Abstract:
Communicating across a power transformer is provided. Processes can include outputting a cyclical voltage at an alternating frequency across a multiple winding transformer and modulating the frequency of the alternating voltage to provide communication across the transformer. Devices and systems can also be employed with applicable features and designs.

Description:
This application is a continuation of U.S. application Ser. No. 14/159,084, which is entitled Communication Within a Power Inverter Using Transformer Voltage Frequency, names Patrick L. Chapman as the inventor, and is U.S. Pat. No. 9,509,232. The &#39;084 application is a continuation of U.S. application Ser. No. 12/832,199, which is also entitled Communication Within a Power Inverter Using Transformer Voltage Frequency, names Patrick L. Chapman as the inventor, and is now U.S. Pat. No. 8,634,216. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present embodiments relate to communicating by a power inverter. 
     2. Related Art 
     Power inverters may be used in various applications to provide alternating current (AC) power to a load using a direct current (DC) power source. In some applications, knowledge of the operating conditions of the DC power source may be desired to control the output. When electrical coupling is permitted, these operating conditions may be communicated to any point in the power inverter through standard wired communication manners. However, in particular applications, due to regulatory and/or safety requirements, a physical isolation barrier may be required. Existence of the isolation barrier may prevent communication of the operating conditions by electrical coupling. 
     SUMMARY 
     According to one aspect of the disclosure, a power inverter having a transformer may communicate information regarding operating conditions of a DC power source through a voltage frequency of the transformer. The power inverter may include an input bridge to receive direct current (DC) power from the DC power source. The input bridge may convert a DC voltage from the DC power source to an AC voltage. The AC voltage may be applied to a first winding in the transformer. The frequency of the AC voltage may be selected by a first controller based on the operating conditions of the DC power source. A second AC voltage may be generated across a second winding in the transformer due to application of the AC voltage applied to the first winding. A second controller may determine the frequency of the second AC voltage. The second controller may determine the operating conditions of the DC power source based on the frequency of the second AC voltage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure may be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like referenced numerals designate corresponding parts throughout the different views. 
         FIG. 1  is a circuit diagram of an example power inverter having an isolation barrier. 
         FIG. 2  is a block diagram of an example controller of the power inverter of  FIG. 1 . 
         FIG. 3  is a block diagram of another example controller of the power inverter of  FIG. 1 . 
         FIG. 4  is a circuit diagram an example portion of the power inverter of  FIG. 1 . 
         FIG. 5  is a circuit diagram another example portion of the power inverter of  FIG. 1 . 
         FIG. 6  is a circuit diagram another example portion of the power inverter of  FIG. 1 . 
         FIG. 7  is one example of an operational flow diagram of the power inverter of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a circuit diagram of a power inverter  100 . In one example, the power inverter  100  may convert direct-current power (DC) to alternating-current (AC) power. The power inverter  100  may receive power from a DC power source  102 . In one example, the DC power source  102  may be photovoltaic-based, such as one or more photovoltaic (PV) modules. In  FIG. 1 , the power source  102  may be represented by a voltage source  104  coupled in series with a resistive element (R s )  106 . The inverter  100  may convert the DC power from the power supply  102  to AC power delivered at an AC output load  108  of the inverter  100 . In alternative examples, other DC power sources may be implemented with the inverter  100 . 
     The inverter  100  may include an input bridge (IB)  110 . The input bridge  110  may include one or more circuit elements coupled to one another to convert the DC power from the DC power supply  102  to AC power. One example of the input bridge  110  is shown in  FIG. 4 . In  FIG. 1 , a line inductance (L l )  112  coupled between the power supply  102  and the input bridge  110  is represented by an inductive element. The line inductance  112  may be one or more inductors used to reduce the current ripple transmitted to the DC power supply  102 . The input bridge  110  may be coupled to a transformer  114  having a primary side  115  and secondary side  117 . The primary side  115  of the transformer may include a first winding  116  and the secondary side  117  may include a second winding  118 . Each of the first winding  116  and the second winding  118  may include more than one winding coupled in series or other configuration. The transformer  114  may have a winding ratio of 1:N to step up or step down the voltage and current from the output of the input bridge  110 . A rectifier (RECT)  119  may be coupled to the second winding  118  of the transformer  114 . 
     The AC power from the transformer  114  may be received by the rectifier  119 . The rectifier  119  may include one or more circuit elements coupled to one another to convert the AC power from the transformer  114  to DC power. One example of the rectifier  119  is shown in  FIG. 5 . The rectified power, voltage and current, may be filtered by a filter capacitance (C f )  120  represented in  FIG. 1  as a capacitive element that is coupled in parallel to the rectifier  119 . The filtered voltage and at least a portion of the current (see  FIG. 4 ) from the rectifier  119  may be received by an output bridge  122 . The output bridge  122  may include one or more circuit elements coupled to one another to convert the filtered DC power to AC power that may be delivered to an AC output load  108 . One example of the output bridge  122  is shown in  FIG. 5 . 
