CA2454848C - A variable frequency power system and method of use - Google Patents
A variable frequency power system and method of use Download PDFInfo
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- CA2454848C CA2454848C CA002454848A CA2454848A CA2454848C CA 2454848 C CA2454848 C CA 2454848C CA 002454848 A CA002454848 A CA 002454848A CA 2454848 A CA2454848 A CA 2454848A CA 2454848 C CA2454848 C CA 2454848C
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Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
- H02P9/10—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
- H02P9/04—Control effected upon non-electric prime mover and dependent upon electric output value of the generator
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Control Of Eletrric Generators (AREA)
Abstract
A variable frequency power system with a power source having a rotating output end a speed control to regulate rotational speed of the rotating output. A generator coupled to and driven by the rotating output of the power source, whereby the speed control of the power source directly controls output power frequency of the generator due to control of rotational frequency of the rotating output. A voltage regulator connected between the generator and the motor regulates output voltage from the generator to the electrical motor load. A system controller controls output power frequency of the generator. The system controller interfaces with the speed control of the power source and configured to monitor generator output and operational conditions of tho electrical motor load. The system controller adjusts the speed control based on generator output and operational conditions of the electrical motor load.
Description
d VARIASLE FREQUENCY POWER SYSTEM AND ME'1'fiOIA OF USE
BACKGROUND
'the present invention generally relates to providing variable electrical power to a three phase electrical motor. Mare speciftcaliy, the present inventa;on relates to varying electrical power to a three phase electrical motor based on varying frequency input turning an electrical generator which provides eiectricai power to the motor, in order to overcome variable condition: encounter by the motor that r~quirc a variation in electrical power to the motor.
~o It is known to use three phase gGncrators to supply the power i:o drive truce phase motors. Normally, fxed power supply systems using three phase generators arc oparstui at rr constant sped to deliver three please electrical eneyy of coxastatit frequency to supply three phase power to three phase motors. There are currently two types of three phase fixed power supply systems in common use today.
Tlu°y are the 50 hertz and the 60 hertz power supply systems, which are used to drive electrical motors rated for 50 or 60 hertz operation, respectively. A, problem with a single generator to supply power to a single motor system i3 that the large starting current required by the E7cl,otoc is normally overcome by suing the generator as much as 4D percent larger than the main motor load to be applied to the generator. If the motor-generator combination is less than 40 gcr~cnt larger than the main electrical motor to be started, then the engine driving the generator usually stalls out when attomptiag W start the motor.
Another ptnbl~ wid7 f xed power supply systems is drat these systems can not vary the fi-cqucacy of the output power to the three please rxzotor, if it is requited.
Some applications of three phase motors require a variable frcqueaey output power to the motor, due 1o varying operational conditions required of the motor_ An example is electrical submersible pumps used in the oil and gas industry at remote pumping stations. Typically, these pumps arc located where there is an inadoquatc local
BACKGROUND
'the present invention generally relates to providing variable electrical power to a three phase electrical motor. Mare speciftcaliy, the present inventa;on relates to varying electrical power to a three phase electrical motor based on varying frequency input turning an electrical generator which provides eiectricai power to the motor, in order to overcome variable condition: encounter by the motor that r~quirc a variation in electrical power to the motor.
~o It is known to use three phase gGncrators to supply the power i:o drive truce phase motors. Normally, fxed power supply systems using three phase generators arc oparstui at rr constant sped to deliver three please electrical eneyy of coxastatit frequency to supply three phase power to three phase motors. There are currently two types of three phase fixed power supply systems in common use today.
Tlu°y are the 50 hertz and the 60 hertz power supply systems, which are used to drive electrical motors rated for 50 or 60 hertz operation, respectively. A, problem with a single generator to supply power to a single motor system i3 that the large starting current required by the E7cl,otoc is normally overcome by suing the generator as much as 4D percent larger than the main motor load to be applied to the generator. If the motor-generator combination is less than 40 gcr~cnt larger than the main electrical motor to be started, then the engine driving the generator usually stalls out when attomptiag W start the motor.
Another ptnbl~ wid7 f xed power supply systems is drat these systems can not vary the fi-cqucacy of the output power to the three please rxzotor, if it is requited.
Some applications of three phase motors require a variable frcqueaey output power to the motor, due 1o varying operational conditions required of the motor_ An example is electrical submersible pumps used in the oil and gas industry at remote pumping stations. Typically, these pumps arc located where there is an inadoquatc local
2 electrical power grid supply or even na power grid supply and it is a wmmon praoticG to use an engine to power the gcncrsmr on the well site to supply power to the electric submersible pump motor. The eugirces are usually diesel, gasolirYe, natural gas, or prapaac powered. It is known that for any given centrifugal pump the rate and head capability of that pump is greatly expanded througle the use of variable speed operation which is accomplished by providing power in the form of variable f~rqucncy power to the motor of the pump. This allows a pump to fit a larger process application due to varying conditions during the time that the pump is installed. In the oil and gas induslzy, a pump can be installed in a well for up to three or four years before being 1o wom out and requiring a repaaeement. Thurittg this bate, the production f3rnm ~ oil ar gas well can change for a number of reasons due to varying canditaans, the isnllowing :uc some cxanrplcs. There is a decline in reservoir pressure due to depletion of the weli_ There is an increaso in reservoir pressure due to vpida~e replaGemont 'fraxrt is~3eCtiDn wells. 'Thexe are changes in fluid produced, as usually oit is decreasing and water is increasing in a well. There could also bn an incrcasC ar decrease in gas produced in the well, which would affect the fluid praduetian of the well_ Thcrc are mechanical problems with the wellbone, such as scaling or parafFn etC., which could cause a producdon decline. Chemicals can be used to remove these mechanical problems that restrict production without removing the pump, which will result is a production increase. Thcsc varying fluid production conditions can be accommodated by the varying of the power supply frequency to the motor of the pump to maximize oil production from welts.
