Is the DRV8312-69M-KIT suitable for a sensorless non-PM motor?

John,

I don't think DRV8312-69 kit is suitable for driving switched relutnace type of motors. It canbe used for other non-PM 3-phase motors such as 3-phase induction motor.

Best Regards

Milan-Motor Applicaiton Team

Milan,

I am surprised at your answer since induction motors and switched reluctance motors operate on the same principle of a rotating magnetic field created by coils in the stator. So I suspect the DRV8312-69 may work with a SR motor and believe the question is still open.

Thanks, John

John,

I should have clearly mentioned my assumption while answering; nevertheless below I clarify my inputs:

The most popular power topology for switched reluctance motor is asymmetric half-bridge inverter as shown in figure below, uses two power switches and two diodes per phase. Assuming simplest two phase SRM, it needs 4-half bridges whereas DRV8312 has only 3. Yesterday answer was based on above assumption.

7288.bpra058.pdf

I did little research on other topologies and found out that there exists Miller topology, which uses only one main power switch and one main diode for all phases together plus one more switch-diode pair per phase. If you are going to use this topology with 2-phase SRM, yes than DRV8312 can support it. Please refer to section5 of attached application note.

I hope this will clarify your doubts.

Best Regards

Milan-Motor Application Team

Milan:

Thanks for your update.

However, I was referring to the DRV8312-69M-KIT not just the DRV8312 chip, and

http://www.ti.com/tool/drv8312-69m-kit#Technical Documents

refers to doc

http://www.ti.com/lit/ug/spruhj1f/spruhj1f.pdf

which says that the "DRV8312 kit" has three full-bridges (17.6.1). Section 17.6.1 of spruhj1f.pdf refers to the user manual spmu276.pdf which shows three full-bridges, assuming that's the correct user manual for the DRV8312-69M-KIT.

However, I don't find a user manual specifically for the DRV8312-69M-KIT. The spmu276.pdf is the "DK-LM3S-DRV8312 BASEBOARD HARDWARE REFERENCE GUIDE." 

Anyhow, it seems as though the DRV8312-69M-KIT has three full-bridges.

Is there a user guide for the drv8312-69m-kit? The page for the kit refers to spruhj0b.pdf which seems more like a white paper for the InstaSpin technology.

John

John,

I couldn’t find the document referred by you in above post; I'm getting error while opening the link. Nevertheless, I got your point and to clarify, all DRV8312 kits have only one device so that means only 3-Half bridges, not 3-full bridge.

I apologies, if any particular document have given you wrong perception.

Generic user guide for Insta-spin support is available on DRV8312-69kit webpage itself:

http://www.ti.com/tool/drv8312-69m-kit#TechnicalDocuments

Board specific user guides are available in motor ware directory and depending upon the directory in your PC, you can find DRV8312 kit user guide at:

\\motorware\motorware_1_01_00_11\docs\boards\drive\drv8312kit_revD\docs

This directory structure is explained in generic user guide. I hope this clarifies your doubts

Best Regards

Milan-Motor Application Team

Hi Milan:

My apologies if I'm bugging you too much but we are desperate for a demo board for our motor.

The URL for that doc that shows the 3 full-bridges is:

http://www.ti.com/lit/ug/spmu276/spmu276.pdf.

It shows that there are 3 full-bridges on page 6 of the doc.

I guess I don't know how to navigate the motorware pages. I tried:

http://www.ti.com/tool//motorware/motorware_1_01_00_11/docs/boards/drive/drv8312kit_revD/docs

and got nothing, just a blank screen. Very annoying to be sure. Then I tried:

http://www.ti.com//motorware/motorware_1_01_00_11/docs/boards/drive/drv8312kit_revD/docs

and got the "Sorry! We couldn't find your page" error message.

John

John,

Page 6 and figure 5 shows only 3-half bridges not 3-full bridges. I don't understand what confusion here?

