Patent Publication Number: US-2016237790-A1

Title: Bulk capacitor charging circuit for mud pulse telemetry device

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to oilfield equipment, and in particular to downhole tools. 
     BACKGROUND 
     Various downhole 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 7600 μg, 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 limiters are inefficient. For example, while charging the bulk capacitor from 60V to 90V at 700 mA, the average power lost per charging cycle is 10.5 watts. 
     Alternatively, an electrical generator powered 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 tool, 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 bulk capacitor from either a battery 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: 
         FIG. 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  FIG. 2 ; 
         FIG. 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; 
         FIG. 3  is a detailed schematic diagram of the bulk capacitor charging circuit of  FIG. 2 , showing details of modified a single-ended primary-inductance converter; 
         FIG. 4  is a flow chart diagram showing logic implemented by the bulk capacitor charging circuit of  FIG. 3 ; 
         FIG. 5  is a simplified block level schematic diagram of the bulk capacitor charging circuit of  FIG. 2  augmented by a battery and battery control circuit to allow charging the bulk capacitor either from the converter or from a battery; 
         FIG. 6  is a detailed schematic diagram of the bulk capacitor charging circuit of  FIG. 5  according to an embodiment; and 
         FIG. 7  is a flow chart diagram showing battery-connection logic implemented by the bulk capacitor charging circuit of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
     Attention is directed to  FIG. 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  FIG. 1  is generally identified by the numeral  20 . 
     MWD system  20  may include land drilling rig  22 . However, teachings of the present disclosure may be satisfactorily used in association with offshore platforms, semi-submersible, 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 or 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  32  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  100  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  91  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  91  having a telemetry device including a bulk capacitor charging circuit  10  or  10 ′ as described below with respect to  FIGS. 2-4 . However other various types of tools may be included in bottom hole assembly  90  as appropriate. 
     Measurement 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 part 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  100 . 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 . 
       FIG. 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  ( FIG. 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  16 . That is, converter  14  selectively transfers charge from generator  12  to bulk 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  91 . In an embodiment, downhole tool  91  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  16  may include multiple discrete capacitors connected together in series, parallel, or a combination thereof. 
     Converter  14  may be located in a downhole tool  91  ( FIG. 1 ), which has a housing  92  that protects the electronic components from the hazards of the downhole environment. Generator  12  and/or bulk capacitor  16  may also be located in housing  92  with converter  14 , as shown in  FIG. 2 . Alternatively, converter  14 , generator  12 , and bulk capacitor  16  may be located in one or more downhole components within bottom hole assembly  90 , for example, as shown in  FIG. 5 . 
     Converter  14  defines a two port network, characterized by a pair of input terminals  13  and a pair of output terminals  17 . Generator  12  is connected to input terminals  13  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 V BC  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 more solenoid-operated valves (not illustrated) for creating mud pressure pulses, control logic  15 , 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 V BC  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 1 , L 2 , capacitor C 3 , diode D 22 , and control switching element Q 13 , which cycles on and off to transfer charge. In 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 Q 13 . Inductors L 1  and L 2  may be discrete uncoupled components, or they may be wound on the same core so as to be coupled. Coupling inductors L 1  and L 2  enables the inductance values to be halved and thus saves space. 
       FIG. 3  is a more detailed schematic diagram of the bulk capacitor charging circuit  10  of  FIG. 2 . In an embodiment, control switching element Q 13  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 Q 13  may be determined by an oscillator, which may be connected to control switching element Q 13  via a driving circuit. In one embodiment, the oscillator is a Schmitt Trigger oscillator formed of a comparator U 1 , resistors R 117 , R 118 , and R 5 , and a capacitor C 44 . 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 Q 6  and Q 9  form the driving circuit that connect the oscillator to control switching element Q 13  via a capacitor C 41  and resistors R 81 , R 94 . 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 13 . 
