Fault tolerant load switch for downhole drilling tools

Abstract

A load switch assembly for providing power from a power source to a load. The assembly includes a switch element configured for connection between the power source and the load and that controls a flow of power from the power source to the load, the switch having an input, an output and a control terminal. The assembly also includes a controller that generates a first control signal based on the power flowing through the switch element; and drive electronics connected between the controller and the control terminal of the switch that draws current from power source to generate a second control voltage at the control terminal so as to control the passage of power through the switch element.

Description

FAULT TOLERANT LOAD SWITCH FOR DOWNHOLE DRILLING TOOLSCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of an earlier filing date from U.S. Provisional Application Serial No. 63 / 632,212 filed April 10, 2024, the entire disclosure of which is incorporated herein by reference.BACKGROUND1. Field of the Invention

[0002] The present invention generally relates to subsurface operations and more particularly to controlling solid state switches in a downhole environment.2. Description of the Related Art

[0003] Boreholes are drilled deep into the earth for many applications such as carbon dioxide sequestration, geothermal production, and hydrocarbon exploration and production. In all of the applications, the boreholes are drilled such that they pass through or allow access to energy or a material (e.g., heat, a gas, or fluid) contained in a formation located below the earth’s surface. Different types of tools and instruments may be disposed in the boreholes to perform various tasks and measurements.

[0004] A load switch assembly is a switch that is used to switch the electrical power supply from a power source to the downhole tools (e.g., load) on or off. Further, isolation of faulty tools or the step-by-step switching on of individual systems for the logical construction of an overall system.

[0005] The assembly usually consists of three main parts, the switch element, drive electronics and an electronic shutdown component (e.g., controller). The switch element itself consists of semiconductor elements such as N-type or P-type MOSFET (metal oxide semiconductor field effect transistor). During the switch-on process, the switch assembly has the task of limiting the inrush current by means of a soft start and of detecting and isolating electrical faults such as short circuits and overloads.SUMMARY

[0006] Disclosed is a load switch assembly for providing power from a power source to a load. The assembly includes: a switch element configured for connection between the power source and the load and that controls a flow of power from the power source to the load, the switch having an input, an output and a control terminal; a controller that generatesa first control signal based on the power flowing through the switch element; and drive electronics connected between the controller and the control terminal of the switch that draws current from power source to generate a second control voltage at the control terminal so as to control the passage of power through the switch element.

[0007] Also disclosed is a method of controlling a load switch assembly for providing power from a power source to a load. The assembly includes a switch element connected between the power source and the load and that controls a flow of power from the power source to the load, the switch having an input, an output and a control terminal. The method includes: generating with drive electronics a switch control voltage; and providing the switch control voltage to the control terminal so as to control the passage of power through the switch element, wherein the switch control voltage is generated by drawing current from the power source through a control transistor in the control electronics.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The foregoing and other features and advantages of the invention are described in conjunction with the accompanying figures:

[0009] FIG. 1 is an example of a system for performing subsurface operations (e.g., downhole, within the earth or below other surface and into a formation) in which the driver circuit disclosed herein can be implemented;

[0010] Although FIG. 1 described herein provides a specific configuration for a drilling system, various other configurations are possible without departing from the scope of the present disclosure. That is, FIG. 1 and the description thereof is provided merely for illustrative and explanatory purposes, and is not intended to be limiting in any way.

[0011] FIG. 2 shows an example load switch assembly according to one embodiment connected between a power source and a load;

[0012] FIG. 3 shows a graph of power though a switch element versus time for different operating conditions according to embodiments disclosed herein; and

[0013] FIG. 4 shows a more detailed version of drive electronics according to one embodiment.DETAILED DESCRIPTION

[0014] As noted above, in the switch element for the load switch is typically a MOSFET. As is known in the art, MOSFETs can operate as voltage controlled current supplies where the gate voltage controls the drain current of the MOSFET. During a so-called “switch-on process,” the drive electronics operate the switch element (or simply “switch” herein) to limit the inrush current by means of a soft start and of detecting and isolating electrical faults such as short circuits and overloads. It has been recognized herein that in the case of overload and short circuit, the switch element is subjected to a high thermal load. The thermal load is generated by the electrical power dissipation generated in the switch element when the switch passes into the linear range of its characteristic curve. The power dissipation of the switch is determined by the current through the switch and the voltage dropped across the switch. If the dynamic thermal characteristics of the switch element and the power dissipation are known, the power dissipation of the switch in the event of an overload can be limited by suitable control for as long as necessary. Previously known methods use a current cutoff. Embodiments herein includes systems and methods for switching a switch element of a load switch in which electrical power dissipation limiting control is used to protect the switch element from destruction, and further includes a current source used to reduce the influence of the input voltage on the drive electronics of a MOSFET switch element. Thus, in embodiment, a technical effect is that electrical power dissipation limitation is used to protect a switch element of a load switch more efficiently as opposed to just limit the current flow through the switch element of the load switch as known in the prior art.

[0015] The systems and methods disclosed herein may protect the switch element of a load switch in a downhole tool from destruction by overload during switch-on by means of a power limiting device.

