BULK CAPACITOR CHARGING CIRCUIT FOR MUD PULSE TELEMETRY DEVICE
TECHNICAL FIELD
Tl e present disclosure relates generally to oilfield equipment, and in particular to
downhole tools.
BACKGROUND
Various downliole tools use mud pulse telemetry to transmit information during drilling
operations. One known method uses a mud pulse generator to create negative pressure
pulses in the borehole. A solenoid is used to open and shut a valve in a system that
generates pressure pulses into a drilling mud. The pulses correspond to a Manchester or
other encoding system to enable signals to be transmitted from the bottom of the borehole
to the surface.
Existing arrangements typically drive the solenoid valve from a high capacitance bulk
capacitor, for instance 76()0m , which stores the required electrical energy and provides a
high current discharge capability for rapidly actuating the solenoid. The bulk capacitor is
charged more slowly than it is discharged, using a lower current rated DC fixed voltage
power supply between the instances of solenoid actuation.
For instance, the bulk capacitor may be charged by one or more batteries, such as a series
of 90V batteries, through a linear current limiter circuit. The purpose of the current limiter
is to prevent damage to the batteries by excessive current during capacitor charging.
However, linear current iimiters are inefficient. For example, while charging the bulk
capacitor from 60V to 90V at 700 m.A, the average power lost per charging cycle is 10.5
watts.
Alternatively, an electrical generator pow ered by mud flow may be used to charge the bulk
capacitor. Because the generator output voltage is proportional to mud flow, which is
variable, a regulated DC power supply circuit is used downstream of the generator to
charge the bulk capacitor. Regulated power supplies tend to be large, add complexity, and
have a limited input voltage range and operating temperature limit. Accordingly, it is
desirable to provide a DC power supply circuit that fits within the limited available space
of the downhole too , extends the range of generator operation, and operates at higher
temperatures.
Additionally, it is desirable to provide a DC power supply circuit that allows both charging
of the bul capacitor from either a bat er or a mud-powered electrical generator.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments are described in detail hereinafter with reference to the accompanying
figures, in which;
Figure 1 is a block-level schematic diagram of a measurement while drilling system
according to a preferred embodiment, showing a . drill string and a drill bit for drilling a .
bore in the earth and a mud pulse telemetry tool disposed in a drill string incorporating the
bulk capacitor charging circuit of Figure 2;
Figure 2 is a simplified block level schematic diagram of a bulk capacitor charging circuit
according to a preferred embodiment, showing a generator for charging the capacitor via a
converter;
Figure 3 is a detailed schematic diagram of the bulk capacitor charging circuit of Figure 2,
showing details of modified a single-ended primary-inductance converter;
Figure 4 is a flow chart diagram showing logic implemented by the bulk capacitor charging
circuit of Figure 3;
Figure 5 is a simplified block level schematic diagram of the bulk capacitor charging
circuit of Figure 2 augmented by battery and battery control circuit to allo charging the
bulk capacitor either from the converter or from a battery;
Figure 6 is a detailed schematic diagram of the bulk capacitor charging circuit of Figure 5
according to an embodiment; and
Figure? is a flow chart diagram showing battery-connection logic implemented by the bulk
capacitor charging circuit of Figure 6.
DETAILED DESCRIPTION
Attention is directed to Figure 1, which shows a measurement while drilling (MWD) or
logging while drilling (LWD) system of the present disclosure. As a generalization, the
system shown in Figure 1 is generally identified by the numeral 20.
MWD system 20 may include land dril ling rig 22. However, teachings of the present
disclosure may be satisfactorily used in association with offshore platforms, semisubmersible,
drill ships and any other drilling system satisfactory for forming a wellbore
extending through one or more downhole formations.
Drilling rig 22 and associated directional drilling equipment 50 may be located proximate
well head 24. Drilling rig 22 also includes rotary table 38, rotary drive motor 40 and other
equipment associated with rotation of drill string 32 within wellbore 60. Annulus 66 may
be formed between the exterior of drill string 32 and the inside diameter of wellbore 60
For some applications drilling rig 22 may also include top drive motor or top drive unit 42.
Blow out preventers (not expressly shown) and other equipment associated with drilling a
wellbore may also be provided at well head 24. One or more pumps 48 may be used to
pump drilling fluid 46 from fluid reservoir or pit 30 to one end of drill string 32 extending
from well head 24. Conduit 34 may be used to supply drilling fluid from pump 48 to the
one end of drilling string 32 extending from well head 24. Conduit 36 may be used to
return drilling fluid, reservoir fluids, formation cuttings and/or downhole debris from the
bottom or end 62 of wellbore 60 to fluid reservoir o pit 30. Various types of pipes, tube
and/or conduits may be used to form conduits 34 and 36.
