Patent Document

BACKGROUND OF THE INVENTION 
     The invention relates generally to charging of rechargeable energy storage systems (e.g., batteries and electric double-layer capacitors and the like) and more particularly to charging storage systems in conditions when a peak line voltage is greater than a storage system voltage due to a low state-of-charge (SOC). 
       FIG. 1  is a prior art schematic block diagram representative of a voltage converter  100  used in some charging systems installed onboard an electric vehicle to charge a high energy capacity battery assembly  105 . In general, circuit  100  describes a boost rectifier for an electric vehicle that includes a set of four transistors (Q 1 -Q 4 ) having an output coupled to a smoothing capacitor Cbus in parallel with battery assembly  105  and an input coupled to an input filter capacitor Cin and a pair of inductors (L 1  and L 2 ). A pair of switches (S 1  and S 2 ) couple the inductors to an AC source, the AC source nominally providing 240 volts at about 70 amps. In normal operation, switch S 1  and switch S 2  are closed and S 3  is open, and converter  100  operates in normal boost mode without difficulties. 
     There are situations wherein the line voltage provides a higher than peak voltage (e.g., +10% greater voltage or about 370 volts (e.g., VRMS*1.1*√{square root over (2)})) and battery assembly  105  is at a lower end of its SOC (e.g., ˜330 volts) that voltage converter  100  cannot charge battery assembly  105  in the normal mode. (Voltage converter  100  cannot charge battery assembly  105  because the described relative voltages results in uncontrollable current flow out of the rectifier into C bus  and into the battery assembly, potentially seriously damaging both of them.) 
     For this non-standard condition, voltage converter  100  includes resistor R trickle  and a switch S 3 . Switch S 1  and switch S 3  are closed and switch S 2  is opened, and R trickle  then reduces input voltage applied to the boost rectifier. In some implementations, one-half of the input voltage is dropped across R trickle , greatly reducing the effective voltage applied to converter  100  (with about 7 amps of charging current available in this trickle charge mode). Voltage converter  100  operates in this non-standard mode until the relative voltage conditions between AC line-in voltage and the voltage level of energy storage assembly  105  is sufficient to reconfigure the converter to normal mode operation (i.e., opening switch S 3  and closing switch S 2 ). 
     While this solution is acceptable in many applications, as storage voltages decrease, it becomes increasingly likely that there is a need for non-standard operation to account for V bat  being lower than the experienced peak voltage from the AC line-in. The solution shown in  FIG. 1  is very lossy and because of the greatly reduced current flow (I tickle ), it is particularly disadvantageous the more frequently that the solution is employed. 
     In the case of solutions to be applied to electric vehicles, there are often tight budgets for space, weight and component costs. Conventional methodologies for solving the problem addressed by the trickle mode shown in  FIG. 1  include addition of separate converters to handle each special case of relative line voltage/SOC conditions or changing the system to employ an isolated topology. 
     Adding separate converters is viewed as undesirable because of extra costs and space. The components in the converters are high performance components configured for this high power/high energy operation and are more expensive than many lower power options. An isolated topology often produces a less efficient solution. Thus neither conventional solution is optimal. 
     A further drawback of the solution shown in  FIG. 1  is that there are situations in which a voltage level of the battery assembly is so low that it would be unsafe to attempt to restore function by trickle charging. 
     What is needed is a voltage converter that is capable of providing high energy to a high performance energy storage assembly for charging the energy storage assembly while efficiently and safely handling conditions of a too “high” line-in voltage relative to a voltage level of the energy storage assembly while also being capable of use in reviving a battery assembly having a very low level state-of-charge. 