[0016] In one embodiment, the systems / methods can control a MOSFET (e.g., a P- channel MOSFET) that is used as a switch element of a load switch in a downhole tool with a controlled current source. The controlled current source receives a current or voltage control signal at its control terminal to turn the switch element of the load switch on and off or gradually open and close the switch element of the load switch. The current at the output of the current source flows through a gate-source resistor of a P-channel MOSFET to generate the gate-source control voltage at the switch element.

[0017] With reference now to FIG. 1 a drilling system 10 that includes a drill string 20 having a drilling assembly 90, also referred to as a bottomhole assembly (BHA), conveyed in a borehole or borehole 26 penetrating an earth formation 60 is illustrated. The drilling system 10 includes a conventional derrick 11 erected on a floor 12 that supports a rotary table 14 that is rotated by a prime mover, such as an electric motor (not shown), at a desired rotational speed. The drill string 20 includes a drill pipe 22 or drilling tubular extendingdownward from the rotary table 14 into the borehole 26. A disintegrating device 50, such as a drill bit attached to the end of the drilling assembly 90, disintegrates the geological formations when it is rotated to drill the borehole 26. The drill string 20 is coupled to a drawworks 30 via a kelly joint 21, swivel 28, traveling block 25, and line 29 through a pulley 23. During the drilling operations, the drawworks 30 is operated to control the weight-on-bit (WOB), which affects the rate of penetration. The operation of the drawworks 30 is well known in the art and is thus not described in detail herein.

[0018] During drilling operations a suitable drilling fluid 31 (also referred to as the “mud”) from a source or mud pit 32 is circulated under pressure through the drill string 20 by a mud pump 34. The drilling fluid 31 passes into the drill string 20 via a desurger 36, fluid line 38 and the kelly joint 21. Fluid line 38 may also be referred to as a mud supply line. The drilling fluid 31 is discharged at the borehole bottom 51 through an opening in the disintegrating device 50. The drilling fluid 31 circulates uphole through the annular space 27 between the drill string 20 and the borehole 26 and returns to the mud pit 32 via a return line 35. In some embodiments, an optional sensor SI in the line 38 provides information about the fluid flow rate. In other embodiments, inlet flow rate may be calculated from a pump rate, and an outlet flow rate may be monitored by a sensor in the return line 35. A surface torque sensor S2 and a sensor S3 associated with the drill string 20 respectively provide information about the torque and the rotational speed of the drill string. Additionally, one or more sensors (not shown) associated with line 29 are used to provide the hook load of the drill string 20 and about other desired parameters relating to the drilling of the borehole 26. The system may further include one or more downhole sensors 70 located on the drill string 20 and / or the drilling assembly 90.

[0019] In some applications the disintegrating device 50 is rotated by rotating the drill pipe 22. However, in other applications, a drilling motor 55 (such as a mud motor) disposed in the drilling assembly 90 is used to rotate the disintegrating device 50 and / or to superimpose or supplement the rotation of the drill string 20. In either case, the rate of penetration (ROP) of the disintegrating device 50 into the formation 60 for a given formation and a drilling assembly largely depends upon the weight-on-bit and the rotational speed of the disintegrating device 50. In one aspect of the embodiment of FIG. 1, the drilling motor 55 is coupled to the disintegrating device 50 via a drive shaft (not shown) disposed in a bearing assembly 57. If a mud motor is employed as the drilling motor 55, the mud motor rotates the disintegrating device 50 when the drilling fluid 31 passes through the drilling motor 55 under pressure. The bearing assembly 57 supports the radial and axial forces of the disintegratingdevice 50, the downthrust of the drilling motor and the reactive upward loading from the applied weight-on-bit. Stabilizers 58 coupled to the bearing assembly 57 and at other suitable locations on the drill string 20 act as centralizers, for example for the lowermost portion of the drilling motor assembly and other such suitable locations.

[0020] A surface control unit 40 receives signals from the downhole sensors 70 and devices via a sensor 43 placed in the fluid line 38 as well as from sensors SI, S2, S3, hook load sensors, sensors to determine the height of the traveling block (block height sensors), and any other sensors used in the system and processes such signals according to programmed instructions provided to the surface control unit 40 (i.e., a surface unit). For example, a surface depth tracking system may be used that utilizes the block height measurement to determine a length of the borehole (also referred to as measured depth of the borehole) or the distance along the borehole from a reference point at the surface to a predefined location on the drill string 20, such as the disintegrating device 50 or any other suitable location on the drill string 20 (also referred to as measured depth of that location, e.g. measured depth of the disintegrating device 50). Determination of measured depth at a specific time may be accomplished by adding the measured block height to the sum of the lengths of all equipment that is already within the borehole at the time of the block-height measurement, such as, but not limited to drill pipes 22, drilling assembly 90, and disintegrating device 50.

[0021] The surface control unit 40 displays desired drilling parameters and other information on a display / monitor 42 for use by an operator at the rig site to control the drilling operations. The surface control unit 40 contains a computer that may comprise memory for storing data, computer programs, models and algorithms accessible to a processor in the computer, a recorder, such as tape unit, memory unit, etc. for recording data and other peripherals. The surface control unit 40 also may include simulation models for use by the computer to process data according to programmed instructions. The control unit responds to user commands entered through a suitable device, such as a keyboard. The control unit 40 can output certain information through an output device, such as a display, a printer, an acoustic output, etc., as will be appreciated by those of skill in the art. The control unit 40 is adapted to activate alarms 44 when certain unsafe or undesirable operating conditions occur.