When it is desired to operate a three phase motor at a variable speed the current method is to input the constant ~reque~xcy three phase power from a generator to a three phase variable speed drive. Sometimes the variable speed drive is rarcnred to as a vfrciable frcqucney drive The variable speed drive supplies three phase power at a variable fxeduency to the three phase motor. 'fhe variable speed drive allows the three phase rnator to bG operated at a variable speed in direct proportion to the variable
When it is desired to operate a three phase motor at a variable speed the current method is to input the constant ~reque~xcy three phase power from a generator to a three phase variable speed drive. Sometimes the variable speed drive is rarcnred to as a vfrciable frcqucney drive The variable speed drive supplies three phase power at a variable fxeduency to the three phase motor. 'fhe variable speed drive allows the three phase rnator to bG operated at a variable speed in direct proportion to the variable
3 frequency of the power supply from the variable speed drive. Sometimes a traazsforrzaer is required between the variable speed drive and the throe phasa motKrr to provide a voltage zxtatch regained by dze three phase motor. Fig. 1 slzows an example of currently used systrms for generating three phase variable ftctjucru:y power to a thrc~
phase 9 motor. The systexxz includes an engine, three phase electrical generator, excitation controller, variable spCed drive, transformer, switchboard, motor eontraller and the motor. The engine speed is controlled by a governor to maintain constant engine speed under vatyir~g load conditions imposed by the generator load and a taffy or sixty Hertz output requirement. The engine is usually mechanically coupled to the clcctrical gane~ator, but other connections are also used. The generator voltage output is controlled by the excitation controller. 'the output voltage o~ the generator is clcctrically connected by cables to the variable speed drive. The output of the variable speed drive is electrically connected by cables to the t~ancformcr. The hansformcr is notxzzally of a mufti-tap configuration w provide the appropriate voltage requi»ed by the ~5 motor. The mufti-tap allows for numerous mover combinations to be us~~i, which also makes it easier to accommodate the cable voltage loss associated with the wide range of cable sizes and lengths required tp reach electric s~tbmersihlc pumps in.;tallcd deep in oil & gas wells. A switehboaxd used as a power disconnect is conne<:ted along the cables between the transformer and the motor. A molar controller is an electronic unit used to control the frequency output of the variable speed drive as n-cluiYCd by the motor based on feedback of varying conditions encounter by the motor. The motor controller also controls the on-off function of the switchboard. The rn.otor controller is connected by cables to the switchboard, and by cables to the variable speed drive to monitor, control, and adjust the power to the motor by numerous progrunmed parameters.
'there are many disadvantages to using a variable speed drive. Use of a variable speed drive reduces the electrical efficiency of the motor and excatcs harmonic spilcc3 on flue gelaerated variable frequency power stippIied to the motor. A variable speed drive reduces the power facwr of the motor. A variable spend drive increases the waste heat
phase 9 motor. The systexxz includes an engine, three phase electrical generator, excitation controller, variable spCed drive, transformer, switchboard, motor eontraller and the motor. The engine speed is controlled by a governor to maintain constant engine speed under vatyir~g load conditions imposed by the generator load and a taffy or sixty Hertz output requirement. The engine is usually mechanically coupled to the clcctrical gane~ator, but other connections are also used. The generator voltage output is controlled by the excitation controller. 'the output voltage o~ the generator is clcctrically connected by cables to the variable speed drive. The output of the variable speed drive is electrically connected by cables to the t~ancformcr. The hansformcr is notxzzally of a mufti-tap configuration w provide the appropriate voltage requi»ed by the ~5 motor. The mufti-tap allows for numerous mover combinations to be us~~i, which also makes it easier to accommodate the cable voltage loss associated with the wide range of cable sizes and lengths required tp reach electric s~tbmersihlc pumps in.;tallcd deep in oil & gas wells. A switehboaxd used as a power disconnect is conne<:ted along the cables between the transformer and the motor. A molar controller is an electronic unit used to control the frequency output of the variable speed drive as n-cluiYCd by the motor based on feedback of varying conditions encounter by the motor. The motor controller also controls the on-off function of the switchboard. The rn.otor controller is connected by cables to the switchboard, and by cables to the variable speed drive to monitor, control, and adjust the power to the motor by numerous progrunmed parameters.
'there are many disadvantages to using a variable speed drive. Use of a variable speed drive reduces the electrical efficiency of the motor and excatcs harmonic spilcc3 on flue gelaerated variable frequency power stippIied to the motor. A variable speed drive reduces the power facwr of the motor. A variable spend drive increases the waste heat
4 generated in all the electrical equipment and wiring on the output side of the vtttiable speed drive, including the tt~t3lsfoYnler, wiring arid the motor, A variable speed drive also requires zrtore frequent maintenance compared to the rest of the electrical equipment in the system. Other disadvantages are associated with the engine, genGretor and transfornner, when using a variable speed drive. The engiile needs to be sued at least twenty peYCerit larger that): the t7faOtor load t0 accommodate the high eleCtYiCal losses in the system- The tranxformcr must have a larger rittnaber of .mnxltiple voltage taps to anticipate Changes i.n motor and cable requirements, which requires a more expensive transformer. Thn transformer core also weeds to be about twenty percent more 1D massive than. standard tr;nsformcts to handle the h8lmOtIlC$ arid low frequency operation. The LrarisFormer also needs higher insulafiomating on the wiYirig to handle the high voltage spikes due to harrixoriiCS. the generator also needs to be about twenty percent more massive than standard gcnurators to handle the harmonics and low freduericy operation. ~'he generator also needs higher insulation rating on the wiring to handic the high voltage spikes due to I)armpnics.
Tt is an object of the prcscat invention to provide a systerri and method to vary the ckxtrical power to a three phase motor without the use of a variable speed drive between the generator and the motor.
SU'MM,A,12Y OF TAE I1~VFN7Pi0~1 A variable ficqucnCy power systetz7. with a power source having a ootating output at2d a speed control to regulate rotational speed of the r4tating output A
generator coupled W antl driven by the rotating output of fhc power source, whereby the speed control of the power source di~t~ectly controls output power frequency of 111e generator due to Control of rotational hequetloy of the rotating Output A voltage regulator corineatad t~~twean the generator and the motor regulates output voltage from the generator to the electrical motor load. A system cpntroller contrail output power frerluency of the generator. The system contmlIer interfaces with the :opted control of the power source and configured to monitor generator output and operational conditions of the electrical motor load. 'fhe system contrpller adjugtg the speed control based on gencratvr outputand opCrationel conditions of tire electrical motor load.
Tt is an object of the prcscat invention to provide a systerri and method to vary the ckxtrical power to a three phase motor without the use of a variable speed drive between the generator and the motor.
