Abstract:
A device and method for more accurately measuring power consumption in a residential application without having to make connections to high voltage sources in a distribution panel. Since the device calculating the power consumption generally needs to be powered to perform its functions (e.g., plugged into wall outlet), the disclosure utilizes the power supply as a voltage source for measuring voltage without having to make connections to the panel.

Description:
BACKGROUND OF THE DISCLOSURE 
     The present disclosure relates to power consumption measurement and, more particularly, to power consumption measurement for residential application. 
     Multi-phase power consumption measurement has been done in industry and by utilities for many years. Typically 2-phase power consumption has been measured at the electricity meters on the sides of homes, and 3-phase power consumption in industry use measured by electricity meters or other devices installed at the industrial location. 
     The equation used to describe the measurement of power consumption is: 
             Energy   ≡     ∫       ∑   i             ⁢         V   i     ·     I   i       ⁢     ⅆ   t                 
where V and I are the voltage and current in each phase expressed as a vector.
 
     There are many electrical circuits and electromechanical devices to make these measurements. Such devices generally take a voltage and a current input. Most recently, such devices typically take a voltage and current measurement for each phase and capture them many times a second and then multiply the instantaneous voltage by the instantaneous current. These values are then stored in a register and normalized to watt-seconds by dividing by the number of samples per second. Examples of existing devices that measure power consumption include the Teridian 78M6612-IGTR/F manufactured by Teridian Semiconductor Corp., or ST Microelectonics STPM Family. 
     In a residential application, however, such prior art approaches are problematic because they generally require two voltage references and two current measurements. Measuring current in a residential application is relatively straightforward and without significant risk. Conventionally, two clamp-on current transformers (CTs) are placed inside a residential power distribution panel and the low voltage leads brought out of the panel and connected to the power measurement device. This generally does not require making any electrical contacts in the box, and makes the installation of the CTs within the range of most handy-men. 
     To get two voltage references, however, two connections need to be made in the panel and high voltage leads brought out of the panel, requiring more care to comply with code and safety regulations. Thus, rather than measure voltage, many prior art devices simply assume a voltage (such as 120 volts for a residential application). This results in less accurate measurements since in many instances the actual voltage will not equal the assumed value. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure provides a device and method for more accurately measuring power consumption in a residential application without having to make connections to high voltage sources in a distribution panel. Since the device calculating the power consumption generally needs to be powered to perform its functions (e.g., plugged into a wall outlet), the disclosure utilizes the voltage at the outlet for measuring voltage without having to make connections to the panel. In accordance with one aspect, a device for measuring power consumption of a household having a conventional 120/240 volt AC power source provided by an electric utility company comprising power lines L 1 , L 2  and N and one or more power outlets coupled to the source for supplying power to energy consuming appliances, is connectable to a power outlet and comprises a metering microcontroller unit having a voltage input for measuring the voltage at the outlet and first and second current inputs for measuring current flowing into the household via lines L 1  and L 2 . The metering microcontroller is configured to calculate power consumption based on the voltage received from the outlet and the two separate current values provided thereto. 
     The current values can be provided to the metering microcontroller unit via first and second current transformers connected to respective lines supplying power to the household. A communication interface can be provided for communicating data relating to power consumption. The communication interface can include a wireless communication interface for communication power consumption information to a remote device. A display for displaying power consumption information to a user can be provided. The device can further comprise a first current transformer connectable to a first line supplying power to the household and a second current transformer connectable to a second line supplying power to the household, the first and second current transformers connected to respective inputs of the metering microcontroller unit. The power supply can include a conventional plug adapted for receipt in a 110 volt outlet. 
     In accordance with another aspect, a system for measuring power consumption of a household comprises a main power distribution panel for receiving first and second power lines and distributing power to at least one household load, an outlet connected to the main power distribution panel for receiving power therefrom, a device for measuring power consumption of a household as set above, a power supply of the device being connected to the outlet, and first and second current transformers each associated with a respective power line for providing a current value to the respective first and second inputs of the device for measuring power consumption. 
     In accordance with another aspect, a device for measuring power consumption of a household comprises a power supply connectable to a household outlet for receiving power therefrom, and a microprocessor connected to the power supply and configured to i) receive a first current value corresponding to a current in a first line supplying power to the household, ii) receive a second current value corresponding to a current in a second line supplying power to the household; iii) detect a voltage value of the power received by the power supply, and iv) calculate power consumption by integrating with respect to time the sum of the voltage value multiplied by the first current value and the negative of the voltage value multiplied by the second current input. The device can further include user interface for enabling a user to input and output data. 
     In accordance with another aspect, a method of measuring power consumption of a two-phase power distribution system having a distribution panel, the method comprises measuring a first current value associated with a first power line supplying power to the distribution panel, measuring a second current value associated with a second power line supplying power to the distribution panel, measuring a voltage value of either the first or second power line via an outlet connected to said first or second line via the distribution panel, and calculating power consumption based on the first current, the second current and the single voltage value. The calculating can include taking an integral with respect to time of the sum of the products of the voltage value and the first current value and the product of the negative of the voltage value and the second current value. The method can further include communicating information related to power consumption to a remote device via a communication interface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an exemplary device and system for measuring power consumption in accordance with the present disclosure. 
         FIG. 2  is an exemplary device for measuring power consumption in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning to the drawing, an exemplary system  10  in accordance with the present disclosure is illustrated. The system  10  includes a main power distribution panel  14  for receiving power from first and second power lines L 1  and L 2  and neutral line N coming from a utility company via meter  16  in conventional domestic arrangement. The distribution panel  14  distributes the power to one or more 120 volt household loads  18 , via L 1  and N or L 2  and N including an outlet  20  served by L 1  and N. Household loads requiring 240 volt supply receive power via L 1  and L 2 . A power consumption measurement device  22  (also referred to herein as a metering device) is connected to the outlet  20 . A pair of current transformers  26   a  and  26   b  are each associated with a respective power line L 1  and L 2  for providing a current measurement in the form of a voltage signal proportional to the current flowing in L 1  and L 2  respectively to respective first and second current inputs I 1  and I 2  of the power consumption measurement device  22 . 
     The exemplary power consumption measurement device  22  includes a power supply connected to the outlet  20  for receiving power therefrom. Device  22  includes a metering microcontroller unit  34  programmed to calculate whole home power consumption. Microcontroller unit  34  has a pair of voltage inputs V 1  and V 2  for receiving a voltage value for V 1  measured across L 1  and N which is the signal supplied to outlet  20  and a second voltage value V 2  which would conventionally be measured across L 2  and N. However, in the device  22 , advantageous use is made of the relationship of V 1  measured across L 1  and N, and V 2  measured across L 2  and N, namely V 1  equals −V 2 . So, rather than requiring a connection to L 2 , the voltage V 1  from outlet  20  is applied to both voltage inputs V 1  and V 2  and the microcontroller is programmed to change the sign of the signal received at V 2 . A system controller  38  is connected to the metering microcontroller unit  34 . A user interface  44 , which can include a display  48  and/or a user input device  52 , is provided for interfacing with a user of the device. 
     The metering microcontroller unit  34  is configured to calculate power consumption based on the voltage of the power signal received at outlet  20 , and two separate current values provided thereto from the current transformers  26   a  and  26   b . This obviates the need to bring high voltage leads out of the distribution panel and, thus, makes installation of the device  22  safer and within the skills of most handy-men. 
     To calculate power consumption in a two-phase power system (such as a residential power system, the equation noted in the background above simplifies to:
 