[0022] The drilling assembly 90 may also contain other sensors and devices or tools for providing a variety of measurements relating to the formation 60 surrounding the borehole 26 and for drilling the borehole 26 along a desired path. Such devices may includeand may be referred to as loads herein and may include, for example, a device for measuring formation properties, such as the formation resistivity or the formation gamma ray intensity around the borehole 26, near and / or in front of the disintegrating device 50 and devices for determining the inclination, azimuth and / or position of the drill string. A logging- whiledrilling (LWD) device for measuring formation properties, such as a formation resistivity tool 64 or a gamma ray device 76 for measuring the formation gamma ray intensity, made according an embodiment described herein may be coupled to the drill string 20 including the drilling assembly 90 at any suitable location. For example, coupling can be above a lower kick-off subassembly 62 for estimating or determining the resistivity of the formation 60 around the drill string 20 including the drilling assembly 90. Another location may be near or in front of the disintegrating device 50, or at other suitable locations. A directional survey tool 74 that may comprise means to determine the direction of the drilling assembly 90 with respect to a reference direction (e.g., magnetic north, vertical up or down direction, etc.), such as a magnetometer, gravimeter / accelerometer, gyroscope, etc. may be suitably placed for determining the direction of the drilling assembly, such as the inclination, the azimuth, and / or the toolface of the drilling assembly. Any suitable direction survey tool may be utilized. For example, the directional survey tool 74 may utilize a gravimeter, a magnetometer, or a gyroscopic device to determine the drill string direction (e.g., inclination, azimuth, and / or toolface). Such devices are known in the art and therefore are not described in detail herein.

[0023] In the above-described example configuration, the drilling motor 55 transfers rotational power to the disintegrating device 50 via a shaft (not shown), such as a hollow shaft, that also enables the drilling fluid 31 to pass from the drilling motor 55 to the disintegrating device 50. In alternative embodiments, one or more of the parts described above may appear in a different order, or may be omitted from the equipment described above.

[0024] Still referring to FIG. 1, other LWD devices (generally denoted herein by numeral 77 and included as loads herein), such as devices for measuring rock properties or fluid properties, such as, but not limited to, porosity, permeability, density, salt saturation, viscosity, permittivity, sound speed, etc. may be placed at suitable locations in the drilling assembly 90 for providing information useful for evaluating the subsurface formations 60 or fluids along borehole 26. Such devices may include, but are not limited to, acoustic or seismic tools, nuclear tools, nuclear magnetic resonance tools, permittivity tools, and formation testing and sampling tools.

[0025] Still referring to FIG. 1, a resistivity tool 64 may be provided that includes, for example, a plurality of antennas including, for example, transmitters 66a or 66b or and receivers 68a or 68b. Resistivity can be one formation property that is of interest in making drilling decisions. Those of skill in the art will appreciate that other formation property tools can be employed with or in place of the resistivity tool 64.

[0026] Any or all of the above tools can receive electrical power from the surface or from another location such as a generator or battery in the BHA 90. Within the BHA or at other location, low-power power supplies to drive circuits and the like can be provided that provide, for example, a 5 V supply voltage that can be used to drive logic or other circuits to open or close the switch element of the load switch. A master electronics is included in the BHA that controls power supply to downhole tools or devices over a bus system inside the BHA configured to provide power and communication to and from the downhole tools. Switch elements are used to connect or disconnect downhole tools to the bus system. The master electronics is monitoring power demand of downhole tools and power dissipation on the switch elements and disconnects downhole tools in case of a failure by opening the switch element (circuit breaker) to isolate a faulty downhole tool. Power provided to the downhole tool via the switch element is generated by a generator in the BHA driven by a mud turbine or by a downhole battery. In embodiments the power is provided to the downhole tools through a wire from a power supply at the surface (wired pipe).

[0027] As shown in FIG. 2, includes schematic illustration of a load switch assembly (load switch) 200 according to one embodiment. The load switch assembly 200 can be used to control the flow a power (e.g., current or voltage or a combination thereof) from an input power source 202 (Voltage source (Vin)) to a load 204. The load switch assembly 200 controls the flow of power to the load (power provision to the load) by controlling operation of load switch element 206 (open or close switch element for short in the load 204, or for high power demands of the load 204 during the switch-on process). The electrical power demanded by the load 204 is referred to herein as the electrical power at the load. During the switch-on process of the switch element 206 the power dissipation in the switch element 206 can be high, leading to an overheating of the switch element 206. Described herein is a circuitry and a method that avoids overheating of the switch element by controlling the switch element (allowing more or less power dissipation in the switch element). The controlling of the switch element is based on measured data allowing to determine the power dissipated in the switch element.

[0028] The switch element 206 can be a MOSFET in one embodiment. In particular, switch element 206 can be a P-MOSFET or an N-MOSFET. While a P-MOSFET is shown below, the skilled artisan could replace the P-MOSFET with an N-MOSFET based on skilled in the art and the disclosure herein. In an alternative embodiment any other type of transistors is used as a switch element, such as a bipolar transistor or an IGBT-FET.

