Abstract:
According to at least one aspect, embodiments herein provide a method for providing regulated DC power to a load, the method comprising receiving input AC power, generating rectified AC power, the rectified AC power derived from the input AC power, converting the rectified AC power into regulated DC output power, and providing the regulated DC output power to an output coupled to the load.

Description:
BACKGROUND OF INVENTION 
       [0001]    1. Field of Invention 
         [0002]    At least some embodiments described herein relate generally to Power Factor Correction (PFC) rectifiers. 
         [0003]    2. Discussion of Related Art 
         [0004]    Isolated AC-DC PFC rectifiers are commonly used in a variety of applications to convert supplied AC power into DC power having a desired voltage level. For example, isolated AC-DC PFC rectifiers are used as chargers or front end converters in high frequency isolated Uninterruptible Power Supply (UPS) systems, in telecommunication systems for providing desired DC voltage (e.g., 48V) to a distribution bus, and in High Voltage Direct Current (HVDC) datacenter power supplies to provide desired DC voltage (e.g., 240V or 380V) to a distribution bus. 
       SUMMARY OF INVENTION 
       [0005]    At least one aspect of the invention is directed to a rectifier system comprising an input configured to be coupled to a power source and to receive input AC power, a first converter coupled to the input and configured to generate, at an output of the first converter, rectified AC power having a desired amplitude, the rectified AC power derived from the input AC power, a rectified AC bus coupled to the output of the first converter, a second converter coupled to the rectified AC bus and configured to receive the rectified AC power from the first converter via the rectified AC bus and convert the rectified AC power into regulated DC output power, an output coupled to the second converter and configured to provide the regulated DC output power to a load coupled to the output, and a first controller coupled to the first converter and configured to operate the first converter at a first frequency to generate the rectified AC power having the desired amplitude. 
         [0006]    According to one embodiment, the rectifier system further comprises a capacitor coupled to the rectified AC bus. In one embodiment, the capacitor is a film type capacitor. 
         [0007]    According to another embodiment, the rectifier system further comprises an input rectifier coupled between the input and the first converter and configured to rectify the input AC power, wherein the rectified AC power generated by the first converter is derived from rectified input AC power provided to the first converter by the input rectifier. In one embodiment, the rectifier system further comprises an input filter coupled between the input rectifier and the first converter. 
         [0008]    According to one embodiment, the first converter is a resonant converter comprising a converter bridge coupled to the input, a resonant tank coupled to the converter bridge, and a rectifier coupled between the resonant tank and the rectified AC bus, wherein the first controller is configured to operate the converter bridge at the first frequency to generate the rectified AC power having the desired amplitude. In one embodiment, the resonant tank comprises an inductor coupled to the converter bridge, a capacitor coupled to the inductor, and a transformer having a primary winding coupled to the capacitor and a secondary winding coupled to the rectifier. 
         [0009]    According to another embodiment, the rectifier system further comprises a second controller coupled to the second converter and configured to operate the second converter at a second operating frequency to generate the regulated DC output power. In one embodiment, the second converter is a boost converter. In another embodiment, the second controller controls the second converter to provide power factor correction on the input AC power. In another embodiment, the second converter comprises an inductor coupled to the rectified AC bus, at least one switch coupled to the inductor, a diode coupled to the switch, and a filter coupled between the diode and the output, wherein the second controller is configured to operate the at least one switch at the second frequency to generate the regulated DC output power. 
         [0010]    According to one embodiment, the first converter is further configured to provide galvanic isolation between the input and the output. 
         [0011]    Another aspect of the invention is directed to a method for providing regulated DC power to a load, the method comprising receiving input AC power, generating rectified AC power, the rectified AC power derived from the input AC power, converting the rectified AC power into regulated DC output power, and providing the regulated DC output power to an output coupled to the load. 
         [0012]    According to one embodiment, generating the rectified AC power includes operating a first converter at a first frequency to generate the rectified AC power with a first amplitude. In one embodiment, generating the rectified AC power further includes operating the first converter at a second frequency to generate the rectified AC power with a second amplitude. In another embodiment, converting the rectified AC power into regulated DC output power includes operating a second converter at an operating frequency to generate the regulated DC output power. In one embodiment, the method further comprises filtering out a high frequency component from at least one of a current provided to the output from the second converter and a current provided to the first converter. In another embodiment, operating the second converter includes operating the second converter to provide power factor correction to the input AC power. 
