CONSTANT CFM CONTROL ALGORITHM FOR AN AIR MOVING SYSTEM UTILIZING A CENTRIFUGAL BLOWER DRIVEN BY AN INDUCTION MOTOR
First Claim
1. A method of achieving a selected constant mass air flow rate for a blower motor of the induction type exhibiting nonlinearity between motor rotational speed, motor control voltage, and air flow rate, comprising:
- a) controlling motor speed through a motor controller by varying an excitation voltage to the motor;
b) determining proportionality constants of flow rate to motor speed for various motor speeds over the operating range of the motor;
c) providing a graph of curves for the various motor speeds plotted against the proportionality constants and the excitation voltages in a memory accessible by the motor controller;
d) setting the controller at a first excitation voltage;
e) measuring a rotational speed of the motor;
f) deriving the proportionality constant for the measured motor speed to determine a fan speed corresponding to the selected air flow rate.
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Accused Products
Abstract
A method and apparatus for achieving constant air flow rate economically utilizes an induction blower motor with control settings determining the motor excitation voltage. A memory stores, for a variety of motor speeds, a graph of the speeds plotted against a proportionality constant of flow rate to fan speed for the selected motor system on one axis and motor control settings on the other axis. The only monitoring necessary to achieve the constant flow rate is thus the sensing of fan rotational speed. The measured fan speed is compared against the proportionality constant needed for the selected constant air flow rate and a motor excitation voltage is derived to achieve that proportionality constant. When the system load changes significantly, thereby causing significant fan speed change, a cascaded control loop is used whereby the speed changed induced by each control voltage adjustment is monitored until the desired constant flow rate is again attained at the new load level.
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Citations
14 Claims
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1. A method of achieving a selected constant mass air flow rate for a blower motor of the induction type exhibiting nonlinearity between motor rotational speed, motor control voltage, and air flow rate, comprising:
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a) controlling motor speed through a motor controller by varying an excitation voltage to the motor;
b) determining proportionality constants of flow rate to motor speed for various motor speeds over the operating range of the motor;
c) providing a graph of curves for the various motor speeds plotted against the proportionality constants and the excitation voltages in a memory accessible by the motor controller;
d) setting the controller at a first excitation voltage;
e) measuring a rotational speed of the motor;
f) deriving the proportionality constant for the measured motor speed to determine a fan speed corresponding to the selected air flow rate. - View Dependent Claims (2, 3)
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4. A method of achieving a constant mass air flow rate for a blower motor of the induction type exhibiting nonlinearity between motor rotational speed, motor control voltage, and air flow rate, comprising:
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a) controlling motor speed through a motor controller by varying an excitation voltage to the motor at selected control settings representative of varied excitation voltages;
b) determining proportionality constants of flow rate to motor speed for various motor speed curves over an operating range of the motor;
c) providing a graph of motor speed curves plotted against the proportionality constants of step b) and control settings of step a) in a memory accessible by the motor controller;
d) setting the motor controller at a first setting for a selected constant mass air flow rate;
e) measuring a rotational speed of the motor;
f) deriving a proportionality constant for the measured motor speed to determine a control setting corresponding to the selected air flow;
g) adjusting the RPM setting according to the proportionality constant of step f);
h) adjusting the control setting to increase or decrease motor speed to achieve the desired RPM setting;
i) deriving a second proportionality constant when the measured speed of the motor has achieved the desired RPM setting; and
j) iteratively adjusting the rotational speed of the motor by repeating steps e)-g). - View Dependent Claims (5)
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6. Apparatus for achieving a constant mass air flow rate for a blower motor of the induction type exhibiting nonlinearity between motor rotational speed, motor control voltage, and air flow rate, comprising:
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a) a motor controller having a microprocessor for receiving a selected constant CFM rate value;
b) a memory having stored therein motor speed curves plotted against proportionality constants of fan speed to air flow on a first axis and motor excitation voltages on a second axis, the memory operably connected to the microprocessor;
c) means for controlling an excitation voltage to the motor, the means for controlling being operably connected to the microprocessor; and
d) a tachometer for sensing the speed of the motor, the tachometer being operably connected to the microprocessor. - View Dependent Claims (7, 8, 9, 10)
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11. Apparatus for achieving a constant mass air flow rate for a blower motor comprising:
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a) means for inputting a selected constant CFM rate to a motor controller;
b) a motor controller having a microprocessor for receiving the input constant CFM rate;
c) memory means having stored therein motor speed curves plotted against proportionality constants on a first axis and motor excitation voltages on a second axis, the memory means operably connected to the microprocessor;
d) means for controlling the excitation voltage to the motor, the means for controlling operably connected to the microprocessor; and
e) means for sensing a speed of the motor, the means for sensing a speed operably connected to the microprocessor. - View Dependent Claims (12, 13, 14)
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Specification