# Integrated Battery Charger for Dual PM motors



## jddcircuit (Mar 18, 2010)

I am working on an integrated battery charger that will work well with Plug-in Hybrid Electric Vehicles (PHEV) that already have dual electric motors in their drive-train. This forum has been a great learning resource for me so far. I appreciate the feedback.

The IBC concept I am implementing is a variation of the Tumanako inverter/converter with some similarities to the AC Propulsion "Reductive Charger". It exploits the dual motor/inverter configuration found in the majority of modern hybrid drive vehicles.








I am very intrigued by the possibility of having a virtually free higher power on-board battery charger. I think that if higher power AC charging is made available, that many PHEV owners (ie Chevy Volt) will be able to realize more all electric driving miles. Faster at home and destination charging will make short plug-in opportunities pay off.

First challenge so far is with the non-isolated nature of this topology allowing some capacitively coupled ground leakage currents to flow. The AC Propulsion patent (US5341075) seems to mitigate this leakage problem by physically isolating the motor frame from the vehicle frame. ACP's isolation method requires too much modification of the motor and inverter construction to be cost effective in my opinion.

My hope is that either passive common mode filtering or some type of active ground current cancellation circuit can work to comply with the Ground Fault Interrupt circuits. The good news is that the topology I am pursuing inherently has lower common mode voltage transients and associated leakage currents to deal with.

There may also be other pitfalls like demagnetization of the rotor magnets but I have not investigated this area completely. I don't expect demagnetization to be an issue since the charging current levels won't exceed the normal operating currents experienced during driving. For induction and switched reluctance motors this is not a concern.

I am attaching a pdf describing the operational theory and some preliminary experimental results. I am happy to discuss any questions, opinions, speculation, or experiences.
View attachment Vehilectric_IBC.pdf


Best Regards
Jeff


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## PStechPaul (May 1, 2012)

There was a discussion of a similar nature a little while ago, although this may be slightly different. Some problems/solutions that I see are:

1. For the boost topology, the battery voltage must be higher than the line voltage. This was addressed in this example by using the vehicle's regenerative DC-DC converter which can run at 360V. But this may not be present in all PHEVs.

2. The boost circuit requires some of the IGBTs of the motor controller to be driven separately from the motor drive circuitry, and this requires getting into the electronics.

3. The capacitive ground currents that affect the GFCI might be accommodated by having a good ground connection from the vehicle and the motor to the eearth ground of the EVSE. The GFCI circuit should be able to read the sum of the supply current out and back, as well as the ground current. The GFCI normally reads the two power lines and any difference is assumed to be external ground current possibly through a person, and thus hazardous. But if this current is properly routed to an earth ground, it can be considered safely handled. However, there is still a limit of how much ground current can be considered appropriate.

4. The alternative method of using the motor windings as a buck converter or filter requires opening one of the motor lead connections, but that may be much easier than messing with the drive internals. The battery voltage is usually lower than the peak voltage of the EVSE, and if not, it can be fairly easily boosted by means of a transformer, capacitive doubler, or PFC circuit. 

5. This charging system must be able to accommodate various EVSEs, including 120 VAC, 220 VAC, and three phase rectified DC. In most cases, both lines will be at other than ground potential, so without isolation, the rest of the charging circuit will need to be isolated from ground, and there may be considerable AC voltage which will cause a lot of capacitive ground current to the chassis (which I assume must always be grounded for safety).


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## dcb (Dec 5, 2009)

the prius buck/boost converter is very helpful as a built in charger (bucks to the battery or boosts to the rail). with a 160v battery, you can boost to 400ish volts from 120 for good pfc, then buck what you need to the battery.

Also it keeps the 170v peak (from 120rms) from going uncontrolled into the battery (i.e. 160v).

Plus you can run it in boost mode as a cap precharger before you plug a motor lead (or two) into the wall.

I'm curious how much current ripple vs frequency a lithium can handle in charge though, or what was used as a filter in this case.


