Example 09: Linear Generator

Example 09: Linear Generator#

Description#

This example demonstrates a standalone Mainspring linear generator simulation. It highlights three key characteristics that distinguish the linear generator from other thermal components:

  1. Fast ramp rate (120%/min) — power changes are effectively instantaneous at 1-minute time steps

  2. No minimum stable load — the generator can operate at any fraction of rated capacity, including very low loads, without shutting down

  3. Flat efficiency — HHV net efficiency is constant at 41.44% regardless of load level

For details on linear generator parameters and configuration, see Linear Generator. For details on the underlying state machine and ramp behavior, see Thermal Component Base.

Scenario#

The simulation runs for 7 hours with 1-minute time steps on a 250 kW unit.

Timeline#

Time (min)

Event Type

Setpoint

State

Description

0

Initial

250 kW

ON (6)

Generator starts on at rated capacity; time_in_state pre-set to min_up_time

10

Command

→ 0

→ STOPPING (7)

Shutdown command; min_up_time pre-satisfied, stopping begins immediately

~10

State

0

→ OFF_HOT (4)

Power reaches 0 within one time step (ramp rate of 120%/min exceeds rated capacity), min_down_time begins counting

~15

State

0

OFF_HOT (4)

min_down_time (5 min) satisfied

20

Command

→ 250 kW

→ HOT_STARTING (5)

ON command issued; min_down_time already satisfied, hot start begins immediately

~21–22

State

—

HOT_STARTING (5)

Hot start in progress; hot_startup_time is 90 s, which spans 2 time steps at dt=60 s

~22

State

250 kW

→ ON (6)

hot_startup_time complete; power ramps to 250 kW within one time step

90

Command

→ 125 kW

ON (6)

Setpoint reduced to 50%; power reaches 125 kW within one time step

120

Command

→ 50 kW

ON (6)

Setpoint reduced to 20%; power reaches 50 kW — note no minimum stable load constraint

180

Command

→ 0

→ STOPPING (7)

Shutdown command; min_up_time satisfied (~153 min on), stopping begins

~180

State

0

→ OFF_HOT (4)

Power reaches 0 within one time step

~225

State

0

→ OFF_WARM (2)

hot_to_warm_time (45 min) elapsed since shutdown; unit transitions from hot to warm

~360

State

0

→ OFF_COLD (0)

hot_to_cold_time (3 hours) elapsed since shutdown; unit transitions from warm to cold

420

End

0

OFF_COLD (0)

Simulation ends

Key Behaviors Demonstrated#

  • Fast ramp: Load changes while ON complete within a single 1-minute time step — the ramp rate (120%/min) exceeds rated capacity, so any setpoint change is met immediately

  • Hot startup duration: hot_startup_time is 90 s, which spans 2 timesteps at dt=60 s; power is not available until the startup sequence completes

  • No minimum stable load: The generator operates at 20% (50 kW) without clamping or shutdown, unlike a gas turbine which typically has a 30–40% minimum

  • Flat efficiency: Efficiency remains 41.44% at 100%, 50%, and 20% load — fuel consumption scales linearly with power output

  • Minimum down time: After shutdown at t=10 min, min_down_time (5 min) is satisfied by t=15 min, so the ON command at t=20 min starts the hot start sequence immediately

  • Cooldown state transitions: After the final shutdown at t=180 min, the unit progresses through OFF_HOT → OFF_WARM (at t≈225 min, after hot_to_warm_time of 45 min) → OFF_COLD (at t≈360 min, after hot_to_cold_time of 3 hours)

Setup#

No manual setup is required. The example uses only the LinearGenerator component which requires no external data files.

Running#

To run the example, execute the following command in the terminal:

python hercules_runscript.py

Outputs#

To plot the outputs, run:

python plot_outputs.py

The plot shows:

  • Power output and setpoint over time (demonstrating fast ramp and no minimum stable load)

  • Operating state transitions

  • Thermal efficiency over time (flat at 41.44% across all load levels)

  • Fuel volume rate over time