Thread: SD540 Motor Controller
View Single Post
  #156   Spotlight this post!  
Unread 04-01-2016, 13:45
philso philso is offline
Mentor
FRC #2587
  
Join Date: Jan 2011
Rookie Year: 2011
Location: Houston, Tx
Posts: 938
philso has a reputation beyond reputephilso has a reputation beyond reputephilso has a reputation beyond reputephilso has a reputation beyond reputephilso has a reputation beyond reputephilso has a reputation beyond reputephilso has a reputation beyond reputephilso has a reputation beyond reputephilso has a reputation beyond reputephilso has a reputation beyond reputephilso has a reputation beyond repute
Re: SD540 Motor Controller
Quote:
Originally Posted by s1900ahon View Post
Ha ha.. I have to LOL on that comment. I'd hardly give myself that attribute. I'm an embedded semiconductor kind of guy (architecture/hardware/software). My experience with power electronics is due to my being employed at Luminary Micro some years ago who built microcontrollers (MCUs) for use in applications such as motor control. Specifically, you can blame me for Jaguar (he ducks as rotten tomatoes are hurled in his direction).



To be clear, I wasn't suggesting that the Cboot voltage was decaying and affecting the Vgs level on the high-side MOSFETs. Actually, the scenario I was thinking about was that the they were over refreshing and therefore incurring an un-necessary drop in efficiency.

The Cboot cap is charged up when the connected terminal (M+ or M-, there is one Cboot for each) is driven low (the low-side MOSFET is turned on). The cap charges through a diode and current limiting resistor. The Cboot charge time is therefore 3-5 RCboot times. But, the firmware in the MCU controls the timing. If you're curious, check out the Jaguar's published schematics.



Yeah, the under voltage would be the VBUS voltage reduced by a divider circuit to an ADC input, being sampled by firmware, and setting a different trip point value or updated software-based filtering to activate exceptional processing. Also a firmware change (likely).



Agreed. From a pure curiosity perspective, I'd like to see this done for all motor controllers. It would provide some insight into the real power loss (IRds(on)). It is easy to see: connect small resistive load across M+/M-, connect scope to M+ and V-(ground), set output to 100% forward, measure duty cycle and frequency on scope.

Scott

Regardless of the opinions other people have of the Jaguar, you clearly did a decent job with the design of the inverter section. I have seen the results of other embedded designers trying to design a 3-phase inverter for automotive applications. This guy clearly just copied a generic schematic for the inverter and did not know how to minimize the inductance in the circuit or how to bypass the inverter. They were using 1200V devices with a DC supply in the range of 300-400V and were still blowing it up. That start-up never got to market.


It would be interesting to see the output of the motor controllers even with no load connected. Issues with excessive inductance in the controller will show up as large spikes, possibly with abnormally slow voltage rise and fall times.
Reply With Quote