Abstract:
An apparatus and method for mounting additional components, such as capacitors, to a DC bus of a motor drive. In one aspect, a motor drive includes an enclosure defining an interior, an input for receiving input electrical power from a power source, an output for providing output electrical power to a load, an intermediate DC circuit including a DC bus located in the interior of the enclosure, and a modular capacitor bus electrically coupled with the intermediate DC circuit, the modular capacitor bus including at least one capacitor mounted thereto. The modular capacitor bus is mountable as a unit to the DC bus.

Description:
BACKGROUND 
       [0001]    The present exemplary embodiment relates generally to electrical power conversion. It finds particular application in conjunction with motor drives, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications. 
         [0002]    Power conversion systems convert electrical power from one form to another and may be employed in a variety of applications such as motor drives for powering an electric motor using power from an input source. Typically, the power converter is constructed using electrical switches actuated in a controlled fashion to selectively convert input power to output power of a desired form such as single or multi-phase AC of a controlled amplitude, frequency and phase to drive an AC motor according to a desired speed and/or torque profile, often in the presence of varying load conditions. In a typical situation, one or more AC motor drives are connected to an AC power bus or point of common coupling along with other loads where a common AC power source provides current to all these loads via the common bus. The AC drives may be equipped with power factor correction (PFC) apparatus to operate the drive at or near unity power factor. Such apparatus&#39; generally include a number of DC bus capacitors that serve to store and release energy as needed by the load to maintain efficient operation. 
         [0003]    The number of DC bus capacitors is at least in part determined by the voltage rating of the motor drive. For example, in one motor drive of a first rating a pair of capacitors can be placed in series to handle the given voltage of the drive. In another motor drive of a higher voltage rating, the same type of capacitors may be placed in three capacitor series with multiple parallel legs of capacitors to achieve the correct overall drive capacitance. This requires more capacitors. For example, a 480V motor drive may use 8 capacitors whereas a 690V motor drive may use 27 capacitors. Thus, as ratings increase, the number of capacitors needed to achieve the correct overall drive capacitance generally increases. 
         [0004]    In a typical drive, the DC bus capacitors are mounted directly to the DC bus. As will be appreciated, as ratings increase a larger and larger space is consumed by the capacitors on the DC bus and within the motor drive enclosure. This has generally been addressed by increasing the size of the motor drive enclosure to accommodate the capacitors, as well as increasing the surface area of the DC bus to increase the space available to mount the capacitors. 
       BRIEF DESCRIPTION 
       [0005]    The present disclosure sets forth an apparatus and method for mounting additional components, such as capacitors, to a DC bus of a motor drive. Aspects of the disclosure allow an increased number of components to be connected to the DC bus, without resorting to increasing the size of the DC bus or the size of the motor drive enclosure, by supporting capacitors on a laminated bus that is mounted to, for example, a main DC bus. This results in a more densely populated power structure, is easier to assemble, and allows power to flow through a parallel power path rather than through the capacitor bus structure resulting in reduced heat buildup, lower operating temperatures, and increased component life. 
         [0006]    In accordance with one aspect of the disclosure, a motor drive comprises an enclosure defining an interior, an input for receiving input electrical power from a power source, an output for providing output electrical power to a load, an intermediate DC circuit including a DC bus located in the interior of the enclosure, and a modular capacitor bus electrically coupled with the intermediate DC circuit, the modular capacitor bus including at least one capacitor mounted thereto. The modular capacitor bus is mountable as a unit to the DC bus. 
         [0007]    The DC bus and/or the capacitor bus can include a laminated bus structure. The capacitor bus can include at least two capacitors arranged in parallel. The at least two capacitors arranged in parallel can be part of a series of capacitors arranged in series. At least a portion of the DC bus and the modular capacitor bus can extend in parallel spaced-apart planes such that air can circulate between the DC bus and the modular capacitor bus. The modular capacitor bus can be supported on the DC bus. The capacitor bus can be mounted and/or secured to the DC bus with at least one fastener. 