     BRIEF SUMMARY OF THE INVENTION 
     Disclosed are methods and systems for a voltage converter that is capable of providing high energy to a high performance energy storage assembly for charging the energy storage assembly while efficiently and safely handling non-standard conditions while also being capable of use in reviving a battery assembly having a very low level state-of-charge. There are two disclosed embodiments, differing in implementation of power factor correction in the “normal” mode. It is to be understood that either implementation may be altered to include or not include power factor correction in normal operation, with power factor correction unavailable in auxiliary operation. A voltage converter for charging an energy storage module from an alternating current line voltage, includes a first charging stage, coupled to the energy storage module, converting the line voltage to a first rectified direct current module charging voltage communicated to the energy storage module, the first rectified direct current module charging voltage greater than the line voltage, the first charging stage including an inductance for communicating a first charging current to the energy storage module; a second charging stage, switchably coupled serially with the first charging stage, down-converting the alternating current line voltage to a second rectified direct current module voltage, the second rectified direct current module voltage less than the first rectified direct current module charging voltage, wherein the second charging stage produces a second charging current not greater than the first charging current; and a controller for selectably switching the second charging stage serially with the first charging stage when the line voltage has a peak value greater than a predefined relationship to a voltage of the energy storage module wherein the second charging stage communicates the second charging current to the energy storage module through the inductance. 
     A power factor correcting voltage converter for charging an energy storage module from an alternating current line voltage, including a rectifier for converting the line voltage to a rectified direct current voltage provided across a first output node and a second output node; a first charging stage, coupled to the energy storage module, converting the rectified direct current voltage to a first rectified direct current module charging voltage communicated to the energy storage module, the first rectified direct current module charging voltage greater than the line voltage, the first charging stage including an inductance for communicating a first charging current to the energy storage module; a second charging stage, coupled to the outputs of the rectifier and switchably coupled serially with the first charging stage, down-converting the rectified direct current voltage to a second rectified direct current module voltage, the second rectified direct current module voltage less than the first rectified direct current module charging voltage, wherein the second charging stage produces a second charging current not greater than the first charging current; and a controller for selectably switching the second charging stage serially with the first charging stage when the line voltage has a peak value greater than a predefined relationship to a voltage of the energy storage module wherein the second charging stage communicates the second charging current to the energy storage module through the inductance. 
     A method for charging an energy storage module from an alternating current line voltage, the method including (a) converting, using a first charging stage coupled to the energy storage module, the line voltage to a first rectified direct current module charging voltage communicated to the energy storage module, the first rectified direct current module charging voltage greater than the line voltage, the first charging stage including an inductance for communicating a first charging current to the energy storage module; (b) down-converting, using a second charging stage switchably coupled serially with the first charging stage, the alternating current line voltage to a second rectified direct current module voltage, the second rectified direct current module voltage less than the first rectified direct current module charging voltage, wherein the second charging stage produces a second charging current not greater than the first charging current; and (c) switching selectably the second charging stage serially with the first charging stage when the line voltage has a peak value greater than a predefined relationship to a voltage of the energy storage module wherein the second charging stage communicates the second charging current to the energy storage module through the inductance. 
     A method for charging of an energy storage module from an alternating current line voltage, the method including (a) converting the line voltage to a rectified direct current voltage provided across a first output node and a second output node; (b) converting the rectified direct current voltage to a first rectified direct current module charging voltage communicated to the energy storage module, the first rectified direct current module charging voltage greater than the line voltage, the first charging stage including an inductance for communicating a first charging current to the energy storage module; (c) down-converting the rectified direct current voltage to a second rectified direct current module voltage, the second rectified direct current module voltage less than the first rectified direct current module charging voltage, wherein the second charging stage produces a second charging current not greater than the first charging current; and (d) switching selectably the second charging stage serially with the first charging stage when the line voltage has a peak value greater than a predefined relationship to a voltage of the energy storage module wherein the second charging stage communicates the second charging current to the energy storage module through the inductance. 
