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A 3-phase BLDC drive combines a DC source, a three-phase inverter, a controller, rotor feedback, current and voltage measurement, and fault protection. For straightforward speed control, six-step commutation is often a practical starting point; for more precise torque or speed control, field-oriented control (FOC) offers more capability at the cost of more computation and implementation work. Choose the method and hardware for the motor’s voltage and current range, startup conditions, performance target, available feedback, and controller resources—not from a reference design’s headline rating alone.
How do I control a 3 phase BLDC motor?
The controller switches the inverter’s six power devices in sequence to create a rotating stator field. The rotor’s position determines when the controller changes the energized phases. The controller also adjusts PWM duty or current commands to regulate speed or torque, reads the measurements required by its control method, and disables or limits drive output when a fault occurs.
Before choosing parts or writing commutation code, record the operating envelope and control goal. These determine whether six-step or FOC is appropriate, whether rotor sensors are needed, what current-sense topology is useful, and which MCU peripherals the drive must provide.
- DC-bus minimum and maximum voltage, plus expected bus transients.
- Motor phase-current requirements, including continuous and peak current, and the intended thermal environment.
- Required speed range, torque behavior, direction control, and whether braking is required.
- Whether the motor must start under load, run smoothly at very low speed, or regulate position.
- Available Hall sensors, encoder or resolver feedback, or a requirement to operate without rotor sensors.
- Available MCU PWM, timer, ADC and comparator resources, along with the measurement and protection functions the application needs.
Choose six-step commutation or FOC
| Control method | What it does | Consider it when | Main implementation trade-off |
|---|---|---|---|
| Six-step (trapezoidal) commutation | Advances through six electrical sectors. In the common sensorless arrangement, two phases conduct and the third floats for back-EMF measurement. | Speed control is the main goal and the motor can start reliably with the chosen sensor or startup procedure. | It uses a comparatively direct commutation sequence, but sensorless operation needs reliable zero-crossing detection and careful timing. |
| Field-oriented control (FOC) | Controls the stator field relative to rotor flux to regulate torque and speed. | The application needs more precise torque or speed behavior and the controller can meet the real-time processing and sensing requirements. | It requires Clarke and Park transforms, inverse transforms, and rotor-angle and velocity information; sensorless FOC estimates those quantities rather than using a simple floating-phase zero-crossing detector. |
Neither method is universally best. Texas Instruments’ 2020 motor-driver selection guide, revised in May 2022, distinguishes speed, torque and position applications and describes how motor and application requirements affect commutation and sensing choices. Its guidance is a vendor selection resource, not an independent comparative trial.
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How does sensorless BLDC motor control work?
Six-step back-EMF detection
In sensorless six-step control, the undriven phase is monitored for back electromotive force (BEMF) while the other two phases are energized. The controller rotates which phase floats as it advances through the commutation sectors. A comparator or ADC can detect the BEMF zero crossing against the appropriate reference.
A zero crossing occurs near the middle of a sector, not at the next commutation boundary. The controller therefore commonly waits about 30 electrical degrees after the crossing before changing sectors. In firmware, that interval is implemented as a delay that changes with electrical speed. Microchip’s “Learn-Six Step Sensorless Brushless DC (BLDC) Motor Commutation” lesson, last modified May 11, 2026, states that “The zero crossing does not occur at the optimal commutation point” and explains the timing relationship.
Noise, timing and speed limits
PWM switching and inductive ringing can obscure the BEMF signal. Filtering and sampling synchronized to the switching cycle can help the controller avoid treating switching disturbance as a zero crossing. At higher speed, winding inductance and inverter switching delay can make current lag; phase advance may compensate, but its amount depends on the motor and power stage and must be tuned for them.
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BEMF-based position information depends on rotor motion. It is strongest once the motor is spinning, so a sensorless drive needs a deliberate startup method—often alignment followed by open-loop acceleration—before it can rely on BEMF feedback. A zero-crossing detector is not the same as sensorless FOC: FOC estimates rotor angle and velocity using a model-based approach with motor-parameter requirements, rather than simply detecting the floating phase’s crossing.
Hall sensor vs sensorless BLDC—which should I use?
| Feedback approach | Position information | Practical fit | Trade-off |
|---|---|---|---|
| Hall sensors | Rotor-sector information is available directly from the sensors. | Useful when startup, low-speed behavior, or dependable sector information matters. | Adds sensors, wiring and integration requirements. |
| Encoder or resolver | Provides position feedback suited to higher-accuracy demands. | Consider for applications requiring tighter position regulation or higher-accuracy feedback. | Adds feedback hardware and its associated integration work. |
| Sensorless BEMF | Infers rotor position from the motor’s back-EMF while it is rotating. | Can reduce sensor hardware for applications centered on speed operation. | Position information is weak or unavailable at standstill and low speed; startup needs a separate strategy. |
Texas Instruments’ selection guide describes its sensorless BEMF approach as typically suited to speed applications: BEMF increases with rotation, position control is not supported by that approach, and torque control is difficult. If the application needs position regulation or predictable operation from standstill, use feedback that supplies rotor position at low speed or confirm that the chosen startup and control approach meets the requirement.
