Model-based fault detection system for electric motors
First Claim
1. A fault detection system for monitoring the operational condition of an electric motor operating with an unknown load comprising:
- sensors coupled to said motor for measuring selected operating parameters; and
computer means coupled to said sensors;
i) for determining, when said motor is operating in a fault free condition, an residual of zero, said first residual derived by multiplying said selected operating parameters by invariants and summing the products;
ii) for selecting a threshold level different than zero,iii and for determining a plurality of residuals of said motor during operation;
said computer means having a memory for comparing each of said plurality of residuals with said first residual and for displaying a message indicative of whether said motor is operating under fault free conditions in the case where said plurality of residuals is less than the threshold level or whether said motor is operating with impending failure in the case where at least one of said plurality of residuals exceeds the threshold level.
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Abstract
The present invention relates to a model based fault detection system and method for monitoring and predicting maintenance requirements of electric motors. Since, the method and system of the present invention is software based and utilizes data obtained from no-intrusive measurements, implementation costs are significantly less than prior art maintenance methods.
The system comprises computer means coupled to sensors which provide continuous real-time information of the input voltage and current and motor speed. The system and method utilize a multivariable experimental modeling algorithm to obtain a mathematical description of the motor. The algorithm compares the modeled result with a measured result and quantifies the comparison in terms of a residual which is generated by subtracting the respective signals. A diagnostic observer analyzes the residual and determines if the motor is fault free or operating in a manner other than fault free. Upon detection of the impending fault, the diagnostic observer evaluates the measured variables of the motor, determines the deviation from the reference value and develops a diagnosis of the likely failed or failing component.
Another embodiment of the present invention is particularly useful in the manufacture of fractional horsepower electric motors and especially in the performance of quality control testing.
161 Citations
21 Claims
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1. A fault detection system for monitoring the operational condition of an electric motor operating with an unknown load comprising:
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sensors coupled to said motor for measuring selected operating parameters; and computer means coupled to said sensors; i) for determining, when said motor is operating in a fault free condition, an residual of zero, said first residual derived by multiplying said selected operating parameters by invariants and summing the products; ii) for selecting a threshold level different than zero, iii and for determining a plurality of residuals of said motor during operation;
said computer means having a memory for comparing each of said plurality of residuals with said first residual and for displaying a message indicative of whether said motor is operating under fault free conditions in the case where said plurality of residuals is less than the threshold level or whether said motor is operating with impending failure in the case where at least one of said plurality of residuals exceeds the threshold level. - View Dependent Claims (2, 3, 4, 5)
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6. A method for monitoring the operation of an electric motor to detect faults capable of causing failure of said motor comprising the steps of:
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providing a model of said motor on a computer; coupling said motor to said computer by a plurality of sensors; measuring a plurality of operating signals of said motor with said sensors; applying said measured plurality of operating signals to solve a linear discrete-time state equation; calculating a residual to compare the solution of said state equation with the solution suggested by said model; determining, based on said calculating and comparison step, whether said motor is operating without a detected fault; correlating said residual to a fault in the event said motor is operating with a detected fault and communicating the existence of said fault to prevent unanticipated motor failure; and repeating said steps, other than said developing a model step, at selected intervals during operation of said motor. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13)
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14. A method for monitoring and detecting faults in an electric motor comprising:
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measuring, when said electric motor is operating in a fault free manner, voltage (V), current (i) and speed (ω
) of said electric motor with a plurality of sensors;multiplying the measured voltage, current and speed of said electric motor with constant invariants; calculating and retaining the result of the discrete state space equations;
space="preserve" listing-type="equation">x(k+1)=A x(k)+B u(k)
space="preserve" listing-type="equation">y(k)=C x(k)where x, u, and y are the n×
1 state vector, the p×
1 input vector, and the q×
1 output vector, respectively, and k denotes discrete time increments and where A, B, and C are known nominal matrices of said electric motor;
repeating the measuring and multiplying steps;calculating the result of the discrete state space equations;
space="preserve" listing-type="equation">x.sub.f (k+1)=A.sub.f X.sub.f (k)+B.sub.f u.sub.f (k)
space="preserve" listing-type="equation">Y.sub.f (k)=C.sub.f x(k)comparing the differences between y(k) and yf (k); and repeating said repeating, calculating and comparing sequence of steps until the difference exceeds a selected threshold. - View Dependent Claims (15, 16)
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17. A system for monitoring the operational condition of an electric motor comprising:
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sensors coupled to said motor for measuring selected operating parameters; and means, coupled to said sensors, for; a) receiving said selected operating parameters when said motor is operating in a fault free condition; b) calculating the result of the discrete state space equations;
space="preserve" listing-type="equation">x(k+1)=A x(k)+B u(k)
space="preserve" listing-type="equation">y(k)=C x(k);where x, u, and V are the n×
1 state vector, the p×
1 input vector, and the q×
1 output vector, respectively, and k denotes discrete time increments and where A, B, and C are known nominal matrices of said electric motor;c) repetitively receiving said selected operating parameters when said motor is operating with an unknown load; d) calculating the result of the discrete state space equations;
space="preserve" listing-type="equation">x.sub.f (k+1)=A.sub.f X.sub.f (k)+B.sub.f u.sub.f (k)
space="preserve" listing-type="equation">y.sub.f (k)=C.sub.f x(k);and e) comparing the differences between Yf (k) and y(k) until said difference exceeds a selected threshold. - View Dependent Claims (18, 19, 20, 21)
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Specification