         [0008]    In accordance with another aspect, a modular capacitor bus that is electrically couplable to an associated DC power bus comprises at least one insulator layer, at least one conductor layer, at least one terminal for electrically coupling the at least one conductor layer to the associated DC power bus, and at least one capacitor terminal for connecting the at least one conductor to an associated capacitor. 
         [0009]    The capacitor bus can include a laminated bus structure, which may include a plurality of positive conductor layers, a plurality of negative conductor layers, and an insulator layer between each of the conductor layers. The capacitor bus can include at least two capacitors arranged in parallel. Each of the at least two capacitors arranged in parallel can be part of a series of capacitors arranged in series. The modular capacitor bus can be generally planar and configured to be mounted to an associated DC power bus in spaced apart relation thereto such that air can circulate around the capacitor bus. 
         [0010]    In accordance with another aspect, a method of mounting a plurality of capacitors to a DC power bus comprises mounting at least one capacitor to a capacitor bus, electrically coupling the at least one capacitor to a conductor of the capacitor bus, mounting the capacitor bus to a DC power bus such that the capacitor bus and DC power bus are in spaced relation to each other, and electrically coupling the capacitor bus to the DC power bus. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic diagram illustrating an exemplary motor drive; 
           [0012]      FIG. 2  is a front elevation view illustrating an exemplary wall-mount integrated regenerative motor drive of  FIG. 1  coupled with a three-phase AC power source and a three-phase AC motor load; 
           [0013]      FIG. 3  is a partial side elevation view in section illustrating an exemplary laminated DC intermediate circuit implementation in the motor drive of  FIGS. 1-2 ; 
           [0014]      FIG. 4  is a simplified schematic diagram illustrating features of the motor drive of  FIGS. 1-2  including a capacitor bus in accordance with the present disclosure; 
           [0015]      FIG. 5  is a perspective view of an exemplary laminated power bus; 
           [0016]      FIG. 6  is an exploded view of the exemplary laminated power bus of  FIG. 5 ; 
           [0017]      FIG. 7  is a perspective view of an exemplary capacitor bus in accordance with the present disclosure; 
           [0018]      FIG. 8  is an exploded view of the exemplary capacitor bus of  FIG. 7 ; 
           [0019]      FIG. 9  is an exploded view of an exemplary power bus and capacitor bus assembly in accordance with the disclosure; 
           [0020]      FIG. 10  is a perspective view of a split DC laminated bus in accordance with the disclosure; and 
           [0021]      FIG. 11  is an exemplary motor drive including the split DC laminated bus of  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Referring now to the figures, several embodiments or implementations of the present disclosure are hereinafter described in conjunction with the drawings, wherein like reference numerals are used to refer to like elements throughout, and wherein the various features are not necessarily drawn to scale. A multi-phase integrated AC regenerative motor drive  100  is hereinafter illustrated and described which includes a novel capacitor configuration in accordance with the disclosure. It will be appreciated that the illustrated embodiments are merely examples, and that the capacitor bus and methods can be used in a wide variety of motor drives and are not limited to the exemplary multi-phase integrated AC regenerative motor drive disclosed herein. The illustrated drive  100  is but one type of motor drive in which aspects of the present disclosure can be embodied. 
         [0023]      FIG. 1  illustrates an exemplary integrated AC regenerative motor drive  100 . The drive  100  includes an input rectifier (converter)  120 , an intermediate DC link circuit with a link capacitance C, an inverter  140 , a precharging circuit  130  with one or more IGBTs Q 1  (two IGBTs Q 1 A and Q 1 B shown in the drawing) and a controller  150  housed within the interior  103  of a single enclosure  102 . As exemplified in  FIG. 2 , the enclosure  102  in one example is a structure preventing user exposure to the internal subsystems and components thereof and providing input terminals  104  for coupling to an AC input source  10  as well as output terminals  106  for connection to a driven AC motor  20 . In certain embodiments, first and second DC output terminals  105  are provided to allow external access to the DC bus of the intermediate circuit, for instance, to power an external inverter or other circuit requiring DC input power. In certain embodiments, moreover, the inverter  140  and the corresponding inverter control component  170  may be omitted, whereby a power conversion system  100  is provided including the housing  102 , an input rectifier  120 , a DC circuit having a capacitance C, and the precharging circuit  130  including one or more IGBTs Q 1  and a controller  150  housed within the interior  130  of the enclosure  102 , with the DC output terminals  105  providing DC output power from the DC circuit as a common bus supply product  100 . 
