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Components::PowerMonitor

The Power Monitor component reads power data from two power monitors. It also keeps two energy totals:

  • The total energy that the satellite uses (TotalPowerConsumption).
  • The total energy that the solar panels supply (TotalPowerGenerated).

The component is passive. A rate group calls the component one time each second (1 Hz).

Hardware

The component uses two INA219 power monitor chips on the I2C bus. Each chip has a Drv::Ina219Manager driver.

Port prefix Driver instance I2C address Schematic name Measurement point
sys ina219SysManager 0x40 Battery Power Monitor The battery line (shunt resistor R109)
sol ina219SolManager 0x41 Solar Power Monitor The solar panel input VSOLAR (shunt resistor R108), before the charger

Note: The INA219 power value has no sign. The sys monitor measures the battery line. Thus, its power value is the same when the battery charges and when the battery discharges. Only the current value has a sign.

Energy Totals

The component calculates energy from power and time. Energy (mWh) = power (W) × time (h) × 1000.

On each run cycle, the component does these steps:

  1. It reads the power from the sys monitor and from the sol monitor.
  2. It reads the current time.
  3. It calculates the time step. The time step is the time between this cycle and the last cycle.
  4. It adds (sys power + sol power) × time step to TotalPowerConsumption.
  5. It adds sol power × time step to TotalPowerGenerated.
  6. It sends the two totals as telemetry.

The component calculates the time step one time only in each cycle. The two totals use the same time step.

The component uses these safety rules:

  • On the first cycle, the component only records the time. It does not add energy.
  • If a power value is less than 0 W or more than 1000 W, the component does not add energy to that total. The other total is not affected.
  • If the time step is 0 s or less, the component does not add energy. This can occur when the clock goes back.
  • If the time step is 10 s or more, the component does not add energy. This can occur when the clock jumps forward.

The component keeps the totals as 64-bit (double) values. It changes them to 32-bit (F32) values only for telemetry and events. This prevents a large rounding error after many days.

The totals start at 0 mWh when the flight software starts. The totals do not stay after a reboot.

The Components::PowerIntegrator class contains the energy logic. This class does not use F Prime or Zephyr. Thus, you can test it with unit tests on a computer.

Usage Examples

Typical Usage

  1. The system creates and starts the component during system startup.
  2. The topology connects the component to:
  3. A rate group (through the run input port).
  4. The sys power monitor driver (through the sys* output ports).
  5. The sol power monitor driver (through the sol* output ports).
  6. On each rate group cycle:
  7. The component calls all six output ports. Each driver reads its chip and sends its own telemetry.
  8. The component updates the two energy totals.
  9. The component sends TotalPowerConsumption and TotalPowerGenerated telemetry.

Read the Total Energy

  1. Look at the TotalPowerConsumption and TotalPowerGenerated telemetry channels.
  2. To get the consumption total as an event, send the GET_TOTAL_POWER command.

Reset a Total

  1. To set the consumption total to 0 mWh, send the RESET_TOTAL_POWER command.
  2. To set the generation total to 0 mWh, send the RESET_TOTAL_GENERATION command.

A reset changes only one total. The other total does not change.

Class Diagram

classDiagram
    namespace Components {
        class PowerMonitorComponentBase {
            <<Auto-generated>>
        }
        class PowerMonitor {
            - PowerIntegrator m_integrator
            + PowerMonitor(const char* compName)
            + ~PowerMonitor()
            - run_handler(FwIndexType portNum, U32 context)
            - RESET_TOTAL_POWER_cmdHandler(FwOpcodeType opCode, U32 cmdSeq)
            - RESET_TOTAL_GENERATION_cmdHandler(FwOpcodeType opCode, U32 cmdSeq)
            - GET_TOTAL_POWER_cmdHandler(FwOpcodeType opCode, U32 cmdSeq)
            - getCurrentTimeSeconds() F64
        }
        class PowerIntegrator {
            - double m_consumption_mWh
            - double m_generation_mWh
            - double m_lastUpdateTime_s
            - bool m_initialized
            + update(double now_s, double consumedW, double generatedW)
            + resetConsumption()
            + resetGeneration()
            + getConsumption_mWh() float
            + getGeneration_mWh() float
        }
    }
    PowerMonitorComponentBase <|-- PowerMonitor : inherits
    PowerMonitor *-- PowerIntegrator : contains

Port Descriptions

Name Type Description
run sync input Starts one power monitor cycle. A rate group calls this port.
sysVoltageGet output Gets the voltage from the sys (battery) power monitor driver.
sysCurrentGet output Gets the current from the sys (battery) power monitor driver.
sysPowerGet output Gets the power from the sys (battery) power monitor driver.
solVoltageGet output Gets the voltage from the sol (solar) power monitor driver.
solCurrentGet output Gets the current from the sol (solar) power monitor driver.
solPowerGet output Gets the power from the sol (solar) power monitor driver.

Commands

Name Description
RESET_TOTAL_POWER Sets the TotalPowerConsumption total to 0 mWh. Sends the TotalPowerReset event.
RESET_TOTAL_GENERATION Sets the TotalPowerGenerated total to 0 mWh. Sends the TotalGenerationReset event.
GET_TOTAL_POWER Sends the TotalPowerConsumptionReading event with the consumption total.

Events

Name Severity Description
TotalPowerReset ACTIVITY_LO The consumption total is now 0 mWh.
TotalGenerationReset ACTIVITY_LO The generation total is now 0 mWh.
TotalPowerConsumptionReading ACTIVITY_LO Gives the consumption total in mWh.