SU'MM,A,12Y OF TAE I1~VFN7Pi0~1 A variable ficqucnCy power systetz7. with a power source having a ootating output at2d a speed control to regulate rotational speed of the r4tating output A
generator coupled W antl driven by the rotating output of fhc power source, whereby the speed control of the power source di~t~ectly controls output power frequency of 111e generator due to Control of rotational hequetloy of the rotating Output A voltage regulator corineatad t~~twean the generator and the motor regulates output voltage from the generator to the electrical motor load. A system cpntroller contrail output power frerluency of the generator. The system contmlIer interfaces with the :opted control of the power source and configured to monitor generator output and operational conditions of the electrical motor load. 'fhe system contrpller adjugtg the speed control based on gencratvr outputand opCrationel conditions of tire electrical motor load.
5 BRIEF DESCRIhTION OF DRAWINGS
Fig_ '1 is a schematic view of a powrs system with a variable Speed drive.
Fig. 2 is a schematic view a variable frequency power system according to the 70 present invention.
Fig. 3 is s Schematic view a variable frequenoy power system aca>rding eo the present imrention.
DET.4D.ED DESCRIPTION
'Z'he present invention is a variable fn:qurncy power sySttat to drive a thrva phase electrical motor at the ftrrquency, voltage and amperage, ag required by the motor operation to drive a driven unit. !'he variable frequency power ~ystom of the present 20 inverdion can be especially applied whore the driven unit is Au electric Submer5ibie putrip Used in the oil and gas industry. The electric submcraible guatp iS
drivcm by alternating euirznt (AC) three pbuae electripal motor which ca~lvbits a norrlincar relationship betwcon rotational spead and torque load due to the inherent characteristics of centrifugal pumping systems. The variable lrGqucmcy power system includes a 2S generator driven by a power spur~ce. The variable frequency power system includes a specially programmed logic circuit in a system, controller, which intcrfacea with the power source of the generator. The pro~amrned logic circuit is desired to monitor atul control the driven unit by monitoring the conditions of the driven unit and controlling the sugpIicd power to the motor. 'The variable frequency ppwer system can be progsanamed with startup, steady-state operation. and emergency shuuiown garametcrs for tbc driven unit 'The driven unit is controlled by varying hhc voltage and frequency of the input AC power to the motor. 'fhbe system conunller would be responsible for adjusting and monitoring the generator output, and would adjust the generator to any voltage and frequency required by the driven unit within the effective operational limits of the generator. Plot only can this etluipment allow for desired steady ;Fate operational paiarneters, it can be set up to allow for completely di#ferent panuneters during start-up of high power draw electrical devices, slush as eleotric motors, or to react to monitored inpuha of the driven unit. The system controller of the d0 variable frequency power system Controls the generator speed and 8utput uoltage, it is capable of accepting inputs from external sources to conerol the operadan of the entire system. In the case of electric submersible pumps, sire-cot draw and pump opcrnting pr2RSi11'8R Can be monitored and generator frequency and voltage can be automatically adjusted due to chat~es im those t~actings, inchuiing icy shuts of the putn~p, is if d. The variable fi~quency powex system can also include a hump machine intcrFacc. The human-machine interface can include a display screen ands input buttons to allow an operator the ability to select desinad ope~atianal and startup routines, monitor operating system parameters, ar to modify operational pa~ranaeters as ~aeeded without requiring in-depth knowledge of the underlying hardware and code of the 20 system controller 'fhe variable frequency power system includes a power source, uninterrupted power supply, generator, excitation controller, sy3tem oontrblltr and switchboard. 'The power source drives the generator and is usually an engine, as is the case when 25 powerins a electric submersible pump in the oil and gas industry. lChe engine is dasi,gned and sized to operate continuously at the maximum power required by the motor. The engine includes a throttle that is regulated by the system controller. The unintetxuptible power supply powers the instrumentation and Control circuits of the sys~tcm aontrollcr, esxcitatiaa conhvllcr and all other electrical components in need of a canst3nt electrical power source. Typically; the uninterruptiblc power supply is an inverter driven off of the engine battery or et~ine auxiliary battery, so that the electrical componcr>ts arc independent of the main power supply output of the gcnc~ator.
The geneaator provides electrical powrer to the motor. The excitation coxrunller is used to adjust voltage output of the gcnciator to the motor and aIsro includes a programmable logic so that tt~a voltage is adjusted accoxdirtg to the fxeqttertcy of the engine-gex{erator combination. 5pccial logic circuit programs are used for start-up and normal operational ranges. The system controller also includes grogramrz~ed logic circuits, whidh monitor operation of flue system and eonttol the throttle on the e~i~.1n the case of the electric submcrsriblc pump, the system controller would nwnitor pump opcaxtin~
cax~dltions. 7lte switchboard provides the Stoplstan', function of the motor and is usually rated for the highest voltage and amp capacity required.
Fig. 2 shows a system for generating three phaxc variable frequency power to a t 5 three phase motor. Tlte system includes as engine with the engine speed controlled by a throttle device. The dine is mechanically coupled to a three phase electrical generator. The generator ix shown as a mufti-tap voltage gcucrxtor. The valtagG output pf the generator is controlled by the excitation controller in order to provide the appt~opriate voltage requixed by the zttotor. .A switchboard is used us a power disconnect 2t7 between the electrical generFUOr and the motnr. A system controller is used to control the frequency output of the electrical generator by controlling the engine throttle dcviec, speesi central settings and also corttrots the on-off function of the switchboard. The variable frequency power system also includes an inverter which suppLlea a constant electrical power source for the inshumentation and control circuit3 l~or the throttle 25 device, excitation conirollcr and tlx system controller. The variable frequency power system catttroller is canr~ecfied by cables to the switchboard and by cables to the engine to monitor, control and adjust the power to the motor by numerous progtaratned parameters in fhc system controller.
Fig. 3 Shows another embodirnerit 4f the prcSent invcnliOn For lcncrdtiag three pktase variable frequency power to a three phase motor. The system includes tire cagine, the engine throttle device and is mechanically coupled to a three phase electrical generator. 1n this case, the generator is shown as a single tap voltage configuration.
