WO2012016062A2

WO2012016062A2 - Multi-leveled phase shifted electric machine system

Info

Publication number: WO2012016062A2
Application number: PCT/US2011/045753
Authority: WO
Inventors: Saeed M. Alipour; John Davis Sink
Original assignee: Direct Drive Systems, Inc.
Priority date: 2010-07-28
Filing date: 2011-07-28
Publication date: 2012-02-02
Also published as: EP2599214A2; WO2012016062A3; CN103125069A

Abstract

A system may include a drive driving a machine. The machine may include a stator having different winding locations distributed evenly across its surface, and a number of coils arranged symmetrically among the winding locations and connected to form N sets of multiple (M) phase windings. For each winding, each corresponding coil may span a single pole to form a full pitch winding. Each winding may be offset with respect to each other to reduce a harmonic content of a magnetic flux within certain frequency range during operation. The drive may include a processing stage that includes N independent modules corresponding to each winding. Each of the N modules may have M output ports for connection to each corresponding winding. Each of the N modules may be powered by a direct current power source, and have an M number of switch matrices that have at least three levels of output.

Description

Multi-Leveled Phase Shifted Electric Machine System

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 61/368,295, entitled "Multi-leveled Phase Shifted Electric Machine System," filed on July 28, 2010, the disclosure of which is hereby incorporated by reference.

BACKGROUND

Some power systems convert mechanical energy into electrical energy and/or convert electrical energy into mechanical energy. For example, generating systems can include a prime mover and an electromechanical element, such as an electric machine that can convert mechanical energy into electrical energy. Similarly, motoring systems can include a mechanical load coupled to an electric machine. Such systems typically include passive or actively controlled power electronic devices to process the electrical energy (e.g., by converting AC (alternating current) to DC (direct current) or vice versa). In addition, such systems can use transformers for isolation or for matching voltage levels in different sections of an electrical distribution network.

SUMMARY

An example power system includes an electric machine with multiple sets of stator windings. Each set of windings is coupled through a switch matrix to a common voltage bus. Each set of windings can be spatially distributed in full pitch around the stator such that stator flux harmonics are substantially reduced. The reduced stator flux harmonics may be associated with phase current harmonic content.

In some implementations, stator windings in the electric machine are connected to substantially reduce or cancel the effect of time-harmonic currents from the power electronics including harmonic orders that are a function of the number of sets of phase windings (N), the number of phases (M) in each set of winding, and the switching frequency of the devices in the power-electronics converter.

Multi-leveling may be used to staircase the voltage waveform or current waveform fed to each set of N machine windings. For example, with N equal to 4, low magnetic flux harmonic content can be achieved without multi-leveling in low voltage applications. Multi-leveling may be used to reduce or minimize the machine's core and coil losses. Multi-leveling with 3S technology can considerably reduce switching losses in adjustable speed drives especially when machine voltage is medium voltage.

In a general aspect, an electric machine system may include a machine and a drive that drives the machine. The machine may include a stator that has a number of winding locations distributed substantially evenly across the stator's surface. The machine may also include a number of coils arranged substantially symmetrically among the number of winding locations and connected to form a number (N) of sets of multiple (M) phase windings. For each of the windings, each of the coils may span a single pole to form a full pitch winding. Each of the N sets of windings may be substantially offset with respect to each other so as to substantially reduce a harmonic content of a magnetic flux within a frequency range during operation. For example, the windings can be spatially (e.g., circumferentially) offset from one another in separate slots of the stator, or the windings may be substantially offset in another manner to reduce the harmonic content of the magnetic flux in the frequency range.

The drive may include a processing stage that includes N substantially independent modules corresponding to each of the N sets of windings. Each of the N modules may have M output ports for connection to each of the corresponding N sets of windings. Each of the N modules may have a first and a second input port that are connectable to a first node and a second node of a voltage bus. Each of the modules may have an M number of switch matrices that have at least three levels of output. The N modules may be conditioning voltage, current, and/or both.

[0001] In some aspects, the N modules may have at least five levels of output. The at least five level switch matrix can be configured to output a voltage at at least five levels of amplitude.

In some aspects, the electrical machine system may include a permanent magnet rotor configured to rotate within the stator. The electrical machine system may further include a submersible pump coupled to the rotor to rotate at the same speed as the rotor. For example, the electrical machine system may include a submersible pump coupled to the rotor to rotate at the same speed as the rotor, the stator, and the coils. The rotor and the submersible pump may be configured to reside in a wellbore. In some aspects, the at least three level switch matrix may be configured to output a voltage at at least three levels of amplitude. In the electrical machine system, a first switch matrix of M switch matrices of a first module outputs a voltage at a first phase and a second switch matrix of M switch matrices of each module outputs a voltage at a second phase different from the first phase. The first switch matrix may output the voltage at the first phase to a first of the coils and the second matrix may output the voltage at the second phase to a second of the coils. The electrical machine system may use parameters such as M equals three and N equals four.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIGS. 1A-1B show schematic representations of example power stages.