Drill string 32 may extend from well head 24 and may be coupled with a supply of drilling
fluid, such as pit or reservoir 30. The opposite end of drill string 2 may include bottom
hole assembly 90 having a rotary drill bit 100 disposed adjacent to end 62 of wellbore 60.
Bottom hole assembly 90 may also include bit subs, mud motors, stabilizers, drill collars,
or similar equipment, as known in the art. Rotary drill bit 00 may include one or more
fluid flow passageways with respective nozzles disposed therein. Various types of drilling
fluids 46 may be pumped from reservoir 30 through pump 48 and conduit 34 to the end of
drill string 32 extending from well head 24. The drilling fluid 46 may flow through a
longitudinal bore (not expressly shown) of drill string 32 and exit from nozzles formed in
rotary drill bit 100.
At end 62 of wellbore 60 drilling fluid 46 may mix with formation cuttings and other
downhole fluids and debris proximate drill bit 100. The drilling fluid will then flow
upwardly through annulus 66 to return formation cuttings and other downhole debris to
well head 24. Conduit 36 may return the drilling fluid to reservoir 30 Various types of
screens, filters and/or centrifuges (not expressly shown) may be provided to remove
formation cuttings and other downhole debris prior to returning drilling fluid to pit 30.
Bottom hole assembly 90 may also include various tools 9 that provide logging or
measurement data and other information about wellbore 60. This data and information
may be monitored by a control system 50. In particular, bottom hole assembly 90 includes
a downhole tool having a telemetry device including a bulk capacitor charging circuit
10 or 10' as described below with respect to Figures 2-4. However other various types of
tools may be included in bottom hole assembly 90 as appropriate.
Measuremen t data and other information may be communicated from end 62 of wellbore
60 through fluid within drill string 32. or the annulus using MWD techniques and converted
to electrical signals at well surface 24. Electrical conduit or wires 52 may communicate
the electrical signals to input device 54. The measurement data provided from input device
54 may then be directed to a data processing system 56. Various displays 58 may be
provided as par of control system 50.
For some applications printer 59 and associated printouts 59 a may also be used to monitor
the performance of drilling string 32, bottom hole assembly 90 and associated rotary drill
bit 00. Outputs 57 may be communicated to various components associated with
operating drilling rig 22 and may also be communicated to various remote locations to
monitor the performance of drilling system 20.
Figure 2 is a simplified schematic diagram of the bulk capacitor charging circuit 10
according to a preferred embodiment that illustrates its principle of operation. A downhole
electrical generator 12 provides a rectified voltage proportional to its rotational speed.
Electrical generator 12 is preferably powered by flow of drilling fluid, which may be
provided to generator 12 via drill string 32 (Figure 1). In some embodiments, the useful
range of voltage of generator 12 is approximately 100 volts to 400 volts. The rectified
voltage is fed to a converter 14, which in turn charges the bulk capacitor 6. That is,
converter 14 selectively transfers charge from generator 12 to bul capacitor 16 as further
described below. Bulk capacitor 16 may be a large capacitor that is specified for storing
energy to be used in operating an actuator (not illustrated) of downhole tool 9 1. In an
embodiment, downhole tool may include a telemetry device, and the actuator may be
the solenoid of a solenoid-operated valve for producing a pressure pulse in the drilling
fluid, for example. Although bulk capacitor 16 is discussed herein as a single capacitor,
one of ordinary skill in the art understands that bulk capacitor 6 may include multiple
discrete capacitors connected together in series, parallel, or a combination thereof.
Converter 14 may be located in a downhole tool (Figure 1), which has a housing 92 that
protects the electronic components from the hazards of the downhole environment.
Generator 12 and/or bulk capacitor 6 may also be located in housing 92 with converter 14,
as shown in Figure 2. Alternatively, converter 14, generator 12, and bul capacitor 6 ma ¬
be located in one or more downhole components within bottom hole assembly 90, for
example, as shown in Figure 5.
Converter 14 defines a two port network, characterized by a pair of input terminals 13 and
a pair of output terminals 7 . Generator 12 is connected to input terminals 3 and provides
a rectified DC voltage that is proportional to its rotational speed. One of the input
terminals 13 is electrically connected to one of the output terminals 17 and may form a
ground or common potential reference point. Bulk capacitor 16 is connected to output
terminals 17.
