Method of digital flux reconstruction with DC elimination
First Claim
1. A method for eliminating direct current components of a flux vector signal representative of a rotating flux field in an alternating current polyphase dynamoelectric machine, the machine having at least one electrical power terminal for each phase, the method comprising the steps of:
- measuring machine terminal voltage at each machine power terminal;
converting the measured machine terminal voltage to equivalent first and second two-phase voltage representative signals;
integrating each of the first and second signals for generating corresponding flux vector component representative signals, each of the flux vector representative signals varying sinusoidally;
detecting consecutive maximum and minimum peaks of each of the sinusoidal flux vector representative signals;
developing a signal representative of a direct current (DC) component of each of the flux vector representative signals by determination of a voltage midpoint between the detected consecutive maximum and minimum peaks; and
subtracting the corresponding direct current component signal from a respective one of each of the first and second signals for eliminating any direct current component in the flux vector signals.
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Abstract
A method for developing current control signals from motor terminal voltage in the control of alternating current electric motors which utilize electric current control signals oriented to the phase of a flux component in a rotating field for applying current so as to control the flux and torque in the motor. The method includes developing flux signals from measurement of motor terminal voltage and integrating those signals to develop corresponding flux signals. In one form, the method eliminates DC components occuring in the resultant flux signals by locating local maxima and minima of the resultant flux signal and correcting the value of the flux integrator so as to provide maxima and minima flux signals having equal absolute values. The method also includes establishing an initial flux in the motor prior to startup which is oriented in a predetermined manner such that initial current applied to the motor can be applied so as to immediately develop torque, if required. The method further provides for initializing the flux integrators and associated logic such that discontinuities attributable to events such as frequency reversals are avoided.
23 Citations
9 Claims
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1. A method for eliminating direct current components of a flux vector signal representative of a rotating flux field in an alternating current polyphase dynamoelectric machine, the machine having at least one electrical power terminal for each phase, the method comprising the steps of:
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measuring machine terminal voltage at each machine power terminal; converting the measured machine terminal voltage to equivalent first and second two-phase voltage representative signals; integrating each of the first and second signals for generating corresponding flux vector component representative signals, each of the flux vector representative signals varying sinusoidally; detecting consecutive maximum and minimum peaks of each of the sinusoidal flux vector representative signals; developing a signal representative of a direct current (DC) component of each of the flux vector representative signals by determination of a voltage midpoint between the detected consecutive maximum and minimum peaks; and subtracting the corresponding direct current component signal from a respective one of each of the first and second signals for eliminating any direct current component in the flux vector signals. - View Dependent Claims (2, 3, 4)
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5. In a system for controlling a polyphase alternating current electric motor using an electric current control signal oriented to a computed rotor flux vector, a method for developing the current control signal from motor terminal voltage comprising the steps of:
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sensing polyphase motor terminal voltage and converting the sensed voltage to a two-phase representation thereof; converting each phase of the two-phase representation to a corresponding pulse train having a variable pulse repetition rate proportional to the amplitude of the sensed motor voltage; counting the pulses in the pulse train; sampling the counted pulses at periodic intervals; obtaining a differentiated value by determining the difference in count value between adjacent samples; integrating the differentiated value to obtain a signal representative of a corresponding component of flux in the motor; determining sequential maxima and minima of each flux component signal; comparing the value of each pair of sequential maxima and minima for obtaining an error value; and modifying the flux signal by a value proportional to the error value. - View Dependent Claims (6, 7, 8, 9)
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Specification