FIG. 2 shows a diagram of an example stator winding configuration in an electric machine.

FIG. 3 is a schematic illustrating the voltage waveform of a three level switch matrix feeding N=4 sets of machine windings.

FIG. 4 is a schematic illustrating the voltage waveform of a five level switch matrix feeding N=2 sets of machine windings.

FIG. 5 is a schematic illustrating both the topology and the associated voltage waveform of a five level switch matrix feeding N=4 sets of machine windings.

FIG. 6 is a schematic illustrating a common converter feeding two motors A and B.

FIG. 7 is a schematic illustrating an example electric machine system.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

A 3S electric machine can include a stator with winding locations distributed substantially evenly across a surface of the stator. A 3S electric machine can further include conductors forming a plurality of coils that are arranged substantially symmetrically among the winding locations. The conductors can be and connected to form a number (N) of sets multiple (M) phase windings. Each of the coils can span a single pole to form full pitch windings for each of the N sets of windings. Each of the N sets of windings can be spatially offset with respect to each other so as to substantially reduce harmonic content of a magnetic flux within a frequency range. In a 3S electric machine, N can be any value greater than one, for example, N can equal 2, 3, 4 or higher values.

An electric machine can include multiple switch matrices. In some instances, an electric machine includes Q active switch matrices, where each of the Q active switch matrices is coupled to one of the N sets of windings. Each set of switch matrices can be fed from a DC bus.

Multi-leveling can be used to stair case the voltage waveform fed to each set of N machine windings. With N equal to 4, low magnetic flux harmonic content can be achieved without multi leveling in low voltage applications. Multi-leveling may be used to reduce or minimize the machine's core and coil losses. Multi-leveling with 3S technology considerably reduces switching losses in adjustable speed drives especially when machine voltage is medium voltage.

FIGS. 1A-1B show example systems capable of converting mechanical energy to electrical energy (e.g., high power DC generation) or electrical energy to mechanical energy (e.g., high-speed motoring applications). As shown in FIG. 1A, a system 100 includes a bank of a number (N) of switch matrices 105a - 105n, an electric machine 110, and a voltage bus 115. Each of the switch matrices 105a - 105n may include an M-phase inverter for motoring, and/or an M-phase diode bridge for generation. Each of the switch matrices 105a - 105n includes a port 120a - 120n, respectively, each of the ports 120a - 120n including a set of terminals (not shown) for connecting to one of N corresponding sets of stator windings on the electric machine 110. In some embodiments, one or more of the ports 120a-120n may include one or more terminals for connection to a neutral point associated with the windings in the winding set in the machine (e.g., for an open delta-configured winding). Each of the switch matrices 105a - 105n also includes a port 125a - 125n, respectively, each of the ports 125a- 125n including a pair of terminals for connecting to the voltage bus 115. The example electric machine 110 shown in FIG. 1A is an example of a 3S machine that includes a stator (not shown) that has N sets of windings. In some examples, the electric machine 110 can include a linear machine. In other examples, the electric machine 110 can include a rotating machine. In various applications, the system 100 may receive mechanical energy and output electrical energy when operating as a generator, and/or the system may receive electrical energy and output mechanical energy when operating as a motor.

In various embodiments, the N sets of windings in the machine 110 are each phase-shifted from each other such that multiple stator current harmonics are substantially reduced during operation of the system 100. The number of harmonics that are substantially reduced is a function of M, the number of phases in each set of windings, and , the number of sets of windings.

[0002] In some examples (e.g., with two winding layers), the number of multiphase (M) winding sets (N) possible for a certain stator configuration may be calculated by:

N= # stator slots/( M · # of poles).

Various embodiments may substantially reduce or cancel harmonics based on the number of sets of windings (e.g., the number of coils per pole). In one embodiment, a 48 slot stator may use, by way of example and not limitation, N=2, or N=4. Various examples may have various numbers of coils per pole, winding layers, number of phases, stator slots, and the like. The first harmonic components that are not substantially reduced or canceled, as a function of the number of sets of windings (N), may be (6N +/- 1) for a three-phase (M=3) system. The phase shift, as a function of the number of phases (M) and the number of sets of windings (N), can be expressed π/(Μ*Ν).

