can maintain the desired resonant frequency in the presence of circuit parameters and load conditions change. This helps reduce the design requirements for resonant circuit components and ensures system stability. Additionally, a model-based design process for the active impedance module is provided.

The above study has been theoretically derived and experimentally verified. The contributions have been presented through a few journal papers and conference papers.