Size the inverter, controller and measurement path
Power stage
A three-phase inverter normally uses six switching devices, or a suitably integrated three-phase driver. Select MOSFETs and gate drivers for the actual bus voltage, motor current, thermal conditions, switching behavior and required gate-drive capability. Peak and continuous ratings are different constraints; the complete power stage—including PCB layout, cooling and protection—must support the intended operating envelope.
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Controller and feedback resources
Match the MCU’s PWM outputs and timers to the switching and commutation scheme. The design may also need ADC channels or comparators for current, bus voltage and phase/BEMF measurements. FOC requires sufficient real-time processing for its transforms and control loops, as well as a usable rotor-angle estimate. Check the controller’s peripheral and software support against the specific method before committing to it.
Current and voltage sensing
Current sensing may use external shunts with current-sense amplifiers or integrated low-side sensing. Choose based on the current visibility required by the control method and the application—not just on the number of channels a driver happens to provide. Current feedback supports current limiting and can support torque control. Measure the DC bus and phase or BEMF signals as required by the chosen algorithm; plan their scaling, sampling timing and safe measurement range into the hardware.
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Organize the firmware as explicit operating states so that the motor cannot move directly from reset to unrestricted switching. A typical sequence is:
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- Initialize and check configuration: Set up PWM, timers, ADCs or comparators, sensor inputs and fault handling. Confirm that the bus and configured motor limits are plausible before enabling power-stage switching.
- Align and start: Use an alignment and startup procedure if the motor or sensorless method needs one. Where required, accelerate open-loop until the selected feedback method is reliable. Define what happens if the rotor fails to start.
- Acquire feedback: Validate Hall transitions, encoder data or BEMF crossings before using them for closed-loop commutation or regulation.
- Run the requested control loop: Update commutation and PWM, and regulate speed, torque or current according to the application. Use current feedback for the intended limit or control function.
- Detect, shut down and recover from faults: Define responses to conditions such as overcurrent, bus overvoltage or undervoltage, overload, startup failure and overtemperature where supported by the design. Specify whether a fault latches, permits restart, or requires a controlled stop.
NXP application note AN12435 (revision 1, June 2020) provides one concrete S32K144 six-step example. It uses a 1 ms speed-loop action period and a 100 microsecond sampling period; those are settings in that example, not universal timing recommendations. The example supports Hall or BEMF rotor-position feedback, bidirectional rotation, current limitation, alignment and startup, and DC-bus current, DC-bus voltage and BEMF measurements. Its listed protections include DC-bus overvoltage and undervoltage, overcurrent, overload and startup failure.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Select development hardware by compatibility, not headline rating
A driver board or evaluation kit can speed development, but its rating is not evidence that it will work with an arbitrary motor. Compare candidate hardware on the parameters that govern your application:
- DC-bus range and motor voltage, continuous-current and peak-current envelope.
- Six-step or FOC support and the available Hall, encoder, resolver or sensorless feedback options.
- Current-sensing topology and channel visibility required by your algorithm.
- MCU processing capability, PWM and measurement peripherals, and available software.
- Startup and low-speed behavior, including whether the design suits starting under load.
- Fault responses, thermal design and the conditions under which ratings apply.
- Whether the board is available as a development platform or is a reference unit intended for validation rather than sale.
| Reference design | Published scope | Availability or use qualification |
|---|---|---|
| Texas Instruments TIDA-00274 | Up to 48 V; 1.9 A peak and 1.25 A RMS continuous. Sensorless trapezoidal commutation; listed protections include short circuit, thermal, shoot-through and undervoltage. | These are specifications for this reference design, not general ratings for BLDC drives. |
| Texas Instruments TIDA-010250 | 1 kW maximum at nominal 200–277 V. Supports sensorless FOC with one to three shunts or Hall/QEI feedback. | TI describes the assembled board as a testing and performance-validation unit, not a product for sale. |
The two designs target materially different voltage, power and control needs. Treat each as an example of a particular implementation, not proof of compatibility with another motor or evidence of current retail stock.
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Validate the drive in stages
Commissioning should start with limited energy and a motor matched to the power stage. Raise speed and load only after basic switching, sensing and shutdown behavior are confirmed.
- Use a current-limited supply and verify the motor and inverter ratings are compatible.
- Check phase order, Hall polarity or selected BEMF phase, PWM polarity and dead time at low risk before attempting normal operation.
- Verify ADC/comparator scaling and sampling timing, and confirm that fault detection actually disables or limits the stage as intended.
- Test startup repeatability, direction changes and the required operating range before applying the expected load.
- Monitor current and temperature across the intended speed, torque and thermal conditions; revise limits or hardware if they exceed the design envelope.
These are prudent engineering checks, not reported bench-test results for the vendor reference designs discussed above. Any performance data published by a vendor applies only to that design and its stated test conditions.
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