Patent Publication Number: US-7724549-B2

Title: Integrated power conditioning system and housing for delivering operational power to a motor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS STATEMENT REGARDING FEDERALLY 
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   SPONSORED RESEARCH OR DEVELOPMENT 
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   BACKGROUND OF THE INVENTION 
   The present invention relates generally to power conditioning systems for driving motors and, more particularly, to an integrated power conditioning system for delivering power suitable for driving a motor that may be enclosed in a common housing. 
   Power plants are linked to power consuming facilities (e.g., buildings, factories, etc.) via utility grids designed so as to be extremely efficient in delivering massive amounts of power. To facilitate efficient distribution, power is delivered over long distances as fixed frequency three-phase alternating current (AC) power. 
   Despite being efficiently distributable, fixed frequency AC power is often not suitable for end use in consuming facilities. In many applications, the power delivered by the utility must be converted or “conditioned” to a useable form. For example, motors and their associated loads are one type of common inductive load employed at many consuming facilities that require power conditioning. 
   To this end, typical power “conditioning” systems configured to condition power for motor systems include AC-to-DC (direct current) rectifiers that convert the utility AC power to DC power applied to positive and negative DC buses (i.e. across a DC link) and an inverter linked to the DC link that converts the DC power back to three-phase AC power having a form suitable to a desired application. A controller controls the inverter in a manner calculated to provide power having a waveform desired for consumption. 
   Specifically, the inverter includes a plurality of switches that can be controlled to link and unlink the positive and negative DC buses to motor supply lines. The linking-unlinking sequence causes voltage pulses on the motor supply lines that together define alternating voltage waveforms. When controlled correctly, by a pulse width modulator (PWM) controller, the waveforms cooperate to generate a rotating magnetic field inside the motor stator core. In an induction motor, the magnetic field induces a field in motor rotor windings. The rotor field is attracted to the rotating stator field and thus the rotor rotates within the stator core. In a permanent magnet motor, one or more magnets on the rotor are attracted to the rotating magnetic field. The rectifier, inverter, and control circuitry are commonly referred to as a motor drive unit. 
   The output of the motor drive unit often includes an output filter in the form of a reactor designed to reduce the peak voltages applied to the motor terminals so that reflected waves are controlled or reduced. These filters are particularly important when the distance between the output of the motor drive unit and the motor input is significant because power stability issues raised by reflected waves are further exacerbated over these long distances. 
   Beyond filters, it is often desirable to include a transformer between the filter and the motor inputs to isolate the motor from the utility supply and/or to step up or step down the fundamental voltage supplied by the motor drive unit to be usable by the motor. Furthermore, the transformer may be used to reduce common mode noise present on the motor supply lines. 
   In this regard, for convenience and serviceability, industrial/commercial motor systems are typically separated into two localities. First, the motor drive unit and filter are generally located in an area near the location where the utility lines deliver power to the facility housing the motor system. In this regard, by arranging the majority of the power “conditioning” components (i.e. motor drive unit, filter, and the like) at a centralized location near the terminal end of the utility lines, human exposure to these high power components can be reduced and servicing procedures streamlined. Second, the transformer and motor are generally located in an area proximate to the motor load. By localizing the transformer and motor components near the motor load, power losses associated with delivering power in a form suitable for driving the motor over long distances are reduced. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention improves upon the above-described systems by providing an integrated power conditioning system for delivering power suitable for driving a motor that may be enclosed in a common housing. In particular, while the motor drive unit may still be arranged separately from the motor and motor load, the filter and transformer may be arranged together in a single housing. Hence, various cost, size, and power consumption savings can be realized. To realize further savings, the filter and transformer may share a common core. 
   In accordance with one aspect of the invention, a device for conditioning power delivered to operate a motor is disclosed. The device includes a sealed housing having at least one input terminal extending through the housing and configured to receive an input power and at least one output terminal extending through the housing and configured to deliver an output power conditioned to power a motor coupled to the output terminal. The device also includes a filter arranged in the housing and that has an input configured to receive the input power from the input terminal. Accordingly, the filter is configured to suppress voltage changes in the input power and deliver a filtered power to an output of the filter. A transformer is included that is arranged in the housing and has an input configured to receive the filtered power from the output of the filter. As such, the transformer is at least configured to electrically isolate the input terminal from the output terminal and deliver a conditioned power from an output of the transformer to the output terminal to power the motor coupled to the output terminal. 