     Simplistically, the preferred embodiments of the present invention provide for a standard boost stage to up-convert line voltage to V Storage . In non-standard conditions when a peak voltage of the line voltage exceeds the energy storage voltage (such as can happen with a low state-of-charge for an energy storage module), an auxiliary pole converter is switched in-line with the boost stage. This auxiliary pole converter down-converts the input voltage and provides a reduced charging current to the energy storage module as long as the non-standard condition exists. Expensive components (e.g., high-energy inductance(s)) are reused by directing the reduced charging current through the boost stage, typically the boost stage is reconfigured as well. A controller disables most boosting and rectification of the boost stage in the non-standard mode operation, the specifics vary based upon the specific topology of the stages and application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a prior art schematic block diagram representative of a voltage converter used in some charging systems installed onboard a electric vehicle to charge a high energy capacity energy storage assembly; 
         FIG. 2  is a schematic block diagram of a bi-directional power factor correcting voltage converter providing high energy to a high performance energy storage assembly for charging the energy storage assembly; and 
         FIG. 3  is a schematic block diagram of a power factor correcting voltage converter providing high energy to a high performance energy storage assembly for charging the energy storage assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention provide methods and systems for a voltage converter that is capable of providing high energy to a high performance energy storage assembly for charging the energy storage assembly while efficiently and safely handling conditions of large relative differences between a line-in voltage and voltage level of the energy storage assembly while also being capable of use in reviving a energy storage assembly having a very low level state-of-charge. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. In the following text, the terms “energy storage assembly” “battery”, “cell”, “battery cell” and “battery cell pack” “electric double-layer capacitor” and “ultracapacitor” may be used interchangeably (unless the context indicates otherwise” and may refer to any of a variety of different rechargeable configurations and cell chemistries including, but not limited to, lithium ion (e.g., lithium iron phosphate, lithium cobalt oxide, other lithium metal oxides, etc.), lithium ion polymer, nickel metal hydride, nickel cadmium, nickel hydrogen, nickel zinc, silver zinc, or other chargeable high energy storage type/configuration. 
     Various modifications to the preferred embodiment and the generic principles and features described herein will be readily apparent to those skilled in the art. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein. 
       FIG. 2  is a schematic block diagram of a bi-directional power factor correcting voltage converter  200  providing high energy to a high performance energy storage assembly  205  for charging energy storage assembly  205  while efficiently and safely handling conditions of large relative differences between a line-in voltage from an AC source  210  and a voltage level of energy storage assembly  205 . AC source  210 , e.g., 240 volts, is coupled to an input of an optional EMI filter  215  having an output coupled to a switching assembly including a pair of single-pole-double-throw switches (switch S 2  and switch S 3 ). A first output port of EMI filter  215  is coupled to a first throw of switch S 2  and a second output port of EMI filter  215  is coupled to a first throw of switch S 3 . The switching assembly, responsive to its state, couples either (i) filtered line voltage from AC source  210  to a boost rectifier  220  or (ii) an auxiliary pole converter  225  to a modified boost rectifier  220 . A second throw of switch S 2  and of switch S 3  are coupled to auxiliary pole converter  225  and the first poles of switch S 2  and of switch S 3  are coupled to boost rectifier  220 . It will be appreciated that, due to the large power requirements, that one or more of the switches (particularly switch S 2  and switch S 3 ) will be implemented by one or more contactors (e.g., relays or the like). 
     In standard operation, the switching assembly communicates the filtered line voltage from AC source  210  to boost rectifier  220  and then to energy storage assembly  205  to provide a standard charging current, for example a charging current of about 70 amps. The switching assembly does this by coupling the poles of switch S 2  and of switch S 3  to the first throws, respectively. In the special voltage condition situation, the switching assembly disconnects EMI filter  215  from direct communication with boost rectifier  220  and communicates auxiliary pole converter  225  to energy storage assembly  205  through a modified boost rectifier  220 . Auxiliary converter  225  provides a “trickle” current (the trickle current may have substantial amps but is less than or equal to the standard charging current), for example in the preferred embodiment the trickle current is about 35 amps in contrast to a standard charging current of 70 amps. The switching assembly does this by coupling the poles of switch S 2  and of switch S 3  to the second throws, respectively. A controller  230  sets the desired states and operation for the switches, transistors, and components of converter  200  as described herein. 