The voltage output of the generator is controlled by the excit<~ttion controller. 'fhe output of tlx: cixfrical generator is clcctricaily connected to s trarLSformcr which LS
norrnaIly of a could-tap contlguratiott to ptrovide the appropriate voltage required by the motor. The switchboard is us~I as 8 power disconnect between thet transfonacr and the motor. The system controller is used to control the freguency output of the electrical 14 generator by controlling the engine thtnttle device. control settings and also controls the oa-off function of the switchbo8rd. The variable fiequcacy power Systcua also iacludcs the inverder which supplies a constant clcctrical power sonrce for the instrumentation and control circuits for the throttle device, excitation controller a~ad the system controller.
Tee engine turns the three phase el~trical generator designed for variable frequency operation. The generator is electrically coupled to the three phase motor.
The l3sottle device is usually a combination of a throttle and electronic speed ~niroller to control the speed of the engiae, sad thus control the fuming frequency of the engine.
WheWby, an increase or decrease in engine speed would in turn increase or decrease the &equcmcy of generated three phase power being supplied to the three phase nwtor by the gencnitor. The excitation controller is a voltage regulator capable of var~ring its voltage output in a programmable maaner to the en$iac speed driving the gcaesstor. The system controller inoerfltces with the throttle device and the excitation controller to monitor, 2s control end regulate the desired operating parameters of the electric motor. The system controller adjusts the speed bBSed on monitored readings and the desired Operating conditions of the mptor for any one particular drive unit application. The monitored readings can be from sensors at the motor or in the case of an electric submersible pump, at the pump itself. Tha unintom~ptiblG power supply keeps W a monitoring, co~ntt~l and adjustnaettt functions opernting during large changes in the frequency of the electrical power being gener8ted to powcx the motor.
The geaeixtor can be set up with a single set of output voltage taps as shown in Fig. 3 or with multiple sets of output voltage taps as shown in Fig. 2. TIC
use of multiple sots of output voltage taps at the generator eliminates the need for a separate transformer, which can be bulky and expensive, and yet allows for a wide range of output voltages to be ptroduced. The operating voltage xu~e of a F;eoet~ator with multiple sets of output voltage taps can be from several hundred volts to several ip thousand volt~c and can be generated at any frequency within the cffoctivc funetio~l speed range of the nnotor-generator combination. Again, generator output is manipulated by the cxcitaaon conaallor, which allows the system eoncroller to canttnl and monitor the output voltage of the gcnaator anywhere within the ofFoctive operational range of the selected output tap of the generator or transformer.
A generator witlx multiple sets of output voltage taps can have a tap selection such as 1810. 2600 &
3644 volts or other suitable rtrtge of low, medium & high volts as is eonvoaient to arrange during the manufacture of a given generator unit, which can be fine tuned by the excitation controller to supply the correct voltage in a range from 900-4200 Volts to the motor for the operation cottditions of the motor required by the drive unit.
Also, a ~tcrator with multiplC sets of output voltage t8ps can be fod into tux extol multiple tap tran5fprmer to achieve an even broader range of operational voltages, if required.
Since the output voltage of the variable frequency power system is monitored and controlled by the sys6em controller, it is possible #v adjust the output voltage of the generator indepextdently of the output frequency, This flexibility allows the variable ticquency power system to vary oa2put voleage linearly with respect to frequency, or to maintain a fixed output vottagc as frequency is varied depending on what is required by the load of the drive unit, a feature which is very useful during the initial startixtg of an electric submersible pump motor. The variable frequency power system allows the starting of high-load electrical equlptl~etl2 by controlling certain as~pccts o~ the cnginc-generator combination that was prcviouxty not possible to do accurately and con5i9tsntly. The system controller of the variable frequency power system can control 5 a startup sequence to start the engine-generator combination and xurz it at idle with no load for a speci$ed wazxzz-1tp period.. Once warm.up is achieved, the 9ystrm controller can begin a s~rtup sequence by bringing the engine to a stat4i><ag frequency, for example rtfteen Hertz, and than give the cngirrc the command to go to full throttle.
As the engine ramps up is speed arid reaches toughly half the final operating speed, the system 70 controller engages the pow~cr to the motor of the drive unit. 7Che final ox>erating speed for many applications is expected to be in the 45 hertz to 60 hertz trirtge.
'this start sequence eliminates the mechanical J<,eaction time inherent to the existing eagine-gencrator combination when a sharp electrical load is ixtiroduced. Another start up method that can be reatizcd with the variable frcquerzey power system ;is for devices with high startup power draws, by using a rednccd startup voltage mctbod. The system controller can control a sCar0.tp sequence to start the engine-generator combination and run it at idle with no load for a speeiCred warm-up period. once warm-up is achieved, the variable frequency power system brings the engine to a Steady operating frequency slighCly below full opeKatixag f~~equency, for example approximately around eighty-five pcrccxrt of full opearating freduenCies. Once up to speed the variable fn-qucncy power system sets the excitation controller to a reduced output voltage its, x range of frfty to ninety percent of the rated voltage to hertz ratio. At this point the sysu:m controller engages tire power to the electrical motor of the driven device, holdixr~ the output voltage fixed at ibc preset reduced voltage regardless of engine speed change.
After a given periad of time elapseq, the sysrtcm coatcoller instructs the excitation cantrol.ler to ramp up the voltage to achieve the roqutrcd volts, to hertz ratio to be delivered to the motor based on the driven device. The system controller then waits until the sysrtcm reaches steady operation at these settings baFore bringing the systerxt to the final operational speed, This second start up sequence takes advantage of the fact that the inertia of the engine and generator is sufficiexit such that the engine: spECd vrill be reduced whila it picks up the additional load, but before the etlgine reaCl'aes a stall sped, it will recover and return tp the required setting Of the Hertz selected for the power to be gCBCratCd tV t~'1~ YnOtOr.
s 'fhe variable frequency power system allows .for start-up nnod~es to be designed tp take advantage of the fact that at low speeds of about thirty Hcrtt, Oz' about ot~-half of it's Full speed" a diesel engine, Or other similar engine driver, can produce up to fifty percent of its full load horsepower and up to sixty ptmxnt of its full iaad torqua, while the electrical motor at this speed driving a centrifugal pump, only Yeclunres twenty-live 14 percent Of the hOrsepOwer of the engine. For the diesel engine to do this., the engine has to be at full throttle, so that the turboebarger is spooled up aztd giving the er~lne the required boost in power.