         [0024]    The drive shown in  FIG. 1  includes an input filter circuit  110  including line reactors connected in series in each of three AC input lines between the three-phase AC source  10  and AC input nodes  112 ,  114  and  116  of the switching rectifier  120 . This drive, moreover, employs a fundamental front end (FFE) rectifier switching control component  160  of the controller  150  providing rectifier switching control signals  162  in a regenerating mode of operation at a frequency approximately equal to the fundamental AC input source frequency (e.g., 50 Hz or 60 Hz typically). 
         [0025]    As seen in  FIG. 1 , the switching rectifier  120  includes AC input nodes  112 ,  114  and  116  coupled with the input terminals  104  for receiving AC power from the source  10 , and provides DC output power to the intermediate DC circuit at nodes  122 A (+) and  124  (−). The illustrated rectifier  120  is a three-phase input, DC output, converter stage including rectifier switching devices S 1 -S 6  operative according to switching control signals  162  from the controller  150 . In the illustrated examples, the rectifier switching devices S 1 -S 6  are IGBTs each having an associated freewheeling diode, but other forms of electrical switching devices can be used. The DC output nodes of the rectifier  120  are coupled with the intermediate DC circuit which includes the precharging circuit  130  disposed in the upper (e.g., positive) current path of the DC link circuit, as well as a DC link capacitance C coupled between the upper and lower DC current paths of the link circuit, with the precharging circuit  130  located between the upper terminal of the link capacitance C and the positive output of the rectifier  120 . 
         [0026]    The inverter  140  in certain embodiments receives DC power from the intermediate DC circuit and provides three-phase AC electrical power to drive the motor load  20  by DC-AC conversion using inverter switching devices S 7 -S 12 , which can be any suitable form of electronically actuatable switching devices, such as IGBTs in the illustrated embodiments. In other possible implementations, the inverter  140  and associated inverter control component  170  can be omitted, and the power conversion system  100  may include DC bus output terminals  105  electrically coupled with the positive and negative DC bus terminals of the intermediate circuit in order to provide DC output power flow to or from an external device (not shown). In some embodiments, moreover, the inverter  140  and associated controller  170  may be included within the drive system  100 , and the drive  100  may provide the DC output terminals  105  for selectively providing DC output power to, or receiving power from, an external device. The active rectifier  120  is operated by rectifier switching control signals  162  from the rectifier controller  160 , and the inverter  140  is operated by inverter switching control signals  182  from the inverter controller component  170  of the controller  150 . Other forms of rectifier and/or inverter switching devices S 1 -S 12  can be used having appropriate control terminals operated according to the switching control signals  162 ,  182  (e.g., semiconductor-based switches such as silicon controlled rectifiers (SCRs), gate turn-off thyristors (GTOs), gate commutated thyristors (GCTs) such as integrated gate commutated thyristors (IGCTs) or symmetrical gate commutated thyristors (SGCTs)), etc.). 
         [0027]    The controller  150  includes a rectifier controller  160 , an inverter controller  170  (omitted in certain embodiments) and a precharge controller  180  operable according to a current operational mode  190 , where the operational mode of the motor drive  100  can be set by an external mode selection signal or value (not shown) from a user or from another system, and/or the mode  190  can be set based on internal conditions within the drive  100 . The controller  150  and the components thereof may be implemented as any suitable hardware/processor-executed software, processor-executed firmware, logic, and/or combinations thereof wherein the illustrated embodiment can be implemented largely in processor-executed software or firmware providing various control functions by which the controller  150  receives feedback and/or input signals and/or values (e.g., setpoint(s)) and provides the switching control signals  162 ,  172 ,  182  to operate the switching devices S 1 -S 6  of the rectifier  120 , the switches S 7 -S 12  of the inverter, and the IGBT(s) Q 1  of the precharging circuit  130 . In addition, the controller  150  and the components  160 ,  170 ,  180 ,  190  thereof can be implemented in a single processor-based or one or more of these can be separately implemented in unitary or distributed fashion by two or more processor devices. 
