Abstract:
A conveyance system includes a machine having a motor; a source of AC power; a drive system coupled to the source of AC power, the drive system to provide multi-phase drive signals to the motor, the drive system including: a first drive having a first converter and a first inverter, the first convertor including a first positive DC bus and a first negative DC bus; a second drive having a second converter and a second inverter, the second convertor including a second positive DC bus and a second negative DC bus; wherein the first positive DC bus and the second DC positive bus are electrically connected and the first negative DC bus and the second negative DC bus are electrically connected.

Description:
TECHNICAL FIELD 
       [0001]    The subject matter disclosed herein relates generally to conveyance systems, and more particularly to a conveyance system having drives arranged in an electrically parallel manner. 
       BACKGROUND 
       [0002]    Conveyance systems, such as elevator systems, use machines to impart force to a car carrying passengers. The machines employed may need to provide varying power levels depending on the application. When an elevator requires a large elevator duty or load, a drive needs be provided to power the elevator machine. Often, a high power drive may not exist, which results in high design costs and lengthy development time to manufacture a suitable drive. Even if a single, large drive exists in the marketplace, costs associated with a single, large drive may be excessive due to specialty components, component availability, etc. 
       BRIEF SUMMARY 
       [0003]    According to an exemplary embodiment, a conveyance system includes a machine having a motor; a source of AC power; a drive system coupled to the source of AC power, the drive system to provide multi-phase drive signals to the motor, the drive system including: a first drive having a first converter and a first inverter, the first convertor including a first positive DC bus and a first negative DC bus; a second drive having a second converter and a second inverter, the second convertor including a second positive DC bus and a second negative DC bus; wherein the first positive DC bus and the second DC positive bus are electrically connected and the first negative DC bus and the second negative DC bus are electrically connected. 
         [0004]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the first converter includes a two level, three phase converter, the first inverter includes a two level, three phase inverter, the second converter includes a two level, three phase converter, and the second inverter includes a two level, three phase inverter. 
         [0005]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include an inductive interface coupled to the first inverter and the second inverter, the inductive interface including a plurality of inductive elements, the inductive interface combining drive signals from the first inverter and the second inverter for each phase of the drive signals; wherein the motor receives the drive signals from the inductive interface. 
         [0006]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the first converter includes a three level, three phase converter, the first inverter includes a three level, three phase inverter, the second converter includes a three level, three phase converter, and the second inverter includes a three level, three phase inverter. 
         [0007]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the first converter includes a first converter neutral point, the first inverter includes a first inverter neutral point, the second converter includes a second converter neutral point, the second inverter includes a second inverter neutral point, the first converter neutral point electrically connected to the first inverter neutral point and the second converter neutral point electrically connected to the second inverter neutral point, wherein the first converter neutral point is not electrically connected to the second inverter neutral point and the first inverter neutral point is not electrically connected to the second converter neutral point. 
         [0008]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the first converter includes a first converter neutral point, the first inverter includes a first inverter neutral point, the second converter includes a second converter neutral point, the second inverter includes a second inverter neutral point, wherein at least one of (i) the first converter neutral point is electrically connected to the second inverter neutral point and (ii) the first inverter neutral point is electrically connected to the second converter neutral point. 
         [0009]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include a neutral point link electrically connecting the first converter neutral point to the first inverter neutral point. 
         [0010]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include a second neutral point link electrically connecting the second converter neutral point to the second inverter neutral point. 
         [0011]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the drive system comprises a first drive controller to provide a first control signal to the first drive and a second drive controller to provide a second control signal to the second drive. 
         [0012]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the first drive controller communicates a location of a reference point in the first control signal to the second drive controller, the second drive controller adjusting a period of the second control signal in response to the location of the reference point in the first control signal. 
         [0013]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the reference point in the first control signal corresponds to point in a PWM control signal. 
         [0014]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include the second drive controller adjusts the period of the second control signal using a phase locked loop. 
         [0015]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the first converter is a three level, three phase converter, the first inverter is a two level, three phase inverter, the second converter is a three level, three phase converter, the second inverter is a two level, three phase inverter and the motor is a six phase motor. 