When the voltage across the bulk capacitor 16 reaches a predetermined charged level,
preferably about 90 volts, a voltage feedback path 18 causes converter 14 to cease charging
the capacitor. Upon actuation of the actuator (not illustrated), for example, one or mo e
solenoid-operated valves (not illustrated) for creating mud pressure pulses, control logic
5, via a control line 20, also causes converter 14 to cease charging bulk capacitor 16 to
enhance circuit efficiency and performance. Under normal operating conditions, at the end
of the actuation sequence, bulk capacitor 16 will have discharged from about 90 volts to 60
volts. If the capacitor voltage VBC drops below a predetermined low level in the idle state,
i.e., when the solenoids are not being actuated, voltage feedback path 18 causes converter
14 to recommence charging capacitor 16 to provide a top-up charge.
In a preferred embodiment, converter 14 is a single-ended primary-inductance converter
("SEPIC"), which includes inductors L , 12, capacitor C3, diode D22, and control
switching element Q , which cycles on and off to transfer charge. n this embodiment,
because converter 14 is a SEPIC, it is capable of having an output voltage that is greater
than, equal to, or less than its input voltage, depending on the duty cycle of the control
switching element Q13. Inductors L and L2 may be discrete uncoupled components, or
they may be wound on the same core so as to be coupled. Coupling inductors LI and L2
enables the inductance values to be halved and thus saves space.
Figure 3 is a more detailed schematic diagram of the bulk capacitor charging circuit 10 of
Figure 2. In an embodiment, control switching element Q13 may be a metal oxide
semiconductor field effect transistor, bipolar transistor, insulated gate bipolar transistor,
junction field effect transistor, or other suitable device.
The duty cycle of the control switching element Q13 may be determined by an oscillator,
which may be connected to control switching element Q13 via a driving circuit. In one
embodiment, the oscillator is a Schmitt Trigger oscillator formed of a comparator U ,
resistors R117, R 8, and R5, and a capacitor C44. As Schmitt Trigger oscillators are
known to routineers in the art, further details are not provided herein. However, the
disclosure is not limited to a particular timing device and other oscillators clocks, or
crystals, for example, may be used as appropriate. Switching elements Q6 and Q9 form the
driving circuit that connect the oscillator to control switching element 3 via a capacitor
C41 and resistors R8 , R94. Discrete or integrated components, or a commercial driver
package, may be used as appropriate, and the driver configuration may be varied as
necessary to support the type of device used for control switching element Q 3.
One of the advantages of a SEPIC over a conventional regulated power supply circuit is
tha a snubber circuit is not required to protect the system trom voltage transients, because
the output filter capacitor itself acts as a snubber. Not having a snubber means that the
circuit runs more efficiently. However, the equivalent series resistance of bulk capacitor
16 together with the inductance of the connecting wires may prevent effective snubbing.
Accordingly, capacitor C may be added to enhance snubbing. Capacitor CI does not
make circuit 0 Jess efficient, as its charge is added to the charge of the bulk capacitor 6.
Resistors R4, R5 and R116 and a voltage source Vcc are used to provide feed-forward
from generator 12 (Figure 2). The feed-forward varies both the frequency of oscillation
and the duty-cycle in a manner that has the effect of keeping the peak current in the control
switching element Q almost constant. The feed-forward function requires that the
switching element driver circuitry inverts the output of the oscillator, as it does in circuit 0
of Figure 3.
Switching elements Qll and Q12 are connected so as to effectively form a logical QRgate.
If the voltage on the gate of either switching element Q , Q is high, then
capacitor C44 is shorted and the oscillator stops running, as described below.
n an embodiment, circuit 10 may include a . converter-enabling circuit coupled between
bulk capacitor 6 and the oscillator that is used to stop the oscillator f om running when
bulk capacitor 6 has charged up to a higher set point, its predetermined fully charged
level, as follows: A voltage divider network of resistors R109 and R106 sense the voltage
C across bulk capacitor 6. The divided voltage is compared with a reference voltage V2
applied to the inverting input of a comparator U2. When the divided voltage exceeds
reference voltage V , comparator U2 outputs a logic high, which turns on switching
element Q , which in turn shorts the inverting input of comparator Ul to ground, thereby
stopping oscillation. Resistor R 3 forms a positive feedback path that provides hysteresis
to ensure that when the voltage across the capacitor bank has dropped below a certain
lower set point, for example due to natural leakage, the oscillator starts back up again to
maintain the required voltage across the capacitor.
