Part Number:DRV8301
Hey there,
I've designed/built my own controller/inverter around the F2805XF series + DRV8301 and am having some teething problems with motor identification + running. My target application is an ebike with a sensibly designed motor. But of course, I would have chosen a nightmare of a motor to troubleshoot the initial hardware with first. Yes, you guessed it, a hobby/RC motor, mainly because they are easy to source and lightweight.
It does not have particularly agreeable parameters but I am unsure of where issues could be. Hardware is certainly one aspect so if I could see how the voltage and current lines are configured/filtered that would be fantastic. The Instaspin reference manual describes hardware voltage filtering but doesn't say anything about current. I would have thought that some hardware low pass would be used on the current sense lines and indeed the DRV8301 datasheet shows some, but presumably that's controller specific. TI doesn't appear to have the schematics for the Instaspin demo boards readily available? I had wondered if they existed until I saw a screen shot on the E2E forums showing part of the current sense layout, so obviously they do. Could I ask whereabouts you can download these from?
My motor appears to have parameters as such...
Rs ~ 0.01ohms
Lsd & Lsq ~ 4uH
Flux 0.00155 V/Hz
Everything stupidly at one end of the difficult spectrum. It also has 14 poles, which requires a particularly high drive frequency to reach anything approaching it's specified operating conditions. It apparently has a working RPM of around 3000 when loaded, but when unloaded can soar to around 40k. After identification has occurred, whenever I try and spin the thing it either immediately stalls and the GUI stops or appears to be driven with barely any current. After one identification + the GUI it repeatedly twitched when I attempted to run it at 100RPM and after a bit of encouragement (a push in the right direction) it actually spun around at 100RPM. But that's as good as it's got.
One small limitation is the maximum frequency that this could theoretically work at. It's possible that I need to operate things faster than the hardware can support to ID the motor. As the end application of the board doesn't require high frequency operation, I've chosen MOSFETs with low RDSon but they have a gate charge of around 90nC. Certainly this is no issue for the DRV8301 when operating at lower frequencies but according to the DRVs datasheet rule of thumb, I shouldn't really operate the board any higher than around 55kHz. Pushing the operating frequency up, from 45 - 60kHz does give a drop in measured flux, from ~0.0016 to 0.0015. Whether or not this indicates a requirement for higher frequency identification I do not know.
Self calibration works flawlessly, RPM appears to be measured accurately, as does Rs and Flux, on the whole. But these could be precise rather than actually accurate.
Many thanks,
Matt.