Transmitter Power Model

Description

The Transmitter Power Model creates a coupling between a Transmitter component and the Power Bus electrical network. It models the transmitter as a Constant Power Load (CPL), dynamically adjusting resistance so the transmitter draws the required power regardless of input voltage variations. The model enforces power availability constraints, disabling transmission when voltage or power falls below operational thresholds.

Example Use Cases

Power Budget Analysis: Evaluate spacecraft power consumption during communication passes with realistic amplifier efficiency.
Battery Sizing: Determine energy storage requirements accounting for RF output power and DC conversion losses.
Brownout Protection: Simulate automatic transmission disable when voltage falls below operational thresholds.

Module Implementation

Power Consumption

The transmitter draws power based on its operating state. When idle, only standby power is consumed. During transmission, additional DC power is required to generate the RF output:

P_{DC} = P_{standby} + \frac{N _{bands} \cdot P _{RF}}{η}

where $P_{standby}$ is the standby power (default 2.5 W), $N_{bands}$ is the number of active frequency bands, $P_{RF}$ is the RF output power per band (default 2 W), and $η$ is the DC-to-RF efficiency (default 0.3).

Constant Power Load Model

The transmitter is modeled as a CPL using quasi-static iteration. Each tick, the resistance is recomputed from the previous tick’s solved voltage:

R = \frac{V ^{2}}{P _{DC}}

where $V$ is the voltage from the previous solve (or nominal voltage $V_{n}$ on the first tick). The voltage is floored at the minimum operational threshold to prevent resistance collapse during transient brownouts.

Brownout Detection

The model monitors two thresholds to determine if sufficient power is available:

Voltage Threshold: The solved voltage must remain above a minimum fraction of the nominal operational voltage (default $V_{n} = 12$ V):

V_{node} \geq V_{n} \times r_{V}

where $r_{V}$ is the minimum voltage ratio (default 0.8).

Power Threshold: The absorbed electrical power must remain above a minimum fraction of the expected DC power:

P_{absorbed} \geq P_{DC} \times r_{P}

where $r_{P}$ is the minimum power ratio (default 0.13). Setting $r_{P} = 0$ disables this check.

Transmission Enable Control

The model controls the transmitter’s CanTransmit flag based on power availability. When voltage or power falls below thresholds, or the circuit is open, transmission is disabled. This prevents RF transmission during power system faults or low-power conditions.

Assumptions/Limitations

The model assumes a purely resistive load; reactive power components are not modeled.
The quasi-static CPL iteration converges over multiple simulation ticks.
Multi-band transmission power scales linearly with the number of active bands.
Transient power draw during transmission startup is not modeled; power consumption changes are instantaneous.
Thermal effects from power dissipation are not coupled to the transmitter thermal model.