I'm not sure if you have install motor-ware, if not done, you can install it via same webpage of DRV8312-69 kit  

http://www.ti.com/tool/drv8312-69m-kit#TechnicalDocuments

Best Regards

Milan

Sorry Milan. My bad. I thought those dual MOSFET circuits were called Full-Bridges. And of course the doc says they are half-bridges and obviously they are half-bridges.

I have downloaded the motorware software and documentation. You mentioned the Miller connection. Would that be straightforward to connect the DRV8312-69M-Kit board to my 3-phase SR motor in the Miller connection? And would the software work ok. It seems like it should be a no-brainer to connect but it seems like my brain may be a bit fuzzy with my mistake on the full-bridges.  <:-|

Thanks, and my apologies for my goof.

John

Milan,

I found some info in a TI doc that shows a SR motor drive using three half-bridges:

http://www.ti.com/lit/an/bpra058/bpra058.pdf

Section 5, Fig 10.

So it seems like the DRV8312-69M-Kit with its three half-bridges should work to drive the SR motor. What do you think?

John

John

You posted back the same application note, I reffered  in my previous post.

Anyway to clarify, Fig10 uses 6-half bridges if you look it carefully. As I suggest in previous post, miller topology mentioned in the application note can work  but only with 2-phase SRMs.

Best Regards

Milan-Motor Application Team

Sorry Milan, I missed the reference to the bpra058.pdf doc in your previous post. However, Fig 10 shows 6 MOSFET's in three half-bridges. I believe that's what is shown in the doc for the DRV8312-69M-Kit where motor phase 1 is driven by MOSFET 1H and MOSFET 2L, motor phase 2 is driven by MOSFET 2H and MOSFET 3L, motor phase 3 is driven by MOSFET 3H and MOSFET 1L. So the schematic for the DRV8312 looks a little different from that of Fig 10 below, but appears to drive the SR motor exactly the same way.

5.1 Asymmetric Half Bridge Inverter
The asymmetric half bridge inverter is the most used inverter. Each machine phase is
connected to an asymmetric half bridge consisting of two power switches and two diodes.
The figure below illustrates the circuit for a 6/8 SR-motor.
Figure 10: Three Phase SR Motor Asymmetric Half Bridge Inverter

Power circuitry[edit]

John

Milan:

Ok, what a shame. Of course I could add my own MOSFET's and diodes external to the board and driven by the DRV8312 chip outputs. Would that do the job for our 3-phase SR motor?

John

John,

DRV8312 is having integrated FETs & predriver so it does not make sense to use them to drive external FETs. There are two ways to go about this:

1. use two DRV8312 & drive them directly from  single MCU.

2. use extenal FETs with single pre-driver  DRV8301 & MCU.

Best Regards

Milan-Motor Application Team

Milan:

Thanks for your answer. Unfortunately my client has given up on me finding a solution for his 3-phase SR motor and is now considering a single-phase design following a design by Amanda Staley in her MS Thesis:

http://scholar.lib.vt.edu/theses/available/etd-08212001-191550/unrestricted/AMS-Thesis.pdf

Her design is a non-microcontroller multi-IC circuit and seems promising as it is fairly simple. So my client is planning to build a 6-pole single-phase motor and is asking me to build a circuit similar to Ms. Staley's design.

I also had been losing hope that TI would have a hardware solution for the SR motor including the software. So I'll see what I can do for my client with his single-phase motor.

Thanks, John

^Milan:

Actually I was referring to the 3-phase SR motors when I implied that I wasn't convinced that TI had a solution, hardware and software, for SR motors. I would hate to build a controller board with the DRV8312 and some MOSFET's and diodes, then find that the DRV8312 and/or the TI software wouldn't work for a 3-phase SR motor. Now I have no confidence that TI has a solution for SR motors. and. I am disappointed since it had looked so promising but perhaps the TI literature is misleading or perhaps I had simply been overly optimistic that TI had a solution for the SR motors.

John