         [0016]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include a second drive system coupled to the source of AC power, the second drive system to provide multi-phase drive signals to the motor, the second drive system including: a further first drive having a further first converter and a further first inverter, the further first convertor including a further first positive DC bus and a further first negative DC bus; a further second drive having a further second converter and a further second inverter, the further second convertor including a further second positive DC bus and a further second negative DC bus; wherein the further first positive DC bus and the further second DC positive bus are electrically connected and the further first negative DC bus and the further second negative DC bus are electrically connected; the motor to receive the drive signals from the further first drive and the further second drive. 
         [0017]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include a first inductive interface coupled to the first inverter and the second inverter, the first inductive interface including a plurality of inductive elements, the first inductive interface combining drive signals from the first inverter and the second inverter for each phase of the drive signals; and a second inductive interface coupled to the further first inverter and the further second inverter, the second inductive interface including a plurality of inductive elements, the second inductive interface combining drive signals from the further first inverter and the further second inverter for each phase of the drive signals; wherein the motor receives drive signals from the first inductive interface and the second inductive interface. 
         [0018]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the first inductive interface generates three phase drive signals; the second inductive interface generates three phase drive signals; and the motor has at least six phases. 
         [0019]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the motor is a 6 phase motor, the first drive system providing three phase drive signals and the second drive system providing an additional three phase drive signals. 
         [0020]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include wherein the number of drive systems comprises N drive systems, the motor being a 3N phase motor. 
         [0021]    In addition to one or more of the features described above or below, or as an alternative, further embodiments could include an elevator car; the machine to control motion of the elevator car. 
         [0022]    Other aspects, features, and techniques of embodiments will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    Referring now to the drawings wherein like elements are numbered alike in the FIGURES: 
           [0024]      FIG. 1  is a block diagram of components of an elevator system in an exemplary embodiment; 
           [0025]      FIG. 2  is a block diagram of a 2 level, 3 phase drive used in an exemplary embodiment; 
           [0026]      FIG. 3A  is a block diagram of a 3 level, 3 phase drive used in an exemplary embodiment; 
           [0027]      FIG. 3B  is a block diagram of a 3 level, 3 phase drive used in an exemplary embodiment; 
           [0028]      FIG. 3C  is a block diagram of a 3 level, 3 phase drive used in an exemplary embodiment; 
           [0029]      FIG. 4  is a block diagram of a drive system including paralleled drives in an exemplary embodiment; 
           [0030]      FIG. 5  is a block diagram of a drive system including paralleled drives in an exemplary embodiment; 
           [0031]      FIG. 6  depicts synchronization of control signals between a first drive and a second drive in an exemplary embodiment; 
           [0032]      FIG. 7  is a block diagram of a drive system including paralleled drives in an exemplary embodiment; 
           [0033]      FIG. 8  is a block diagram of a drive system including paralleled drive systems, each including parallel drives, in an exemplary embodiment; and 
           [0034]      FIG. 9  is a block diagram of a drive system including paralleled converters in an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]      FIG. 1  is a block diagram of components of an elevator system  10  in an exemplary embodiment. Although embodiments are described with respect to an elevator system, it is understood that embodiments may be applied to other conveyance systems (e.g., trains, automobiles, marine). Elevator system  10  includes a source of AC power  12 , such as an electrical main line (e.g., 440 volt, 3-phase). The AC power  12  is provided to a regenerative drive system  20 . As described in further detail herein, drive system  20  includes a plurality of drives arranged in a parallel electrical configuration. Each drive may include a converter to convert the AC power  12  to a DC voltage. Each drive may include an inverter to convert the DC voltage to multiphase, AC drive signals. Drive signals from the drive system  20  are supplied to a multiphase machine  22  to impart motion to elevator car  23 . In an exemplary embodiment, machine  22  includes a multiphase, permanent magnet synchronous motor. 
