Buck/Boost voltage and Regen

[TheSilverBuick]

I see my original expectation of boosting lower battery voltage up to run the MGR is out of scope for either the Gen2 or 3 inverters, but from the reading I've done, it sounds like one of the primary uses of the bucking circuitry is to reduce regen voltages to the Prius battery voltage, and it seems like this is not done with either Gen2 or 3 boards? How do the inverters handle high voltages on regen back into the battery? I plan on using a BMS, would I need too pick one capable of handling widely varying input voltages?

I have both a Prius Gen 2 inverter and a Prius C/Yaris inverter and a local guy with a stack of Gen3 Prius if a need a genuine Gen3 inverter. So if any of them have different options/characteristics on buck/boosting can they be outlined here?

Thanks!

[johu]

For regen the actual inverter governs the regen current and the voltage is just a result of that current and your batteries internal resistance. No need to use the buck converter in that case.

The bucking circuitry is only used for charging from the grid. So say your battery is 200V and you rectify 240V split phase using the MG1 inverters diodes. Not sure what rectifying split phase results in, lets say it is 350V. Now the buck module is used to buck down 350V to 200V. More precisely, it is used to draw a certain current from the grid, and, again the voltage is just a result of that current and your batteries internal resistance.

EDIT: just checked in ltspice, 240V split phase rectified follows the sqrt(2) formula, so would be 338V DC

[TheSilverBuick]

Okay, I understand the voltage being based on battery resistance and current generated from the motor.

What is Toyota's use of the buck/boost then if the Prius/Yaris cars were not capable of plugging into the grid? I saw Damien used it to buck voltages down to the DC-DC converter, but in the OE application the Prius batteries were not high enough voltages to need that to feed the DC-DC converter.

[johu]

To be honest, the existence of the buck/boost converter is a total mystery to me as you can achieve the same with field weakening. Want to lower regen current at high rpm -> field weakening. Want to produce torque past base speed -> field weakening. Not sure if the concept was unheard of back when the first Prius came out...

[TheSilverBuick]

Thank you for the response. Sounds reasonable. Sometimes there are different tools for the same job, and this may be the case.

[Eflyers]

John Kelly, in one of his excellent videos, has some info about the boost/buck starting ~ 1:23 :

[Eflyers]

To be honest, the existence of the buck/boost converter is a total mystery to me as you can achieve the same with field weakening. Want to lower regen current at high rpm -> field weakening. Want to produce torque past base speed -> field weakening. Not sure if the concept was unheard of back when the first Prius came out...

As I recall, a boost/buck converter was not used in the G1 Prius controller and was added to G2 (and subsequent) controllers to address consumer complaints about a lack of power. Rather than increasing the battery voltage(higher cost, complexity, and other problems) or motor size to increase power, the converter was added to the G2 controller. Over-volting a motor is a great way to get more power, if the motor can handle it. Indeed, as John Kelly points out in the referenced video, many hybrid vehicle controllers today have buck/boost converters.

[celeron55]

I'll go ahead and quote myself from the MGR thread:

It's starting to look like even above 100km/h the converter is really not there because the electric motors would need it at the boost converter's rather low power rating. I'm now thinking when the ICE is putting out high power at high rpm, the MGs need to stay out of field weakening in order to handle the power, and that means they naturally operate at elevated voltage as MG1 generates the voltage. The buck/boost converter is there just to continue interfacing the MG rail to the battery in that situation.

It's again the eCVT nature of the system. If it was primarily designed for battery electric propulsion and not for converting the full range of ICE output to different final output rpms, it would be designed without the boost converter.

It would be impossible to convert the ICE's torque output at maximum rpm and throttle to electricity and back if the MGs were in field weakening.