Apparatus and method for determining the operation of an induction motor
First Claim
1. Apparatus for the determination of the load resistance of a rotating field motor, having a squirrel cage rotor, supplied under three terminal voltages and three line currents, comprising:
- first means for sensing said three terminal voltages and means for sensing two of said line currents for deriving corresponding sensed signals;
second means responsive to said sensed signals for deriving direct and quadrature voltage and current component signals representative of said sensed terminal voltages and line currents;
third means responsive to said direct and quadrature voltage and current component signals for deriving the following quantity in real time;
motor overall reactance 2WX /I12 ; and
fourth means for deriving with said quantity a representation of the load resistance RL in accordance with the formula;
space="preserve" listing-type="equation">R.sub.L =ω
.sub.1 (L.sub.M +L.sub.2){[a-ω
.sub.1 L.sub.M L.sub.2 /(L.sub.M +L.sub.2)]/[ω
.sub.1 L.sub.M -a]}.sup.1/2 whereLM is the leakage inductance,L1 is the stator inductance,L2 is the rotor inductance,ω
1 is the terminal line frequency,WX being the reactive power equal to (V1 I1 Sin φ
)1/2I1 being the stator current, V1 the stator voltageφ
the phase angle between V1 and I1,a is the air gap reactance equal to 2WX /I12 -ω
1 L1, the parallel combination of stator and rotor leakage reactances ω
1 LM L2 /(LM +L2), and the stator leakage reactance ω
1 L1, thereby to provide a signal representative of the instantaneous load resistance RL of the motor.
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Accused Products
Abstract
From the sensed input voltages and currents fed into a standard induction motor the stator resistance is known instantaneously through a direct and quadrature treatment of the sensed quantities from which are derived at least four of the following five quantities: the motor overall reactance, the motor overall real impedance, the air gap reactance, the parallel combination of stator and rotor leakage reactances and the stator leakage reactance. This derivation uses the motor intrinsic characteristics at rest, while those four quantities are used in ascertaining the stator resistance instantaneously and recurrently during motor operation, thus, without any sensing means on the motor itself. The load reactance is also determined with the above-stated five quantities. From the knowledge of the stator resistance and the load resistance, a simulated two-phase network is provided and used to ascertain any of the key process variables typically used in an induction motor drive, such as shaft speed, slip, flux, torque. The temperature and load of a standard induction motor are known without sensing and the motor can be remotely controlled for protection against overheating, or overload.
43 Citations
14 Claims
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1. Apparatus for the determination of the load resistance of a rotating field motor, having a squirrel cage rotor, supplied under three terminal voltages and three line currents, comprising:
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first means for sensing said three terminal voltages and means for sensing two of said line currents for deriving corresponding sensed signals; second means responsive to said sensed signals for deriving direct and quadrature voltage and current component signals representative of said sensed terminal voltages and line currents; third means responsive to said direct and quadrature voltage and current component signals for deriving the following quantity in real time;
motor overall reactance 2WX /I12 ; andfourth means for deriving with said quantity a representation of the load resistance RL in accordance with the formula;
space="preserve" listing-type="equation">R.sub.L =ω
.sub.1 (L.sub.M +L.sub.2){[a-ω
.sub.1 L.sub.M L.sub.2 /(L.sub.M +L.sub.2)]/[ω
.sub.1 L.sub.M -a]}.sup.1/2where LM is the leakage inductance, L1 is the stator inductance, L2 is the rotor inductance, ω
1 is the terminal line frequency,WX being the reactive power equal to (V1 I1 Sin φ
)1/2I1 being the stator current, V1 the stator voltage φ
the phase angle between V1 and I1,a is the air gap reactance equal to 2WX /I12 -ω
1 L1, the parallel combination of stator and rotor leakage reactances ω
1 LM L2 /(LM +L2), and the stator leakage reactance ω
1 L1, thereby to provide a signal representative of the instantaneous load resistance RL of the motor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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Specification