In an embodiment circuit 10 may include a converter-disabling circuit coupled to the
oscillator that shuts down the oscillator when bulk capacitor 6 is required to discharge
through the solenoids for valve actuation, as follows: A control signal 20 from appropriate
control logic is connected to the non-inverting input of a comparator U3 via a resistor
R2. A reference voltage V-. provides a predetermined set point for the comparator U3 at its
inverting input. When control signal 20 is high, comparator U3 outputs a logic high, which
turns on switching element Q12, which in turn shorts the inverting input of comparator Ul
to ground, thereby stopping the oscillator from running and control switching element Q 3
from cycling. This optional function results in a more efficient operation of circui t 10.
Switching element Q 2 also shuts down the oscillator if the drain current through control
switching element Q 3 is excessive. This drain current is sensed by resistor R6 and fed to
the comparator 3 via resistors R84, R 5 and capacitor C2. Reference voltage V provides
a predetermined set point for the comparator U3. Resistor R83 provides hysteresis.
Figure 4 represents the operation of the bul capacitor charging circuit 10 of Figure 3.
Referring to Figures 3 and 4, decision block 200, which assesses whether the bulk
capacitor 16 is actively discharging into the solenoid, is implemented by control logic 5,
comparator U3 and its associated circuitry, and switching element Q12. Decision block
202 assesses whether the bulk capacitor 16 is fully charged, and it is implemented by the
voltage divider resistors R1G9, R1G6, comparator U2, feedback resistor 113, and
switching element Qll. Decision block 204 assesses whether the current flowing through
the drain terminal of control switching element Q13 is too high, and it is implemented by
resistor R6, comparator U3 and its associated circuitry, and switching element Q12.
If any one or more of the conditions of decisions blocks 200, 202, 204 exists, i.e., if the
bul capacitor 16 is actively discharging, if the bulk capacitor 16 is fully charged, or if
there is excessive drain current through control switching element Q13, then the oscillator
is disabled, as shown in state block 2 0. Otherwise, the oscillator is enabled as shown in
state block 212.
If the oscillator is disabled, it will remain in the disabled state 210 so long as the voltage
VBC across bulk capacitor 6 remains above the lower set point, which is determined by the
value of the hysteresis resistor Rl 13 as described above. Such logic is depicted in Figure 4
by decision block 206.
Figure 5 is a block level schematic diagram of a bulk capacitor charging circuit 10'.
Circuit 10' of Figure 5 is essentially the same as circuit 10 of Figure 2, except it is
augmented to allow charging of the bulk capacitor 6 from either generator 12 connected at
input terminals 13 or from a battery 19 connected at output terminals 17 via. a batter}
control circuit 9. Although discussed in terms of a singular battery 9, one skilled in the
art understands that battery 19 may consists of series or parallel combinations of several
discrete battery cells.
Under battery operation, electric charge is transferred from battery 19 into bulk capacitor
6 via battery control circuit 9. In an embodiment, battery control circuit 9 may perform
one or more of the following functions: Connecting battery 9 to bulk capacitor 16 when a
battery-supply mode of operation is desired by the operator; limiting current flow through
battery 19 while charging bulk capacitor 16 using the battery; disconnecting battery 19
during the time that bulk capacitor 6 is being discharged into the actuator; and preventing
the charging of hulk capacitor 16 by battery 19 when generator 12 is operating by
disconnecting battery 19 from bulk capacitor 6 .
Battery control circuit 9 may include a battery-enabling switching element that is coupled
by a control line 7 to control logic 15, which when in a first state serves to connect battery
to bulk capacitor 16 when a battery-supply mode of operation is desired by the operator
and when in a second state to disconnect batter}' 19 during the time that bu capacitor 16
is being discharged into the actuator. Battery control circuit 9 may also include a . batterydisabling
circuit that is coupled by a signal path 8 to output terminal 7 so as to sense when
generator 12 is charging bulk capacitor 16 and automatically disconnect battery 19 from
bulk capacitor 16 during such periods.
Figure 6 is a detailed schematic diagram of bulk capacitor charging circuit 10' of Figure 5
Many of the circuit elements and functions are essentially the same as circuit 10 of Figure
3 and to avoid repetition are not discussed again..
