Abstract:
The invention relates generally to downhole measurement tools having a regulated voltage power supply and methods of use thereof. The downhole measurement tools are associated with electrical submersible pumps for providing a stabilization technique for a five (5) volt power supply over a wide temperature range. A voltage regulator circuit for the downhole measurement tools has a temperature dependent resistance to adjust the feedback of the regulated voltage to compensate for the temperature coefficient effects of the other components in the regulator circuit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Not Applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not Applicable. 
     REFERENCE TO A SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING APPENDIX 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to downhole measurement tools having a regulated voltage power supply and method of use thereof, and more particular relates to downhole measurement tools associated with electrical submersible pumps (ESPs) for providing a stabilization technique for a five (5) volt power supply over a wide temperature range. 
     2. Description of the Related Art 
     Various types of downhole equipment, such as pumps and similar devices, are used to move fluids from beneath the surface of the earth to the surface. Well known applications include oil and gas wells and water wells. A typical downhole arrangement would include a string composed of a series of tubes or tubing suspended from the surface. One type of well-known pump is a downhole electrical submersible pump. The electrical submersible pump either includes or is connected to a downhole motor which is sealed so that the whole assembly is submerged in the fluid to be pumped. The downhole motor is connected to a three-phase power source at the surface and operates beneath the level of fluid downhole in order to pump the fluid to the surface. 
     In the common design of many downhole measurement tools associated with an electrical submersible pump, they are connected to the Y-point of the downhole motor of the electrical submersible pump and to the electrical ground of the downhole system. The three-phase power supply for the electrical submersible pump is isolated from the electrical ground, and the downhole measurement tool utilizes this feature to communicate to an associated surface equipment of a downhole system by low frequency modulation of a current or voltage supplied by the associated surface equipment. The downhole measurement tool is coupled to the electrical submersible pump and used to monitor certain downhole parameters, such as pressure and temperature, of a subterranean bore-hole. 
     With the various protective mechanisms in place, and the several thousand feet of cable involved, the DC voltage supplied to the downhole measurement tool may vary from about nine (9) to about one-hundred (100) volts as information is sent back to the surface equipment from the downhole measurement tool. As the downhole measurement tool is subjected to higher temperature environments, the increased temperature exceeds the operational capabilities of the internal circuitry of most currently available five (5) volt regulator devices. While some specially-graded or designed five (5) volt regulators are available for such high temperature environments, these regulators are extremely expensive compared to low temperature five (5) voltage regulators. 
     Since the DC current requirements for the circuitry in the downhole measurement tool is relatively low between about eight (8) and twelve (12) milliamps, and can be allowed to vary by about 5%, discrete devices, i.e. transistors, Zener diodes, and resistors, can be used to provide a five (5) volt supply at the required temperature; however, the temperature coefficient of the forward-biased PN junction voltages involved prohibits good voltage regulation over the temperature range from about 25° C. to about 175° C. 
     It is therefore desirable to provide downhole measurement tools having an improved regulated voltage power supply and method of use thereof. 
     It is further desirable to provide downhole measurement tools associated with ESPs that provide a stabilization technique for a five (5) volt power supply over a wide range of operating temperatures. 
     It is still further desirable to provide a five (5) volt regulator circuit for downhole measurement tools, which is low cost and provides better voltage regulation than is achieved with the standard discrete-device voltage regulator circuits. 
     It is yet further desirable to provide a voltage regulator circuit for downhole measurement tools having a temperature dependent resistance to adjust the feedback of the regulated voltage to compensate for the temperature coefficient effects of the other components in the regulator circuit. 
     Other advantages and features of the invention will be apparent from the following description and from the claims. 
     BRIEF SUMMARY OF THE INVENTION 
     In general, in a first aspect, the invention relates to a regulated voltage power supply circuit capable of stabilizing low frequency modulation of a current or voltage supplied to a downhole measurement tool over a wide range of temperatures. The circuit includes an input/output to receive the supplied voltage and to transmit a regulated voltage. The circuit also includes a voltage feedback path through the circuit, and a temperature dependent device in the feedback path in a manner to regulate the varying voltage to the regulated voltage as an operational temperature of the circuit is increased. 
     In general, in a second aspect, the invention relates to a downhole system capable of regulating an output voltage between an electrical submersible pump and a downhole measurement tool during increased operational temperatures. The downhole system includes an electrical coupling between a Y-point of a downhole motor of the electrical submersible pump and the downhole measurement tool, and also includes a voltage feedback path having at least one temperature dependent device in the feedback path. The temperature dependent device regulates the voltage based on the increased operational temperature of the system. 
     The operational temperature of the circuit and/or the system may range between about 25° C. to about 175° C. The temperature dependent device may be a resistance temperature device that stabilizes the regulated voltage by adjusting a feedback signal through the circuit and/or the system. A plurality of resistors may also be in the feedback path, and the nominal resistance of the resistance temperature device in conjunction with the plurality of resistors provides temperature compensation over a range of the operational temperatures. In particular, the resistance temperature device may be a 1000 ohm surface mount temperature-dependent resistance having a nominal 0.00385 (European curve) coefficient. 
     In general, in a third aspect, the invention relates to a method of regulating a modulating voltage between an electrical submersible pump and a downhole measurement tool during increased operational temperatures. The method includes electrically coupling a Y-point of a downhole motor of the electrical submersible pump to the downhole measurement tool, regulating the modulating voltage using a voltage feedback path during the increased operational temperature, and maintaining a constant signal through the feedback path via a resistance temperature dependent device in the feedback path. 
