Abstract:
A regenerative clamping circuit for a power converter using clamping diodes to transfer charge to a clamping capacitor and a regenerative converter to transfer charge out of the clamping capacitor back to the power supply input connection. The regenerative converter uses a switch connected to the midpoint of a series connected inductor and capacitor. The ends of the inductor and capacitor series are connected across the terminals of the power supply to be in parallel with the power supply.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and is a continuation-in-part of U.S. Provisional Patent Application Ser. No. 61/945,590, filed on Feb. 27, 2014 entitled ACTIVE ENERGY RECOVERY CLAMPING CIRCUIT TO IMPROVE THE PERFORMANCE OF POWER CONVERTERS, which is hereby incorporated by reference in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with government support under grant DE-AR0000111 awarded by the United States Department of Energy (ARPA-E). The United States government has certain rights in the invention. 
    
    
     REFERENCE TO A MICROFICHE APPENDIX 
     Not Applicable. 
     RESERVATION OF RIGHTS 
     A portion of the disclosure of this patent document contains material which is subject to intellectual property rights such as but not limited to copyright, trademark, and/or trade dress protection. The owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the Patent and Trademark Office patent files or records but otherwise reserves all rights whatsoever. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to improvements in power converters. More particularly, the invention uses clamping diodes to transfer excess energy to a storage capacitor to temporarily store the excess energy until it can be recycled back into the host power converter. In particular, the present invention relates specifically to an active energy recovery clamp circuit including a clamping circuit and a regenerative converter. 
     2. Description of the Known Art 
     As will be appreciated by those skilled in the art, power supply topologies are known in various forms. Patents disclosing information relevant to power supplies include: U.S. Pat. No. 8,427,120, issued to Cilio on Apr. 23, 2013 entitled Coupled inductor output filter; U.S. Pat. No. 4,703,409, issued to Spreen on Oct. 27, 1987 which is entitled Coupled power supply inductors for reduced ripple current; U.S. Pat. No. 7,317,305, issued to Stratakos et al. on Jan. 8, 2008 which is entitled Method and apparatus for multi-phase dc-dc converters using coupled inductors in discontinuous conduction mode; U.S. Pat. No. 7,449,867, issued to Wu et al. on Nov. 11, 2008 which is entitled Multi-phase buck converter with a plurality of coupled inductors; and U.S. Pat. No. 7,498,783, issued to Johnson on Mar. 3, 2009 which is entitled Extending the continuous mode of operation for a buck converter. Patents and/or applications relating to coupled inductors also include the basic electrical components of the present design as noted by United States Patent No. 2009/0179713 filed by Zeng et al. published on Jul. 16, 2009 entitled Low pass filter incorporating coupled inductors to enhance stop band attenuation. Each of these patents and applications is hereby expressly incorporated by reference in their entirety. 
     From these prior references it may be seen that these prior art patents are very limited in their teaching and utilization, and an improved active energy recovery clamp is needed to overcome these limitations. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improved active energy recovery clamp, AERC, circuit comprised of a clamping circuit and a regenerative converter. The AERC circuit is applied to a host power converter to provide improved performance. The clamping circuit of the AERC uses a diode for each power device on the host converter where the peak voltage stress must be clamped. The clamping diodes transfer excess energy from the switching node to a capacitor that stores the energy for a brief period. This energy is then recycled back to the input of the host power converter using the regenerative converter. The AERC circuit is shown below where it is used on a push-pull converter topology and the regenerative converter is a buck topology. These and other objects and advantages of the present invention, along with features of novelty appurtenant thereto, will appear or become apparent by reviewing the following detailed description of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       In the following drawings, which form a part of the specification and which are to be construed in conjunction therewith, and in which like reference numerals have been employed throughout wherever possible to indicate like parts in the various views: 
         FIG. 1  is a circuit diagram of the active energy recovery clamp circuitry with a push-pull converter as the host. 
         FIG. 2  shows waveforms from the push-pull converter with active energy recovery clamp. 
         FIG. 3  shows an active energy recovery clamp circuitry vs. resistor-capacitor-diode clamp efficiency comparison of a push-pull converter. 
