Abstract:
In at least one embodiment, an apparatus for controlling a switching frequency of at least one power switch in a vehicle is provided. The apparatus comprises a power conversion circuit including a power switch. The power conversion circuit is configured to convert a first energy signal into a second energy signal and to control the power switch to operate at a first switching frequency, the first switching frequency generating a first set of harmonics. The power conversion circuit is further configured to receive frequency information from an entertainment device, the frequency information generating a second set of harmonics. The power conversion circuit is further configured to select a second switching frequency, the second switching frequency generating a third set of harmonics. The power conversion circuit is further configured to perform a distance measurement using the first set of harmonics, the second set of harmonics, and the third set of harmonics.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application Ser. No. 61/245,838 filed on Sep. 25, 2009, which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The embodiments of the present invention generally relate to an apparatus and method for controlling the switching frequency of a power converter in a vehicle. 
       BACKGROUND 
       [0003]    In order to ensure quality radio reception, vehicle original equipment manufactures (OEMs) generally establish low thresholds for electromagnetic (EM) radiated emissions for various electrical devices positioned within a vehicle. In order to meet such thresholds, various filters and/or shielding mechanisms may be implemented within a particular electrical device to prevent internally generated electrical noise from leaving the electrical device. While these filters and/or shielding mechanisms may be effective in reducing EM radiated emissions, the filters and/or shielding mechanisms may consume space, may be difficult to assemble, and may increase the overall cost of the electrical device. 
       SUMMARY 
       [0004]    In at least one embodiment, an apparatus for controlling a switching frequency of at least one power switch in a vehicle is provided. The apparatus comprises a power conversion circuit including a power switch. The power conversion circuit is configured to convert a first energy signal into a second energy signal and to control the power switch to operate at a first switching frequency, the first switching frequency generating a first set of harmonics. The power conversion circuit is further configured to receive frequency information from an entertainment device, the frequency information generating a second set of harmonics. The power conversion circuit is further configured to select a second switching frequency, the second switching frequency generating a third set of harmonics. The power conversion circuit is further configured to perform a distance measurement using the first set of harmonics, the second set of harmonics, and the third set of harmonics. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The embodiments of the present invention are pointed out with particularity in the appended claims. However, other features of the various embodiments will become more apparent and will be best understood by referring to the following detailed description in conjunction with the accompany drawings in which: 
           [0006]      FIG. 1  depicts a system for controlling the switching frequency of a power converter in accordance to one embodiment of the present invention; 
           [0007]      FIG. 2  depicts a method for controlling the switching frequency of a power converter in accordance to one embodiment of the present invention. 
           [0008]      FIG. 3  depicts an example of a time domain waveform for a first switching frequency and a second switching frequency; 
           [0009]      FIG. 4  depicts an example of a frequency domain waveform for the first switching frequency and the second switching frequency; and 
           [0010]      FIG. 5  depicts an example of test measurement data obtained from a power converter. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0012]    The embodiments of the present invention generally provide for, but not limited to, a system and method for adjusting the switching frequency of a power converter in a vehicle. Such a condition may minimize the effect of EM interference in a vehicle for any device in the vehicle that is required to transmit audio and/or video signals for a vehicle occupant. The system and/or method may, among other things, monitor a particular frequency at which the device in the vehicle is tuned to and adjust the switching frequency within the power converter such that switching frequency and its harmonics do not overlap the tuned frequency of the electrical device. 
         [0013]    The embodiments of the present invention as set forth in  FIGS. 1-5  generally illustrate and describe a plurality of controllers (or modules), or other electrically based components. All references to the various controllers and electrically based components and the functionality provided for each, are not intended to be limited to encompassing only what is illustrated and described herein. While particular labels may be assigned to the various controller(s) and/or electrical component(s) that are disclosed, such labels are not intended to limit the scope of operation for the controllers and/or the electrical components. The controllers may be combined with each other and/or separated in any manner based on the particular type of electrical architecture that is desired or intended to be implemented in the vehicle. The controllers and/or electrical components may be combined with each other and/or separated in any manner based on the particular type of electrical architecture that is desired in the vehicle. It is generally recognized that each controller and/or module/device disclosed herein may include, but not limited to, any number of microprocessors, ICs, memory devices (e.g., FLASH, RAM, ROM, EPROM, EEPROM, or other suitable variants thereof), and software which co-act with one another to perform the various functions set forth below. 
         [0014]      FIG. 1  depicts a system  10  for controlling at least one switching frequency in a vehicle in accordance to one embodiment of the present invention. The system  10  includes a power conversion circuit  14 , an entertainment device  16 , and at least one vehicle battery  18 . In one example, the power conversion circuit  14  may be implemented as a battery charger. An external power supply  12  positioned in, but not limited to, a building (residential or commercial) or charging station transfers AC energy therefrom to the power conversion circuit  14 . The power conversion circuit  14  converts the AC energy into DC energy for the purpose of charging the battery  18 . 
         [0015]    The power conversion circuit  14  includes a controller  20 , a first AC to DC converter  22 , a DC to AC converter (or power converter)  24 , a transformer  26 , and a second AC to DC converter  28 . The controller  20  is generally configured to transmit one or more command signals to the AC to DC converter  22 , the DC to AC converter  24 , and the AC to DC converter  28  to control the operation of these converters. The command signal may include synchronization signals that may set the switching frequency for one or more of these devices. This operation will be discussed in more detail below. 
         [0016]    In one example, the power conversion circuit  14  may form a battery charger module. It is recognized however, that the embodiments of the present invention may be applied to any power converter that utilizes a switching frequency to control the operation of at least one power switch. For example, embodiments of the present invention may be implemented in a power inverter within a vehicle. The power inverter may be a device that converts DC energy into AC energy such that the vehicle occupant may be able to power an AC powered portable device with the AC energy while in the vehicle. 
         [0017]    In general, the first AC to DC converter  22  receives the AC energy from the external power supply  12 . The first AC to DC converter  22  converts the AC energy into DC energy (or bulk DC energy). The bulk DC energy provides a reservoir of DC power. A capacitor  30  stores the DC energy for consumption by the DC to AC converter  24 . The DC to AC converter  24  receives the bulk DC energy and converts such DC input into an AC output that is shaped in the form of a square wave output. 
         [0018]    The DC to AC converter  24  includes a transformer  35  having a primary winding and a secondary winding, at least one power switch  34  and a power supply  36 . It is recognized that the power switch may be implemented as a transistor or other suitable device. The controller  20  is configured to control particular switching frequency of the at least one power switch  34 . For example, the at least one power switch  34  is operably coupled to the power supply  36  and to a center tap of the primary winding. The controller  20  controls the at least one power switch  34  such that the switch  34  may be rapidly switched back and forth to allow current to flow back to the DC source (e.g., capacitor  30 ) via two alternate paths (e.g., one path from one end of the primary and the other path from the other end of the primary). The change in direction of current in the primary winding of the transformer  35  causes the secondary winding to provide the AC output therefrom. The AC output is generally a square shaped output. 
         [0019]    The transformer  26  receives and increases the AC voltage output. The AC to DC converter  28  receives the increased AC voltage and converts the same into an increased DC voltage. The AC to DC converter  28  controls the flow of the increased DC voltage into a capacitor  31 . The capacitor  31  discharges the increased DC voltage to the battery  28  for storage purposes. In general, the increased DC voltage may be 400 V or other suitable value. 
         [0020]    The conversion chain described above (e.g., AC to DC converter  22 , the DC to AC converter  24 , and the AC to DC converter  28 ) may isolate the input AC energy (e.g., from the external power supply  12 ) and the final DC output (e.g., from the power conversion circuit  14 ). While the AC input from the external power supply  12  may be provided directly to the transformer  26  due the low frequency (e.g., 50 or 60 Hz) of a common power system, the size of the transformer  26  may be large when compared to what may be needed when high switching frequency is used. 
         [0021]    It is recognized that the switching frequency as performed by the DC to AC converter  24  may generate electromagnetic interference (EMI). Such EMI may affect the performance of one or more electrical devices in the vehicle. For example, an entertainment device  16  positioned in the vehicle may have its performance affected due to such EMI. The entertainment device  16  may be a radio or other device that is capable of transmitting audio and/or video signals to one or more occupants in the vehicle. The presence of EMI may degrade the transmission of the audio and/or video signals from the entertainment device  16 . It is contemplated that in order to minimize or reduce the effects of the EMI that is caused by the switching frequency exhibited by the DC to AC converter  24 , the switching frequency of the power switches  34  may be adjusted such that the switching frequency is moved away from the frequency at which the entertainment device  16  is tuned to. In other words, the power conversion circuit  14  ensures that its switching frequency does not interfere with the frequency reception (e.g., AM/FM) of the entertainment device  16 . 
         [0022]    The power conversion circuit  14  may be operably coupled to the entertainment device  16  via a communication data bus  40 . The communication data bus  40  may be, but not limited to, a high/medium speed controller area network (CAN) or Local Interconnect Network (LIN). In general, the power converter  14  and the entertainment device  16  may communicate with one another via data messages that are transmitted in binary form over the communication bus. The entertainment device  16  may transmit frequency information corresponding to a channel in which the entertainment device  16  is tuned to when transmitting the audio and/or videos signal. Such information may be transmitted over the bus  40 . The controller  20  may control the DC to AC converter  24  to adjust the switching frequency of the power switch  34  so that the harmonics attributed to the switching frequency of the power switch  34  is moved away from harmonics of the frequency information that is being used by the entertainment device  16 . It is recognized that the controller  20  may control any device that utilizes a power switch and switching frequency such that the harmonics of the switching frequency for the power switch is moved away from the harmonics of the frequency information that is being used by the entertainment device. The controller  20  may selectively control the switching frequency of the power switch  34  in real time based on the frequency reception of the entertainment device  16 . 
         [0023]      FIG. 2  depicts a method  50  for controlling the switching frequency of the power converter  24  in accordance to one embodiment of the present invention. One or more of the operations described below may be modified, omitted or rearranged as needed based on the desired criteria of a particular implementation. 
         [0024]    In operation  52 , the controller  20  receives the frequency information from the entertainment device  16  over the bus  40 . For example, in the event the occupant has tuned the entertainment device  16  to an AM station, the entertainment device  16  transmits frequency information corresponding to the tuned AM station to the controller  20 . 
         [0025]    In operation  54 , the controller  20  calculates a first distance (or separation) value of the switching frequency that is being used to switch the power switch  34  of the power converter  24  and the frequency information of the AM station. For example, the controller  20  may monitor the harmonics generated due to the switching frequency that is currently being used to switch the power switch  34  and the harmonics generated as a result of the entertainment device  16  being tuned to a particular frequency. The first distance value generally corresponds to a distance between a first set of harmonics that are attributed to the current switching frequency and a second set of harmonics that may be attributed to the frequency in which the entertainment device  16  is tuned to. 
         [0026]    In operation  56 , the controller  20  calculates a second minimum frequency distance (or separation) value between the closest harmonic of a switching frequency that is either randomly selected or preselected and that could be used to switch the power switch  34  of the power converter  24  and the frequency information of the AM station. For example, the controller  20  may monitor the harmonics that are generated by the randomly or preselected switching frequency and the harmonics generated as a result of the frequency information that the entertainment device  16  is tuned to. The second frequency distance value generally corresponds to a distance between the first set of harmonics that are attributed to the randomly selected or pre-selected switching frequency and the second set of harmonics that may be attributed to the frequency in which the entertainment device  16  is tuned to. 
         [0027]    In operation  58 , the controller  20  selects the distance value that is the largest. For example, if the first distance value is greater than the second distance value, then the controller  20  may continue to use the current switching frequency to switch the power switch  34 . If the second distance value is greater than the first distance value, then the controller  20  selects randomly selected or pre-selected frequency as the switching frequency to control the power switch  34 . 
         [0028]      FIG. 3  depicts an example of a time domain plot  80  for a first switching frequency and a second switching frequency. Waveform  82  depicts the time domain for the first switching frequency. Waveform  84  depicts the time domain for the second switching frequency. As exhibited, the waveforms  82  and  84  are at slightly different frequencies from one another. 
         [0029]      FIG. 4  depicts an example of a frequency domain plot  90  for the first switching frequency and the second switching frequency. Waveform  92  depicts the frequency domain for the first switching frequency (e.g., the first switching frequency as illustrated in waveform  92  is generally 245 KHz). Waveform  94  depicts the frequency domain for the second switching frequency (e.g., the second switching frequency as illustrated in waveform  94  is generally 255 KHz). 
         [0030]      FIG. 5  depicts test measurement data obtained from the DC to AC converter  24  in one example. Peaks  1 ,  3 ,  5 ,  7  and  9  correspond to harmonics of a first switching frequency. Peaks  2 ,  4 ,  6 , and  8  correspond to harmonics of a second switching frequency. These harmonics may be selectively moved closer or apart from one another by adjusting the switching frequencies accordingly. 
         [0031]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.