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## jddcircuit (Mar 18, 2010)

Thanks for the feedback.



PStechPaul said:


> 1. For the boost topology, the battery voltage must be higher than the line voltage. This was addressed in this example by using the vehicle's regenerative DC-DC converter which can run at 360V. But this may not be present in all PHEVs.


You are correct this is a boost topology that requires the DC voltage to be higher than the peak AC voltage.



PStechPaul said:


> 2. The boost circuit requires some of the IGBTs of the motor controller to be driven separately from the motor drive circuitry, and this requires getting into the electronics.


I am not sure what you mean. If you are saying that this requires a controller software change you are correct. There is no intrusive electrical change needed other than the connection to one phase terminal of each motor.



PStechPaul said:


> 3. The capacitive ground currents that affect the GFCI might be accommodated by having a good ground connection from the vehicle and the motor to the eearth ground of the EVSE. The GFCI circuit should be able to read the sum of the supply current out and back, as well as the ground current. The GFCI normally reads the two power lines and any difference is assumed to be external ground current possibly through a person, and thus hazardous. But if this current is properly routed to an earth ground, it can be considered safely handled. However, there is still a limit of how much ground current can be considered appropriate.


The screen capture in the document is showing the common mode current (ground leakage) which is the sum of both AC conductors. Ideally the sum=0. The same magnitude but opposite direction on both conductors. The leakage current can't be solved by having a better ground. The only way I have found to counter the leakage current is by creating a path for it reenter the supply conductors. I am using a simple common mode filter for this purpose right now. I am also researching active circuits that react to the measured leakage.



PStechPaul said:


> 4. The alternative method of using the motor windings as a buck converter or filter requires opening one of the motor lead connections, but that may be much easier than messing with the drive internals. The battery voltage is usually lower than the peak voltage of the EVSE, and if not, it can be fairly easily boosted by means of a transformer, capacitive doubler, or PFC circuit.


I am confused. Messing with the drive internals is the objective that is why it is referred to as integrated. The topology I am proposing seems to require the least amount of hardware modification compared to the others.




PStechPaul said:


> 5. This charging system must be able to accommodate various EVSEs, including 120 VAC, 220 VAC, and three phase rectified DC. In most cases, both lines will be at other than ground potential, so without isolation, the rest of the charging circuit will need to be isolated from ground, and there may be considerable AC voltage which will cause a lot of capacitive ground current to the chassis (which I assume must always be grounded for safety).


This configuration works with AC and DC. I am anticipating there being significant capacitance between the DC supply and the AC supply throughout the system. This alternating modulation method is known to reduce that problem in Bridgeless PFC boost front ends for AC/DC converters.

Best Regards
Jeff


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## jddcircuit (Mar 18, 2010)

IMO, This topology seems to be unique in how it takes advantage of the high terminal magnetizing inductance of PM motors without creating (60Hz) motor oscillation. Another advantage is that there is always a low frequency voltage reference through an IGBT body diode between the AC supply and DC supply which helps to reduce common mode currents.

I have not tried the AC propulsion nor the Tumanako configuration on a PM motor to see what kind of oscillating torque gets created in the motor. If anyone has experience with that it would be very interesting to me.

Thanks
Jeff


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## dcb (Dec 5, 2009)

The use of any permanent magnet near an inductor to facilitate DC bias is an interesting concept (polarity matters). http://ieeexplore.ieee.org/xpl/logi...re.ieee.org/xpls/abs_all.jsp?arnumber=5770892


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## jddcircuit (Mar 18, 2010)

My through motor charging invention using a Prius Motor and Inverter has been progressing.

My patent application recently got published here

http://www.freepatentsonline.com/20150231978.pdf

My latest experiment results charging my small battery pack of only 48 cells in series (approx 158V) only 40Ah wide (6.3kW).

