# Patent

## Title
Electric horizontal directional drilling machine system

## Abstract

An electric horizontal directional drilling machine. An electric horizontal directional drilling machine is powered by an electric power assembly. The power assembly is made up of a fuel cell and inverter, or multiple fuel cells with synchronized inverters, are used to power an electric motor controller and electric motor. The electric motor operates hydraulic pumps used to advance a drill string and downhole tool through the earth and operate various machine functions. Mechanical functions of the drilling machine may also be satisfied through the use of electric rotary actuators (e.g., motors) and linear actuators (e.g., linear motors and solenoids).

## Background
CROSS REFERENCE TO RELATED APPLICATION
This application claims the benefit of U.S. application Ser. No. 11/456,800 filed Jul. 11, 2006, now U.S. Pat. No. 7,461,707, which claims the benefit of U.S. Provisional Application No. 60/698,244 filed Jul. 11, 2005, the contents of which are incorporated fully herein by reference.


FIELD OF THE INVENTION
The present invention relates to machines used to form horizontally deviated boreholes in the upper portion of the earth's surface. More particularly, the present invention relates to electrically powered machines for horizontal direction drilling.
BACKGROUND OF THE INVENTION
Horizontal directional drilling (HDD) is a widely accepted construction alternative to open-cut trenching. The use of HDD is preferred in many construction applications because it can emplace utility lines and conduits, such as power lines, gas lines, telephone lines, and fiber optic cables, without disturbing surface structures (roads and sidewalks), existing landscaping, trees, and shrubs; or when open-cut trenching is impractical or impossible because of existing surface structures or other obstacles such as rivers, streams, lakes, and ponds. HDD emplaces these utility structures by forming a borehole under the surface of the earth without open-cut trenching.
HDD activities are intrinsically transient or itinerant. The HDD machine typically is brought to the jobsite by truck or trailer, along with all necessary drilling components, tools, and adjuncts (drill rod, water tanks, water, drilling mud, conduits, and the like). The HDD machine is taken from the truck or trailer and placed on the ground in a proper orientation with respect to the intended drill path. A small pit, called the entrance pit, typically is dug slightly ahead of the HDD machine to allow the drill rod and drill bit to enter the ground at the correct orientation. The HDD machine then advances the drill rod through the ground as it is navigated by various means known to those skilled in the art. The HDD machine typically continues to advance the drill rod and drill bit until the drill bit reaches the desired location. Typically, a small pit (called the exit pit or target pit) is dug as the far terminus of the bore path.
The product line (typically a power line, gas line, telephone line, fiber optic cable, or other underground utility) is then installed in the borehole by any of several different techniques. If the product line is small and of a suitable construction, it may be attached to the end of the drill bit—or to a special fitting which replaces the drill bit—and simply may be pulled through the newly-created bore hole as drill rod is removed from the machine end of the drill string. In other cases, a small-diameter conduit (for example, PVC plastic conduit) may be attached to the end of the drill bit and pulled through the newly created bore hole as drill rod is removed from the machine end of the drill string. Once the conduit is emplaced, product lines may be either pulled or blown through the newly emplaced conduit. If the product lines are large in diameter, as might be the case for water lines, the drill bit is replaced by a larger-diameter backreamer which is, in turn, connected to the product line or a conduit. The backreamer enlarges the borehole as the backreamer and product line or conduit are pulled back through the borehole while drill rod is removed from the machine end of the drill string. After the product is installed, connections are made at the entrance and exit pits and the pits are then filled with earth, at which time the HDD machine with its related apparatus is placed back on the truck or trailer for removal to the next job site or to a storage facility in anticipation of the next job.