Yt is therefore erxvision~i that start-up rseeds can be cpnfrgured as folIow~
Run 1 s the c~ nr at no load for warm up. Set tha systc~ controller for tutacdug tlae ~aaotac at desired speed or current limit desired. Aa immediate or Slow ramp Can be accommodated. When the system controller gives signal to start the motor, then engine neZds w slow down to idle speed of about t:'fkeen Hear., and then receives the signal to go to the set speed, axtd whila the engine is under full tftmttie and gaioiatg speed, khen 20 the switchboard engages the motor. About thirty Hnrez would be a ;food point for engaging the motor. The engine will slow down slightly while picking up the motor load and then will continue on to its set speed oc current setking far the motor.
The variable fre~qucncy power system has many advantages over systems using a 25 variable speed drive. .The advance include increa,Red electrical efficiency no clcctricat L,armonics, an increase in the electrical power factor, an i:ocrease in motor ef~lciency, an increase in motor loading cagabilitics, a decrease in motor opcratiag temperature, and less electrical stress on the electrical insulation propertiEa of the motor windings and al l other electrical wires in the main cable and generator.
Another benefit of the variable frequency power system is it allows for the implementation of new pnoccsses which negates the current practice of over sizing the engine or generator The variable frequency power system results in a package which is smaller suad therefore easier to transport, lowers capital costs, is ug to twenty-five percent more energy ei~cient as a result of the elimination of ttze variable speed drive, barxrtonics and transformer, ultimately require less maintenance arid provide of longC;r Iifc of the System. In tk~e case of electric submersible pumps used by the oil and gag industry, the incorporation of all these features into one package provides a system that:
cari be used in remote locations without requiring the purchase of multiple deviocs which can be 1a'tore expensive and much mere bulky. The variable fi~quency ppwcr system includes the connection of the motor to an electrical centrifugal pump, an electrical fan or an electrical gas compressor pump.
While diff'ercnt embodiments of the invention have been described in detail herein, it wilt he apgrcciatcd by those sltillrd in the art that various modiffications and alternatives to the embodiments could be developed in light of the overall teachings of the disclosure. Accordingly, the pat~icular arrangements are i I/u.,~.tive only arid are npt linutin,~ as to the scope of the invention that is to be given the full breadth of any and all equivalents thereof.
Fig_ '1 is a schematic view of a powrs system with a variable Speed drive.
Fig. 2 is a schematic view a variable frequency power system according to the 70 present invention.
Fig. 3 is s Schematic view a variable frequenoy power system aca>rding eo the present imrention.
DET.4D.ED DESCRIPTION
'Z'he present invention is a variable fn:qurncy power sySttat to drive a thrva phase electrical motor at the ftrrquency, voltage and amperage, ag required by the motor operation to drive a driven unit. !'he variable frequency power ~ystom of the present 20 inverdion can be especially applied whore the driven unit is Au electric Submer5ibie putrip Used in the oil and gas industry. The electric submcraible guatp iS
drivcm by alternating euirznt (AC) three pbuae electripal motor which ca~lvbits a norrlincar relationship betwcon rotational spead and torque load due to the inherent characteristics of centrifugal pumping systems. The variable lrGqucmcy power system includes a 2S generator driven by a power spur~ce. The variable frequency power system includes a specially programmed logic circuit in a system, controller, which intcrfacea with the power source of the generator. The pro~amrned logic circuit is desired to monitor atul control the driven unit by monitoring the conditions of the driven unit and controlling the sugpIicd power to the motor. 'The variable frequency ppwer system can be progsanamed with startup, steady-state operation. and emergency shuuiown garametcrs for tbc driven unit 'The driven unit is controlled by varying hhc voltage and frequency of the input AC power to the motor. 'fhbe system conunller would be responsible for adjusting and monitoring the generator output, and would adjust the generator to any voltage and frequency required by the driven unit within the effective operational limits of the generator. Plot only can this etluipment allow for desired steady ;Fate operational paiarneters, it can be set up to allow for completely di#ferent panuneters during start-up of high power draw electrical devices, slush as eleotric motors, or to react to monitored inpuha of the driven unit. The system controller of the d0 variable frequency power system Controls the generator speed and 8utput uoltage, it is capable of accepting inputs from external sources to conerol the operadan of the entire system. In the case of electric submersible pumps, sire-cot draw and pump opcrnting pr2RSi11'8R Can be monitored and generator frequency and voltage can be automatically adjusted due to chat~es im those t~actings, inchuiing icy shuts of the putn~p, is if d. The variable fi~quency powex system can also include a hump machine intcrFacc. The human-machine interface can include a display screen ands input buttons to allow an operator the ability to select desinad ope~atianal and startup routines, monitor operating system parameters, ar to modify operational pa~ranaeters as ~aeeded without requiring in-depth knowledge of the underlying hardware and code of the 20 system controller 'fhe variable frequency power system includes a power source, uninterrupted power supply, generator, excitation controller, sy3tem oontrblltr and switchboard. 'The power source drives the generator and is usually an engine, as is the case when 25 powerins a electric submersible pump in the oil and gas industry. lChe engine is dasi,gned and sized to operate continuously at the maximum power required by the motor. The engine includes a throttle that is regulated by the system controller. The unintetxuptible power supply powers the instrumentation and Control circuits of the sys~tcm aontrollcr, esxcitatiaa conhvllcr and all other electrical components in need of a canst3nt electrical power source. Typically; the uninterruptiblc power supply is an inverter driven off of the engine battery or et~ine auxiliary battery, so that the electrical componcr>ts arc independent of the main power supply output of the gcnc~ator.
The geneaator provides electrical powrer to the motor. The excitation coxrunller is used to adjust voltage output of the gcnciator to the motor and aIsro includes a programmable logic so that tt~a voltage is adjusted accoxdirtg to the fxeqttertcy of the engine-gex{erator combination. 5pccial logic circuit programs are used for start-up and normal operational ranges. The system controller also includes grogramrz~ed logic circuits, whidh monitor operation of flue system and eonttol the throttle on the e~i~.1n the case of the electric submcrsriblc pump, the system controller would nwnitor pump opcaxtin~
cax~dltions. 7lte switchboard provides the Stoplstan', function of the motor and is usually rated for the highest voltage and amp capacity required.