         [0013]    According to one embodiment, the method further comprises rectifying the input AC power, wherein generating rectified AC power includes generating rectified AC power derived from rectified input AC power. 
         [0014]    At least one aspect of the invention is directed to a rectifier system comprising an input configured to be coupled to a power source and to receive input AC power, an output configured to be coupled to a load and to provide regulated DC output power to the load, and means for isolating the input from the output, for converting the input AC power into rectified AC power, and for converting the rectified AC power into the regulated DC output power. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]    The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings: 
           [0016]      FIG. 1  is a block diagram of a common isolated PFC rectifier system; 
           [0017]      FIG. 2  is a block diagram of a PFC rectifier system according to at least one embodiment of the current invention; 
           [0018]      FIG. 3  is a circuit diagram of a PFC rectifier system according to at least one embodiment of the current invention; 
           [0019]      FIG. 4  provides a graph showing different waveforms related to the operation of a PFC rectifier system according to at least one embodiment of the current invention; 
           [0020]      FIG. 5  is a block diagram of a multi-phase PFC rectifier system according to at least one embodiment of the current invention; and 
           [0021]      FIG. 6  is a block diagram of a system upon which various embodiments of the current invention may be implemented. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Examples of the methods and systems discussed herein are not limited in application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The methods and systems are capable of implementation in other embodiments and of being practiced or of being carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. In particular, acts, components, elements and features discussed in connection with any one or more examples are not intended to be excluded from a similar role in any other examples. 
         [0023]    Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Any references to examples, embodiments, components, elements or acts of the systems and methods herein referred to in the singular may also embrace embodiments including a plurality, and any references in plural to any embodiment, component, element or act herein may also embrace embodiments including only a singularity. References in the singular or plural form are not intended to limit the presently disclosed systems or methods, their components, acts, or elements. The use herein of “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. References to “or” may be construed as inclusive so that any terms described using “or” may indicate any of a single, more than one, and all of the described terms. In addition, in the event of inconsistent usages of terms between this document and documents incorporated herein by reference, the term usage in the incorporated references is supplementary to that of this document; for irreconcilable inconsistencies, the term usage in this document controls. 
         [0024]    As discussed above, isolated AC-DC PFC rectifiers are commonly used in a variety of different applications. One common isolated PFC rectifier system  100  is shown below in  FIG. 1 . The PFC rectifier  100  includes a non-isolated front end PFC boost rectifier  102  coupled to an isolated DC-DC converter  104  via an internal DC bus  106 . The non-isolated PFC boost rectifier  102  receives, at its input  103 , AC power from a mains power source  101  and generates an intermediate high voltage DC voltage  107  (e.g., 400V) on the internal DC bus  106  across a bulk capacitor (C 1 )  108 . The bulk capacitor (C 1 ) is typically a relatively large electrolytic capacitor. The DC-DC converter  104  receives the intermediate high voltage DC voltage  107  and regulates the voltage  109  provided to the output  110  of the rectifier  100 . The DC-DC converter  104  also provides isolation between the input and the output  110  of the rectifier  100 . 
         [0025]    The use of large bulk capacitors, such as electrolytic capacitors, in rectifier applications (e.g., as shown in the traditional rectifier  100  of  FIG. 1 ) and in general power converters has potential drawbacks such as limited life, low reliability, low life expectancy, and increased size. Accordingly, an isolated and highly reliable PFC rectifier system is described herein that addresses the above issues related to the use of large bulk capacitors such as electrolytic capacitors. 
         [0026]      FIG. 2  is a block diagram of a PFC rectifier system  200  according to at least one embodiment of the current invention. The PFC rectifier system  200  includes an input  201 , a rectifier  202 , a resonant DC-DC converter  204 , an internal rectified AC bus  206 , a return bus  207 , a PFC boost converter  208 , and an output  210 . 
         [0027]    An input of the rectifier  202  is coupled to the input  201 . An output of the rectifier  202  is coupled to the resonant DC-DC converter  204  via an input line  214  and a return line  216 . A first capacitor  218  is coupled between the input line  214  and the return line  216 . The internal rectified AC bus  206  and the return bus  207  are coupled between the resonant DC-DC converter  204  and the PFC boost converter  208 . The internal rectified AC bus  206  is coupled to an output  215  of the resonant DC-DC converter  204 . A second capacitor  209  is coupled between the internal rectified AC bus  206  and the return bus  207 . The output  210  is coupled to an output of the PFC boost converter  208 . The input  201  is configured to be coupled to an AC mains power source  203 . The output  210  is configured to be coupled to a load  211 . In one embodiment, the load  211  is a string of batteries. In other embodiments, the load  211  may be a single battery or another type of load. 
