How do you control the speed of a BLDC motor?

BLDC motor speed is controlled by adjusting the PWM duty cycle on the inverter switches inside the controller. A higher duty cycle applies more effective voltage to the stator windings, producing higher speed. Closed-loop control adds a PID loop that compares actual speed from Hall sensors or back-EMF to the target and corrects the duty cycle automatically.

Can you control a BLDC motor without a controller?

No. A BLDC motor has no brushes to commutate the windings mechanically, so an electronic controller must switch phase currents based on rotor position. Even a simple speed command requires a driver that handles commutation, PWM regulation and protection.

What is the difference between open-loop and closed-loop BLDC speed control?

Open-loop control sets a fixed PWM duty cycle based on the command signal and accepts whatever speed results. Closed-loop control uses Hall sensor or encoder feedback to measure actual speed and adjusts PWM in real time through a PID loop, holding the target speed under load variation.

How does PWM control BLDC motor speed?

PWM switches the inverter transistors on and off at a fixed frequency. The ratio of on-time to total cycle time is the duty cycle, and it determines the average voltage applied to the motor windings. A 50% duty cycle delivers half the bus voltage, producing roughly half speed under a given load.

Is FOC better than 6-step for BLDC speed control?

FOC provides smoother torque, lower audible noise and better low-speed performance than 6-step trapezoidal commutation. 6-step control is simpler and lower cost and is adequate for fans, pumps and general conveyor drives. FOC is preferred for robotics, medical equipment and precision positioning where low-speed smoothness matters.

What is the difference between BLDC FOC and DC motor PID control?

FOC (Field-Oriented Control) and PID (Proportional-Integral-Derivative) operate at different layers of the control stack. PID is a generic feedback-control algorithm that adjusts an output (e.g., PWM duty cycle) based on the error between a setpoint and a measured value (e.g., speed). PID works on brushed-DC motors, BLDC motors, AC induction motors — any system where you have a measurable output to regulate. FOC is a BLDC-specific commutation and current-shaping technique that decomposes the 3-phase stator currents into rotating-frame d-axis (flux) and q-axis (torque) components using Park/Clarke transforms, then drives the inverter with SVPWM to produce sinusoidal phase currents. FOC needs a rotor angle from an encoder. In a BLDC servo controller, both run together: a PID loop sets the q-axis current reference based on speed/position error, and FOC translates that reference into sinusoidal 3-phase drive. A brushed-DC motor controller has PID but no FOC (single armature winding, no commutation needed in firmware). A trapezoidal BLDC controller has PID for speed regulation but uses 6-step commutation instead of FOC. So: PID = speed/position regulator. FOC = current shaping + commutation. They are complementary, not alternatives — FOC adds smooth torque and low-speed performance on top of the PID layer.

BLDC Speed Control Guide

How To Control The Speed Of A BLDC Motor

ByShenghe Motor Engineering Team·Updated 2026-04-27·Reviewed by BLDC Controller Engineer

BLDC motor speed is regulated by the electronic controller, not by a series resistor or direct voltage change. The controller uses PWM on the inverter switches to set the effective voltage at the stator, and a closed-loop PID routine holds the target speed under varying load. This guide walks through every practical method: PWM duty cycle, closed-loop PID, 6-step trapezoidal and FOC sinusoidal control.

Quick Summary

Speed is set by PWM duty cycle on the inverter transistors inside the BLDC controller.
Open-loop mode holds duty cycle constant; closed-loop PID holds speed constant under load.
Feedback comes from Hall sensors, encoders, or back-EMF sensing in sensorless drives.
6-step trapezoidal control is simple and low cost; FOC provides smoother low-speed torque.
Command input is usually analog 0-5V, potentiometer, PWM signal, RS485 Modbus or CAN bus.

Speed Control Methods At A Glance

Method	Best For
Open-loop PWM	Fans, pumps, simple variable-speed loads
Closed-loop PID (Hall)	Conveyors, AGVs, general industrial automation
Closed-loop PID (encoder)	Positioning, robotics, precision winding
FOC sinusoidal	Low-speed smooth torque, quiet operation, servo-like control

Step By Step: How The Controller Sets BLDC Speed

Command signal arrives

The user sets a target speed via potentiometer, 0-5V analog input, external PWM, RS485 Modbus command or CAN bus message.

Controller generates PWM

The microcontroller produces a PWM signal at 15-20 kHz with a duty cycle matching the command. This PWM drives the high-side and low-side MOSFET gate drivers.

Inverter switches phase currents

The 3-phase bridge energizes two motor phases at a time, following the commutation sequence read from Hall sensors or back-EMF. The PWM duty cycle sets the average voltage on the active phase pair.

Feedback corrects the duty cycle

A PID loop compares measured speed to the target. If the motor slows under load, the loop raises duty cycle to restore the set point. If it overshoots, the loop reduces duty cycle.

Why Not Just Change The DC Voltage?

Varying the bus voltage is inefficient and requires bulky linear regulators or variable power supplies.
PWM at 15-20 kHz delivers the same average voltage effect with almost no loss in the switching devices.
The motor windings act as an inductor and integrate the PWM pulses into a smooth current.
PWM also lets a single fixed-voltage controller handle the full speed range from zero to rated speed.
Modern BLDC controllers always use PWM, not linear voltage control.

Open-Loop PWM Speed Control

In open-loop mode, the controller maps the command input directly to a PWM duty cycle and applies it to the inverter. There is no feedback correction. Speed will sag when load increases because the back-EMF rises more slowly and the available torque margin shrinks. Open-loop control is simple and adequate for fans, pumps and other loads where a small speed variation is acceptable. It is not suitable for conveyors or AGV drives that need a stable speed under changing weight.