Fig. 2 shows a system for generating three phaxc variable frequency power to a t 5 three phase motor. Tlte system includes as engine with the engine speed controlled by a throttle device. The dine is mechanically coupled to a three phase electrical generator. The generator ix shown as a mufti-tap voltage gcucrxtor. The valtagG output pf the generator is controlled by the excitation controller in order to provide the appt~opriate voltage requixed by the zttotor. .A switchboard is used us a power disconnect 2t7 between the electrical generFUOr and the motnr. A system controller is used to control the frequency output of the electrical generator by controlling the engine throttle dcviec, speesi central settings and also corttrots the on-off function of the switchboard. The variable frequency power system also includes an inverter which suppLlea a constant electrical power source for the inshumentation and control circuit3 l~or the throttle 25 device, excitation conirollcr and tlx system controller. The variable frequency power system catttroller is canr~ecfied by cables to the switchboard and by cables to the engine to monitor, control and adjust the power to the motor by numerous progtaratned parameters in fhc system controller.
Fig. 3 Shows another embodirnerit 4f the prcSent invcnliOn For lcncrdtiag three pktase variable frequency power to a three phase motor. The system includes tire cagine, the engine throttle device and is mechanically coupled to a three phase electrical generator. 1n this case, the generator is shown as a single tap voltage configuration.
The voltage output of the generator is controlled by the excit<~ttion controller. 'fhe output of tlx: cixfrical generator is clcctricaily connected to s trarLSformcr which LS
norrnaIly of a could-tap contlguratiott to ptrovide the appropriate voltage required by the motor. The switchboard is us~I as 8 power disconnect between thet transfonacr and the motor. The system controller is used to control the freguency output of the electrical 14 generator by controlling the engine thtnttle device. control settings and also controls the oa-off function of the switchbo8rd. The variable fiequcacy power Systcua also iacludcs the inverder which supplies a constant clcctrical power sonrce for the instrumentation and control circuits for the throttle device, excitation controller a~ad the system controller.
Tee engine turns the three phase el~trical generator designed for variable frequency operation. The generator is electrically coupled to the three phase motor.
The l3sottle device is usually a combination of a throttle and electronic speed ~niroller to control the speed of the engiae, sad thus control the fuming frequency of the engine.
WheWby, an increase or decrease in engine speed would in turn increase or decrease the &equcmcy of generated three phase power being supplied to the three phase nwtor by the gencnitor. The excitation controller is a voltage regulator capable of var~ring its voltage output in a programmable maaner to the en$iac speed driving the gcaesstor. The system controller inoerfltces with the throttle device and the excitation controller to monitor, 2s control end regulate the desired operating parameters of the electric motor. The system controller adjusts the speed bBSed on monitored readings and the desired Operating conditions of the mptor for any one particular drive unit application. The monitored readings can be from sensors at the motor or in the case of an electric submersible pump, at the pump itself. Tha unintom~ptiblG power supply keeps W a monitoring, co~ntt~l and adjustnaettt functions opernting during large changes in the frequency of the electrical power being gener8ted to powcx the motor.
The geaeixtor can be set up with a single set of output voltage taps as shown in Fig. 3 or with multiple sets of output voltage taps as shown in Fig. 2. TIC
use of multiple sots of output voltage taps at the generator eliminates the need for a separate transformer, which can be bulky and expensive, and yet allows for a wide range of output voltages to be ptroduced. The operating voltage xu~e of a F;eoet~ator with multiple sets of output voltage taps can be from several hundred volts to several ip thousand volt~c and can be generated at any frequency within the cffoctivc funetio~l speed range of the nnotor-generator combination. Again, generator output is manipulated by the cxcitaaon conaallor, which allows the system eoncroller to canttnl and monitor the output voltage of the gcnaator anywhere within the ofFoctive operational range of the selected output tap of the generator or transformer.
A generator witlx multiple sets of output voltage taps can have a tap selection such as 1810. 2600 &
3644 volts or other suitable rtrtge of low, medium & high volts as is eonvoaient to arrange during the manufacture of a given generator unit, which can be fine tuned by the excitation controller to supply the correct voltage in a range from 900-4200 Volts to the motor for the operation cottditions of the motor required by the drive unit.
Also, a ~tcrator with multiplC sets of output voltage t8ps can be fod into tux extol multiple tap tran5fprmer to achieve an even broader range of operational voltages, if required.
Since the output voltage of the variable frequency power system is monitored and controlled by the sys6em controller, it is possible #v adjust the output voltage of the generator indepextdently of the output frequency, This flexibility allows the variable ticquency power system to vary oa2put voleage linearly with respect to frequency, or to maintain a fixed output vottagc as frequency is varied depending on what is required by the load of the drive unit, a feature which is very useful during the initial startixtg of an electric submersible pump motor. The variable frequency power system allows the starting of high-load electrical equlptl~etl2 by controlling certain as~pccts o~ the cnginc-generator combination that was prcviouxty not possible to do accurately and con5i9tsntly. The system controller of the variable frequency power system can control 5 a startup sequence to start the engine-generator combination and xurz it at idle with no load for a speci$ed wazxzz-1tp period.. Once warm.up is achieved, the 9ystrm controller can begin a s~rtup sequence by bringing the engine to a stat4i><ag frequency, for example rtfteen Hertz, and than give the cngirrc the command to go to full throttle.
As the engine ramps up is speed arid reaches toughly half the final operating speed, the system 70 controller engages the pow~cr to the motor of the drive unit. 7Che final ox>erating speed for many applications is expected to be in the 45 hertz to 60 hertz trirtge.
'this start sequence eliminates the mechanical J<,eaction time inherent to the existing eagine-gencrator combination when a sharp electrical load is ixtiroduced. Another start up method that can be reatizcd with the variable frcquerzey power system ;is for devices with high startup power draws, by using a rednccd startup voltage mctbod. The system controller can control a sCar0.tp sequence to start the engine-generator combination and run it at idle with no load for a speeiCred warm-up period. once warm-up is achieved, the variable frequency power system brings the engine to a Steady operating frequency slighCly below full opeKatixag f~~equency, for example approximately around eighty-five pcrccxrt of full opearating freduenCies. Once up to speed the variable fn-qucncy power system sets the excitation controller to a reduced output voltage its, x range of frfty to ninety percent of the rated voltage to hertz ratio. At this point the sysu:m controller engages tire power to the electrical motor of the driven device, holdixr~ the output voltage fixed at ibc preset reduced voltage regardless of engine speed change.
