driving STEVAL-IHM023V2 without controller

[florian]

Posted on March 19, 2014 at 17:24

We are working with the STEVAL-IHM023V2 to drive a brushless DC motor of 24V. The set up is to be used in an academic environment and will be used as set up for students. As it is their task to make the control algorithm (from current set point to switching pattern based on Hall sensors) we did not buy the controller of ST. The tests we did so far were successful but it is not possible to keep one leg of the inverter open (in a stable way). The only way we found so far to keep both upper and lower switch open was to keep both connection points floating (which cannot be the right option). Is there anyone who has tried to do the same and knows a solution?

#steval-ihm023v2

[Gigi]

Posted on March 20, 2014 at 14:31

Ciao

Maybe I don't understand your question but it is normal that if you want to keep a leg (and also any of the switches of the inverter) open you need to keep inactive the relative inputs. This means in case of  STEVAL-IHM023V2 the J5 pin: 3,7,11 to GND (these inputs are active high) 5,9,13 to Vdd (these inputs are active low) Of course if you keep them floating they will be bring to the inactive state by means of internal pull up or pull down resistor. Ciao Gigi

[florian]

Posted on March 24, 2014 at 09:32

Hello Gigi,

thank you for your answer but we deduced that already from the datasheet.Let me rephrase my question:take any 3 phase load (3 resistors for example: R_A, R_B and R_C). We want a current through R_A and R_B, so I_A=-I_B and I_C=0. Therefor the upper switch in phase A has to be closed, the lower switch in phase B has to be closed and all the other switches have to be left open. My question: is this possible with the 3 phase bridge?We know that this should work if we send 5V to the upper and lower switch in phase A, 0V to the upper and lower switch in phase B and a different voltage to the upper and lower switch in phase C (for example 0V to the upper and 5V to the lower).Do you see our mistake because this isn't working on our setup? Thanks in advance!Florian

[florian]

Posted on March 27, 2014 at 15:45

Is there anyone else who had this problem or tried to drive the STEVAL by themself? 

For ST: is there a way we can get some more information on how you drive the STEVAL from the microcontroller?

[Gigi]

Posted on March 31, 2014 at 11:55

Ciao Florian,

The modality that you mention is one of the basic configuration of the 6-step driving that shall be supported by a 3 phase bridge and I don't see any problem to be applied with the STEVAL-IHM023V2. Which is the behaviour that you get when you provide the input as you describe? 5V to the upper and lower switch in phase A, 0V to the upper and lower switch in phase B, 0V to the upper and 5V to the lower in phase C If you get all switches open probably you have to take care also to the pin1 of the J5. It is the Emergency Stop usally used for over current protection. This should be pull up otherwise all swicthes are forced open. Ciao

[florian]

Posted on March 31, 2014 at 14:32

Hello Gigi,

I did what you proposed and measured all the signals down to where they enter the chip. In other words: I'm certain of the input signals as you stated them.What was the output: both switches in phase A remain open, the upper switch in phase B remains open, the lower switch in phase B closed and the switches of phase C remained open. I also measured the SD pin (connected to pin 1 of J5) and it stayed high the whole time so that's not the problem. Conclusion: normal behavior for phase B and C, not for phase A where the upper switch should have closed.Any idea what this could be? I use 3 resistors as load, each 7W, connected in star, R=100 OhmKind regards,Florian

[Gigi]

Posted on March 31, 2014 at 14:45

Ciao Florian,

Probably you need to charge the boot capacitors before to turn on the high side switches. This mean that you have to apply first a configuration with the three low side switched closed for a while (10ms for instance) and then your configuration. After a while the boot cap will be discharged so is better to apply a PWM for the high sides. Ciao Gigi

[florian]

Posted on April 01, 2014 at 09:11

Hello Gigi,

when I do that I get a gate voltage of 33V which goes down (linear) to 30V and then instantlydrops towards 0V. All this takes place in 18ms, in other words the upper switch is closed for 18ms. Is this what you expected?I used some PWM signals before to test the bridge and that didn't work so I'll document that and send it through tomorrow.Regards,Florian

[Gigi]

Posted on April 01, 2014 at 09:23

Ciao Florian,

it is reasonable because the boot capacitor will be discharged when the high side is turned on for this reasion you need to apply a PWM because during the off time the boot cap are re-charged. Ciao

[florian]

Posted on April 01, 2014 at 12:16

Hello Gigi,

I have been thinking about what you said, here's an example to state what I think:(S_1 is upper, S_2 is lower, ... ... ...)I_A=+1, I_B=-1, I_C=0S_1 closed, S_2 open, S_3 open, S_4 closed, S_5 open, S_6 openI_A=+1, I_B=0, I_C=-1S_1 closed, S_2 open, S_3 open, S_4 open, S_5 open, S_6 closedI_A=0, I_B=+1, I_C=-1S_1 open, S_2 open, S_3 closed, S_4 open, S_5 open, S_6 closedI_A=-1, I_B=+1, I_C=0S_1 open, S_2 closed, S_3 closed, S_4 open, S_5 open, S_6 openI_A=-1, I_B=0, I_C=+1S_1 open, S_2 closed, S_3 open, S_4 open, S_5 closed, S_6 openI_A=0, I_B=-1, I_C=+1S_1 open, S_2 open, S_3 open, S_4 closed, S_5 closed, S_6 openIf we go from step 2 to 3, then S_3 has to close but in step 2, S_3 and S_4 were open... In other words the condensator will not be charged and S_3 cannot close... UNLESS the next step (in 6 step drive) is within 18ms...PWM will not solve this problem because phase B has to stay open in step 2 (so no PWM).Measurements also show this... If the frequency of my signal is high enough then current flows as it is suppose to. If I lower the frequency (lower speed of the motor) and the phase has to stay open for more then 18ms, the current doesn't flow anymore as we want it. The reason for this is because the upper switch doesn't want to close anymore.