[0029] As noted above, the switch element 206 can overheat during start up under certain conditions. As shown in FIG. 2, the load switch includes a controller 208 and drive electronics 210. The controller 208, generally, receives information about operation of the switch element 206 and generates a first control signal CTL1 based thereon. The first control signal CTL1 can be a voltage in one embodiment. The first control signal CTL1 is provided to a control terminal 226 of the drive electronics 210 which, in turn, provides a second control signal CTL2 at the control terminal of the switch element 206 that controls the operation of the switch element. For example, the second control signal CTL2 could be a voltage provided to a control terminal (e.g., a gate connected to control terminal 224) of switch element 206. By controlling CTL2 the switch element 206 can be used to connect the power source 202 to the load 204 and provide power to a downhole tool represented by the load 204. The magnitude of the voltage (CTL2) provided to the control terminal 224 of the switch element will, therefore, control the flow of power through the switch element 206. The flow of power herein refers to the power dissipated in the switch element. The first control voltage is also referred to herein as first control voltage CTL1. The second control voltage is also referred to herein as second control voltage CTL2.

[0030] As shown in FIG. 2, the switch element 206 has an input 220 (e.g. source of the switch element), and a control terminal 224 (e.g. gate of the switch element). In situations where the switch element is a MOSFET, the voltage provided at the control terminal controls the flow of power through the switch element 206 and the power dissipated in the switch element.

[0031] In a typical system, the second control signal (CTL2) provided to control the gate voltage (e.g. gate-source voltage) of the switch element is based on a current limit to be passed through the switch rather than the electrical power limit disclosed herein. Having only a current limitation can lead to restrictions in the operating range to sufficiently protect the switch element in all load ranges. In particular, it is noted that with a pure current limitation, the switch-off threshold must be lowered so that the switch is not overloaded, e.g. in the event of a short circuit. Lowering the current cut-off threshold severely limits the operating range of the switch element during normal operation, such as when capacitive loadswith corresponding transient currents are switched on. In case of a bipolar transistor the basis is connected to the control terminal 224 and the second control signal (CTL2) is a voltage between the basis and the collector or emitter.

[0032] As noted above, herein, control of the switch element 206 is based on a power measurement representative for the power dissipation in the switch element 206. Power measurement and monitoring can be used to distinguish between harmful and harmless high currents, since current and voltage measurement directly measure the power dissipation of the switch element, which determines heating (temperature increase in the switch element). If heating is, for example, too great during turn on, the switch element 206 can be damaged. By monitoring power dissipation, such damage can be reduced or avoided by embodiments herein.

[0033] As shown the circuit 200 includes a current sensor 211 and a voltage sensor 212. The current sensor 211 measures a current (I) through the switch element 206. The current sensor 211 is shown as being connected between the switch element 206 and load 204. The skilled artisan will realize that the current sensor 211 could be between the power source 202 and the switch element 206. The current sensor 211 measures the current passing from the power source to the load 204. In one embodiment, the current sensor 211 measures current passing from the input 220 to the output 222. The current sensor may include a shunt resistor used to measure a voltage and determine the current based on measured voltage and resistance of the shunt resistor.

[0034] The voltage sensor 212 can measure a voltage (U) across the switch element 206 as illustrated in FIG. 2. As shown, the voltage sensor 212 is connected across the input 220 and the output 222 of the switch element 206 and thereby measures a switch element voltage between the input and the output. Of course, resistors or other elements could be added utilized around the switch element 206 and the voltage sensor 212 could measure the voltage across the switch element and the other elements. In either case, the voltage sensor 212 will, therefore, measure a voltage that is based on the switch element voltage between the input 220 and the output 222. The voltage sensor may include a voltage divider at the input 220 and a voltage divider at the output 211 to measure a voltage at the input and a voltage at the output of the switch element 206. Based on the input voltage and the output voltage a voltage difference is determined that defines the voltage drop (voltage U) over the switch element 206. The power at the load Pioad is defined by the voltage across the load Uioad and the current through the switch I (= Iioad), not shown.

[0035] As noted above, the controller 208 receives information about the power dissipated across the switch element 206. To that end, the system 200 includes a multiplier 214 that receives U and I and calculates the power dissipation from U and I. The multiplier outputs a power dissipation level P to the controller 208. P is the power dissipated at the switch element 206. In one embodiment the multiplier includes an analog / digital converter (A / D converter) and a multiplier processor, such as a digital signal processor (DSP). The A / D converter converts the analog measurement signals (1 and U) received from the current and voltage sensors and provides the converted digital signals to the multiplier processor. The multiplier processor calculates the power dissipation P based on I and U. In an embodiment the multiplier is included in the controller 208 (e.g. controller 208 is a micro controller). In an alternative embodiment the multiplier is an electronic circuit that allows analog multiplication of I and U to calculate the power dissipation P. In this embodiment the conversion to a digital signal is performed after the multiplication and before P is provided to the controller 208.