Energy≡∫V 1 ·I 1 +V 2 ·I 2 dt
 
     Since most residential home power installations in the US are 120V/240V, the V 2  is the above equation equals −V 1 . This means that the integral above can be further simplified to:
 
Energy≡∫V 1 ·I 1 −V 1 ·I 2 dt
 
     Thus, it will be appreciated that the single voltage source (e.g., the outlet  20 ) can be used by the power consumption measurement device  22  to calculate the whole power consumption. 
     Once the power consumption is calculated, data relating to the power consumption can be communicated to a user via the user interface  44 . For example, the power consumption information, such as kilowatt hours consumed, can be displayed on the display  48 . The user interface  44  could also be configured to display a colored indicator based on instantaneous power consumption. For example, a green indicator could be displayed when power consumption is below a certain threshold value, while a red indicator could be displayed when power consumption is above a certain threshold value. 
     The power consumption device  22  can further include a communication interface  56  for communicating with other devices. For example, the power consumption measurement device could be connected to the internet for transmitting and/or receiving data relating to power consumption to a remote device or service, such as a server at a power company. The power consumption measurement device could also be adapted to communicate with a home energy management device of a home energy management (HEM) system. An exemplary HEM system is described in commonly-assigned U.S. patent application Ser. No. 12/559,636 filed on Sep. 15, 2009, which is hereby incorporated by reference herein in its entirety. 
     Turning now to  FIG. 2 , an exemplary physical embodiment of the metering device is illustrated in the form of a wall mountable unit  80  including a standard two prong plug  82  adapted to be received in a conventional outlet. The wall mountable unit  80  takes the shape of a “wall wart” that is can be plugged into a wall outlet which supports the unit  80  as well as provides power thereto. Of course, the metering device can come in a wide variety of form factors, and the wall wart embodiment in merely exemplary. 
     The unit  80  includes a housing  84  in which the components of  FIG. 1  such as the power supply  30 , metering microcontroller unit  34 , system controller  38 , communication interface, etc., may be housed. First and second current input ports I 1  and I 2  are provided for connection to current transformers or the like for receiving a current reading. Although not shown in  FIG. 2 , the unit  80  can include a user interface having one or more LEDs, a display, buttons etc. for enabling a user to interface with the unit  80 . Alternatively, the user interface may be remote from the unit  80  and utilize a communication interface integral with the unit  80  for connecting the unit  80  to the remote interface. For example, a home computer or cell phone or other device having a user interface could be adapted to communicate with the unit  80  for operation thereof. 
     It will now be appreciated that the present disclosure provides a power consumption measurement device that can be easily installed, and receives a voltage measurement from a standard outlet resulting in a more accurate measurement. By placing the outlet near the distribution panel, the device can be installed easily by most handy-men. 
     The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations.