Electranix Corporation

AC-AC Solid-State Distribution Transformer

The transformer is a key component of the electrical system that transfers electrical energy from one electrical circuit at one voltage to another voltage through the process of electromagnetic induction. Solid-State Transformers (SST) are an emerging technology that is rapidly growing and has been regarded as a ground-breaking innovation to replace the century-old bulky conventional transformers with a lighter, smaller, and smarter architecture. This paper shows one possible approach of AC-AC power transformation using pure solid-state switches and passive components without an intermediate magnetically-based transformer. It is based on the concept of capacitor-based transformation of power from one voltage level to another. It offers some useful features: (1) internal redundancy sufficient to obviate the need for the spare transformer normally supplied with magnetic transformation, (2) absence of toxic insulating oil, (3) ease of manufacture, being modular in construction, (4) inherent phase-shifting capability, and (5) the ability to convert between primary and secondary nodes differing in frequency and/or wave-shape. The new architecture enriches the existing SST family and introduces a configuration that requires fewer converter stages. The simulation results will show that the proposed SST can transform one AC voltage to another AC voltage using pure solid-state devices and be bi-directional, exactly as a magnetically-based conventional transformer, but with even more functions, such as fast and dynamic control over the output voltage, and fully controllable output power by shifting the phase angle of the transformer output voltage. In addition, the grid side reactive power can be controlled. Another unique feature is to use the resonant circuits for soft switching (zero-current switching) while charge exchanging between the first node and the transformer, and between the second node and the transformer. The total DC voltage of the submodule (SM) column is stable, and the individual SM capacitor voltage is sorted and balanced. The over-current protection mechanism detects faults and isolates the transformer. The results will successfully demonstrate that the proposed distribution SST is a pure solid-state transformer that only uses a single converter stage and no magnetically-based transformer but still has the function of the conventional transformer, as well as it provides additional features that can contribute to the future smart distribution grid.

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