Control Pilot

Control Pilot#

This document outlines the technical specifications, measurement process, and testing guidelines for the control pilot system. Key takeaways include:

  1. ADC sampling achieves a resolution of 2 μs with error <0.5%.

  2. Voltage fluctuation thresholds and hysteresis values are configurable to ensure reliable operation.

  3. The system distinguishes between transient issues that warrant logging (anomalies) and safety violations that require stopping charging (errors).

  4. Testing guidelines provide clear criteria for verifying state-specific voltages.

Overview#

  • Frequency: 1 kHz (1 ms per cycle)

  • ADC: 500 kSPS @ 8 MHz; 500 samples per ms

    • Resolution: 2 μs, measurement error < 0.5%

  • Sampling Period: 10 ms

  • Duty Cycle:

    • Adjustable range: 2–100%

      • Measurements below 1% are constrained by hardware limitations.

    • Measurable range: 1–100%

    • Resolution: 1%, error < 0.5%

Compliance with Standards#

This design aligns with the following international standards:

  • IEC 61851: Electric vehicle conductive charging system requirements.

  • SAE J1772: Standards for EV charging connectors and protocols.

Error Handling#

The system prioritizes user convenience by not interrupting charging for transient issues within valid ranges, while strictly enforcing safety boundaries defined by international standards.

Anomaly vs Error State#

The system distinguishes between anomaly detection(for monitoring) and error states(for charging control).

Anomaly Detection (Monitoring Only)#

It is designed to track quality metrics for debugging and maintenance without interrupting charging.

Minor fluctuations within valid voltage ranges indicate potential issues (EMI, loose connection, contact bounce) but should NOT interrupt user charging. These are logged for maintenance purposes.

It gets triggered by signs of instability, such as:

  • Voltage fluctuation > 50mV between consecutive measurements

  • Voltage in forbidden hysteresis zones

  • Excessive transition samples ≥ 15 outliers (> 30μs transition time)

The values in the example are adjustable and can be tuned to fit the actual environment.

Measurement Process#

  1. ADC Sampling

  2. Conversion to millivolts

  3. High/Low signal distinction

  4. Outlier Removal

  5. Duty Cycle Calculation

  6. Boundary Check (for anomaly detection)

  7. State Update

Implementation Notes#

  • Sampling Details:

    • ADC sampling capacitor: 30 pF; resistance: 500 Ω; sufficient sampling time.

    • 500 samples per 1 ms (2 μs/sample).

  • Boundary Definition:

    • Boundary values are derived from theoretical calculations and can be referenced in this spreadsheet.

    • Anomaly detection functionality captures real-world measurement variances, and configurable voltage hysteresis can compensate for these variances.

  • Voltage Segmentation:

    • High/low distinction is set at 1V and is configurable.

    • Unused voltages in IEC 61851/J1772 standards minimize false filtering.

  • Hysteresis (Asymmetric Thresholds):

    • 500 mV gap for each state (configurable) to prevent rapid oscillation (chattering)

    • Uses different thresholds based on transition direction:

      • Upward transition(lower state → higher state): Uses upward threshold (higher voltage required)

      • Downward transition(higher state → lower state): Uses downward threshold (lower voltage required)

    • Example: State A/B boundary

      • State B → State A: Requires ≥ 10.75V

      • State A → State B: Requires ≤ 10.25V

      • Forbidden zone: 10.25V ~ 10.75V (triggers PILOT_ERROR_FLUCTUATING)

    • Initial state is UNKNOWN, which uses downward threshold for first measurement

  • Anomaly Detection (Monitoring):

    • Voltage fluctuation: Typically below 30mV; 20mV margin added

      • Threshold: > 50mV between consecutive measurements (configurable)

      • Action: Increment PilotAnomalyCount metric only (charging continues)

    • Excessive transitions: Typically 20μs (10 samples); 10μs margin added

      • Threshold: ≥ 15 outlier samples, equivalent to ≥ 30μs transition time (configurable)

      • Action: Increment PilotAnomalyCount metric only (charging continues)

  • Adjustable Parameters:

    • Sampling interval

    • Voltage for high/low distinction

    • Noise margin

    • Transition time

    • State voltage hysteresis

    • Number of ADC samples

  • When adjusting the sampling interval, the number of buffers introduced for lock-free programming should also be reviewed.

The following table summarizes the measured voltage ranges for different duty cycles under various states (12V, 9V, 6V). Values represent millivolts measured at the corresponding duty cycle.

Duty

12V_H

12V_L

9V_H

9V_L

6V_H

6V_L

100%

3.141

0

2.871

0

2.541

0

75%

3.141

554

2.871

554

2.541

554

50%

3.141

554

2.871

554

2.541

554

25%

3.138

554

2.871

554

2.541

554

5%

3.135

554

2.871

554

2.541

554

Production Testing Guidelines#

  • Verify status-specific voltages fall within the expected range:

    • Command: test cp (via CLI).

Status

High Voltage

Low Voltage

A(12V)

3.279V

3.065V

B(9V)

2.958V

2.744V

C(6V)

2.637V

2.424V
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