SPRUHJ1I January 2013 – October 2021 TMS320F2802-Q1 , TMS320F28026-Q1 , TMS320F28026F , TMS320F28027-Q1 , TMS320F28027F , TMS320F28027F-Q1 , TMS320F28052-Q1 , TMS320F28052F , TMS320F28052F-Q1 , TMS320F28052M , TMS320F28052M-Q1 , TMS320F28054-Q1 , TMS320F28054F , TMS320F28054F-Q1 , TMS320F28054M , TMS320F28054M-Q1 , TMS320F2806-Q1 , TMS320F28062-Q1 , TMS320F28062F , TMS320F28062F-Q1 , TMS320F28068F , TMS320F28068M , TMS320F28069-Q1 , TMS320F28069F , TMS320F28069F-Q1 , TMS320F28069M , TMS320F28069M-Q1
Inertia is an important piece of information needed to precisely control the mechanical system. InstaSPIN-MOTION provides a robust inertia identification feature via SpinTAC Velocity Identify that obtains an accurate estimation of inertia, while accounting for the influence of friction within the sensorless application. Currently, SpinTAC Velocity Identify does not actively consider the load torque. In order to get the appropriate value, the load torque, such as gravity for crane-type applications or compressed fluid in compressor applications, needs to be removed or minimized.
SpinTAC Velocity Identify estimates the inertia in the units A / [krpm/s]. This is different from the traditional unit for inertia of Kg * m2. The unit A / [krpm/s] represents the amount of torque required to accelerate the system. It is proportional to the SI unit Kg * m2. The relationship is based on the amount of torque that the motor can produce. The SpinTAC controller needs to know how much torque is required to accelerate the system and thus uses this non-traditional unit for inertia.
SpinTAC Velocity Identify produces a very accurate inertia result. Figure 8-2 is a plot of the inertia identification result of the same motor for 100 tests of the inertia identification process. As you can see the inertia identification is extremely repeatable. The maximum and minimum values for these trials are within 0.5% of the average value for 100 tests. Once SpinTAC Velocity Identify is correctly estimating your system inertia it will produce a result with similar levels of repeatability.
The estimated inertia is an input to both SpinTAC speed and position controllers. However, the SpinTAC controller is extremely robust and can tolerate a wide range of inertia variation. This feature is valuable in applications where the inertia of the system changes over time.
Figure 8-3 compares the performance of the SpinTAC speed controller with a range of wrong inertia setting. This was tested by applying a torque disturbance to a motor system. The inertia value provided to the SpinTAC speed controller was set to different values to highlight the range of inertia error that can be tolerated by the controller. This shows that the SpinTAC speed controller can tolerate an inertia mismatch of up to eight times. The best performance is realized when the inertia value is match with the application, but if the inertia of the system changes the SpinTAC speed controller remain stable.
SpinTAC Velocity Identify provides a method to quickly and easily estimate the system inertia. It applies a continuous torque profile to the motor and uses the speed feedback to calculate the motor inertia. This is an open loop test that is designed to run as part of the development process. Once the inertia is identified, it can be set as the default value and does not need to be estimated again unless there is a change in your system.
During inertia identification, the motor spins in a positive direction and will then spin briefly in a negative direction. If this cannot be accomplished in your system there are special considerations that will need to be taken into account. The description of these considerations in discussed in Section 8.6.