In an embodiment, batter}' control circuit 9 may have a current limiter including diode
D200, transistor Q200 and resistor R200. The current limiting transistor Q200 is turned on
by biasing at its gate from the positive terminal of battery 1 through resistors R93 and
R201 . Although the current limiier described herein is a linear current limiter, a switch
mode current limiter may also be used as appropriate.
In an embodiment, signal path 8 (Figure 5) and a portion of battery control circuit 9 define
a battery-disabling circuit that implements the function of preventing the charging of bulk
capacitor 16 by battery 9 when generator 12 (Figure 5) is operating as follows: Current
through node charges bulk capacitor 16 via resistor R98, a low Ohmic value resistor.
Some of the output current flows through a parallel path-—into the emitter of switching
element Ql and out of its base via resistor R 0 thereby turning on switching element
Ql. Switching element Ql then turns on switching element Q5 by applying voltage to its
gate via the voltage divider network consisting of resistors R85 and R92. Switching
element Q5 in turn prevents current flow through the current limiier transistor Q200 by
shorting the gate-source potential at transistor Q200 to zero, thereby ensuring that bul
capacitor 16 is charged up solely by the generator and not by battery 30. In this sense,
current limiter transistor Q200 also acts as an "on-off ' switching element.
Battery control circuit 9 may also have a battery-enabling switching element SWl. Under
battery operation, current flows from the positive terminal of battery 9 into bulk capacitor
16, through battery-enabling switching element S the current limiter circuit described
above, and back to the negative terminal of battery 30. Switch SWl disconnects batter}'
during the time th at the capacitor bank is being discharged into the solenoids. Batteryenabling
switching element S may be controlled by control logic 15, manually, or by
other suitable arrangement. Alternatively, the function implemented by battery-enabling
switching element SWl may instead be implemented by the current limiter transistor Q200
by using control logic 5 to selectively short the gate-source potential at transistor Q200 to
zero.
Figure 7 represents the operation of the battery-connection circuitry of Figure 6. Referring
to Figures 6 and 7, decision block 220 assesses whether battery-enabling switching element
SWl is open or closed, and decision block 222 assesses whether converter 14 is charging
bulk capacitor 16, i.e., whether the generator 12 (Figure 4) is operating. In the specific
embodiment disclosed, decision block 222 is implemented by switching elements Q , Q5,
current limiter transistor Q200 and resistors R98, R100, R93, R921. If either of the
conditions of decisions blocks 220, 222 exists, then battery 19 is disconnected from bulk
capacitor 16, as shown in state block 230. Otherwise, battery 19 is connected to bulk
capacitor 6 for charging, as shown in state block 232.
In summary, a downhole tool, drilling system, and a method and arrangement for charging
a . bulk capacitor have been described. Embodiments of the downhole tool may generally
have a housing, a bulk capacitor disposed in the housing and arranged for energy storage,
an electrical generator disposed in the housing and fluidly coupled to a supply of
pressurized fluid for prime moving the generator, and a single-ended primary-inductance
converter disposed in the housing and selectively coupled between the bu k capacitor and
the generator so as to transfer electric charge from the generator to the bulk capacitor when
the voltage across the bulk capacitor is between a lower set point and a higher set point.
Embodiments of the drilling system may generally have a drill string, a drill bit carried by
the drill string, a mud pulse telemetry device carried by the drill string, an electrical
generator coupled to the telemetry device and fluidly coupled to a supply of pressurized
fluid for prime moving the generator, and a single-ended primary-inductance converter
coupled to the telemetry device and the generator for powering the telemetry device.
Embodimen ts of the method for charging a bul capacitor may generally include providing
in the downhole tool a bulk capacitor that is electrically coupled to an actuator for
powering the actuator, providing in the downhole tool an electrical generator, coupling a
single-ended primary-inductance converter between the bulk capacitor and the generator so
as to transfer charge from the generator to the bulk capacitor, charging the bulk capacitor
by the generator via the converter, and at least partially discharging the bulk capacitor
through the actuator to power the actuator. Finally, embodiments of the apparatus for
charging a bu capacitor may generally include a bulk capacitor arranged for energy
storage, an electrical generator, a single-ended primary-inductance converter selectively
coupled between the bulk capacitor and the generator so as to transfer electric charge from
the generator to the bulk capacitor when the voltage across the bulk capacitor is between a
lower set point and a higher set point, and a battery selectively coupled across the bu
capacitor so as to transfer electric charge from the battery to the bulk capacitor when a .
battery-enabling switching element is in a first state and to disconnect the battery from the
capacitor when the battery-enabling switching element is in a second state.