A typical contemporary HDD machine consists of a number of specialized mechanisms and mechanical devices. For example, the prime mover (or primary source of operating power) is an internal combustion engine. The internal combustion engine is almost always a diesel engine, although smaller units may occasionally employ gasoline engines. The internal combustion engine then drives mechanisms and devices which generate thrust and pullback forces (advancing or retracting the drill string) and rotational forces (rotating the drill string in the desired direction). The internal combustion engine also operates other equipment, such as a hydraulic pump, providing operating power to various machine mechanisms such as pipe grippers (vise jaws which grip the drill pipe while making or breaking connections between individual drill rod segments), hydraulic motors providing operating power to install anchoring augers, positioning mechanisms to raise and lower the machine frame, and rod handlers to reduce the amount of manual effort required to add or store drill rod before or after use. Machine operation is often done using hydraulic valves and hydraulic cylinders; although some HDD machines have machine controllers which are electrically powered and which, in some cases, provide varying degrees of machine automation.
Internal combustion engines are the mainstay of portable construction equipment, and they have a great many desirable features for industrial applications. These features include portability, maturity of the technology, generally acceptable reliability, and the use of readily available fuel. However, other operating characteristics of internal combustion engines are equally well known but much less desirable. Internal combustion engines are noisy, particularly in the sizes required for underground construction, making their use in residential and urban settings increasingly objectionable. Internal combustion engines are known to produce various pollutants, particularly small particulate emissions, sulfur oxides, and nitrous oxides. Even with uncommon care, the fuels and lubricants required by internal combustion engines inevitably will be leaked or spilled, and the resulting soil contamination is increasingly objectionable. Diesel engines are especially well known for these undesirable operating characteristics. Such undesirable operating characteristics are a particular problem for the underground construction industry because diesel engines are the most common internal combustion engines in underground construction equipment.
The operational drawbacks of internal combustion engines have been tolerated, until now, because HDD activities are essentially transient in nature. However, the mood of the times is changing. Noise abatement is a serious issue in many communities, and air and soil pollution are equally serious issues and increasingly frequent legislative issues. Noise, air and soil pollution, and similar matters are important domestically, and some European requirements are far more stringent than those in the United States. Pollution and other environmental considerations are normally addressed by requiring noise abatement and pollution control equipment on the internal combustion engine, resulting in added complexity, maintenance difficulties, and additional cost.
The present invention teaches the use of electrically powered underground construction and ancillary equipment to avoid the drawbacks associated with internal combustion engines. As an interim step, it may be necessary to use a remote electrical generator set to provide portable operating power to the operative HDD equipment set. However, the ultimate objective of the present invention is to provide operating power by means of fuel cells. The advantages of this invention are set forth in the following paragraphs.
SUMMARY OF THE INVENTION
This invention is directed to the replacement of internal combustion engines by means which permit operation from a variety of electrical sources. A fuel cell and inverter, or a manifold of multiple modular fuel cells with synchronized inverters, are especially preferred embodiments of this invention. Necessary mechanical functions conventionally accomplished with internal combustion engines and hydraulic devices are, in most preferred embodiments, satisfied through the use of electric rotary actuators (e.g., motors) and linear actuators (e.g., linear motors and solenoids).
The present invention is directed to an electrically powered horizontal direction drilling machine. The machine comprises an electric power assembly, an electric motor operatively connected to the power assembly, a drill string, having a first end and a second end, a drive system powered by the electric motor and operatively connectable to the first end of the drill string, and a downhole tool connectable to the second end of the drill string. The power assembly comprises at least one direct current power source, and an inverter operatively connected to each of the at least one power sources. The machine is further characterized in that the drive system is adapted to advance the drill string and the downhole tool through the earth



DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a horizontal directional drilling machine of the present invention.
FIG. 2 is a block diagram for an electrically powered drilling machine designed in accordance with the present invention.
FIG. 3 illustrates a fuel cell-inverter combination for use with the present invention.
FIG. 4 shows a three phase example of fuel cell-inverter combinations for use with the present invention.
FIG. 5 illustrates single phase example of fuel cell-inverter combinations for use with the present invention.



DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention contemplates a complete system-level redesign with realignment of existing HDD functions, as will be discussed in detail. A simple, practical, and immediate first embodiment replaces the internal combustion engine prime mover with an electric motor or electric motors while retaining conventional hydraulic machine mechanisms. A more desirable second embodiment would replace all present-day hydraulic functions, actuators, and effectors with electrical apparatus, specifically including motors for rotary functions and linear actuators or other arrangements for thrust. The most desirable embodiment would incorporate fuel cells as the primary power source rather than a conventional electromechanical generator set or an electrical connection to the commercial electrical power grid. The advantages and implementation details of a fuel cell embodiment will be discussed in detail below.
The scope of this invention extends to all necessary ancillary apparatus, including vacuum extractors, mud mixers, and mud pumps. In all cases, replacement of internal combustion engines by electrical actuators is highly desirable, and the use of fuel cells to provide operating power to the electric actuators is most desirable.
With reference now to the drawings in general and to FIG. 1 in particular, there is shown therein a schematic representation of a HDD drilling machine 10. The machine 10 operates using an energy source 12. In conventional HDD drilling machines, the energy source 12 is a petroleum-based fuel such as gasoline or diesel fuel. In accordance with the present invention as yet to be described, the fuel source 12 may be electrical power provided by various sources. In a conventional HDD drilling machine 10 where the energy source 12 is petroleum-based fuel, the energy source is converted to mechanical power by the prime mover or movers 14—such as gasoline or diesel internal combustion engines—which convert the hydrocarbon fuel's energy content to mechanical power by the combustion process, as is well known in the mechanical arts. The engines, or prime movers 14, are connected to and drive the rotation and movement of the drill string 15 and consequently the downhole tool 17.
The HDD machine 10 also makes use of many different actuators 16 and effectors for various machine functions. These actuators 16 and effectors are often hydraulic mechanisms deriving their operating power from hydraulic pumps driven by the prime mover 14. Other devices in the actuator/effector 16 category are control valves and the like which direct hydraulic energy to hydraulic cylinders or other apparatus to produce a desired action.
There are, at the system level, certain system functions 18 which may or may not be present on a given HDD machine 10. Examples of system-level functions 18 are fluid handling components 20 (mud mixers and mud pumps) which provide the drilling fluids normally required during the HDD process; navigation, guidance, and control elements 22 which provide the HDD machine operator with information needed to guide the drill bit through the subsurface to the desired exit point; machine automation and control functions 24 which reduce the amount of manual effort required to perform the bore; and obstacle detection apparatus 26 which, in conjunction with the navigation, guidance, and control elements 22, help avoid existing subsurface infrastructure and perform a safer bore.
Many of the system functions operate somewhat or entirely independently of other system functions. For example, navigation, guidance, and control elements 22 ordinarily are provided from units which are functionally separate from the machine control functions. The integrating entity in commercial HDD practice is usually the HDD machine operator, and successful integration of the disparate system elements is largely a matter of individual operator interest, ability, and attentiveness.
Referring now to FIG. 2, a detailed block diagram of a HDD system in accordance with the present invention is shown. The information in FIG. 2 may be related to the high-level function description provided by FIG. 1 as discussed in detail in the following paragraphs.
Power Sources
The HDD system 30 of the present invention may draw operating power from a number of significantly different electrical power sources. Electrical power sources may be alternating current (AC) electrical power sources. As shown in FIG. 2, suitable AC power sources would include, but are not limited to, the commercial electrical power grid 32, diesel or gasoline 34, and LPG or other fuel gas electromechanical generator sets 36. Satisfactory electromechanical generator sets are available from a number of commercial sources and represent mature technologies. The output of most generator sets 36 typically is a single-phase or multi-phase alternating current (AC) waveform, but an AC waveform is not a requirement. As will be discussed later, the present invention could make highly effective use of generator sets with direct current (DC) outputs.
The HDD system 30 of the present invention may also use direct current (DC) electrical power sources. The preferred DC power source, as shown in FIG. 2, is a fuel cell 38 which, as is known to those skilled in the appropriate arts, produces DC electricity from a variety of energy feedstocks without combustion—the energy conversion is produced by direct chemical reaction. Thus, suitable fuel cell 38 feedstocks may be—depending on fuel cell type—gasoline, suitably prepared diesel fuel, JP-4, LPG liquids, compressed natural gas, hydrogen, kerosene, and other typically hydrogen-rich feedstock fuels. Among the many advantages of fuel cells 32 is the ability to produce electrical energy from familiar, commonly available petroleum-based fuels without the need for combustion. The byproducts of fuel cell 32 operation are generally water and carbon dioxide, but without the noxious gaseous and particulate byproducts associated with combustion. However, alternative sources of DC electricity could be used, including such sources as biomass digesters 40, solar power or lead-acid storage batteries 42, and the like.
