Building a GEVCU
I built up a GEVCU 4.2 controller board that will be used to control the DMOC (pictures). The main processor on the GEVCU is an ARM Cortex M3 84MHz processor. It is packaged in a 144 pin LQFP device. This is the first time I have soldered a LQFP surface mounted device (SMD), but I found it was not much more difficult than soldering any other SMD. However, I have not done any SMD soldering for a few months and I did have some initial problems with configuring the ARM processor because of a soldering error. Paulo Almeida helped me out, via email. Many improvements have been made in the code over the past 6 months by Paulo, Collin Kidder, Charles Galpin and Michael Neuweiler. Once I have the drivetrain together I need to test the GEVCU 4.2 with my throttle and brake setup. The throttle is easy to test because it is used to spin the motor. The throttle is a duel potentiometer and will be connected directly to the throttle cable on the 320i. Two potentiometers are used as a safely measure. A hydraulic pressure transducer is use for the brake transducer and the signal is used to control regeneration or regen in the motor. Regen is a process where the motor is turned into a generator and the output is used to charge the batteries. Even with a lot of braking regen only leads to a 5 to 10% recovery of energy. The actual regen and throttle setup will have to wait until car is on the road for it to be fine tuned. The throttle and brake are 0 to 5V analog signals that have to be calibrated in the GEVCU code. These settings are accessed through a web page that is hosted by an embedded server in the ConnectOne WiFi device (pictures).
Once the throttle and brake are configured I then need to design all the circuits that will use the digital I/O on the GEVCU. One circuit will use one of the MOSFET outputs to control a precharge circuit for the DMOC. Because it has a huge capacitance it is necessary to precharge the DMOC with a low voltage, controlled current before applying the full battery pack voltage otherwise the high current inrush can fuse the contactor. Another one of the MOSEFT outputs will be setup to output a pulse width modulated (PWM) signal that will drive the tachometer in the instrument panel. One of the digital inputs will be for an enable switch for the whole system.