Patent Publication Number: US-2015084616-A1

Title: System and method of measuring power produced by a power source

Description:
CLAIM OF PRIORITY 
     This application claims the benefit of priority of U.S. patent application Ser. No. 13/451,008, entitled “SYSTEM AND METHOD OF MEASURING POWER PRODUCED BY A POWER SOURCE,” filed on Apr. 19, 2012, the benefit of priority of which is claimed hereby, and which is incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     Embodiments pertain to a system and method of measuring power produced by a power source, and more particularly to a system and method of measuring power produced by a power source using measured currents and voltages. 
     BACKGROUND 
       FIG. 1  illustrates an example 2-element prior art power measurement system  100 . The power measurement system  100  includes a first voltage measuring element  101 A and a second voltage measuring element  101 B. First voltage measuring element  101 A measures the voltage difference between phase A voltage Va and phase B voltage Vb. Second voltage measuring element  101 B measures the voltage difference between phase C voltage Vc and phase B voltage Vb. 
     The power measurement system  100  includes a first current measuring element  102 A and a second current measuring element  102 B. First current measuring element  102 A measures the phase A current Ia. Second current measuring element  102 B measures the phase C current Ic. 
     One of the drawbacks with using 2-element prior art power measurement system is that the power measurement system  100  is unable to accurately measure power on an unbalanced load L (i.e., when the phase A current Ia is not equal to the phase B current Ib or is not equal to the phase C current Ic). 
       FIG. 2  illustrates an example 3-element prior art power measurement system  200 . The power measurement system  200  includes a first voltage measuring element  201 A, a second voltage measuring element  201 B and a third voltage measuring element  201 C. First voltage measuring element  201 A measures the phase A voltage Va. Second voltage measuring element  201 B measures the phase B voltage Vb. Third voltage measuring element  201 C measures the phase C voltage Vc. 
     The power measurement system  200  includes a first current measuring element  202 A, a second current measuring element  202 B and a third current measuring element  202 C. First current measuring element  202 A measures the phase A current Ia. Second current measuring element  202 B measures the phase B current Ib. Third current measuring element  202 C measures the phase C current Ic. 
     One of the drawbacks with using 3-element prior art power measurement system  200  is that the power measurement system  200  requires three voltage transformers and three current transformers. The power measurement system  200  also requires three voltage measuring channels and three current measuring channels. Therefore, there is added cost associated with utilizing the power measurement system  200 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example 2-element prior art power measurement system. 
         FIG. 2  illustrates an example 3-element prior art power measurement system. 
         FIG. 3  illustrates an example single-phase power measurement system. 
         FIG. 4  illustrates an example three-phase power measurement system. 
     
    
    