         [0028]    The rectifier  202  receives AC power from the AC mains power source  203 , via the input  201 , rectifies the AC power, and provides rectified AC power  205  to the resonant converter  204  via the input line  214 . The resonant DC-DC converter  204  converts the rectified AC voltage  205  to regulated rectified AC voltage  213  on the internal rectified AC bus  206  (i.e., across the second capacitor  209 ). According to one embodiment, the first and second capacitors  209 ,  218  are polypropylene capacitors; however, in other embodiments, different types of capacitors may be utilized. For example, in one embodiment, the first and/or second capacitors  209 ,  218  are film type capacitors with high ripple current handling capability. 
         [0029]    The switching frequency of the resonant DC-DC converter  204  determines a level of the regulated rectified AC voltage  213  provided to the internal rectified AC bus  206 . In one embodiment, the switching frequency of the resonant DC-DC converter  204  is controlled by a frequency controller  220 . Operation of the frequency controller  220  is discussed in greater detail below. The resonant DC-DC converter may also provide galvanic isolation between the input  201  and the output  210  of the rectifier system  200 . 
         [0030]    According to one embodiment, the resonant DC-DC converter  204  is an LLC converter; however, in other embodiments, the converter  204  may be any other type of isolated or non-isolated resonant converter. Also, in other embodiments, the converter  204  may be any other type of isolated or non-isolated DC-DC converter. 
         [0031]    The regulated rectified AC voltage  213  on the internal rectified AC bus  206  (and across the second capacitor  209 ) is provided to the PFC boost converter  208 . The PFC boost converter  208  receives the regulated rectified AC voltage  213  from the internal rectified AC bus  206 , converts the regulated rectified AC voltage  213  into DC power having desired DC voltage, and provides the DC power to the output  210 . In one embodiment, the PFC boost converter  208  is controlled by a current controller  222 . Operation of the current controller  222  is discussed in greater detail below. According to one embodiment, the PFC boost converter  208  is controlled such that the AC current at the input of the resonant converter  204  is in phase with mains input voltage. 
         [0032]      FIG. 3  is a more detailed circuit diagram of the PFC rectifier system  200  according to at least one embodiment of the current invention. The PFC rectifier system  200  includes the input  201 , the rectifier  202 , an input filter  302 , the resonant DC-DC converter  204 , the internal rectified AC bus  206 , the return bus  207 , the PFC boost converter  208 , the return line  216 , and the output  210 . The input filter  302  includes a first inductor  304  and the first capacitor  218 . The resonant DC-DC converter  204  includes a converter bridge  306 , a resonant tank  309 , a rectifier bridge  314 , and the second capacitor  209 . In one embodiment, the converter bridge  306  is a full-bridge converter including a plurality of switches (Q 1 -Q 4 )  307   a - 307   d ; however, in other embodiments, the converter bridge may be configured differently. In one embodiment, the switches (Q 1 -Q 4 )  307   a - 307   d  are Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFET); however, in other embodiments, different types of switches and/or transistors may be utilized. In one embodiment, the resonant tank  309  includes a second inductor  308 , a third capacitor  310 , an inductor (L m )  313 , and a transformer  312 ; however, in other embodiments the resonant tank  309  may be configured differently. The PFC boost converter  208  includes a third inductor  316 , a switch  318 , a diode  320 , and a high frequency filter  322 . According to one embodiment, the high frequency filter  322  includes a fourth inductor  326  and a fourth capacitor  324 ; however, in other embodiments, the high frequency filter may be configured differently. 
