FACTS Devices in Power Systems: Types, Working Principles and Applications

Introduction

Modern electrical power systems must transmit large amounts of electrical energy while maintaining acceptable voltage, power flow, stability and power quality. Increasing demand, long transmission lines, renewable-energy integration and heavily loaded networks make power-system control more challenging.

Flexible AC Transmission Systems (FACTS) provide power-electronic-based solutions for improving the controllability and utilization of AC transmission networks. FACTS controllers can regulate voltage, control reactive power, modify transmission-line impedance, control power flow and improve dynamic performance.

What Are FACTS Devices?

FACTS devices are static controllers installed in electrical transmission networks to provide fast and controllable compensation. Their important objectives include voltage regulation, reactive-power compensation, power-flow control, voltage-stability improvement, transient-stability improvement, transmission congestion management and power-oscillation damping.

Classification of FACTS Devices

Shunt FACTS Controllers

Shunt controllers are connected in parallel with the power system. Important examples are the SVC and STATCOM. Their primary function is reactive-power and voltage control.

Series FACTS Controllers

Series controllers are connected in series with a transmission line. Examples include TCSC and SSSC. They can modify the effective impedance of a transmission line and influence active-power flow.

Combined Series-Shunt Controllers

The best-known example is the UPFC. It combines shunt and series converter functions through a common DC link.

SVC

The Static VAR Compensator is a thyristor-based shunt FACTS controller. An SVC generally uses combinations of thyristor-controlled reactors, thyristor-switched capacitors and harmonic filters. By controlling the effective reactive susceptance, an SVC can inject or absorb reactive power and regulate bus voltage.

SVC applications include transmission voltage control, reactive-power compensation, voltage-stability improvement, flicker reduction and power-oscillation damping.

STATCOM

A STATCOM is a voltage-source-converter-based shunt FACTS controller. It generates a controllable AC voltage and exchanges reactive current with the power system. STATCOMs provide fast dynamic voltage support and are especially useful in renewable-energy applications.

TCSC

A Thyristor Controlled Series Capacitor modifies the effective series reactance of a transmission line. TCSC applications include power-flow control, transmission-capacity improvement, power-oscillation damping and transient-stability improvement.

SSSC

The Static Synchronous Series Compensator is a converter-based series FACTS controller. It injects a controllable voltage into the transmission line and can influence active and reactive power transfer.

UPFC

The Unified Power Flow Controller is one of the most versatile FACTS controllers. A UPFC contains two voltage-source converters connected through a common DC link. The shunt converter performs STATCOM-type functions while the series converter performs SSSC-type functions.

FACTS Devices and Renewable Energy

Modern grids contain increasing amounts of solar and wind generation. Renewable generation can introduce voltage fluctuations, variable power injection, reactive-power requirements and transmission congestion. FACTS controllers can provide fast voltage and power-flow control and therefore support renewable integration.

FACTS Devices in MATLAB and Simulink

A typical simulation project can include a three-phase source, transformer, transmission line, load, FACTS controller, measurement blocks and a control system. Researchers can compare system performance before and after installing a FACTS controller.

Typical results include bus voltage, active power, reactive power, line current, power-angle response and voltage recovery.

FACTS Research Project Ideas

• STATCOM for voltage stability
• SVC for reactive-power compensation
• UPFC for power-flow control
• FACTS for renewable-energy integration
• FACTS placement using PSO or genetic algorithms
• STATCOM control using fuzzy logic
• FACTS for transient-stability improvement

Internships and Industrial Training

Students and researchers interested in practical electrical-engineering projects can work on power-system simulation, FACTS controllers, renewable energy, MATLAB/Simulink and power-electronics applications.

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Conclusion

FACTS devices are important tools for controlling modern AC power systems. SVC and STATCOM provide shunt compensation, TCSC and SSSC provide series control, while UPFC combines series and shunt functions. MATLAB/Simulink-based FACTS projects provide an excellent way to study voltage control, reactive power, power flow and power-system stability.