BRUIN FORMULA RACING · CASE STUDY 03

Thermal Response During Dynamic Running

Bruin Formula Racing — Battery, inverter, coolant, and power-module temperature analysis

This study examines how battery, inverter, coolant, and power-module temperatures changed during the dynamic portion of the logged run. The analysis compares peak temperature rise, cooling behaviour, and the different response rates of fast-heating power electronics and slower thermal systems.

347-channel source log
93.6 s dynamic-running segment
1 Hz thermal resampling
Inverter and BMS telemetry
Python / pandas / Matplotlib

Measured results

Key metrics

Highest recorded module temperature: 38.99°C
Largest module temperature rise: 3.49°C
Inverter hot-spot rise: 3.10°C
Coolant temperature rise: 0.70°C
BMS average peak rise: 1.47°C

System context

Where the heat comes from

The battery supplies direct-current electrical energy to the inverter. The inverter rapidly switches that DC supply into controlled three-phase current for the motor. These switching and conduction processes are not perfectly efficient, so part of the electrical energy becomes heat inside the inverter power modules and surrounding electronics.

Battery DC
Inverter
Three-phase motor current
Motor torque

BMS average: The average battery temperature reported by the Battery Management System.
Coolant: The temperature of the liquid carrying heat away from the inverter and related components.
Inverter hot spot: The hottest monitored internal region of the inverter.
Control board: The lower-power electronics that process commands, read sensors, and control the inverter’s switching.
Modules A, B, and C: The three inverter power sections responsible for producing the motor’s three-phase electrical supply.

Project question

What was investigated?

The analysis was designed to answer three questions: which components experienced the largest short-term temperature rise, how quickly did different parts of the system respond to changing load, and did inverter temperature behaviour align with periods of repeated motor torque demand?

Analysis workflow

Method

01
Select validated thermal channels

Use:
- bms.avg_t
- bms.hi_t
- bms.lo_t
- inv.cool_t
- inv.all.hot_spot_temp
- inv.all.control_board_temp
- inv.all.module_a_temp
- inv.all.module_b_temp
- inv.all.module_c_temp
- inv.rpm
- inv.tq_fb
Isolate dynamic running

The same dynamic-running section used in the motor analysis was selected, beginning at approximately 65 seconds and ending at approximately 158 seconds.
Resample thermal data

Temperature signals were resampled to 1 Hz because thermal behaviour changes much more slowly than the original high-frequency telemetry. Short gaps were interpolated only where appropriate.
Calculate thermal changes

For each component, the starting and ending temperatures were estimated using the average of the first and final five seconds. The maximum recorded value was used to calculate peak temperature rise.
Compare inverter modules

Modules A, B, and C were compared individually to check whether the three power sections exhibited similar heating and cooling behaviour.
Align torque and temperature

Delivered torque and thermal data were grouped by whole elapsed seconds. Torque was smoothed over three seconds, while inverter temperatures were smoothed over five seconds to make the overall load and thermal trends easier to compare.
Interpret thermal lag

Temperature peaks were not expected to occur at exactly the same moment as torque peaks because heat generation, conduction, sensor response, and cooling introduce a delay.

Line chart comparing BMS average, coolant, inverter hot-spot, and control-board temperatures during the dynamic-running segment. — System temperatures across the 93.6-second dynamic-running segment. Select the plot to inspect the full-resolution figure.

Result 01 · System temperatures

The inverter hot spot accumulated heat most clearly

The inverter hot spot rose from 33.70°C to a peak of 36.80°C, an increase of 3.10°C. It ended at 36.58°C, retaining most of the accumulated heat near the end of the segment.