Any of the foregoing embodiments may include any one of the following elements or
characteristics, alone or in combination with each other: A solenoid powered by the bulk
capacitor; a battery selectively coupled across the bulk capacitor so as to transfer electric
charge from the battery to the bulk capacitor when a battery-enabling switching element is
in a first state and to disconnect the battery from the bulk capacitor when the batteryenabling
switching element is in a second state; a battery-disabling circuit coupled between
the converter and the battery-enabling switching element and arranged to place the batteryenabling
switching element in the second state when the converter is transferring electric
charge from the generator to the bulk capacitor; a current imite coupled between the
battery and the bulk capacitor and arranged to limit electric current flow between the
battery and the bulk capacitor; the converter defines a two port network with first and
second input terminals and first and second output terminals, the second input terminal
being electrically connected to the second output terminal, the generator is electrically
connected to the first and second input terminals, and the bulk capacitor is electrically
connected to the first and second output terminals, the converter includes first and second
inductors and a first capacitor, each being characterized by first and second terminals, the
converter includes a diode defining an anode and a cathode, the first terminal of the first
inductor is electrically connected to the first input terminal, the first terminal of the first
capacitor is electrically connected to the second terminal of the first inductor, the anode of
the diode is electrically connected to the second terminal of the first capacitor, the cathode
of the diode is electrically connected to the first output terminal, and the second terminal of
the second inductor is electrically connected to the second input terminal, and the converter
includes a control switching element operatively coupled between the first terminal of the
first capacitor and the second input terminal; the first and second inductors are wound
about a common core; an oscillator operatively coupled to the control switching element so
as to cycle the control switching element and thereby transfer charge from the generator to
the bulk capacitor; a converter-enabling circuit operatively coupled between the bulk
capacitor and the oscillator and arranged to prevent cycling of the control switching
element when the voltage across the bulk capacitor exceeds the higher set point and to
allow cycling of the control switching element when the voltage across the bulk capacitor
drops below the lower set point; the converter-enabling circuit includes a comparator that
senses a potential that is proportional to the voltage across the bulk capacitor, and a
positive feedback path for providing hysteresis; a converter-disabling circuit operatively
coupled to the oscillator and arranged to prevent cycling of the control switching element
when the bulk capacitor is discharging; a telemetry device tha includes a solenoidoperated
valve for producing a pressure pulse in the supply of pressurized fluid; enabling
the converter when a voltage across the bulk capacitor drops be ow a lower set point so that
the generator charges the bulk capacitor; disabling the converter when the voltage across
the bulk capacitor exceeds a higher set point so that the generator does not charge the bulk
capacitor; providing a battery in the downhole tool; selectively coupling the battery by a
battery- enabling switching element across the bulk capacitor; enabling the battery-enabling
switching element so as to transfer electric charge from the battery to the bul capacitor;
disabling the battery-enabling switching element so as to disconnect the battery from the
bulk capacitor when the converter is transferring electric charge from the generator to the
bulk capacitor; disabling the converter when the bulk capacitor is discharging through the
actuator; actuating the valve; fluidly coupling the valve to a source of fluid; and creating
pressure pulses in the source of fluid by actuating the valve.
The Abstract of the disclosure is solely for providing the United States Patent and
Trademark Office and the public at large with a way by which to determine quickly from a
cursory reading the nature and gist of technical disclosure, and it represents solely one or
more embodiments.
While various embodiments have been illustrated in detail, the disclosure is not Hmited to
the embodiments shown. Modifications and adaptations of the above embodiments may
occur to those skilled in the art. Such modifications and adaptations are in the spirit and
scope of the disclosure.
WHAT IS CLAIMED
1. A downhole too , comprising:
a housing;
a bulk capacitor disposed in said housing and arranged for energy storage;
an electrical generator disposed in said housing and fluidly coupled to a supply of
fluid for powering said generator; and
a single -ended primary-inductance converter disposed in said housing and
selectively coupled between said bulk capacitor and said generator so as to transfer electric
charge from said generator to said bulk capacitor when the voltage across said bulk
capacitor is between a . lower set point and a higher set point.
The downhole tool of claim 1, further comprising:
an actuator powered by said bulk capacitor.
3. The downhole tool of claim further comprising:
a battery selectively coupled across said bulk capacitor by a battery control circuit
to transfer electric charge f om said battery to said bulk capacitor and to isolate said battery
from said bulk capacitor when said converter is transferring electric charge from said
generator to said bulk capacitor.