         [0028]    The exemplary controller  150  operates in one of three different modes, including a first mode for precharging the DC link capacitance C, a second mode for conducting regenerative current toward the AC source  10 , and a third mode (motoring) for providing drive power to operate the AC motor  20 . In certain embodiments, non-regenerative systems  100  are provided, in which the controller  150  operates only in the first mode for precharging the DC capacitance C and the third mode for providing output power, whether via the DC output terminals  105  (common bus supplied product  100 ) and/or providing AC output power for driving a motor load. In one or more of these operational modes, the controller  150  utilizes various feedback information including measured input line-line or line-neutral voltages Va, Vb, Vc, sensed AC input line current values Ia, Ib, Ic (obtained via current sensors disposed between the input filter circuit  110  and the rectifier  120  in one example), measured DC link voltage VDC, and/or sensed AC output currents and voltages Iu, Iv, Iw and Vu, Vv, Vw, etc. In addition, the controller  150  includes suitable interface circuitry in order to receive the various input and/or feedback signals and/or values, as well as suitable driver circuitry for generating switching control signals  162 ,  172 ,  182  of suitable electrical characteristics to actuate the associated switching devices S 1 -S 6 , Q 1 , S 7 -S 12  operated according to the signals. As seen in  FIG. 2 , moreover, the motor drive  100  may include a user interface accessible from the exterior of the enclosure  102  by which a user may interact with the controller  150  in order to set operating values (e.g., setpoints, mode  190 , etc.), view sensed operating conditions, etc. 
         [0029]    The switching control signals  162 ,  172  for the switching devices S 1 -S 12  of the rectifier  120  and/or inverter  140  may be provided by the controller  150  using any suitable switching scheme, which may involve one or more pulse width modulation (PWM) techniques including without limitation vector modulation (SVM), selective harmonic illumination (SHE), etc. In addition, the various components within the control system  150  may operate according to setpoint source other signals/values provided by another one of the control components. For instance, the inverter control  170  during normal motoring operation may provide a DC voltage setpoint signal or value to the rectifier controller  160 , with the rectifier controller  160  regulating its output voltage according to the setpoint from the inverter controller  170 . Moreover, operation of the rectifier  120 , the precharging circuit  130 , and the inverter  140  are coordinated by the controller  150  and the components  160 ,  180 , and  170  thereof based on the currently selected operational mode  190 . 
         [0030]    Referring also to  FIG. 3 , the illustrated intermediate DC link circuit may be constructed in certain embodiments using a laminated plate structure including a pair of upper (+) conductive (e.g., aluminum) conductor portions  122 A and  122 B separated by the precharging circuit  130  and together constituting a first DC current path  122 , as well as a second conductive (e.g., aluminum) plate  124  constituting a lower (−) DC current path  124 , with the plates  122  and  124  being separated by an intervening electrical insulator layer  128 . In certain embodiments, moreover, a third conductive (e.g., aluminum) plate  126  may be provided for a DC ground or system common spaced from the other plates using an insulative layer  128 , where the various switching devices S 1 -S 12  and Q 1  may be electrically and mechanically connected to the corresponding plates  122 ,  124  using bolts and/or other fasteners for connection through associated holes in the plates  122 ,  124 ,  126  and insulation layers  128  to provide conductive connection where appropriate and spacing to avoid electrical connection where a given switching device terminal is passing through a conductive plate to which it is not to be electrically connected. In some embodiments, the conductive plates and insulating layers can also be combined into a single printed circuit board (PCB) to accomplish the same design goals, and the laminated structures of the present disclosure are not limited to any one type of construction. In the past, capacitors would be mounted directly to the laminated plate structure of the DC link circuit illustrated in  FIG. 3 . 