Each of the N sets of windings is connected to a corresponding one of the ports 120a - 120n. Within the machine 110, each of the sets of windings is electrically isolated from the other windings. When motoring, energy is separately delivered from the voltage bus 115 to each set of windings through the corresponding switch matrix 105a - 105n. When generating, energy is separately supplied from each set of windings through the corresponding switch matrix 105a - 105n to the voltage bus 115. The switch matrices 105a - 105n are examples of conditioning modules. Additional or different types of conditioning modules may be used. In various implementations, a voltage on the bus 115 may be substantially unipolar. The voltage bus 115 includes a positive rail (e.g., node) that connects to a positive terminal of each of the ports 125a - 125n, and a negative rail (e.g., node) that connects to a negative terminal of each of the ports 125a - 125n. The voltage bus 115 receives a DC voltage from the switch matrices 105a-105n. In some implementations, the switch matrices 105a-105n may invert the unipolar voltage on the voltage bus 115. For example, each of the switch matrices 105a-105n can invert the voltage using an M- phase inverter.

In certain implementations, the switch matrices 105a-105n use the inverted voltage to supply an AC waveform to drive each of the corresponding M-phase windings in the machine 110. The switch matrices 105a-105n may be coordinated, for example, to provide controlled current, voltage, torque, speed, and/or position, for example. Switches in the switch matrices may be operated, in some examples, near the fundamental electrical frequency supplied to the machine, or at a frequency substantially above the fundamental frequency. Techniques for controlling switches in the switch matrices may include, but are not limited to, vector control, field-oriented control, phase control, peak current control, average current control, and/or pulse width modulation, or combinations of these or other techniques.

In some systems, switching frequency may be based on factors, such as the output fundamental frequency, the harmonic levels required in the line current, load impedance, type of semiconductor device and drive topology used, for example. In general, switching losses may be, for example, directly related to switching frequency. A maximum junction temperature or safe operating area may typically be specified in the manufacturer's data sheets.

Supplying high power (e.g., 1 Megawatt or more) in high speed applications (e.g., 8000 rpm or above) can present various practical challenges to the design of AC machines and the associated drive electronics. In designing such systems, one challenge involves losses associated with stator harmonic currents. For example, the stator harmonic currents can cause extra copper and iron losses in the stator core. In some examples, the stator harmonic current may also inject harmonic components into the air gap magnetic field that couples into the rotor, increasing losses in the rotor. The system 100 mitigates the harmonic currents by utilizing a phase shift related to the number of sets of winding (N) and the number of phases (M) in each set of winding. In one example, the system 100 reduces the harmonic components in the harmonic currents up to the (6N +/- 1) component (e.g., for N = 4, the first harmonic component in the harmonic currents would be the 23rd and the 25th components).

Accordingly, the voltage ripple frequency on the voltage bus 115 may be at (6Nfmax), where f_max is the maximum output frequency of the electric machine. Typically, f_max is in the kilohertz range for a high speed machine. In some examples, the quality of the voltage bus 115 is improved without using high frequency switching insulated gate bipolar transistors (IGBTs) or with substantially reduced filtering.

A drive and machine may be considered as a system. Design criteria may typically include matching the machine and the drive together. In some cases, the drive cost may exceed the actual machine and hence optimizing the overall system based on the AC drive or power electronics may be the most cost effective approach.

In some embodiments, the switch matrices 105a-105n can be connected in combinations of series and/or parallel to interface to the voltage bus 115. As shown in FIG. IB, a system 150 includes the switch matrices 105a-105n to be connected as a series combination of pairs of paralleled switch matrices. For example, the switch matrix 105a is connected in series with the switch matrix 105b, and the switch matrix 105n-l is connected in series with the switch matrix 105n. In this example, groups of the series connected switch matrices 105a-105n are connected in parallel to interface with the voltage bus 115.

FIG. 2 shows an example stator-winding configuration 300 of the electric machine 110. In some examples, the winding configuration 300 can be used in a 48 slot/4 pole stator. In the depicted configuration representation, the configuration 300 includes 48 slots as represented by the vertical lines. Some slot numbers associated with their corresponding slots are presented as numbers overlaid on the vertical lines.

In some embodiments, the stator configuration 300 can split the N slots separately. In one example, the stator includes a series of tooth structures that separate the N slots. For example, N phases can be inserted in those N slots (Al, A2, A3 ... AN) of the stator configuration 300. The stator configuration 300 may then include N sets of three phase windings. In some examples, each winding set can include a single turn coil running in full pitch on the stator. In other examples, each winding set can include multi-turn coil running in full pitch on the stator.

In some embodiments, the slot opening dimensions may be substantially equal. For example, the tooth widths may be substantially equal. In other embodiments, the stator configuration 300 can include toothless stator designs (e.g., toroidal windings), such as when the winding is formed substantially in the stator core material.

In the depicted example, the configuration 300 includes 4 slots per pole. In one example, the stator configuration 300 can include equal number of slots in each of the poles. For example, each pole of the stator may include 12 slots. The configuration 300 splits the 12 slots of each pole separately. For example, three phases (M=3) can be inserted in the 12 slots of the stator. As a result, the stator may be configured to have 4 sets of three phase windings (e.g., N =4). In some embodiments, the windings can be distributed such that each slot contains only one phase. In the depicted example, phase A of winding 1 (Al) occupies slots 1, 13, 25, 37, and phase A of winding 2 (A2) occupies slots 2, 14, 26, 38.

