Variable Frequency Drive

In the website www.abb.co.in you can search for a 400-page Drives Guide which explains in detail.

http://en.wikipedia.org/wiki/Direct_torque_control

http://en.wikipedia.org/wiki/Vector_control_(motor)

Also try the "AC Tech" or other variable speed drive manufacturer website (or internet search) for more information. Alternatively I believe this question has been answered before on CR4.

This previous thread may also help:

http://cr4.globalspec.com/thread/52196/VVVF-Drives-Vector-and-Scalar-Modes

- MS

Nutshell overview in non-tech language:

High precision control of VFD outputs is necessary in some applications, especially when torque control is more important than speed control. "Sensorless Vector Control" is, unfortunately, a relatively loose description of a technology that can be implemented in a variety of ways, some better than others. The issue at hand when you want precision is called "overshoot" of the output to the motor. A VFD puts out a PWM signal that makes the motor respond in a given way, but if the output response is too slow to adjust for minor fluctuations in the load, the motor's torque response may get a little sloppy (at a micro-like level). "Cheap" SVC drives can have a lot of overshoot, mainly because the processing power of the micro-processor in the VFD has too many things to do at once. Better VFDs use more powerful mPs or use parallel processors; one dedicated to doing the firing control, the other to do all the other tasks. DTC on the other hand inherently defines a method of precise control with very little overshoot in the design, so basically if a VFD says it is using DTC, then it is inherently more precise than a cheap SVC drive. But in my opinion, there are very good SVC drives out there that can rival the performance of DTC, just unfortunately the terminology moniker "SVC" is the same as those that cannot, so it requires more investigation.

However, 95% of applications we all run in to every day don't need that kind of precision anyway, so the capability is relatively meaningless.

Not read my question (Last line)

Simple explaination???

Wow, I boiled down 400 pages of technical text into one paragraph and you still complain?

Whiner...

thanks for you efforts.

: )

I've been trying to find a webcast back in 2009 from these people relating to your question but to no avail.

It was highly informative and they used for illustration one of the state-of-the-art hybrid vehicle's (Prius) logic controller block diagram for the purpose relating to your questions even.

I will try to do my best to further inquire but I do not even remember the title of that webcast seminar.

However, you can also try to contact them.

Direct torque control method is new styel control policy in alternating current drive field after vector control method. direct torque control methods dont need complicated coupling computation and multifarious coordinate commutation. Direct torque method controls directly motor torque in stator coordinate, and produces PWM signal by discrete deuce control.

Sensorless vector control is a mature technology whose origins to back to the early seventies. However, many high performance induction motor drives are still being proposed since some problm are still not solved. Sensorless operation mode has attracted much attention and two main approaches can be considered: Those based on the field orientation principles to carry out the control and the direct torque control which is inherently a sonsorless method. Both have their own weaknesses and a lot research work has been done trying to solve them.