The HDD system 30 of the present invention includes two devices which permit the HDD machine 30 to operate from almost any electrical power source. The first device is a rectifier assembly 44 which is used-to produce DC power from an AC source, as is well known in the electrical arts. The second device is an inverter 46, also known to those skilled in the electrical arts, which is used to produce AC power from a DC source. As will be discussed below, a particular type of inverter 46 is a critical system component for effective fuel cell 38 use.
Fuel Cells and Synchronized Inverters
The ability to use electrical power from a variety of sources is a particularly acute requirement for the successful application of fuel cells 38, a highly preferred source of electrical power. A fuel cell 38 typically delivers DC power at various voltages. Contemporary fuel cells 38 with power ratings in the multiple kilowatt range often provide either 28 Volt or 48 Volt DC power, but fuel cell output voltages are not yet standardized. Fuel cells are in an early stage of development at the present time, and fuel cells capable of providing power for machines with horsepower ratings required for HDD applications are relatively few. However, 5 kW to 10 kW rated fuel cells are commercially available on a limited basis, although devices of widely varying power ratings are available in one form or another.
This is a serious complication for would-be fuel cell 38 users who must provide a prime mover 14 (i.e., a large electric motor or motors) with adequate power for the task at hand, but who also must cope with power sources of significantly different characteristics and capabilities. The present invention provides a modular solution to the source power/load power problem.
It is a specific feature of the present invention to provide a means whereby fuel cells 38 may be used in modular or even standardized modular, power increments. For the sake of example only, assume the existence of a reliable standard commercial 5 kW fuel cell 38 unit. We now describe how multiple 5 kW fuel cells may be economically combined to supply operating power, in 5 kW increments, to a wide range of different electric motors by the use of synchronized AC power inverters.
For example, assume an HDD machine 30 may require 20 HP maximum shaft horsepower for an HDD application. For this discussion, assume the conversion between mechanical power and electrical power is given by the well-known approximation 1.00 HP=0.75 kW. Then, a 100% efficient mechanical device delivering 20 HP shaft horsepower would require 15 kW of source electrical power. It would be particularly desirable to provide this power using multiple standard modular fuel cells 38 of, say, 5 kW rated capacity if such fuel cells were readily available from a commercial source. This desire to achieve the required power capacity may be realized by multiple inverter units 46 capable of being synchronized with other inverters using a synchronizer 48.
As shown in FIG. 3, the fuel cell 38 provides DC power and is operatively connected to the inverter 46. As previously discussed, the fuel cell 38 may have a feedstock input 50 and an exhaust or byproduct capability 52. The inverter 46 converts the DC power from the fuel cell to AC, and may be used with a clock 54 and synchronizer 48 for combining multiple fuel cell 38 inputs. The AC power output from the inverter 46 may also be provided to a transformer unit 56 for appropriate voltage regulation as needed.
Again, for the sake of example only, assume 100% efficient energy conversion in the electrical inverters. The arrangement of FIG. 3 allows fuel cells 38 to produce power in 5 kW increments at a nominal output voltage of, for example, 48 VDC. Using synchronous inverters 46, electrical power from each individual fuel cell 38 is efficiently transformed and combined into a single AC power source especially advantageous for use with commercially available AC motor controllers and AC motors. If a larger, later, HDD machine 30 should require a 40 HP (30 kW) electric motor, six identical 5 kW fuel cell/inverter units could be used to produce the required electrical power using a single standardized fuel cell/inverter modular power unit. The flexibility, redundancy, and economies of scale of this arrangement are noteworthy and are identified as particular objectives of the present invention.
In addition, the ability to synchronize power inverters now allows the ability to mix fuel cell units of different power capacities and operating voltages. For example, it now does not matter that one fuel cell may be rated at 5 kW, 28 VDC, while another fuel cell may be rated at 10 kW, 48 VDC—if both inverters are capable of producing the same AC output voltage from a reasonable range of DC input voltages and may be synchronized, each fuel cell can operate in optimal fashion while relying on the synchronization of their respective inverters to present a single AC power line with desired AC output amplitude and frequency. Thus, the wide-input synchronized inverter is a key component in the ability to use mixed-characteristic fuel cells and other DC power sources to produce AC power suitable for HDD machine use.
FIG. 4 illustrates one way to implement the inventive concept. In FIG. 4, each fuel cell 38 and inverter 46 makes up a single-phase AC power unit 58. Each fuel cell/inverter power unit 58 is designated as master unit or follower unit according to its position in a power assembly 60—the fuel cell/inverter power units 58 themselves are identical and completely interchangeable. The AC electrical power output from each single-phase fuel cell/inverter power unit 58 may be connected using transformers 56 to a three-phase transformer or, as shown, is directly connected with others to form a power assembly and in particular a three-phase power source 62, for a typical electric motor controller. A three-phase power transformer, if used, may be either a wye-connected or delta-connected transformer.