Although several examples are described as having particular numbers of slots, phases, turns, poles, and the like, such examples are given by way of example and not limitation, as other configurations are contemplated.

In some examples, the configuration 300 can substantially mitigate harmonics in the stator iron and in an air gap between the stator and the rotor. For example, the configuration 300 can substantially reduce an impact of the 5th and 7th harmonic components in the phase currents on the generator from an iron loss and torque ripple standpoint. In the depicted example, the first non-cancelled harmonic components in the air gap flux can be at (6N ± 1). In some embodiments, the first non-cancelled harmonic flux components in the machine may be at 2*M*(N ± 1).

In certain applications, such as subsea, distance between machine and drive electronics is far, and also number of cable entries and the penetrator size needs to be limited to reduce cost and increase reliability. As a result, N is often 2, or N=3 if redundancy is desired. When N is less than 4, magnetic flux harmonic content is increased which has adverse effect on machine rotor temperature.

One effective method to keep magnetic flux harmonics low is to use multi- leveling of the voltage waveform that feeds each set of N windings in 3S machines. By adding more steps into the individual voltage waveforms that feed each set of N windings, the machine's air gap magnetic flux can follow the reference waveform more closely and inherently result in lower harmonic components. Multi-leveling is also desirable when fed voltages to each set of N windings need to be greater than 480 Vrms, in some instances, greater than 750 Vrms. Higher voltages may be necessary to enhance motor performance.

In certain applications, it is desired to keep the number of cables between the machines and drive electronics to a minimum. For example when N=4, the number of cables is (3 phases * 4 windings) 12. A high number of cables is especially expensive and not desirable for when distance between machine and drive electronics is greater than 100 feet.

The lowest N sets of windings when using 3S technology is 2, in which case, the number of cables is reduced to (3 phases * 2 windings =) 6. Using a two-level switch matrix when N=2 would result in high harmonics. To keep magnetic flux harmonic level low as is the case with N=4, multi-leveling of voltage waveform or current waveform can be used.

FIG. 3 shows the voltage waveform of a three-level switch matrix feeding N=4 sets of machine windings. The figure illustrates air gap flux summation for an example 3S machine using the N=4 machine windings. Each machine winding may be fed by the three-level neutral point clamp half bridge switch matrix as shown in the top four graphs in FIG. 3. In each of the five graphs as shown, the horizontal axis represents the phase in each operation cycle, from 0 to 360 degrees (or 0 to 2π rad). The vertical axis in the top four graphs represents a voltage VL-N of a unit step of windings #1 310, #2 320, #3 330 and #4 340. The vertical axis in the bottom graph represents the summation of air gap flux of windings #1 310, #2 320, #3 330 and #4 340. In the bottom graph, only a portion of the summation representation is shown to avoid redundancy.

[0003] In this example embodiment, the air gap flux is proportional to the voltage (i.e., VL-N). Therefore the step voltage shown in the top four graphs can also represent the air gap flux generated by each winding. The windings #1 310, #2 320, #3 330 and #4 340 have different phases, offsetting by 15 degrees. The duration for each step voltage is 120 degrees, followed by a 60 degrees ground voltage. Each positive and negative step voltage occurs in turn. This creates a three-level (-1, 0, 1) rectangular step function as shown in the top four graphs. The figure shows a general pattern of air gap flux without representing specific quantified value.

When all of the four windings effects are superpositioned together, because the air gap flux can be linearly summed, a staircase function 350 that resembles a sinusoidal function can be created as shown in the bottom graph of FIG. 3. In this implementation, N=4, making the peak flux four times the flux generated by each winding. In some embodiments, N may be of a different number, the summation of the air gap flux may therefore exhibit a different pattern.

The staircase waveform 350 generated from the three-level windings can have low distortion and reduce the dv/dt stresses, improving electromagnetic compatibility. Using multilevel converter may reduce common-mode voltage, so as to decrease the stress in motor bearings. Input current for such multilevel system can also be lowered.

[0004] In some embodiments, the three-level waveform generated in the windings #1 310, #2 320, #3 330 and #4 340 may be generated via various conversion techniques. For example, a cascaded H-bridges converter with separate dc sources may be used. A diode clamped (neutral-clamped) structure similar to the current disclosure may also be used. A capacitor clamped (flying capacitor) converter structure may also be used.

In some embodiments, the three-level waveform of the windings #1 310, #2 320, #3 330 and #4 340 may use various modulation and control techniques to generate a system required waveform. For example, a sinusoidal pulse width modulation, a selective harmonic elimination modulation, and/or a space vector modulation may be used.

