Abstract:
At least three alternative stiff current supply power converter topologies provide fixed current to a respective electric load such as a motor, or a non-inductive electric load using either a current source or a pseudo current source. The stiff current power converter topologies reduce the size of passive components within each of the topologies, thus reducing the overall packaging of each of the components and subsystems formed by each of the components. Each of the topologies have a stiff current source, a driver having power electronics formed therein to drive the associated electric load, wherein the stiff current source and the driver operate to deliver a stiff but controllable current to the electric load.

Description:
FIELD OF THE INVENTION 
   The present invention generally relates to power converter topologies for use in the field of delivering a stiff current power source or a pseudo stiff current power source to an electric load. 
   With very few exceptions, motor drives are designed based on stiff voltage sources, where the power sources are provided with small internal impedance, which hold a bus voltage steady even with substantial load current fluctuation. A stiff voltage power supply provides a constant voltage to a motor driver that remains constant independent of load demands on the driver. The benefits of this approach include simple topology, simple control requirements, and fast responses. 
   Prior art  FIG. 1  shows a functional block diagram of a voltage source topology  20  having a stiff voltage power supply or source  22 , an inverter, which may be in the form of a traction drive,  26 , and a motor  28 . 
   Additionally, motor drives based on stiff voltage sources similar to the topology shown in  FIG. 1  are typically associated with non-conforming events such as short-circuit currents—which may allow unwanted transients to damage an electronic circuit. A short circuit may be formed when the voltage remains constant, and the resistance may be negligible, thus allowing the current to rapidly increase and form a short circuit between a negative and a positive terminal of the stiff voltage power supply. 
   While existing devices suit their intended purpose, the need remains for a device and method that uses a stiff current supply topology to provide a—controllable current to a load, and that allows for flexible packaging options to efficiently package components located within the stiff current supply topology. 
   SUMMARY 
   In one aspect of the technology, a device and method is provided that uses a stiff current supply topology to provide a controllable current to a load, and that allows for flexible packaging options to efficiently package components located within the stiff current supply topology. 
   In an aspect of the technology, a current source power converter topology delivers a stiff current source to power an electric load. The topology has a driver with power electronics to drive the load and at least one capacitor coupled to the load and to the power electronics to prevent transients from damaging the current source power converter. 
   In another aspect of the technology, a pseudo current source power converter topology delivers power to an electric load using a pseudo current source to power the electric load formed from a stiff voltage source and a first capacitor, and an inductor coupled in series with the stiff voltage source and further in series with the first capacitor to hold a current delivered to the electric load stiff. A driver having power electronics drives the electric load and has two switches and a second capacitor, wherein the two switches alternate between open and closed positions to regulate the voltage on the second capacitor. 
   A pseudo current source power converter topology having an electric load, and a battery formed from a voltage source connected to a first capacitor packed in a first package; an inductor coupled in series with the battery, wherein the inductor operates to an electric load; a battery formed from a voltage source and a first capacitor connected in parallel with the voltage source, wherein the battery has an associated first package; an inductor coupled in series with the battery within a second package, and a combination electric load and associated driver packaged within a third package and cooperates with the battery and the inductor to provide a stiff but controllable current to the electric load. 
   A method of using each of the topologies is also provided. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects, features and advantages of the present invention will become apparent from the following detailed description and the appended drawings in which: 
       FIG. 1  illustrates a functional block diagram of a prior art voltage source topology. 
       FIG. 2   a  illustrates a functional block diagram of a current source power converter topology system having a stiff current source, an electric subsystem or power electronics, and a motor in accordance with one aspect of the technology. 
       FIG. 2   b  illustrates detailed schematics of a current source power converter topology that provides a current source, power electronics, and a motor in accordance with one aspect of the technology. 
       FIG. 2   c  illustrates detailed schematics of a current source power converter topology that provides a current source, power electronics, and a motor in accordance with one aspect of the technology. 
       FIG. 2   d  illustrates detailed schematics of an alternative current source power converter topology system having a pseudo current source, power electronics and a motor in accordance with one aspect of the technology. 
       FIG. 2   e  illustrates detailed schematics of an alternative current source power converter topology similar to the current source power converter topology disclosed in  FIG. 2   d , wherein a pseudo current source is provided as a battery and an inductor that are each packaged separately in accordance with one aspect of the technology. 
       FIG. 2   f  illustrates detailed schematics of another current source power converter topology similar to the current source power converter topology disclosed in  FIG. 2   e , further having suppressors in communication with the separately packaged inductor to prevent arcing within the current topology in accordance with one aspect of the technology. 
       FIG. 2   g  illustrates detailed schematics of another current source power converter topology similar to the current source power converter topology disclosed in  FIG. 2   e  further providing rectification means in communication with the separately packaged inductor to prevent arcing within the current source power converter topology in accordance with one aspect of the technology. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present area of technology relates to use of current source topologies that provide stiff current source or pseudo current sources to deliver a stiff but controllable current to a load. The current source topologies of the present area of technology operate to keep a current delivered to the load stiff but controllable, independent of the load demands. In each of the topologies of the disclosed herein, a source is provided that operates to hold electric current stiff throughout the current source system. The benefits of each of the current source or pseudo current sourced topologies eliminate the effect of potential short-circuit non-conforming events that, without the use of the present area of technology, may operate to damage the associated electronics. 
   Referring now to the drawings, in particular,  FIG. 2   a  illustrates a functional block diagram of a current source power converter topology system  30  having a stiff current source  32 , an electric subsystem or power electronics  34 , and a load  36 . The load  36  may be any electric load such as, but not limited to an electric motor, a DC load, and a non-inductive load. As shown in  FIGS. 2   b - 2   g , the load  36  is provided for illustrative purposes as a three-phase electric motor. Additionally, the power electronics shown in  FIGS. 2   b - 2   g  each operate to drive the motor and further provide a plurality of switches, shown as six switches, in each of the schematics that cooperate to control the motor using a technology such as pulse width modulation (PWM) scheme as is known in the art and as is described in detail in U.S. Pat. No. 4,511,835, which is herein incorporated by reference. The six switches are shown as switches S 3 -S 8  in  FIG. 2   b ; switches S 13 -S 18  in  FIG. 2   c ; and switches S 21 -S 26  in  FIGS. 2   d - 2   e.    
   An application of the present area of technology shown in  FIGS. 2   a - 2   g  may be used in many applications that have come or may come into existence requiring stiff but controllable current delivery to a load. An example of such an application may be, but is not limited to use of the present area of technology in a vehicle such as a hybrid or parallel hybrid electric vehicle having traction control, wherein the load  36  may be an electric traction motor, and wherein the power electronics  34  may be a traction drive. While many other applications may exist for the present technology, as used herein for illustrative purposes with reference to  FIGS. 2   b - 2   g , the power electronics of each of the disclosed current and pseudo source power converter topologies is a traction drive defined by an associated power converter or power electronics and the load is an electric traction motor. 
     FIGS. 2   b - 2   g  illustrate alternative detail views of the schematics that may be used to define each of the elements  32 ,  34 ,  36  disclosed in the power converter topology  30  shown in  FIG. 2   a . More particularly,  FIGS. 2   b - c  illustrate detailed schematics of two alternative current source power converter topologies that each provide a current source, power electronics, and a motor.  FIG. 2   d  illustrates detailed schematics of an alternative current source power converter topology system having a pseudo current source, power electronics and a motor.  FIG. 2   e  illustrates detailed schematics of an alternative current source power converter topology similar to the current source power converter topology disclosed in  FIG. 2   d , wherein a pseudo current source is provided as a battery and an inductor that are each packaged separately.  FIG. 2   f  illustrates detailed schematics of another current source power converter topology similar to the current source power converter topology disclosed in  FIG. 2   e , additionally having alternative suppressors in communication with the separately packaged inductor.  FIG. 2   g  illustrates detailed schematics of another current source power converter topology similar to the current source power converter topology disclosed in  FIG. 2   e  further providing rectification means in communication with the separately packaged inductor to prevent arcing within the current topology. Like elements shown in each of the respective  FIGS. 2   b - 2   g  will be referred to with corresponding like reference numbers. 
     FIG. 2   b  illustrates a schematic of a current source power converter topology  38  having a stiff current source  40 , power electronic&#39;s  42 , and a motor  44 , wherein the power electronics  42  operate to deliver power to the motor  44 . The stiff current source  40  integrates a preregulator, with a voltage source, wherein the preregulator and the voltage source cooperate to form the current source  40 . 