         [0033]    The input  201  of the system  200  is configured to be coupled to an AC source  203  (e.g., AC mains). An input of the rectifier  202  is coupled to the input  201 . An output of the rectifier is coupled to a first terminal of the first inductor  304 . A second terminal of the first inductor is coupled to the return line  216  via the first capacitor  218 . The second terminal of the first inductor is also coupled to the drains of switch Q 1   307   a  and switch Q 3   307   b . The source of switch Q 1   307   a  is coupled to the drain of switch Q 2   307   c . The source of switch Q 3   307   b  is coupled to the drain of switch Q 4   307   d . The sources of switch Q 2   307   c  and switch Q 4   307   d  are coupled to the return line  216 . The source of switch Q 3   307   b  is also coupled to a first end of a primary winding  315  of the transformer  312 . A second end of the primary winding  315  of the transformer  312  is coupled to the source of switch Q 1   307  (and the drain of switch Q 2   307   c ) via the third capacitor  310  and the second inductor  308 . The gate of each switch in the converter bridge  306  is coupled to the frequency controller  220 . 
         [0034]    The inductor (L m )  313  represents the inductance seen across the transformer  312 . In one embodiment, the inductor  313  is realized by introducing an air gap in the core of the transformer  312  (i.e., between the first winding and the second winding); however, in other embodiments, the inductor (L m )  313  is realized using an additional inductor coupled across the first winding of the transformer  312 . 
         [0035]    A first end and a second end of a secondary winding  317  of the transformer  312  are coupled to the rectifier bridge  314 . An output of the rectifier bridge  314  is coupled to a first terminal of the third inductor  316  via the internal rectified AC bus  206 . The rectifier bridge  314  is also coupled to the boost converter  208  via the return bus  207 . The second capacitor  209  is coupled between the internal rectified AC bus  206  and the return bus  207 . A second terminal of the third inductor  316  is coupled to the anode of the diode  320 . The drain of the switch  318  is also coupled to the anode of the diode  320 . The source of the switch  318  is coupled to the return bus  207 . The gate of the switch  318  is coupled to the current controller  222 . The cathode of the diode  320  is coupled to a first terminal of the fourth inductor  326 . The fourth capacitor  324  is coupled between the first terminal of the fourth inductor  326  and the return bus  207 . A second terminal of the fourth inductor is coupled to the output  210  of the system  200 . The output of the system  200  is configured to be coupled to at least one battery  211 . According to one embodiment, the fourth inductor  326  is removed and replaced with a short. 
         [0036]      FIG. 4  provides a graph showing different waveforms  400 ( a - e ) related to the operation of the PFC rectifier system  200 . Waveform  400   a  illustrates input AC mains voltage (V 1 )  402  in relation to input current (I 1 )  404  of the system  200 . Waveform  400   b  illustrates current (I 2 )  408  from the rectifier  202  into the input filter  302 , current (I 3 )  410  from the input filter  302  into the resonant converter  204 , and voltage (V C1 )  406  across the first capacitor  218 . Waveform  400   c  illustrates current (I 4 ) through the second inductor  308  and voltage (V 2 ) across the source of switch Q 3   307   b  and switch Q 1   307   a . Waveform  400   d  illustrates current (I 5 ) from the second winding of the transformer  312  to the rectifier bridge  314  and voltage (V 3 ) across the second winding of the transformer  312 . Waveform  400   e  illustrates current (I 6 )  420  out of the rectifier bridge  314 , current (I 7 )  422  into the boost converter  208 , voltage (V C2 )  424  across the second capacitor  209 , and the voltage (V Batt ) across the battery  211 . Operation of the PFC rectified system  200  is discussed in greater detail below with regard to  FIGS. 3 and 4 . 
         [0037]    The rectifier  202  receives input AC mains voltage (V 1 )  402  from the AC source  203  and rectifies the input AC mains voltage (V 1 )  402 . The rectified AC voltage (V C1 )  406  is provided to the resonant converter  204  via the input filter  302 . The input current (I 3 )  410  of the resonant converter  204  is rectified resonant current (I 4 )  412 . The input current (I 3 )  410  contains low-frequency and high-frequency current components. The input filter  302  diverts the switching frequency component of current (I 3 )  410  to the first capacitor  218  as current (I C1 )  409 . The input filter  302  allows the low-frequency component of current (I 3 )  410  to pass from the output of the rectifier  202  through the first inductor  304 . According to one embodiment the first inductor  304  of the input filter  302  is a separate inductor; however, in other embodiments, the inductance of the first inductor  304  may be provided by another device such as a cable or an Electro-Magnetic Interference filter. 
