Patent Publication Number: US-2018043790-A1

Title: Active rectifier topology

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to rectifier modules for vehicular power systems, and more specifically to an active rectifier module for electric and/or hybrid electric vehicles. 
     BACKGROUND 
     Certain ground vehicles, such as those utilized in military and similar applications, use hybrid electric or pure electric based power systems. A typical electric power system architecture includes one or more un-regulated permanent magnet generators coupled to an active rectifier for providing DC power to a power distribution system. The active rectification places a ripple current on the power provided to the power distribution system. The ripple currents are, in turn, typically filtered out via the use of a low-impedance DC-link capacitor. 
     As dependence on the electric systems for power within the vehicle increase, integration of an active rectifier into the small, complex structured, high thermal and mechanical stress environment of a vehicle system becomes more difficult. Passive components of an active rectifier contribute substantially to the necessary size of the active rectifier. By way of example, the capacitors required to provide a low-impedance DC link, and provide minimal electromagnetic interference (EMI) are a major factor in the necessary size of such a rectifier system. Further, the size and utilization of the passive components can require an active cooling supply to maintain the power system temperatures below a temperature where the electronics are susceptible to damage. 
     SUMMARY OF THE INVENTION 
     In one exemplary embodiment an active rectifier module includes a matrix converter having a plurality of phase inputs and a plurality of phase outputs, a rectifier including a plurality of inputs, each connected to a corresponding phase output in the plurality of phase outputs, a filter capacitor connected across a DC output of the rectifier, and a DC output configured to provide DC power to a load. 
     In another example of the above described active rectifier module the rectifier is a passive rectifier. 
     In another example of any of the above described active rectifier modules the rectifier is an active rectifier. 
     In another example of any of the above described active rectifier modules the active rectifier is a bi-directional active rectifier. 
     In another example of any of the above described active rectifier modules a current at the plurality of phase inputs has a first frequency, a current at the plurality of phase outputs has a second frequency, and the second frequency is greater than the first frequency. 
     Another example of any of the above described active rectifier modules further includes a DC bus filter connecting the DC output of the rectifier to the filter capacitor. 
     In another example of any of the above described active rectifier modules the matrix converter includes a first set of active switching elements and a second set of active switching elements. 
     In another example of any of the above described active rectifier modules the first set of active switching elements are arranged as a rectifier and the second set of active switching elements are arranged as an inverter. 
     In another example of any of the above described active rectifier modules the first set of active switching elements are switched on and off in synchronization with the source voltage and the second set of active switching elements are configured to be controlled by a pulse width modulated control signal. 
     Another example of any of the above described active rectifier modules further includes a controller controllably connected to each of the active switching elements and configured to output control signals. 
     In another example of any of the above described active rectifier modules the controller is controllably connected to the rectifier, and configured to output a pulse width modulated control signal to the rectifier. 
     In another example of any of the above described active rectifier modules further includes a power source connected to the DC output, and a controller controllably connected to the active rectifier module and configured to cause the rectifier to provide an engine start. 
     In one exemplary embodiment an active rectifier module for a vehicle includes a matrix converter having a plurality of phase inputs and a plurality of phase outputs, wherein an AC frequency of the plurality of phase inputs is a first value, an AC frequency at the plurality of phase outputs is a second value, and the second value is higher than the first value, a rectifier including a plurality of inputs, each connected to a corresponding phase output in the plurality of phase outputs, and a DC output configured to provide DC power to a load. 
     In another example of the above described active rectifier module for a vehicle the rectifier is a passive rectifier. 
     In another example of any of the above described active rectifier modules for a vehicle the rectifier is an active rectifier. 
     In another example of any of the above described active rectifier modules for a vehicle the active rectifier is a bi-directional active rectifier. 
     An exemplary method for reducing ripple currents in an active rectifier module includes receiving AC power at a first frequency, converting the AC power to a second frequency using a matrix converter, the second frequency being higher than the first frequency, and rectifying the converted AC power into DC power using a rectifier circuit. 
     In a further example of the above described exemplary method for reducing ripple currents in an active rectifier module converting the AC power to the second frequency using the matrix converter, includes converting the AC power to a DC power using a first set of active switching elements within the matrix converter and converting the resultant DC power to an AC power using a second set of active switching elements within the matrix converter. 
     Another example of any of the above described exemplary methods for reducing ripple currents in an active rectifier module further includes receiving DC power at an output of the rectifier circuit, converting the DC power into a constant frequency AC power using the rectifier circuit, converting the AC power into a variable voltage variable frequency power using the matrix converter, and providing the variable voltage variable frequency power to provide an engine start. 
     Another example of any of the above described exemplary methods for reducing ripple currents in an active rectifier module further includes controlling the matrix converter using a pulse width modulated control signal. 
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates an exemplary active rectifier module for an electric or a hybrid electric vehicle. 
         FIG. 2  schematically illustrates a more detailed example of an active rectifier module. 
         FIG. 3  schematically illustrates an alternate detailed example of an active rectifier module. 
         FIG. 4  schematically illustrates the example active rectifier module of  FIG. 3 , configured to operate as an engine starter. 
     
    
    
     DETAILED DESCRIPTION OF AN EMBODIMENT 
       FIG. 1  schematically illustrates an exemplary active rectifier module  10  for utilization within an electric vehicle or a hybrid electric vehicle. The active rectifier module  10  includes a matrix converter  20  with a polyphase input  22  and a polyphase output  24 . While illustrated herein as three-phase inputs/outputs  22 ,  24 , the matrix converter  20  can be configured to use any number of phases of a polyphase power system. In some examples, the matrix converter  20  can be implemented using bidirectional switches. In other example presented here, the matrix converter  20  can utilize unidirectional switches arranged in two conventional pulse width modulated converters without use of dc link capacitor. The matrix converter  20  is controlled via a controller  102  connected to the active rectifier module  10  via any known control mechanism. 
     Connected to the phase inputs  22  of the matrix converter  20  are multiple phases  32 ,  34 ,  36  of a three phase power generation system  30 . In some examples, the three phase power generation system  30  can be a permanent magnet generator. In alternative systems, the three phase power generation system  30  can be any other generator type and the matrix converter  20  can provide similar functions. Similarly, the power generation system can, in other examples, have any number of phases  32 ,  34 ,  36  and is not limited to the three phase example. 
     Connected to the polyphase output  24 , is a rectifier circuit  40 . The rectifier circuit  40  can be any rectifier type and receives the polyphase output  24 . The rectifier circuit  40  converts the polyphase output  24  into a DC output  42 . The DC output  42  can be connected to a load  50 , such as a power distribution bus, and provides DC power to the load  50 . A DC link capacitor  60  is included across the DC output  42 , and provides a filtering effect to the DC output, removing most, of the ripple currents introduced to the power transmission by the matrix converter  20  and the rectifier circuit  40 . 
     During operation of the active rectifier module  10 , the matrix converter  20  receives three phase AC power from the power generation system  30 . The received power has a first current frequency, dependent on the power generation system  30 . The matrix converter  20  converts the AC power to AC power with a second frequency, and outputs the power at the second frequency on the polyphase power outputs  24 . The frequency of the current provided across the polyphase outputs  24  is substantially higher than the current frequency of the power provided by the power generation system  30 . By way of example, in some embodiments, the current frequency at the polyphase outputs  24  is variable from 180 Hz to 600 Hz, while the frequency at the polyphase inputs  22  is constant and in the range of 1 kHz-2 kHz or higher. 
     As can be appreciated by one of skill in the art, the majority of the physical size of an active rectifier module, such as the active rectifier module  10 , is due to the DC link capacitor being required to be sized for the ripple currents introduced by the rectifier circuit  40 . By substantially increasing the frequency of the power entering the rectifier circuit  40  using the matrix converter  20 , relative to the power exiting the power generation system  30 , the magnitude of the ripple currents, and thus the required physical size of the DC link capacitor  60 , is substantially reduced and the temperature tolerances of the DC link capacitor can be increased. 
     Further, the size increase of the active rectifier module  10  due to the inclusion of the matrix converter  20  is less than the size decrease due to the smaller DC link capacitor  40 , and the overall size of the active rectifier module  10  is decreased, relative to existing active rectification systems. 
     In some examples, such as the examples of  FIGS. 2-4 , the size of the DC link capacitor can be even further decreased through the utilization of inductance-capacitance (LC) filter optimization and tuning. 
     With continued reference to  FIG. 1 , and with like numerals indicating like elements,  FIG. 2  schematically illustrates a more detailed example of the active rectifier module  10  of  FIG. 1 . The controller  102  is connected to the active rectifier module  10  and controls operation of active components within the active rectifier module  10 . By way of example, the controller  102  can be a dedicated controller, a general vehicle controller, or any other controller type. 
