Paul and Sabrina's Cheap 3 Phase Inverter (AC Controller) with Field Oriented Control

[e*clipse]

Hello danibjor - welcome!

I, too would like to share the electronics for the charger.

The patent you're referencing was ( I think ) first used by ACPropulsion, and may have been used on the GM EV-1.

One of the larger parts of a boost converter is the inductor, and the clever thing about this design is it actually uses the motor for that job.

I wonder - can this be done with a wye connected motor? Also, can this be done with a BLDC motor without causing the motor to move when plugged in?

- E*clipse

[danibjor]

If you look at the scematics on the patent, they use a rectifier between the mains and the motor - so you feed it with DC, not AC voltage. No sine wave = no rotations?

But I guess the controller have to know about what's happening, so it could go into "regen" mode?

[e*clipse]

Originally Posted by danibjor

If you look at the scematics on the patent, they use a rectifier between the mains and the motor - so you feed it with DC, not AC voltage. No sine wave = no rotations?

But I guess the controller have to know about what's happening, so it could go into "regen" mode?

two important points:
1) rectified AC is not smooth DC. It's actually quite "lumpy." Basically what any rectifier does is invert the negative part of the sin wave to be positive. A full wave rectifier with a 60Hz sin wave input will have a 120Hz set of all positive waves (half wave lumps). It's not smooth DC yet; that will require further filtration.
2) Standard Boost converters put a pulsed voltage into an inductor for their operation. It would be possible to use the motor controller to switch the IGBT's for this job. The inductor stores part of the energy, then releases it the next cycle. The need to store part of the energy drives the inductor size for the converter. Using a higher switching frequency allows a smaller inductor, to a point. MPPT boost converters will vary the duty cycle depending on the part of the rectified "DC" waveform present. This will help keep current and voltage in phase.

Anyway, as shown in the drawings, one phase leg of the 3 phase motor will have current flowing through it. This current won't be alternating, as in reversing sign. However it won't be DC constant. Further, even if it were constant DC, current flowing in the phase leg would cause the magnets in the rotor to align with the stator. Yes, it won't rotate around, but it could move up to about 45 degrees in a 4 pole pair BLDC motor.

This is the main problem I see with using a BLDC motor. I don't think it would be an issue for an induction motor, because you wouldn't induce current in the rotor. I don't know how wye vs delta connection would affect it's operation in an induction motor. Perhaps there's a clever way to put exactly opposite currents into a BLDC motor such that a net zero torque could be produced? The charger would have to know the rotor's position and somehow connect to all three phases to pull that one off.

- E*clipse

[thingstodo]

Originally Posted by e*clipse

Oh, I may see something here, regarding your shielding.

Generally, you don't want to connect the shield to both the main circuit board's ground and the "satellite" circuit boards ground. The shield should only connect to the main circuit board's ground. Otherwise, you can get current loops that are separate (and dynamic) from the normal ground.

This point was emphasized in my EMI class, as well as the instructions for shielding the inputs on my Sumitomo VFD.

Hope this helps,

E*clipse

The 'shield' was connected to the negative on the power supply. 'Both sides' referred to the power supply side and the encoder side of my circuit board with the voltage divider. There was no termination of the shield on the encoder side.

Like I said - the noise was very bad on the scope. I wondered if the scope probes were acting as an antenna - not the aluminum foil - but the encoder signal was not making it to the AC Controller board in a usable way.

[thingstodo]

Originally Posted by MPaulHolmes

I started testing the sensorless late last night. It was using just a bit too much processing time to smooth out and correct Ialpha, Ibeta, Valpha, Vbeta, and derivative(Ialpha) and derivative(Ibeta), so I'm bumping it up to 29.5MHz instead of the 14.7MHz. oh well! haha. An extra 0.3watt or something like that for sensorless.

29.5 Mhz it is! More SPEED .. MORE POWER .. !

I think the ground loop thing might be right. Also, the stepped down +5v signal would be from the +24v supply, which was unfiltered, whereas the +5v supply from the controller was filtered, so combining the 2 5v signals might introduce 5v noise?

Not sure on that one. The 24V goes to the encoder directly. The 15ish volt A and B channels are voltage divided .. so I guess that would be noisy .. but they share a ground so the reference works. I could use an opto-coupler to transfer the signal from 15V to 5V, then use the 5V from the controller .. but then again, we won't need the encoder soon!

The nice thing is you can short circuit the 5v regulator all day long and it won't care, so I doubt anything too terrible is broken. Plus, the 64 tick encoder on the motor is more than enough. PLus, it will be sensorless in no time! so who cares! haha.

Looking forward to sensorless!

[danibjor]

Originally Posted by e*clipse

two important points:
1) rectified AC is not smooth DC. It's actually quite "lumpy." Basically what any rectifier does is invert the negative part of the sin wave to be positive. A full wave rectifier with a 60Hz sin wave input will have a 120Hz set of all positive waves (half wave lumps). It's not smooth DC yet; that will require further filtration.

True

Originally Posted by e*clipse

Anyway, as shown in the drawings, one phase leg of the 3 phase motor will have current flowing through it. This current won't be alternating, as in reversing sign. However it won't be DC constant. Further, even if it were constant DC, current flowing in the phase leg would cause the magnets in the rotor to align with the stator. Yes, it won't rotate around, but it could move up to about 45 degrees in a 4 pole pair BLDC motor.

This is the main problem I see with using a BLDC motor. I don't think it would be an issue for an induction motor, because you wouldn't induce current in the rotor. I don't know how wye vs delta connection would affect it's operation in an induction motor. Perhaps there's a clever way to put exactly opposite currents into a BLDC motor such that a net zero torque could be produced? The charger would have to know the rotor's position and somehow connect to all three phases to pull that one off.

- E*clipse

Here in Norway we have 3-phase 400v, so that would make for a supercharger if 3-phase could be used - all built into the inverter without much extra cost.

Charging a 6-800v batterypack with decent range would take some time with a regular charget - not to mention the price tag on a charger of that scale.

If the controller can handle the charging too - that would be a great leap forward in DIY EV.

- Daniel

[thingstodo]

Originally Posted by danibjor

Hi all. New here..

As e*clipse says - Welcome!

This is the project that wants me to try going electric. One of my criterias is that the car should perform like it did (or better) on petrol.

A good criteria for a fun-to-drive car. My standards are a bit lower - I need to get to work and back home without getting run over by other drivers

One thing I have in mind is charging. I don't want to use a lot of space (and weight) on a big charger to top off the batteries needed to keep up with inverter. I've been doing some research and found this: google.com/patents/US4920475

If you look at the 3th picture - "all you need" is a rectifier and a filter on the mains to charge the car using the motor controller's regen function. - or is it?

I looked at the third picture. What I see is ..
- the bridge rectifier appears to have negative tied to the negative bus on the battery pack
- the positive of the rectifier goes to one lead of the motor - lets call it C phase
- the control algorithmn is then to cycle the positive C phase transistor to allow current flow into the battery positive, charging the battery pack
- the controller sees battery charging as negative amps and positive volts on C phase
- the controller may track pack voltage, and it may track phase to phase voltage on the motor ... but it likely does not track C phase to pack voltage

This is not really what I would call 'regen' but it sounds quite interesting as long as your battery pack voltage can be charged by the available voltage from your outlet.

My 125V pack can be charged by 110V * 1.414 (root 2) = 155.5V peak bridge rectified DC with AC ripple on top. I have seen about 160V DC if the voltage is closer to 120VAC, including bridge diode drop of about 1.5V.

If I were to run the Siemens motor in a car, it would likely be closer to 350VDC on the pack, which is above 220V * 1.414 = 311V .. so you get into the boost stuff that e*clipse talks about

If it's doable - is this somthing that this controller can handle?

My opinion would be - not yet.

Another question: How does the controller know the voltage sendt (also with regen) back to the batteries? I mean, so you don't get an early new years eve show..

I know that the pack voltage is a setting in the controller, but I don't know if the pack voltage is measured.