FIG. 4 shows the voltage waveform of a five level switch matrix feeding N=2 sets of machine windings. This figure illustrates air gap flux summation for an example 3S machine using the N=2 machine windings. Each machine winding may be fed by the five-level neutral point clamp half bridge switch matrix as shown in the top two graphs in FIG. 4. In each of the three graphs as shown, the horizontal axis represents the phase in each operation cycle, from 0 to 360 degrees (or 0 to 2π rad). The vertical axis in the top two graphs represents a voltage VL-N of a unit step of windings from #1 410 and #2 420. The vertical axis in the bottom graph represents the summation of air gap flux of windings #1 and #2. In the bottom graph, only a portion of the summation representation is shown to avoid redundancy.

In this example embodiment, the air gap flux is proportional to the voltage (i.e., VL-N). Therefore, the voltage waveform shown in the top two graphs can also represent the air gap flux generated by each winding. The windings #1 410 and #2 420 have different phases, offset by 15 degrees. The duration for each step voltage is 150 degrees, followed by a 30 degrees ground voltage. Each positive and negative staircase voltage occurs in turn. The staircase voltage includes a step of one unit and a step of two units, with the two-unit step occurring 30 degrees later and ending 30 degrees sooner than the one-unit step. This creates a five-level (-2, -1, 0, 1, 2) rectangular step function as shown in the top two graphs. The figure shows a general pattern of air gap flux without representing specific quantified value.

When both the two windings effects are superpositioned, because the air gap flux can be linearly summed, a staircase function 430 that resembles a sinusoidal function can be created as shown in the bottom graph of FIG. 4. This graph is similar to that in FIG. 3, showing a same flux profile can be achieved when N equals to different numbers. In this implementation, N=2. In some embodiments, N may be of a different number, the summation of the air gap flux may therefore exhibit a different pattern.

In some embodiments, the five-level waveform generated in the windings #1 410 and #2 420 may be generated via various conversion techniques. For example, a cascaded H-bridges converter with separate dc sources may be used. A diode clamped (neutral-clamped) structure similar to the current disclosure may also be used. A capacitor clamped (flying capacitor) converter structure may also be used.

In some embodiments, the five-level waveform of the windings #1 410 and #2 420 may use various modulation and control techniques to generate a system required waveform. For example, a sinusoidal pulse width modulation, a selective harmonic elimination modulation, and/or a space vector modulation may be used.

FIG. 5 shows both the topology and the associated voltage waveform of a five level switch matrix feeding N=4 sets of machine windings. This figure illustrates an application for an example 3S machine using N=4 inverter modules. The inverter modules 515, 525, 535, and 545 are each of five-level, similar to that of FIG. 4. In this implementation, the 3S inverter modules are feeding each of N motor windings 516, 526, 536, and 546 the modulated power (e.g., voltage waveform as shown, and/or current waveform in some embodiments). For N=4, this figure illustrates four 3S modules #1 515, #2 525, #3 535 and #4 545 feeding respectively to four 3S motor windings 516, 526, 536, and 546 that are space shifted from -22.5 degrees to 22.5 degrees at 15 degrees interval. The inverter modules 515, 525, 535, and 545 are example conditioning modules that can be used to process energy between a voltage bus and the windings of the electric machine. Conditioning modules can include voltage conditioning modules, current conditioning modules, or modules configured to condition additional or different properties of an electrical signal.

The 3S modules are used to drive the 3S motors to achieve several benefits, in some instances. For example, using multi-level inverter with space shifted 3S motors allows reducing the number of N sets of windings and operating a 3S machine at higher voltages and frequencies than without multi-leveling. Operating the 3 S machine at higher voltages can enhance performance and manufacturing in some cases. The space shifting 3S technology reduces harmonics to (N*M*2)+\-l, where M is the number of phases. For N=2 and M=3, all harmonics below 11^th order can be eliminated in some cases.

The 3S modules can use the multi-level waveforms to power each N motor winding to target certain harmonics for elimination above (N*M*2)+\-l. In addition, the multi-level waveform (e.g., voltage, current, and/or both) with the 3S technology integrates both benefits for magnetic flux harmonic elimination, and reduction of stator coil and core losses.

The top row 510 of the four illustrates the 3S module #1 515, which is a five- level NPC/H-Bridge inverter, feeding the three phases (with Al shown) of the 3S motor winding 516 (-22.5) degrees space shifted winding. The 3S module #1 515 may include a power supply of +Va_c-i and -Vd_c-i, a neutral ground connection, two sets of diodes Dl and D2, and two sets of switching transistors Ql through Q4. The 3S Module #1 515 generates a five-level phase to neutral voltage waveform at a time origin, and output to the three phases (with phase Al shown) of the 3S motor winding 516 at a (-22.5) degree space shift. The state of the switches Q 1 through Q4 is controlled by an external controller, which may control the phase, magnitude, duration, and/or other parameter of the switches. One example of voltage levels and switching states is shown in the following Table 1.