     One of the advantages of a SEPIC over a conventional regulated power supply circuit is that a snubber circuit is not required to protect the system from 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 1  may be added to enhance snubbing. Capacitor C 1  does not make circuit  10  less efficient, as its charge is added to the charge of the bulk capacitor  16 . 
     Resistors R 4 , R 5  and R 116  and a voltage source V CC  are used to provide feed-forward from generator  12  ( FIG. 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 13  almost constant. The feed-forward function requires that the switching element driver circuitry inverts the output of the oscillator, as it does in circuit  10  of  FIG. 3 . 
     Switching elements Q 11  and Q 12  are connected so as to effectively form a logical OR-gate. If the voltage on the gate of either switching element Q 11 , Q 12  is high, then capacitor C 44  is shorted and the oscillator stops running, as described below. 
     In an embodiment, circuit  10  may include a converter-enabling circuit coupled between bulk capacitor  16  and the oscillator that is used to stop the oscillator from running when bulk capacitor  16  has charged up to a higher set point, its predetermined fully charged level, as follows: A voltage divider network of resistors R 109  and R 106  sense the voltage V BC  across bulk capacitor  16 . The divided voltage is compared with a reference voltage V 2  applied to the inverting input of a comparator U 2 . When the divided voltage exceeds reference voltage V 2 , comparator U 2  outputs a logic high, which turns on switching element Q 11 , which in turn shorts the inverting input of comparator U 1  to ground, thereby stopping oscillation. Resistor R 113  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 V BC  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  16  is required to discharge through the solenoids for valve actuation, as follows: A control signal  20  from appropriate control logic  15  is connected to the non-inverting input of a comparator U 3  via a resistor R 2 . A reference voltage V 1  provides a predetermined set point for the comparator U 3  at its inverting input. When control signal  20  is high, comparator U 3  outputs a logic high, which turns on switching element Q 12 , which in turn shorts the inverting input of comparator U 1  to ground, thereby stopping the oscillator from running and control switching element Q 13  from cycling. This optional function results in a more efficient operation of circuit  10 . 
     Switching element Q 12  also shuts down the oscillator if the drain current through control switching element Q 13  is excessive. This drain current is sensed by resistor R 6  and fed to the comparator U 3  via resistors R 84 , R 85  and capacitor C 2 . Reference voltage V 1  provides a predetermined set point for the comparator U 3 . Resistor R 83  provides hysteresis. 
       FIG. 4  represents the operation of the bulk capacitor charging circuit  10  of  FIG. 3 . 
     Referring to  FIGS. 3 and 4 , decision block  200 , which assesses whether the bulk capacitor  16  is actively discharging into the solenoid, is implemented by control logic  15 , comparator U 3  and its associated circuitry, and switching element Q 12 . Decision block  202  assesses whether the bulk capacitor  16  is fully charged, and it is implemented by the voltage divider resistors R 109 , R 106 , comparator U 2 , feedback resistor R 113 , and switching element Q 11 . 
     Decision block  204  assesses whether the current flowing through the drain terminal of control switching element Q 13  is too high, and it is implemented by resistor R 6 , comparator U 3  and its associated circuitry, and switching element Q 12 . 
     If any one or more of the conditions of decisions blocks  200 ,  202 ,  204  exists, i.e., if the bulk capacitor  16  is actively discharging, if the bulk capacitor  16  is fully charged, or if there is excessive drain current through control switching element Q 13 , then the oscillator is disabled, as shown in state block  210 . 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 V BC  across bulk capacitor  16  remains above the lower set point, which is determined by the value of the hysteresis resistor R 113  as described above. Such logic is depicted in  FIG. 4  by decision block  206 . 