Recorded temperature changes

BMS average: Start 23.60°C Peak 25.07°C End 24.15°C Peak rise 1.47°C End change +0.55°C
Coolant: Start 33.40°C Peak 34.10°C End 33.96°C Peak rise 0.70°C End change +0.56°C
Inverter hot spot: Start 33.70°C Peak 36.80°C End 36.58°C Peak rise 3.10°C End change +2.88°C
Control board: Start 32.41°C Peak 33.81°C End 33.69°C Peak rise 1.41°C End change +1.29°C

Line chart comparing temperatures of inverter Modules A, B, and C during dynamic running. — Inverter power-module temperatures during changing torque demand. Select the plot to inspect the full-resolution figure.

Result 02 · Inverter modules

The three inverter modules responded consistently to changing demand

Modules A, B, and C followed closely matched heating and cooling patterns. Their temperatures rose during repeated periods of motor demand and fell rapidly after torque demand ended.

Module A reached the highest absolute temperature at 38.99°C, while Module C showed the largest rise from its starting temperature at 3.49°C.

Module temperature changes

Module A: Start 35.62°C Peak 38.99°C End 34.08°C Peak rise 3.37°C End change −1.54°C
Module B: Start 34.98°C Peak 38.01°C End 33.77°C Peak rise 3.03°C End change −1.22°C
Module C: Start 34.90°C Peak 38.39°C End 33.55°C Peak rise 3.49°C End change −1.35°C

Bar chart comparing the peak temperature rise of battery, coolant, inverter hot spot, control board, and three inverter modules. — Peak temperature rise relative to each component’s starting temperature. Select the plot to inspect the full-resolution figure.

Result 03 · Peak temperature rise

Power electronics showed the largest short-term thermal response

The inverter hot spot and three power modules experienced peak rises of approximately 3.0–3.5°C. Coolant rose by only 0.70°C, while the BMS average and control board rose by approximately 1.4°C.

The faster power-module response is consistent with heat being generated directly in the high-current switching components, while coolant and battery temperatures respond more slowly because of their larger thermal mass.

Peak temperature rise by component
Component	Peak rise
BMS average	1.47°C
Coolant	0.70°C
Inverter hot spot	3.10°C
Control board	1.41°C
Module A	3.37°C
Module B	3.03°C
Module C	3.49°C

Dual-axis line chart comparing delivered motor torque with inverter hot-spot and average module temperature over elapsed time. — Delivered torque and inverter-temperature trends aligned by elapsed time. Select the plot to inspect the full-resolution figure.

Result 04 · Torque and thermal response

Module temperatures followed repeated periods of motor demand

The average inverter-module temperature generally increased after sustained high-torque periods and fell during lower-load or zero-torque operation. The inverter hot-spot temperature responded more slowly and retained accumulated heat after individual torque events had ended.

Observed timing

High torque around 80–84 seconds was followed by a module-temperature peak.
Repeated demand around 116–121 seconds was followed by a larger thermal peak.
Strong operation around 130–136 seconds preceded the highest module temperatures.
Once delivered torque fell to zero near 149 seconds, average module temperature dropped rapidly.
The inverter hot spot remained elevated for longer, showing greater thermal inertia.

What the results show

Engineering interpretation

Power modules

The inverter power modules reacted quickly to changing motor load, producing repeated temperature peaks during high-demand operation.

Hot-spot accumulation

The inverter hot spot warmed more gradually and retained most of its temperature rise near the end of the segment.

Cooling response

Module temperatures dropped rapidly once torque demand ended, whereas the coolant, battery, and hot-spot signals changed more slowly.

Module consistency

The three inverter modules followed similar temperature patterns, with only small differences in absolute temperature and peak rise.

Analysis boundary

Scope of the result

This analysis describes short-term thermal response during a 93.6-second dynamic-running segment. It is useful for comparing component behaviour and identifying thermal lag, but it does not establish steady-state temperatures or validate reliability across a full endurance event.

Summary

Key takeaway

The inverter power modules responded quickly to repeated motor demand, reaching peak temperature rises of approximately 3.0–3.5°C before cooling rapidly when torque demand ended. The inverter hot spot accumulated heat more gradually and retained most of its rise, while coolant and battery temperatures changed more slowly over the short dynamic segment.