For many electric drive projects, “proper testing” still means a bench supply, a real motor, some loads – and a lot of lab time. Hardware-in-the-loop (HIL) promises repeatable scenarios, virtual loads and better coverage. But HIL also costs money and engineering effort. So when does it actually pay off?
What we mean by “lab bench” and “HIL” in this article
- Lab bench: real inverter + real motor + physical load, tested manually or with simple scripting.
- HIL: real controller hardware (often STM32-based) connected to a real-time simulator that emulates motor, mechanics and environment.
We focus on electric drive systems and motor control (e.g. STM32 FOC, protection logic). For more on the drive context, see drive systems and engineering & firmware services.
What a classic lab bench does well
The lab bench is still the fastest way to answer many practical questions:
- Does the motor actually start and run with your FOC implementation?
- What does noise, vibration and mechanical behaviour feel like?
- Is the power stage behaving thermally under realistic conditions?
- Do connectors, harnesses and mechanics survive real handling?
With a well-structured bench and scripts, you can automate a surprising amount: start-up tests, speed ramps, basic protection checks. Bench testing is also cheap to extend – another motor, another inverter, another prototype on the table.
Where the lab bench starts to limit you
Limitations usually appear in three areas:
- Coverage: rare faults, corner conditions, extreme environments are hard or unsafe to reproduce.
- Repeatability: “same” test next week might mean different state of motor, cables, operator, environment.
- Throughput: manual setup and supervision limit how many scenarios you can realistically run.
For example: how often do you really test “overvoltage during regen at low temperature with worn bearings and a near-empty battery”? On a bench, these scenarios are expensive to create, so they tend to remain untested or tested only once.
What HIL brings to the table
A hardware-in-the-loop setup replaces the real motor and mechanical system with a real-time model. Your inverter or control board “thinks” it is driving the real plant, but the plant is simulated.
- Real control firmware, real PWM, real protection logic.
- Simulated motor, mechanics, environment, sensors and loads.
- Scenarios can be scripted, repeated and combined – including “unfriendly” faults.
In practice, HIL shines when:
- You need to explore fault cases and rare combinations in a safe way.
- You want to regression-test a complex STM32 control stack after each change.
- Several teams or suppliers need a shared, repeatable reference for “what the system does”.
Quick decision helper – is HIL worth exploring now?
| Situation | Bench only | Bench + HIL |
|---|---|---|
| Single product, low volume, simple drive | Usually enough | Only if there are strong safety / liability drivers |
| Complex drive with many modes & safety functions | Risky, gaps in coverage likely | Worth considering |
| Multiple variants & long product family lifecycle | High manual regression effort | HIL often pays off over time |
| Strict safety / regulatory requirements | Bench may be insufficient alone | HIL often becomes a key tool |
If your team already struggles to repeat tests reliably and still misses issues in the field, that is usually a strong indicator that some form of HIL or advanced lab automation could help.
Cost and complexity: what HIL really demands
HIL is not “just” a box you plug in. To get useful results you need:
- A suitable real-time platform and I/O (often including fast analog, digital and encoder interfaces).
- Plant models for motor, mechanics, power supply and environment – at the right level of detail.
- Integration work between your STM32 board and HIL rig (signal scaling, timing, synchronisation).
- Test scenarios and scripts that reflect your real use cases and risks.
This is engineering work. For some drive projects, a smaller step – like structured lab automation and better logging – delivers more value for less effort. That is where services like remote testing & STM32 motor control consulting often start.
Where HIL is usually most valuable in the lifecycle
HIL tends to pay off most in three phases:
- Architecture & concept: exploring control strategies and protection concepts before hardware is final.
- Integration & validation: systematically covering fault cases and edge conditions.
- Regression over time: ensuring changes to firmware or parameters do not break existing behaviour.
For early FOC tuning and bring-up of STM32 control, a good bench is usually enough. As you move toward pre-series and series, HIL becomes more attractive – especially for complex drive systems as described in “From Prototype to Series: A Maturity Model for Electric Drive Systems” (assuming this page exists or will exist under that handle).
Middle ground: structured lab automation before full HIL
Between “manual bench” and “full HIL” there is a very useful middle ground:
- Standardised test benches with fixed wiring, fixtures and safety concepts.
- Scripted test sequences (start-up, ramps, fault injection where safe).
- Central logging of key signals for later analysis and regression.
Many teams see a big quality jump just by formalising lab tests and logging. HIL can then build on this foundation instead of replacing everything at once.
How HIL interacts with FOC tuning, protection and updates
HIL does not replace good control design – it extends how you can stress-test it:
- FOC tuning: you still need solid real-time optimisation and control loop integration. HIL lets you replay the same load cases and disturbances across versions.
- Start-up & low speed: once your start-up & low-speed tuning works on the bench, HIL can expose how it behaves under weird conditions (e.g. sudden load changes, parameter drift).
- Protection & fault handling: with HIL you can trigger overcurrent, overvoltage and other faults systematically as part of protection & testing.
- Updates & bootloaders: HIL helps regression-test your dual-slot, rollback and secure boot flows without risking real hardware in every scenario.
Simple rule-of-thumb: when HIL is likely worth it
HIL starts to make economic sense when several of the following are true:
- You have (or expect) multiple drive variants over years.
- Your drive has non-trivial safety or compliance requirements.
- Field failures are expensive (service visits, downtime, warranty).
- Your team spends a lot of time re-running similar lab tests manually after changes.
- You need to coordinate behaviour across several suppliers or teams.
In those cases, a well-designed HIL environment often pays back through reduced field issues, faster validation and more confident updates.
FAQ: HIL vs lab bench for electric drives
Does HIL replace physical testing?
No. You will always need some amount of physical testing for acoustics, mechanical effects and final validation. HIL complements the bench by covering scenarios that are hard, unsafe or too time-consuming to test physically.
Is HIL only for very large companies?
Historically yes, but not anymore. There are now smaller-scale HIL setups and even “DIY-style” rigs built from real-time PCs and I/O cards. The key question is not company size but whether your drive complexity and lifecycle justify the investment.
Can we start small and grow our HIL setup?
Absolutely. Many teams start with structured lab automation and a small real-time setup for a few critical scenarios. Over time they add more models, interfaces and test cases as the product family and requirements grow.
How does HIL fit into our existing processes?
HIL is a tool, not a process. You can integrate it into V-model, Agile or Stage-Gate development. It typically becomes part of integration, system test and regression stages, alongside classic bench and field tests.
Next steps if you are considering HIL
If you are unsure whether HIL is worth it for your drive project, a short, structured assessment often helps more than debating tools or platforms.
Typical first steps:
- Review your current testing approach for an existing drive (bench, scripts, logging).
- Identify the top 5–10 scenarios you cannot test easily today.
- Estimate potential cost of field issues vs cost of better test infrastructure.
From there, you can decide whether to strengthen lab automation first, define a minimal HIL scope, or stay with a well-structured bench. If you would like to discuss a specific drive system, you can reach us via the contact page or through engineering & firmware consulting and drive systems.
0 comments