   In accordance with another aspect of the invention, a power conditioning device configured to deliver power condition to drive a motor is disclosed. The device includes a filter having a plurality of windings extending from an input configured to receive unconditioned power to an output configured to deliver filtered power. The plurality of windings is configured to suppress voltage changes in the unconditioned power. The device also includes a transformer that has a set of primary windings configured to receive the filtered power from the output of the filter and a set of secondary windings electrically isolated from the primary windings to deliver a conditioned power to power a motor coupled thereto. The device also includes a shared metal core extending through plurality of windings of the filter and the primary windings and secondary windings of the transformer. 
   In accordance with yet another aspect of the invention, a device for conditioning power delivered to operate a motor is disclosed that includes a housing having an interior and an exterior. The housing also includes at least one input terminal extending from the interior to the exterior to receive an input power and at least one output terminal extending from the interior to the exterior to deliver an output power conditioned to power a motor coupled to the output terminal. The device also includes a reactor arranged in the interior of the housing and that has an input configured to receive the input power from the input terminal. The reactor is configured to suppress voltage changes in the input power and deliver a filtered power to an output of the reactor. A transformer is included that is arranged in the interior of the housing and has an input configured to receive the filtered power from the output of the reactor. In this regard, the transformer is at least configured to electrically isolate the input terminal from an output terminal and deliver a conditioned power from an output of the transformer to the output terminal to power the motor coupled to the output terminal. Additionally, the device includes a common metal core extending through the reactor and the transformer to couple magnetic flux therebetween. 
   Various other features of the present invention will be made apparent from the following detailed description and the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic representation of a motor system including a power conditioning device in accordance with the present invention; 
       FIG. 2  is a cross-sectional and schematic view of a single phase portion of the power conditioning device of  FIG. 1  having an integrated filter and transformer device arranged in a common housing; 
       FIG. 3  is a single phase circuit diagram representation of the integrated filter and transformer device of  FIG. 2 , showing basic input and output terminations and additional terminations that include additional filtering and damping components external to the housing; 
       FIG. 4   a  is a circuit diagram of the integrated filter and transformer device of  FIG. 1  shown in a three-phase application and including an inductor-capacitor filter having a wye capacitor configuration; 
       FIG. 4   b  is a circuit diagram of the integrated filter and transformer device of  FIG. 1  shown in a three-phase application and including an inductor-capacitor filter having a delta capacitor configuration; 
       FIG. 5   a  is a circuit diagram of the integrated filter and transformer device of  FIG. 1  shown in a three-phase application and including an inductor-capacitor filter having a wye capacitor configuration and a feedback loop; 
       FIG. 5   b  is a circuit diagram of the integrated filter and transformer device of  FIG. 1  shown in a three-phase application and including an inductor-capacitor filter having a wye capacitor configuration and another feedback loop configuration; 
       FIG. 5   c  is a circuit diagram of the integrated filter and transformer device of  FIG. 1  shown in a three-phase application and including an inductor-capacitor filter having a wye capacitor configuration and a pair of feedback loops; 
       FIG. 5   d  is a circuit diagram of the integrated filter and transformer device of  FIG. 1  shown in a three-phase application and including an inductor-capacitor filter having a wye capacitor configuration and another feedback loop configuration; 
       FIG. 6  is a single phase circuit diagram representation of the integrated filter and transformer device of  FIG. 1  including multiple line reactors for connection to parallel inverter outputs; 
       FIG. 7   a  is a schematic representation of a three-phase integrated filter and transformer device having a common metal core arranged according to a first configuration; 
       FIG. 7   b  is a schematic representation of a three-phase integrated filter and transformer device having a common metal core arranged according to another configuration, in which the filter inductor section contains an E-type core lamination and gap on the “I” section of the reactor core section; 
       FIG. 7   c  is a schematic representation of a three-phase integrated filter and transformer device having a common metal core arranged according to yet another configuration, in which the reactor gap is arranged in the middle core section of the filter inductor; and 
       FIG. 7   d  is a schematic representation of a three-phase integrated filter and transformer device having a common metal core arranged according to still another configuration. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to  FIG. 1 , the present invention will be described in the context of a motor control system  10 . The motor control system  10  includes a power supply  12  and a motor drive unit  14 . The power supply  12  provides power to the motor drive unit  14  that, in turn, converts the power to a more usable form for a three-phase motor  16  that drives an associated load  18 . 