         [0038]    Upon receiving the rectified AC voltage (V C1 )  406 , the converter bridge  306  is operated by the frequency controller  220  (e.g., by transmitting signals to the gates of the switches (Q 1 -Q 4 )  307   a - 307   d ) to generate the desired voltage V 2    414 . According to one embodiment, the frequency controller  220  operates the converter bridge  306  at a switching frequency (F SW ) with 50% duty cycle in a complementary Pulse Width Modulation (PWM) mode to generate the AC voltage V 2 . However, in other embodiments, the frequency controller  220  may configure the switching frequency and PWM differently. 
         [0039]    The AC voltage V 2    414  is provided to the resonant tank  309 . The resulting resonant current (I 4 )  412  in the resonant tank  309  is a sine wave. According to one embodiment, the switches (Q 1 -Q 4 )  307   a - 307   d  of the converter bridge  306  are operated by the frequency controller  220  to implement soft-switching (i.e., Zero-Cross Switching (ZCS)). Also, as the amplitude of the voltage V 2    414  varies sinusoidally, the amplitude of current I 4    412  may have similar variation. 
         [0040]    As the voltage V 2    414  is provided to the transformer  312  of the resonant tank  309 , the primary winding  315  of the transformer  312  is energized and corresponding voltage (V 3 )  418  and current (I 5 )  416  is generated in the secondary winding  317  of the transformer  312 . According to one embodiment, the turns ratio of the transformer  312  is 1; however, in other embodiments, the turns ratio of the transformer  312  may be configured differently. The voltage V 3    418  and current I 5    416  are provided to the rectifier bridge  314 . The resulting rectified current I 6    420  is output by the rectifier bridge  314  and the rectified voltage V C2    424  is generated across the second capacitor  209 . The second capacitor  209  absorbs the high frequency current ripple (I C2 )  421  of current I 6    420  and allows the low-frequency current component of current I 6    420  to pass to the boost converter  208  as current I 7    422 . According to one embodiment, the value of the second capacitor  209  is relatively low. For example, in one embodiment, the second capacitor  209  has a capacitance of 1 μF-2.2 μF. However, in other embodiments, the second capacitor  209  may be configured differently. 
         [0041]    Due to its relatively low value, the second capacitor  209  allows the voltage across it (i.e., voltage V C2    424 ) to vary in response to input voltage variation. For example, as shown in  FIG. 5 , the voltage V C2   424  is a scaled version of the rectified input voltage V C1    406 . The frequency controller  220  can regulate (i.e., increase or decrease to a desired level) the amplitude of the rectified sine wave voltage V C2    424  across the second capacitor  209  by controlling (i.e., increasing or decreasing) the switching frequency (F SW ) of the resonant converter  204 . 
         [0042]    The PFC boost converter  208  is controlled by the current controller  222  such that the current I 7    422  drawn from the resonant converter  204  is proportional to the rectified sine wave voltage V C2   424  across the second capacitor  209 . Accordingly, the input to the PFC boost converter  208  can be realized as a virtual resistor, whose resistance value depends on the total output power of the system  200 . The high frequency filter  322  at the output of the system  200  diverts the high frequency (i.e., the switching frequency) current components in the diode  320  to the fourth capacitor  324 . According to one embodiment, the values of the fourth inductor  326  and the fourth capacitor  324  are low. For example, in one embodiment the fourth inductor  326  has an inductance of 10 μH-25 μH and the fourth capacitor  324  has a capacitance of 1 μF-2.2 μF. However, in other embodiments, the fourth inductor  326  and the fourth capacitor  324  may be configured differently. The DC and the second harmonic (i.e., low frequency) current components in the diode are passed to the output  210  of the system  200  as output current (I BATT )  427 . The PFC boost converter  208  may provide Power Factor Correction (PFC) of the system  200 . 
         [0043]    Control of the system  200  is discussed below with regard to  FIG. 2 . As discussed above, the frequency controller  220  operates the resonant converter  204  with 50% duty cycle PWM. The controller  220  monitors the output of the resonant converter  204 . For example, in one embodiment, a signal (V in   _   PFC )  224  representing the output voltage of the converter  204  (i.e., the voltage V C2    424 ) is passed to an RMS calculation module  226  which generates a signal (V in   _   PFC   _   RMS )  230  that represents the RMS output voltage of the converter  204 . The frequency controller  220  calculates the difference between the calculated RMS output voltage of the converter and a reference RMS output voltage (V in   _   PFC   _   RMS *)  228 . The difference between the calculated voltage and the reference RMS output voltage is processed through a Proportional-Integral (PI) controller within the controller  220 . Based on the output of the PI controller, the frequency controller  220  sets the switching frequency of the resonant converter  204 . In one embodiment, the frequency of the converter  204  is set at the resonant frequency at or about the nominal input voltage. The frequency of the converter  204  may be increased above or decreased below the resonant frequency during high line and low line conditions, respectively, to regulate the output voltage (V C2 )  424  of the converter  204 . 