4. The downhole tool of claim 3, wherein:
said battery control circuit includes a current limiter coupled between said battery
and said bulk capacitor and arranged to limit electric current flow between said battery and
said bul capacitor.
5. The downhole tool of claim 1, wherein:
said converter defines a two port network with first and second input terminals and
first and second output terminals, said second input terminal being electrically connected to
said second output terminal;
said generator is electrically connected to said first and second input terminals, and
said bul capacitor is electrically connected to said first and second output terminals;
said converter includes first and second inductors and a first capacitor, each being
characterized by first and second terminals;
said converter includes a diode defining an anode and a cathode;
said first terminal of said first inductor is electrically connected to said first input
terminal, said first terminal of said first capacitor is electrically connected to said second
terminal of said first inductor, said anode of said diode is electrically connected to said
second terminal of said first capacitor, said cathode of said diode is electrically connected
to said first output terminal, and said second terminal of said second inductor is electrically
connected to said second input terminal; and
said converter includes a control switching element operatively coupled between
said first terminal of said first capacitor and said second input terminal.
6. The downhole tool of claim 5, wherein:
said first and second inductors are wound about a common core.
7. The downhole tool of claim 5, further comprising:
an oscillator operatively coupled to said control switching element to cycle said
control switching element
8. The downhole tool of claim 5, further comprising:
a converter-enabling circuit operatively coupled between said bulk capacitor and
said oscillator and arranged to prevent cycling of said control switching element when the
voltage across said bul capacitor exceeds said higher set point and to allow cycling of said
control switching element when the voltage across said bulk capacitor drops below said
lower set point.
9. The downhole tool of claim 8, wherein:
said converter-enabling circuit includes a comparator that senses a potential that is
proportional to the voltage across said bulk capacitor, and a positive feedback path for
providing hysteresis.
10. The downhole tool of claim 7, further comprising:
a converter-disabling circuit operatively coupled to said oscillator and arranged to
prevent cycling of said control switching element when said bulk capacitor is discharging.
11. The downhole tool of claim 2, wherein:
said downhole tool includes a telemetry device that includes a solenoid-operated
valve for producing a pressure pulse in said supply of fluid.
12. A drilling system, comprising:
a drill string;
a supply of fluid flowing through said drill string;
a drill bit carried by said drill string;
a mud pulse telemetry device carried by said drill string;
an electrical generator carried by said drill string and fiuidly coupled to said supply
of fluid for powering said generator; and
a single-ended primary-inductance converter coupled to said telemetry device and
said generator for powering said telemetry device.
13. .The drilling system of claim 2 further comprising:
a battery electrically coupled to said telemetry device by a battery control circuit for
selectively powering said telemetry device.
14. The drilling system of claim 12 wherein:
said telemetry device includes a valve actuated by a solenoid;
the drilling system further comprises a bulk capacitor electrically coupled to said
solenoid for powering said solenoid; and
said converter is electrically coupled to said bulk capacitor for charging said bulk
capacitor.
15. The drilling system of claim 12, wherein:
said converter defines a two port network with first and second input terminals and
first and second output terminals, said second input terminal being electrically connected to
said second output terminal;
said generator is electrically connected to said first and second input terminals, and
said bulk capacitor is electrically connected to said first and second output terminals;
said converter includes first and second inductors and a first capacitor, each being
characterized by first and second terminals;
said converter includes a diode defining an anode and a cathode;
said first terminal of said first inductor is electrically connected to said first input
terminal, said first terminal of said first capacitor is electrically connected to said second
terminal of said first inductor, said anode of said diode is electrically connected to said
second terminal of said first capacitor, said cathode of said diode is electrically connected
to said first output terminal, and said second terminal of said second inductor is electrically
connected to said second input terminal; and
said converter includes a control switching element operatively coupled between
said first terminal of said first capacitor and said second input terminal.
16. The drilling system of claim 15, wherein:
said first and second inductors are wound about a common core.
17. The drilling system of claim 15, further comprising:
an oscillator operatively coupled to said control switching element to-cycle said
control switching element.
18. The drilling system of claim 15, further comprising:
a converter-enabling circuit operatively coupled between said bulk capacitor and
said oscillator and arranged to prevent cycling of said control switching element when the
voltage across said bulk capacitor exceeds said higher set point and to allow cycling of said
control switching element when the voltage across said bulk capacitor drops below said
lower set point.
