I²t protection

From Granite Devices Knowledge Wiki
Revision as of 22:51, 19 October 2017 by Tero K (Talk | contribs)

(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)

Jump to: navigation, search

I²t protection is a motor overload protection method based on motor thermal modeling. I²t is a kind of sensorless motor over temperature protection.

Protection mechanism[edit | edit source]

Motor heat generation is typically dominated by resistive heat dissipation. The heat dissipation of resistance is proportional to flowing current in power of two. I²t algorithm assumes resistive dissipation being the only heat source of motor which is good enough estimate to prevent motor burning.

I²t protection continuously estimates how much motor is dissipating heat compared to its rated heat dissipation. At 100% of rated current, heat dissipation is at maximum sustainable level. Care need to be taken only when driving more current than rated current.

I²t algorithm will simply limit output current to rated current level if algorithm calculates that motor temperature is already at maximum. If calculated temperature is below maximum, then higher (peak) currents are allowed. In other words:

  • Current/torque setpoint is internally clamped to a user defined Peak current limitMMC if I²t calculation shows temperature rise to be less than motor's maximum safe level
  • Current/torque setpoint is internally clamped to a user defined Continuous current limitMCC if I²t calculation shows temperature rise to be equal or grater than motor's maximum safe level

Currentlimits graph i2t.png

Parameters[edit | edit source]

Granity will display the actual current limitation reason in the Testing tab. In this example the limit reason is I²t protection, so drive has dropped Actual current limit to the value of MCC parameter.
When configuring I²t protection, only one GDtool parameter needs to be set:
Motor time constant
Time in seconds how long it takes motor temperature rise to 63% from idle temperature to maximum allowed temperature when motor is driven continuously with 100% of rated current. If unsure, use low values (<500 seconds) to have error in safe direction.

See also[edit | edit source]


In no event the Product Information or parts hereof shall be regarded as guarantee of conditions or characteristics. The Product Information or any part thereof may also not be regarded as a warranty of any kind. No liability of any kind shall be assumed by Author with respect to Product Information or any use made by you thereof, nor shall Author indemnify you against or be liable for any third party claims with respect to such information or any use thereof.

As content of this Wiki may be edited by user community, Granite Devices Oy or it's affiliates do not take any responsibility of the contents of this Wiki. Use information at your own risk. However, Granite Devices staff attempts to review all changes made to this Wiki and keep information trustworthy.

Without written consent, Granite Devices' Products or Intellectual Property shall not be used in situations or installations where living beings, material property, or immaterial property could be harmed by the operation, features or failures of Product. Products may only be used in a way where hazards like moving parts, electric shock, laser radiation, or fire can't be realized even if the content of this Wiki would suggest otherwise.