After a given periad of time elapseq, the sysrtcm coatcoller instructs the excitation cantrol.ler to ramp up the voltage to achieve the roqutrcd volts, to hertz ratio to be delivered to the motor based on the driven device. The system controller then waits until the sysrtcm reaches steady operation at these settings baFore bringing the systerxt to the final operational speed, This second start up sequence takes advantage of the fact that the inertia of the engine and generator is sufficiexit such that the engine: spECd vrill be reduced whila it picks up the additional load, but before the etlgine reaCl'aes a stall sped, it will recover and return tp the required setting Of the Hertz selected for the power to be gCBCratCd tV t~'1~ YnOtOr.
s 'fhe variable frequency power system allows .for start-up nnod~es to be designed tp take advantage of the fact that at low speeds of about thirty Hcrtt, Oz' about ot~-half of it's Full speed" a diesel engine, Or other similar engine driver, can produce up to fifty percent of its full load horsepower and up to sixty ptmxnt of its full iaad torqua, while the electrical motor at this speed driving a centrifugal pump, only Yeclunres twenty-live 14 percent Of the hOrsepOwer of the engine. For the diesel engine to do this., the engine has to be at full throttle, so that the turboebarger is spooled up aztd giving the er~lne the required boost in power.
Yt is therefore erxvision~i that start-up rseeds can be cpnfrgured as folIow~
Run 1 s the c~ nr at no load for warm up. Set tha systc~ controller for tutacdug tlae ~aaotac at desired speed or current limit desired. Aa immediate or Slow ramp Can be accommodated. When the system controller gives signal to start the motor, then engine neZds w slow down to idle speed of about t:'fkeen Hear., and then receives the signal to go to the set speed, axtd whila the engine is under full tftmttie and gaioiatg speed, khen 20 the switchboard engages the motor. About thirty Hnrez would be a ;food point for engaging the motor. The engine will slow down slightly while picking up the motor load and then will continue on to its set speed oc current setking far the motor.
The variable fre~qucncy power system has many advantages over systems using a 25 variable speed drive. .The advance include increa,Red electrical efficiency no clcctricat L,armonics, an increase in the electrical power factor, an i:ocrease in motor ef~lciency, an increase in motor loading cagabilitics, a decrease in motor opcratiag temperature, and less electrical stress on the electrical insulation propertiEa of the motor windings and al l other electrical wires in the main cable and generator.
Another benefit of the variable frequency power system is it allows for the implementation of new pnoccsses which negates the current practice of over sizing the engine or generator The variable frequency power system results in a package which is smaller suad therefore easier to transport, lowers capital costs, is ug to twenty-five percent more energy ei~cient as a result of the elimination of ttze variable speed drive, barxrtonics and transformer, ultimately require less maintenance arid provide of longC;r Iifc of the System. In tk~e case of electric submersible pumps used by the oil and gag industry, the incorporation of all these features into one package provides a system that:
cari be used in remote locations without requiring the purchase of multiple deviocs which can be 1a'tore expensive and much mere bulky. The variable fi~quency ppwcr system includes the connection of the motor to an electrical centrifugal pump, an electrical fan or an electrical gas compressor pump.
While diff'ercnt embodiments of the invention have been described in detail herein, it wilt he apgrcciatcd by those sltillrd in the art that various modiffications and alternatives to the embodiments could be developed in light of the overall teachings of the disclosure. Accordingly, the pat~icular arrangements are i I/u.,~.tive only arid are npt linutin,~ as to the scope of the invention that is to be given the full breadth of any and all equivalents thereof.
Claims (30)
1. A variable frequency power system for starting and powering an electrical motor load comprising:
a power source with a rotating output, said power source having a speed control to regulate rotational speed of said rotating output, said rotational speed of said rotating output being rotational frequency of said rotating output;
a generator coupled to and driven by said rotating output of said power source, whereby speed control of said power source directly controls output power frequency of said generator to produce a desired output frequency from said generator due to control of rotational frequency of said rotating output;
a voltage regulator connected between said generator and the motor to regulate output voltage emanating from said generator for a supply voltage to an electrical motor load; and a system controller to control output power frequency of said generator to be said desired output frequency, said system controller connected to interface with said speed control of said power source; said system controller configured to monitor generator output and operational conditions of said electrical motor load, said system controller configured to adjust said speed control of said power source based on generator output and operational conditions of said electrical motor toad to maintain said desired output frequency.
a power source with a rotating output, said power source having a speed control to regulate rotational speed of said rotating output, said rotational speed of said rotating output being rotational frequency of said rotating output;
a generator coupled to and driven by said rotating output of said power source, whereby speed control of said power source directly controls output power frequency of said generator to produce a desired output frequency from said generator due to control of rotational frequency of said rotating output;
a voltage regulator connected between said generator and the motor to regulate output voltage emanating from said generator for a supply voltage to an electrical motor load; and a system controller to control output power frequency of said generator to be said desired output frequency, said system controller connected to interface with said speed control of said power source; said system controller configured to monitor generator output and operational conditions of said electrical motor load, said system controller configured to adjust said speed control of said power source based on generator output and operational conditions of said electrical motor toad to maintain said desired output frequency.
2. The variable frequency power system of claim 1, wherein said power source is an engine powered by a fuel source.
3. The variable frequency power system of claim 1, further including an uninterruptible power supply to power electronics of said variable frequency power system independently of said generator.
page 14
page 14
4. The variable frequency power system of claim 1, wherein said voltage regulator is an excitation controller which includes programmable logic so that voltage is adjusted according to rotational frequency of said engine and said generator.
5. The variable frequency power system of claim 1, wherein said generator is configured as multi-tap voltage generator.
6. The variable frequency power system of claim 1, wherein said motor is connected to an electrical submersible pump.
7. The variable frequency power system of claim 1, further including a transformer between said generator and said electrical motor load.
8. The variable frequency power system of claim 1, further including a switchboard connected between said generator and said electrical motor load to act as a shutdown switch between said generator and said motor, said switchboard controlled by said system controller.
9. The variable frequency power system of claim 1, wherein said power source is an engine powered by a fuel source; and further including an uninterruptible power supply to power electronics of said variable frequency power system independently of said generator.
