When the load applied to a brushless DC (BLDC) motor changes—whether an increase or a decrease—the motor can maintain a relatively constant speed.
This capability is enabled by closed-loop speed control. The motor controller continuously monitors the motor's actual speed and dynamically adjusts the current supplied to the motor to compensate for load variations. When a load change occurs, the controller detects the resulting speed deviation and responds accordingly. During this process, the motor's speed may fluctuate momentarily before gradually returning to the target speed.
The time it takes to return to the target speed depends on several factors, including the rotor inertia, load inertia, and the controller's response characteristics (such as PID tuning). In general, a system with lower combined inertia and a well-tuned controller will recover more quickly.
Note that the load change must remain within the motor's rated torque capacity for this automatic speed regulation to function properly.