What Is the Meaning of "Sensorless Initial Speed" in a Brushless Drive?

The parameter "Sensorless Initial Speed" (also referred to as Starting Torque No Sense Initial Speed) can be found in the brushless drive manual.

Sensorless Initial Speed is the preset synchronous speed given to a sensorless motor at startup. It is used specifically for the initial startup moment in sensorless mode and is adjusted in conjunction with the starting torque to facilitate motor startup. This parameter can be ignored in sensored mode.

Its purpose is to provide an "initial guiding speed" from the drive when the sensorless motor starts, helping the motor transition smoothly from standstill to rotation.

Core Function:

Since a sensorless motor lacks a position sensor and does not know the rotor's position at startup, applying force directly can cause jitter, failure to rotate, or even stalling.

This initial speed acts like a "starting signal." The drive first outputs a magnetic field at the set low speed (e.g., a few hundred RPM), gently pulling the rotor to follow. Once the speed stabilizes, it switches to normal control.

Key Characteristics:

1. The speed does not need to be very high—just sufficient to initiate motor movement and avoid excessive torque during startup.
2. The drive automatically completes the switch from "initial guidance → normal operation" without manual intervention.

Updated on: 30/10/2025