Variable DC link for BLDC

Ed Walker

Other Parts Discussed in Thread: DRV8301

I've been evaluating the Hercules RM46 MCU using the DRV8301-RM46 kit for controlling my motor, but it has occurred to me that the motor control methods may not be ideal for my motor. I have read that very low inductance, high-speed motors benefit from a variable DC link approach instead of conventional PWM (mostly from a motor heating perspective). I have looked around, but I'm having trouble finding a suitable eval kit to demonstrate the variable DC link approach.

I am thinking that a C2000 may be a better approach for the Variable DC Link since it involves a SIX STEP inverter with multiple PWM inputs.

Does TI have any examples of Variable DC Link with BLDC motor control?

over 12 years ago

0 Ed Walker over 12 years ago

Prodigy 5 points

Here are some research (link1, link2, link3) articles on “VARIABLE DC LINK”, a means having a DC-DC converter in-front of the source for the motor or more particularly the source to whichever H-Bridge is chosen. This is a sensor based design that requires hall effect sensors on each phase. Usually a control algorithm is used that adjusts Vin and Duty Cycle based on the motor speed. This would overall allow for finer tuning of the currents through PWM control.

Our Insta-Spin technology is not only sensorless, but uses current flux for commutation. This is where we really stand out vs. traditional control methods. Traditional sensorless motor control measured zero-crossing on the Back EMF which is quite unreliable at low RPM. That could be cause for excess heat, but with our FOC we can reliably deliver the exact amount of energy to efficiently spin the motor up to speed.

I would say, TI does not have an algorithm developed to control a motor that both changes duty cycle and Vin but instead utilizes the most efficient methodology (FOC) when presented with a constant DC link.

It seems one could utilize the DRV8301 and an External DC/DC with a c2000 to recreate the same technology. But the development of the control algorithm that could dynamically change Vin would be a R&D project.

Excellent Wiki that covers the technology we have available today http://processors.wiki.ti.com/index.php/TMS320C2000_Motor_Control_Primer
Closest thing to Variable Link DC control we have: http://www.ti.com/lit/ml/sprt615a/sprt615a.pdf

This document goes into the control theory behind a FOC + Variable DC Link and uses a c2000. http://projekter.aau.dk/projekter/files/14498144/s08_Stefan_Partyka.pdf