UBC Theses and Dissertations

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UBC Theses and Dissertations

Active adaptive auxiliary circuit for stabilizing dc distribution systems with constant power loads Pizniur, Oleksandr


The portion of high-bandwidth power converters in modern DC distribution systems has been increasing and is projected to dominate over time. These devices having fast response act as constant power loads (CPLs) and possess the so-called negative incremental input impedance characteristics at the input terminals, which may ultimately cause dynamic interactions and instability at certain interfaces in the system. Most existing approaches that address this problem use passive or active damping to reshape the source/load impedances so that stability may be achieved. The drawbacks of most existing methods include energy losses in passive components and/or requirement of changing the internal controls in existing loads. This thesis presents a new active damping methodology using an auxiliary converter circuit to stabilize DC distribution systems with CPLs. A simplified single frequency criterion is proposed for identifying the damping parameters. The proposed auxiliary converter circuit exchanges the energy between very strong power bus and a potentially unstable bus with CPLs, which requires very small injected damping current and achieves lossless damping (conserves the energy during transients). The methodology may operate by emulating fixed or operating-point-depended virtual RC values of the equivalent damping, with the latter having potential advantages of achieving faster damping. To verify and demonstrate the proposed concept, the auxiliary converter circuit has been designed and built with innovative compensated average current control mode. The experimental studies have been carried out on a reduced scale subsystem of a DC microgrid installed by Alpha Technologies Ltd., in Kaiser building at UBC. It is envisioned that the proposed active damping methodology using low-power auxiliary converter circuit may be very cost-effective and practical solution for the future DC systems with modular design and multiple sources/loads being constructed by different vendors with limited knowledge of their parameters and access to their internal controls.

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