A power flow control subsystem having multiple configurations is described. The subsystem is three-way configurable: as a transportable configuration, as a deployable configuration, and as a transmission line configuration. The transportable configuration includes a collection of impedance injection modules and at least one bypass module carried on a wheeled vehicle such as a trailer. The deployable configuration is an assembly of the collection of impedance injection modules and at least one bypass module, operable to perform power flow operations. The transmission line configuration includes connection of a deployable configuration to a phase of a high voltage transmission line for performing power flow control. The deployable configuration may be open or closed frame. The deployable configurations may be mounted on one or more wheeled vehicles in a mobile subsystem, or semi-permanently mounted at a ground site.