Abstract:
A system for controlling a switch reluctance machine is provided. The system includes multiple phases located in the switch reluctance machine, each phase having multiple machine coils. Each machine coil is independently connected to a positive side switch circuit and a negative side switch circuit. Each positive side switch circuit is in electrical parallel connection with the other positive side switch circuits, and configured to control the flow of current through the machine coil to which it is connected. Similarly, the negative side switch circuits are connected in electrical parallel and configured to control the flow of current through the machine coil to which they are connected. The positive side and negative side switch circuits may be provided in a buck boost configuration or two half bridge configurations.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention generally relates to a converter switch circuit and coil configuration for a switched reluctance machine. 
     2. Description of Related Art 
     Many converter switch circuits have been designed for interfacing with switch reluctance machines. Switched reluctance machines (SRM) may require a large driving current based on the application and performance parameters of the SRM. If the SRM requires a high current draw, special high current electronic components must be used. Often, the high current components must be located on a separate board from low power electronics to minimize radio frequency interference and provide for proper heat dissipation. 
     One solution for providing higher current flow to switch reluctance machines while utilizing low power electronic components includes using several smaller discrete components in a parallel configuration to provide sufficient current flow to operate the switched reluctance machine. The parallel configuration allows the use of more commercially available components and reduces the overall cost of the electronics. In addition, the heat dissipation can be spread across multiple components allowing for a shared circuit board between the converter switch circuit and other low power electronics. Further, smaller parallel power switches provide better flexibility to integrate the motor and converter in one enclosure to provide improved space optimization. 
     However, one problem encountered with parallel power switches is that current sharing problems may arise. Even with matching the characteristics of the power switches, the power switches may not turn on or off at exactly the same time. The switching delay between the parallel power switches forces one of the power switches to carry much more than the maximum rated current during the delay time. The current through the switch that turns on earlier will be at least twice the normal current. This will cause more heat on the early power switch and will eventually damage the switch. The unbalanced sharing of current between parallel power switches, even for a short time, may cause power switch failures and ultimately destroy the converter itself. The damage of the first power switch overloads the next switch in parallel, and so on, creating a chain reaction until the whole converter is destroyed. Breakdown may be stopped, if the fault can be detected and the converter can be shut down very quickly. However, it is very difficult to detect the fault and shut off the converter in time. Another way to prevent the chain reaction breakdown of the power switches is to choose oversize components and heat sinks. However, using oversized components negatively affects cost and assembly complexity. 
     In view of the above, it is apparent that there exists a need for an improved converter switch circuit for a switched reluctance machine. 
     SUMMARY 
     In satisfying the above need, as well as overcoming the enumerated drawbacks and other limitations of the related art, the present invention provides a system for controlling a switch reluctance machine. 
     The system includes multiple phases located in the switch reluctance machine, each phase having multiple machine coils. Each machine coil is independently connected to a positive side switch circuit and a negative side switch circuit. Each positive side switch circuit is in electrical parallel connection with the other positive side switch circuits, and configured to control the flow of current through the machine coil to which it is connected. Similarly, the negative side switch circuits are connected in electrical parallel and configured to control the flow of current through the machine coil to which they are connected. The positive side switch circuit may be provided in a buck configuration and negative side switch circuits may be provided in a boost configuration or both switch circuits may be provided in half bridge configurations. 
     In the buck and boost configuration, each positive side switch or buck configuration circuit includes a power switch and a diode, the positive side switch circuit being in electrical connection with a positive side of the machine coil between the power switch and diode. Similarly, each negative side switch circuit or boost configuration includes a power switch and a diode, the negative side switch circuit being in electrical connection with a negative side of the machine coil between the power switch and diode. Preferably, the power switches are N-channel MOSFETs, however other power switches may be used. A capacitor is in electrical parallel connection with the power switch and diode and mounted in close proximity therewith to provide DC line filtering and snubbing of switch-off transients. 