[0036] The controller 208 shown in FIG. 2 also includes other inputs such as first and second power thresholds Pthrl and Pthr2. The power thresholds are in fact power dissipation thresholds. Pthrl is a lower-level threshold which will be used to cause the controller 208 to reduce power dissipation at the switch element 206. Pthr2 is an upper-level threshold that when reached or exceeded cause the switch element 206 to stop conducting (fully opening the switch element) and thus, stop the switch-on process and the power dissipation. Fully opening the switch element 206 corresponds to a control signal CTL2 equals to 0V. The controller includes a non-volatile memory that stores a firmware code, which controls the operation of the controller. The firmware code includes information on the power thresholds Pthrl and Pthr2. It will be understood by those skilled in the art that the firmware code can include additional thresholds used by the controller to control the output signal CTL1.

[0037] Reference will now be made to both FIGs. 2 and 3 and an example operation of the circuit 200 of FIG. 2 will be described.

[0038] FIG. 3 shows three different possible power dissipation scenarios, determined based on measurements of U and I across the switch element 206, during power-on situations (switch-on) illustrated by power dissipation vs time waveforms Pl, P2 and P3. In situation / waveform Pl, the power dissipation during the switch-on process increases rapidly and exceeds the upper threshold Pthr2. The opening of the switch element 206 is stopped by the controller 208 to protect the switch element from overheating.

[0039] In situation P2, the power dissipation is given a time limit (defined by tl) to get out of the critical range A. Herein, the critical range A is a power dissipation range that is to be avoided if possible and can extend downward from the upper threshold Pthr2 to a power level that is less than Pthrl. In situation P2, when the waveform first crosses Pthrl, the ramping up of current and / or voltage through the switch (power dissipation) can be slowed / stopped. This causes the power to fall and thus the power dissipation can then be ramped up again. In FIG. 3, two different shut-off conditions are shown and the controller 208 can operate on one or both of them. First, if the number of times (Nt) Pthrl is exceeded the switch-on process is stopped. When the threshold Pthrl is exceeded, in response the controller 208 adjusts the control signal CTL1 to stop the opening process of the switch element 206, or to gradually opening the switch element to reduce the power limitation as shown in P2. If a predetermined number of Pthrl exceedings are encountered the switch element fully opened to interrupt the switch-on process to protect the switch element from being overheated and destroyed. In FIG. 3, there are 4 times illustrated by way of example (Nt = 4). Alternatively, or in addition, if the power dissipation P remains in the critical range A that exceeds a time period (e.g., tl) the process can also be stopped. The number of times a specific threshold is allowed to be exceeded is programmed to the controller (firmware). The same holds true for the time period tl . The lower limit of the critical range is determined by operational conditions, such as a sample rate of voltage sensor 212 and / or current sensor 211, switch element 206 reaction time, multiplier 214 processing time, controller 208 processing time, etc. The operational conditions provide to the system a sensitivity or idleness.

[0040] In situation P3, the lower-level threshold Pthrl is reached and then power dissipation ramping is stopped by opening the switch and as can be seen, the power dissipation across the switch element 206 reduces out of the critical range A and then the power-on process can be completed. This shows that defining a critical range A and setting smart control parameters (Pthrl, Pthr2, tl, Nt) allows more tolerant switch-on handling than a usual purely current based switch element control as used in the prior art. Controlling the switch element based on the power dissipation provides direct control of the critical condition which would destroy the switch element and which is the heat generation inside the switch caused by the power dissipation. In FIG. 3 are exemplary displayed three switch-on scenarios. Many more scenarios are possible.

[0041] As noted above, the switch element 206 can be used to connect the power source 202 to the load 204. Load 204 can have an arbitrary impedance. The load 204 represents a downhole tool in one embodiment. The switch element 206 is controlled by thecontrol signal CTL2. As noted above, the control signal CTL2 is generated by a drive electronics 210 based on the control signal CTL1. For example, in the case of a P-channel MOSFET as the switch element, the control signal CTL2 is the output signal of the controlled current source described below.

[0042] The signal CTL1 is normally (in normal operation, or no short or overheating of switch element) the control signal for generating a so-called soft start switch-on ramp. That means in normal case the amplitude of the control signal CTL1 changes slowly until the switch element 206 is completely conductive (e.g., switch element closed). In the event of a fault at the output 222 of the switch element 206 (e.g., the sensor 212, 211 measure a short circuit) (overload or short circuit, high power dissipation), the switch-on ramp or the control signal CTL1 is influenced by the controller 208 (acting as a power limiter) in such a way that when the permissible power dissipation Pthrl is exceeded, instead of closing (e.g., becoming more conductive) further, the switch element 206 is slightly re-opened at an appropriately adapted speed, as a result of which the power dissipation does not increase further. For this purpose, the amplitude of the control signal CTL1 is maintained or reduced by the controller 208. The control signal CTL1 can be in one embodiment a control voltage or in another embodiment a control current. A fault at the output may be a short in a downhole tool, which is represented by load 204 in FIG. 3.

[0043] As noted above, the input signal for the controller 208 is the power dissipation P calculated from the voltage U and current I measured by voltage sensor 212 and current sensor 211. Over time, the power dissipation P is limited by or to a threshold value Pthrl (first safety threshold) (See FIG. 2) as long as the measured power dissipation P is measured within the critical range A.

[0044] If the power dissipation P leaves the critical range A (e.g., due to a change in the load conditions, (e.g. decrease of inrush current with capacitive load) as shown by waveform P3, the power limitation stops and switching-on process of the switch element 206 is continued in the normal intended manner.

