Compensation for input voltage variation in an electric motor drive
First Claim
1. A method of compensating for deviations in actual DC link voltage from a desired DC link voltage in an electric drive system including a machine controller that controls a machine in response to a speed signal, the machine including a rotor, and stator windings, the rotor rotating at an actual rotor speed during operation of the machine, wherein the machine controller selectively applies the actual DC link voltage to the machine stator windings, the method comprising the steps of:
- periodically sampling the actual DC link voltage and converting the sampled DC link voltage into a digital representation;
periodically sampling the actual rotor speed and converting the sampled actual rotor speed to a digital representation;
generating a compensation factor from the digital representation of the sampled DC link voltage;
multiplying the digital representation of the actual rotor speed by the compensation factor to produce a compensated speed signal; and
transmitting the compensated speed signal to the electric machine controller and using the compensated speed signal to control the application of the actual DC link voltage to the machine stator windings.
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Accused Products
Abstract
The present invention employs digital circuitry to compensate for variations in DC link voltage transmitted to a switched reluctance machine. The digital voltage compensation system of the present invention periodically samples the DC link voltage and actual rotor speed, then supplies the samples in digital form to a microcontroller that derives a compensated speed signal to compensate for changes in DC link voltage.
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Citations
13 Claims
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1. A method of compensating for deviations in actual DC link voltage from a desired DC link voltage in an electric drive system including a machine controller that controls a machine in response to a speed signal, the machine including a rotor, and stator windings, the rotor rotating at an actual rotor speed during operation of the machine, wherein the machine controller selectively applies the actual DC link voltage to the machine stator windings, the method comprising the steps of:
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periodically sampling the actual DC link voltage and converting the sampled DC link voltage into a digital representation; periodically sampling the actual rotor speed and converting the sampled actual rotor speed to a digital representation; generating a compensation factor from the digital representation of the sampled DC link voltage; multiplying the digital representation of the actual rotor speed by the compensation factor to produce a compensated speed signal; and transmitting the compensated speed signal to the electric machine controller and using the compensated speed signal to control the application of the actual DC link voltage to the machine stator windings.
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2. A method of compensating for deviations in actual DC link voltage from a desired DC link voltage in an electric drive system including a machine controller that controls a machine in response to a speed signal, the machine including a rotor, and stator windings, the rotor rotating at an actual rotor speed during operation of the machine, wherein the machine controller selectively applies the actual DC link voltage to the machine stator windings, the method comprising the steps of:
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periodically sampling the actual DC link voltage and converting the sampled DC link voltage into a digital representation; periodically sampling the actual rotor speed and converting the sampled actual rotor speed to a digital representation; generating a compensation factor from the digital representation of the sampled DC link voltage, wherein the compensation factor corresponds to the desired DC link voltage divided by the actual DC link voltage; multiplying the digital representation of the actual rotor speed by the compensation factor to produce a compensated speed signal; and transmitting the compensated speed signal to the electric machine controller and using the compensated speed signal to control the application of the actual DC link voltage to the machine stator windings.
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3. A method of compensating for deviations in DC link voltage from a predetermined voltage level in an electric drive system including a rotating machine, comprising the steps of:
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taking a plurality of DC link voltage samples over a period of time and converting the voltage samples into a plurality of digital representations; averaging the voltage samples by adding the digital representations of the samples and dividing the sum by the number of samples to derive a digital representation of the average DC link voltage; converting the digital representation of the average DC link voltage into a digital compensation factor; sampling a voltage signal representative of the rotational speed of the machine and converting the sampled voltage signal into a digital speed representation; multiplying the digital speed representation by the digital compensation factor to produce a digital compensated speed signal; and using the compensated signal to control the electric machine.
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4. A system for compensating for deviations in DC link voltage from a predetermined voltage level in an electric drive system including an electric machine having a rotor, the electric drive system comprising:
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means for sampling the DC link voltage periodically and converting the sampled DC link voltage into a digital representation; means for sampling an actual rotor speed of the electric drive system periodically and converting the sampled actual rotor speed to a digital representation; means for comparing the digital representation of the sampled DC link voltage to a digital representation of the predetermined voltage level to provide a digital representation of the deviation of the sampled DC link voltage from the predetermined voltage level; and means for generating a compensated rotor speed signal by adjusting the sampled actual rotor speed with reference to the deviation of the sampled DC link voltage from the predetermined voltage level; and means for transmitting the compensated rotor speed signal to the electric drive system. - View Dependent Claims (5, 6, 7, 8, 9)
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10. A method of compensating for deviations in actual DC link voltage from a desired DC link voltage in an electric drive system including a machine controller that controls a machine in response to a speed signal, the machine including a rotor, and machine stator windings, the rotor rotating at an actual rotor speed during operation of the machine, and wherein the machine controller selectively applies the actual DC link voltage to the machine stator windings, the method comprising the steps of:
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periodically sampling the actual DC link voltage and converting the sampled DC link voltage into a digital representation; periodically sampling the actual rotor speed and converting the sampled actual rotor speed to a digital representation; producing a compensated speed signal by scaling the digital representation of the actual rotor speed as a function of the relationship between the actual DC link voltage and the desired DC link voltage; and transmitting the compensated speed signal to the electric machine controller and using the compensated speed signal to control the application of the actual DC link voltage to the machine stator windings. - View Dependent Claims (11, 12, 13)
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Specification