     Boost rectifier  220  may be constructed in various ways, a preferred implementation is shown in  FIG. 2 . Boost rectifier  220  of the preferred implementation includes a pair of high current inductances (L 1  and L 2 —though this implementation may be accomplished with a single inductance) having first nodes coupled to a pole of switch S 2  and switch S 3  respectively and second nodes coupled to a full rectifying bridge having four NPN insulated gate bipolar transistors Q 1 -Q 4  (IGBTs) and a smoothing capacitor C bus . (In some implementations, a set of MOSFETs may be used.) EMI filter  215  has a first output port coupled to a first throw of switch S 2 . The second node of inductance L 1  is coupled to an emitter of transistor Q 3  and a collector of transistor Q 4 . EMI filter  215  has a second output port coupled to a first throw of switch S 3 . The second node of inductance L 2  is coupled to an emitter of transistor Q 1  and a collector of transistor Q 2 . The collectors of transistor Q 1  and transistor Q 3  are coupled to a first plate of smoothing capacitor C bus  and a first terminal of energy storage assembly  205 . The emitters of transistor Q 2  and transistor Q 4  are coupled to a second plate of smoothing capacitor C bus  and to a second terminal of energy storage assembly  205 . The components of boost rectifier  220  are sized for very high current levels, such as for example, currents used in charging the energy storage modules of an electric vehicle or other automotive or industrial application. As indicated above, these currents may be on the order of about 70 amps in the preferred embodiment. 
     As noted above, there are times when the line-in voltage from AC source  210  is high and the voltage of energy storage assembly  205  is low that converter  200  does not operate properly without auxiliary converter  225  switched in-line. Controller  230  detects this voltage condition and reconfigures converter  200  by switching in auxiliary pole converter  225  and modifying operation of boost rectifier  220 . To increase efficiency from reusing components, auxiliary pole converter  225  is switched in at the correct location to reuse inductances L 1  and L 2  which requires reconfiguration of transistors Q 1 -Q 4  as well to disable rectification and boosting in boost rectifier  220 . 
     Auxiliary pole converter  225  includes a rectifier  235 , an NPN IGBT Q t , a diode D t , and a filter capacitor C t . When auxiliary pole converter  225  is switched in by coupling the poles of switch S 2  and switch S 3  to the second throws, respectively, controller  230  statically turns transistor Q 2  and Q 3  to the “ON” state. A first input port of rectifier  235  is coupled to the first output port of EMI filter  215  and a second input port of rectifier  235  is coupled to the second output port of EMI filter  215 . A first rectified voltage node of rectifier  235  is coupled to a first plate of filter capacitor C t  and to a collector of transistor Q t . A second rectified voltage node of rectifier  235  is coupled to a second plate of filter capacitor C t , to an anode of diode D t , and to a second throw of switch S 3 . A cathode of diode D t  is coupled to an emitter of transistor Q t  and to a second throw of switch S 2 . 
     Converter  200  controls current by switching transistor Q t . Components of auxiliary pole converter  225  are advantageously sized to be larger and supply a greater auxiliary trickle current than that provided by the prior art, in a more efficient manner, but still less charging current than the standard charging current. For example, the preferred implementation sizes the components of auxiliary pole converter  225  to provide about 35 amps of trickle current efficiently in contrast to the 7 amps provided by the prior art in a lossy manner. The efficiencies of the present invention include less energy lost through heat and less time spent in the trickle charge mode, resulting in a doubly efficient solution. Additionally, as noted it is possible that with different energy storage module designs, it may become the case that converter  200  will operate more frequently in the special condition mode that would require more frequent use of auxiliary pole converter  225 . The more often that auxiliary pole converter  225  is needed, the greater the advantages of using the present invention, particularly in the high-performance automotive and industrial applications using high-performance energy storage modules. 
     Rectifier  220  does implement power factor correction in standard mode (it can do power factor correction in standard mode but it will not do power factor correction in auxiliary mode). For many implementations, power factor correction may not be a requirement, particularly as the non-standard charge situation addressed by auxiliary pole converter  225  is expected to be a temporary transient condition, and because of the present design providing significantly greater trickle currents, the time that the auxiliary pole is switched is greatly reduced. However, for some applications power factor correction may be required or desired. 
