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Intelligent Power Modules

Intelligent Power Modules

Intelligent Power Modules

(OP)
Hi,

I'm designing a 3 phase motor drive for a 3 phase BLDC drive. The drive should operate from a 440V 3 phase system and should be capable of handling 5kW to 7kW.

I've been looking for a package which integrates all the IGBTs and the drive electronics from manufacturers such as IOR and Fairchild. They all offer very good solutions but only upto 400V working voltage.

The best solution I found yet is from Mitsubishi semiconductor (Powerex). The part no is PS12036. It integrates all the IGBTs, drive ccts and provides protection such as over current protection, control side under voltage shutdown, shoot through lock out etc.

Do you guys have any suggestions?  

RE: Intelligent Power Modules

Maybe better way would be on-the-shelf servo amp including motion controller - for example Elmo (www.elmomc.com)?     

RE: Intelligent Power Modules

(OP)
Blacksea,

I considered that option but 2 points

The motor is a custom design and run at a very low speed generating high torque and short operating time. Couldn't find a suitable controller.

Ultimately the drive and the motor will be packaged as a single unit. So I thought it's better to tryout our own design.  

RE: Intelligent Power Modules

(OP)
itsmoked

IXSY has CBI IGBT modules but they do not integrate the gate drive ICs. I was looking to see if IPMs are available with the HV gate drive ICs integrated as well

RE: Intelligent Power Modules

"They all offer very good solutions but only up to 400V working voltage. "

What most drive manufacturers do is use the 400V "class" devices and test to higher voltages, i.e. 480VAC input. By the way, use 480V, not 440V as a design spec. Only legacy systems still have 440V any more.


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RE: Intelligent Power Modules

ShamilaWije,
First, I hope designed by you motor would be as standard one, i.e. 3-phases wye-connected with 4...8 pairs of poles. BTW  what's about position sensor?
Second, Elmo amp is very compact and have integtated with MPC motors.
And finally, current sense and sampling, IGBT drivers interface, filters for current / velocity / position loops, PCB design for high voltage and current - too many problems for such design...  

RE: Intelligent Power Modules

IMHO the on module protections (especially Short Circuit Protection) is worth ever penny.  If you try to design your own, expect fire, smoke, and big bangs a number of times.

RE: Intelligent Power Modules

1. Very often IPM modules are choosen for the design assuming that this would allow an easy design without much of power electronics knowledge.

This is definetly not the case

2. The IPM you mentioned contain driver circuits, but they do not contain the signal isolation and the driver power supply to SELV level.

3. In such a direct drive application as you describe, take care to consider power cycling. With low output frequency the junction temperature of the die
- will reach the same value as having the peak current of the sinewave as DC
- will vary over time
- the variation will cause degradation of the bond finally leading to failure. Read manufacturers on this and consult a technical representative. Considering that, Ihave doubts that the module you have choosen provides sufficient current capability.


4. A further pitfall of this drives is that parasitic capacitances of the motor winding are significantly higher than usual. This may cause
- EMC-Problems
- Unintended SC-tripping
- increased swicthing loss



 

RE: Intelligent Power Modules

Electricuwe;

1. Absolutely true.  Designing Power Electronics without some thought results in "Big Bangs." This does not happen with 3.3V logic circuits.  i.e., the consequencies of design erors in Power Electronics has more dire results.

2.Yes, fast optical Isolators and power supplies for the Gate Drive signals must be provided. Other than that the supplies must be floating, this is not a really big problem.

3. The Worst Case Values must be sought and respected.  Otherwise see "Big Booms."  Thermal cyclying and wire bond failure is a feature of all power electronics.

4.Motor winding capacitance-use small series inductors in the motor leads (on the circuit board).

EMI.  A life time of study (and disappontment).

SC tripping-see series inductors.

Increased switching losses? Where when using an IPM?

RE: Intelligent Power Modules

(OP)
Thanks guys for the response.

electricuwe

2. The IPM you mentioned contain driver circuits, but they do not contain the signal isolation and the driver power supply to SELV level.

Yes i understand that the signal isolation is not provided. But if need be I can optically couple the signals as needed while isolating the microcontroller supply from the IPMs control cct supply. Although this is strictly not since I can use the same supply for the microcontroller while isolating all the signals to the outside. Such as comm lines and Digital I/O etc.
By the way what is SELV level?

3. In such a direct drive application as you describe, take care to consider power cycling. With low output frequency the junction temperature of the die
- will reach the same value as having the peak current of the sinewave as DC
- will vary over time
- the variation will cause degradation of the bond finally leading to failure. Read manufacturers on this and consult a technical representative. Considering that, Ihave doubts that the module you have choosen provides sufficient current capability.


Yes I understand the current capability is not quite enough for the power rating I mentioned(about 5Arms according to the datasheet) but lets assume its enough for this discussion. smile

4. A further pitfall of this drives is that parasitic capacitances of the motor winding are significantly higher than usual. This may cause
- EMC-Problems
- Unintended SC-tripping
- increased swicthing loss


Can you please elaborate on the parasitic capacitance and how the IPM effect this.
 

RE: Intelligent Power Modules

ShamilaWije,

let me go more into details.

3. Even the RMS current rating of 5 A does not take into consideration effects of power cycling. Low frequency operation may lead to further derating if long lifetime is expected.