   The motor drive unit  14  includes variety of components, such as a rectifier  20 , an inverter  22 , and a controller  24 . During operation, the power supply  12  provides three-phase AC power, for example, as received from a utility grid over transmission power lines  26 . However, it is also contemplated that the power supply  12  may be designed to deliver single-phase power. In either case, the nominal line voltage delivered by the power supply  12  is dependent on the particulars of the motor  16 , load  18 , and power available to the power supply  12  to drive the motor drive  14 . For example, as addressed above, the power supply  12  may be a transmission power receptacle, in which case, the power available to the motor control system  10  will be dependent upon the specifics of the geographic region in which the motor control system  10  is located (e.g. 50 Hz/60 Hz or 220 V/380V). 
   Accordingly, the rectifier  20  is designed to receive AC power from the power supply  12  and convert the AC power to DC power. It is contemplated that various types of rectifiers may be employed to convert the AC power to DC power. For example, some rectifiers, such as a pulse width modulated (PWM) rectifier, are active and include a plurality of switching transistors. PWM rectifiers may be advantageously employed where energy present in the motor windings is regeneratively supplied back to the power supply  12  when the motor  16  is disconnected. 
   On the other hand, a passive rectifier, such as a multiple phase (e.g., 6, 18, or 24) diode rectifying bridge used in conjunction with a bus capacitor and filters, could be used that would not require input from the controller  24 . In the case of a passive rectifier, power may be dissipated in braking resistors (not shown) coupled across the motor windings when the motor  16  is disconnected. 
   In either case, the inverter  22  is positioned between positive and negative DC buses  28 ,  30  of the rectifier  20  output. As is well known in the motor control arts, the inverter  22  includes a plurality, for example, six switching devices (e.g., BJTs and the like) that are positioned between the positive and negative DC buses  28 ,  30  and output supply lines  32  of the inverter  22 , such that the PWM controller  24  can open and close specific combinations of the switches to sequentially generate positive and negative DC voltage pulses on each of the supply lines  32 . By opening and closing the switches of the inverter  22  in specific sequences, the motor drive unit  14  generates AC power having controllable amplitudes and frequencies on each of the supply lines  32 . 
   Ideally, each of the lines  32  is linked to a separate one of three-phase windings of the motor  16 . By providing known sequences of AC power across the motor windings, the motor  16  is driven to turn a drive shaft  34  that, in turn, drives the load  18 . However, in actuality, it is often necessary to include additional power conditioning components between the output of the inverter  22  and the input of the motor  16 . As; will be described below, the present invention includes a consolidated power conditioning device  36  that provides a variety of additional power conditioning functions, such as filtering and isolation to protect against voltage waves created by the inverter  22  and reflected by the motor  16 . In particular, one device is created that reduces changes in the voltage supplied to a motor, which reduces peak voltage induced by reflected waves. 
   Furthermore, the additional power conditioning device  36  can be configured to step up or step down the voltage supplied from the inverter  22  to be more suitable for use by the motor  16 . In this regard, a step-up configuration will be described, that includes a power source from the inverter  22 , which may be designed to deliver low-voltage (e.g., less than 600V), high-current power. The power conditioning unit  36 , which is typically located proximate motor drive unit  14 , may be configured as a step-up voltage transformer to provide power to a medium voltage motor and load a significant distance away. The power conditioning unit  36  may employ taps to compensate for the voltage drop and losses associated with transmitting the power over significant distances, such as power lines  38  extending from the power conditioning unit  36  to the motor  16  and load  18 . A similar configuration and description for a step-down transformer configuration is also contemplated. 
   Referring now to the single phase circuit representation in  FIG. 2 , the power conditioning device  36  includes a filter inductor  40  and a transformer  42  arranged within a common housing  44 . The housing  44  may also hold an insulating and heat conducting material and/or dielectric  46 . For example, it is contemplated that the material  46  may include oil or the like. Additionally, as will be described in greater detail below, it is contemplated that the filter inductor  40  and transformer  42  share a common core  48 , such as an iron or other flux coupling core. 
   By arranging the filter inductor  40  and transformer  42  in a common housing  44  a number of advantages are achieved over traditional systems employing filters and transformers located separately, and often in differing localities. First, as shown in  FIG. 2 , the filter inductor  40  is immersed in insulating and heat conducting materials  46  that are not typically available to the filter inductor  40  but commonly used with the transformer  42 . Accordingly, cooling systems, such as fans and the like, and the associated enclosures that are often employed to cool a separately located filter are not necessary. Second, by arranging the filter inductor  40  within a sealed housing  44  along with the transformer  48 , the filter inductor  40  is protected from the elements and; thus, the operational life of the filter inductor  40  is extended. Furthermore, by arranging the filter inductor  40  and transformer  42  in a common locality and within a common housing  44 , it is possible to easily reconfigure the system for varying input and output power requirements. 