     In  FIG. 1 , the inverter  100  may include a line filter  123  to filter output voltage of the output bridge  122  prior to the AC power being delivered to the output load  108 . One example of the line filter  123  is shown in  FIG. 6 . In  FIG. 1 , the output load  108  may be a residential AC load having a split-phase configuration such as that found at residential premises in a United States electrical grid. In other examples, the output load  108  may be an industrial premises or any other load configured to receive AC power. 
     The output load  108  may be represented as a first voltage source (v l1 )  107  and a second voltage source (v l2 )  109  having an earth ground coupled between the two voltage sources  107  and  109 . The output load  108  may also be represented as including a first line inductance (L OL1 )  111  and a second line inductance (L OL2 )  113  coupled between a respective voltage source  107  and  109  and the output bridge  122 . An output sense resistor (R so )  125  may be coupled between the output bridge  122  and the line filter  123 . Current flowing through the output sense resistor  125  may be used to determine the current being provided to the output load  108 . 
     Inverters such as the inverter  100  may implement an isolation barrier. An isolation barrier may provide at least one point of complete physical disconnection between components of the inverter  100 . Use of the transformer  114  allows the inverter  100  to function with the existence of an isolation barrier. A physical gap exists between the first winding  116  and the second winding  118  with power being transferred through varying the mutual magnetic flux shared by the first winding  116  and the second winding  118  in order to induce a voltage across the second winding  118 . No physical connection is used in providing electrical energy from the primary side  115  to the secondary side  117 , thus, providing an isolation barrier. Use of an isolation barrier may be required in some circumstances due to regulatory requirements or safety concerns. 
     Use of an isolation barrier prevents the inverter  100  from having a common earth ground shared by all components of the inverter  100 . Instead, portions of the inverter  100  may have separate groundings that may or may not be connected to an earth ground. Separate groundings allow a respective portion of the inverter  100  to be locally grounded, but may not be at the same potential as other portions. For example, in  FIG. 1 , the inverter  100  may be grounded separately on both the primary side  115  and the secondary side  117  of the transformer  114 . The inverter  100  may be grounded on the DC side of the input bridge  110 , as indicated by ground connection  126  in  FIG. 1 . The inverter  100  may also be grounded on the secondary side of the transformer  114 . In particular, the inverter  100  may also be grounded on the DC side of the output bridge  122 , or alternatively on the AC side of the output bridge  122 , as shown by ground connections  128  and  130 , respectively. In alternative examples, the groundings may be connected to other locations on the inverter  100  on the primary side  115  and/or the secondary side  117  of the inverter  100 . 
     During operation of the inverter  100 , knowledge of the operating conditions of the power supply  102  may be desired, such as the instantaneous voltage V DC  and current I DC . While these conditions may be monitored on the primary side  115  of the transformer  114 , due to the isolation barrier in the inverter  100 , no common physical connections are present connecting both the primary side  115  and secondary side  117  for monitoring. However, knowledge of the operating conditions on the primary side  115  of the transformer  114  may be desired to be available on the secondary side  117  of the transformer  114  in order to control power being delivered to the output load  108  or for informational purposes. 
     In  FIG. 1 , the inverter  100  may include a primary side controller (PSC)  132  and a secondary side controller (SSC)  134 . The primary side controller  132  may determine the operating conditions (e.g., current, voltage, impedance, capacitance, other characteristics, or combinations thereof) from the power supply  102 , such as the voltage V DC , from a sensor  133 . The sensor  133  may be a voltage divider circuit or other circuit configured to sense the voltage produced by the power source  102 . An input sense resistor (R si )  135  may be used to provide the current I DC , or a current representative of I DC  to the primary side controller  132 . Based on the operating conditions, the primary side controller  132  may generate one or more control signals  136  to control the output of the input bridge  114 , as explained in further detail in  FIG. 2 . 
     During operation, the input bridge  110  may be controlled to generate an output voltage v ib  having a series of pulses alternating in polarity supplied to the first winding  116  of the transformer  114 . Supplying the output voltage v ib  to the first winding  116  may cause a primary voltage v pri  to be applied across the first winding  116 . Current flowing from the input bridge  110  (see  FIG. 4 ) into the first winding  116  may cause the first winding  116  to experience a change in magnetic flux resulting in a secondary voltage v sec  being created in the second winding  118  on the secondary side  117  of the transformer  114 . 
