A power flow controller with a stable reversing capability

Power flow in an alternating current transmission line is controlled by injecting, into the transmission line, a series compensating voltage, which is either in phase or in opposite phase with the reactive component of the transmission line voltage. A voltage source converter (VSC) generates the compensating voltage. The VSC is operated by a controller, which determines the angle of the transmission line voltage from voltage measurements taken at spaced-apart points on the transmission line. Operation of the converter with a voltage control method results in an increase in power flow when the compensating voltage is injected in opposite phase with the voltage across the transmission line effective reactance. The compensating voltage, injected in phase with the voltage across the transmission line effective reactance, decreases the power flow, at first, from the uncompensated value and reduces to zero when the compensating voltage equals the voltage across the transmission line effective reactance without compensation. Further increase in the compensating voltage in the same direction increases the power flow in the reverse direction. The novelty of the proposed controller is that it allows the line current and the power flow to be reduced to nearly zero and be reversed with absolute stability. The existing controller does not allow a near zero line current operating condition because a reactance control method relies primarily on the existence of the line current