Telemetry

Name Type Unit Description
TotalPowerConsumption F32 mWh The total of sys power plus sol power over time. The component sends it on each cycle.
TotalPowerGenerated F32 mWh The total of sol power over time. The component sends it on each cycle.

Note: TotalPowerConsumption adds the battery power and the solar power. It is not a measurement of the system load. The battery power value has no sign (see Hardware). Thus, battery charge is also added.

Sequence Diagrams

Run Cycle

sequenceDiagram
    participant Rate Group
    participant Power Monitor
    participant Power Integrator
    participant System Power Driver
    participant Solar Power Driver

    Rate Group->>Power Monitor: run(portNum, context)

    Power Monitor->>System Power Driver: sysVoltageGet()
    System Power Driver-->>Power Monitor: voltage

    Power Monitor->>System Power Driver: sysCurrentGet()
    System Power Driver-->>Power Monitor: current

    Power Monitor->>System Power Driver: sysPowerGet()
    System Power Driver-->>Power Monitor: sysPowerW

    Power Monitor->>Solar Power Driver: solVoltageGet()
    Solar Power Driver-->>Power Monitor: voltage

    Power Monitor->>Solar Power Driver: solCurrentGet()
    Solar Power Driver-->>Power Monitor: current

    Power Monitor->>Solar Power Driver: solPowerGet()
    Solar Power Driver-->>Power Monitor: solPowerW

    Power Monitor->>Power Integrator: update(now_s, sysPowerW + solPowerW, solPowerW)
    Note over Power Integrator: Calculate one time step.<br/>Add energy to both totals.

    Power Monitor->>Power Monitor: tlmWrite_TotalPowerConsumption()
    Power Monitor->>Power Monitor: tlmWrite_TotalPowerGenerated()

Unit Tests

The unit tests are in PROVESFlightControllerReference/test/unit-tests/test_PowerMonitor_PowerIntegrator.cpp. To run them, use make test-unit.

Name Description Output Coverage
StartsAtZero Makes sure that a new integrator has two totals of 0 mWh. Both totals are 0 mWh. Constructor
FirstUpdateOnlyEstablishesTimeBase Makes sure that the first cycle adds no energy. Both totals are 0 mWh. update() first cycle
TimeBaseAtZeroSeconds Makes sure that a first time of 0 s operates correctly. Both totals are 1 mWh. update() first cycle
BothTotalsCreditedWithFullTickPeriod Does 3600 cycles at 1 Hz. Makes sure that each total gets the full time step (issue #526). Each total is power × 1 h. update()
NonUniformTickPeriod Uses time steps of different lengths. Each total is power × 2 s. update()
InvalidPowerSkipsOnlyThatTotal Sends a power value that is out of range for one total. Only that total does not change. Power range check
TimeJumpsAreNotIntegrated Moves the clock forward and back. Energy is added only for the 1 s steps. Time step check
ResetsAreIndependent Resets one total, then the other total. A reset changes only one total. resetConsumption(), resetGeneration()
LongDurationAccumulationKeepsPrecision Does 30 days of cycles at 1 Hz. The error is less than 0.0001 %. Double precision totals

Requirements

Name Description Validation
PWR-MON-REQ-001 The component shall respond to scheduler calls on the run port. Integration test
PWR-MON-REQ-002 The component shall get the voltage from the system power driver on each run cycle. Integration test
PWR-MON-REQ-003 The component shall get the current from the system power driver on each run cycle. Integration test
PWR-MON-REQ-004 The component shall get the power from the system power driver on each run cycle. Integration test
PWR-MON-REQ-005 The component shall get the voltage from the solar panel power driver on each run cycle. Integration test
PWR-MON-REQ-006 The component shall get the current from the solar panel power driver on each run cycle. Integration test
PWR-MON-REQ-007 The component shall get the power from the solar panel power driver on each run cycle. Integration test
PWR-MON-REQ-008 The component shall add the energy of the system power plus the solar power to TotalPowerConsumption on each run cycle. Unit test, Integration test
PWR-MON-REQ-009 The component shall add the energy of the solar power to TotalPowerGenerated on each run cycle. Unit test
PWR-MON-REQ-010 The component shall use the same time step for both totals. The time step shall be the time since the last run cycle. Unit test
PWR-MON-REQ-011 The component shall not add energy to a total when its power value is less than 0 W or more than 1000 W. Unit test
PWR-MON-REQ-012 The component shall not add energy when the time step is 0 s or less, or 10 s or more. Unit test
PWR-MON-REQ-013 The component shall send TotalPowerConsumption and TotalPowerGenerated telemetry on each run cycle. Inspection
PWR-MON-REQ-014 The RESET_TOTAL_POWER command shall set only TotalPowerConsumption to 0 mWh. Unit test
PWR-MON-REQ-015 The RESET_TOTAL_GENERATION command shall set only TotalPowerGenerated to 0 mWh. Unit test
PWR-MON-REQ-016 The GET_TOTAL_POWER command shall send the consumption total in the TotalPowerConsumptionReading event. Integration test

Change Log

Date Description
2025-11-03 Initial Power Monitor component
2026-09-25 Both energy totals now use the same time step. Before this change, TotalPowerGenerated was approximately 700 times too low (#526). The totals now use double precision. Added the PowerIntegrator unit tests. The SDD now uses Simplified Technical English.