         [0036]      FIG. 2  is a block diagram of a 2 level, 3 phase drive  30  used in exemplary embodiments. Drive  30  includes a converter  32  having 3 phase legs, R, S and T. Each phase leg, R, S and T, includes switches controlled by control signals from a drive controller to convert AC power to DC power across a first DC bus  34  (e.g., positive) and a second DC bus  36  (e.g., negative). Drive  30  includes an inverter  40  having 3 phase legs, W, V, U. Each phase leg, W, V, and U, includes switches controlled by control signals from a drive controller to convert DC power across the DC bus  34 ,  36  to AC drive signals to power motor  21 , which is part of machine  22 . 
         [0037]      FIG. 3A  is a block diagram of a 3 level, 3 phase drive  50  used in an exemplary embodiment. Drive  50  includes a converter  52  having 3 phase legs, R, S and T. Each phase leg, R, S and T, includes switches controlled by control signals from a drive controller to convert AC power to DC power across a first DC bus  34  (e.g., positive) and a second DC bus  36  (e.g., negative). Converter  52  is a neutral point clamped (NPC) converter, in which the neutral points in each phase leg R, S, and T are connected at a common, converter neutral point  53 . Drive  50  includes an inverter  54  having 3 phase legs, W, V, U. Each phase leg, W, V, and U, includes switches controlled by control signals from a drive controller to convert DC power across the DC bus  34 ,  36  to AC drive signals to power motor  21 , which is part of machine  22 . Inverter  54  is a neutral point clamped (NPC) inverter, in which the neutral points in each phase leg W, V, and U are connected at a common, inverter neutral point  55 . An optional neutral point link  58  may be used to electrically connect the converter neutral point  53  to the inverter neutral point  55 . 
         [0038]      FIG. 3B  is a block diagram of a 3 level, 3 phase drive  51  used in an exemplary embodiment. Drive  51  includes a converter  52  having 3 phase legs, R, S and T. Each phase leg, R, S and T, includes switches controlled by control signals from a drive controller to convert AC power to DC power across a first DC bus  34  (e.g., positive) and a second DC bus  36  (e.g., negative). Converter  52  is a T-type converter. Drive  51  includes an inverter  54  having 3 phase legs, W, V, U. Each phase leg, W, V, and U, includes switches controlled by control signals from a drive controller to convert DC power across the DC bus  34 ,  36  to AC drive signals to power motor  21 , which is part of machine  22 . Inverter  54  is a T-type inverter. An optional neutral point link  58  may be used to electrically connect a converter neutral point to an inverter neutral point. 
         [0039]      FIG. 3C  is a block diagram of a 3 level, 3 phase drive  53  used in an exemplary embodiment. Drive  53  includes a converter  52  having 3 phase legs, R, S and T. Each phase leg, R, S and T, includes switches controlled by control signals from a drive controller to convert AC power to DC power across a first DC bus  34  (e.g., positive) and a second DC bus  36  (e.g., negative). Converter  52  is an AT-type converter. Drive  53  includes an inverter  54  having 3 phase legs, W, V, U. Each phase leg, W, V, and U, includes switches controlled by control signals from a drive controller to convert DC power across the DC bus  34 ,  36  to AC drive signals to power motor  21 , which is part of machine  22 . Inverter  53  is an AT-type inverter. An optional neutral point link  58  may be used to electrically connect a converter neutral point to an inverter neutral point. 
         [0040]      FIG. 4  is a block diagram of a drive system including paralleled drives in an exemplary embodiment. As shown in  FIG. 4 , two drives  30  and  30 ′ are connected in parallel to provide drive signals to motor  21 . Each drive  30  and  30 ′ is controlled by a separate drive controller,  60  and  62 , respectively. Drive controllers  60  and  62  provide control signals to the drives  30  and  30 ′, respectively, to control generation of the drive signals to motor  21 . Drive controllers  60 ,  62  may be implemented using a general-purpose microprocessor executing a computer program stored on a storage medium to perform the operations described herein. Alternatively, drive controllers  60 ,  62  may be implemented in hardware (e.g., ASIC, FPGA) or in a combination of hardware/software. 
