Entirely Transformerless Universal Direct-Injection Power-Flow Controller

Abstract: An increasing penetration of renewable energy resources, electric vehicle chargers, and energy storage systems into low-voltage power grids causes several power management and stability problems, such as reverse power flow, (local) overload lines, and over- / under-voltage. Previous power-flow and soft-open-point solutions are bulky and expensive. They need transformers and large magnetics, some on grid frequency, others more compact at high frequency. Even suggested circuits with high-frequency transformers still struggle with cost and size. We present a compact partial power-conversion high-current full-power-flow control circuit without a single transformer. We combine silicon and silicon-carbide, each with their specific advantages for current-dense direct injection. The circuit further needs fewer semiconductors than previous concepts. The circuit links a shunt converter through a non-isolated inverter bidirectionally with low-voltage series modules that practically float with their respective phases can serve between different feeders in low-voltage power grids. We analyze the circuit mathematically and evaluate the operation in simulation and experimental results.