Abstract:
Circuit configurations for controlling an AC motor drive system wherein the control systems include redundancy features to compensate for possible failed system components.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention provides a system for controlling an electric machine and providing redundancy for system components. 
         [0003]    2. Description of the Prior Art 
         [0004]    In a conventional power system, high speed motors are directly coupled to high speed machinery and controlled by a high frequency output, pulse width modulation based, AC drives. However, the size, weight, efficiency, operating costs and system availability of the drive systems make the high speed motors not widely utilized. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention provides a system for controlling a space-shifted, split-phase stator AC motor drive system. The following topologies have been developed to implement the above control system: 
         [0006]    1. An AC motor drive system wherein a dc/ac inverter is divided into N number of inverter modules; a control strategy that allows a single inverter to go off-line and the power output on the each remaining module increased by 1/(N-1); a spare inverter and all of the active inverters tied into a switch matrix; upon a failure, the faulted sub-module is taken off-line and the spare is switched in its place. 
         [0007]    2. An AC motor drive system where the ac/dc rectifier is divided into N number of rectifier modules; a control strategy that allows one module to go off-line and the power output on the remaining modules increased by 1/(N-1); a spare module and all of the active modules tied into a switch matrix; upon a failure, the faulted module is taken off-line and the spare is switched in its place. 
         [0008]    3. The 3-phase sub-modules previously described are further reduced to single phase sub modules (also known as phase modules). Since the spare module is identical to the sub modules in the system, the smaller and lower cost of the submodules means a lower overall cost increase for the redundant system. 
         [0009]    4. The command and control features that are part of the present invention are as follows: The control scheme for sub-modules utilize gate signals which are phase-shifted accordingly, based on the phase-shift of the corresponding winding. The sub-modules have the same current waveform with a 60/N degree time delay. Because of the symmetric current waveform and combination of the waveform time-shift and winding space-shift, the harmonics are cancelled out and result in a more sinusoidal magnetic flux in the air gap of the machine. 
         [0010]    5. A centralized control configuration where a central controller synchronizes with the machine and controls all sub-modules. 
         [0011]    6. A master-slave configuration where each power inverter sub-module has its own controller. In addition, a controller serves as the master control and synchronizes with the machine, and other controllers synchronize with master controller via a high-speed data link loop. Since all the controllers are identical, the role of the master controller can be rotated between all the modules. When one controller fails, the next controller will be picked up and serve as the master controller and keep the system running. 
         [0012]    7. An independent-sync configuration where each module synchronizes independently to the electric machine. When one controller fails, the rest of the controllers will share the load of the failed sub-module. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0013]    For a better understanding of the present invention as well as other objects and further features thereof, reference is made to the following description which is to be read in conjunction with the accompanying drawing wherein the sole figure illustrates the system of the present invention. 
           [0014]      FIG. 1A  shows a space-shifted, split-phase stator AC motor drive system where the dc/ac inverter is divided into a plurality of inverter modules; 
           [0015]      FIG. 1B  illustrates a motor drive system that allows a single inverter to go off-line while increasing the power on the remaining system inverters; 
           [0016]      FIG. 1C  illustrates a spare inverter and active inverters coupled to a switch matrix; 
           [0017]      FIG. 2A  shows a space-shifted, split-phase stator AC motor drive system wherein the dc/ac rectifier is divided into modules; 
           [0018]      FIG. 2B  illustrates a system that enables a single module to be off-line while raising the power to the remaining modules; 
           [0019]      FIG. 2C  illustrates a configuration wherein a spare module and the remaining modules are coupled to a switch matrix; 
           [0020]      FIG. 3A  illustrates a system wherein 3-phase sub-modules are reduced to a single phase module; 
           [0021]      FIG. 3B  illustrates how the spare inverter shown in  FIG. 3A  is inserted into the system when a single-phase inverter fails; 
           [0022]      FIG. 4  illustrates the gate signals which control the system inverters; 
           [0023]      FIG. 5  shows a centralized control configuration wherein a central controller controls all the system sub-modules; 
           [0024]      FIG. 6  shows a master-slave configuration wherein each inverter has its own controller; and 
           [0025]      FIG. 7  illustrates a distributed controller configuration wherein each module synchronizes independently to the motor. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0026]    Referring now to  FIG. 1  A, a space-shifted, split-phase stator motor drive system  10  is illustrated and wherein the dc/ac inverter disclosed in co-pending application Ser. No. 11/715,450, filed May 21, 2007 and assigned to the assignee of the present invention, is replaced with N number of three phase inverter modules  12 ,  14  . . .  18  (in this example, N equals 4). The output of rectifier  20  is coupled to the inputs of the inverter modules as shown. The output of the inverter modules are coupled to space-shifted split phase motor  22 . 