     In addition, the step of maintaining the constant signal can also include adjusting a feedback ratio with temperature to cause a voltage at an emitter of a first transistor to increase to compensate for voltage changes at a base of a second transistor and across a pair of diodes due to a change in the operational temperatures. Moreover, the method can also include selecting a nominal resistance of the resistance temperature device in conjunction with a plurality of resistors of the feedback path, and providing temperature compensation based on the increased operational temperature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an electrical schematic of an example of the circuitry of the downhole measurement tool in accordance with an illustrative embodiment of the downhole measurement tools having an improved regulated voltage power supply and method of use thereof disclosed herein. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The circuits and methods discussed herein are merely illustrative of specific manners in which to make and use the invention and are not to be interpreted as limiting in scope. In particular, the invention is exemplified for use in a downhole measurement tool, but is not so limited as it can be used for any electrical apparatus that requires a low current five (5) volt regulated supply at temperatures up to about 175° C. 
     Further, while the circuits and methods have been described with a certain degree of particularity, it is to be noted that many modifications may be made in the construction and the arrangement of the structural and function details disclosed herein without departing from the scope of the invention. It is understood that the invention is not limited to the embodiments set forth herein for purposes of exemplification. 
     A regulated voltage power supply circuit and method  10  is provided herein to stabilize over a wide range of temperatures low frequency modulation of a current or voltage supplied to a downhole measurement tool by the associated surface equipment. The circuit and method  10  apply to the downhole measurement tool (not shown) electrically coupled to the Y-point of an electrical submersible pump (not shown). As is common with three-phase powered electrical submersible pumps, a downhole motor that has three field coils with each of the field coils having a common connection at one end, the Y-point, and their other ends are respectively coupled through leads to a source of three-phase power (not shown). The source of three-phase power produces alternating voltage on the three field power leads, which are out of phase with respect to one another by one hundred and twenty degrees. The Y-point of the downhole motor of the electrical submersible pump is electrically coupled to an input capacitor  12  at one end of the circuit  10  for regulating voltage over a wide temperature range, and the other end of the circuit  10  is connected to additional circuitry, as appropriate, of the downhole measurement tool. 
     While the downhole measurement tool is operating, an unregulated DC voltage is input to the regulator circuit  10 , and typically varies from about nine (9) to about thirty-two (32) volts. As schematically illustrated in  FIG. 1 , transistor  14  functions as a series pass element, with transistor  14  base connected to the collector of transistor  16 , where transistor  16  serves to control the current into the base of transistor  14  to regulate the output from the emitter of transistor  14 . Transistor  16  functions as the primary gain element in the feedback path to control the signal to the base of transistor  14 . 
     Diode  18  and diode  20  are current regulating diodes. Diode  18  provides a stable current to diode  22 , which is a Zener diode, and functions as the primary voltage reference in the circuit. Current regulating diode  20  provides a stable current to the base of transistor  14  and collector of transistor  16 . The feedback effect of transistor  16  controls the amount of current that flows into the base of transistor  14 , which provides the overall voltage regulating function. 
     Resistors  24 ,  26 , and  28  form the feedback path from the emitter output of transistor  14  through transistor  16  to control the voltage at the emitter of transistor  14 . Diodes  30  and  32  are used as series elements. The variation of forward voltage drop across diodes  30  and  32  due to temperature change is used to compensate for other voltage variations with temperature in the circuit  10 , and allow the voltage at the emitter of transistor  14  to be sufficiently high to provide a suitable feedback current to the base of transistor  16  through the resistor  24 ,  26 , and  28  feedback path. Resistor  28  is a temperature-dependent resistance, and provides the additional temperature dependent compensation for the circuit  10 . 
     In the exemplary embodiment, the circuit and method  10  include the temperature-dependent resistance for  28 , as shown in  FIG. 1 , to adjust the feedback ratio with temperature to cause the voltage at the emitter of transistor  14  to increase enough to compensate for the difference in voltage change at the base of transistor  16  and that cross diodes  30  and  32 . The temperature-dependent resistance resistor  28  allows the output voltage from the circuit  10  to be more stable over the required temperature range. 
     As illustrated in  FIG. 1 , diodes  18  and  20  may be 1N5297 current regulating diodes, which are nominal 1 milliamp current flow devices that minimize the overall quiescent current of the regulator circuit  10  while still supplying sufficient current through diode  22 . Diode  22  may be a 1N5231C, which is a nominal 5.1 volt 2% tolerance Zener diode that is operated at a low enough current in order to exhibit an actual breakdown of about 4.7 volts at 25° C. Diode  22  and operating point of the circuit and method  10  may be chosen to be near the point of minimum temperature coefficient for Zener diodes. 
     Transistor  14  can be a 2N3440, which is a silicon NPN transistor with a gain of between 40 and 150, and packaged in a metal can suitable for the temperature range of about 25° C. to about 175° C. Transistor  16  can be a 2N2222, which is a silicon NPN transistor with a gain of at least 50, and packaged in a metal can suitable for the operational temperature range. Diodes  30  and  32  may be 1N5627, which are silicon diodes suitable for the operational temperature range. Resistor  28  is a 1000 ohm surface mount temperature-dependent resistance, with a nominal 0.00385 (European curve) coefficient. Capacitor  12  can be a nominal 0.68 microfarad ceramic capacitor suitable for the input voltage and operational temperature range. While the circuit and method  10  of the invention are illustrated and exemplified using the particular components discussed above, a person having ordinary skill in the art will appreciate that other components with similar characteristics may be utilized. 
     Whereas, the circuits and methods have been described in relation to the drawings and claims, it should be understood that other and further modifications, apart from those shown or suggested herein, may be made within the scope of the invention.