Stability design criteria and volt var control for distribution system with single phase solid state transformers
Due to recent advancements in semiconductor technology, power electronic converters for high voltage, high power, and high frequency applications will soon be commercially available. Conventional single phase distribution transformers are replaced by solid state transformers (SST) in a distribution test system to investigate their interactive dynamics. Under certain circumstances, instabilities due to harmonic resonance are observed. A design criterion for solid state transformer during no load conditions has been proposed in order to avoid instability using an impedance-based analysis. Stability assessment is also extended to include the impact of distribution system voltages and system wide impedance analysis. It is shown that if the SST filters throughout the system are designed with regards to the proposed stability criterion, then system stability is guaranteed regardless of configuration. This leads to two resulting applications: (1) the order in which the SSTs are connected to the system will not generate instability if the criterion is satisfied, and (2) a system configuration change due to a fault will not produce instability. In distribution power systems, feeder voltages can be very sensitive to changes in load and/or distributed generation. A solid-state-transformer-based local voltage control strategy is introduced to reduce variability distribution system bus voltages. An on-line dynamic volt-var control (VVC) algorithm is proposed to regulate bus voltages by injecting or absorbing reactive power through a solid state transformer. The main goal of the algorithm is to enforce strict voltage constraints on the system voltages. The proposed control algorithm is validated in both a radial and meshed distribution system. "--Abstract, page iii.
Missouri University of Science and Technology
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