Table 1. Voltage levels and switching states

The second row 520 illustrates the 3S module #2 525, which is another five- level NPC/H-Bridge inverter, feeding the three phases (with A2 shown) of the 3S motor winding 526 (-7.5) degrees space shifted winding. The 3S module #2 525 may include a power supply of +Va_c-i and -Vd_c-i , a neutral ground connection, two sets of diodes D l and D2, and two sets of switching transistors Q l through Q4. The 3S Module #2 525 generates a five-level phase shifted phase to neutral voltage waveform and output to the three phases (with phase A2 shown) of the 3 S motor winding 526 at a (-7.5) degree space shift. The state of the switches Q l through Q4 is controlled by an external controller, under a switching scheme similar to that of the 3S module #1 515, as shown in Table 1.

The third row 530 illustrates the 3 S module #3 535, which is another five-level NPC/H-Bridge inverter, feeding the three phases (with A3 shown) of the 3S motor winding 536 7.5 degrees space shifted winding. The 3 S module #3 535 may include a power supply of +Va_c-i and -Vdc-i , a neutral ground connection, two sets of diodes D l and D2, and two sets of switching transistors Q l through Q4. The 3S Module #3 535 generates a five-level phase shifted phase to neutral voltage waveform and output to the three phases (with phase A3 shown) of the 3 S motor winding 536 at a 7.5 degree space shift. The state of the switches Q l through Q4 is controlled by an external controller, under a switching scheme similar to that of the 3S module #1 515, as shown in Table 1.

The fourth row 540 illustrates the 3 S module #4 545, which is another five- level NPC/H-Bridge inverter, feeding the three phases (with A4 shown) of the 3 S motor winding 546 22.5 degrees space shifted winding. The 3S module #4 545 may include a power supply of +Va_c-i and -Vd_c-i , a neutral ground connection, two sets of diodes D l and D2, and two sets of switching transistors Q l through Q4. The 3S Module #4 545 generates a five-level phase shifted phase to neutral voltage waveform and output to the three phases (with phase A4 shown) of the 3 S motor winding 546 at a 22.5 degree space shift. The state of the switches Q l through Q4 is controlled by an external controller, under a switching scheme similar to that of the 3S module #1 515, as shown in Table 1.

FIG. 6 is a schematic illustrating a common converter feeding two motors A and B. The example system 600 includes a common converter 610 and a subsystem 620 that includes a 3 S inverter module system and a 3 S motor system. The common converter 610 provides basic power source to the subsystem 620. The converter 610 may be an electromagnetic transformer, a switched-mode power supply, a DC to DC converter, and/or other electromagnetic power source. The converter 610 may also include different types of rectifiers.

The converter 610 may include a voltage source that is electromagnetically coupled with the direct current power source of the subsystem 620. The direct current power source provides +Va_c and -Va_c voltages to the 3S modules in the subsystem 620.

The subsystem 620 may include two motors A and B, their switching modules #1 to #4, and the respective motor windings A, B and C (e.g., Al , A2, A3, and A4 to the respective #1 , #2, #3 and #4 switching modules). In this implementation, the motors A and B may be operated at different loading conditions, such as speeds and torques. The motors A and B use 3S technology that substantially reduces harmonics by space shifting conductor coils.

The switching modules #1 to #4 of motor A may be similar to the 3S modules #1 to #4, that are multi-level NPC/H-bridge inverters, as shown in FIG. 5. In some embodiments, the switching modules #1 to #4 of motor A's multi-level waveform may be generated via various conversion techniques. For example, a cascaded H-bridges converter with separate dc sources may be used. A diode clamped (neutral-clamped) structure similar to the current disclosure may also be used. A capacitor clamped (flying capacitor) converter structure may also be used.

In some implementations, the switching modules #1 to #4 of motor A's multilevel waveform may use various modulation and control techniques to generate a system required waveform. For example, a sinusoidal pulse width modulation, a selective harmonic elimination modulation, and/or a space vector modulation may be used.

Similarly, the switching modules #1 to #4 of motor B may be similar to the 3S modules #1 to #4, that are multi-level NPC/H-bridge inverters, as shown in FIG. 5. In some implementations, the switching modules #1 to #4 of motor 5's multi-level waveform may be generated via various conversion techniques. For example, a cascaded H-bridges converter with separate dc sources may be used. A diode clamped (neutral-clamped) structure similar to the current disclosure may also be used. A capacitor clamped (flying capacitor) converter structure may also be used.

In some implementations, the switching modules #1 to #4 of motor 5's multilevel waveform may use various modulation and control techniques to generate a system required waveform. For example, a sinusoidal pulse width modulation, a selective harmonic elimination modulation, and/or a space vector modulation may be used.