         [0031]    Turning to  FIG. 4 , and in accordance with the present disclosure, a split laminated DC bus structure is schematically illustrated. It will be appreciated that this split laminated DC bus structure can be implemented in the motor drive  100  described above, and enables a more densely-packed motor drive to be assembled to achieve higher top-of-frame ratings for a given enclosure. As will now be described, the exemplary split laminated DC bus structure includes a separate capacitor bus  180  mounted to and electrically coupled with a DC bus, wherein the capacitor bus supports a capacitance in spaced relation to the main DC bus. 
         [0032]    Turning to  FIGS. 5 and 6 , an exemplary DC power bus is illustrated and identified generally by reference numeral  200 . The DC power bus  200  includes multiple layers of insulators I and conductors C that are sandwiched together to form a laminated structure having both a positive bus and a negative bus isolated between respective insulator layers. The DC power bus  200  includes a plurality of terminals T, or connection points for electrically coupling the DC power bus  200  with other components, such as the capacitor bus as will be described. In addition, the DC power bus  200  includes terminals  204  for electrically coupling the DC power bus with the capacitor bus, as will be described in more detail below. In addition, other contacts  208  are provided for connecting other typical components to the DC power bus. It will be appreciated that the DC power bus  200  can be implemented as an intermediate DC link circuit, such as described in  FIG. 3   
         [0033]    Turning to  FIGS. 7 and 8 , an exemplary capacitor bus  210  in accordance with the present disclosure is illustrated. It will be appreciated that the illustrated capacitor bus  210  is a laminated bus having multiple layers of insulators I and conductors C sandwiched together and otherwise generally constructed in a similar manner as the DC power bus. Depending on the particular desired arrangement of capacitors on the capacitor bus, there may be multiple pairs of positive and negative conductor layers in the capacitor bus  210  to allow parallel connection of one or more series of capacitors with the DC power bus  200 . The illustrated exemplary capacitor bus  210  includes a first positive conductor CP 1  and a first negative conductor CN 1  forming a first pair of conductors, a second positive conductor CP 2  and a second negative conductor CN 2  forming a second pair of conductors. A plurality of capacitor terminals CT are arranged in pairs for coupling capacitors to the respective conductors. Thus, two (or more) banks of capacitors can be mounted to the capacitor bus  210  in series, and said banks then connected to the DC power bus in parallel (such as is shown in  FIG. 4 ). 
         [0034]    For connecting the capacitor bus  210  to the DC power bus, a number of terminals T are also provided on the capacitor bus for connection to mating terminals T of the DC power bus. As will be appreciated, the capacitor bus  210  can have multiple parallel branches of capacitors mounted in series, and each parallel branch of capacitors can be configured to be electrically coupled to the DC power bus. 
         [0035]    With further reference to  FIGS. 9 and 10 , an exemplary split laminated DC bus  220  in accordance with the disclosure is illustrated. The split laminated DC bus  220  includes DC power bus  200  and capacitor bus  210  mounted together and secured with fasteners, such as hex screws  230 . Spacers, bushing, or the like can be used to support the capacitor bus  210  in spaced relation to the DC power bus  200  such that air can circulate between the respective buses. This can increase the ability of heat to dissipate from the buses to thereby reduce temperatures during operation. It will be appreciated that one or more capacitors can be mounted to the surface of the capacitor bus  210  opposite the DC power bus  200  such that said capacitors extend from the capacitor bus  210  in a direction away from the DC power bus  200  (not shown in  FIG. 10 ). 
         [0036]    Turning now to  FIG. 11 , the split laminated DC bus  220  is shown installed in an exemplary motor drive  250 . The motor drive  250  includes an enclosure  254  in which the various motor drive components are supported including the split DC laminated bus  250 . A portion of the enclosure  254  has been removed to expose the split DC laminated bus  250 . As can be seen, the DC power bus  200  is mounted to a frame F of the motor drive with fasteners, such as bolts  260 . The capacitor bus  210  is mounted to the DC power bus  210 , and a plurality of capacitors C are mounted to the capacitor bus  210  in the manner described above 
         [0037]    The exemplary embodiment has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.