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Energy Monitoring Subsystem - Coggle Diagram
Energy Monitoring Subsystem
User Requirements
Accurately measure energy delivered to the vehicle so device can bill or stop charging precisely
Provide real-time reporting of voltage, current, instantaneous power and accumulated energy
Be safe to install without breaking functionality of the rest of the system
Be resilient to measurement errors and provide a fail-safe on sensor or comms (stop charging)
Persist energy totals for session logging and audit (survive power interrupts)
Functional Requirements
Measure the following
Sample voltage and current
True power
Integration into energy
Communicate measured parameters to MCU
Meet at least approximately 1% energy accuracy under normal operating conditions
Provide data updates every second
Support initial calibration and periodic recalibration
Detect failures, e.g.
Sensor failure
CT open
UART comms failure
Assert a fault to the Control Subsystem
Store per-session energy totals in non-volatile memory
Ensure measurement circuitry and comms are galvanically safe for the other electronic components
Compare meter energy with MCU integrated power for double-checking
Design Specifications
Sensor & Metering Hardware
Measures:
Vrms
Irms
Active Power
Apparent Power
Power factor
Frequency
Energy (kWh)
Accuracy
Around 1% depending on module
Current range
0 - 100A
Voltage
230 VAC minimum
Update interval
Around 1 seconds
Current Transformer (CT)
Single-turn CT around live conductor feeding to charger only
CT must be rated for maximum current
Physical Integration & Wiring
Ensure placement of energy monitoring device within the enclosure
Use of insulated cable, strain relief, fuses and cable glands are required
Ensure no direct DC coupling from mains to MCU
Communication & Protocol
Ensure baud rate is set correctly
Study the energy monitoring device's packet protocol to ensure reliable communication
Set a reasonable polling interval
Failure of communication of energy monitoring data must be notified to Control Subsystem
Verify responses using checksum or CRC
Potential components
Energy monitoring device
PZEM-004T
ADE7753
ATM90E26
ADE9078
Current transformer
Open CT
CT-SP-5A-330mV
Closed CT
RS PRO Flying Lead Current Transformer
Communication Protocols
Modbus RTU
RS485