The 3 S modules transmit multi-level waveform power to the motor windings of each phase. In FIG. 6, transmission to the phase A is shown. The phase differences may be similar to that in FIG. 5, from -22.5 degrees to 22.5 degrees at 15-degree intervals. For both motors A and B, the motor windings may include four space shifted windings. Each of the four windings is connected to a 3 S multi-level module. This connection schematic enables one common convertor to power two separate motors and each motor has an individual switching module and corresponding windings to couple with the modules for reducing harmonics. In some embodiments, the common convertor 610 may be connected to three or more motors that include multi-level switching modules and space shifted windings. In some instances, an electric machine can include a power stage operating in a motoring mode to supply torque to a load. The electric machine can further include a stator and a rotor that includes a number of windings. The stator may include space- shifted, split-phase windings, with a total number of phases = M*N, where N is the number of independent, isolated neutral, M-phase winding sets. In certain implementations, N may be selected based on the number of slots in the stator, number of rotor poles, and the amount of harmonic cancellation required. There can be a /(Μ*Ν) electrical phase difference between adjacent M-phase windings. Similar stator structure and winding layout considerations may be applied for motoring and generating applications.

FIG. 7 shows an example electric machine system 700, which includes an electric machine 702 coupled to a companion device 704. The example electric machine 702 can operate as a generator, producing electrical power from mechanical movement, operate as a motor producing mechanical movement from electricity, or alternate between generating electrical power and motoring. In generating electrical power, a prime mover supplies mechanical movement to the electric machine 702, and the electric machine 702 converts the mechanical movement into electrical power. In certain instances, the companion device 704 may be the prime mover. In motoring, the mechanical movement output from the electric machine 702 can drive another device. In certain instances, the electric machine 702 can drive the companion device 704. In certain instances, the electric machine 702 can operate to motor and drive the prime mover during specified conditions, and switch to generating electrical power and be driven by the prime mover during specified conditions. The electric machine 702 can be configured for primarily generating electrical power, primarily motoring, or to be reasonably efficient at both generating electrical power and motoring.

In general terms, the electric machine 702 includes a stationary member and a movable member that, by interaction of magnetic fields, generates electrical power as the movable member moves relative to the stationary member and/or moves the movable member as electrical power is applied to the stationary member. Rotor 706 is coupled to the companion device 704 to drive the companion device 704 and/or be driven by the companion device 704. While FIG. 7 illustrates a horizontally-oriented electric machine coupled to a horizontally-oriented companion device 704, other implementations may provide for a vertically-oriented electric machine coupled to and capable of driving vertically-oriented companion devices, among other orientations. Additionally, in other instances, the electric machine 702 can be another type of electric machine. For example, the electric machine 702 can be a linear electric machine, where the movable member is a linearly reciprocating shaft. The example electric machine 702 shown in FIG. 7 can operate as an alternating current (AC), synchronous, permanent magnet (PM) electric machine having a rotor 706 that includes permanent magnets and stator 708 that includes a plurality of formed or cable windings about a core. In other instances, the electric machine can be an other type of electric machine, such as an AC, asynchronous, induction machine where both the rotor and the stator include windings or another type of electric machine. In certain instances, the electric machine 702 is carried by and contained within a housing 710. The housing 710 can be wholly separate from the companion device 704, separate from and coupled to the companion device 704, or partially or wholly shared with the companion device 704 (i.e., the electric machine 702 and companion device 704 carried by and contained within a common housing).

In instances where the companion device 704 is a prime mover, the companion device can include a number of different possible devices. For example, the prime mover may include one or more of a fluid motor operable to convert fluid (gas/liquid) flow into mechanical energy, a gas turbine system operable to combust an air/fuel mixture and convert the energy from combustion into mechanical energy, an internal combustion engine, and/or other type of prime mover. In instances where the companion device 704 is driven by the electric machine 702, the companion device can include a number of different possible devices. For example, the companion device 704 can include one or more of a rotating and/or reciprocating pump, rotating and/or reciprocating compressor, mixing device, or other device. Some examples of pumps include centrifugal pump, axial pump, rotary vane pump, gear pump, screw pump, lobe pump, progressive cavity pump, reciprocating positive displacement or plunger pump, diaphragm pump, and/or other types of pumps. Some examples of compressors include centrifugal compressor, axial compressor, rotary vane compressor, screw compressor, reciprocating positive displacement compressor and/or other types of compressors. The electric machine 702 can be coupled to two or more companion devices 704 at the same time.

Although shown with a single companion device 704, the electric machine 702 can also be coupled to two or more companion devices 704 (to drive and/or be driven by the devices 704). In certain instances, one or more companion devices 704 can be provided at each end of the electric machine 702. For example, in a configuration with two companion devices 704, one may be provided at one end of the electric machine 702 and another provided at an opposing end of the electric machine. In another example, a configuration with two companion devices 704 can have one provided at one end of the electric machine 702, and another coupled to the first companion device. Also, if multiple companion devices 704 are provided, they need not all be of the same type of companion device.