   For example, in accordance with one embodiment, it is contemplated that a plurality of taps  50  may be provided that extends from the housing  44 . In this regard, beyond input and output taps  52 ,  54  and neutral taps  56 , additional reconfiguration taps  58  may be included that enable a user to quickly change/adjust the configuration of the system. 
   For example, as shown, additional taps  58  may be included that provide access to center taps on the transformer  42  to change input and output characteristics and/or compensate for variations in the reactance of the filter inductor  40 . However, it is contemplated that a wide variety of taps beyond those illustrated in  FIG. 2  may be included to enable ready reconfiguration of the device  36  by selecting different tap configurations. For example, the additional taps  58  may be designed to step-up or step-down (or neither) the voltage supplied to the motor, as dictated by a given application. 
   Additionally, it is contemplated that other taps may be provided that are designed to receive additional filters, such as capacitors. For example, referring to  FIG. 3 , which shows a single phase representation of power conditioning unit  36 , it is contemplated that a variety of additional taps  58  may be included to enable user-selection of a variety of electrical configurations between the filter inductor  40 , the transformer  42 , and any additional filters  60 , such as additional capacitive or inductive filters or even resistive elements. In this regard, desired configurations may include a resistor arranged in parallel with the line reactor filter inductor  40  to reduce reflected wave voltage spikes and reduce common mode noise currents, such as described in commonly assigned U.S. Pat. No. 5,990,654, entitled “Apparatus for Eliminating Motor Voltage reflections and Reducing EMI currents”, which is incorporated herein by reference. It may also include the use of a plurality of additional components  64  forming sections of tuned circuits. Such tuned sections of circuits may include series-resonant, sine-wave filters, such as described in commonly assigned U.S. Pat. No. 6,208,537, entitled “Series Resonant Sinewave Output Filter and Design Methodology,” which is incorporated herein by reference. These tuned sections function to wave shape the discrete positive and negative PWM voltage pulses of the inverter  22  at the filter inductor  40  input. Accordingly, a sine wave voltage at fundamental output frequency of the inverter  22  is transferred to the input of the transformer  42 . 
   In other cases, it is contemplated that the additional components  64  may simply include capacitors connected in a delta or wye configuration for use with a drive voltage source inverter topology. For example, referring to a three phase schematic of components connected/integrated with the filter/housing  44  in  FIGS. 4   a  and  4   b , two such LC filter configurations are shown where the additional components  64  are capacitors connected through the additional taps  58  in a wye configuration and a delta configuration, respectively. 
   Furthermore, building upon the configurations shown in  FIGS. 4   a  and  4   b  and referring now to  FIGS. 5   a  through  5   d , it is contemplated that various feedback loops may be included to improve system stability, improve line-ground voltage wave shape, or reduce further common mode noise. For example, in  FIG. 5   a  a feedback loop  66  extends from the set of wye configured capacitors arranged as the additional components  64  to the negative DC bus  30  of the rectifier  20  output. However, as shown in  FIG. 5   b , it is also contemplated that the feedback loop  66  may extend to the positive DC bus  28  of the rectifier  20  output or, as shown in  FIG. 5   c , two sets of additional components  64   a ,  64   b  may be connected to the additional taps  58  that include corresponding feedback loops  66   a ,  66   b  extending to the positive DC bus  28  and the negative DC bus  30 , respectively. Also, referring to  FIG. 5   d , a three-level PWM inverter including multiple switches (e.g., twelve switches) and multiple diodes (e.g., eighteen) with a neutral clamp point brought out  22   a  may be used, whereby the feedback loop  66  can be designed to extend between the additional components  64  and an input  68  to the three-level PWM inverter  22   a  between the positive DC bus  28  and the negative DC bus  30 . Alternatively, a feedback loop  66  may be returned to a two level PWM inverter, whereby the feedback loop  66  is connected to the midpoint of the DC Bus capacitor bank. In this case, the feedback loop  66  is connected to the neutral wye connection point of capacitor components  64 , which is brought to near zero voltage to thereby reduce common mode voltage further. 
   Within each of the configurations described with respect to  FIGS. 5   a - 5   d  it is contemplated that a wide variety of variations may be used. For example, delta configurations, floating wye neutrals, high resistance grounded wye neutrals, or solid grounded wye neutrals/corner grounded delta configurations designed to reduce common mode noise on the motor cables. Furthermore, it is contemplated that an auto-transformer may be used to compensate for voltage drops across the filter inductors  40 . 
