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
Most direct drive washing machine use motors with a low rated speed. In these applications it is important to decrease the VelPos parameter. This parameter is located in the configuration structure of the SpinTAC Velocity Identify global structure. The VelPos value represents the goal speed in pu/s of the inertia identification process. If the goal speed is greater than twice the rated speed of the motor, inertia identification will fail because the motor will not be able to achieve enough speed. Decreasing VelPos means that the goal speed of the inertia identification process will be lower and will allow the process to succeed. Using field weakening to increase the speed of the motor during the inertia identification process is not recommended. Field weakening will impact the relationship between speed and torque.
Figure 8-8 is the speed feedback during the inertia identification process for a direct drive washing machine. You should notice that the motor spins at its rated speed of approximately 360 rpm for longer than 5 seconds. This means that the motor never reached the goal speed specified in the VelPos configuration parameter and SpinTAC Velocity Identify timed out and ended the inertia identification process.
Direct drive washing machines also feature a large amount of back emf and rapid deceleration could cause an over-voltage condition on the DC bus. Reducing the Goal Speed will cause the motor to have less deceleration and will generate less voltage on the DC bus. The Goal Speed is set by the VelPos parameter.
Figure 8-9 is a plot that shows the voltage on the DC bus during the inertia identification process. The speed feedback is provided for reference. You should notice that the DC bus rises to 400 volts during the inertia identification process when the Goal Speed is set to 400 RPM. In order to eliminate this large rise in voltage, the VelPos configuration parameter is decreased. When the Goal Speed is set to 200 RPM, the DC bus stays below 350 volts during the entire inertia identification process.