Proper phasing between inverters 46 is maintained by electrical lead/lag networks 64 (note that 240° of lag is electrically equivalent to 120° of lead) in the power connection assembly 60, making it possible for all inverters to be identical. Likewise, the master clock 54 setting the frequency is located on the assembly 60—each single-phase fuel cell/inverter unit 58 synchronizes itself to the master clock. In a preferred implementation, the master clock 54 will incorporate the phasing networks, or their digital equivalent, to produce three tightly synchronized clock signals which establish highly accurate phase relationships between the individual units. According to the local requirements in the geographical location in which a given HDD machine 30 is to be used, the master clock 54 may be adjusted to provide 50 Hz operation, rather than 60 Hz operation, if desired. Other frequencies of operation (for example, 400 Hz) can be used if desired—the frequencies used in this discussion are presented for illustration only and should not be construed to be limiting in any respect.
Referring now to FIG. 5, there is shown therein a single-phase implementation of a power assembly for the present invention. For simplicity, the individual fuel cell 38 and inverter 46 combination units 58 do not contain individual transformers. Instead, each unit is connected to a corresponding winding on a large multiple-primary, single-secondary transformer 66 which then combines the power from each fuel cell/inverter combination unit 58 by transformer action. In the single-phase case, no master/follower designation is necessary since the output of each unit 58 is understood to maintain the same phase relationship with the master clock 54. A control unit 67 is preferably included and operatively connected to the inverters 46 in each of the power units 58. The control unit 67 provides control signals to the inverters 38, allowing the inverters to maintain frequency and amplitude in response to the control signals. This arrangement is especially flexible, as the individual fuel cell/inverter units 58 may have considerably different ratings as individual units—the process of power addition is done by the multiple-primary transformer 66. Those familiar with the electrical arts will appreciate that the arrangement of FIG. 5 may be generalized to a poly-phase arrangement within the spirit of this teaching.
FIGS. 4 and 5 are presented for purposes of illustration only and are not to be considered limiting in any respect. There is a rich background of technology in the electrical arts associated with electrical power generation and electrical power distribution, and teachings from this pool of knowledge may be used to form many other combinations which are considered to be within the scope of this invention.
Prime Movers
The prime movers 14 of present-day HDD machines are internal combustion engines. While gasoline internal combustion engines are not unknown in the HDD industry, the diesel internal combustion engine is unquestionably the predominant power source. Internal combustion engines have a long history in portable power applications—they are a mature technology with hitherto acceptable reliability, and they use readily available fuels from an exceptionally well-developed distribution network. However, internal combustion engines—and diesel engines in particular—are noisy, smelly mechanical devices which require regular, frequent maintenance and which produce noxious pollutants and particulate emissions as consequences of combustion. The perceived acceptability of internal combustion engines is, at least in part, something of a fiction sustained by familiarity with these very common devices and simple accommodation and acceptance of their less desirable operating characteristics. Electric motors, on the other hand, are capable of truly remarkable operating lifetimes if they are given a modicum of maintenance and if they are not abused.
For these reasons and others, an electric HDD machine 30 is a decided improvement over one powered by a diesel engine. Routine field operating experience with experimental electric HDD machines over a period of several years supports this assertion. Electric motors are very quiet, they are very clean, they require very little maintenance, and they are very reliable.
With reference again to FIG. 2, the prime mover 14 for use with the HDD machine 30 of the present invention is preferably composed of two distinct yet tightly interconnected pieces—the electric motor proper 68 and the motor controller 70. The electric motor 68 may be a single-phase or polyphase AC machine, but it may also be a DC machine. The motor 68 is operatively connected to the drive system 72 of the HDD machine 30 to control thrust/pullback and rotation of the drill string.
In most cases, the HDD machine 30 will preferably use one or more three-phase AC motors or one or more large DC motors as the prime mover 14. Each motor type (AC or DC) has its own operating characteristics, and engineering tradeoffs between motor types can be made to obtain operating characteristics most important to a particular HDD machine 30 design. For example, the electric HDD machines 30 referenced above may incorporate three-phase variable speed AC motors to provide the greatest flexibility in controlling direction and speed of rotation, even though a DC motor might be the motor of choice for another type of HDD machine in which exceptional low-speed rotating torque is the predominant consideration. Such differences in electric motor operating characteristics can give electric motors pronounced advantages over internal combustion engines in many operating regimes.