         [0044]    As also discussed above, the current controller  222  operates the PFC boost converter  208 . The controller  222  monitors the output of the PFC boost converter  208 . For example, in one embodiment, a signal (v Out )  232  representing the output voltage of the PFC boost converter  208  (i.e., the voltage V Batt    426 ) and a signal (i Out )  236  representing the output current of the PFC boost converter  208  (i.e., the current I Batt    427 ) are passed to an output voltage/current module  234 . In one embodiment, the output voltage/current module  234  is a PI controller; however, in other embodiments, the output voltage/current module  234  may be configured differently. The output voltage/current module  234  compares the output voltage of the PFC boost converter  208  with a reference output voltage (v Out *)  233 , compares the output current of the PFC boost converter  208  with a reference output current (i Out *)  237 , and based on the difference between the voltage and current signals, determines the output voltage/current error of the PFC boost converter  208 . Based on the calculated voltage/current error, the output voltage/current module outputs a reference signal (i Peak *)  238  that represents the peak amplitude of the input current of the PFC boost converter  208 . The reference signal (i Peak *)  238  is provided to a current reference generation module  240 . 
         [0045]    The current reference generation module  240  multiplies the signal (i Peak *)  238  by the signal (V in   _   PFC )  224  representing the output voltage of the converter  204  to generate the reference signal (i PFC *)  242  which represents a reference input current of the PFC boost converter  208 . The current controller  222  calculates a PFC boost converter input current error based on the difference between the reference signal (i PFC *)  242  and the signal (i PFC )  244  which represents the calculated input current of the PFC boost converter  208 . Based on the calculated input current error, the current controller  222  provides PWM pulses to the PFC boost converter  208  to regulate the PFC boost converter  208 . 
         [0046]    According to one embodiment, the current reference generation module  240  also receives signals Sin θ  246  and signal i in    248 . Signal Sin θ  246  is a mains voltage template which is in phase with mains voltage (V 1 )  402 . In one embodiment, the signal Sin θ  246  is kept in phase with mains voltage (V 1 )  402  through the use of a Phase Locked Loop (PLL)  252 . Signal i in    248  represents the input current of the converter  204 . The current reference generation module  240  may use signals Sin θ  246  and i in    248  to modify the PFC input current reference signal (I PFC *)  242  such that the mains current  404  has low Input current Total Harmonic Distortion (I_THD) and near unity Power Factor (PF). In such case, the PFC boost converter input current  422  can be allowed to have little low frequency distortion, as control of the mains current  404  may be a higher priority. 
         [0047]    According to one embodiment, a plurality of the PFC rectifier systems  200  may be included within a larger rectifier system. For example, in one embodiment as shown in  FIG. 5 , a rectifier system  500  includes at least one rectifier module  502  that includes a plurality of rectifier sub-modules  504  (e.g., each sub-module being one of the PFC rectifier systems  200 ). Each sub-module  504  is fed input power from one phase  506  of a multi-phase mains power source (e.g., three-phase mains) and operates on the input power as discussed above. The output of each sub-module  504  are connected in parallel to an output of the rectifier module  502 . The output of the rectifier module  505  is coupled to a load/battery bus  508  which is coupled to a load/battery. In such a three phase rectifier system  500 , the sum of all second harmonic (i.e., low frequency) current components of the three sub-modules  504  is zero, so the battery  510  will not experience any low frequency current ripple. 
         [0048]      FIG. 6  illustrates an example block diagram of computing components forming a system  600  which may be configured to implement one or more aspects disclosed herein. For example, the system  600  may be communicatively coupled to a rectifier system and configured to operate the rectifier system as described above and perform the controller functions in the embodiments described above. 
