I need to design a model of grid, including "high voltage" feeder, a Delta/star transformer and "low-voltage" lines, to show how it is controlled and how single phase/3 phase loads and distributed generation do affect voltage quality. Obviously, there is no high voltage involved, the grid is running around 24Vac (the voltage display are hacked to show 230V between phase and neutral)
I already did such model using a VESC+motor mechanically coupled to a generator (=another brushless motor) to feed the grid, and a custom app to control output voltage (increasing duty cycle when the measured motor current would increase, up to a threshold meaning a fault) and startup ramps. (picture https://www.facebook.com/aimontefiore/photos/a.1680954238683719/16809584...).
Now I want to make it lighter and more efficient, using directly the VESC + 3 phase LC output filter to feed my "grid" at constant frequency / controlled voltage. (to simulate the transformer substation taps)
First question: what is the simplest way to do it, preferably with a custom app (ie without need to change mcpwm_foc.c) It seems relatively similar to running with fixed foc_openloop_rpm and controlled duty mode ?
Otherwise, there will be strong current imbalance (the model is here to show how unbalanced current affect voltage quality much more) - is it a potential issue ?
Thks, Pierre
Interesting project. void mcpwm_foc_set_openloop(float current, float rpm) is close to what you want, but it runs current control and not duty control, as you pointer out. It would be quite straight forward for me to implement a new mode void mcpwm_foc_set_openloop_duty(float duty, float rpm) that does the same thing, but with duty cycle control. I will have a look on Friday after I get home from work.
Tks a lot Benjamin. I think it might be also be useful for some funny applications to get 50Hz ac voltage (3 phase delta, or single phase) out of storage batteries - and higher voltages using a 50Hz transformers...
As for the mcpwm_foc_set_openloop function, in case I set a large enough current, and the load is very low, will it simply generate 3 phase voltages with the largest possible amplitude ?
Actually, I think a mcpwm_foc_set_openloop_duty function would even be more flexible if there were 3 duties, corresponding to phase A, B and C (so that I could adjust the output voltage per phase, using a customs app, in response to the loads measured on each phase). Don't know if the svm function allows for that.
Was there any more development on this? Being able to adapt the VESC stuff to be a pure-sin inverter would be awesome for off-grid applications!
Good idea, did you drop it into feature request?
@ frank I put in the request