The other portion of the prime mover 14—the motor controller 70—is a device which translates operator commands into appropriate modifications of the motor's 68 power source. The motor controller 70 may do nothing more than control motor 68 speed and the direction of rotation, or the controller may provide sophisticated programming with controlled torque profiles, different operating speed ranges, programmed accelerations and decelerations, and high-speed data communication between the motor controller 70, a computer (not shown), and a display unit (not shown). The sophistication of existing commercial motor controllers gives an electric HDD unit functional capabilities not readily available with conventional mechanical and hydraulic HDD machine controls.
In many cases, the motor controller 70 contains a power supply which converts AC input power to DC, then inverts the DC power thus produced to provide variable frequency, variable amplitude polyphase AC power to the motor 68. Such controllers 70 may be used very effectively with the fuel cell 38 and synchronous inverter 46 combination already described, since many motor controllers can operate from single-phase AC, polyphase AC, or even DC input power of suitable magnitude.
Actuators and Effectors
Machine actuators and effectors 16 are those mechanisms which provide functional capability to the machine 30 allowing the operator to add or remove drill pipe in the drill string using pipe grippers 74, store and retrieve drill pipe in the pipe box using drill pipe or rod handlers 76, position the machine frame before the job starts with frame positioners 78, anchor the machine to the ground to withstand reaction forces during drilling using an anchoring system 80, apply lubricant to drill pipe fittings to prevent sticking and galling, and so on. Those skilled in the art will appreciate that an encyclopedic listing of all actuators and effectors 16 is difficult, if not impossible, because these mechanisms continue to evolve as HDD machines 30 become more sophisticated, increasingly safer, and easier to use.
A great many HDD machines use hydraulic motors to rotate the drill pipe, and for this reason hydraulic power is readily available on most HDD machines. As a consequence, many actuators and effectors 16 are hydraulically operated. Mid-range and more sophisticated HDD machines 30 often have at least a rudimentary electrical system for various purposes, including machine control, safety features, and automation functions. It must be emphasized that a great many electric actuators are possible in an electric HDD machine 30. An electric HDD machine 30 is more amenable to electric actuators, electric control, and automation by virtue of the flexibility and sophistication of commercial electric motor controllers. Specifically, familiar functions now existing on contemporary internal combustion engine driven HDD machines will be provided using significantly different technologies in an electrically driven HDD machine. These developments will be part of the natural evolution of the electric HDD machine 30.
For example, many existing HDD machines use hydraulically operated vise jaws as grippers 74 which hold the drill pipe while pipe connections are being made up or broken apart. It is not difficult to imagine that equally effective, if not superior, gripping mechanisms will be developed using solenoid-actuated vise jaws, electromagnetic grippers, electric motors and ball screws, and similar developments. Linear motors or conventional electric motors and captive ball screws can accomplish other HDD actuator and effector 16 tasks such as positioning and leveling. Drill rod positioners and drill rod handlers 76 have similar opportunities for electromechanical developments which fit effectively and efficiently in the all-electric HDD machine 30 concept.
System-Level Functions
Most conventional HDD drilling operations require other apparatus to perform the drilling task efficiently and safely. Typical system-level functions 18 involve the mud and fluid system 20, machine and operator safety, machine control 24, navigation and guidance 22, mapping, and obstacle detection 26. These will be discussed briefly in the following paragraphs. Just as was the case in the discussion of actuators and effectors 16, those skilled in the art will appreciate that an encyclopedic listing of all system-level functions 18 is difficult, if not impossible, because these functions continue to evolve as HDD machines 30 become more sophisticated, increasingly safer, and easier to use. An electric HDD machine 30 is expected to be more amenable to the incorporation and integration of system-level functions 18 into the overall HDD system concept by virtue of the flexibility and sophistication of commercial electric motor controllers 70. These developments will be part of the natural evolution of the electric HDD machine 30.
The fluid system 20 provides the mixing and pressurized delivery of fluid, most often water-based drilling mud, to the HDD machine 30 and drill string. Drilling fluid is forced down the drill pipe annulus, exiting the drill pipe annulus via a small nozzle or nozzles immediately behind the drill bit. Drilling fluid has a number of important functions, including lubrication of the drill bit and drill pipe in the borehole, stabilization of the borehole, cooling the drill bit, and carrying cuttings from the borehole to the surface. The fluid tanks are normally located on a trailer remote from the HDD machine 30, although smaller HDD machines may have a self-contained mud tank as part of the HDD unit. The fluid system 20 mixes dry drilling mud preparations with water and then maintains some level of circulation to prevent settling in the fluid tank. The fluid system 20 provides a pump to force the drilling fluid through a hose to the HDD machine 30, where the fluid enters the drill pipe annulus through a special swivel. Failure of the fluid system ordinarily brings HDD operations to a halt until the problem is rectified.