       FIG. 5  is a block level schematic diagram of a bulk capacitor charging circuit  10 ′. Circuit  10 ′ of  FIG. 5  is essentially the same as circuit  10  of  FIG. 2 , except it is augmented to allow charging of the bulk capacitor  16  from either generator  12  connected at input terminals  13  or from a battery  19  connected at output terminals  17  via a battery control circuit  9 . Although discussed in terms of a singular battery  19 , 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  16  via battery control circuit  9 . In an embodiment, battery control circuit  9  may perform one or more of the following functions: Connecting battery  19  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  16  is being discharged into the actuator; and preventing the charging of bulk capacitor  16  by battery  19  when generator  12  is operating by disconnecting battery  19  from bulk capacitor  16 . 
     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  19  to bulk capacitor  16  when a battery-supply mode of operation is desired by the operator and when in a second state to disconnect battery  19  during the time that bulk capacitor  16  is being discharged into the actuator. Battery control circuit  9  may also include a battery-disabling circuit that is coupled by a signal path  8  to output terminal  17  so as to sense when generator  12  is charging bulk capacitor  16  and automatically disconnect battery  19  from bulk capacitor  16  during such periods. 
       FIG. 6  is a detailed schematic diagram of bulk capacitor charging circuit  10 ′ of  FIG. 5 . Many of the circuit elements and functions are essentially the same as circuit  10  of  FIG. 3  and to avoid repetition are not discussed again. 
     In an embodiment, battery control circuit  9  may have a current limiter including diode D 200 , transistor Q 200  and resistor  8200 . The current limiting transistor Q 200  is turned on by biasing at its gate from the positive terminal of battery  19  through resistors R 93  and R 201 . Although the current limiter described herein is a linear current limiter, a switch mode current limiter may also be used as appropriate. 
     In an embodiment, signal path  8  ( FIG. 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  19  when generator  12  ( FIG. 5 ) is operating as follows: Current through node  11  charges bulk capacitor  16  via resistor R 98 , a low Ohmic value resistor. 
     Some of the output current flows through a parallel path—into the emitter of switching element Q 1  and out of its base via resistor R 100 —thereby turning on switching element Q 1 . Switching element Q 1  then turns on switching element Q 5  by applying voltage to its gate via the voltage divider network consisting of resistors R 85  and R 92 . Switching element Q 5  in turn prevents current flow through the current limiter transistor Q 200  by shorting the gate-source potential at transistor Q 200  to zero, thereby ensuring that bulk capacitor  16  is charged up solely by the generator and not by battery  30 . In this sense, current limiter transistor Q 200  also acts as an “on-off” switching element. 
     Battery control circuit  9  may also have a battery-enabling switching element SW 1 . Under battery operation, current flows from the positive terminal of battery  19  into bulk capacitor  16 , through battery-enabling switching element SW 1 , the current limiter circuit described above, and back to the negative terminal of battery  30 . Switch SW 1  disconnects battery  19  during the time that the capacitor bank is being discharged into the solenoids. Battery-enabling switching element SW 1  may be controlled by control logic  15 , manually, or by other suitable arrangement. Alternatively, the function implemented by battery-enabling switching element SW 1  may instead be implemented by the current limiter transistor Q 200  by using control logic  15  to selectively short the gate-source potential at transistor Q 200  to zero. 
       FIG. 7  represents the operation of the battery-connection circuitry of  FIG. 6 . Referring to  FIGS. 6 and 7 , decision block  220  assesses whether battery-enabling switching element 
     SW 1  is open or closed, and decision block  222  assesses whether converter  14  is charging bulk capacitor  16 , i.e., whether the generator  12  ( FIG. 4 ) is operating. In the specific embodiment disclosed, decision block  222  is implemented by switching elements Q 1 , Q 5 , current limiter transistor Q 200  and resistors R 98 , R 100 , R 93 , R 921 . 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  16  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 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. 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. Embodiments of the method for charging a bulk 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 bulk 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 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 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 battery-enabling 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 battery-enabling switching element in the second state when the converter is transferring electric charge from the generator to the bulk capacitor; a current limiter 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 that includes a solenoid-operated valve for producing a pressure pulse in the supply of pressurized fluid; enabling the converter when a voltage across the bulk capacitor drops below 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 bulk 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 limited 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.