Some embodiments may yield one or more advantages. For example, some systems may have reduced weight and volume of the machine because of the higher fundamental frequency when using standard AC converter topologies and cooling methods. In some embodiments, output capabilities of the AC drive components, such as the semiconductor devices, may be increased by using low switching frequency while still maintaining low harmonic distortion in the line current. Optimized stator size may be obtained based on reduced requirements to handle switching harmonic losses that may be associated with higher frequency PWM inverter operation or with use of only one three-phase diode bridge. Harmonic coupling/ heating into the rotor may be substantially reduced. Modular design on the power converter may provide substantial fault tolerance in some embodiments, which may yield improved redundancy and higher availability. Stress on the stator winding insulation may be reduced, and/or insulation voltage level of the windings may be reduced by making different connections to the number of turns per coil and the number of coils per pole. Some embodiments may achieve generally high system efficiency and lower overall cost. Some embodiments may not need PWM control techniques, and/or may provide gear-less high-speed AC converter systems.

A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. An electric machine system, comprising:

a stator with a plurality of winding locations distributed substantially evenly across a surface of the stator; and

a plurality of conductors formed into a plurality of coils arranged substantially symmetrically among the plurality of winding locations and connected to form a number (N) of sets of multiple (M) phase windings, wherein for each of the windings, each of the coils spans a single pole to form a full pitch winding, and wherein each of the N sets of windings are substantially offset with respect to each other so as to substantially reduce a harmonic content of a magnetic flux within a first frequency range during operation; and

a processing stage that includes N substantially independent conditioning modules corresponding to each of the N sets of windings, each of the N conditioning modules having M output ports for connection to each of the corresponding N sets of windings, and having a first and a second input port, wherein the first and second input ports for each of the N conditioning modules are connectable to a first node and a second node of a voltage bus, each of the modules having an M number of switch matrices, each switch matrix having at least three levels of output.

2. The electric machine system of claim 1, wherein each of the conditioning modules has an at least five level switch matrix.

3. The electric machine system of claim 2, wherein the at least five level switch matrix is configured to output a voltage at least five levels of amplitude.

4. The electric machine system of claim 1, further comprising a permanent magnet rotor configured to rotate within the stator.

5. The electric machine system of claim 4, further comprising a subsea pump or compressor coupled to the rotor to rotate at the same speed as the rotor.

6. The electric machine system of claim 4, further comprising a submersible pump coupled to the rotor to rotate at the same speed as the rotor and the stator, the plurality of conductors, the rotor and the submersible pump configured to reside in a wellbore.

7. The electric machine system of claim I, wherein the at least three level switch matrix is configured to output a voltage at at least three levels of amplitude.

8. The electric machine system of claim I, wherein a first switch matrix of M switch matrices of a first module outputs a voltage at a first phase and a second switch matrix of M switch matrices of the first module outputs a voltage at a second phase different from the first phase.

9. The electric machine system of claim 8, wherein the first switch matrix outputs the voltage at the first phase to a first of the plurality of conductors and the second matrix outputs the voltage at the second phase to a second of the plurality of conductors.

10. The electric machine system of claim 1, wherein M equals three.

11. The electric machine system of claim 1, wherein N equals four.

12. The electric machine system of claim 1, wherein the windings carry a current having a π/(Μ*Ν) electrical phase difference between adjacent winding locations during operation.

13. A method for providing for electromechanical energy conversion, the method comprising:

providing an electric machine that includes:

processing energy between the electric machine and a voltage bus using a processing stage that includes N substantially independent conditioning modules corresponding to each of the N sets of windings, each of the N conditioning modules having M output ports for connection to each of the corresponding N sets of windings, and having a first and a second input port, wherein the first and second input ports for each of the N conditioning modules are connectable to a first node and a second node of a voltage bus, each of the modules having an M number of switch matrices, each switch matrix having at least three levels of output.

14. The method of claim 13, wherein the windings carry a current having a /(Μ*Ν) electrical phase difference between adjacent winding locations during operation.

15. The method of claim 13, wherein processing energy between the electric machine and the voltage bus includes providing electrical power from the N conditioning modules to the N sets of windings.

16. The method of claim 13, wherein M equals three.

17. The method of claim 13, wherein N equals four.

18. The method of claim 13, wherein processing energy between the electric machine and the voltage bus includes:

a first switch matrix of M switch matrices of a first module outputting a voltage at a first phase; and

a second switch matrix of M switch matrices of the first module outputting a voltage at a second phase different from the first phase.

19. The method of claim 13, wherein processing energy between the electric machine and the voltage bus includes:

the first switch matrix outputting the voltage at the first phase to a first of the plurality of conductors; and

the second matrix outputting the voltage at the second phase to a second of the plurality of conductors.