DC offset compensator
First Claim
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1. A method of compensating for dc offset in a three phase ac current signal, comprising the steps of:
- providing a sample of the ac current signal;
generating a rotating vector (r) from the sample;
extracting a dc offset from the sample;
removing the dc offset from the ac current signal; and
generating a Park vector representing a total measured current vector (iT) from the sample using the formula;
iT=(⅔
)(Ia+(a)(Ib)+(a2)(Ic));
where a=exp(j2π
/3), Ia equals the amplitude of the phase current A (Ia=I sin(wt)), Ib equals the amplitude of the phase current B (Ib=I sin(wt+π
/3)) and Ic equals the amplitude of the phase current C (Ic=I sin(wt+2π
/3)) and w=frequency and t=time;
wherein the three phases of the ac current signal comprise a phase current A, a phase current B, and a phase current C.
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Abstract
A dc offset compensator receives a three phase ac current signal as an input and provides a dc offset signal correction voltage as an output. The dc offset compensator comprises a processor configured to sample the ac current signal, generate a rotating vector (r) from the sample, extract a dc offset from the sample and to generate a dc offset signal correction voltage from the dc offset. A method of compensating for dc offset in a three phase ac current signal is also presented.
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Citations
16 Claims
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1. A method of compensating for dc offset in a three phase ac current signal, comprising the steps of:
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providing a sample of the ac current signal;
generating a rotating vector (r) from the sample;
extracting a dc offset from the sample;
removing the dc offset from the ac current signal; and
generating a Park vector representing a total measured current vector (iT) from the sample using the formula;
iT=(⅔
)(Ia+(a)(Ib)+(a2)(Ic));
where a=exp(j2π
/3), Ia equals the amplitude of the phase current A (Ia=I sin(wt)), Ib equals the amplitude of the phase current B (Ib=I sin(wt+π
/3)) and Ic equals the amplitude of the phase current C (Ic=I sin(wt+2π
/3)) and w=frequency and t=time;
wherein the three phases of the ac current signal comprise a phase current A, a phase current B, and a phase current C. - View Dependent Claims (2, 3, 4, 5)
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6. A method of compensating for dc offset in a three phase ac current signal comprising a phase current A, a phase current B, and a phase current C and comprising the steps of:
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sampling the ac current signal;
generating a rotating vector (r) from the sample using the formula;
r=exp(θ
*);
where θ
* equals a first estimated angle;
generating a Park vector representing a total measured current vector (iT) from the sample using the formula;
iT=(⅔
)(Ia+(a)(Ib)+(a2)(Ic));
where a=exp(j2π
/3), Ia equals the amplitude of the phase current A (Ia=I sin(wt)), Ib equals the amplitude of the phase current B (Ib=I sin(wt+π
/3)) and Ic equals the amplitude of the phase current C (Ic=I sin(wt+2π
/3)) and w=frequency and t=time;
extracting a dc offset from the sample by;
subtracting a first estimated dc offset current vector (iDC*) from the total measured current vector (iT) to obtain a first estimated positive sequence current vector (iP*);
generating a vector cross product of the first estimated positive sequence current vector (iP*) and the rotating vector (r) to obtain an a vector cross product;
integrating the vector cross product to obtain a second estimated angle θ
**;
using the new estimated angle θ
** in the step of generating a rotating vector (r);
subtracting the first estimated dc offset current vector (iDC**) from the total measured current vector (iT) to obtain a second estimated positive sequence current vector (iP**);
transforming the second estimated positive sequence current vector (iP**) from a stationary reference frame into a synchronous reference frame by multiplying the second estimated positive sequence current vector (iP**) by exp((j)(−
θ
**)) to obtain a transformed vector;
comparing the transformed vector to zero;
returning the transformed vector to the stationary reference frame by multiplying the transformed vector by exp(jθ
**) to again obtain the second estimated positive sequence current vector (iP**);
subtracting the second estimated positive sequence current vector (iP**) from the total measured current vector (iT) to obtain the first estimated dc offset current vector (iDC*);
comparing the first estimated dc offset current vector (iDC*) to zero;
converting the first estimated dc offset current vector (iDC*) to a dc offset signal correction voltage indicative of the dc offset;
outputting the dc offset signal correction voltage; and
removing the dc offset from the ac current signal by combining the dc offset signal correction voltage with the ac current signal. - View Dependent Claims (7)
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8. A dc offset compensator receiving as an input a three phase ac current signal comprising a phase current A, a phase current B, and a phase current C, and providing as an output a dc offset signal correction voltage, the compensator comprising:
