GB2396064A

GB2396064A - Apparatus for filtering harmonics from a wave output

Info

Publication number: GB2396064A
Application number: GB0328665A
Authority: GB
Inventors: Kurt Ledoux; William C Pelton
Original assignee: Schlumberger Holdings Ltd
Current assignee: Schlumberger Holdings Ltd
Priority date: 2001-06-25
Filing date: 2002-06-11
Publication date: 2004-06-09
Anticipated expiration: 2022-06-11
Also published as: GB2396064B; GB0328665D0

Abstract

An apparatus designed to filter harmonics from a wave output, comprising a variable speed drive 18 having a power source, a plurality of single bridge inverters 58, at least one step-up transformer 70 and at least one parallel inductor 62. The apparatus may also have a sine wave filter 80 coupled to the variable speed drive to extract harmonic components from a high carrier frequency output signal.

Description

GB 2396064 A continuation (74) Agent and/or Address for Service: Sensa

Gamma House, Enterprise Road, Chilworth Science Park, SOUTHAMPTON, Hampshire, SO16 7NS, United Kingdom

FILTERING APPARATUS

FIELD OF THE INVENTION

The present invention relates generally to electrical submersible pumping systems BACKGROUND OF THE INVENTION

Electric submersible pumping systems typically comprise a submersible electric motor which is driven by a variable speed drive. A typical system comprises a pump, an electric motor and a motor protector deployed in a wellbore. The submersible motor is used to power the pump, to permit pumping of the production fluids to the surface or some point above the surface of the earth. A typical submersible motor, used to pump production fluids from beneath the earth's surface, has an outer housing substantially sealed from the production fluid environment and sized to fit within standard wellbore casings. An exemplary submersible motor is a three-phase induction-type motor, having a shaft rotatably mounted within the housing such that it is in general alignment with the axis of the wellbore when residing in the wellbore.

Power may be supplied to the submersible electric motor via a power cable that runs along the deployment system. Typically, the power cable is banded or supported along either the outside or the inside of the deployment system. Generally, the power cable is routed to the electric motor to supply electric power thereto, and the submersible pump is powered by the motor by way of an appropriate drive shaft.

The variable speed drive is used to control the speed at which the motor operates and to facilitate an overall increase in efficiency of operation. However, variable speed drives can create undesirable harmonics. For example, certain harmonics created by the operation of the motor cause problems such as voltage distortion, zero-crossing noise, overheating of transformers, nuisance tripping of circuit breakers, and over-stressing of power factor correction capacitors. The lower harmonics are particularly troublesome because they are larger, therefore less attenuated by the system impedance and more difficult to remove at the source. Additional losses arise due to the production of harmonic generated fields.

Furthermore, harmonics, whether propagated or not, cause increased losses in the transformer windings and core. Presently, separate components such as filters are used to reduce the amount of harmonics in the signal output by the variable speed drive. Although, this solution produces some results, the filter components are separate from the variable speed drive.

Additionally, there are still harmonics produced that are not filtered out by these components.

These harmonics remain to produce the aforementioned undesirable affects.

SUMMARY OF THE INVENTION

According to the present invention, there is provided an apparatus designed to filter out harmonics from a wave output, the apparatus comprising: a variable speed drive having: a power source; and a plurality of components coupled to the power source positioned within the variable speed drive, the plurality of components comprising: a plurality of single bridge inverters; at least one step-up transformer coupled to the plurality of single bridge inverters; and at least one parallel inductor coupled to the plurality of single bridge inverters and to the step-up transformer, the plurality of components cooperating to filter harmonics from an output signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: FIG. I is a system diagram according to an exemplary embodiment of the present technique; FIG. 2 is front elevational view of an electric submersible pumping system, according to an exemplary embodiment of the present technique; FIG. 3 is a block diagram of an exemplary method to reduce harmonics produced by a variable speed drive; FIG. 4 is a block diagram of an alternative exemplary technique to reduce harmonics produced by the variable speed drive; and FIG. 5 is a block diagram of another alternative exemplary technique for reducing harmonics produced by the variable speed drive.

DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present invention will be described below.

It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-

related constraints, which may vary from one implementation to another. Moreover, it should

be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

Turning to Fig. 1, a typical operating system 10 is illustrated. The operating system 10 is used to control an electric submersible pumping systems.

In the present embodiment, a variable speed drive 18 is generally coupled to the motor 16. Further, the variable speed drive 18 is also coupled to a control assembly 19. The control assembly 19 typically comprises a plurality of elements to operate the operating assembly 12.