         [0041]    Drives  30  and  30 ′ are 2 level, 3 phase drives, such as that shown in  FIG. 2 . Drives  30  and  30 ′ are placed in parallel by electrically connecting the positive DC bus  34  of drive  30  to the positive DC bus  34  of drive  30 ′ and electrically connecting the negative DC bus  36  of drive  30  to the negative DC bus  36  of drive  30 ′. The  3  phase drive signals from drives  30  and  30 ′ are connected to an inductive interface  70 , which combines each respective phase from the drives  30  and  30 ′ through inductive elements (e.g., inductors). For example, phase W from drive  30  and phase W from drive  30 ′ are connected to each other through separate inductive elements in the inductive interface  70 , and then applied to one winding of 3-phase motor  21 . Phases V and U are connected in a similar manner. Inductive interface  70  allows for combining phases from two separate drives  30  and  30 ′. Inductive interface  70  also acts as a voltage suppression filter. Although two drives  30  and  30 ′ are shown in  FIG. 4 , it is understood that embodiments may include more than two drives connected in parallel. 
         [0042]      FIG. 5  is a block diagram of a drive system including paralleled drives in an exemplary embodiment. As shown in  FIG. 5 , two drives  50  and  50 ′ are connected in parallel to provide drive signals to motor  21 . Each drive  50  and  50 ′ is controlled by a separate drive controller,  60  and  62 , respectively. Drive controllers  60  and  62  provide control signals to the drives  50  and  50 ′, respectively, to control generation of the drive signals to motor  21 . 
         [0043]    Drives  50  and  50 ′ are 3 level, 3 phase drives, such as that shown in  FIGS. 3A-3C . Drives  50  and  50 ′ are placed in parallel by electrically connecting the positive DC bus  34  of drive  50  to the positive DC bus  34  of drive  50 ′ and electrically connecting the negative DC bus  36  of drive  50  to the negative DC bus  36  of drive  50 ′. Further, the inverter neutral point  55  of drive  50  is connected to converter neutral point  53  of drive  50 ′. Alternatively, the converter neutral point  53  of drive  50  is connected to inverter neutral point  55  of drive  50 ′. In other embodiments, the connection between the inverter neutral point  55  (converter neutral point  53 ) of drive  50  to the converter neutral point  53  (inverter neutral point  55 ) of drive  50 ′may be eliminated, and only the DC buses connected between drives  50  and  50 ′. 
         [0044]    The 3 phase drive signals from drives  50  and  50 ′ are connected to an inductive interface  70 , which combines each respective phase from the drives  50  and  50 ′ through inductive elements. For example, phase W from drive  50  and phase W from drive  50 ′ are connected to each other through separate inductive elements in the inductive interface  70 , and then applied to one winding of 3-phase motor  21 . Phases V and U are connected in a similar manner. Inductive interface  70  allows for combining phases from two separate drives  50  and  50 ′. Although two drives  50  and  50 ′ are shown in  FIG. 5 , it is understood that embodiments may include more than two drives connected in parallel. 
         [0045]    To facilitate combining the drive signals of separate drives (e.g.,  30 / 30 ′ or  50 / 50 ′) at the inductive interface  70 , it is beneficial that the drive signals at the output of the drives be synchronized. Due to variations in the drive controllers and drives, using identical control signals may not result in synchronized outputs from the drives. In order to aid in synchronizing the outputs from two or more drives, drive controllers  60  and  62  execute a process to align the control signals provided to the respective drives.  FIG. 6  depicts a first control signal  80  from drive controller  60  for one phase of the inverter  40  of drive  30 , for example, and a second control signal  82  from drive controller  62  for one phase of the inverter  40  of drive  30 ′, for example. The control signals may be pulse width modulation signals, commonly used in n-level drives. In operation, a reference point  84  of the control signal is defined. As shown in  FIG. 6 , the reference point  84  is a minimum value of the control signal, however, any reference point may be used. During operation, first drive controller  60  communicates to the second drive controller  62  when the reference point has occurred in control signal  80 . Second drive controller  62  then determines when the reference point occurs in control signal  82 . If there is a difference between when the reference point occurs in the first control signal  80  and when the reference point occurs in the second control signal  82 , then one or both of the drive controllers  60  and  62  may adjust the period of the drive signal such that the reference points occur at the same time. The first drive controller  60  or second drive controller  62  may use known techniques to adjust the period of the drive signal, such as a phase locked loop technique to reduce error between when the reference point occurs in control signal  82  and when the reference point occurs in control signal  84 . This improves synchronization of the drive signals between drives  30  and  30 ′, which allows smaller inductive elements to be used in inductive interface  70 . The control signal synchronization of  FIG. 6  may be used with any number of drives, and is not limited to two drives. The control signal synchronization of  FIG. 6  may be used with the drives other than those shown in  FIG. 4 . 