[0045] If the power dissipation P, due to permanent overload, remains too long in a critical range A (e.g., waveform P2), the controller 208 stops the entire switch-on process after a time tl. The time tl is designed according to the dynamic thermal characteristics of the switch element so that the critical point of destruction is not reached. If, in spite of the control or regulation - e.g., due to a second fault - the critical power range A is exceeded (e.g., waveform Pl) the power dissipation is limited by or to a safety threshold Pthr2 (secondsafety threshold) (See FIG.2) . When the second afety threshold is reached or exceeded the entire switch-on process is immediately interrupted by the controller 208.

[0046] In one embodiment, to adapt the operating range of the load switch to the ambient temperature, if necessary, the parameters of the control (safety thresholds Pthrl and Pthr2) or the regulation (e.g. sensitivity of reaction if a safety threshold is exceeded) can be adapted in a suitable manner depending on the measured ambient temperature Tenv that is provided to the controller 208. The ambient temperature is determined by the controller using a temperature sensor (not shown). Beside adapting the parameter of control to the ambient temperature Tenv, the regulation can have a certain sensitivity or idleness which depends on operating conditions of the circuitry (mainly temperature of electronic components). As displayed in FIG. 3 waveform P2 overshoots the Pthrl safety threshold by varying amount of power dissipation. The first event of exceeding the safety threshold Pthrl shows a slower reacting system (overshoot greater) than the second event of exceeding the safety threshold Pthrl, where the overshoot is smaller. The sensitivity or idleness of the system is of advantage, as it prevents the system from toggling between two conditions. In an alternative embodiment the idleness can be replaced or supplemented by a hysteresis around the first safety threshold Pthrl. That is, when the power dissipation P during the switch-on process detected by the controller 208 increases, the safety threshold Pthrl is encountered at a lower value than it is encountered when the power dissipation P is decreasing after the controller has opened the switch element gradually to decrease P. This leads to the switch element is closed at a lower safety threshold value Pthrl (to again increase P) than it is opened to reduce the power dissipation P. The hysteresis may be defined based on the Pthrl level, such as Pthrl minus 0.5% to 5%, 2% to 10%, or 5% to 15%. The lower limit of the critical range A is then 0.5% to 5%, 2% to 10%, or 5% to 15% smaller than the Pthrl level.

[0047] FIG. 4 shows a more detailed version of the circuit of FIG. 2. FIG. 4 uses a controlled current source to adjust the control signal CTL2 used to close the switch element 206 during turn on, for example.

[0048] In more detail, the drive electronics 210 receive control signal CTL1 at the control terminal 226 (voltage U208, UgSQi, respectively, between control terminal 226 and GND) from the controller 208 as described above. Based on this, a current Idl can be drawn over R2, R3 QI, and R1 from the power source 202 and creates a voltage CTL2 on R2 to control the switch element 206.

[0049] In even more detail, switch element 206 in FIG. 4 is shown as a P-channelMOSFET. The drive electronics 210 acts as a current source used to drive switch element206. QI is configured to act as a current source. The control signal CTL2 is a negative voltage on the control terminal 224 (voltage between gate and source of the switching element or the voltage between control terminal 224 and input 220 of the switch element).

[0050] As illustrated, the drive electronics 210 includes a control transistor QI with a current feedback resistor Rl. The transistor QI is controlled by control signal CTL1 (voltage between gate and source of QI) and can have an optional first scaling resistor R4 connected between the gate of QI (control terminal 226) and the controller 208. The drain-source channel of transistor QI is connected between the control terminal 224 of the switch element 206 and ground. The feedback resistor Rl is connected between the source of transistor QI and ground.

[0051] As noted above, the control signal CTL1 controls conduction through the control transistor QI allowing it to pass current from the input 228 of QI (drain) to the output 230 (source) of QI. QI is shown as a P-MOSFET in FIG. 4 but other elements could be used (e.g., N-MOSFET, bipolar transistor, IGBT-FET, or any other type of transistor).

[0052] Other circuits e.g. with operational amplifiers or current controlled current sources are also suitable for the realization of the current source.

[0053] A second resistor R2 is connected between input 220 and the control transistor QI. As QI is opened, it allows current to flow through R2 to ground (GND) (through Rl and optional scaling resistor R3). This flow of current through resistor R2 leads to the generation of a voltage over R2, represented by the second control signal (CTL2) that is provided to the gate of the switch element 206 (e.g., the P-channel MOSFET) illustrated in FIG. 4. R2 is also referred to as control resistor.