Although the fluid system 20 is an essential part of most HDD operations, it is often treated as a separate unit. The present invention specifically identifies the desirability of providing fluid system 20 status information to the HDD machine 30 operator via an electrical, fiber-optic, RF, or IR data link. Likewise, the present invention specifically identifies the desirability of providing operator control of the fluid system via electrical, fiber-optic, RF, or IR data link from the operator's console. Many fluid systems 20 use a small gasoline-driven pump unit to mix and circulate drilling mud and then deliver drilling mud to the HDD machine swivel; this invention recognizes the desirability of replacing the small gasoline-driven pump unit by an electric motor powered through the fluid umbilical and controlled via electrical, fiber-optic, RF, or IR data link from the operator's console.
Machine and Operator Safety
Operator and general workplace safety are major considerations in the design of any piece of construction equipment. HDD machinery is no exception; those familiar with the HDD industry know that construction injuries can be very severe or fatal. Accordingly, injury prevention and safety are major objectives of HDD machine 30 design.
A great many safety features already are, or easily could be, electrical/electronic in nature. One such example is the ability to disable machine rotation when the operator in not in the operator's seat; another example would be inhibition of machine movement when unauthorized personnel are within a given radius of the machine. Electric motors and motor controllers are particularly designed for electrical/electronic interfaces and safety switches, whereas the diesel engine and hydraulic actuators typically found on existing HDD machines are far less conveniently adapted to electrical/electronic control intervention. It is a particular aim of this invention to improve operator and workplace safety by facilitating the interaction of electrical/electronic interfaces between the electric motor controller, safety switches, safety sensors, and other HDD machine 30 control functions.
Machine Control
Electric motors 68 and their controllers 70 are particularly designed for electrical/electronic interfaces and safety switches, whereas the diesel engine and hydraulic actuators typically found on existing HDD machines are far less conveniently adapted to electrical/electronic control intervention. It is a particular aim of this invention to improve operator and workplace safety by facilitating the interaction of electrical/electronic interfaces between the electric motor controller 70 and HDD machine 30 automation functions.
Navigation and Guidance
Efficient borehole creation is a major objective of the HDD machine 30, but navigation and guidance 22 of the bore path is of critical importance to success of the drilling operation—there is great risk in attempting to form a borehole without the ability to navigate and guide the drill bit around obstacles and existing infrastructure. Those familiar with the art are aware that navigation and guidance 22 functions are relatively well developed yet still emerging, but existing navigation and guidance functions are largely independent of machine operation in practice. That is, navigation and guidance information may be provided by a variety of means, but navigation and guidance information ordinarily is communicated to the operator rather than directly to machine control elements. There are ongoing efforts within the industry to automate machine operations—as, for example, automated pipe loading—but there is little reasonable opportunity to automate borehole formation given the lack of flexibility characteristic of conventional diesel engines and typical hydraulic controls.
Electric motors 68 and motor controllers 70 are particularly designed for electrical/electronic interfaces, making the long-sought automation of the boring process far easier to accomplish with an all-electric HDD machine 30 implementation. It is a particular aim of this invention to improve operator effectiveness and workplace safety by facilitating the interaction of electrical/electronic interfaces between navigation and guidance 22 electronics, the electric motor controller, and other HDD machine 30 functions.
Borepath Planning and Mapping
Integration of borepath planning and borepath mapping in the context of automated boring is far easier to accomplish using electric machines, their controllers, and all-electric actuators.
Obstacle Detection
Rapid and efficient borehole creation is of little consequence if the borehole is in the wrong place or if the drill bit strikes existing infrastructure during the boring process. Electric motors 68 and motor controllers 70 are particularly designed for electrical/electronic interfaces and safety switches, whereas the diesel engine and hydraulic actuators typically found on existing HDD machines are far less conveniently adapted to electrical/electronic control intervention. It is a particular aim of this invention to improve operator and workplace safety by facilitating the interaction of electrical/electronic interfaces between obstacle detection 26 apparatus, the electric motor controller 70, and other HDD machine 30 functions.
Various modifications can be made in the design and operation of the present invention without departing from its spirit. Thus, while the principal preferred construction and modes of operation of the invention have been explained in what is now considered to represent its best embodiments, it should be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