     The control signals  136  generated by the primary side controller  132  may control the duty cycle d (pulse width) and/or the frequency f p  of the pulses of the output voltage v ib . During operation, the input bridge  110  may be controlled by the primary side controller  132  to produce a voltage including pulses at a desired frequency f p . Thus, the frequency of the primary side voltage v pri  may have a frequency of f p  resulting in the secondary side voltage v sec  having a frequency of f p  as well. During operation, the frequency f p  may be varied within a particular range without any significant adverse effects regarding the desired output of the inverter  100 . Varying the frequency f p  may allow information regarding the operating conditions of the power supply  102  to be conveyed to the secondary side  117  of the transformer  114  without physical connection to the primary side  115  of the transformer  114  or without the need to implement other manners of communication between the primary side  115  and the secondary side  117 , such as wireless communication (e.g., light emitting diodes, radio frequency transmission, capacitive coupling, etc.) between the primary side controller  132  and the secondary side controller  134 . 
     As the input bridge  110  generates pulses applied to the first winding  116  to generate the voltage v ib , the secondary side controller  134  may detect the secondary voltage v sec  across the second winding  118  through one or more sensors  140 , such as voltage divider circuit, for example. The secondary voltage v sec  may be received by a rectifier  142 . The secondary voltage v sec  may be buffered and scaled by a scaling device  143 , such as an op amp, comparator, or other suitable device, in order to be compatible with logic-level integrated circuits. The output voltage v ro  of the rectifier  142  may be a unipolar pulse train with a frequency double that of the voltage v sec −frequency f p . The secondary side controller  134  may determine the operating conditions of the power supply  102  based on the output voltage v ro  as further described with regard to  FIG. 3 . A communication device  146  may be used to transmit the operating conditions wirelessly, such as to a central authority for processing and analysis. In other examples, operating conditions of the DC power supply may be communicated through power lines electrically coupled to the output load  108  as an alternative to the communication device  146  or used in tandem. 
       FIG. 2  is a block diagram of an example of the primary side controller  132 . In one example, the primary side controller  132  may be a microcontroller including a processor  200 , a memory  202 , clock  203 , and I/O ports. The memory  202  may include one or more memories and may be non-transitory computer-readable storage media or memories, such as a cache, buffer, RAM, removable media, hard drive or other computer readable storage media. Computer readable storage media may include various types of volatile and nonvolatile storage media. Various processing techniques may be implemented by the processor  200  such as multiprocessing, multitasking, parallel processing and the like, for example. The processor  200  may include one or more processors. 
     The processor  200  may include an analog-to-digital converter (ADC)  204 . Alternatively, the ADC  204  may be separate from the processor  200 . The ADC  204  may receive the voltage V* DC  and current I* DC  of the power supply  102 , which may be a voltage and current representative of the voltage V DC  and the current I DC , respectively, or the actual voltage V DC  and the current I DC . The ADC  204  may digitize these signals into one or more data signals  206  and provide the data signals  206  to a frequency determination module (FDM)  208 . The modules are software, hardware or some combination thereof executable by a processor, such as the processor  200 . Software modules may include instructions stored in the memory  202 , or other memory device, that are executable by a processor or processors. Hardware modules may include various devices, components, circuits, gates, circuit boards, and the like that are executable, directed, and/or controlled for performance by a processor. The FDM  208  may determine the frequency f p  of the input bridge  110  output based on the current operating conditions of the power supply  102 . 
     During operation, the FDM  208  may receive the data signals  206  from the ADC  204  indicative of the power supply voltage V DC  and current I DC . The FDM  208  may include a read module (RM)  210 . The read module  210  may receive the data signals  206  from the ADC  204  to determine the voltage V DC  and current I DC  based on the data signals  206  and, in one example, the read module  210  may determine if the data signals  206  are valid. The FDM  208  may also include an update module (UM)  212 . The update module  212  may receive a clock signal from the clock  203  used to generate a periodic update signal (UPD)  219 . The periodic update signal  219  may indicate to the read module  210  the time at which the read module  210  may sample the data signals  206 . The periodic update signal  219  may be generated at a predetermined update period of T update . In other examples, the update period T update  may be dynamically adjusted during operation of the inverter  100 . 
     Upon receipt and completion of any validation techniques, the read module  210  may provide the data  206  to an encoding module (EM)  214 . In the example of  FIG. 2 , the encoding module  214  may retrieve encoding data  216  from the memory  202 . The encoding data  216  may indicate a particular frequency at which to control the frequency f p  of output voltage V ib  in order to convey the operating conditions of the power supply  102  to the secondary side  117  of the transformer  114 . In one example, the encoding data  216  may include one or more tables mapping particular frequency values to particular operating condition points of the power supply  15   102 . Table 1 below is one example of the encoding data  216  in which the desired operating frequency range of the input bridge  110  has a midpoint of approximately 50 kHz. 
     