[0054] The level of CTL2 will be based on the current flowing through the control transistor QI. As CTL 1 increases, more current will flow through QI and, thus, through R2 / R1 (and optionally R3). As QI operates as a current source, the voltage drop across R2 determines the voltage on R2 (control signal CTL2). The Resistor Rl is the current feedback resistor for the control element QI. Assume a constant voltage CTL1 and a certain drain voltage Udi from drain of QI to source or GND, respectively. A certain current Idl will be the result. If the drain voltage Udi increases for any reason to a higher level Ud2, the current Idl would also increase to Id2 if Rl was not present. Because Rl is present, a higher current would create a higher voltage drop across Rl and this would decrease the gate-source voltage UgSQi of QI. As such, a change in Udi to Ud2 would not change the current Idl through QI. This effect is the current feedback. When QI is closed (drain-source channel conducting) resistor R3 is pulled to ground level (voltage drop across Rl neglectable). The resistor R3builds in fact a voltage divider with R2 (voltage drop UgSQ2 (CTL2) across R2 and voltage drop UR3 across R3). If QI is closed completely the voltage drop across R2 must not exceed the maximum UgSQ2 of Q2 (the load switch), that is why we need R3. Indeed, R1 may be omitted in some case. (R1 has a very low value compared to R2 and R3, R1<<R2, R1<<R3).

[0055] The current through the resistor R2 is independent of the input voltage (Vin) of the power source 202 and the voltage across the switch element 206 (V) because the drive electronics 210 compensate for a fluctuating input voltage Uin with resistor R1 and only the control signal CTL1 (first control voltage) determines the current through R2 and thus the turn-on ramp. This is achieved due to QI acting as a current source. Even if the voltage Uin varies, the current through R2 remains constant, resulting in a constant voltage UgSQ2 and constant control signal CTL2, respectively. In other words, only the controller 208 with the control signal CTL1 controls the control signal CTL2 (UgSQ2) based on the information about the power dissipation P in the switch element 206. Despite fluctuating input voltages Uin, this leads to uniform switch-on ramps at the output 222 of the switch element 206.

[0056] Set forth below are some embodiments of the foregoing disclosure:

[0057] Embodiment 1: A load switch assembly for providing power from a power source to a load. The assembly includes: a switch element for connection between the power source and the load and configured to provide power to the load, the switch element having a first input, a first output, a first control terminal, the switch element dissipating power during a switch-on process; a controller that generates a first control signal based on the power dissipation on the switch element; and drive electronics connected between the controller and the first control terminal of the switch element that draws current from the power source and that causes a second control signal based on the first control signal at the first control terminal so as to control the power dissipation on the switch element.

[0058] Embodiment 2: The load switch assembly of any prior embodiment, further comprising: a current sensor that measures a current (I) passing from the power source to the load; and a voltage sensor that measures a voltage (U) between the first input and the first output of the switch element. The current (I) and the voltage (U) represent the power dissipation on the switch element on which the first control signal is based.

[0059] Embodiment 3 : The load switch assembly of any prior embodiment, wherein the second control signal is a voltage.

[0060] Embodiment 4: The load switch assembly of claim 2, further comprising a multiplier that receives the current (I) and the voltage (U) and multiplies them to determinethe power dissipation on the switch element, and the controller using the determined power dissipation.

[0061] Embodiment 5: The load switch assembly of any prior embodiment,, wherein the controller uses a first power threshold and controls the first control signal based on the first power threshold and the power dissipation on the switch element.

[0062] Embodiment 6: The load switch assembly of any prior embodiment,, wherein the controller is configured to adjust the first control signal when the first power dissipation exceeds the first power threshold.

[0063] Embodiment 7: The load switch assembly of any prior embodiment,, wherein the controller uses a second power threshold and is configured to cause the switch element to cease power provision to the load when the second threshold is exceeded.

[0064] Embodiment 8: The load switch assembly of any prior embodiment, wherein the controller is configured to cause the switch element to cease power provision to the load if the first threshold is exceeded for more than a predetermined number of times or the power dissipation remains in a critical range for longer than a predetermined time period.

[0065] Embodiment 9: The load switch assembly of any prior embodiment, wherein the critical range includes a power dissipation range between the first power threshold and the second power threshold.

[0066] Embodiment 10: The load switch assembly of any prior embodiment, wherein the drive electronics acts as a current source.

[0067] Embodiment 11: The load switch assembly of any prior embodiment, wherein the current source includes: a control transistor connected between the first control terminal of the switch element and ground. The control transistor includes a second input and a second output and a second control terminal. The current source also includes: a feedback resistor connected between the control transistor and ground; and a control resistor connected between the first input and the first control terminal of the switch element.

[0068] Embodiment 12: The load switch assembly of any prior embodiment, wherein the control transistor receives the first control signal at the second control terminal and generates the second control signal between the first input and the first control terminal of the switch element.

[0069] Embodiment 13: The load switch assembly of any prior embodiment, wherein as the first control signal increases, the second control signal increases.

[0070] Embodiment 14: A method of controlling a load switch assembly of any prior embodiment. The method includes: generating with drive electronics a switch control signal;and providing the switch control signal to the control terminal so as to control the provision of power through the switch element, wherein the switch control signal is generated based on the power dissipation on the switch element.

[0071] Embodiment 15: The method of any prior method embodiment, further comprising: providing to a controller first and second power thresholds; and generating a drive electronics control signal based on the power dissipation on the switch element, and the first and second power thresholds.

[0072] Embodiment 16: The method of any prior method embodiment, further comprising: reducing the drive electronics control signal when the first power threshold is exceeded.

[0073] Embodiment 17: The method of any prior method embodiment, further comprising: causing the switch element to cease providing power to the load when the second threshold is exceeded.