     In the described configuration, power switches and machine coils provide all the benefits of the parallel switching but many of the problems associated with current sharing are eliminated. The switches and diodes form individual buck or boost configurations for each machine coil, instead of conventional paralleling of discrete switches. In this arrangement, the machine coils are not paralleled inside the machine, as is typically provided. Instead, two terminals per machine coil are accessible outside of the machine. Each positive terminal is connected to a buck configuration and each negative terminal is connected to a boost configuration. 
     In the half bridge configuration, each positive side and negative side switch circuit includes two power switches. The positive side switch circuit being in electrical connection with a positive side of the machine coil between the two power switches. Similarly, the negative side switch circuit being in electrical connection with a negative side of the machine coil between the two power switches. Preferably, the power switches are N-channel MOSFETs, however other power switches may be used. A capacitor is in electrical parallel connection with the two power switches and mounted in close proximity therewith to provide DC line filtering and snubbing of switch-off transients. 
     As described above, the machine coils are not paralleled inside the machine, as is typically provided. Instead, two terminals per machine coil are accessible outside of the machine. Each positive terminal is connected to a half bridge configuration and each negative terminal is connected to a separate half bridge configuration. 
     Further objects, features and advantages of this invention will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic of a converter switch circuit including a buck and a boost configuration in accordance with the present invention; 
         FIG. 2  is a schematic of a converter switch circuit for 3-phase 6/4 switched reluctance machine in accordance with the present invention; and 
         FIG. 3  is a schematic of a converter switch circuit including two half bridge configurations in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Now referring to  FIG. 1 , a converter circuit  10  for controlling a SRM  11  embodying the principles of the present invention is provided. The converter circuit  10  includes a first positive side switch circuit  12 , a second positive side switch circuit  13 , a first negative side switch circuit  14 , a second negative side switch circuit  15 , and a power source  26 . 
     A phase of the SRM  11  includes a first machine coil  16  and a second machine coil  18 . The first machine coil  16  is wrapped around a first magnetic core  20 , while the second machine coil  18  is wrapped around a second magnetic core  24  located opposite the first magnetic core  20 . 
     The first positive side switch circuit  12  is in electrical communication with the positive side of the first machine coil  16  and the first negative side switch circuit  14  is in communication with the negative side of the first machine coil  16 . Similarly, the second positive side switch circuit  13  is in communication with the positive side of the second machine coil  18  and the second negative side switch circuit  15  is in communication with the negative side of the second machine coil  18 . 
     The first positive side switch circuit  12  includes power switch  28  and a diode  32 . Power switch  28  is preferably an N-channel MOSFET, although, a P-channel MOSFET or other more complex power switches such as IGBTs or other commonly known switches may be used. The drain of power switch  28  is connected to the first side of the power source  26 . The source of power switch  28  is connected to a positive side of the first machine coil  16  and a cathode of diode  32 . To complete the first positive side switch circuit, the anode of diode  32  is connected to the second side of the power source  26 . The gate of power switch  28  is connected to a gate driver (not shown). To reduce parasitic bus inductance and switching transients, capacitor  36  is connected between the drain of power switch  28  and the anode of diode  32 . 
     The second positive side switch circuit  13  includes a second power switch  30  and a diode  34 . Power switch  30  is preferably an N-channel MOSFET, although, a P-channel MOSFET or other more complex power switches such as IGBTs or other commonly known switches may be used. The drain of power switch  30  is connected to the first side of the power source  26 . The source of power switch  30  is connected to a positive side of the second machine coil  18  and a cathode of diode  34 . To complete the first positive side switch circuit, the anode of diode  34  is connected to the second side of the power source  26 . The gate of power switch  30  is connected to the gate driver. To reduce parasitic bus inductance and switching transients, capacitor  36  is connected between the drain of power switch  30  and the anode of diode  34 . 