Thus, the control assembly 19 may comprise computers, system controllers, and other such devices. In this embodiment, the variable speed drive 18 is directly coupled to a system controller 20. It should be noted that, although, the variable speed drive is illustrated as being coupled to a system controller 20, the variable speed drive 18 may be coupled to various other elements. For instance, the variable speed drive 18 may be directly coupled to a computer 22.

However, in the illustrated embodiment, the system controller 20 is coupled to the computer 22, which is further coupled to an operator control system 24. The operator control system 24 is coupled to a series of peripheral devices 26. The peripheral devices 26 may comprise a keyboard, a printer, a display and other such devices. Additionally, the operator control system 24 may be controlled by a remote system 28. The operator control system 24 typically is controlled by an operator or by a series of instructions such as programs implemented in the computer 22. Further, a power source 29 is coupled to the operating assembly 12, the control assembly 19 and the variable speed drive 18.

Referring generally to Figure 2, an electric submersible pumping system is indicated at 30. Pumping system 30 may comprise a variety of components depending on the particular application or environment in which it is used. The system 30 includes at least one centrifugal pump 32 coupled to motor 16, and a motor protector 36 under the control of variable speed drive 18.

In the illustrated example, pumping system 30 is designed for deployment in a well 38 within a geological formation 40 containing desirable production fluids, such as petroleum.

In a typical application, a wellbore 42 is drilled and lined with a wellbore casing 44.

Wellbore casing 44 may include a plurality of openings 46 through which production fluids flow into wellbore 42.

Pumping system 30 is deployed in wellbore 42 by a deployment system 48 that can have a variety of forms and configurations. For example, deployment system 48 may

comprise tubing 50 connected to pump 32 by a connector 52. Power is provided to submersible motor 16 via a power cable 54. Motor 16, in turn, is controlled by the variable speed drive 18 and powers the centrifugal pump 32 which draws production fluid in through a pump intake 56 and pumps the production fluid to the surface via tubing 50. Additionally, the production fluids may be pumped to the surface through tubing 50 or through the annulus formed between deployment system 48 and wellbore casing 44. It should be noted that the illustrated submersible pumping system 30 is merely one exemplary embodiment. For instance, a horizontal pumping system may be an alternate embodiment.

It is generally appreciated by those skilled in the art that harmonic stresses produced by a variable speed drive cause problems in motors and especially those used in electrical submersible pumping systems. Further, these harmonic stresses may also cause problems with cables, penetrators and transformers. The present technique provides a method for reducing these harmonic stresses generated by the variable speed drive.

Conventional electric submersible pumping systems comprise components such as step-up transformers and cables with considerable amounts of capacitance and inductance and small amounts of resistance. As can be appreciated by those skilled in the art, when these components exist in the same circuit, a natural resonance condition occurs. This natural resonance condition causes voltage ringing to occur which produces undesirable effects such as harmonics. Thus, an output of the variable speed may include these undesirable components. Also, a carrier frequency produced by the variable speed drive can introduce detrimental harmonic effects to the system. Typically, the higher the carrier frequency, the greater the spread between the harmonics generated. However, utilizing a filter when the carrier frequency is higher allows the sinusoidal voltage to be cleaner when it is output. The harmonic voltages do not contribute to the motor power output, but instead produce wasted volt amperes. Thus, one way of reducing the voltage stresses such as harmonics in a submersible pumping system is to filter the output of the variable speed drive. As mentioned above, in prior systems a filter is utilized to extract the harmonics from the output. In the present technique, however, the harmonics produced by the variable speed drive 18 are extracted using components within the variable speed drive 18, rather than having an additional filter. However, in certain applications, a filter may also be used in combination with the filtering capability of variable speed drive 18 to extract harmonics from the voltage

output. Implementation of the present technique where the variable speed drive itself acts as a filter allows for a more economical system.

Figure 3 illustrates an implementation of the present technique to provide an optimum sine wave output from variable speed drive 18. The exemplary variable speed drive 18 comprises components such as single bridge inverter, step-up transformers and inductors that are utilized in a manner that filters unwanted harmonics. Additional components such resistors may also be utilized to generate an output. In the present embodiment, the variable speed drive 18 is illustrated having a plurality of single bridge inverters 58. Typically, a power source (not shown) produces a frequency that is input to the three phase single bridge inverters 58. The inverters 58 convert DC signals to AC signals through a switching method.

The single bridge inverters 58 are typically configured in parallel to provide a greater output from the variable speed drive 18. As a result of the greater output, the motor 16 is provided with increased power. The increased power generally corresponds to a greater number of single bridge inverters 58 in the variable speed drive 18. Thus, an output AC signal 60 is transmitted from the inverters 58 into a series of parallel inductors 62 that are typically placed in parallel within the variable speed drive 18, so that the inductance within the drive 18 may be reduced. Consequently, a signal 64 is output from the parallel inductors 62 with reduced inductance. Optionally, the signal 64 may be transmitted to a sine wave filter 66, which filters out other or additional harmonic components from the signal 64.

