Apparatus for Measuring Distortion Power Quality Index and Method of Operating the Apparatus

• US 20100131243A1
• Filed: 11/08/2007
• Published: 05/27/2010
• Est. Priority Date: 08/24/2007
• Status: Active Grant

• Current Assignee: Industry Academic Cooperation Foundation
• Original Assignee: Industry Academic Cooperation Foundation
• Inventors: Lee, Soon, Park, Jung-Wook
• Granted Patent: US 8,185,358 B2
• Time in Patent Office: Days
• US Class Current: 702/198
• CPC Class Codes: G01R 19/2513 Arrangements for monitoring electric power systems, e.g. power lines or loads; Logging

Abstract

A method of measuring a power quality index, including: measuring a total current waveform of an ingress from a customer, and a current waveform and a voltage waveform of each of at least one load installed at the customer; computing a load composition (LC) of the customer using the total current waveform of the ingress and the current waveform of each of the at least one load; computing a total harmonic distortion (THD) of each of the at least one load using the current waveform and the voltage waveform of each of the at least one load; and computing a distortion power quality index (DPQI) of each of the at least one load using the LC and the THD.

Claims

1. A method of measuring a power quality index, comprising:

measuring a total current waveform of an ingress from a customer, and a current waveform and a voltage waveform of each of at least one load installed at the customer;

computing a load composition (LC) of the customer using the total current waveform of the ingress and the current waveform of each of the at least one load;

computing a total harmonic distortion (THD) of each of the at least one load using the current waveform and the voltage waveform of each of the at least one load; and

computing a distortion power quality index (DPQI) of each of the at least one load using the LC and the THD.

2. The method of claim 1, wherein the customer includes a point of common coupling (PCC) and at least one nonlinear load.

3. The method of claim 1, wherein the computing of the LC comprises:

computing a modeling function with respect to a configuration of each of the at least one load using the total current waveform of the ingress and the current waveform of each of the at least one load; and

computing a load coefficient with respect to each of the at least one load through an optimization method from the modeling function.

4. The method of claim 3, wherein the modeling function is represented as,

$[$

∑

n = 0 N - 1 

i 1 

( n ) ·

i 1 

( n ) ∑

n = 0 N - 1 

i 2 

( n ) ·

i 1 

( n ) …

∑

n = 0 N - 1 

i n - 1 

( n ) ·

i 1 

( n ) ∑

n = 0 N - 1 

i n 

( n ) ·

i 1 

( n ) ∑

n = 0 N - 1 

i 1 

( n ) ·

i 2 

( n ) ∑

n = 0 N - 1 

i 2 

( n ) ·

i 2 

( n ) …

∑

n = 0 N - 1 

i n - 1 

( n ) ·

i 2 

( n ) ∑

n = 0 N - 1 

i n 

( n ) ·

i 2 

( n ) ⋮

⋮

…

⋮

⋮

∑

n = 0 N - 1 

i 1 

( n ) ·

i n - 1 

( n ) ∑

n = 0 N - 1 

i 2 

( n ) ·

i n - 1 

( n ) …

∑

n = 0 N - 1 

i n - 1 

( n ) ·

i n - 1 

( n ) ∑

n = 0 N - 1 

i n 

( n ) ·

i n - 1 

( n ) ∑

n = 0 N - 1 

i 1 

( n ) ·

i n 

( n ) ∑

n = 0 N - 1 

i 2 

( n ) ·

i n 

( n ) …

∑

n = 0 N - 1 

i n - 1 

( n ) ·

i n 

( n ) ∑

n = 0 N - 1 

i n 

( n ) ·

i n 

( n ) ] [ 

k 1 k 2 

⋮

k n - 1 k n ] 

= [ ∑

n = 0 N - 1 





( n ) ·

i 1 

( n ) ∑

n = 0 N - 1 





( n ) ·

i 2 

( n ) ⋮

∑

n = 0 N - 1 





( n ) ·

i n - 1 

( n ) ∑

n = 0 N - 1 





( n ) ·

i n 

( n ) ] ,

and the load coefficient is k₁ through k_n.

5. The method of claim 3, further comprising:

optimizing the LC through the optimization method, and

wherein the optimization method is any one of a conjugate gradient method and a Broyden Fletcher Goldfarb Shanno (BFGS) method.

6. The method of claim 1, wherein the computing of the THD comprises:

performing a discrete fast Fourier transform (DFFT) of the current waveform and the voltage waveform of each of the at least one load;

computing a current THD with respect to a current flowing in each of the at least one load using the discrete fast Fourier transformed current waveform; and

computing a voltage THD with respect to a voltage applied to each of the at least one load using the discrete fast Fourier transformed voltage waveform.

7. The method of claim 6, wherein the current THD and the voltage THD are computed by,

$\mathrm{THD}$

( i n ) = ( ∑

n = 0 ∞



i h 2 / i 1 ) ×

100.

8. The method of claim 6, wherein the computing of the DPQI comprises:

computing an absolute value of a difference between the current THD and the voltage THD with respect to each of the at least one load; and

multiplying the absolute value by the LC with respect to each of the at least one load.

9. The method of claim 1, further comprising:

comparing a distortion power generation amount with respect to each of the at least one load of the customer through the DPQI of each of the at least one load.

