WHAT IS FACTS AND HOW IT WORKS FOR POWER FACTOR CORRECTION?

FACTS is the acronym for Flexible AC Transmission Systems, and refers to a group of devices used to overcome certain limitations in static and dynamic transmission capacity of electrical networks. FACTS devices are advanced power electronic systems used to enhance the controllability, stability, and efficiency of electrical power networks. For power factor correction, these devices dynamically manage reactive power to optimize the power factor and overall power quality.​

What Are FACTS Devices?

FACTS encompasses several technologies such as SVC (Static VAR Compensator), STATCOM (Static Synchronous Compensator), thyristor-switched capacitors (TSC), and thyristor-controlled reactors (TCR). These devices use high-speed power electronics to inject or absorb reactive power in real time, which helps maintain system voltage quality, stability and correct power factor under rapidly changing load conditions.​

How FACTS Devices Handle Reactive Power Compensation

• Shunt Controllers: Devices like Static Var Compensators (SVC) and Static Synchronous Compensators (STATCOM) are connected in parallel with transmission lines or buses. They inject or absorb reactive power by dynamically switching capacitor or reactor banks, or by using self-commutated voltage-source converters (VSCs) to produce reactive power independently, thereby maintaining voltage stability.​
• Series Controllers: Devices such as thyristor-controlled series capacitors (TCSC) and Static Synchronous Series Compensators (SSSC) are inserted directly into series with transmission elements. They alter the line impedance by dynamically controlling series compensation, which indirectly affects reactive power flow and enhances stability.​

FACTS devices used for power quality improvement include:

• Static Synchronous Compensator (STATCOM): Controls voltage by dynamic reactive power compensation, improves voltage stability, reduces flicker, and enhances power factor correction.
• Static VAR Compensator (SVC): Provides dynamic voltage control and reactive power support to reduce voltage sags and improve power quality.
• Unified Power Flow Controller (UPFC): Controls voltage, power flow, and system stability simultaneously by adjusting voltage magnitude, phase angle, and line impedance.
• Static Synchronous Series Compensator (SSSC): Controls series voltage and compensates reactive power to improve power flow and reduce harmonics.
• Thyristor Controlled Series Compensator (TCSC): Controls series capacitive reactance dynamically, improving system stability and power quality.
• Inter-phase Power Flow Controller (IPFC): Controls power flow in multi-phase systems to mitigate harmonics and balance loads.
• Dynamic Voltage Restorer (DVR): Injects voltage to compensate for voltage sags/swells, thus improving power quality at sensitive load points.​

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These devices enhance power quality by providing fast, adaptive voltage regulation, harmonic mitigation, flicker reduction, and reactive power compensation, especially in systems with variable loads and renewable generation.

How FACTS Work for Power Factor Correction

• FACTS devices monitor the system’s reactive power requirements and regulate reactive power flow by switching capacitors, reactors, or using voltage-source converters.
• FACTS inject capacitive reactive power to counteract the lagging reactive power generated by inductive loads like motors and transformers, actively keeping the power factor close to unity.​
• This dynamic regulation is much faster and more adaptive compared to traditional steps of fixed and automatically switched capacitor banks, especially under highly variable or nonlinear load profiles in modern industrial applications.​
• Industrial plants deploy FACTS for real-time compensation of reactive power, helping prevent penalties from low power factor, reducing losses, and enabling larger load capacities without grid upgrades.​
• FACTS also provide active harmonic filtering, improving both power quality (e.g., by reducing THD) and the operating life of equipment.

FACTS devices offer fine-tuned and high-speed power factor control, making them suitable for environments with frequent or unpredictable load changes, such as those found in process industries and smart grids.​

Implementation Mechanism

• Real-Time Control: These devices continuously monitor system parameters like bus voltages, line currents, and power flows and adjust their reactive power output accordingly.​
• Power Electronic Converters: Modern FACTS devices employ high-speed power electronic converters such as IGBTs or GTOs to produce or absorb reactive power swiftly, supporting fast voltage regulation during load fluctuations or contingencies.​
• Susceptance Control: In models like the variable shunt susceptance model, FACTS devices are represented as adjustable reactances (susceptances). They modify the network’s reactive susceptance in real-time, which directly influences

FACTS Device Choice Criteria

• Type of Control Needed: Devices differ by whether they control voltage magnitude, phase angle, or impedance, and whether they act by shunt (parallel), series, or combined methods.
• Dynamic Response Requirement: For fast dynamic compensation, devices like STATCOM or SVC are preferred. STATCOM offers fast continuous reactive power control, while SVC uses thyristor-switched capacitors/reactors.
• Power Level and Voltage: The rating of compensation (MVAR level) and voltage level guide device size and technology choice.
• Load and System Conditions: Nature of load (inductive, capacitive, or nonlinear), system stability issues, and presence of harmonics influence device design.
• Cost and Maintenance: First-generation devices with thyristors (SVC, TCSC) tend to be less costly but less flexible than IGCT/IGBT-based STATCOM or UPFC devices.

Table for FACTS Device Choice

Criteria	SVC	STATCOM	UPFC	TCSC
Control Function	Shunt reactive power	Shunt reactive power	Series + shunt flow	Series capacitive
Response Speed	Moderate (ms to s)	Fast (sub-ms to ms)	Very fast	Moderate
Voltage Support	Good	Excellent	Excellent	Limited
Power Flow Control	No	Limited	Yes	Yes
Cost	Lower	Higher	Highest	Moderate
Complexity	Moderate	Higher	Highest	Moderate

Control strategies to reduce harmonics and flicker with FACTS devices include following approaches:

Harmonics Reduction Strategies

• 12-Pulse Converter Configuration: Using 12-pulse voltage source converters in STATCOM reduces harmonics injected into the system compared to 6-pulse converters, minimizing waveform distortion.
• Phase-Shifting Transformers: Phase shifting between parallel converter bridges helps cancel certain harmonic orders, reducing total harmonic distortion (THD).
• RLC Filtering: Passive filters (RLC), combined with STATCOM or SVC reduce harmonic currents generated by switching devices.
• PWM Control with Selective Harmonic Elimination: Pulse width modulation with switching patterns designed to minimize specific harmonics.

Active Filtering: Advanced FACTS devices sometimes incorporate active filter functions to detect and compensate harmonics dynamically.​

Flicker Mitigation Strategies

• Instantaneous Reactive Power Control: FACTS devices rapidly inject or absorb reactive power in response to flicker-causing load changes (e.g., arc furnaces, welding), stabilizing voltage fluctuations.
• Voltage Control at Point of Common Coupling (PCC): Maintaining a stable voltage at the PCC reduces visible flicker on lighting.
• Adaptive Control Algorithms: Novel control schemes that extract voltage disturbance components and suppress flicker actively by modifying STATCOM firing angles.
• Combination of Fixed Capacitors and TCR/FCTCR Devices: These thyristor-controlled devices help smooth voltage variations by fast switching of reactive power elements.
• Dynamic Voltage Regulation: Continuous modulation of reactive power output minimizes voltage dips and spikes leading to flicker.​

FACTS devices use advanced converter topologies, filtering, and real-time control algorithms to reduce harmonics and mitigate voltage flicker effectively. Techniques such as multi-pulse converters, phase-shifting transformers, RLC filters, and rapid reactive power control at the PCC combine to improve overall power quality in grids with nonlinear and flicker-prone loads.