Computer Power Model

Description

The Computer Power Model is a Power Node Model that simulates power consumption for a Computer component. It models the computer as a Constant Power Load (CPL), where the effective resistance is dynamically adjusted so the computer draws approximately the same power regardless of input voltage variations. The model supports automatic shutdown on power loss and restart when power is restored.

Example Use Cases

Spacecraft Power Simulation: Model realistic onboard computer power draw across operational and transitional states.
Power Budget Analysis: Evaluate power budgets with state-dependent consumption values.
Brownout Protection: Simulate automatic computer shutdown when voltage or power falls below operational thresholds.

Module Implementation

Power Consumption by State

The model defines configurable power consumption values for each computer state:

State	Default Power (W)	Load Scaled
Running	3.0	Yes
Safe	1.0	Yes
Shutdown	0.0	No
Starting	4.0	Yes
ShuttingDown	3.5	No
EnteringSafeMode	1.0	Yes
ExitingSafeMode	3.0	Yes

For load-scaled states, the actual power consumption is:

P = P_{state} \times L

where $P_{state}$ is the base power for the current state and $L \in [0, 1]$ is the computer load factor.

Constant Power Load Model

A real computer power supply adjusts its effective input impedance to draw constant power regardless of voltage. Since the circuit solver uses linear resistors, this model employs quasi-static iteration: each simulation tick, the resistance is recomputed from the previous tick’s solved voltage so the linear resistor converges toward true CPL behavior.

The resistance is calculated as:

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

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

Brownout Detection

The model monitors two thresholds to detect insufficient power conditions:

Voltage Threshold: The solved voltage must remain above a minimum fraction of the nominal operational voltage (default $V_{n} = 5$ V):

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

where $r_{V}$ is the minimum voltage ratio (default 0.9).

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

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

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

State Management

The power model automatically manages the computer’s operational state:

Power Loss: When voltage or power falls below thresholds, or the circuit becomes open, the model shuts down the computer from Running or Safe states and sets the ModelShutdown flag.
Power Restored: When power is restored and the computer is shut down with ModelShutdown set, the model automatically restarts the computer.

If a Computer Radiation Error Model is attached and has triggered a permanent failure, the model will not restart the computer.

Assumptions/Limitations

The model requires a valid parent Computer component to function.
The quasi-static CPL iteration converges over multiple simulation ticks; instantaneous constant-power behavior is not achieved in a single step.
Power consumption values are fixed per state and do not account for dynamic workload variations beyond the load factor.
The ShuttingDown state does not use the load factor, representing a fixed shutdown sequence power draw.
Brownout detection only triggers shutdown from stable Running or Safe states, not from transitional states.

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