Transmission line power flow controller

• US 5,420,495 A
• Filed: 04/19/1993
• Issued: 05/30/1995
• Est. Priority Date: 04/19/1993
• Status: Expired due to Fees

• Current Assignee: Electric Power Research Institute
• Original Assignee: Electric Power Research Institute Incorporated
• Inventors: Hingorani, Narain G.
• Primary Examiner(s): Stephan, Steven L.
• Assistant Examiner(s): Riley, Shawn
• Application Number:
  US08/048,858
• Time in Patent Office: 771 Days
• Field of Search: 323/208, 323/209, 323/210, 323/211, 323/218, 323/293, 323/352, 323/356, 307/127
• US Class Current: 323/218
• CPC Class Codes: G05F 1/66 Regulating electric power

Abstract

A transmission line power flow control system and method selectively reverses power flow direction and controls power flow level over a transmission line. A capacitor having a variable capacitive impedance is selectively inserted in series with the line. The capacitor has a maximum capacitive impedance magnitude which exceeds the magnitude of the inductive impedance of the transmission line. A switching device in parallel with the capacitor inserts and removes the capacitor from the line. The capacitor maybe inserted and removed in a stepwise fashion using several modules, or in a gradual fashion by using inductors in series with the modular switching devices. In response to measurements of power flow parameters, such as line current and line to ground voltages, a controller controls the switching device(s) to selectively vary the net impedance of the transmission line to control the direction and magnitude of power flow therethrough.

Claims

1. A power flow control system to control the direction of power flow on a transmission line, comprising:

a capacitor;

a switching device to selectively couple said capacitor to said transmission line;

a sensor for monitoring current flowing through said transmission line; and

a controller responsive to said sensor to actuate said switching device, said controller including

a line current limiter to identify line current on said transmission line above a specified maximum current magnitude limit,

a deadband control device responsive to said sensor to establish a deadband range of impedance values and an operative range of impedance values for said transmission line, said operative range of impedance values including negative reactance impedance values and positive reactance impedance values, said line current limiter and said deadband control device generating output signals that are applied to said switching device such that said switching device selectively couples said capacitor to said transmission line

to maintain said line current on said transmission line below said specified maximum current magnitude limit, and

to maintain said transmission line impedance within said operative range of impedance values and outside of said deadband range of impedance values, and thereby vary said capacitor'"'"'s reactive power compensation to said transmission line in such a manner as to control the direction of power flow on said transmission line.

2. The power flow control system of claim 1 wherein:

said capacitor forms a portion of a plurality of capacitor modules; and

said switching device forms a portion of a plurality of switching modules, each of said switching modules of said plurality of switching modules being connected in parallel to a corresponding capacitor of said plurality of capacitor modules.

3. The power flow control system of claim 2 further including one or more inductors in series with one or more of said plurality of switching modules.

4. A method of controlling the direction of power flow on a transmission line, comprising the steps of:

sensing current flow through a transmission line to establish a sensed current signal;

comparing said sensed current signal to a specified maximum current magnitude limit and generating a maximum current control signal to maintain said current flow through said transmission line below said maximum current magnitude limit;

comparing the impedance of said transmission line with a deadband range of impedance values and an operative range of impedance values for said transmission line, said operative range of impedance values including positive reactance impedance values and negative reactance impedance values, said comparing step including the step of generating a deadband control signal to maintain said transmission line impedance within said operative range of impedance values and outside of said deadband range of impedance values; and

applying said maximum current control signal and said deadband control signal to a switching device that selectively connects a capacitor to said transmission line so as to vary said capacitor'"'"'s reactive power compensation to said transmission line in such a manner as to control the direction of power flow on said transmission line.

5. The method of claim 4 further comprising the steps of:

applying said maximum current control signal and said deadband control signal to a plurality of switching modules, each of said switching modules including a switching device connected in parallel with a capacitor.