Abstract:
A method and system are provided for updating a duty cycle for a power converter. The system and method operate the power converter to compute a first duty cycle during a first pulse-width modulation period and updating a second duty cycle for a second pulse-width modulation period at the completion of the first pulse-width modulation period. Next a third duty cycle for a third previous pulse-width modulation period is updated at the completion of the first pulse-width modulation period.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/983,017 filed on Apr. 23, 2014. 
    
    
     TECHNICAL FIELD 
     The technical field generally relates to power converters, and more particularly relates to updating the duty cycle of a power converter. 
     BACKGROUND 
     Power converters are typically used in alternative fuel vehicles to convert the battery or fuel cell energy to alternating current (AC) power that is used by AC motors to propel the vehicle. In pulse-width modulated (PWM) power converters, a controller generates PWM command signals that controls the timing and duty cycles of switches in the power converter to provide multi-phase (e.g., three-phase) power to the motors. However, due to the time period allocated or available for duty cycle calculations being a fraction of the total PWM period in multi-phase power converters, it is not possible to update duty cycle calculations without the risk of overwriting previously scheduled PWM transitions. Overwriting previously scheduled PWM transitions may cause power ripples that could damage or reduce the life of fuel cells. 
     Accordingly, it is desirable to provide a method for updating duty cycles in a multi-phase power converter without incurring the risk of overwriting previously scheduled PWM transitions. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. 
     SUMMARY 
     A system is provided for updating the duty cycle of a power converter. In one embodiment, the apparatus includes an energy source and a power converter coupled to the energy source for converting energy from the energy source into multi-phase power signals. A pulse-width modulator provides pulse-width modulation control signals to the power converter and a controller provides duty cycle information for each of the multi-phase power signals. The controller computes first duty cycle information during a first pulse-width modulation period and updates second duty cycle information for a second pulse-width modulation period at the completion of the first pulse-width modulation period. The controller also updates third duty cycle information for a third previous pulse-width modulation period at the completion of the first pulse-width modulation period. 
     A method is provided for duty cycle updates for a power converter. In one embodiment, the method includes computing a first duty cycle during a first pulse-width modulation period and updating a second duty cycle for a second pulse-width modulation period at the completion of the first pulse-width modulation period. Next a third duty cycle for a third previous pulse-width modulation period is updated at the completion of the first pulse-width modulation period. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The exemplary embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: 
         FIG. 1  is a block diagram of a vehicle in accordance with an embodiment; 
         FIG. 2  is a block diagram of a power converter in accordance with an embodiment; and 
         FIG. 3  is a timing diagram illustrating a duty cycle update method in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the application and uses. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
     In this document, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Numerical ordinals such as “first,” “second,” “third,” etc. simply denote different singles of a plurality and do not imply any order or sequence unless specifically defined by the claim language. 
     Additionally, the following description refers to elements or features being “connected” or “coupled” together. As used herein, “connected” may refer to one element/feature being directly joined to (or directly communicating with) another element/feature, and not necessarily mechanically. Likewise, “coupled” may refer to one element/feature being directly or indirectly joined to (or directly or indirectly communicating with) another element/feature, and not necessarily mechanically. However, it should be understood that, although two elements may be described below, in one embodiment, as being “connected,” in alternative embodiments similar elements may be “coupled,” and vice versa. Thus, although the schematic diagrams shown herein depict example arrangements of elements, additional intervening elements, devices, features, or components may be present in an actual embodiment. 
     Finally, for the sake of brevity, conventional techniques and components related to vehicle electrical and mechanical parts and other functional aspects of the system (and the individual operating components of the system) may not be described in detail herein. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent example functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in an embodiment of the invention. It should also be understood that  FIGS. 1-3  are merely illustrative and may not be drawn to scale. 
       FIG. 1  illustrates a vehicle  10 , according to one embodiment of the present invention. The vehicle  10  includes a chassis  12 , a body  14 , four wheels  16 , and an electronic control system  18 . The body  14  is arranged on the chassis  12  and substantially encloses the other components of the vehicle  10 . The body  14  and the chassis  12  may jointly form a frame. The wheels  16  are each rotationally coupled to the chassis  12  near a respective corner of the body  14 . 