         [0027]      FIG. 1B  is similar to  FIG. 1A  and illustrates the situation wherein 3 phase inverter  14  fails; in this case, the system is designed to increase the power output from operating inverter modules  12 ,  16  and  18  by 1/(N-1). 
         [0028]      FIG. 1C  is similar to  FIG. 1B  with the addition of a spare inverter module  24 . The active inverter modules  12 ,  14 ,  16  and  18  are connected to a switch matrix for connecting spare  3  phase inverter  24  into the power system if one of the active inverter modules fails. In the example illustrated in the figure, inverter  14  has failed and spare inverter  24  is switched into the system to replace failed inverter  14 . 
         [0029]      FIG. 2A  shows a space-shifted, split-phase stator AC motor drive system  40  wherein the single ac/dc rectifier  20  of  FIGS. 1A-1C  is replaced with rectifier modules  42 ,  44 ,  46  and  48 . Each rectifier/inverter combination is separate from the others. 
         [0030]      FIG. 2B  illustrates the situation wherein phase inverter  14  fails; the power output on independent modules is increased by a third {1/(N-1)}. In this case, rectifier  44  is also removed from the system. 
         [0031]      FIG. 2C  shows a system similar to that of  FIG. 2B  with the addition of spare rectifier  50  and spare inverter  52 . In the example illustrated, when inverter  14  fails, rectifier  50  and inverter  52  are switched into the system in place of faulted modules  14  and  44 . All the active inverter modules are connected into a switch matrix. 
         [0032]      FIG. 3A  illustrates a system wherein the three phase inverter modules of  FIGS. 1A-1C  and  2 A- 2 C are reduced to single phase sub-module inverters  60 ,  62  . . .  82  (twelve total). Two spare single phase inverter modules  84  and  86  are provided and can be switched into the system by matrix  90  when any active inverter module fails. Switch matrix  90  comprise bi-directional switch components which can be relays, contactors, bi-directional gate turn-off (GTO) thyristors or anti-parallel silicon controlled rectifiers (SCR). 
         [0033]      FIG. 3B  illustrates the situation wherein the single phase inverter  66  of  FIG. 3A  fails; in this case, switch  92  is opened to isolate inverter  66  and spare  84  is connected into the circuit instead of inverter  66  and applying power to motor  22 . The system further illustrates that additional spare inverters, such as inverter  86 , can be connected to the circuit in case of two inverters failing at the same time. Furthermore, more spare modules can be added to the system to further increase redundancy features of the invention. 
         [0034]      FIG. 4  illustrates the gate signals that will control the inverters shown in  FIGS. 5-7 . The gate signals for the inverter sub modules will be phase-shifted accordingly, based on the phase-shift of the corresponding winding. In the example illustrated, N (number of windings on motor) is four, the phase-shift being calculated by dividing 60 by N, 15 degrees in this case. The output voltages of each sub-module are also phase-shifted by 15 degrees, the sub-modules thus having the same current waveform with a 15 degree time delay. Because of the symmetric current waveform and combination of time-shift and space-shift, the harmonics are cancelled where results in a sinusoidal signal to the motor and a resultant sinusoidal flux. 
         [0035]      FIG. 5  shows a centralized control system wherein central controller  100  synchronizes with machine  102  via feedback lead  104  and controls inverter sub-modules  106 ,  108  . . .  112 . 
         [0036]      FIG. 6  illustrates a master-slave configuration wherein each inverter has its own controller. In the example illustrated, controller  200  serves as the master controller and synchronizes with machine  102 . Slave controllers  202 ,  204  and  206  synchronize with master controller  200  via a high speed data loop. Since all the controllers are identical, the function of master controller  20  can be alternated between all the modules. If one controller fails, the next controller will function as the master controller and maintain system operation. 
         [0037]      FIG. 7  illustrates an independent synchronization configuration system wherein each inverter module synchronizes independently to machine  102 . In this configuration, a data bus is used to communicate between the drive and system level controller. If one controller fails, the rest of the controller will pick up the load and maintain system operation. 
         [0038]    While the invention has been described with reference to its preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its essential teachings.