10. The method of claim 1, further comprising:

standardizing by dividing the DPQI of each of the at least one load by a sum of DPQIs of the at least one load; and

comparing a distortion power generation amount with respect to each of the at least one load of the customer through the standardized DPQI of each of the at least one load.

11. A computer-readable recording medium storing a program for implementing the method according to any one of claims 1 through 10.

12. An apparatus for measuring a power quality index, comprising:

a current waveform measurement unit measuring a total current waveform of an ingress from a customer, and a current waveform of each of at least one load installed in the customer;

a voltage waveform measurement unit measuring a voltage waveform of each of the at least one load;

an L C computation unit computing an LC of the customer using the total current waveform of the ingress and the current waveform of each of the at least one load;

a THD computation unit computing a THD of each of the at least one load using the current waveform and the voltage waveform of each of the at least one load; and

a DPQI computation unit computing a DPQI of each of the at least one load using the LC and the THD.

13. The apparatus of claim 12, wherein the customer includes a PCC and at least one nonlinear load.

14. The apparatus of claim 12, wherein the LC computation unit computes a modeling function with respect to a configuration of each of the at least one load using the total current waveform of the ingress and the current waveform of each of the at least one load, and computes a load coefficient with respect to each of the at least one load through an optimization method from the modeling function to compute the LC.

15. The apparatus of claim 14, wherein the modeling function is represented as,

$[$

∑

n = 0 N - 1 

i 1 

( n ) ·

i 1 

( n ) ∑

n = 0 N - 1 

i 2 

( n ) ·

i 1 

( n ) …

∑

n = 0 N - 1 

i n - 1 

( n ) ·

i 1 

( n ) ∑

n = 0 N - 1 

i n 

( n ) ·

i 1 

( n ) ∑

n = 0 N - 1 

i 1 

( n ) ·

i 2 

( n ) ∑

n = 0 N - 1 

i 2 

( n ) ·

i 2 

( n ) …

∑

n = 0 N - 1 

i n - 1 

( n ) ·

i 2 

( n ) ∑

n = 0 N - 1 

i n 

( n ) ·

i 2 

( n ) ⋮

⋮

…

⋮

⋮

∑

n = 0 N - 1 

i 1 

( n ) ·

i n - 1 

( n ) ∑

n = 0 N - 1 

i 2 

( n ) ·

i n - 1 

( n ) …

∑

n = 0 N - 1 

i n - 1 

( n ) ·

i n - 1 

( n ) ∑

n = 0 N - 1 

i n 

( n ) ·

i n - 1 

( n ) ∑

n = 0 N - 1 

i 1 

( n ) ·

i n 

( n ) ∑

n = 0 N - 1 

i 2 

( n ) ·

i n 

( n ) …

∑

n = 0 N - 1 

i n - 1 

( n ) ·

i n 

( n ) ∑

n = 0 N - 1 

i n 

( n ) ·

i n 

( n ) ] [ 

k 1 k 2 

⋮

k n - 1 k n ] 

= [ ∑

n = 0 N - 1 





( n ) ·

i 1 

( n ) ∑

n = 0 N - 1 





( n ) ·

i 2 

( n ) ⋮

∑

n = 0 N - 1 





( n ) ·

i n - 1 

( n ) ∑

n = 0 N - 1 





( n ) ·

i n 

( n ) ] ,

and the load coefficient is k₁ through k₄.

16. The apparatus of claim 14, wherein the LC computation unit optimizes the LC through the optimization method, and the optimization method is any one of a conjugate gradient method and a BFGS method.

17. The apparatus of claim 12, wherein the THD computation unit performs a DFFT of the current waveform and the voltage waveform of each of the at least one load, computes a current THD with respect to a current flowing in each of the at least one load using the discrete fast Fourier transformed current waveform, and computes a voltage THD with respect to a voltage applied to each of the at least one load using the discrete fast Fourier transformed voltage waveform.

18. The apparatus of claim 17, wherein the THD computation unit computes the current THD and the voltage THD using

$\mathrm{THD}$

( i n ) = ( ∑

n = 0 ∞



i h 2 / i 1 ) ×

100.

19. The apparatus of claim 17, wherein the DPQI computation unit computes the DPQI through DPQI_P=LC_P*|THD_I,p−

THD_V,pcc|, where LC is the LC of the customer, p is a type of a customer load, THD_I,p is a current THD in each of the at least one load, and THD_V,pcc is a voltage THD in a PCC.

20. The apparatus of claim 12, wherein the DPQI computation unit compares a distortion power generation amount with respect to each of the at least one load of the customer through the DPQI of each of the at least one load.

21. The apparatus of claim 12, wherein the DPQI computation unit standardizes by dividing the DPQI of each of the at least one load by a sum of DPQIs of the at least one load, and compares a distortion power generation amount with respect to each of the at least one load of the customer through the standardized DPQI of each of the at least one load.

22. A wattmeter, comprising:

a current waveform measurement unit measuring a total current waveform of an ingress from a customer, and a current waveform of each of at least one load installed in the customer;

a voltage waveform measurement unit measuring a voltage waveform of each of the at least one load;

an LC computation unit computing an LC of the customer using the total current waveform of the ingress and the current waveform of each of the at least one load;

a THD computation unit computing a THD of each of the at least one load using the current waveform and the voltage waveform of each of the at least one load; and

a DPQI computation unit computing a DPQI of each of the at least one load using the LC and the THD.