     The first negative side switch circuit  14  includes a third power switch  40  and a diode  46 . The cathode of diode  46  is connected to the power source  26 . The anode of diode  46  is connected to the negative side of the first machine coil  16  and the drain of power switch  40 . The source of power switch  40  is connected to the second side of the power source  26  to complete the first negative side switch circuit. To reduce parasitic bus inductance and switching transients, capacitor  52  is connected between the cathode of diode  46  and the source of power switch  40 . 
     The second negative side switch circuit  15  includes a fourth power switch  42  and a diode  48 . The cathode of diode  48  is connected to the power source  26 . The anode of diode  48  is connected to the negative side of the second machine coil  18  and the drain of power switch  42 . The source of power switch  42  is connected to the second side of the power source  26  to complete the second negative side switch circuit. To reduce parasitic bus inductance and switching transients, capacitor  54  is connected between the cathode of diode  48  and the source of power switch  42 . 
     Each positive terminal of the SRM  11  is connected to a buck configuration, such as positive side power switch  12  and  13 , and each negative terminal is connected to a boost configuration, such as negative side power switch  14  and  15 . In addition, the same gate pulses are provided for power switch  28  and  30 . Similarly, the gate pulses for power switches  40 ,  42  are also the same. Therefore, the configuration provides individual parallel buck and boost configurations for each of the machine coils improving reliability and fault tolerance of the circuit. The operation and current through each machine coil, as well as, the corresponding power switches do not depend on the current through other machine coils and their corresponding switches. Therefore, the current through each switch is limited by R p , (phase resistance of each coil). However, if discrete components were used in parallel the current would have been limited by R p /2 (two coils in parallel), and if the power switches did not turn on at exactly the same time, the current through one of the power switches would exceed its limit. 
     Using the configuration described above, during the time period where one of the switches is not turned on, the machine coil is not energized. The machine, in this condition, may suffer from a load unbalance and its performance may be compromised thereby producing less torque or having more torque ripples. However, the performance deterioration is not significant considering the short time period and the potential reliability benefits of the provided configuration. In addition, this configuration provides improved packaging options. The individual link capacitor for each buck and boost configuration may be located within a close proximity of the power switches. Further, the same capacitor can be used for effective DC line filtering, as well as, for snubbing the switch off transients of the corresponding switches. 
     Now referring to  FIG. 2 , a converter switching circuit  57  embodying the principles of the present invention is provided for switching a three phase 6/4 (six stator poles and 4 rotor poles) switched reluctant machine  56 . 
     Positive side switch circuits  60 ,  61  and negative side switch circuits  62 ,  63  provide switching for phase A coil configuration  64 . For controlling the first phase A machine coil  92 , the positive side switch circuit  60  includes power switch  68  and diode  70 . The drain of power switch  68  is connected to the first side of power source  58  and the anode of diode  70  is connected to the second side of power source  58 . The source of power switch  68  is connected to a first side of the first phase A machine coil  92  and the cathode of diode  70 . To reduce parasitic bus inductance and switching transients, capacitor  72  is connected between the drain of power switch  68  and the anode of diode  70 . 
     The negative side switch circuit  62  includes a power switch  80  and a diode  82 . The cathode of diode  82  is connected to a first side the power source  58 , and the source of power switch  80  is connected to the second side of power source  58 . The anode of diode  82  is connected to the second side of the first phase A machine coil  92  and the drain of power switch  80 . To reduce parasitic bus inductance and switching transients, capacitor  84  is connected between the cathode of diode  82  and the source of power switch  80 . 
     For controlling the second phase A machine coil  94 , positive side switch circuit  60  includes power switch  74  and a diode  76 . The drain of power switch  74  is connected to the first side of the power source  58  and the anode of diode  76  is connected to the second side of power source  58 . The source of power switch  74  is connected to a first side of the second phase A machine coil  94  and a cathode of diode  76 . To reduce parasitic bus inductance and switching transients, capacitor  78  is connected between the drain of power switch  74  and the anode of diode  76 . 