     The vehicle  10  may be any one of a number of different types of vehicle, such as, for example, a sedan, a wagon, a truck, or a sport utility vehicle (SUV), and may be two-wheel drive (2WD) (i.e., rear-wheel drive or front-wheel drive), four-wheel drive (4WD), or all-wheel drive (AWD). The vehicle  10  may also incorporate any one of, or combination of, a number of different types of engines, such as, for example, a gasoline or diesel fueled combustion engine, a “flex fuel vehicle” (FFV) engine (i.e., using a mixture of gasoline and alcohol), a gaseous compound (e.g., hydrogen and/or natural gas) fueled engine, a combustion/electric motor hybrid engine, and an electric motor. 
     In the exemplary embodiment illustrated in  FIG. 1 , the vehicle  10  is a hybrid vehicle, and further includes an actuator assembly  20 , a battery, fuel cell or a high voltage direct current (DC) power source  22 , a power converter assembly  24 , and a radiator  26 . The actuator assembly  20  includes a combustion engine  28  (in hybrid vehicle embodiments) and an electric motor/generator (or motor)  30 . As will be appreciated, the electric motor  30  includes a transmission therein, and although not illustrated also includes a stator assembly (including conductive coils), a rotor assembly (including a ferromagnetic core), and a cooling fluid (i.e., coolant). The stator assembly and/or the rotor assembly within the electric motor  30  may include multiple electromagnetic poles (e.g., sixteen poles), as is commonly understood. 
     Still referring to  FIG. 1 , in one embodiment, the combustion engine  28  and the electric motor  30  are integrated such that both are mechanically coupled to at least some of the wheels  16  through one or more drive shafts  32 . The radiator  26  is connected to the frame at an outer portion thereof and although not illustrated in detail, includes multiple cooling channels therein that contain a cooling fluid (i.e., coolant) such as water and/or ethylene glycol (i.e., “antifreeze”) and is coupled to the engine  28  and the inverter  24 . In exemplary embodiments, the power converter assembly  24  comprises a direct current-to-direct current (DC/DC) converters boost converter to raise the input voltage provided by the DC power source (e.g., battery or fuel cell) that is provided to a multi-phase motor (e.g., three phases) via an inverter. 
     Referring to  FIG. 2 , a power converter system  24 , in accordance with an exemplary embodiment of the present invention, is shown. The power converter system  24  includes a boost converter  38  coupled to a power source  22  and to an inverter  40 . The boost converter  38  and the inverter  40  each communicate with the electronic control system(s)  18  and  18 ′ respectively. In some embodiments the electronic control system(s)  18  and  18 ′ are independent systems. As will be appreciated, in other embodiments, the control system(s) could be a common control system, different cores of a multi-core processor or processor operating in a distributed processing system. The electronic control system  18  (or  18 ′) includes a processor  35  (or  35 ′) coupled to a memory  37  (or  37 ′). The processor  35  computes duty cycle information for boost converter that are stored in the memory  37  and provided to the boost converter as will be described below in connection with  FIG. 3 . The boost converter  38  is coupled to an input of the inverter  40  that provides multi-phase (e.g., three phase) power to a motor  30  via lines  29 . Although the exemplary embodiment of  FIG. 2  utilizes three phases, it will be appreciated that any number of phases for the multi-phase motor  30 . 
       FIG. 3  illustrates a timing diagram useful for understanding the duty cycle update method provided by the present disclosure. The various tasks performed in connection with the method of  FIG. 3  may be performed by software, hardware, firmware, or any combination thereof. For illustrative purposes, the following description of the method of  FIG. 3  may refer to elements mentioned above in connection with  FIGS. 1-2 . In practice, portions of the method of  FIG. 3  may be performed by different elements of the described system. It should also be appreciated that the method of  FIG. 3  may include any number of additional or alternative tasks and that the method of  FIG. 3  may be incorporated into a more comprehensive procedure or process having additional functionality not described in detail herein. 