     Within the matrix converter  20  are multiple actively controlled power switches  110 . The actively controlled power switches  110  are arranged in two cascade connected converters. The first converter  112  is a current source rectifier, while the second converter  114  is a voltage source inverter. The rectifier configuration  112  actively converts the received AC power from the power generation system  30  into a DC power. The inverter configuration  114  then converts the DC power from the first six pulse rectifier configuration  112  back into AC power. The inverter configuration  114  is operated at a substantially higher frequency than the rectifier configuration  112 . In this way, the matrix converter  20  is configured to receive a power output from the power generation system  30 , and convert the power output to a new AC power output at the substantially higher frequency. 
     Once the frequency of the AC power has been increased by the matrix converter  20 , the power is provided to the rectifier circuit  40 , as described above. In the example of  FIG. 2 , the rectifier circuit  40  is a passive rectifier circuit utilizing six diodes arranged in a bridge configuration. One of skill in the art, having the benefit of this disclosure will appreciate that any other passive rectification topology could be utilized for passive rectification with minimal modifications to the illustrated system. 
     Also included within the rectifier circuit  40  are multiple filter inductors  120  and inductor resistor pairs  122 . The inductor resistor pairs  122  function as damper circuits to ensure stable system operation in the presence of constant power load  50  (negative impedance load). The inductors  120  and the inductor resistor pairs  122  operate to tune the inductance of the passive filter and optimize the output to further reduce ripple currents and transients, according to known methodologies. 
     In alternative examples, active rectification can be utilized in place of the six pulse passive rectifier utilized as the rectifier circuit  40  in  FIG. 2 . With continued reference to  FIGS. 1 and 2 , and with like numerals indicating like elements,  FIG. 3  schematically illustrates a modified example of the active rectifier module of  FIG. 1 , with the utilization of an active rectifier instead of the passive six pulse rectifier of  FIG. 2 . 
     As compared to the example of  FIG. 2 , the matrix converter  20  of the example of  FIG. 3  is identical, including the arrangement of multiple active switching elements, such as controlled power switches  110 , in two power converter configurations  112 ,  114 , and the operations of the matrix converter  20  are functionally the same. 
     In place of the passive rectifier is an active rectifier  210 . The active rectifier  210  is controlled by the controller  102 , and arranged as a six pulse active rectifier. In alternative examples, the active rectifier  210  can be any similar active rectifier and function in a similar manner. Further aiding the utilization of the active rectifier  210  is the inclusion of boost inductors  220  connecting the output of the matrix converter  20  to the input of the active rectifier  210 . The boost inductors  220 , the PWM rectifier  240  and the dc link capacitor form active rectification circuit to convert AC power from the matrix converter into regulated DC power. 
     In the example of  FIG. 3 , the active rectifier  210  is a bi-directional rectifier, and allows boosting the output voltage with a reduced output voltage filter size. In other examples, the matrix converter  110  may produce variable voltage constant frequency output, while the active rectifier circuit  40  operates at the optimal duty cycle. In other examples, both active rectifier circuit  40  and matrix converter  110  may coordinate controls to optimize system efficiency for different operating speed and load conditions. 
     In yet further examples, such as the example illustrated in  FIG. 4 , a power source  310  can be connected in parallel with the load  50  via a switching element  312 . By doing so, the active rectifier module  10  can provide for an electric engine start. In the example of  FIG. 4 , the DC power from the power source  310  is received by the rectifier circuit  40  at the DC output of the rectifier circuit  40 . The DC power is converted into a constant frequency AC power by the rectifier circuit  40 , and provided to the matrix converter  20 . The matrix converter  20  then converts the AC power into a variable voltage variable frequency (VVVF) power, which is provided to start the engine. The power of the variable voltage variable frequency is controlled by the operations of the matrix converter  20  or the rectifier circuit  40 . In other examples, the active rectifier circuit  40  may provide VVVF power to the matrix converter, while the matrix converter  110  output follows input voltage and frequency from the active rectifier circuit  40 . In other examples, both active rectifier circuit  40  and matrix converter  110  may coordinate controls to optimize system efficiency for different operating speeds. 
     While specific topologies are illustrated in the examples of  FIGS. 2-4 , one of skill in the art, having the benefit of this disclosure will appreciate that alternative topologies can be utilized to similar effect, and still fall within the above disclosure. 
     It is further understood that any of the above described concepts can be used alone or in combination with any or all of the other above described concepts. Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.