19. The drilling system of claim 8, wherein:
said converter-enabling circuit includes a comparator that senses a potential that is
proportional to the voltage across said bulk capacitor, and a positive feedback path for
providing hysteresis.
20. The drilling system of claim 17, further comprising:
a converter-disabling circuit operatively coupled to said oscillator and arranged to
prevent cycling of said control switching element when said bulk capacitor is discharging.
21. A method for operating a downhole tool, comprising:
providing in said downhole tool a bulk capacitor that is electrically coupled to an
actuator for powering said actuator;
providing in said downhole tool an electrical generator;
coupling a single-ended primary-inductance converter between said bulk capacitor
and said generator so as to transfer charge from said generator to said bulk capacitor;
charging said bulk capacitor by said generator via said converter; and
at least partially discharging said bu k capacitor through said actuator to power said
actuator.
22. The method of claim 2 1 further comprising:
enabling said converter when a voltage across said bulk capacitor drops below a
lower set point so that said generator charges said bulk capacitor; and
disabling said converter when the voltage across said bulk capacitor exceeds a .
higher set point so that said generator does not charge said bulk capacitor.
23. The method of claim 21 further comprising:
providing a battery in said downhole tool;
selectively coupling said battery by a battery control circuit across said bulk
capacitor;
transferring electric charge from said battery to said bulk capacitor; and
isolating by said battery control circuit said battery from said bulk capacitor when
said converter is transferring electric charge from said generator to said bulk capacitor.
24. The method of claim 2 further comprising:
disabling said converter when said bulk capacitor is discharging through said
actuator.
The method of claim 1 further comprising:
telemetering data by actuating said valve.
26. The method of claim 21 wherein:
said actuator is a solenoid that is operatively coupled to a valve; and
the method further comprises actuating said valve.
27. The method of claim 26 further comprising:
fluidly coupling said valve to a source of fluid;
creating pressure pulses in said source of fluid by actuating said valve.
28. An arrangement for charging a bulk capacitor, comprising:
a bulk capacitor arranged for energy storage;
an electrical generator;
a single-ended primary-inductance converter selectively coupled between said bulk
capacitor and said generator so as to transfer electric charge from said generator to said
bulk capacitor when the voltage across said bulk capacitor is between a lower set point and
a higher set point; and
a battery selectively coupled across said bulk capacitor so as to transfer electric
charge from said battery to said bulk capacitor when a battery-enabling switching element
is in a first state and to disconnect said battery from said capacitor when said batteryenabling
switching element is in a second state.
29. The arrangement of claim 28, further comprising:
a battery-disabling circuit coupled to said converter and arranged to place said
battery-enabling switching element in said second state when said converter is transferring
electric charge from said generator to said bulk capacitor; and
a current limiter coupled between said battery and said bulk capacitor and arranged
to limit electric current flow between said battery and said bulk capacitor.
30. The arrangement of claim 28, wherein:
said converter defines a two port network with first and second input terminals and
first and second output terminals, said second input terminal being electrically connected to
said second output terminal;
said generator is electrically connected to said first and second input terminals, and
said bulk capacitor is electrically connected to said first and second output terminals;
said converter includes first and second inductors and a first capacitor, each being
characterized by first and second terminals;
said converter includes a diode defining an anode and a cathode;
said first terminal of said first inductor is electrically connected to said first input
terminal, said first terminal of said first capacitor is electrically connected to said second
terminal of said first inductor, said anode of said diode is electrically connected to said
second terminal of said first capacitor, said cathode of said diode is electrically connected
to said first output terminal, and said second terminal of said second inductor is electrically
connected to said second input terminal; and
said converter includes a control switching element operatively coupled between
said first terminal of said first capacitor and said second input terminal.
31. The arrangement of claim 30, further comprising:
an oscillator operatively coupled to said control switching element so as to cycle
said control switching element;
a converter-enabling circuit operatively coupled between said bulk capacitor and
said oscillator and arranged to prevent cycling of said control switching element when the
voltage across said bulk capacitor exceeds said higher set point and to allow cycling of said
control switching element when the voltage across said bulk capacitor drops below said
lower set point wherein said converter-enabling circuit includes a comparator that senses a
potential that is proportional to the voltage across said bulk capacitor, and a positive
feedback path for providing hysteresis; and
a converter-disabling circuit operatively coupled to said oscillator and arranged to
prevent cycling of said control switching element when said bulk capacitor is discharging.