Electronics > Projects, Designs, and Technical Stuff
Shoot-through 3 phase bridge? gate drive waveform
Yansi:
There are some better mitigation techniques for the negative voltage clamping, apart from improving the PCB layout: Place the gate resistor in the source lead connection and then add a clamp diode from DCbus- to the Vs terminal of the driver IC. But it also has some other disadvantages.
ghoetic:
It works without load now https://youtu.be/NztFkpEPASs.
in video probing highside gate. showing transition from low to high frequency including overmodulation.
what i did:
replaced irs2334.
replaced bs caps to 1uF
replace 10uF bulk to 47uF
changed gate resistor lowest i had, 150ohm
tested it with just replacing the resistors but it tripped. so in my haste iforgot to check for what it tripped. which after changing resistor i noticed it was undervoltage... maby works with 20 ohms resistor and 2.2uF bs caps.maby the driver was bad?
going for a motor load soon. :-+
Jay_Diddy_B:
Hi,
For clarification:
You changed
C10 to 47uF
C11,C12 and C13 to 1uF
R22-R27 to 150 \$\Omega\$
and you replaced U4
Other Observations
Brake IGBT
You may need to add another IGBT. This IGBT connects a high power resistor across the DC bus if the DC bus too high. The DC bus will rise if you decelerate rapidly. Energy from the mechanical rotation will be transferred back to the bus.
Opto-couplers in the linear mode
The two analog channels for setting speed control and trip level is bad design practice. The transfer function is strongly dependent on the current transfer ratio, CTR, of the opto-coupler.
I suggest that you encode the signals with PWM.
Something like the LTC6992:
Read the datasheet to lower the frequency to around 20kHz.
Filter the signal on the isolated side to obtain the analog voltage.
Isolated supply
These TMR 1211 modules are not really designed to provide safety isolation from the mains.
The datasheet shows:
The insulation system is Functional
The 1600V dc is for 60s.
Compare to Traco TIM series:
This is safety rated.
EMC
You will need to add some EMC countermeasures.
You will need a filter including a CM choke on the input
Probably need RC circuits on the U,V,W outputs
The switching edges from the PWM waveform will be capacitively coupled in the motor to ground.
Regards,
Jay_Diddy_B
Le_Bassiste:
--- Quote from: jmelson on June 09, 2020, 04:41:59 pm ---I build both brush and brushless motor drives, using IR gate drivers. One of the things about them is that they cannot stand the midpoint (U, V, W)
or VS1, 2, 3 going much below zero. I had to put ultrafast diodes across the low-side FET to prevent that. Now, in my case, it only was a problem with an inductive load. So, assume you have the high-side transistor on, sourcing 10 + A current out to the load, and then shut off the high-side transistor.
The load inductance will try to continue accepting current from the drive, and the midpoint of the two transistors drops below ground.
It turns out the body diodes in these fets will allow forward voltages of 10-12 V for well over a microsecond before they start to conduct. That's why an unltrafast diode is needed. I use an ESD3 for this.
What happens is that as the midpoint drops to around -7 V currents start leaking all over the gate driver chip, and eventually, it turns on BOTH transistors at the same time. Using a digital scope and creeping up on the current where this started to happen, I was able to capture the event without catastrophic failure.
Jon
--- End quote ---
^this. these IR gate drivers are notorious for latching "ON", even at far lower levels than jon is mentioning. IIRC, there's an old IR app note about the IR2113 floating around, explaining this behavior and ways to mitigate it. and no, testing without load doesn't cut it. the issue is mostly related to di/dt at the halfbridge's output, so test your contraption at full load _and_ overload. everything else is a testing placebo and will fly into your face further down your project timeline.
good luck!
ghoetic:
--- Quote from: Jay_Diddy_B on June 10, 2020, 11:26:59 am ---Hi,
For clarification:
(Attachment Link)
You changed
C10 to 47uF
C11,C12 and C13 to 1uF
R22-R27 to 150 \$\Omega\$
and you replaced U4
Other Observations
Brake IGBT
You may need to add another IGBT. This IGBT connects a high power resistor across the DC bus if the DC bus too high. The DC bus will rise if you decelerate rapidly. Energy from the mechanical rotation will be transferred back to the bus.
Opto-couplers in the linear mode
(Attachment Link)
The two analog channels for setting speed control and trip level is bad design practice. The transfer function is strongly dependent on the current transfer ratio, CTR, of the opto-coupler.
I suggest that you encode the signals with PWM.
Something like the LTC6992:
(Attachment Link)
Read the datasheet to lower the frequency to around 20kHz.
Filter the signal on the isolated side to obtain the analog voltage.
Isolated supply
(Attachment Link)
These TMR 1211 modules are not really designed to provide safety isolation from the mains.
The datasheet shows:
(Attachment Link)
(Attachment Link)
The insulation system is Functional
The 1600V dc is for 60s.
Compare to Traco TIM series:
(Attachment Link)
(Attachment Link)
This is safety rated.
EMC
You will need to add some EMC countermeasures.
You will need a filter including a CM choke on the input
Probably need RC circuits on the U,V,W outputs
The switching edges from the PWM waveform will be capacitively coupled in the motor to ground.
Regards,
Jay_Diddy_B
--- End quote ---
Clarifications right on!
super helpful tips! :-+ :-+ :-+
you are right about the functional part. i totally missed it. My design is based on AN1660 from microchip but with some modifications.
Spinning and injection brakeing a no load motor:
https://youtu.be/SNKqk37RwU8
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