4. Switching losses of IPM (as well as for standard IGBT modules and discete IGBTs) are measured assuming an inductive load. A standard electric motor connected directly to the module comes quite close to representing such a load. However, if a long cable is involved or the motor is designed for low operating frequency there is significant parasitic capacitance connected to the module unless you connect further components in between as suggested by sreid.
At each switching of the module this charging and discharging of the capacitances leads to high peak currents and most of the energy stored in the parasitic capacitances has to be dissipated by the IGBTs inside the module additional to the conduction losses and the swithing losses for inductive load.

RE: Intelligent Power Modules

Even worse than the motor winding capacitance, the motor Iron has the permiability of air to fast switching edges.  Initially it appears that you are driving an air core inductor until the iron "catches up."  The series inductors minimize this effect which, along with the capacitance, can cause some truly impressive high current spikes.

RE: Intelligent Power Modules

(OP)
Thanks guys for the info.

Can you give me some guidance on either measuring or estimating these capacitances and permiability effects. Also how do I choose the required series inductance assuming I know the above data.

RE: Intelligent Power Modules

As a general rule, the bigger the inductor the better.  Ferrite or powered iron code (for high frequency performance).  The inductor has to handle the peak motor current without saturating so for PC board area considerations you will be limited to 10s to 100s of microhenrys.

RE: Intelligent Power Modules

(OP)
Thanks sreid. I'll see if I can get some actual measurements on the motor I'm working on.

RE: Intelligent Power Modules

(OP)
Thanks for the info. I'm already using avago opto-isolators and LEM current transducers. So I seem to be on the rught track. smile

RE: Intelligent Power Modules

Even the smallest SkiiP is severly oversized for this application.

RE: Intelligent Power Modules

Can I assume that you are using only two current loops,say Phase R Current and Phase S Current and

Phase T Current = -[ Phase R current +Phase S Current]

RE: Intelligent Power Modules

Error in the last post.  The equation should be

Phase T Voltage = -[Phase R Voltage + Phase S Voltage]

RE: Intelligent Power Modules

(OP)
I thought your first equation is the correct one. If the 3 phases are Y connected you just have to apply KCL to the point right?

RE: Intelligent Power Modules

KCL is?

RE: Intelligent Power Modules

Kirchhoff's Current Law.

RE: Intelligent Power Modules

Clearly the three currents sum to zero in the motor.  But with three current loop drives never exactly sum to zero; offsets and scaling differences.  This can result in "Current Fights."

Worse, there are an infinate nubber of voltages on the motor phases that will give zero current in all phases.
0 V, 0 V, 0V will give zero current but so will 1 V, 1 V, 1 V.  There are ways to handle this but, IMHO, is to use two current loops and drive the third phase with the proper "Compliance Voltage."

There are then no current fights, 0 voltage equals zero current and you don't have to pay for the third current sensor.

And the Intellmod (Powerex) takes care of short circuits for all three phases so the third current sensor is not needed for that function.

I have thousands of servo amplifiers in the field that are implemented just that way.

I have never seen this in any Textbook but it is commom in the servo industry.

Are you going to Soft or Hard Switch and how do you plan to handle the dead band if soft switching (also called center based PWM).

RE: Intelligent Power Modules

(OP)
what is exactly meant by 'current loop'? Is it the feedback loop created by taking the current sensor output?

I guess sreid you are referring to self commutation when you say soft switching am I right? If so I'm planing to do hard switching. I am planing to use a IGBT module. Also a constant deadband will be set.  

RE: Intelligent Power Modules

PWM amplifiers today all implement a curren loop to drive the motor phases.  The loop is a summing junction with a current command input and the current sensor as the current feedback,  A Proportional Integral (PI)controller amplifies the difference between I Command and I Actual to drive the PWM Switches.

Almost all three phase PWM bridges are implemented as center based (Soft) switching.  This means that for a zero current command, all three phase legs are being driven with a 50% duty cycle with a small dead band to eliminate "Shoot Through" between top and bottom transistors.  This causes a dead band which may or not be important in the servo.

RE: Intelligent Power Modules

sreid: PWM with 50% duty cycle have "bipolar" method. And more modern servo amp use improved "unipolar" one due to lower current ripple.

RE: Intelligent Power Modules

(OP)
I agree with blacksea. There are 2 main variations how you can do PWM switching Bipolar and Unipolar.

In bipolar mode you switch from +V to -V and then again to +V. If your duty cycle is 50% then the average voltage would be 0. Since we are changing the voltage by 2*V the there is a higher current ripple than in the unipolar switching. (EMC considerations)

In the unipolar method you switch from +V to 0 the back to +V. Here to achieve 0 average volts you have to give 0 duty. (less current ripple).

There is a variation of unipolar called Advance Unipolar. This is used in ELMO drives

RE: Intelligent Power Modules

A Star for ShamilaWije, Advanced Unipolar (or what ever a particular vendoe calls it) is the best combination of zero crossover distortion and minimum switching power losses.

RE: Intelligent Power Modules

(OP)
Thanks for the star sreid.

By the way I measured the capacitance of each phase of our BLDC motor with a LRC meter and found out that there was about 200nF of capacitance in each phase.

By looking at the current wave form going in to each phase I could see two spikes one when the PWM swithes on and one when it swithes off.

So I tried adding some additional inductances on to each phase. (about 1mH). This reduced the spikes of the current wave form out of the power module.

So thanks again guys for the info.

I'll try to post some results in coming weeks.

RE: Intelligent Power Modules

ShamilWije: reason of current spikes with PWM switching maybe low recovery of free wheling didodes in parallel with switch. As pls check its recovery time.

RE: Intelligent Power Modules

(OP)
I thought voltage spikes are the result of higher recovery time. Anyway I'm using a IPM from IRF IRAMY20UP60. This should be able to go upto 15kHz without any problem.

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