Protoype realization and first tests

A first prototype has been assembled and the testing phase has ended successfully.

The tests have been performed with a cheap brushless motor available for model plane pilots in RC-shops. A magnet was attached to the rear part of the motor shaft for position measurment with the Hall-sensor. The test setup looks like this:

Along with testing, basic functionality has been implemented in software. The following features are available and some performance parameters have been determined:

• Angular resolution of the Hall sensor is 2048 steps per revolution with ± 1 LSB accuracy. This gives an angle readout with accuracy of ± 0.17°. At the moment, the calculation of the angle from the analog voltages of the Hall sensor which are converted with 10 bit ADCs uses up the most CPU power.
• 10 bit ADCs are used for current measurement on all three phases. Positive and negative currents currents can be measured in the range of ± 45 A at each phase. The resolution is approximately 100 mA.
• The circuit board has been manufactured from 0.5 mm thick glass-fiber reinforced substrate. The design was thermally optimized and allows laminating the board to solid metal with a thin isolation layer. One protoype has been laminated with a 3 mm thick aluminum sheet. In fact the thermal coupling is so good that soldering without pre-heating of the unit is impossible. The high current paths on the circuit board will be optimized in the next version. So far, however, the board handles a motor current of 30 A. Note that this means average of 60 A that pass through the board (what goes in one phase has to come out at the others). The limiting factor for the maximum current is a parasitic ringing effect. Thermally the board could take motor current well above 30 A.
• An SVPWM (space vector pulse width modulation) has been implemented to take control of the three-phase motor voltage. The PWM-frequency is 10 kHz. At a motor current of 30 A and a supply voltage of 15 V, a heating of the unit by a few degrees has been observed. This confirmes that the switching of the FETs which are fed by 2 A gate drivers is very efficient. Transition times in the range of 40-60 ns have been measured for the FET pairs.
• Basic implementation of a closed loop motion control using a simple P-regulator has been completed and the response of the motor motion has been recorded. The recording of current and position and SVPWM control voltage is also carried out in the microcontroller and can be read using the USB port connection. If the regulator is properly tuned the position regulation accuracy is in the range of the accuracy of the Hall sensor.