Compressor control system for a portable ventilator

A portable ventilator apparatus comprising:

• a brushless DC (BLDC) motor;
• a compressor within a portable ventilator, said compressor driven by said BLDC motor;
• a plurality of sensors providing a plurality of analog signals representative of an angular position of said BLDC motor;
• a computation circuit configured to compute said angular position and a speed of said BLDC motor from said plurality of analog signals;
• and
• a speed control servo for driving said angular speed to a command speed.

A method for controlling an electric motor comprising a plurality of analog sensors sensing a magnetic flux associated with rotation of a rotor, said method comprising

• sampling the outputs of said plurality of analog sensors to obtain a plurality of digitized sensor signals, said sampling occuring at a constant sample rate;
• subtracting a first digitized signal associated with a first sensor from a second digitized signal associated with a second sensor to obtain a first sinusoidal value related to an angular position of said rotor, said first sensor and said second sensor offset from each other by 180 degrees;
• deriving said angular position from said first sinusoidal value;
• deriving said angular speed from said angular position;
• and
• applying said derived angular speed to a speed control servo to drive said rotor to a desired angular speed.

A method of calibrating a speed servo comprising an electric motor having a magnet attached to a rotor shaft and a plurality of pairs of opposing analog sensors positioned in a circle adjacent to said magnet, said method comprising:

• rotating said rotor shaft at a constant speed;
• for each pair of opposing analog sensors, subtracting a digitized sensor signal of a first analog sensor from a digitized sensor signal of a second analog sensor to obtain a sinusoidal signal;
• and
• for each quadrant, determining a plurality of coefficents of a polynomial equation fitted to a plurality of said sinusoidal signals.