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a processor configured to sample the ac current signal, to generate a rotating vector (r) from the sample, extract a dc offset from the sample, to generate a dc offset signal correction voltage from the dc offset, and to generate a Park vector representing a total measured current vector (iT) from the sample;
wherein the processor generates a Park vector using the formula;
iT=(⅔
)(Ia+(a)(Ib)+(a2)(Ic));
where a=exp(j2π
/3), Ia equals the amplitude of the phase current A (Ia=I sin(wt)), Ib equals the amplitude of the phase current B (Ib=I sin(wt+π
/3)) and Ic equals the amplitude of the phase current C (Ic=I sin(wt+2π
/3)) and w=frequency and t=time.- View Dependent Claims (9)
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10. A dc offset compensator of receiving a three phase ac current signal as an input and providing a dc offset signal correction voltage as an output, comprising:
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a processor is configured to sample the ac current signal, to generate a rotating vector (r) from the sample, to extract a dc offset from the sample, and to generate a dc offset correction voltage from the dc offset, wherein the processor is configured in a first block to;
generate a rotating vector (r) based on a first estimated angle (θ
*);
generate a Park vector representing the total measured current vector (iT) from the total measured current;
subtract an estimated a dc offset current vector (iDC*) from the total measured current vector (iT) to obtain a first estimated positive-sequence current vector (iP*);
calculate a vector cross product of the first positive-sequence current vector and the rotating vector (r); and
integrate the vector cross product and output a second estimated angle (θ
**);
the processor is configured in a second block to receive the total measured current vector (iT) and the estimated angle (θ
**) and to;
subtract the first estimated positive sequence current (iP*) from the total measured current (iT) to obtain an error signal;
multiply the error signal by the complex conjugate of the rotator vector (r);
compare the error signal to zero;
filter the error signal to remove high frequency components so that the remaining signal is a dc voltage;
operate on the dc voltage signal with a regulator;
multiply the output of the regulator by the rotating vector (r), thereby providing a new estimated positive sequence current (iP*);
subtract the new estimated positive sequence current (iP*) from the total measured current vector (iT) to develop the first estimated dc offset current vector iDC* content of the ac current signal;
convert the first estimated dc offset current vector (iDC*) to a dc offset signal correction voltage indicative of the dc offset; and
output the dc offset signal correction voltage.
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11. A dc offset compensator receiving a three phase signal from a source and providing a correction signal to an inverter, comprising:
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an input for receiving a total measured current from the source;
a processor connected to the input and configured in a first block to;
generate a rotating vector (r) based on a first estimated angle (θ
*);
generate a Park vector representing the total measured current vector (iT) from the total measured current;
subtract an estimated a dc offset current vector (iDC*) from the total measured current vector (iT) to obtain a first estimated positive-sequence current vector (iP*);
calculate a vector cross product of the first positive-sequence current vector and the rotating vector (r); and
integrate the vector cross product and output a second estimated angle (θ
**);
the processor configured in a second block to receive the total measured current vector (iT) and the estimated angle (θ
**) and to;
subtract the first estimated positive sequence current (iP*) from the total measured current (iT) to obtain an error signal;
multiply the error signal by the complex conjugate of the rotator vector (r);
compare the error signal to zero;
filter the error signal to remove high frequency components so that the remaining signal is a dc voltage;
operate on the dc voltage signal with a regulator;
multiply the output of the regulator by the rotating vector (r), thereby providing a new estimated positive sequence current (iP*);
subtract the new estimated positive sequence current (iP*) from the total measured current vector (iT) to develop the first estimated dc offset current vector iDC* content of the ac current signal;
convert the first estimated dc offset current vector (iDC*) to a dc offset signal correction voltage indicative of the dc offset; and
output the dc offset signal correction voltage the processor configured in a third block to receive the total measured current vector (iT) and the estimated angle (θ
**) and to;
compare the first estimated dc offset current vector (iDC*) to zero; and
convert the first estimated dc offset current vector (iDC*) to a voltage correction signal for input to the inverter. - View Dependent Claims (12, 13, 14, 15, 16)
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Specification