     The example of  FIG. 3  also illustrates a three phase (A, B and C) exemplary embodiment, however, it will be appreciated that any number of phases may be employed in any particular implementation. In  FIG. 3 , three duty cycle calculation periods  100 ,  102  and  104  are illustrated. Duty cycle information is computed during these periods for each of three PWM periods  106 ,  108  and  110 . More specifically, a trailing edge time  106 ′,  108 ′ and  110 ′ and a leading edge time  106 ″,  108 ″ and  110 ″ are computed. The leading edge time and trailing time define a duty cycle time interval during which switches within the boost converter  38  are open and closed to generate the higher power signal for the inverter  40 . At some point ( 100 ′) during the duty cycle calculation period  100  for the next PWM A, a beginning time  112  and ending time  114  are computed by the processor ( 35  in  FIG. 2 ) and stored in memory ( 37  in  FIG. 2 ). After completion of the PWM duty cycle calculation period  100  (for the next PWM A) and during the PWM duty cycle calculation period  102  (for the next PWM B) the processor  35  retrieves from the memory  37  the beginning time for the next PWM A  112 ′ and the ending time for the current PWM C  122 ′ (previously stored in prior PWM duty cycle calculation periods) and uses this duty cycle information to write from block  124  a leading edge time  126  computed in the previous PWM duty cycle calculation period for the next PWM A  106 ″ and a trailing edge time  128  computed in the PWM duty cycle calculation period two cycles previous for the next PWM C  110 ′. More specifically, the beginning time  112 ′ for the next PWM A is used to update the leading edge time  106 ″ for the next PWM A and the ending time  122 ′ for the current PWM C is used to update the trailing edge time  110 ″ for the current PWM C. The update operation (block  124 ) may be implemented in some embodiments are a direct memory access (DMA) operation, may be implemented as a part of the interrupt service routine (ISR) which invokes PWM duty cycle calculation period B  102  or as a portion of the PWM duty cycle calculation routine itself. 
     In a similar manner, at some point ( 102 ′) during the duty cycle calculation period  102  for the next PWM B, a beginning time  116  and ending time  118  are computed by the processor ( 35  in  FIG. 2 ) and stored in memory ( 37  in  FIG. 2 ). After completion of the PWM duty cycle calculation period  102  (for the next PWM B) and during PWM duty cycle calculation period  104  (for the next PWM C) the processor  35  retrieves from the memory  37  the beginning time for the next PWM B  116 ′ and the ending time for the current PWM A  114 ′ (previously stored as discussed above) and uses this duty cycle information to write from block  124 ′ a leading edge time  126 ′ computed in the previous PWM duty cycle calculation period for the next PWM B  108 ″ and a trailing edge time  128 ′ computed in the PWM duty cycle calculation period two cycles previous for the current PWM A  106 ′. More specifically, the beginning time  116 ′ for PWM B is used to update the leading edge time  108 ″ for the next PWM B and the ending time  114 ′ for PWM A is used to update the trailing edge time  106 ′ for the current PWM A. 
     Also in a similar manner, at some point ( 104 ′) during the duty cycle calculation period  104  for PWM C, a beginning time  120  and ending time  122  are computed by the processor ( 35  in  FIG. 2 ) and stored in memory ( 37  in  FIG. 2 ). After completion of the PWM duty cycle calculation period  104  (for the next PWM C) and during PWM duty cycle calculation period  100  (for the next PWM A) the processor  35  retrieves from the memory  37  the beginning time for the next PWM C  120 ′ and the ending time for the current PWM B  118 ′ (previously stored as discussed above) and uses this duty cycle information to write from block  124 ″ a leading edge time  126 ″ computed in the previous PWM duty cycle calculation period for the next PWM C  110 ″ and a trailing edge time  128 ″ computed in the PWM duty cycle calculation period two cycles previous for the current PWM B  108 ′. More specifically, the beginning time  120 ′ for the next PWM C is used to update the leading edge time  110 ″ for PWM C and the ending time  118 ′ for the current PWM B is used to update the trailing edge time  108 ′ for the current PWM B. 
     In summary, during any particular PWM duty cycle calculation period, beginning and ending times for the next corresponding PWM are computed and stored in memory. After completion of this PWM duty cycle calculation period, the leading edge time is updated for the next PWM corresponding to the previous duty cycle calculation period, and a trailing edge time is updated for the current PWM, the duty cycle of which was calculated two PWM duty cycle calculation periods previous. By writing these duty cycle update in this manner, overwriting PWM transitions is avoided by performing the writing operations when these PWM transitions cannot occur. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. For example, while the exemplary embodiment is described and illustrated as an automotive vehicle, the advantage afforded by the present disclosure would benefit any electric powered vehicle, including, but not limited to, off-road vehicles and watercraft. Moreover, any application involving a boost converter could benefit from the teachings of the present disclosure. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the appended claims and the legal equivalents thereof.