10. The variable frequency power system of claim 9, wherein said voltage regulator is an excitation controller which includes programmable logic so that voltage is adjusted according to rotational frequency of said engine and said generator.
11. The variable frequency power system of claim 9, further including a transformer between said generator and said electrical motor load.
page 15
page 15
12. The variable frequency power system of claim 9, further including a switchboard connected between said generator and said motor to act as a shutdown switch between said generator and said motor, said switchboard controlled by said system controller.
13. A method of controlling power and frequency of power supplied to an electrical motor toad, using a variable frequency power system including a power source with a rotating output, the power source having a speed control to regulate rotational speed of the rotating output, the rotational speed of the rotating output being rotational frequency of the rotating output; a generator coupled to and driven by the rotating output of the power source, whereby speed control of the power source directly controls output power frequency of the generator to produce a desired output frequency from said generator due to control of rotational frequency of the rotating output; a voltage regulator connected between the generator and the motor to regulate output voltage emanating from the generator; and a system controller to control output power frequency of the generator to be the desired output frequency, the system controller connected to interface with the speed control of the power source; the system controller configured to monitor generator output and operational conditions of the motor, the system controller configured to adjust the speed control of the power source based on generator output and operational conditions of the motor to maintain the desired output frequency, comprising:
determining the proper frequency of power output from the generator which is required by the motor; and adjusting the speed of the power source to adjust the frequency of the power output of the generator by using the system controller to manipulate the speed control of the power source while monitoring the frequency of the power outputted from the generator, thereby controlling the frequency of the power outputted by the generator.
determining the proper frequency of power output from the generator which is required by the motor; and adjusting the speed of the power source to adjust the frequency of the power output of the generator by using the system controller to manipulate the speed control of the power source while monitoring the frequency of the power outputted from the generator, thereby controlling the frequency of the power outputted by the generator.
14. The method of claim 13, wherein said power source is an engine power by a fuel source.
page 16
page 16
15. The method of claim 13, further including an uninterruptible power supply to power electronics of said variable frequency power system independently of said generator.
16. The method of claim 13, further including monitoring operating conditions of a unit driven by the motor and adjusting the speed of the power source to adjust the frequency of the power output of the generator to the desired output frequency based on required power needs of the unit driven by the motor.
17. The method of claim 13, further including using the system controller to control a startup sequence to start the power source and generator combination by running the power source at idle with no load from the motor for a specified warm-up period, once warm-up is achieved, using the system controller to adjust the rotational output of the power source to a starting frequency, then using the system controller to adjust the rotational output of the power source to full speed, when the power source ramps up in rotational speed and reaches roughly half final operating rotational speed, using the system controller to engage power from the generator to the motor.
18. The method of claim 17, further including monitoring operating conditions of a unit driven by the motor and adjusting the speed of the power source to adjust the frequency of the power output of the generator based on required power needs of the unit driven by the motor.
19. The method of claim 13, wherein power engaged from the generator to the motor when the rotational speed of the rotational output of the power source is at about thirty Hertz.
20. The method of claim 13, further including using the system controller to control a startup sequence of the power source and generator combination by running the power source at idle with no load from the motor for a specified warm-up period, once warm-up is achieved, increasing the rotational speed of the rotating output of the power source to a page 17 steady operating frequency slightly below full operating frequency the power source while regulating output voltage from the generator at a reduced output voltage using the voltage regulator, using the system controller to engage the power from the generator to the motor while holding the output voltage fixed at the reduced voltage regardless of change in rotational speed of the power source, after a given period of time elapses, then using system controller to command the voltage regulator to ramp up the output voltage of the generator to achieve the required volts to hertz ratio required by the motor, finally waiting until the system reaches steady operation before bringing the power source to the final operational speed.
21. The method of claim 20, wherein the rotational speed of the rotating output of the power source before engaging power to the motor is set for the steady operating frequency is approximately around five-sixths of full operating frequencies.
22. The method of claim 20, wherein the reduced output voltage is about fifty to ninety percent the rated voltage required by the motor.
23. The method of claim 20, further including monitoring operating conditions of a unit driven by the motor and adjusting the speed of the power source to adjust the frequency of the power output of the generator based on required power needs of the unit driven by the motor.
24. The method of claim 13, further including using the system controller to control a startup sequence starting sequence where normal operating range of the motor will be in a range of forty to sixty Hertz and a set point of operational frequency of the outputted power is selected in the system controller, using the system controller to return the power source to an idle speed after initial warm up and then setting the rotational speed of the power source at a higher set speed level, As the power source gains speed and gets up to a speed of about thirty Hertz, then engage power from the generator to the motor.
page 18
page 18
25. The method of claim 24, further including monitoring operating conditions of a unit driven by the motor and adjusting the speed of the power source to adjust the frequency of the power output of the generator based on required power needs of the unit driven by the motor.
26. The method of claim 13, further including using the system controller to control a startup sequence of the power source and generator combination where the normal operating range of the motor will be in a range of fifty to sixty Hertz range a set point of operational frequency of the outputted power is selected in the system controller, using the system controller set the rotational speed of the power source such that the rotational speed is sufficient to prevent stalling of the power source while the power source picks up motor load when the power is engaged from the generator to the motor and allowing the power source to recover and return to the required setting of the Hertz selected for the power to be generated to the motor.
27. The method of claim 26, further including monitoring operating conditions of a unit driven by the motor and adjusting the speed of the power source to adjust the frequency of the power output of the generator based on required power needs of the unit driven by the motor.
28. The variable frequency power system of claim 1, wherein said motor is connected to an electrical centrifugal pump.
29. The variable frequency power system of claim 1, wherein said motor is connected to an electrical fan.
30. The variable frequency power system of claim 1, wherein said motor is connected to an electrical gas compressor pump.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002454848A CA2454848C (en) | 2003-12-30 | 2003-12-30 | A variable frequency power system and method of use |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002454848A CA2454848C (en) | 2003-12-30 | 2003-12-30 | A variable frequency power system and method of use |
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| CA2454848A1 CA2454848A1 (en) | 2005-06-30 |
| CA2454848C true CA2454848C (en) | 2009-05-19 |
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| CA002454848A Expired - Lifetime CA2454848C (en) | 2003-12-30 | 2003-12-30 | A variable frequency power system and method of use |
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Effective date: 20240102 |