       FIG. 3  is a schematic block diagram of a power factor correcting voltage converter  300  providing high energy to a high performance energy storage assembly  305  for charging energy storage assembly  305  while efficiently and safely handling conditions of large relative differences between a line-in voltage from an AC source  310  and a voltage level of energy storage assembly  305 . AC source  310 , e.g., 240 volts, is coupled to an input of an EMI filter  315  having an output coupled to an input of a rectifier  320 . Rectifier  320  includes a first rectified voltage node which is coupled to a first throw of a single pole, double throw switch S 2 . The pole of switch S 2  is coupled to a converter stage  325  and a second throw of switch S 2  is couple to an auxiliary pole converter  330 . It will be appreciated that, due to the large power requirements, that one or more of the switches (particularly switch S 2 ) will be implemented by one or more contactors (e.g., relays or the like). 
     In standard operation, the pole of switch S 2  is coupled to the first throw which communicates the filtered rectified line voltage from AC source  310  to converter stage  325  and then to energy storage assembly  305 . In the special voltage condition situation, switch S 2  communicates auxiliary pole converter  330  to energy storage assembly  305  through a modified converter stage  325  by coupling the pole of switch S 2  to the second throw. Auxiliary converter  330  provides a “trickle” current (the trickle current may have substantial amps but is less than or equal to the standard charging current), for example in the preferred embodiment the trickle current is about 35 amps in contrast to a standard charging current of 70 amps. A controller  335  sets the desired states and operation for the switches, transistors, and components of converter  300 . 
     Converter stage  325  may be constructed in various ways, a preferred implementation is shown in  FIG. 3 . Converter stage  325  of the preferred implementation includes a high current inductance L 1  having a first node coupled to a pole of switch S 2  and a second node coupled to both an anode of a diode D 1  and to a collector of an NPN IGBT Q 1 . A cathode of diode D 1  is coupled to a first plate of a smoothing capacitor C bus  and a first terminal of energy storage assembly  305 . An emitter of transistor Q 1  is coupled to a second rectified voltage node of rectifier  320 , a second plate of smoothing capacitor C bus  and a second terminal of energy storage assembly  305 . The components of converter stage  325  are sized for very high current levels, such as for example, currents used in charging the energy storage modules of an electric vehicle or other automotive or industrial application. As indicated above, these currents may be on the order of about 70 amps in the preferred embodiment. 
     As noted above, there are times when the line-in voltage from AC source  310  is high and the voltage on energy storage assembly  305  is low that converter  300  does not operate properly without auxiliary converter  330  switched in-line. Controller  335  detects this condition and reconfigures converter  300  by switching in auxiliary pole converter  330  (changing throws of switch S 2  and closing switch S 3 ) and reconfiguring operation of converter stage  325 . To increase efficiency from reusing components and to provide power factor correction, auxiliary pole converter  330  is switched in at the correct location to reuse rectifier  320  and inductance L 1  and controller  335  statically turns transistor Q 1  “OFF” which puts diode D 1  in series with inductance L 1  (and disables boosting of converter stage  325 ). 
     Auxiliary pole converter  330  includes an NPN IGBT Q t , a diode D t , and a filter capacitor C t . A first terminal of a single pole single throw switch S 3  is coupled to the first rectified voltage node of rectifier  320 . A second terminal of switch S 3  is coupled to a first plate of filter capacitor C t  and to a collector of transistor Q t . A second plate of filter capacitor C t  is coupled to the second rectified voltage node of rectifier  320  and to an anode of diode D t . A cathode of diode D t  is coupled to an emitter of transistor Q t  and to a second throw of switch S 2 . 