## Claims

1. An electrical power assembly comprising:
a plurality of direct current power sources;
a plurality of inverters, each one of the plurality of inverters operatively connected to one of each of the plurality of power sources;
an electrical transformer having a plurality of transformer input windings and a single transformer output winding;
wherein each inverter is connected to a transformer input winding;
a control unit operatively connected to each inverter; and
wherein each inverter is adapted to maintain frequency and amplitude in response to control signals from the control unit.

2. The assembly of claim 1, wherein each of the direct current power sources comprises a fuel cell.

3. The assembly of claim 2, wherein the transformer has a plurality of output windings.

4. The assembly of claim 3, wherein the control unit is adapted to maintain a timing relationship between the plurality of inverters.

5. The assembly of claim 3, wherein the control unit is adapted to maintain a timing relationship between the plurality of inverters.

6. The assembly of claim 1 further comprising a plurality of synchronizers, such that one each of the synchronizers is coupled to one of each of the plurality of inverters.

7. The assembly of claim 1 wherein the plurality of inverters each comprise a single phase inverter.

8. The assembly of claim 1 wherein the transformer coupled to each inverter is adapted to provide a common voltage.

9. An electrical power assembly comprising:
a plurality of direct current power sources;
a plurality of inverters, each one of the plurality of inverters operatively connected to one of each of the plurality of power sources;
an electrical transformer having a plurality of transformer input windings and a single transformer output winding;
wherein each inverter is connected to a transformer input winding;
a control unit operatively connected to each inverter, wherein the control unit sends control signals to each inverter to maintain a timing relationship between the plurality of inverters.

10. The assembly of claim 9, further comprising a clock assembly connected to the control unit and the plurality of inverters; and wherein the clock assembly is adapted to provide clock signals to the plurality of inverters.

11. The assembly of claim 9 further comprising a plurality of synchronizers, such that one each of the synchronizers is coupled to one of each of the plurality of inverters.

12. The assembly of claim 9 wherein the plurality of inverters each comprise a single phase inverter.

13. The assembly of claim 9 wherein the transformer coupled to each inverter is adapted to provide a common voltage.