       
         
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Current/ 
                   
                   
                   
                   
                   
                   
               
               
                 Voltage 
                 0 A 
                 0.5 A 
                 1.0 A 
                 1.5 A 
                 . . . 
                 10 A 
               
               
                   
               
             
             
               
                   0 V 
                 49,500 
                 49,550.5 
                 49,551 
                 49,551.5 
                 . . . 
                 49,509.5 
               
               
                   
                 Hz 
                 Hz 
                 Hz 
                 Hz 
                   
                 Hz 
               
               
                  0.5 V 
                 49,510 
                 49,510.5 
                 49,511 
                 49,511.5 
                 . . . 
                 49,519.5 
               
               
                   
                 Hz 
                 Hz 
                 Hz 
                 Hz 
                   
                 Hz 
               
               
                  1.0 V 
                 49,520 
                 49,520.5 
                 49,521 
                 49,521.5 
                 . . . 
                 49,529.5 
               
               
                   
                 Hz 
                 Hz 
                 Hz 
                 Hz 
                   
                 Hz 
               
               
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
               
               
                 50.0 V 
                 50,490 
                 50,490.5 
                 50,491 
                 50,491.5 
                 . . . 
                 50,499.5 
               
               
                   
                 Hz 
                 Hz 
                 Hz 
                 Hz 
                   
                 Hz 
               
               
                   
               
             
          
         
       
     