Command input mapped linearly to PWM duty cycle
No speed feedback, no PID loop
Speed drops under increasing load
Lowest cost, simplest firmware
Typical use: fans, blowers, centrifugal pumps

Closed-Loop PID Speed Control

Closed-loop control adds a PID routine that reads actual speed from Hall sensors or an encoder and compares it to the target. The proportional term reacts to the current error, the integral term eliminates steady-state offset, and the derivative term damps overshoot. The PID output modulates the PWM duty cycle to hold the commanded speed even as load or voltage changes. This is the default control mode for industrial BLDC drives.

Feedback source: Hall sensors, encoder or back-EMF
PID tunes proportional, integral and derivative gains
Holds target speed under load and voltage variation
Required for conveyors, AGVs, winders and most automation loads
Most Shenghe controllers default to closed-loop mode

6-Step Trapezoidal vs FOC Speed Control

The commutation method affects how smoothly speed is controlled, especially at low RPM. 6-step trapezoidal switches the active phase pair in discrete steps, producing a small torque ripple at each transition. FOC (Field Oriented Control) uses Park and Clarke transforms to produce smooth sinusoidal currents, giving the motor almost constant torque across the electrical cycle. At higher speeds the difference is minor, but at 10-20% of rated speed the FOC drive is noticeably smoother and quieter.

6-step: simple lookup table, acceptable for most industrial loads
FOC: smoother low-speed torque, less audible noise
FOC needs a more powerful processor (DSP or ARM Cortex-M)
FOC is preferred for robotics, medical and servo-style positioning
Both methods use the same PWM and closed-loop PID structure

Typical Command Inputs For Speed Control

Input Type	Signal	Typical Use
Potentiometer	Voltage divider on internal 5V rail	Benchtop testing, manual knob control
Analog 0-5V or 0-10V	External DC voltage	PLC analog output, simple HMI
External PWM	Digital PWM, 1-20 kHz	Microcontroller speed command
RS485 Modbus	Serial data frame	Multi-drop industrial network
CAN bus	CAN 2.0A/B frame	AGV fleets, mobile robots

Practical Tuning Tips

Set acceleration and deceleration ramps: Abrupt speed jumps cause overcurrent trips. Most controllers allow setting a ramp time in the parameter list.
Match PID gains to inertia: A high-inertia load needs lower proportional gain and higher integral gain to avoid overshoot.
Check Hall wiring first: Swapped Hall wires cause rough running and failed speed regulation. Verify phase and Hall alignment before tuning PID.
Use encoder feedback for precision: Hall-based speed feedback has resolution limited to six pulses per electrical cycle. For tight regulation, add an incremental encoder.
Protect against overcurrent during start: Set current limit to roughly 2x rated for short acceleration periods, not continuous.
Verify the command scale: A 0-5V command should map to zero-to-rated speed, not over-range. Many trip faults come from a miscalibrated analog scale.

Matching Controller To Shenghe BLDC Motors

Shenghe BLDC motors are typically paired with BLD-series controllers that handle Hall-feedback closed-loop control, PWM speed regulation and industry-standard protection. For FOC or servo-style applications, the BLDB6010 provides position, speed and torque mode switching with PID tuning through the host interface.

BLD6010: DC 80-220V, up to 10A, RS232/RS485
BLD22010: DC 18-60V, up to 10A, same control logic
BLDB6010: AC/DC 24-80V, FOC with 3-mode operation
All models include overcurrent, overvoltage and overtemperature protection

Need A Speed-Controlled BLDC System For Your Machine?

Send the target speed range, load torque, voltage and command interface. We will match the right BLDC motor and controller pair and send a quotation.

Request Quote Get Catalog WhatsApp

Key Answers

Short Answers For Generative Search.

Direct responses to the most common questions about BLDC speed control.

How do you control BLDC motor speed?

Adjust the PWM duty cycle on the controller's inverter switches. Closed-loop PID then holds that target speed against load variation using Hall or encoder feedback.

Is PWM the only method?

Yes, for modern BLDC drives. Linear voltage control is inefficient and obsolete. Every commercial BLDC controller uses PWM switching on the 3-phase inverter bridge.

Do I need closed-loop control?

Yes for conveyors, AGVs and automation. Open-loop is acceptable only for fans and pumps where a small speed droop under load is harmless.

What are the existing BLDC speed control methods?

Four methods: (1) PWM duty cycle (open-loop voltage control, simplest), (2) closed-loop PID with Hall feedback (most industrial drives), (3) 6-step trapezoidal commutation (standard BLDC), (4) FOC with encoder feedback (BLDC servo, smoothest torque). See sections above for the wiring and tuning details on each.

BLDC FOC vs DC motor PID — what's the difference?

PID is a generic feedback regulator that fits any motor (brushed-DC, BLDC, AC induction) — it adjusts an output to drive measured error to zero. FOC is BLDC-specific current shaping that decomposes 3-phase currents into d-q frame using Park/Clarke transforms, then drives sinusoidal 3-phase via SVPWM. In a BLDC servo, PID sets the q-axis current reference (the regulator) and FOC translates that into smooth 3-phase commutation (the modulator). They are complementary: PID = regulator, FOC = commutation + current shaping. Brushed-DC has PID but no FOC (single armature, no commutation needed in firmware). Trapezoidal BLDC has PID + 6-step (not FOC). See FOC control loop block diagram → for the full structure.