Of coursce it is possible. I think there is no general answer to this question because there are a large variety of the sensorless control algorithms. In the other hand, the most of the practical control algorithms for three-phase induction and PM-motors are adaptive and use the premeasured motor parameters only as an initial approximation for observers. So such control schemes must provide the stable contol even with some (not too big) errors in the premeasured motor parameters.

So Thanks Vadim Kazakbaev

But I think the motor's stability is not enough.For example in efficiency improvement applications the filter doesn't allow to work at best point (because of mentioned errors).

Yes, it is so. I am not informed about research works on the topic yet. But, as I know so far, the use of the additional filters between the converter and the motor is a rather rare case. In the first, why do you need the filter?

PWM pulses reflect when they reach to the motors terminal and this cause overvoltages (about twice of DC_Link voltage). I want to use filter to reduce it.

then we can work on efficiency improvement.

The overvoltage you mention takes place only in the case of a very long cable. It is a comparatively rare case for motors of a large rated power. In this case the installation of the frequency converter directly on the motor housing may be a better and a cheaper solution (see, for example, the picture in the attachment).

yes, you're right.

thanks for your attention vadim.🌷

Hi Mahdi. I know this may be a bit late as a reply for you. In general I agree with Vadim especially about long cables. However a lot depends on the type of motor wiring (Y, Delta, inside Delta) and the type of filter used. About filters, from years of experience in EMC testing, I am against filters between any controller and load, be it phase angle of VF. Vadim mentioned the algorithims in controllers. There are also 'sensorless' types that actively monitor load behaviour and vary parameters accordingly. These are known as self learning. A filter will give a false "picture" to the controller's measurements resulting in incorrect parameter compensation by the controller. It can actually destroy the controllers power units (thyristors or IGBTs). So, always keep filters only on the supply side. Remember that different filters are designed for different conditions not one size fits all.

Now for the over voltage spikes...It depends when you observe these - ramp-up, stable running or ramp-down conditions. It is natural that during ramp-down overvoltage occurs due to a phase shift between the motor and the supply frequency as the motor decelerates. The motor will be acting like an out-of-phase generator against the supply from the controller. So theoretically your phasor can result in 2x supply voltage.

Last comment from me. Small motors may actually be worse as they usually reach >75% rotation speed in a few milliseconds (over accelerate) and usually are highly inductive. Hope this helps you a bit to understand better motor control.

Hi Alex Agius . Thanks for your attention and very good comments.

I'm a little confused. whats the effect of motor winding?Is there any reference book that explain this issue?

I understood its better not to use filter between load and controller. So what should we do to reduce over_voltages?

Except long cables ,nowadays because of very fast switches and short rise_times ,we can see over voltages during stable conditions. fast pulses can drive some components that are not modeled for controller.

Hi Mahdi Mahyari. Depending on what energy these O/V conditions are carrying, you may consider using MOVs of the correct voltage and not smaller than S20. It also depends on the frequency of the transients but MOV react in 5ns. However beware that MOVs have a lifetime and their end of life is not pretty. They can explode so protect them by a fuse on every phase. You may wish to attach an o/scope image or CSV file of the o/v to help understand better what you are up against.

In addition to passive filters and the other approaches Alex mentioned, it is possible, for example, to limit the voltage Gradients using the IGBT active gate drivers. See the folliwing paper:Conference Paper Voltage Gradient Limitation of IGBTs by optimised Gate-Curre...

hi

so thanks Alex Agius and Vadim Kazakbaev .