COMPRESSOR CONTROL SYSTEM FOR A PORTABLE VENTILATOR
A method and apparatus for controlling a brushless DC (BLDC) motor over a wide range of angular speeds is presented. Analog magnetic sensors provide continuous signal measurements related to the rotor angular position at a sample rate independent of rotor angular speed. In one embodiment, analog signal measurements are subsequently processed using an arctangent function to obtain the rotor angular position. The arctangent may be computed using arithmetic computation, a small angle approximation, a polynomial evaluation approach, a table lookup approach, or a combination of various methods. In one embodiment, the BLDC rotor is used to drive a Roots blower used as a compressor in a portable mechanical ventilator system.
1 - 35 . (canceled)
36 . A portable ventilator apparatus comprising:
a compressor disposed within the portable ventilator;
a brushless direct current (BLDC) motor, said compressor driven by said BLDC motor;
a plurality of sensors disposed within the portable ventilator that provide a plurality of analog signals, said plurality of analog signals representative of an angular position of said BLDC motor;
a computation circuit disposed within the portable ventilator and in communication within the plurality of sensors configured to compute said angular position of said BLDC motor from said plurality of analog signals; and
a speed control servo disposed within the portable ventilator and in communication with said BLDC motor for driving an angular speed of the BLDC motor to a command speed provided to said computation circuit.
37 . The apparatus of claim 36 , wherein each of said plurality of sensors comprises an analog Hall effect sensor.
38 . The apparatus of claim 36 , wherein each of said plurality of sensors comprises an anisotropic magneto-resistive (AMR) sensor.
39 . The apparatus of claim 36 , wherein said plurality of analog sensors is four analog sensors arranged ninety degrees apart from each other in a circular pattern.
40 . The apparatus of claim 36 , wherein said command speed is calculated by a flow-rate control loop to provide a required flow-rate through said compressor.
41 . The apparatus of claim 40 , wherein said required flow rate is calculated by a pressure control function.
42 . The apparatus of claim 36 , wherein said computation circuit comprises a processor.
43 . The apparatus of claim 36 , wherein said computation circuit computes said angular position from said plurality of analog signals using an arctangent function.
44 . The apparatus of claim 36 , wherein said computation circuit computes said angular position from said plurality of analog signals using a table lookup function.
45 . The apparatus of claim 36 , wherein said computation circuit computes said angular position from said plurality of analog signals using polynomial evaluation.
46 . The apparatus of claim 36 , further comprising an analog-to-digital converter which samples said plurality of analog signals at a constant sample rate, and which provides corresponding digital values to said computation circuit.
47 . The apparatus of claim 36 , wherein said computation circuit comprises a plurality of stored coefficient values for computing said angular position from a polynomial equation.
48 . The apparatus of claim 47 , wherein said plurality of coefficient values comprises a set of coefficients associated with each quadrant of a rotation.
49 . The apparatus of claim 36 , wherein said speed control servo drives the BLDC motor in accordance with said angular position.
50 . A portable ventilator apparatus comprising:
a compressor disposed within the portable ventilator;
a brushless direct current (BLDC) motor, said compressor driven by said BLDC motor;
a plurality of sensors disposed within the portable ventilator that provide a plurality of analog signals, said plurality of analog signals representative of an angular position of said BLDC motor;
a computation circuit disposed within the portable ventilator and in communication with the plurality of sensors configured to compute an angular speed of said BLDC motor from said plurality of analog signals; and
a speed control servo disposed within the portable ventilator and in communication with said BLDC motor for driving said angular speed of the BLDC motor to a command speed provided to said computation circuit.
51 . The apparatus of claim 50 , wherein each of said plurality of sensors comprises an analog Hall effect sensor.
52 . The apparatus of claim 50 , wherein each of said plurality of sensors comprises an anisotropic magneto-resistive (AMR) sensor.
53 . The apparatus of claim 50 , wherein said plurality of analog sensors is four analog sensors arranged ninety degrees apart from each other in a circular pattern.
54 . The apparatus of claim 50 , wherein said command speed is calculated by a flow-rate control loop that provides a required flow-rate through said compressor.
55 . The apparatus of claim 54 , wherein said required flow rate is calculated by a pressure control function.
56 . The apparatus of claim 50 , wherein said computation circuit comprises a processor.
57 . The apparatus of claim 50 , wherein said computation circuit computes said angular position from said plurality of analog signals using an arctangent function.
58 . The apparatus of claim 50 , wherein said computation circuit computes said angular position from said plurality of analog signals using a table lookup function.
59 . The apparatus of claim 50 , wherein said computation circuit computes said angular position from said plurality of analog signals using polynomial evaluation.
60 . The apparatus of claim 50 , further comprising an analog-to-digital converter which samples said plurality of analog signals at a constant sample rate, and which provides corresponding digital values to said computation circuit.
61 . The apparatus of claim 50 , wherein said computation circuit comprises a plurality of stored coefficient values for computing said angular position from a polynomial equation.
62 . The apparatus of claim 61 , wherein said plurality of coefficient values comprises a set of coefficients associated with each quadrant of a rotation.
63 . A portable ventilator apparatus comprising:
a compressor disposed within the portable ventilator;
a brushless direct current (BLDC) motor, said, compressor driven by said BLDC motor;
a plurality of sensors disposed within the portable ventilator that provide a plurality of analog signals, said plurality of analog signals representative of an angular position of said BLDC motor;
a computation circuit disposed within the portable ventilator and in communication with the plurality of sensors configured to compute an angular speed of said BLDC motor from said plurality of analog signals; and
a speed control servo disposed within the portable ventilator and in communication with said BLDC motor for driving said angular speed of the BLDC motor to a command speed provided in said computation circuit.
64 . The apparatus of claim 63 , wherein said BLDC motor has a rotor having a rotor shaft having a rotor shaft tip and forming a rotor shaft axis, further comprising:
a PC board positioned perpendicular to said rotor shaft of said BLDC motor;
wherein said sensors are each positioned on said PC board at an equal radial distance from the rotor shaft axis.
65 . The apparatus of claim 64 , wherein a magnet, having a radius, is placed on said rotor shaft tip.
66 . The apparatus of claim 65 , wherein said radial distance from the rotor shaft axis and each of said sensors is 0.17 inches, and wherein the radius of said magnet is 0.09 inches.
67 . The apparatus of claim 65 , wherein said radial distance from the rotor shaft axis and each of said sensors is less than 0.17 inches.
68 . The apparatus of claim 65 , wherein said radial distance from the rotor shaft axis and each of said sensors is greater than 0.17 inches.
69 . The apparatus of claim 65 , wherein each of said plurality of sensors are placed adjacent to said magnet.