         [0049]    The system  600  may include for example a general-purpose computing platform such as those based on Intel PENTIUM-type processor, Motorola PowerPC, Sun UltraSPARC, Texas Instruments-DSP, Hewlett-Packard PA-RISC processors, or any other type of processor. System  600  may include specially-programmed, special-purpose hardware, for example, an application-specific integrated circuit (ASIC). Various aspects of the present disclosure may be implemented as specialized software executing on the system  600  such as that shown in  FIG. 6 . 
         [0050]    The system  600  may include a processor/ASIC  606  connected to one or more memory devices  610 , such as a disk drive, memory, flash memory or other device for storing data. Memory  610  may be used for storing programs and data during operation of the system  600 . Components of the computer system  600  may be coupled by an interconnection mechanism  608 , which may include one or more buses (e.g., between components that are integrated within a same machine) and/or a network (e.g., between components that reside on separate machines). The interconnection mechanism  608  enables communications (e.g., data, instructions) to be exchanged between components of the system  600 . 
         [0051]    The system  600  also includes one or more input devices  604 , which may include for example, a keyboard or a touch screen. The system  600  includes one or more output devices  602 , which may include for example a display. In addition, the computer system  600  may contain one or more interfaces (not shown) that may connect the computer system  600  to a communication network, in addition or as an alternative to the interconnection mechanism  608 . 
         [0052]    The system  600  may include a storage system  612 , which may include a computer readable and/or writeable nonvolatile medium in which signals may be stored to provide a program to be executed by the processor or to provide information stored on or in the medium to be processed by the program. The medium may, for example, be a disk or flash memory and in some examples may include RAM or other non-volatile memory such as EEPROM. In some embodiments, the processor may cause data to be read from the nonvolatile medium into another memory  610  that allows for faster access to the information by the processor/ASIC than does the medium. This memory  610  may be a volatile, random access memory such as a dynamic random access memory (DRAM) or static memory (SRAM). It may be located in storage system  612  or in memory system  610 . The processor  606  may manipulate the data within the integrated circuit memory  610  and then copy the data to the storage  612  after processing is completed. A variety of mechanisms are known for managing data movement between storage  612  and the integrated circuit memory element  610 , and the disclosure is not limited thereto. The disclosure is not limited to a particular memory system  610  or a storage system  612 . 
         [0053]    The system  600  may include a general-purpose computer platform that is programmable using a high-level computer programming language. The system  600  may be also implemented using specially programmed, special purpose hardware, e.g. an ASIC. The system  600  may include a processor  606 , which may be a commercially available processor such as the well-known Pentium class processor available from the Intel Corporation. Many other processors are available. The processor  606  may execute an operating system which may be, for example, a Windows operating system available from the Microsoft Corporation, MAC OS System X available from Apple Computer, the Solaris Operating System available from Sun Microsystems, or UNIX and/or LINUX available from various sources. Many other operating systems may be used. 
         [0054]    The processor and operating system together may form a computer platform for which application programs in high-level programming languages may be written. It should be understood that the disclosure is not limited to a particular computer system platform, processor, operating system, or network. Also, it should be apparent to those skilled in the art that the present disclosure is not limited to a specific programming language or computer system. Further, it should be appreciated that other appropriate programming languages and other appropriate computer systems could also be used. 
         [0055]    As described above, the resonant converter  204  is utilized with a boost converter  208 ; however, in other embodiments, the resonant converter  204  may be utilized with other types of converters to regulate the system. 
         [0056]    As also described above, multiple controllers are utilized to operate the system; however, in other embodiments, a single controller may be configured to operate the entire system. 
         [0057]    As described above, the input filter  302  is coupled between the rectifier  202  and the converter  204 ; however, in other embodiments the input filter  302  is coupled between the input  201  and the rectifier  202 . 
         [0058]    As described above, the resonant converter  204  is a full-bridge converter; however, in other embodiments, the converter  204  may be a half-bridge converter or some other type of converter. 
         [0059]    As described above, the converter  208  includes a single switch  318 ; however, in other embodiments, the converter  208  may include any number of switches. 
         [0060]    Such a system as described above may be utilized in a UPS, in a HVDC Datacenter, in a telecommunication system, or in any other type of system utilizing rectification. 
         [0061]    As described herein, an isolated and highly reliable PFC rectifier system is provided that addresses the above issues related to the use of large bulk capacitors such as electrolytic capacitors. By utilizing an internal rectified AC bus rather than an internal DC bus, the need for large bulk capacitors, such as electrolytic capacitors, may be eliminated. 
         [0062]    Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.