     The negative side switch circuit  63  includes a power switch  86  and a diode  88 . The cathode of diode  88  is connected to a first side the power source  58 , and the source of power switch  86  is connected to the second side of power source  58 . The anode of diode  88  is connected to the second side of the second phase A machine coil  94  and the drain of power switch  86 . To reduce parasitic bus inductance and switching transients, capacitor  90  is connected between the cathode of diode  88  and the source of power switch  86 . 
     Positive side switch circuits  100 ,  101  and negative side switch circuits  102 ,  103  provide switching for phase B coil configuration  104 . For controlling the first phase B machine coil  132 , the positive side switch circuit  100  includes power switch  108  and diode  110 . The drain of power switch  108  is connected to the first side of power source  58  and the anode of diode  110  is connected to the second side of power source  58 . The source of power switch  108  is connected to a first side of the first phase B machine coil  132  and the cathode of diode  110 . To reduce parasitic bus inductance and switching transients, capacitor  112  is connected between the drain of power switch  108  and the anode of diode  110 . 
     The negative side switch circuit  103  includes a power switch  120  and a diode  122 . The cathode of diode  122  is connected to a first side the power source  58 , and the source of power switch  120  is connected to the second side of power source  58 . The anode of diode  122  is connected to the second side of the first phase B machine coil  132  and the drain of power switch  120 . To reduce parasitic bus inductance and switching transients, capacitor  124  is connected between the cathode of diode  122  and the source of power switch  120 . 
     For controlling the second phase B machine coil  134 , positive side switch circuit  101  includes power switch  114  and a diode  116 . The drain of power switch  114  is connected to the first side of the power source  58  and the anode of diode  116  is connected to the second side of power source  58 . The source of power switch  114  is connected to a first side of the second phase B machine coil  134  and a cathode of diode  116 . To reduce parasitic bus inductance and switching transients, capacitor  118  is connected between the drain of power switch  114  and the anode of diode  116 . 
     The negative side switch circuit  103  includes a power switch  126  and a diode  128 . The cathode of diode  128  is connected to a first side the power source  58 , and the source of power switch  126  is connected to the second side of power source  58 . The anode of diode  128  is connected to the second side of the second phase B machine coil  134  and the drain of power switch  126 . To reduce parasitic bus inductance and switching transients, capacitor  130  is connected between the cathode of diode  128  and the source of power switch  126 . 
     Positive side switch circuits  140 ,  141  and negative side switch circuits  142 ,  143  provide switching for phase C coil configuration  144 . For controlling the first phase C machine coil  172 , the positive side switch circuit  140  includes power switch  148  and diode  150 . The drain of power switch  148  is connected to the first side of power source  58  and the anode of diode  150  is connected to the second side of power source  58 . The source of power switch  148  is connected to a first side of the first phase C machine coil  172  and the cathode of diode  150 . To reduce parasitic bus inductance and switching transients, capacitor  152  is connected between the drain of power switch  148  and the anode of diode  150 . 
     The negative side switch circuit  142  includes a power switch  160  and a diode  162 . The cathode of diode  162  is connected to a first side the power source  58 , and the source of power switch  160  is connected to the second side of power source  58 . The anode of diode  162  is connected to the second side of the first phase C machine coil  172  and the drain of power switch  160 . To reduce parasitic bus inductance and switching transients, capacitor  164  is connected between the cathode of diode  162  and the source of power switch  160 . 
     For controlling the second phase A coil  174 , positive side switch circuit  141  includes power switch  154  and a diode  156 . The drain of power switch  154  is connected to the first side of the power source  58  and the anode of diode  156  is connected to the second side of power source  58 . The source of power switch  154  is connected to a first side of the second phase C machine coil  174  and a cathode of diode  156 . To reduce parasitic bus inductance and switching transients, capacitor  158  is connected between the drain of power switch  154  and the anode of diode  156 . 
