Double modulation control (DMC) for dual full bridge current flow controller (2FB-CFC)

Power flow control in multi-terminal DC grids can be accomplished through the connection in series of a controlled voltage source converter to a line. Having finite energy, the voltage source requires a means for either power recycling or additional source of power to regulate its voltage. An interline dual full bridge current flow controller (CFC) provides the capability to recycle power from one line to another through the voltage source in addition to controlling the power flow on either line. This paper proposes a control methodology that fulfils both control objectives. A double modulation controller (DMC) implements one modulating signal and two control signals to control the duty ratio of the converters simultaneously. The first control signal is proportional to the required reduction in the line current. The second control signal is implemented to regulate the voltage to either a set average value or to a value that is proportional to the amount of reduction in current.