UPFC for Enhancing Power System Reliability

This paper discusses various aspects of unified power flow controller (UPFC) control modes and settings and evaluates their impacts on the power system reliability. UPFC is the most versatile flexible ac transmission system device ever applied to improve the power system operation and delivery. It can control various power system parameters, such as bus voltages and line flows. The impact of UPFC control modes and settings on the power system reliability has not been addressed sufficiently yet. A power injection model is used to represent UPFC and a comprehensive method is proposed to select the optimal UPFC control mode and settings. The proposed method applies the results of a contingency screening study to estimate the remedial action cost (RAC) associated with control modes and settings and finds the optimal control for improving the system reliability by solving a mixed-integer nonlinear optimization problem. The proposed method is applied to a test system in this paper and the UPFC performance is analyzed in detail.

Nomencluture

Power flow equation.

ESRAC

Expected squared of remedial action cost.

Active and reactive power injection of parallel inverter.

Magnitude and phase angle of parallel inverter voltage.

Active and reactive power injection of series inverter.

Magnitude and phase angle of series inverter voltage.

Magnitude and phase angle of PB .

Difference between PB and SB voltages.

Active and reactive power injection of PS.

Currents of PB and SB.

Equivalent reactance of parallel transformer.

Equivalent reactance of series transformer.

NC

Number of selected contingencies.

NLD

Number of load points.

and

Probability and frequency of contingency .

Duration of contingency (in hours).

Curtailed load cost (in U.S$) of contingency .

Curtailed load at point for contingency (j) (in megawatts).

Curtailment cost of load point for duration (in U.S.$/megwatt-h).

Remedial action cost of contingency .

Re-dispatch cost of generating unit (g) (in U.S.$/MW).

MW re-dispatch of unit in contingency .

NG

Number of generating units.

Active and reactive power of unit (g).

Generation cost of unit .

Max and Min active power generation for unit .

Max and Min reactive power generation for unit .

Vectors of active and reactive power generation, respectively.

Vectors of magnitude and phase angle of bus voltages.

Magnitude of voltage of bus .

Loading of line .

Max loading of line

NB and NL

Number of buses and lines, respectively.

Voltage and current of PB for contingency .

Voltage of PB and SB for contingency when UPFC is disconnected.

Self-impedance of SB for contingency .

Mutual impedance of PB and SB for contingency .

Max and Min voltage of inverters.

Max current of inverters.

and

Variables for PS and SS control modes.

Sensitivity of to .

Sensitivity of to .

Sensitivity of to .

Estimated when the control modes and injections of PS and SS are and .

Post-contingency reactive injection of PS for contingency for and .

Post-contingency active injection of SS for contingency for and .

Post-contingency reactive injection of SS for contingency for and .

Post-contingency active injection of PS for contingency for and .