In the present technique, the inductance provided by the parallel inductors 62 is utilized to extract harmonic components from the output signal 60. In other words, the parallel inductors 62 are utilized as components for filtering out unwanted frequencies. For example, the parallel inductors 62 provide an inductance similar to inductors otherwise provided in a conventional sine wave filter 66. The variable speed drive inductance is used to filter out the harmonics from the output 60 produced by the single bridge inverters 58. As a result, no separate filter or a less complex and less expensive sine wave filter 66 may be used, e.g. filter 66 may have a reduced number of inductors.

Figure 4 illustrates an alternative embodiment, wherein the single bridge inverter 58 may be coupled to a step-up transformer 70 within the variable speed drive 18. As mentioned above, the single bridge inverter 58 converts the DC signal to the AC signal 60. In the present embodiment, the signal 60 is transmitted to the step-up transformer 70, which increases the voltage output. The step-up transformer outputs the increased voltage signal 72 to an optional sine wave filter 74, which transmits a sine wave output 76 to the motor 16.

s

It should be noted that the step-up transformer 70 produces a leakage inductance that serves as a filter inductance to permit use of the stepup transformer 70 as a filter component.

As a result, all of the components designed within the variable speed drive 18 may be integrated to provide filtering qualities, thereby permitting omission of a separate sine wave filter or at least the use of a less expensive sine wave filter to filter out the remaining harmonics produced by the variable speed drive 18. For example, optional sine wave filter 74 is less complex, e.g. fewer inductors, resulting in a less expensive filter.

Figure 5 illustrates an alternative embodiment wherein the components described in Fig. 3 and 4 are integrated to produce effects similar to those generated by a conventional sine wave filter. Particularly, the plurality of single bridge inverters 58 in parallel are coupled to parallel inductors 62. Furthermore, the parallel inductors 62 are coupled to the step-up transformer 70 within the variable speed drive 18. An output signal 78 may be transmitted to an optional sine wave filter 80. As mentioned above, the parallel inductors 62 provide inductance and the step-up transformer 70 provides additional leakage inductance, which may be used as filtering components to extract harmonics from the output signal 78 produced by the variable speed drive 18. This combination again results in the ability to omit a separate filter or to utilize a less complex sine wave filter 80.

It should be further noted that the multiple windings on the transformer 70 also can be utilized to eliminate the parallel inductors 62. As can be appreciated by those skilled in the art, the additional windings within the transformer 70 provide a similar output as the parallel inductors 62. Additionally, the increased switching of the single bridge inverters 58 may increase the carrier frequency produced by the variable speed drive 18. As mentioned above, the harmonics associated with higher carrier frequencies are easier to filter, resulting in the ability to use a less complex and less expensive sine wave filter with the overall system.

While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the following appended claims.

Claims

1. An apparatus designed to filter out harmonics from a wave output, the apparatus comprlsmg: a variable speed drive having: a power source; and a plurality of components coupled to the power source positioned within the variable speed drive, the plurality of components comprising: a plurality of single bridge inverters; at least one step-up transformer coupled to the plurality of single bridge inverters; and at least one parallel inductor coupled to the plurality of single bridge inverters and to the step-up transformer, wherein the plurality of components cooperate to filter harmonics from an output signal.

2. The apparatus as in claim 1, further comprises a sine wave filter coupled to the variable speed drive.

3. The apparatus as in claim 1, wherein the output signal is inputted into an electric motor.

4. The apparatus as in claim 2, wherein the sine wave filter is designed to extract harmonic components from the output signal produced by the variable speed drive.

5. The apparatus as in claim 1, wherein the plurality of single bridge inverters are configured to produce a high carrier frequency output signal.

6. The apparatus as in claim 4, wherein the sine wave filter is used to extract harmonic components from the high carrier frequency output signal.

7. The apparatus as in claim 1, wherein the at least one parallel inductor is configured to generate an inductance adapted to filter harmonic components in the output signal.

8. The apparatus as in claim 2, wherein the at least one parallel inductor is used in combination with the plurality of single bridge inverters and the sine wave filter to filter out harmonic components in the output signal.

9. The apparatus as in claim 1, wherein the at least one step-up transformer in combination with the plurality of single bridge inverters extract harmonic components in the output signal.

10. The apparatus as in claim 9, wherein the leakage inductance generated by the step-up transformer is used in combination with the plurality of single bridge inverters, the at least one parallel inductor and the sine wave filter to extract harmonic components in the output signal.

11. The apparatus as in claim 1, wherein the output signal is a sine wave voltage signal.