Control Performance Standard 1 (CPS1)

CPS1 is calculated as a ratio of the 12-month rolling average of ACE × ΔFrequency to a target bound derived from the interconnection's frequency bias. A value ≥ 100% indicates compliance. The formula is:

CPS1 = (2 - CF) × 100%

where CF is the compliance factor:

CF = [Σ(ACE_i × ΔF_i)] / [-10B × n × ε₁²]

• ACE_i: One-minute average Area Control Error
• ΔF_i: One-minute average frequency deviation
• B: Balancing authority's frequency bias (MW/0.1 Hz)
• ε₁: RMS frequency error target for the interconnection
• n: Number of one-minute periods in the rolling year

CPS1 evaluates performance using one-minute average values of both ACE and frequency deviation, synchronized to the clock minute. This averaging:

• Filters out high-frequency noise from instantaneous ACE fluctuations
• Aligns all balancing authorities to identical measurement periods
• Prevents manipulation through rapid control pulses

The product of the one-minute averages determines whether a balancing authority was helping or hurting frequency during that minute. A negative product (ACE and frequency have opposite signs) indicates supportive behavior.

CPS1 imposes an asymmetric performance requirement that tightens as frequency deviation increases:

• When frequency is on-schedule (ΔF ≈ 0), the standard allows wide ACE variability
• When frequency deviation is large, the allowable ACE narrows proportionally
• This creates a self-regulating mechanism: balancing authorities causing large ACE in the direction of frequency error are penalized most severely

The target bound is -10B × ε₁², where ε₁ is a fixed RMS frequency error target specific to each interconnection (e.g., 0.018 Hz for the Eastern Interconnection).

Unlike CPS2 which evaluates monthly performance, CPS1 uses a trailing 12-month window that updates continuously:

• Each new month's data replaces the same month from the prior year
• Prevents seasonal gaming where poor performance in one period is offset by exceptional performance in another
• Requires sustained operational discipline across all seasons and load conditions
• A single month of severe non-compliance can drag the rolling average below 100% for an entire year

This long evaluation period reflects the statistical nature of the standard—it measures chronic behavior, not isolated incidents.

The frequency bias coefficient (B) is a critical input to CPS1 calculation. It represents the balancing authority's expected MW response per 0.1 Hz of frequency deviation:

• A correctly set bias reflects the area's natural governor response plus any frequency-responsive load
• Under-reporting bias makes CPS1 easier to achieve but degrades interconnection frequency support
• Over-reporting bias makes CPS1 harder to achieve but provides excessive support
• NERC requires bias to be at least 1% of peak load per 0.1 Hz

The bias term appears in the denominator of the compliance factor, directly scaling the allowable ACE envelope.

CPS1 operates alongside two other NERC control standards, each serving a different purpose:

• CPS1: Statistical, long-term measure of ACE-frequency correlation (this standard)
• CPS2: Bounds ACE magnitude within L10 limits for 90% of 10-minute periods each month
• BAAL: Real-time operational limit preventing ACE from exceeding a frequency-dependent threshold

While CPS2 and BAAL constrain magnitude, CPS1 constrains direction. A balancing authority could pass CPS2 while failing CPS1 if its ACE consistently opposes frequency recovery.

The instantaneous input signal to CPS1 calculations. ACE represents the total generation-load imbalance requiring correction, combining the net interchange deviation with a frequency bias component.

• Formula: ACE = (NIA - NIS) - 10B × (FA - FS)
• NIA = Net Interchange Actual, NIS = Net Interchange Scheduled
• B = Frequency Bias Coefficient in MW/0.1 Hz
• FA = Actual Frequency, FS = Scheduled Frequency
• CPS1 evaluates the statistical relationship between ACE and frequency error over rolling 12-month windows

A critical parameter in the ACE equation that quantifies a balancing authority's expected response to frequency deviations. Expressed in MW/0.1 Hz, this setting ensures each entity contributes its fair share to interconnection frequency support.

• Must be set at least equal to the balancing authority's frequency response characteristic
• Prevents entities from leaning on neighbors during frequency events
• Directly impacts CPS1 compliance because it shapes the ACE value used in the statistical calculation
• Incorrect bias settings can mask or exaggerate actual control performance

The physical capacity resource that enables CPS1 compliance. Regulation reserve consists of synchronized, responsive generation or load resources that can increase or decrease output within seconds to continuously correct minute-to-minute ACE fluctuations.

• Deployed automatically by the AGC system every 2-6 seconds
• Must be sufficient to cover normal ACE variability within CPS1 bounds
• Insufficient regulation reserve leads to degraded CPS1 scores and potential non-compliance
• Can be provided by generators, battery energy storage, or demand-side resources