   While the above-described configurations include a (single- or three-phase) line filter inductor  40 , a wide variety of filter types and configurations may be integrated within the housing  44 . For example, referring now to  FIG. 6 , it is contemplated that multiple line reactors  40   a ,  40   b ,  40   z  may be integrated within the housing  44  and coupled to the transformer  42 , such as is desirable when motor drive units are employed that include multiple, parallel inverters. The reactors prevent circulating current between parallel inverters and also help to balance fundamental current supplied by each voltage source inverter in parallel. 
   As described above, the filter inductor and transformer are not only commonly located in a housing  44  but actually share a common core  48 . By doing so, the overall size of the combined filter inductor  40  and transformer  42  may be reduced. In particular, referring to  FIG. 7   a , in the case of a three-phase system, by sharing a common core  48 , the overall size of the filter inductor  40  and transformer  42  can be reduced since the top three-phase leg of filter inductor  40  can be eliminated and integrated into the bottom leg  70  of the three-phase transformer  42  on the common core  48 . That is, by sharing a common core  48 , a leg  70  of the core  48  is common to both the filter  40  and the transformer  42 ; thus, eliminating the need for one of the legs that would be included if separate cores were used. This shared leg  70  may be interleaved with each phase leg  71   a ,  71   b ,  71   c  to isolate the filter inductor  40  and the transformer  42  from the magnetic flux of the other. Alternatively, referring to  FIG. 7   b , it is also contemplated that an E-core  76  may be used to form the core of the filter  40 , which is then interleaved with the phase legs  71   a ,  71   b ,  71   c  of the transformer  42 . 
   Another feature of the common core  48  is an air gap  72  that is designed to keep the filter  40  within a linear operational range and protect against saturation. While  FIG. 7   a  shows the air gap  72  arranged proximate to the filter inductor  40  and away from the transformer  42 , it may also be formed between the filter inductor  40  and the transformer  42 . That is, it is contemplated that the air gap  72  may be arranged on in each phase leg of the filter inductor  40 . 
   Opposite the air gap  72 , the common core  48  may include a butt gap or a set of interleaved laminations that close the core  48  near the transformer  42  so that it can withstand DC offset currents. Such lamination termination configurations are known in the art. Additionally, in the case of interleaved laminations  74 , core losses are advantageously controlled. 
   Referring now to  FIG. 7   c , rather than including the air gap  72  on one side of the filter inductor  40 , it is contemplated that the air gap  72  may be formed within a portion of the core  48  located within the filter inductor  40 . In particular, it is contemplated that the air gap  72  may be formed within the core  48  and aligned with a gap  78  formed in the windings of the filter inductor  40 . Also, by arranging the air gap  72  within the filter inductor  40  and away from the transformer  42 , the air gap  72  further limits fringing flux that could otherwise enter the housing  44  from the filter inductor  40 . As such, the amount of separation required between the housing  44  and combined filter inductor  40 /transformer  42  may be further reduced. 
   However, referring now to  FIG. 7   d , in some arrangements, such as when the filter inductor  40  will be used under conditions that would not cause saturation, the air gap may be eliminated. That is, while the elimination of the air gap will cause the filter inductor  40  to operate as a non-linear reactor, such a configuration may be desirable when the system will not be used under conditions that could cause the filter inductor  40  to saturate. 
   While  FIGS. 7   a  through  7   d  illustrate three-phase systems, it is likewise contemplated that single-phase systems may be utilized in a similar manner. Additionally, other variations are contemplated, such as integrating course and fine tap switches into the transformer primary and secondary windings or, as described above, various additional taps may be included, such as a tapped primary windings of the transformer  42 . 
   Therefore, the above-described system provides an integrated power conditioning system for delivering power suitable for driving a motor that may be enclosed in a common housing. Accordingly, while the motor drive unit may still be arranged separately from the motor and motor load, the filter inductor and transformer may be arranged together in a single housing with external filter resistors capacitors or inductors. Hence, various cost, size, and power consumption savings can be realized, as well as use of only a single thermal cooling and electrically insulating medium. For example, the integrated filter and transformer may advantageously share a common core having any of a variety of shared features. 
   The above-described system is particularly advantageous when used with low-voltage drive systems that are designed to feed medium-voltage motors or motors with long cables that are susceptible to reflected wave and common mode noise. Furthermore, the above-described system provides a transformer configuration that is capable of handling DC offsets and low frequency sub-harmonics often associated with the output of PWM inverter motor drives. 
   The present invention has been described in terms of the preferred embodiments, and it should be appreciated that many equivalents, alternatives, variations, and modifications, aside from those expressly stated, are possible and within the scope of the invention. Therefore, the invention should not be limited to a particular described embodiment.