I was looking at some of the SimPowerSystems examples for motor drives and noticed strange behavior in the DC bus currents. For example in ac7_example (AC7 - Brushless DC Motor Drive During Speed Regulation), the bus voltage is well regulated but the current fluctuates rapidly from positive to negative:
This doesn't seem physical, as I would expect the sign of the current to follow the torque. Does anyone have an explanation for this?
Additionally, in ac7_example_comparison (AC7 - Comparison Between Detailed and Simplified Models), bus currents are plotted and look correct, but the output signals were passed through a discrete transfer function:
The transfer function makes the output look right, but the actual current still fluctuates.