Partial-Power Flow Controller, Voltage Regulator, and Energy Router for Hybrid AC-DC Grids

Abstract: The share of electronically converted power from renewable sources, loads, and storage is continuously growing in the low- and medium-voltage grids. These sources and loads typically rectify the grid AC to DC, e.g., for a DC link, so that a DC grid could eliminate hardware and losses of these conversion stages. However, extended DC grids lack the stabilizing nature of AC impedances so that the voltage is more fragile and power flows may need active control, particularly if redundancy as known from AC, such as rings and meshing, is desired. Furthermore, a DC infrastructure will not replace but will need to interface with the existing AC grid. This paper presents a partial-power energy router architecture that can interface multiple AC and DC lines to enable precise control of voltages and both active as well as reactive power flows. The proposed system uses modular low-voltage high-current series modules supplied through dual active bridges. These modules only need to process a small share of the voltage to control large power flows. The topology reduces component size, cost, energy losses, and reliability more than three times compared to conventional technology. The optional integration of battery energy storage can furthermore eliminate the need for the sum of the power flows of all inputs to be zero at all times. Through dynamic voltage injection relative to the line voltage, the modules effectively balance feeder currents, regulate reactive power, and improve the power factor in AC grids. Real-time hardware-in-the-loop and prototype measurements validate the proposed energy router's performance under diverse operating conditions. Experimental results confirm the series module's functionality in both AC and DC grids as an effective solution for controlling extended grids, including power sharing, voltage, and power quality.