     In one example, the desired operating condition to convey to the secondary side  117  may be the voltage V DC  and current I DC  provided by the power supply  102 . Table 1 includes a frequency corresponding to a voltage and current for the voltage V DC  and the current I DC , in increments of 0.5 V and 0.5 A, from a range of 0V to 50V and 0 A to 10 A. The output voltage v ib  of the input bridge  110  may be controlled at one of the particular frequencies listed in Table 1 to convey a corresponding operating condition point. In alternative examples, the encoding data  216  may include other data allowing selection of the frequency f p , such as equation-based data, frequency shift keying, or orthogonal frequency division multiplexing. 
     In using tables, such as Table 1, the encoding module  214  may round the instantaneous values of the current I DC  and voltage V DC  in order to select the corresponding frequency. Upon selection of the frequency by the FDM  208 , the frequency f p  may be provided to a pulse width modulator (PWM)  218 . The PWM  218  may also receive the data  206  to determine the duty cycle d independently from the FDM  208 . The PWM  218  may generate the control signals  136  based on the data  206  and frequency f p  provided by the FDM  208 . 
       FIG. 3  is a block diagram of an example of the secondary side controller  134 . The secondary side controller  134  may be a microcontroller that includes a processor  300 , memory  302 , as well as I/O ports, and clock (CLK)  304 . The processor  300  may include an ADC  306 . Alternatively, the ADC  306  may be separate from the processor  300 . The ADC  306  may receive and digitize the voltage Vro and provide a data signal  308  indicative of the voltage Vro to a condition determination module (CDM)  310  executed by the processor  300  or other hardware. The CDM  310  may determine the operating conditions conveyed through the frequency fp based on the data signal  308 . The CDM  310  may include a pulse counter module (PCM)  312 . The PCM  312  may determine the number of pulses included in the voltage Vro signal over a predetermined read period T read . 
     The number of pulses  314  may be relayed from the PCM  312  to a decoding module (DM)  316 . The decoding module  316  may determine the operating conditions corresponding to the number of pulses counted over by the PCM  312  over the period T read . In one example, the decoding module  316  may implement decoding data  318  stored on the memory  302 . The decoding data  318  may include various operating points of the operating conditions of the power supply  102  that correspond to the number of pulses read over the period T read . In one example, the decoding data  318  may include one or more tables having operating conditions of the power supply  102 . In one example, a desired output frequency range of the input bridge  110  may have a midpoint of approximately 50 kHz. The frequency f p  may be modulated within a range of about +/−5% of a particular switching frequency, however, in order to convey operating condition information regarding the power supply  102  to the secondary side  117  of the transformer  114 . Other tolerances are possible. The decoding data  318  may include tables having a number of possible operating conditions points of the power supply  102 . Each possible operating condition points in the table may correspond to a particular number of pulses counted by the pulse counter over the period of T read . 
     Table 2 includes an example of a table that may be included in the decoding data  318 . 
                                                                           TABLE 2               Voltage/                               Current   0 A   0.5 A   1.0 A   1.5 A   . . .   10 A                                  0 V   99000   99001   99002   99003   . . .   99019        0.5 V   99020   99021   99022   99023   . . .   99039        1.0 V   99040   99041   99042   99043   . . .   99059       . . .   . . .   . . .   . . .   . . .   . . .   . . .       50.0 V   100980   100981   100982   100983   . . .   100999                    
Table 2 may be applied to the situation in which the voltage produced of the power supply  102  is to be conveyed to the nearest 0.5 V and the current produced by the power supply  102  is to be conveyed to the nearest 0.5 A. In Table 2, approximately 50 kHz may be the midpoint of the frequency range in which the output of the input bridge  114  is desired to operate resulting in 100 discrete voltage values and 20 discrete current values that may occur according to Table 2. Thus, there are a total of 2,000 possible combinations of voltage and current. As such, 2,000 possible pulse counts are used within the given time frame. When the frequency f p  is at 50 kHz, the pulse counter module  148  may count 100,000 pulses. There would be a 2001 pulse difference between 99 kHz, (99,000 pulses per second) and 101 kHz (101,000 pulses per second). Based upon Table 2, the secondary side controller  134  determines the voltage and current of the power supply  102  based on the counted number of pulses over the read period T read . In Table 2, the read period T read  is one second.
 