     The negative side switch circuit  143  includes a power switch  166  and a diode  168 . The cathode of diode  168  is connected to a first side the power source  58 , and the source of power switch  166  is connected to the second side of power source  58 . The anode of diode  168  is connected to the second side of the second phase C machine coil  174  and the drain of power switch  166 . To reduce parasitic bus inductance and switching transients, capacitor  170  is connected between the cathode of diode  168  and the source of power switch  166 . 
     Now referring to  FIG. 3 , a converter circuit  210  for controlling a SRM  211  embodying the principles of the present invention is provided. The converter circuit  210  includes a first positive side switch circuit  212 , a second positive side switch circuit  213 , a first negative side switch circuit  214 , a second negative side switch circuit  215 , and a power source  226 . 
     SRM  211  includes a first machine coil  216  and a second machine coil  218 . The first machine coil  216  is wrapped around a first magnetic core  220 , while the second machine coil  218  is wrapped around a second magnetic coil  224  located opposite the first magnetic core  220 . 
     The first positive side switch circuit  212  is in electrical communication with the positive side of the first machine coil  216  and the first negative side switch circuit  214  is in communication with the negative side of the first machine coil  216 . Similarly, the second positive side switch circuit  213  is in communication with the positive side of the second machine coil  218  and the second negative side switch circuit  215  is in communication with the negative side of the second machine coil  218 . 
     The first positive side switch circuit  212  includes a first and second power switch  228 ,  232 . The first and second power switch  228 ,  232  are preferably an N-channel MOSFET, although, a P-channel MOSFET or other more complex power switches such as IGBTs or other commonly known switches may be used. The drain of power switch  228  is connected to the positve side of the power source  226 . The source of power switch  228  is connected to a first side of the first machine coil  216  and a drain of power switch  232 . To complete the first positive side switch circuit, a source of power switch  232  is connected to the second side of the power source  226 . The gate of power switch  228  and  232  are connected to a gate driver (not shown). To reduce parasitic bus inductance and switching transients, capacitor  236  is connected between the drain of power switch  228  and the source of power switch  232 . 
     The second positive side switch circuit  213  includes a third and fourth power switch  230 ,  234 . The third and fourth power switch  230 ,  232  are preferably an N-channel MOSFET, although, a P-channel MOSFET or other more complex power switches such as IGBTs or other commonly known switches may be used. The drain of power switch  230  is connected to the first side of the power source  226 . The source of power switch  230  is connected to a positive side of the second machine coil  218  and a drain of power switch  234 . To complete the first positive side switch circuit, a source of power switch  234  is connected to the second side of the power source  226 . The gate of power switch  230  and  234  are connected to the gate driver. To reduce parasitic bus inductance and switching transients, capacitor  236  is connected between the drain of power switch  230  and the source of power switch  234 . 
     The first negative side switch circuit  214  includes a fourth and fifth power switch  240 ,  246 . The drain of power switch  246  is connected to the power source  226 . A source of power switch  246  is connected to the negative side of the first machine coil  216  and the drain of power switch  240 . The source of power switch  240  is connected to the second side of the power source  226  to complete the first negative side switch circuit. To reduce parasitic bus inductance and switching transients, capacitor  252  is connected between the drain of power switch  246  and the source of power switch  240 . 
     The second negative side switch circuit  215  includes a seventh and eighth power switch  242 ,  248 . A drain of power switch  248  is connected to the power source  226 . A source of power switch  248  is connected to the negative side of the second machine coil  218  and the drain of power switch  242 . The source of power switch  242  is connected to the second side of the power source  226  to complete the second negative side switch circuit. To reduce parasitic bus inductance and switching transients, capacitor  254  is connected between the drain of power switch  248  and the source of power switch  242 . 
     A three phase 6/4 switched reluctance machine can be readily provided as in  FIG. 2 , by substituting a half bridge configuration into each of the positive side and negative side switch circuits as described above. 
     As a person skilled in the art will readily appreciate, the above description is meant as an illustration of implementation of the principles this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation and change, without departing from spirit of this invention, as defined in the following claims.