UPFC Explained: Working Principle, Control Strategy and Applications

Introduction

The Unified Power Flow Controller (UPFC) is one of the most versatile FACTS devices used for controlling electrical power transmission. It combines series and shunt voltage-source converters connected through a common DC link.

Why Is UPFC Needed?

Power in an interconnected transmission system does not necessarily flow along the path operators would prefer. Power flow depends on transmission-line impedance, voltage magnitude, voltage angle, network topology, generation and load conditions.

UPFC Configuration

• Shunt voltage-source converter
• Series voltage-source converter
• Common DC-link capacitor
• Shunt coupling transformer
• Series coupling transformer
• Measurement and control system

Shunt Converter

The shunt converter performs functions similar to a STATCOM. It can regulate bus voltage, supply or absorb reactive power and maintain the DC-link voltage while exchanging real power with the series converter.

Series Converter

The series converter injects a controllable voltage into the transmission line. The magnitude and phase of the injected voltage determine its effect on transmission power flow.

UPFC Working Principle

The UPFC operates by controlling the series-injected voltage while maintaining the required DC-link energy balance. The series converter can exchange real and reactive power with the transmission system, while the shunt converter manages the DC-link power balance and provides reactive support.

Active Power Control

The series converter can change the effective power-transfer conditions of the line. This makes UPFC useful for congestion management, load-flow control, power-transfer optimization and management of parallel-line loading.

Reactive Power Control

The UPFC can also provide reactive-power compensation. Reactive power affects bus voltage, line current, transmission losses and voltage stability.

UPFC Control Strategy

A typical UPFC controller contains measurement blocks, Phase Locked Loop, abc-dq transformation, voltage controller, active-power controller, reactive-power controller, DC-link controller, current controllers and PWM generators.

UPFC for Voltage and Transient Stability

A major disturbance such as a short circuit can cause generator rotor-angle oscillations, voltage changes and power-flow variations. A properly controlled UPFC can modify power flow during and after disturbances and contribute to improved dynamic performance.

UPFC in MATLAB/Simulink

A MATLAB/Simulink UPFC project can contain a generator, transformer, transmission line and load with the UPFC connected to the transmission corridor. Simulations can be performed under normal conditions, increased loading, three-phase faults, load variation and generation variation.

Important Simulation Results

• Sending-end voltage
• Receiving-end voltage
• Active power
• Reactive power
• Line current
• DC-link voltage
• Power-angle response
• Transient oscillations

UPFC Advantages

• Active-power-flow control
• Reactive-power control
• Voltage regulation
• Improved transmission utilization
• Dynamic compensation
• Improved system controllability

UPFC Limitations

UPFC is more complex than simple shunt or series compensation. Challenges include higher cost, complex converter control, protection requirements and more complicated modeling.

UPFC Research Project Ideas

• UPFC for IEEE 9-bus systems
• UPFC for IEEE 14-bus systems
• UPFC for voltage stability
• UPFC for transient stability
• UPFC power-flow control
• UPFC with fuzzy control
• UPFC with ANN control
• PSO-based UPFC placement

Internships and Industrial Training

Electrical and electronics students can develop UPFC and FACTS simulation projects using MATLAB/Simulink as part of academic internships and research projects.

Training opportunities include Internships in Pondicherry, Internships in Chennai, Internship in Cuddalore, Tamil Nadu, and Internship in Chidambaram, Tamil Nadu.

The Center for Industrial Training can support interdisciplinary training in Embedded Systems, Automation and IoT. Students interested in modern power electronics can also explore an Electric Vehicles Training and Testing Center.

Internship and Projects are available in online mode and offline mode.

Contact: +91-9952749533

Conclusion

UPFC is a highly flexible FACTS controller capable of controlling voltage and transmission-line power flow through coordinated series and shunt converters. It is an important subject for power-system research, MATLAB/Simulink simulation and advanced electrical-engineering projects.