         FIG. 4  shows the loss reduction when using the active energy recovery clamp circuitry instead of a resistor-capacitor-diode clamp for a push-pull converter. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIG. 1  of the drawings, one exemplary embodiment of the present invention is generally shown as a power converter system  1  using an active energy recovery clamp circuit  100 , also known as AERC circuit  100 , comprised of a clamping circuit  300  and a regenerative converter  200 . The AERC circuit  100  is electrically connected between a direct current voltage supply Vdc and a host converter  10 . 
     The direct current voltage supply Vdc has a positive output supplying an input node  11  and a negative terminal. 
     The host power converter  10  includes a transformer TX. The transformer is a 1:1:n:n type transformer with the polarities as shown by standard dot convention noting phase relationship of the windings. The ends of the windings will be referred to as dot ends and clear ends. For this description only, a top dot will be described as phase one and a bottom dot will be scribed as phase two. Thus, the transformer TX includes an input phase one first winding W 1 , an input phase two second winding W 2 , an output phase one third winding W 3 , and an output phase two fourth winding W 4 . 
     The input phase one first winding W 1  dot end is electrically connected to the input node  11 . The input phase one first winding W 1  clear end is electrically connected to the drain of the first switch power device S 1  forming the first switch connection Sc 1  in the switching node SN. The first switch connection Sc 1  is also connected to the anode of the first clamping diode Dc 1 . The source of the first switch power device S 1  is electrically connected to negative terminal of the direct current voltage supply VDC. 
     The input phase two second winding W 2  clear end is electrically connected to the input node  11 . The input phase two second winding W 2  dot end is electrically connected to the drain of the second switch power device S 2  forming the second switch connection Sc 2  in the switching node SN. The second switch connection Sc 2  is also connected to the anode of the second clamping diode Dc 2 . The source of the second switch power device S 2  is electrically connected to negative terminal of the direct current voltage supply VDC. 
     The gates of the first switch power device S 1  and the second switch power device S 2  are frequency timed at a switching frequency Fsw to drive the power converter  10 . 
     The output phase one third winding W 3  dot end is electrically connected to the first end of the output inductor Lo and the output phase two fourth winding W 4  clear end. The output phase one third winding W 3  clear end is electrically connected to the cathode of the first converter diode D 3 . 
     The output phase two fourth winding W 4  clear end is electrically connected to the first end of the output inductor Lo and the output phase one third winding W 3  dot end. The output phase two fourth winding W 4  dot end is electrically connected to the cathode of the second converter diode D 4 . The anode of the second converter diode D 4  is electrically connected to the anode of the first converter diode D 3 . 
     The second end of the inductor Lo is electrically connected to the top of the output capacitor Co and the first end of the output resistor Ro. The bottom of the output capacitor Co is electrically connected to the second end of the output resistor Ro and the anodes of the first converter diode D 3  and the second converter diode D 4 . 
     The regenerative converter  200  includes a regenerative inductor Lr, regenerative diode Dr, and regenerative switch Sr. The regenerative inductor Lr is electrically connected between the input node  11  and the cathode of the regenerative diode Dr. The cathode of the regenerative diode Dr is also electrically connected to the source of the regenerative switch Sr, and the anode of the regenerative diode Dr is electrically connected to the negative terminal of the voltage supply VDC. The gate of the regenerative switch Sr is frequency timed with a regenerative frequency Fr and driven to control the regeneration back to the input node  11 . The drain of the regenerative switch Sr is connected to the clamping circuit  300  at one terminal of the energy storage device, shown as a clamping capacitor Cc. 
     The clamping circuit  300  includes a first clamping diode Dc 1 , second clamping diode Dc 2 , and an energy storage device shown as a clamping capacitor Cc. The energy storage device can be any device that can capture and store the power to be regenerated and is shown as a clamping capacitor Cc in the preferred circuit embodiment shown. The top terminal of the clamping capacitor Cc is connected to the regenerative converter  200  at the drain of the regenerative switch Sr, and the bottom terminal is connected to the negative terminal of the voltage supply VDC. Both the cathode of the first clamping diode Dc 1  and the cathode of the second clamping diode Dc 2  are connected to the top terminal of the clamping capacitor Cc and the drain of the regenerative switch Sr. The anode of the first clamping diode Dc 1  is connected to the drain of the first switch power device S 1 . The anode of the second clamping diode Dc 2  is connected to the drain of the second switch power device S 2 . 