     When auxiliary pole converter  330  is switched in, controller  335  statically turns Q 1  to the “OFF” state. Converter  300  controls current in the special mode as auxiliary converter  330  acts as a buck converter reducing the line in voltage. Components of auxiliary pole converter  330  are advantageously sized to be larger and supply a greater auxiliary trickle current than that provided by the prior art, in a more efficient manner, but still less than or equal to the standard charging current. For example, the preferred implementation sizes the components of auxiliary pole converter  330  to provide about 35 amps of trickle current efficiently in contrast to the 7 amps provided by the prior art in a lossy manner. The efficiencies of the present invention include less energy lost through heat and less time spent in the trickle charge mode, resulting in a doubly efficient solution. Additionally, as noted it is possible that with different energy storage module designs, it may become the case that converter  300  will operate more frequently in the special condition mode that would require more frequent use of auxiliary pole converter  330 . The more often that auxiliary pole converter  330  is needed, the greater the advantages of using the present invention, particularly in the high-performance automotive and industrial applications using high-performance energy storage modules. 
     It is also an attendant advantage of the disclosed embodiments that the voltage level from the auxiliary pole converters may be bucked down sufficiently low that the auxiliary pole converter voltages from converter  200  and converter  300  may be used in safely reviving a damaged battery module. The prior art is unable to provide a safe voltage for recharging such a battery module using the voltage drop across a resistor. 
     The system above has been described in the preferred embodiment of charging a multicell energy storage module used in electric vehicle (EV) systems. In the description herein, numerous specific details are provided, such as examples of components and/or methods, to provide a thorough understanding of embodiments of the present invention. One skilled in the relevant art will recognize, however, that an embodiment of the invention can be practiced without one or more of the specific details, or with other apparatus, systems, assemblies, methods, components, materials, parts, and/or the like. In other instances, well-known structures, materials, or operations are not specifically shown or described in detail to avoid obscuring aspects of embodiments of the present invention. 
     Reference throughout this specification to “one embodiment”, “an embodiment”, or “a specific embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention and not necessarily in all embodiments. Thus, respective appearances of the phrases “in one embodiment”, “in an embodiment”, or “in a specific embodiment” in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics of any specific embodiment of the present invention may be combined in any suitable manner with one or more other embodiments. It is to be understood that other variations and modifications of the embodiments of the present invention described and illustrated herein are possible in light of the teachings herein and are to be considered as part of the spirit and scope of the present invention. 
     It will also be appreciated that one or more of the elements depicted in the drawings/figures can also be implemented in a more separated or integrated manner, or even removed or rendered as inoperable in certain cases, as is useful in accordance with a particular application. 
     Additionally, any signal arrows in the drawings/Figures should be considered only as exemplary, and not limiting, unless otherwise specifically noted. Furthermore, the term “or” as used herein is generally intended to mean “and/or” unless otherwise indicated. Combinations of components or steps will also be considered as being noted, where terminology is foreseen as rendering the ability to separate or combine is unclear. 
     As used in the description herein and throughout the claims that follow, “a”, “an”, and “the” includes plural references unless the context clearly dictates otherwise. Also, as used in the description herein and throughout the claims that follow, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise. 
     The foregoing description of illustrated embodiments of the present invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed herein. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes only, various equivalent modifications are possible within the spirit and scope of the present invention, as those skilled in the relevant art will recognize and appreciate. As indicated, these modifications may be made to the present invention in light of the foregoing description of illustrated embodiments of the present invention and are to be included within the spirit and scope of the present invention. 
     Thus, while the present invention has been described herein with reference to particular embodiments thereof, a latitude of modification, various changes and substitutions are intended in the foregoing disclosures, and it will be appreciated that in some instances some features of embodiments of the invention will be employed without a corresponding use of other features without departing from the scope and spirit of the invention as set forth. Therefore, many modifications may be made to adapt a particular situation or material to the essential scope and spirit of the present invention. It is intended that the invention not be limited to the particular terms used in following claims and/or to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include any and all embodiments and equivalents falling within the scope of the appended claims. Thus, the scope of the invention is to be determined solely by the appended claims.

Technology Category: 4