         [0046]      FIG. 7  is a block diagram of a drive system including paralleled drives in an exemplary embodiment. Drive controllers  60  and  62  may be used in the embodiment of  FIG. 7  to control drives  90  and  90 ′.  FIG. 7  depicts the use of hybrid drives  90  and  90 ′, where the converter sections are 3 level, 3 phase converters  52  and the inverter sections are 2 level, 3 phase inverters  40 .  FIG. 7  also depicts an architecture that does not use an inductive interface  70 . In  FIG. 7 , motor  21  is a 6 phase motor. Each phase of the 3 phase drive signals from drives  90  and  90 ′ is connected to an individual phase of motor  21 . Motor  21  may have two (or four) sets of galvanic electrically isolated windings sharing the same stator and generating torque on a common rotor. This architecture can be expanded by adding additional drives and using a motor with a higher number of phases (e.g., 3 three-phase drives with a 9 phase motor, 4 three-phase drives with a 12 phase motor). 
         [0047]      FIG. 8  is a block diagram of an architecture including paralleled drive systems, each including parallel drives, in an exemplary embodiment.  FIG. 8  depicts the use of multiple drive systems  100  and  100 ′, each including parallel drives  50  and  50 ′. Drive controllers  60  and  62  may be used in the embodiment of  FIG. 8  to control drives  50  and  50 ′. In the example of  FIG. 8 , two drive systems  100  and  100 ′ (each similar to that in  FIG. 5 ) are used to power a 6 phase motor  21 . Each drive system  100  and  100 ′ generates a 3 phase drive signal output, where each phase is applied to a winding of motor  21 . Motor  21  may have sets of galvanic electrically isolated windings sharing the same stator and generating torque on a common rotor. It is understood that other drive systems may be used in parallel, and embodiments are not limited to the drive system of  FIG. 5 . Each drive system  100  and  100 ′may employ control signal synchronization as described with reference to  FIG. 6 . This architecture can be expanded by adding additional drive systems  100  and using a motor with a higher number of phases (e.g., 3 drive systems with a 9 phase motor, 4 drive systems with a 12 phase motor). In general terms, the system may include N drive systems, with a motor being 3N phase motor. 
         [0048]      FIG. 9  is a block diagram of a drive system including paralleled converters and paralleled inverters in an exemplary embodiment. AC power  12  is provided to separate reactors  120  and  120 ′ and then to converters  122  and  122 ′. The output of converters  122  and  122 ′ is supplied to a DC bus  124 , which parallels the positive and negative DC outputs from converters  122  and  122 ′. An inverter  126  is made up of two parallel, 3 level IGBT inverters controlled by a single controller and single gate drive. The inverters use identical or nearly identical IGBTs, and thus may be controlled by a single controller and gate drive signal, applied to the IGBTs in parallel. 
         [0049]    Embodiments include the use of paralleled drives in order to meet high load demands without the need to design or source a single, high power drive. Using parallel drives, and optionally parallel drive systems, allows the drive system to meet load demands through multiple, lower power drives. This eliminates the cost and/or development time associated with a single, higher power drive. 
         [0050]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. While the description has been presented for purposes of illustration and description, it is not intended to be exhaustive or limited to the form disclosed. Many modifications, variations, alterations, substitutions, or equivalent arrangement not hereto described will be apparent to those of ordinary skill in the art without departing from the scope of the disclosure. Additionally, while the various embodiments have been described, it is to be understood that aspects may include only some of the described embodiments. Accordingly, embodiments are not to be seen as being limited by the foregoing description, but is only limited by the scope of the appended claims.