     The AERC circuit  100  is applied to a host power converter  10  to provide improved performance. The clamping circuit  300  of the AERC  100  uses a diode DC 1 , DC 2  for each power device S 1 , S 2  on the host converter  10  where the peak voltage stress must be clamped. The clamping diodes DC 1 , DC 2  transfer excess energy from the switching node SN to a capacitor CC that stores the energy for a brief period. This energy is then recycled back to the input node  11  of the host power converter  10  using the regenerative converter  200 .  FIG. 1  shows the AERC circuit  100  where it is used on a push-pull converter  10  topology and the regenerative converter  200  is a buck topology. Note that while the host converter  10  is shown as a push-pull converter, the AERC circuitry  100  can be applied to any power converter  10  with voltage spike issues. 
     Advantages provided by the AERC circuitry  100  to the host converter  10  include limiting the voltage spike across the main power devices S 1 , S 2 ; recirculating the energy stored in the clamping capacitor CC back to the input node  11 ; adding damping to the system  1  without adding significant losses; and improving the overall efficiency of the host converter  10 . The AERC circuitry  100  also benefits from complete circuit decoupling that allows for the regenerative converter  200  to operate at any arbitrary switching frequency independent of the switching frequency of the host converter  10 . This allows for lower performance, and lower cost, components LR, SR, DR to be utilized for the regenerative converter  200  when compared to those used for the host converter  10 . Also by operating at a lower frequency the efficiency of the regenerative converter  200  can be very high. 
     The AERC circuitry  100  can provide benefits specifically to the push-pull converter  10  topology. The push-pull converter  10  is conventionally limited in its application due to the energy stored in the leakage inductance of the transformer. This energy is linearly proportional to the switching frequency and exponentially proportional to the output current. The utilization of AERC circuitry  100  negates these limitations by allowing all of this energy to be recycled very efficiently. The AERC circuitry  100  concept was experimentally tested on a push-pull converter  10 . 
       FIG. 2  shows the waveforms from push-pull converter  10  with AERC circuitry  100  with Vdc=300V, Vo=240V, Ro=40Ω, Fsw=200 kHz. Experimental efficiency results are shown in  FIG. 3  for a push-pull converter  10  with 300 V input applied and a switching frequency of 200 kHz for the push-pull converter  10  and 20 kHz for the regenerative converter  200  where the AERC circuitry  100  is compared to a conventional resistor-capacitor-diode clamp, RCD clamp, that uses a resistor to dissipate all of the excess energy as heat. It can be seen that the AERC circuitry  100  provides a significant improvement in the converter efficiency across all of the levels of output power. The amount of power loss saving vs. the output power of the converter is summarized in  FIG. 4  that shows the power loss reduction when using the AERC circuitry  100  instead of an RCD clamp for a push-pull converter  10  with 300 V input applied and a switching frequency of 200 kHz for the push-pull converter  10  and 20 kHz for the regenerative converter  200 . 
     Reference numerals used throughout the detailed description and the drawings correspond to the following elements:
         power converter system  1     direct current power supply Vdc   host power converter  10     first switch power device S 1     second switch power device S 2     switching node Sn   output resistor RO   output capacitor CO   output inductor LO   first converter diode D 3     second converter diode D 4     transformer TX   first winding W 1     second winding W 2     third winding W 3     fourth winding W 4     switching frequency Fsw   input node  11     active energy recovery clamp circuit  100     regenerative converter  200     regenerative inductor Lr   regenerative diode Dr   regenerative switch Sr   clamping circuit  300     first clamping diode Dc 1     second clamping diode Dc 2     clamping capacitor Cc       

     From the foregoing, it will be seen that this invention well adapted to obtain all the ends and objects herein set forth, together with other advantages which are inherent to the structure. It will also be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. Many possible embodiments may be made of the invention without departing from the scope thereof. Therefore, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense. 
     When interpreting the claims of this application, method claims may be recognized by the explicit use of the word ‘method’ in the preamble of the claims and the use of the ‘ing’ tense of the active word. Method claims should not be interpreted to have particular steps in a particular order unless the claim element specifically refers to a previous element, a previous action, or the result of a previous action. Apparatus claims may be recognized by the use of the word ‘apparatus’ in the preamble of the claim and should not be interpreted to have ‘means plus function language’ unless the word ‘means’ is specifically used in the claim element. The words ‘defining,’ ‘having,’ or ‘including’ should be interpreted as open ended claim language that allows additional elements or structures. Finally, where the claims recite “a” or “a first” element of the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements.