Abstract:
In at least one embodiment, an apparatus for providing age-compensation control for a power converter is provided. The apparatus comprises a controller for being coupled to a power converter including a plurality of phases for converting a first input signal into a first output signal. The controller is configured to activate at least one first switch for a first phase from the plurality of phases for converting the first input signal into the first output signal. The controller is further configured to determine an aging condition for the at least one first switch for the first phase based on an equivalent time, Teq of the at least one first switch, wherein Teq corresponds to an amount of time the at least one first switch is active and on an operating temperature of the at least one first switch while the at least one first switch is active.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional Application No. 61/710,165 filed on Oct. 5, 2012, the disclosure of which is incorporated in its entirety by reference herein. 
    
    
     TECHNICAL FIELD 
     Embodiments disclosed herein generally related to an apparatus and method for controlling an operation for one or more switches in a power converter to compensate for aging. 
     BACKGROUND 
     It is known to provide a multi-phase switching converter. One example of such an implementation is disclosed in U.S. Pat. No. 6,362,608 (“the &#39;608 patent”) to Ashburn et al. 
     The &#39;608 patent discloses multi-phase switching converters and methods that provide fast response and low ripple on the converter inputs and outputs. The converters include multiple converter stages that are normally operated in sequence into a common load. However, upon sensing that operation of one of the converter stages does not bring the converter back into regulation, multiple converter stages are operated until regulation is reestablished, after which the converter stages are operated in sequence again. In the embodiment disclosed, upon sensing that operation of one of the converter stages does not bring the converter back into regulation, all converter stages are operated until regulation is reestablished, after which the converter stages are operated in sequence again starting with the stage with the lowest inductor current. 
     SUMMARY 
     In at least one embodiment, an apparatus for providing age-compensation control for a power converter is provided. The apparatus comprises a controller for being coupled to a power converter including a plurality of phases for converting a first input signal into a first output signal. The controller is configured to activate at least one first switch for a first phase from the plurality of phases for converting the first input signal into the first output signal. The controller is further configured to determine an aged condition for that the at least one first switch for the first phase based on an equivalent time, Teq of the at least one first switch, wherein Teq corresponds to an amount of time the at least one first switch is active and on an operating temperature of the at least one first switch while the at least one first switch is active. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments of the present disclosure 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: 
         FIG. 1  depicts a system for controlling an operation of one or more switches in a power converter in accordance to embodiment; 
         FIG. 2  depicts a method for controlling the operation of the one or more switches in the power converter in accordance to embodiment; 
         FIG. 3  depicts a method for setting a number of active phases in accordance to one embodiment; and 
         FIG. 4  depicts various waveforms corresponding to aspects of the system in accordance to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     The embodiments of the present disclosure generally provide for a plurality of circuits or other electrical devices. All references to the circuits and other electrical devices and the functionality provided by 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 circuits or other electrical devices disclosed, such labels are not intended to limit the scope of operation for the circuits and the other electrical devices. Such circuits and other electrical devices may be combined with each other and/or separated in any manner based on the particular type of electrical implementation that is desired. It is recognized that any circuit or other electrical device disclosed herein may include any number of microprocessors, integrated circuits, memory devices (e.g., FLASH, random access memory (RAM), read only memory (ROM), electrically programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), or other suitable variants thereof) and software which co-act with one another to perform operation(s) disclosed herein. 
       FIG. 1  depicts a system (or apparatus)  10  for controlling an operation of one or more switches  12   a - 12   n  (“ 12 ”) (or phases) in a power converter  14  in accordance to embodiment. The system  10  comprises a controller  16  that is operably coupled to the power converter  14  for activating/deactivating one or more of the switches  12 . It is recognized that the power converter  14  may be used in connection with a vehicle for purposes of charging one or more vehicle batteries (not shown). In one example, the power converter  14  may be implemented as a 3-phase power converter (e.g., buck circuit). In one example, the power converter  14  may be an interleaved power converter that utilizes a parallel architecture, in which many quasi-autonomous converters, such as phases, are implemented in parallel to create a single large power converter. 
     The switches  12  may each be implemented as a metal-oxide-semiconductor field effect transistor (MOSFET) or other suitable device. In general, in order to increase efficiency, a different number of phases (e.g., i, j, k, etc.) may be activated depending on the total current (I T ) flowing through the power converter  14 . In other words, at different times, the power converter  14  may have, but not limited to, one, two or three, phases working. As such, the system  10  may equalize the use of all phases in order to keep all phases or switches  12  with similar wear. For a multiphase converter, a phase is generally defined as one portion of the circuit that is placed between an input and a load and copies of such a circuit are placed in parallel with one another between the input and the load. As such, each phase may be activated at equally spaced intervals over a switching frequency. In reference to  FIG. 1 , each phase is generally defined as one or more switches that are generally coupled together with a respective inductor  15 . For example, phase i generally comprises inductor  15   a , switch  12   a  and switch  12   b , phase j generally comprises inductor  15   b , switch  12   c  and switch  12   d , and phase k generally comprises inductor  15   c , switch  12   e  and switch  12   n . It is contemplated that each phase may include additional or less components than those shown in  FIG. 1  and that the phases depicted in  FIG. 1  are provided for illustrative purposes. 
     It is contemplated that the overall use for each phase (or aging of each phase) may be determined based on the overall time that each phase has been operational at specific operating conditions. 
     For example, an “equivalent operating time” Teq may be defined as:
 
 Teq=ΣΔt·Ea/[k   B ·( T   J     —     MAX   −T   J )]  (Eq. 1)
 
     where Teq is computed at some interval times Δt (normally with same duration) for each phase, Teq is generally defined as the time in which a switch  12  is operating at a given temperature and is generally indicative of the aging of the switch  12 ; 
     where Ea is a constant, defined as activation energy that generally provides an indication of the effect that the operating conditions (temperature, etc.) has on the life of the one or more of the switches  12 ; 
     where k is the Boltzmann constant; 
     where T J     —     MAX  is a maximum junction temperature that a switch  12  can withstand, such information may be provided by a manufacturer data sheet; 
     where T J  is the actual junction temperature of the switch  12  and is calculated as:
 
 T   J   =T   ambient   +R   TH   *P   D   (Eq. 2)
 
     where T ambient  is the ambient temperature near a printed circuit board (PCB) of the power converter  14 , which may be obtained via temperature sensor  18  positioned about each switch  12 , R TH  is the component thermal resistance for the switch  12  (which may depend on the type of switch or the PCB which may be further determined based on such factors and may also be determined experimentally), and P D  is the power dissipated in conduction computed using measured voltages and currents. For example, a shunt  20  may be positioned about one or more of the switches  12  to enable one or more current sensors  22  to measure the current across one or more of the switches  12  when such switches  12  are active. In addition, one or more voltage sensors  24  are used to measure Vin (an input voltage) and Vout (an output voltage). The controller  16  may determine P D  based on such measured current and voltage values. As a first approximation, Pd may be further defined or estimated as P D =P ON +P SW . In which, P ON  is generally defined as the conduction losses when the switch  12  is ON and P SW  is generally defined as the power dissipated when the switch  12  is switching. P ON  and P SW  may be obtained by virtue of the voltage and current measurements noted above in addition to design/component parameters information. 
       FIG. 2  depicts a method  50  for controlling the operation of the one or more switches  12  in the power converter  14  in accordance to embodiment. 
     In operation  52 , the controller  16  determines all voltages (at the input and output of the converter  14  (e.g., Vin and Vo)), currents (for each phase) and temperature (e.g., ambient temperature is obtained near the switches  12 ) are measured. 
     In operation  54 , the controller  16  determines the number of phases that are to be activated. In general, any number of algorithms may be provided for determining the number of phases that are to be activated. 
     One algorithm includes a current sharing scheme. This scheme includes in the activation, one phase (of N phases) for each Nth fraction of total output current (I T ). The example of the manner in which the controller  16  determines the number of phases is set forth in  FIG. 3  which will be explained in more detail below. 
     For instance, the power converter  14  (e.g., DC/DC converter) with 3 phases may have an output current (e.g., I T ) that is limited to a maximum value of, for example,  36 A (I max ). Each phase generally provides or contributes to a portion of the maximum current value I T . 
     In operation  54   a , the controller  16  determines whether the output current I T  is less than a first predetermined current (I 1 =I max /3) (e.g.,  12 A). If this condition is true, then the method  50  sets the number of active phases to 1 and proceeds to operation  56   a . If this condition is not true, then the method  50  proceeds to operation  54   b.    
     In operation  54   b , the controller  16  determines whether the output current I T  is greater than the first predetermined current (I 1  where I 1 =I max /3) (e.g.,  12 A) and less than a second predetermined current (I 2  where I  2 =I max *2/3) (e.g.,  24 A). If this condition is true, then the method  50  sets the number of active phases to 2 and proceeds to operation  56   b . If this condition is not true, then the method  50  proceeds to operation  54   c.    
     In operation  54   c , the controller  16  determines whether the output current I T  is greater than the second predetermined current (I 2 ) (e.g.,  24 A). If this condition is true, then the method  50  sets the number of active phases to 3 and proceeds to operation  56   c . If this condition is not true, then the method  50  proceeds to operation  54   a.    
     Executing operations  54   a ,  54   b , and  54   c  enable the system  10  to determine the number of phases that are actives at any loop. 
       FIG. 4  depicts waveforms  90  and  92  which indicate the phases that are activated based on the aging condition of each phase. 
     In reference to  FIG. 2 , in operation  56   a , the controller  16  activates only one phase. 
     In operation  56   b , the controller  16  activates two phases. 
     In operation  56   c , the controller  16  activates three phases. 
     In operation  58 , the controller  16  determines the aging of the phases (e.g., i, j, and/or k) (i.e., for operations  56   a ,  56   b , and  56   c ). To perform this operation, the “equivalent operating time” (Teq) for each phase is periodically computed and accumulated in a variable. The determination of which phases are aging is set forth in more detail in connection with operations  60   a - 60   c ,  62   a - 62   c , and  64 . The variable for each phase as shown in connection with  FIG. 2  may be defined as Teq #i , Teq #j , and Teq #k . If the phase is working at high power and/or high temperature, this variable (i.e., Teq) will increase faster while, if the phase is working at low power and/or low temperature, this variable (i.e., Teq) will increase slowly. 
     In operation  60   a , the controller  16  determines whether Teq for phase i (or Teq #i ) exceeds a first fixed value. If this condition is true, then the method  50  moves to operation  62   a . If not, then the method  50  moves to operation  60   b.    
     In operation  60   b , the controller  16  determines whether Teq for phase j (or Teq #j ) exceeds a second fixed value. If this condition is true, then the method  50  moves to operation  62   b . If not, then the method  50  moves to operation  60   c.    
     In operation  60   c , the controller  16  determines whether Teq for phase k (or Teq #k ) exceeds a third fixed value. If this condition is true, then the method  50  moves to operation  62   b . If not, then the method  50  moves to operation  60   c.    
     The operations of  62   a ,  62   b , and  62   c  correspond to when the value of the accumulated Teq #i , Teq #j , and/or Teq #k  variable is higher than the first fixed value, the second fixed value, and/or the third fixed value, respectively. It is recognized that the first fixed value, the second fixed value, and the third fixed value may be similar to one another or different than one another. With the operations of  62   a ,  62   b , and  62   c , the corresponding phase that exceeds the fixed value is stopped (e.g., see Teq #1 =0, Teq #j =0, Teq #k =0) or until other phases reach this value or all phases are needed. As an example, waveforms  94 ,  96 ,  98 , and  100  as shown in  FIG. 4  shows the evolution over time of these variables for the output current described and using T=2 (or fixed value=2). 
     In addition to the operations of  62 ,  62   b , and  62   c  being indicative of each time the accumulated Teq #i , Teq #j , and/or Teq #k  variable reaches the first, second, and/or third fixed values (or T), respectively, such operations also indicate that a counter named Taging (e.g., Taging #i , Taging #j , or Taging #k ) is increased by the value stored in the accumulated Teq #i , Teq #j , and/or Teq #k  variable. As such, the counter, Taging may store “normalized” information on the aging of each phase. Waveforms  102 ,  104 , and  106  depict examples of values as stored in corresponding counters Taging #i , Taging #j , or Taging #k . 
     In operation  64 , the controller  16  determines whether the values in any one or more the corresponding counters Taging #i , Taging #j , or Taging #k  exceed a predefined maximum threshold T MAX . If this condition is true, then the method  50  moves to operation  66 . If not, then the method  50  moves back to operation  52 . 
     In operation  66 , the controller  16  reports out or transmits data indicating that one or more of the phases in the power converter  14  has reached a maximum aged status (or maximum aged condition) and that the corresponding switch within the phase that exhibits the maximum aged condition will stop operating. 
     It is recognized that if the junction temperature of a particular switch  12  in a phase reaches a maximum operating junction temperature, the “equivalent operating time” (Teq) goes to ∞, thereby indicating that the switch  12  will be destroyed (or rendered inoperable) (see operations  64  and  66 ). With the proposed method  50 , it may be assured that all phases will have a similar Taging. As noted in connection with operation  66 , if one of the phases reaches a predefined threshold T MAX , the system  10  may report that the power converter  14  (or phase) has reached the maximum “AGED” status and its corresponding switch(s)  12  may be stopped. The maximum AGED status generally indicates that a phase has been operating for a large amount of time at stressed conditions of temperature and/or current. 
     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.