Doing useful things with the Prius Gen2 buck/boost converter

[johu]

Many hybrid inverters feature a buck/boost converter. It can step down the voltage from the motor to the battery side to charge the battery with a fast spinning motor. And it can boost the voltage from the battery to the motor side to make the motor spin fast from the battery. Battery voltage in hybrids is typically about 200V.

In addition they feature a DC/DC converter from HV to 12V to run the "car" systems. It sits on the battery side of the converter.

The Prius Gen2 inverter features this and due to its not too integrated design we can faff around with it.

First of all, when using the Prius inverter to power an actual EV we will find that the converter is "in the way" as it sits between the battery and motor side and is a bit of a weak link, limiting battery current to about 100A.

Secondly we will find that when using a regular 400V style battery salvaged from a PHEV or EV the voltage exceeds the rated input voltage of the DC/DC converter.

With a simple mod we can fix both these problems

We disconnect the positive battery cable from the boost converter input and reconnect it to the boost converter output i.e. the motor side of the converter. This has 2 consequences
1. The inverter bus is now straight connected to our HV battery and can draw as much power as it can handle
2. The DC/DC converter still sits on the buck converter output and by running the latter at, say, 50% duty cycle will feed it with the 200V it expects

With the Gen2 inverter this has a 3rd consequence: in parallel with the DC/DC converter there is an auxiliary inverter. If we replace its output IGBTs with a bridge rectifier and feed 120 or 230V AC to it we will have a rectified DC voltage of 150 to 300V on the boost converter input. So now when we run the boost converter it will feed current into out HV battery - we have created a simple mains charger.

[Jacobsmess]

This is exciting

[MattsAwesomeStuff]

With a simple mod we can fix both these problems

I have a second inverter with its top off I will try to take pictures of if I can figure out exactly what to do based on your diagram.

Also, does any of what you described require using new pins or telling the buck/boost what to do? Any code or software? Or does it just happen by being connected?

[Keo]

I assume the same can be done with the gs450h inverter? Does it also have the auxiliary inverter to run the same setup as with this?

[johu]

Also, does any of what you described require using new pins or telling the buck/boost what to do? Any code or software? Or does it just happen by being connected?

Sorry, just found this. With the SMT version of the Prius controller this is integrated. In drive mode the "user PWM" pin runs the boost converter at a fixed rate. In charge mode the regular PWM runs it in current control mode.
Here we do indeed need additional hardware: an extra current sensor that measures current delivered by the AC/DC.

I assume the same can be done with the gs450h inverter? Does it also have the auxiliary inverter to run the same setup as with this?

There is no replacement logic board for Lexus inverters. I don't know if the buck/boost converter can be controlled with the Serial protocol? And I'm pretty sure it has no aux inverter.

[Keo]

Ok thanks. I'll moving forward with the gen2 Prius since it's relatively cheap where I live. I'm thinking of running a 100v 100ah to the boost converter to get anything around 25kw to run the motor. I don't need much power since there's no traffic where I stay and 60kmph top speed is enough. Between running via the boost converter vs direct to inverter I don't know which is best since I can't get a high voltage battery pack here in Africa without importing and that will more than double my costs

[johu]

The booster is limited to 100A, so this will get you 10 kW

[MattsAwesomeStuff]

With the SMT version of the Prius controller this is integrated.

Good news, I also bought one of those 2nd hand from someone who went a different way. So I have both hardwares.

In drive mode the "user PWM" pin runs the boost converter at a fixed rate. In charge mode the regular PWM runs it in current control mode.
Here we do indeed need additional hardware: an extra current sensor that measures current delivered by the AC/DC.

Stupid question, how does it know whether it's in charge mode, and is charge mode also what happens during regen?

Do I need to install an extra current sensor, or does the SMT board come with a way to interface with one built into the inverter?

[johu]

Good news, I also bought one of those 2nd hand from someone who went a different way. So I have both hardwares.

Is it version 1.3? Early versions don't have the user PWM connection.

Stupid question, how does it know whether it's in charge mode, and is charge mode also what happens during regen?

Because you explicitly command charge mode https://openinverter.org/wiki/Battery_Charging
Regen=Drive Mode

Do I need to install an extra current sensor, or does the SMT board come with a way to interface with one built into the inverter?

Yes. The board has 4 inputs. You use two inputs for ONE inverter power stage and one for the extra sensor. You need to juggle a bit to have the same current to voltage ratio as the built in ones. You could regard the latter as cosmetic. Say the extra sensor outputs 50 mV/A and the built-in ones 25 mv/A it just means you need to command double the charge current.

[MattsAwesomeStuff]

Is it version 1.3? Early versions don't have the user PWM connection.

*checks*

V1.1

Whelp, nevermind I guess.

[johu]

So charging feature would work but not powering the dcdc converter while driving.

[MattsAwesomeStuff]

So charging feature would work but not powering the dcdc converter while driving.

Oh, I misunderstood.

In the video you shared, you say it uses the A/C inverter to do this? I was somewhat planning on using my A/C inverter to run the A/C. Though that said, I also have the A/C off of a Gen3 which only needs PWM fed to it as the inverter is onboard the compressor.

Does the charging feature both buck and boost too? Or is that feature lost on earlier versions?

[johu]

Via the A/C inverter it will just boost
Via MG1 it will just buck. You need an additional relay to connect the battery to the buck side while charging. At least then you don't need the extra current sensor because it will use the MG1 ones