10.3 Automatic Generation Control (AGC) systems

Automatic Generation Control (AGC) systems are crucial for maintaining power system stability. They keep frequency steady and balance power between areas by adjusting generator outputs. AGC constantly monitors frequency and power flows, calculates errors, and sends control signals to generators.

The heart of AGC is the Area Control Error (ACE), which measures the mismatch between generation and load. AGC uses ACE to adjust generator outputs, aiming to keep it at zero. Key components include frequency sensors, tie-line meters, and control center computers that run AGC algorithms.

AGC System Purpose and Components

Objectives and Functions

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• Minimizes frequency deviations maintains power interchanges between control areas at scheduled values
• Distributes required change in generation among participating units economically
• Operates by continuously monitoring system frequency and tie-line power flows, calculating Area Control Error (ACE), and sending control signals to generating units to adjust power output

Key Components and Architecture

• Frequency sensors measure system frequency in real-time
• Tie-line power flow meters monitor power exchanges between control areas
• Control center computer systems run AGC software algorithms and control logic
• Communication links (SCADA, telemetry) transmit measurements and control signals between control center and generating units
• Typically implemented as centralized control system with control center receiving measurements from remote locations and issuing control commands to generating units

Area Control Error in AGC

ACE Definition and Calculation

• Represents instantaneous mismatch between generation and load within control area, considering scheduled power interchanges with neighboring areas
• Calculated as linear combination of frequency deviation and net interchange deviation: ACE = (NIA - NIS) + 10B(FA - FS)
  • NIA: Net Interchange Actual, NIS: Net Interchange Scheduled
  • FA: Actual Frequency, FS: Scheduled Frequency
  • B: Frequency Bias Factor (MW/0.1 Hz)
• Positive ACE indicates power deficit (under-generation or over-load), negative ACE indicates power surplus (over-generation or under-load)

Role in AGC Operation

• Key input to AGC system drives control actions to maintain generation-load balance
• AGC aims to drive ACE towards zero by adjusting power output of participating generating units
• Frequency Bias Factor (B) determines control area's contribution to frequency regulation based on frequency deviation
• Represents amount of generation change needed to compensate for given change in frequency (MW/0.1 Hz)
• Helps distribute frequency regulation responsibility among control areas in interconnected system

AGC for Frequency and Power Control

Real-time Operation and Control Logic

• Operates in real-time, continuously monitoring system frequency and tie-line power flows
• Adjusts power output of generating units to maintain desired frequency and power interchange values
• Control logic typically consists of proportional-integral (PI) controller and participation factor matrix
  • PI controller determines required change in generation based on ACE signal
  • Participation factor matrix distributes required change among participating generating units
• PI controller parameters (gain, time constant) tuned for balance between fast response and stability, considering generating unit and power system characteristics

Coordination with Generating Units and Other Control Systems

• Sends raise or lower pulses to governor systems of participating generating units to adjust power output
  • Pulse duration and interval determined by AGC control logic and unit response characteristics
• Coordinates with other control systems (voltage, reactive power) for stable and secure power system operation
• Interfaces with Energy Management System (EMS) for economic dispatch, reserve management, and other functions

AGC Parameter Impact on Performance

Key Parameters and Their Effects

• Frequency Bias Factor (B) affects control area's contribution to frequency regulation and overall stability
  • Larger B leads to greater contribution but may increase wear and tear on generating units
• PI controller gains determine speed and stability of AGC response
  • Higher gains enable faster response but may cause overshoots and oscillations
  • Lower gains provide slower but more stable response
• Participation factors determine distribution of required generation change among participating units
  • Based on unit capacity, ramp rates, and economic considerations
  • Optimal selection improves efficiency and reliability of AGC system

Performance Evaluation and Optimization

• Generating unit response characteristics (ramp rates, deadbands, time delays) affect overall AGC performance
  • Faster, more responsive units improve AGC performance but may increase operational costs and equipment wear
• AGC performance evaluated through simulations, field measurements, and statistical analysis
  • Metrics include frequency and tie-line power deviations, control effort, and economic dispatch
• Parameter optimization balances multiple objectives (frequency regulation, economic dispatch, equipment life) based on system requirements and constraints
• Advanced techniques (adaptive control, machine learning) can improve AGC performance by adapting to changing system conditions and optimizing parameters in real-time