     A read/update module (R/U)  320  may provide a read signal (RD)  322  and an update signal (UD)  324  to both the pulse count module  312  and the decoding module  316 . The read/update module  320  may receive a clock signal from the clock  304  used to generate the read signal  322  and update signal  324 . The read signal  322  may indicate to the PCM  312  the time at which to start counting the pulses in the data signal  308 . Upon receiving the update signal  324 , the PCM  312  may restart the counting. The read signal  322  and the update signal  324  may be coordinated such that read signal  322  is sent after the update signal  324 . The read signal  322  may also indicate a duration of time over which to count the pulses or an end time. In one example, T update  may be much greater than T read . For example, T read  may be one second in duration, while T update  may be several minutes. In such an example, the pulse counter module  312  may count the number of pulses over several periods of T read  and take the average number of pulses per read period T read . This average value may be used to by the encoding module  316  to identify the operating condition of the power supply. 
     The secondary side controller  134  may also detect the frequency of the secondary voltage v sec  without use of the rectifier  142 . In one example, the scaling device  143  may be an available device within the secondary side controller  134 . The scaling device  143  may scale the secondary voltage v sec  and the secondary side controller  134  may detect the frequency directly from the scaled version of the secondary voltage v sec . The encoding data  318  may include data representative of that shown in Table 1. 
       FIG. 4  is a circuit diagram of an example of the power supply  102 , and input bridge  110 , transformer  114 , and rectifier  119  of the inverter  100 . In  FIG. 4 , the power supply  102  of  FIG. 2  may be a photovoltaic module  400  including one or more photovoltaic cells. In  FIG. 4 , the PV module  400  is grounded and may generate a voltage Voc based on the received solar energy. A filter capacitor C pu  is coupled in parallel to the PV module  400 . The current I DC  may be supplied from the PV module  400 . 
     The input bridge  110  may include a plurality of switches  404 . Each switch  404  in  FIG. 4  is individually designated as SWI- 4 . In the example of  FIG. 4 , each switch  404  is embodied as a metal oxide semiconductor field-effect transistor (MOSFET). The term MOSFET may refer to other field effect transistors, such as those having a gate material other than metal, such as polysilicon (polycrystalline silicon) or other suitable gate material. The term MOSFET may also include insulated gate bipolar transistors (IGBTs) and insulated-gate field-effect transistors (IGFETs) as well. Other suitable switch types may be used for SWI through SW 4 . In  FIG. 4 , each switch  404  may include an intrinsic body diode  406 , individually designated as BD  1 - 4 . Each switch  404  may include a gate (G), drain (D), and source (S). The switches  404  may be coupled to one another in order to convert the DC power generated by the power supply  102  to AC power. The input bridge  110  may supply the AC power to the first winding  116  of the transformer  114 . The input bridge  110  may be controlled by the primary side controller  132  (not shown) through the control signals in order to provide the current to the first winding  116  alternating the polarity of the supplied current in order to generate a voltage across the second winding  118 . 
     The primary side controller  132  may generate the controls signals  136  to operate the switches  404  in such a manner. The control signals  136  generated by the primary side controller  132  may include a pair of control signals C 1  and C 2 . The first winding  116  may be coupled to the input bridge  114  such that when control signal C 1  is applied to the gates of switches SW 1  and SW 4  and the control signal C 2  is not applied to the switches SW 2  and SW 3 , the current IDe may flow through the switches SW 1  and SW 4 . Current flowing through the switches SW 1  and SW  4  may be considered positive in polarity with respect to the first winding  116 . When negative current with respect to the first winding  116  is desired, the control signal C 2  may be applied to the switches SW 2  and SW 3  and the control signal C 1  is not applied to the switches SW 1  and SW 2 , the current may flow through the switch SW 2 , through the first winding  116 , and through the switch SW 3 . The frequency with which the switching signals C 1  and C 2  are alternately applied to the switches  204  represents the frequency with which the output pulses of the input bridge  114  are applied to the first winding  116 —frequency fp. The length of time the switch pairs SW 1 - 4  and SW 2 - 3  remain on determines the width (duty cycle d) of a particular pulse. 
     Upon generation of the pulses of the input bridge  114  to the first winding, the secondary voltage Vsec may be generated across the second winding  118 . The rectifier  119  may include a plurality of diodes  210 , individually designated as D 1 -D 4  in  FIG. 4 , coupled to one another to convert the AC power received from the secondary side  117  of the transformer  114  to DC power. In  FIG. 4 , the second winding current i sec  may be considered positive with respect to the second winding  118  in the direction indicated in  FIG. 4 . Positive current i sec  flowing through the second winding  118  will also flow through diodes D 2  and D 3 , causing the rectifier output current i r  to be positive with respect to the output load  108  (not shown). When the current i sec  induced in the second winding  118  is negative, the current i sec  will flow through the diodes D 1  and D 4 , causing the current if to be positive with respect to the output load. Thus, the current flowing out of the rectifier  119 , current i sec  will be DC current. A portion of the current i r , designated as i cf , will flow the filter capacitor C f , the difference of current i b  will flow towards the output bridge  108 . 
