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Published on Jan 19, 2010
I finally returned to the motor controller test circuit. I left it because I realized that the drivetrain was only 1 of 3 things wrong with conventional cars. they are also too heavy and have poor aerodynamics so I looked into redoing the whole car and not just the engine so I came up with the Freeranger concept car and for that my high voltage controller design was not suited. now I've resumed power electronics work in order to gain general experience with power electronics and I've finally added the microcontroller and programmed it to regulate the buck circuit. in these tests it's programmed to do 1kHz PWM gaining up and down the output from 0% to 100% to 0% every 2 seconds. The circuit actually worked but I overlooked a minor issue that the Atmega8 chip doesn't come online immediately after power up but waits for 100-200ms and that left the gate of the IGBT floating and if the load was high enough that fried the chip. at first I thought it was inductive banging so I added a protective capacitor on the supply side of the IGBT and a freewheel diode on the load side. still fried the IGBT on startup. 2 down. then I realized it flashes on started and the Atmega is programmed to start from 0 so I realized the gate was floating and I added a 10k pulldown resistor on the Atmega pwm pin (you can see it show up next to the atmega at the end of the video) and now the circuit works beautifully. seems to be able to handle much more than the 1800 or so watts of the 3 halogen lamps but I'm afraid to add more because the house fuse might go and I lose all power in my apartment. After about 1minute at 1800watt the IGBT sink gets to about 45degrees celcius. a minute more and it feels like 60. the diode is cold as ice which is to be expected as there is no signifcant inductance. the caps show no heating at all. under the 1800 watt load the voltage at the rectifier seemed to fluctuate between 270 and 310V. The lights surprisingly emit a 1kHz ringing from the PWM. a good opportunity to test spread spectrum switching to see if low frequency switching can be silent by varying the frequency rapidly. learning how to program the Atmega8 was a bitch. a messy little chip with many options and a verbose documentation. I used an USBtiny programmer to put the program into the chip and AVRstudio to compile and debug the code. next is adding potentiometer throttle input to the atmega and program it to control the light intensity according to throttle. closer to an actual motor controller. then it'll be a huge dimmer switch : )