Charging Power 4.9kW
Efficiency 93% combined (including extra DC/DC conversion stage)
Leakage Current 3.5mA using simple common mode filter
Total Harmonic Distortion 4.3% using interleaved switching

Some scope captures showing the 
AC plugin Voltage and Current








Battery Voltage and Current








Math functions for input and output power, 93% efficiency








I don't foresee any issues going to higher power once it is in my car and I have a larger battery pack and the liquid cooling loop hooked up.

Regards
Jeff


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## PStechPaul (May 1, 2012)

The scope trace for battery current and voltage shows the voltage to be fairly steady, as expected, but the current seems to have a lot of AC ripple. It's hard to tell the actual amplitude from the scope trace, as the current waveform appears to be 10V/div, and the voltage is 100V/div.


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## jddcircuit (Mar 18, 2010)

PStechPaul said:


> The scope trace for battery current and voltage shows the voltage to be fairly steady, as expected, but the current seems to have a lot of AC ripple. It's hard to tell the actual amplitude from the scope trace, as the current waveform appears to be 10V/div, and the voltage is 100V/div.


Yes, The battery current does ripple a lot. The units should read 10A/div, sorry. 

I have my software holding the DC bus to 360V (not shown) which is just above the peak AC voltage. Regulating a fixed bus voltage will make the battery current ripple lagging the AC input current.

It would be possible to make the battery current ripple less and let the bus voltage fluctuate more to absorb the power variation. I don't have a sensor on the battery current so this is how I am doing it for now.

I don't think the battery cares either way.

I think there is some opportunity for optimizing my regulation loops for the line current and bus voltages which could smooth things out a bit.

Jeff


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## jddcircuit (Mar 18, 2010)

jddcircuit said:


> Yes, The battery current does ripple a lot. The units should read 10A/div, sorry.
> 
> I have my software holding the DC bus to 360V (not shown) which is just above the peak AC voltage. Regulating a fixed bus voltage will make the battery current ripple lagging the AC input current.
> 
> ...



I wanted to get rid of the battery current ripple mentioned above. So I added a hall effect battery current sensor needed to regulate the PWM of the buck/boost converter between the high voltage DC bus and the battery.

Here is a scope capture showing the AC grid current (green) and the regulated battery current (yellow). This is a quick and dirty only using a simple Proportional gain. Once I add some Derivative gain it will flatten out even more but this is fine for now to show me it can work.









I also uploaded a power point presentation that I made trying to promote the invention. I am comparing it to a couple other integrated charging methods. Download it and let me know what you think. There are action buttons that allow you to drill down into different sections.

https://drive.google.com/open?id=0ByvAoBSpt8yfR3JzR1FPMEMzVXc

Regards
Jeff


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## dcb (Dec 5, 2009)

very nice touch, is there enough info out there to see if it would work on a p85d or a p90d type setup? Are you utilizing the toyota buck converter?


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## jddcircuit (Mar 18, 2010)

dcb said:


> very nice touch, is there enough info out there to see if it would work on a p85d or a p90d type setup? Are you utilizing the toyota buck converter?


Yes I am using the toyota buck converter. The battery in this experiment is only 48 LFP cells so 158V nominal. The peak AC voltage is 340V so the through motor boost using the dual motors and inverters produces a DC bus voltage higher than 340V. I then buck it down into the lower voltage battery using the built in DC/DC converter.

You mention the p85d type. I have not tried it but I assume it would. I did get the opportunity to present the idea to Tesla engineers. They have concerns about the non-isolation aspect and the fact that they don't have a DC converter to handle the higher bus voltage.

I am continuing to develop the idea. I have some ideas to address the safety perception that some of the OEMs have in regards to non-isolation. I recently got the ground leakage current down to 3.5mA so now I can comply with 5mA GFI protected circuits.

I am also working on an active circuit for further reducing the ground leakage currents and to detect and interrupt the connection if an anomaly occurs. Measuring the leakage current is also a good indicator for the integrity of the motor winding insulation and can offer some valuable diagnosis perhaps if it were to degrade over time.

Thanks
Jeff


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