[0074] Embodiment 18: The method of any prior method embodiment, comprising: causing, with the controller, the switch element to cease providing power if the first threshold is exceeded for more than a predetermined number of times or the power dissipation on the switch element remains in a critical range for longer than a predetermined time period.

[0075] Embodiment 19: The method of any prior method embodiment, wherein the critical range extends from a power level below the first power threshold to the second power threshold.

[0076] Embodiment 20: The method of any prior method embodiment, generating the switch control signal includes measuring current through the switch element, measuring voltage across the switch element, and determining the power dissipation on the switch element based on the measured current and voltage.

[0077] The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Further, it should be noted that the terms “first,” “second,” and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms “about”, “substantially” and “generally” are intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. For example, “about” and / or “substantially” and / or “generally” includes a range of ± 8% of a given value.

[0078] The teachings of the present disclosure may be used in a variety of well operations. These operations may involve using one or more treatment agents to treat a formation, the fluids resident in a formation, a borehole, and / or equipment in the borehole, such as production tubing. The treatment agents may be in the form of liquids, gases, solids, semi-solids, and mixtures thereof. Illustrative treatment agents include, but are not limited to, fracturing fluids, acids, steam, water, brine, anti-corrosion agents, cement, permeability modifiers, drilling muds, emulsifiers, demulsifiers, tracers, flow improvers etc. Illustrative well operations include, but are not limited to, hydraulic fracturing, stimulation, tracer injection, cleaning, acidizing, steam injection, water flooding, cementing, etc.

[0079] While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited.

Claims

CLAIMSWhat is claimed is:

1. A load switch assembly for providing power from a power source to a load, the assembly comprising: a switch element for connection between the power source and the load and configured to provide power to the load, the switch element having a first input, a first output, a first control terminal, the switch element dissipating power during a switch-on process; a controller that generates a first control signal based on the power dissipation on the switch element; and drive electronics connected between the controller and the first control terminal of the switch element that draws current from the power source and that causes a second control signal based on the first control signal at the first control terminal so as to control the power dissipation on the switch element.

2. The load switch assembly of claim 1, further comprising: a current sensor that measures a current (I) passing from the power source to the load; and a voltage sensor that measures a voltage (U) between the first input and the first output of the switch element; wherein the current (I) and the voltage (U) represent the power dissipation on the switch element on which the first control signal is based.

3. The load switch assembly of claim 2, wherein the second control signal is a voltage.

4. The load switch assembly of claim 2, further comprising a multiplier that receives the current (I) and the voltage (U) and multiplies them to determine the power dissipation on the switch element, and the controller using the determined power dissipation.

5. The load switch assembly of claim 1, wherein the controller uses a first power threshold and controls the first control signal based on the first power threshold and the power dissipation on the switch element.

6. The load switch assembly of claim 5, wherein the controller is configured to adjust the first control signal when the first power dissipation exceeds the first power threshold.

7. The load switch assembly of claim 5, wherein the controller uses a second power threshold and is configured to cause the switch element to cease power provision to the load when the second power threshold is exceeded.

8. The load switch assembly of claim 5, wherein the controller is configured to cause the switch element to cease power provision to the load if the first power threshold isexceeded for more than a predetermined number of times or the power dissipation remains in a critical range for longer than a predetermined time period.

9. The load switch assembly of claim 8, wherein the critical range includes a power dissipation range between the first power threshold and the second power threshold.

10. The load switch assembly of claim 1, wherein the drive electronics acts as a current source.

11. The load switch assembly of claim 10, wherein the current source includes: a control transistor connected between the first control terminal of the switch element and ground; the control transistor including a second input and a second output and a second control terminal; a feedback resistor connected between the control transistor and ground; and a control resistor connected between the first input and the first control terminal of the switch element.

12. The load switch assembly claim 11, wherein the control transistor receives the first control signal at the second control terminal and generates the second control signal between the first input and the first control terminal of the switch element.

13. The load switch assembly of claim 12, wherein as the first control signal increases, the second control signal increases.

14. A method of controlling a load switch assembly for providing power from a power source to a load, the assembly comprising a switch element connected between the power source and the load and that provides power to the load, the switch element having an input, an output and a control terminal, the switch element dissipating power during a switchon process, the method comprising: generating with drive electronics a switch control signal; and providing the switch control signal to the control terminal so as to control the provision of power through the switch element, wherein the switch control signal is generated based on the power dissipation on the switch element.

15. The method of claim 14, further comprising: providing to a controller first and second power thresholds; and generating a drive electronics control signal based on the power dissipation on the switch element, and the first and second power thresholds.

16. The method of claim 15, further comprising: reducing the drive electronics control signal when the first power threshold is exceeded.

17. The method of claim 15, further comprising: causing the switch element to cease providing power to the load when the second threshold is exceeded.

18. The method of claim 15, further comprising: causing, with the controller, the switch element to cease providing power if the first threshold is exceeded for more than a predetermined number of times or the power dissipation on the switch element remains in a critical range for longer than a predetermined time period.

19. The method of claim 14, wherein generating the switch control signal includes measuring current through the switch element, measuring voltage across the switch element, and determining the power dissipation on the switch element based on the measured current and voltage.

20. The method of claim 18, wherein the drive electronics comprises a transistor that acts as a current source, the current of the current source is controlled by the drive electronics control signal.

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