Nick Kirkby

my head is numb from staring at Field Oriented Control code for over a month, so please accept this brief interlude before I document that part of the process.

about

This thing:

DSC_1773DSC_1767  DSC_1772

is the boost converter brick for the 2nd generation Prius inverter assembly.  Its location in the assembly is circled in red below.  It is a half bridge with integrated drive electronics.  It already includes all the necessities such as gate drivers, an isolated high side supply, and extras like a bus voltage signal scaled from 0-5v and a temperature sensor.  Oh yeah, and the signal stuff is totally isolated from the power stage.  Just feed it PWM and logic power.

boost_converter_location

Above: the inverter assembly.  The inductor is circled in green and the capacitor is the big black thing that sits on top of the inverter brick.  The inductor and the boost module together make a boost converter.  It takes 200V on the battery side and boosts it up to 400V (or so) on the inverter side.  By conservation of power, the current that goes in is roughly twice the current that goes out.  (IV_in = IV_out)  Check out the wiki and this video on boost converters for more information.inside_schema

How To turning it on

fortunately, the pinout can be had in the wiring diagram and info on what waveforms should look like is found in “hybrid control manual P112” or something like that.  The relevant parts are posted below:

priusdcdc priusdcdcpins

boost_converter_signal

In summary:

IGCT – 12V of logic power

GCNV – logic ground

OVH – pink wire wants 5V.  Usually supplied by the inverter.

CSDN – shutdown signal.  tie it to logic ground.

CPWM – gate drive PWM (inverting).  Expects 0-10V PWM.  Nominal switching frequency 2kHz.  Gets sad past about 25 kHz.

extras:

battery voltage monitor VL:

VL = 0.5 +1/100(Orange wire with spade terminal – CN screw terminal)  [ranges from 0-5V]

CT – temperature sensor.  curve is somewhere in the hybrid control manual.

 

I spent an hour or so trying to figure out how to turn it on.  Luckily, the second inverter assembly that Bayley and I bought through ebay came with the little wiring harness that connects the inverter brick to the boost brick and the ECU.  I cut the boost brick connector free of the harness and labeled the wires.  Their colors correspond to those listed in the images above.

IMG_0632

The logic power supply drew decreasing current with increasing voltage, indicative of a Switched Mode Power Supply (SMPS).  That was all good, but I couldn’t get it to start switching.  Fortunately, pkrogen was around.  he noticed that my PWM input was wrongly centered at 0V instead of +5V with 10Vpp.  That fixed it.  The yellow trace is PWM input and the blue trace is the output at the center of the half bridge.

IMG_0633  IMG_0635

The Logical Next Step – Driving a Subwoofer

Well we have this nice big isolated half bridge module… It’s good for about 20kW  (when attached to a water block.. d’oh!)  Half bridges are used in lots of things, including:

tesla coils

induction heaters

power converters (buck, boost, resonant split pi whatever the heck)

motor drivers (usually two half bridges to make an H-bridge or three to make a three-phase bridge like the ones in the inverter module)

speaker drivers (called Class D switching amplifiers)

IMG_0636

To make audio input into PWM, I used this circuit.  It may look vaguely familiar to folks who have looked at the materials for 6.131.

awful_schema

The 555 makes a triangle wave which is compared with an oscillating audio input by the LM311.  The output is PWM which has a duty cycle dependent on the audio input.  like this:

mapping

and here in real life:

IMG_0638IMG_0639

You can see some of the jiggle in the yellow PWM trace.  There was no voltage on the bus in this scope capture, so the blue trace doesn’t move too much.

IMG_0637  IMG_0640

and here, as thousands of pictures with a poor quality audio track: