PMSM motor driver from scratch - Page 1
Forum section: electronics / projects

author: leblanc
author_rank: Regular Contributor
timestamp: March 28, 2016, 12:07:14 am
content: Hello EEVblog people.I have an idea for a project that involves driving a PMSM motor, something about the size of an electric scooter motor. By my calculations, I'll need a DC power supply that can provide me with approximately 1kW. An off-the-shelf 1kW supply would cost me a fair amount for just one component of the system.I decided instead that I'd build the electronics for the whole system, probably not the most economical way for some parts of it, but I'm just starting my career as an engineer, the experience gained building this will be far more valuable than the BOM cost.Power:AC --> Line filter --> (maybe PFC, probably not this version) --> Rectifier --> DC to DC (push-pull converter) --> 3-phase H-bridgeControl, sensors, etc.:DSP, hall-effect sensors for phase current, phase voltage measurements, bus voltage measurement, rotary encoder, gate driversI will certainly have several questions along the way, so I thought I'd start a thread and post all of them in here. Please feel free to comment and give suggestions/feedback.I'm starting off with the input filtering and AC-DC rectification. This is what I've got:NTC1: SL22 5R012VAR1: ERZ-V10D471C1, C2: R463I347000N0ML1: 8119-RCC3, C4: GA355QR7GF222KW01LD1, D2, D3, D4: GBJ1510-BPC5: ?So the NTC is for inrush limiting. At startup it'll be cold and appear as 5ohm, but once current starts flowing in there, it drops to 30mOhm. With this kind of power, I might need to consider a fixed resistor with a bypass relay, but for now I don't see why this the NTC would be an issue (other than if someone turns it off then on rapidly...).The varistor is just for surge supression.C1 and C2 are X-type (line to line) capacitors, they shunt differential mode noise.C3 and C4 are Y-type (line to chassis) capacitors, they shunt common mode noise.The common mode choke does just that, helps stops common mode noise from coming in or out.For D1, D2, D3, D4, I chose a bridge rectifier IC instead of getting four diodes because I'll just need a single heatsink instead of 4. Any heatsink suggestions btw?C5 is the bulk capacitor. I had a bit of trouble picking this one. The output voltage of this stage goes to the input of the DC-to-DC converter stage, so I'm not sure what that will mean for capacitance and ripple current rating. I'll need something rated at least 200V, ideally 250V, because the output of the rectifier will be 170V or so. If we want less than +/- 5% ripple on the output of this stage, we need at least a few millifarads. I would imagine 250V capacitors with capacitance of a few millifarads are likely to be a bit expensive. Space is not a constraint, so putting a few in parallel is not an issue.

author: SeanB
author_rank: Super Contributor
timestamp: March 28, 2016, 08:35:23 am
content: 220uF 200V capacitors are very common in PC power supplies, so using 5 in parallel will work here, and they will be cheap. I would suggest a 25A 1kv bridge rectifier, as the peak current to charge those caps will be within the single cycle limit for the rectifier, and 1kV is not more expensive over a 400V unit. Would suggest a more robust input inrush protection, like a series choke as well to limit spikes, otherwise you will blow up the NTC with time.

author: dugherd
author_rank: Contributor
timestamp: May 21, 2016, 12:03:53 am
content: leblanc,I am looking into a PMSM motor drive project similar to what you described. Have you made any progress on the control/drive stage? How do you plan on implementing this?