   The stiff current source provides a voltage source  46 , an inductor  48  in electrical communication with the voltage source, a first switch S 1 , and a second switch S 2 , wherein S 1  and S 2  alternate between alternating open and closed positions and cooperate with the voltage source  46  and the inductor  48  to deliver stiff but controllable current to the motor. S 1  and S 2  each respectively may be coupled to the inductor  48  and are used to control the amount of current flowing through the inductor  48 . By switching S 1  on when S 2  is off, and then by switching S 1  off and S 2  on, the current delivered to the motor can be controlled. Determination of the current flowing through the current source power converter topology  38  may be based on known motor parameters, such as delivered torque, or alternatively, may be measured by current measuring means known in the art such as, but not limited to a shunt, or a current sensor. 
   In operation, initially, S 1  is closed, and S 2  is opened. When S 1  is closed, and thus, S 2  is open, S 1  is connected in series with the voltage supply and the inductor  48  to provide a current I 1  through the inductor  48  which stores energy in a magnetic field and then delivers a current I 3  to the motor. When S 1  is opened and S 2  is closed, the source of current supplied by the voltage source  46  is eliminated and the inductor sources the stored energy as the current I 3  defined by an inductance (L) of the inductor multiplied by a change in an instantaneous current divided by a change in time (L*di/dt). When the switch S 1  is opened, and the switch S 2  is closed, a current I 2  flows from the inductor  48  to deliver the current I 3  to the motor. The path of the currents I 2  and I 3  flowing through the system when S 2  is closed forms a closed loop through the inductor and the motor, thus, eliminating the voltage supply from the loop. Once the current I 3  drops below a predetermined minimum threshold, the switch S 1  closes and the switch S 2  opens and the cycle repeats when the current sourced exceeds a predetermined maximum threshold keeping the current stiff but controllable. Thus, the inductor  48  operates to smooth out or regulate transient current flowing through the power converter topology. Optionally, capacitors C 1 -C 3  may be provided to suppress transient currents occurring during cycling of the motor. 
     FIG. 2   c  illustrates an alternative aspect shown as  50  of the current topology disclosed in  FIG. 2   b .  FIG. 2   c  illustrates use of a current source  52  defined by voltage source  58 , an inductor  60 , and four switches S 9 -S 12  that cooperate to provide a stiff but controllable current to the traction device. When closed, switches S 10  and S 11  function in a similar manner to the switches S 1  and S 2  shown in  FIG. 2   b . Additionally, switches S 9  and S 12  provide a negative voltage current source. Switches S 13 -S 18  operate in a similar manner to the switches S 3 -S 8  shown in  FIG. 2   b . Also, capacitors C 4 -C 6  operate in a similar manner to capacitors C 1 -C 3  to suppress transient currents occurring during cycling of the motor. 
   While the present area of technology illustrates use of a motor, a non-inductive load may be used as an alternative load. When a noninductive load replaces the motor, then optionally, each of the three capacitors C 1 , C 2 , C 3  or C 4 , C 5 , C 6  (as shown in  FIG. 2   c ) may be eliminated from the current source system shown in both  FIGS. 2   b - 2   c.    
     FIG. 2   d  illustrates a schematic of a pseudo current source power converter topology  62  driving a traction drive having power electronics  66  with pre-regulation capability.  FIG. 2   d  shows a bulky inductor  72  typically associated with a boost converter, and integrated with a voltage source  70 , thus, operating as pseudo current source  64 . The topology shown in  FIG. 2   d  is considered as a pseudo current source because, the inductor  72  operates to hold the current stiff but controllable during transients, which is the signature of a current source. The combination of a battery and an inductor cannot regulate the steady state current, therefore, the topology shown in  FIG. 2   d  is considered a pseudo-current source power converter topology. 
     FIG. 2   d  shows a pre-regulator stage comprised of S 19  and S 20  to regulate the inductor current and the energy to C 8 . The method of regulating the inductor current initially allows current to flow into the inductor  72  by opening and closing a pair of switches S 19  and S 20 . Initially, S 19  is open and S 20  is closed. As current flows through the inductor  72 , magnetic energy is stored in the inductor  72 . When the switch S 20  opens and S 19  is closed, the inductor  72  discharges the energy stored into the capacitor C 8  and operates to charge the capacitor C 8 . The voltage Vc 8  measured across the capacitor C 8  is equal to a voltage Vb measured across the voltage source  70  plus a voltage V L  measured across the inductor  72  when S 20  opens where V L  equals L*(di/dt). Thus, due to the voltage boost properties of the boost converter, a voltage across the capacitor C 8  will be at a higher voltage then the source Vb. Capacitor C 7  is used to provide transient current to the inductor  72 . The inductor  72  stores current, and the stored current becomes a current source, and wherein C 8  has a higher voltage than V b  across the voltage source  70  this combination cooperates to form a pseudo-current source. 