       FIG. 5  is circuit diagram of an example of the output bridge  122 . The output bridge  122  may include a plurality of switches  500 , individually designated as SW 5 -S, coupled to one another to convert the DC power received from the rectifier  119  to AC power. The switches  500  may be similar to the switches  404  in  FIG. 4 . For example, the switches  500  may be MOSFET switches each having an intrinsic body diode  502 , individually designated as BD 5 - 8 . The switches  500  may receive control signals CS 3  and CS 4  from the secondary side controller  134  (not shown) or other suitable controller. Operating in manner similar to the input bridges  114 , when switches SW 5  and SWS receive control signals CS 3  and switches SW 6  and SW 7  do not receive control signal CS 4 , the current i b  will flow through switches SW 5  and SWS causing the output current i oc  of the output bridge  122  to be positive with respect to the output load  108 . When the control signals C 3  and C 4  are alternated, e.g., switches SW 2  and SW 3  turned on and SW 1  and SW 4  turned off, the current i oc  and voltage v oc  may be negative in polarity with respect to the output load  108 . 
       FIG. 6  is a circuit schematic of an example of the line filter  123  connected to the output load  108 . The line filter  123  may include filter inductances (L lf1 )  600  and (L lf2 )  602  each individually represented as a single inductor. However, the filter inductances  600  and  602  may each include single or multiple inductors. A filter capacitance (C lf )  604  may be electrically coupled between the filter inductances  600  and  602  and connected in parallel with the output load  108 . 
     During operation, the current i oc , when positive with respect to the output load, may flow through the filter inductance L l1  in the direction indicated in  FIG. 6 . A portion of the current i oc  may flow through the filter capacitor  604 , represented as current I lf . The difference in current, current i load , may flow through the output load  108 . The line filter  123  acts to smooth the output current i oc  flowing from the output bridge  122 . As the inverter  100  continues to operate, the polarity of the current i oc  alternates flowing through the output load  108  in an opposite direction as that described. 
       FIG. 7  is an operational flow diagram of example communication of information associated with the power supply  102  by the inverter  100 . In one example, the primary side controller  132  and the second side controller  134  may be initialized (block  700 ) such as an initial start-up or system reboot scenario. Upon initialization, the read period T read  and the update period T update  may be set (block  702 ). The primary side controller  132  may determine the operating conditions of the power supply  102  (block  704 ), such as the voltage and/or current, for example. The primary side controller  132  may determine a corresponding frequency and/or PWM of the operating conditions (block  706 ), such as through look-up tables, predetermined equations, or other manner. 
     The primary side controller  132  may control the input bridge  110  to output a voltage having the determined frequency and/or PWM (block  708 ). The voltage of the input bridge  110  may be applied to the primary winding  116  of the transformer  114  generating the secondary voltage v sec  across the secondary winding  118 . The secondary side controller  134  may determine the frequency and/or PWM of the secondary voltage v sec  over the read period T read  (block  710 ). The secondary side controller  134  may determine the operating conditions of the DC power source  102  based on the frequency and/or PWM of the secondary voltage v sec  (block  712 ). The primary side controller  132  may determine if the update period T update  (block  714 ) has expired. Upon expiration of the update period T update , the primary side controller  132  may determine the current operating conditions of the DC power supply. If the update period T update  has not expired, the primary side controller  134  may continue to determine the frequency and/or PWM of the secondary voltage v sec  during the read period T read . 
     While  FIGS. 1-7  illustrate and describe communication using the transformer  114  through the inverter  100 , such communication may be extended to various power converter and inverter topologies. For example, communication via the transformer  114  may be applied to various power converters used to convert AC power to DC power, such as buck, boost, and flyback converters, for example. While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. The various embodiments described herein include a variety of electrical elements and combinations of electrical elements, such as inductors, capacitors, voltage sources, switches, resistors, diodes, and power converters electrically coupled in various manners. The described example configurations of electrical elements and devices are examples that may be embodied through equivalent configurations having additional or fewer of the described elements, circuits, and devices, and alternative elements, alternative circuits, and/or alternative devices while remaining within the scope of invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.