     DETAILED DESCRIPTION 
     The following description and the drawings sufficiently illustrate specific embodiments to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Portions and features of some embodiments may be included in, or substituted for, those of other embodiments. Embodiments set forth in the claims encompass all available equivalents of those claims. 
       FIG. 3  illustrates an example system  300  for measuring power produced by a power source  310  (e.g., a single-phase power source). The system  300  includes a voltage sensor  301  for sensing a voltage difference between a first voltage V1 and a second voltage V2. The system  300  further includes a current sensor  302  for sensing a current difference between a first current I1 and a second current I2. A power measuring device  303  determines the power produced by the power source  300  using the voltage difference sensed by the voltage sensor  301  and the current difference sensed by the current sensor  302 . 
     In some embodiments, the voltage sensor  301  measures the first voltage V1 and measures the second voltage V2 and the voltage sensor  301  subtracts the second voltage V2 from the first voltage V1 to determine the voltage difference. In other embodiments, the voltage sensor  301  directly measures the voltage difference between the first voltage V1 and the second voltage V2. 
     In some embodiments, the current sensor  302  measures the first current I1 and measures the second current I2 and the current sensor  302  subtracts the second current I2 from the first current I1 to determine the current difference. In other embodiments, the current sensor  302  directly measures the current difference between the first current I1 and the second current I2 (see, e.g.,  FIG. 3 ). 
     In the example embodiment that is illustrated in  FIG. 3 , a first conductor  304  carries the first current I1 and a second conductor  305  carries the second current I2. In addition, the illustrated current sensor  302  is a current transformer such that the first conductor  304  extends through the current transformer  302  and carries the first current I1 in one direction D1, and the second conductor  305  extends through the current transformer  302  and carries the second current I2 in an opposite direction D2. The size and shape of the first and second conductors  304 ,  305  and the current transformer  302  will depend in part on the amount of power that will be sensed using the system  300 . 
       FIG. 4  illustrates an example system  400  for measuring power produced by a power source  410  (e.g., a three-phase power source). The system  400  includes a first voltage sensor  401 A for sensing a first voltage difference between a first voltage Va and a second voltage Vb and a second voltage sensor  401 B for sensing a second voltage difference between a third voltage Vc and the second voltage Vb. 
     The system  400  further includes a first current sensor  402 A for sensing a current difference between a first current Ia and a second current Ib, and a second current sensor  402 B for sensing a current difference between a third current Ic and the second current Ib. The system  400  further includes a power measuring device  403  that determines the power supplied by the power source  410  using the first and second voltage differences and the first and second current differences. 
     In the example embodiment that is illustrated in  FIG. 4 , system  400  further includes (i) a first conductor  404  that carries the first current Ia; (ii) a second conductor  405  that carries the second current Ib; and (iii) a third conductor  406  that carries the third current Ic. As an example, the illustrated first current sensor  402 A may be a first current transformer such that the first conductor  404  extends through the first current transformer  402 A and carries the first current in one direction D1, and the second conductor  405  extends through the first current transformer  402 A and carries the second current in an opposite direction D2. In addition, the second current sensor  402 B may be a second current transformer such that the second conductor  405  extends through the second current transformer  402 B and carries the second current Ib in one direction D3 and the third conductor  406  extends through the second current transformer  402 B and carries the third current Ic in an opposite direction D4. 
     It should be noted that other embodiments are contemplated where the power measuring device  403  (i) calculates a third voltage difference using the first and second voltage differences; and (ii) calculates a third current difference using the first and second current differences. The power measuring device  403  then determines the power produced by the power source  410  using the first, second and third voltage differences and the first, second and third current differences. 
     A method of measuring power produced by a power source  310  will now be described with reference to  FIG. 3 . The method includes measuring a voltage difference between a first voltage V1 and a second voltage V2 and measuring a current difference between a first current I1 and a second current I2. The method further includes calculating power produced by a power source  310  using the voltage difference and the current difference. 
     In some embodiments, measuring a voltage difference between the first voltage V1 and the second voltage V2 includes (i) measuring a first voltage V1; (ii) measuring second voltage V2; and (iii) calculating the voltage difference by subtracting the second voltage V2 from the first voltage V1. In other embodiments, measuring a voltage difference between the first voltage V1 and the second voltage V2 includes directly measuring the voltage difference. 
     In some embodiments, measuring a current difference between the first current I1 and the second current I2 includes (i) measuring a first current I1; (ii) measuring a second current I2; and (iii) calculating the current difference by subtracting the second current I2 from the first current I1. In other embodiments, measuring a current difference between the first current I1 and the second current I2 includes directly measuring the current difference. Embodiments are contemplated where calculating power produced by a power source  410  includes using the voltage difference and the current difference to obtain of an average of the product of the voltage difference and current difference over a period of time. 
     A method of measuring power produced by a power source  410  will now be described with reference to  FIG. 4 . The method includes measuring a first voltage difference between a first voltage Va and a second voltage Vb, and measuring a second voltage difference between a third voltage Vc and the second voltage Vb. The method further includes determining a third voltage difference by using the second voltage difference and the first voltage difference. 
     In an example embodiment, the third voltage difference may be calculated by subtracting the second voltage difference from the first voltage difference (i.e., (Va−Vb)−(Vc−Vb)=(Va−Vc)). 
     The method further includes measuring a first current difference between a first current Ia and a second current Ib, and measuring a second current difference between a third current Ic and the second current Ib. The method further includes determining a third current difference by using the second current difference and the first current difference. 
     In an example embodiment, the third current difference may be calculated by subtracting the second current difference from the first current difference (i.e., (Ia−Ib)−(Ic−Ib)=(Ia−Ic)). 
     The method also includes calculating power produced by the three-phase power source  410  using the first, second and third voltage differences and the first, second and third current differences. In some embodiments, determining a third voltage difference by using the second voltage difference and the first voltage difference includes subtracting the second voltage difference from the first voltage difference; and/or determining a third current difference by using the second current difference and the first current difference includes subtracting the second current difference from the first current difference. 
     The systems and methods described herein may be able to accurately measure power on an unbalanced load L (i.e., when the phase A current is not equal to the phase B current or is not equal to the phase C current). In addition, the systems and methods described herein may be able to accurately measure power using only two current transformers and two voltage transformers. 
     The Abstract is provided to comply with 37 C.F.R. Section 1.72(b) requiring an abstract that will allow the reader to ascertain the nature and gist of the technical disclosure. It is submitted with the understanding that it will not be used to limit or interpret the scope or meaning of the claims. The following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate embodiment.