   In  FIG. 2   d , a pseudo current source system  62  is provided and has a voltage source  70 , an inductor  72  coupled in series with the voltage source  70 , and a capacitor C 7  connected in parallel with the voltage source  70  and shares a common node with the inductor  72 . The voltage source  70 , the capacitor C 7  and the inductor  72  are grouped together in a single package or housing  74  and may be considered a pseudo-current source. Typically, the current source  52  shown in  FIGS. 2   b  and  2   c  having a power source with integrated switches and an integrated inductor are difficult to be placed within a vehicle. A battery  78  typically would not be packaged with switches and electronics. With inductor  72  in a location separate from the power electronics portion of the traction drive  66 , the traction drive  66  can be packaged in a more compact manner, thus allowing more freedom in determining packaging designs. 
     FIG. 2   e  illustrates a pseudo current source power converter topology  76  that operates in a similar manner to the topology shown in  FIG. 2   d , however the inductor  72  is packaged within packaging  80 , separate from a battery  78  formed by the voltage source  70  and the capacitor C 7  connected in parallel. In some applications, such as in a motor vehicle, packaging the inductor  72  in the same package as the battery  78  might not be feasible. Thus, if the battery  78  cannot accommodate the inductor  72  in the same package, the inductor may be packaged alone, as shown in  FIG. 2   e . The schematic for the circuit shown in  FIG. 2   e  is functionally the same as the circuit shown in  FIG. 2   d  but provides additional packaging flexibility because the inductor  72  is packaged separately from the battery  78  and from the power electronics  82 . The switches s 19  and s 20  and a smaller capacitor C 8  is part of the traction drive power electronics. 
   However, the topology  76  shown in  FIG. 2   e  may produce arcing if an interconnection to the inductor  72  is broken. To reduce the potential for arcing, voltage suppressors may be provided. 
     FIG. 2   f  illustrates the same pseudo current source power converter topology as shown in  FIG. 2   e  with additional protection against transient voltages.  FIG. 2   f  provides metal-oxide varistors (MOVs) type suppression wherein arcing is a side effect of an open current formed at the inductor voltages rise quickly and needs to be suppressed. Additionally, suppression is provided to further prevent transients from propagating through an entire system such as a vehicle between the inductor  72  and at least one of the traction drive  66  defining the power electronics, the motor  68 , and an alternative non-inductive load. Suppression operates to prevent transient voltage from exceeding a certain amount when the system is operating to regulate the voltage. At least one transient voltage suppressor across the inductor  72  may be provided. As shown in  FIG. 2   f , alternatively a plurality of voltage suppressors Z 1 , Z 2 , and Z 3  are provided in parallel with the inductor  72 . The suppressors Z 1 , Z 2 , and Z 3  may be (MOVs) or other bi-directional transient-voltage clipping devices. It may not be necessary to include all three suppressing components. The suppressor may be installed as needed, depending the requirements of the system and associated cost limitations. 
   An alternative way to reduce arcing associated with the topology disclosed in  FIG. 2   e  is to divert the magnetic energy stored within the inductor to another form, such as electric energy as shown the pseudo power source topology circuit  94  shown in  FIG. 2   g . At least one diode in combination with an additional capacitor C 9  to accomplish the diversion of energy. Alternatively, a plurality of diodes, shown as four diodes D 1 , D 2 , D 3 , and D 4  as shown in  FIG. 2   g  are placed in parallel with the inductor  72  to rectify or shunt the magnetic energy in the inductor  72  to electric energy stored in capacitors C 8  and/or C 9 . However, not all four diodes may be required. The necessity depends on both the current direction and, similar to the suppression components disclosed with respect to  FIG. 2   e , the port(s) associated with the topology requiring protection. In operation, to dissipate the electric energy stored in C 9 , the energy may be delivered to the traction drive and motor through an optional switch S 28 , wherein S 28  may be replaced by a direct connection if necessary. Additionally, the energy stored in C 9  may be diverted for use in another application or alternatively, may be dissipated in a resistor (not shown). 
   While several aspects have been presented in the foregoing detailed description, it should be understood that a vast number of variations exist and these aspects are merely an example, and it is not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the foregoing detailed description provides those of ordinary skill in the art with a convenient guide for implementing a desired aspect of the invention and various changes can be made in the function and arrangements of the aspects of the technology without departing from the spirit and scope of the appended claims.