I think that the voltage and current to the motor are measured while the controller outputs are in the middle of their ON state - am I right, Paul?

The batteries are actually quite forgiving about charging at a higher voltage. The voltage applied minus voltage of the pack gives the electrons incentive to move. The internal battery resistance (a vague concept on it's own) determines the charging current. As the batteries 'fill up' the pack voltage increases, the charging current drops. The trick appears to be to determine when to stop charging and declare the batteries 'full' without overcharging them. The battery suppliers seem to describe a recipe, perhaps 2, that will get you to 'charged' batteries. If you don't follow the recipe, you need to count coulombs (amp-hours) out of and into the pack very carefully .. or try stopping early and measuring how much energy you can get back out to figure out how much more you could have put in ...

Other PWM chargers appear to check current out in the middle of the charge pulse and voltage of the pack in the middle of their 'off' period

- About me: Engineer in automation (industrial) - great interest in programming, electronics and cars

Another automation guy! Woohoo!

[thingstodo]

Originally Posted by danibjor

If you look at the scematics on the patent, they use a rectifier between the mains and the motor - so you feed it with DC, not AC voltage. No sine wave = no rotations?

But I guess the controller have to know about what's happening, so it could go into "regen" mode?

Did I miss something in the circuit?

The connections from the bridge rectifier appear to be pack - and what I called motor C phase. If there is only one connection to the motor, there will be no rotation at all?

Are you referring to one of the other pictures?

[thingstodo]

Originally Posted by e*clipse

Anyway, as shown in the drawings, one phase leg of the 3 phase motor will have current flowing through it.

I missed this part. Where is that?

The second drawing shows an inductor, but it does not appear to be part of the motor

The third drawing shows the bridge going direct to the pack - and one motor lead. No connection to a second motor lead = no current?

I guess it would help if I READ the patent instead of ASSUMING ...

Using C phase positive transistor would, in my opinion, be a version of a 'bad-boy' charger. That was what I was talking about, which is not what you guys were talking about - sorry

Using B or A or perhaps both positive transistors would perform a boost of sorts through one or two phases of the motor ... I get it!

Here in Norway we have 3-phase 400v, so that would make for a supercharger if 3-phase could be used - all built into the inverter without much extra cost.

Charging a 6-800v batterypack with decent range would take some time with a regular charget - not to mention the price tag on a charger of that scale.

If the controller can handle the charging too - that would be a great leap forward in DIY EV.

- Daniel

I'm pretty confident that using C phase positive transistor only would give you charging into the 550V range. It could be a bit of a challenge to cool that one transistor, since it is generating all of the heat. But there is no inductor, so no boost, and some timing or detection may be required to get the batteries a consistent charging voltage/current.

For the boost charger, with no smoothing caps on the supply side ...
- simple - boost without checking voltage and have the batteries charge faster when the 'lumpy' voltage input is higher and slower when the 'lumpy' voltage is lower?
- more complicated programming - vary the length of each boost pulse to allow only a set value of amp-seconds through. A higher voltage gets a shorter pulse, a lower voltage gets a longer pulse .. up to a certain maximum.
- more complicated hardware - detect zero crossing of each phase before the rectifier. That would give you a good idea what the voltage is on the terminals (or you could add a fast-ish A/D channel). So you could time the start of charging boost pulse and length of pulse to get the output boost/output voltage you are looking for .. maybe.

Characterizing the motor and getting pretty darned accurate values would be important for the last one. Not so important for the other two.

[danibjor]

Originally Posted by thingstodo

A good criteria for a fun-to-drive car. My standards are a bit lower - I need to get to work and back home without getting run over by other drivers

Well, you don't have to make the end goal on day one. But it has to be modular enough to reach the goal without throwing away everything every time you upgrade it.

Motors can be upgraded. Batteries added to the pack without throwing away old stuff. BMS should be somewhat modular so it can be extended.

A 200kw controller would go a long way. And this one is really affordable - and the power stage can be upgraded.

I found a used Nissan Leaf motor (those are rated 80kw/110hp and 280nm) - for just over $2k. Somthing like that would be more than enough to get to work.