Patent Publication Number: US-10790665-B2

Title: Power control systems and methods

Description:
RELATED APPLICATIONS 
     This application, U.S. patent application Ser. No. 16/128,339 filed Sep. 12, 2016 is a continuation of U.S. patent application Ser. No. 15/263,234 filed Sep. 12, 2016, now U.S. Pat. No. 10,074,981, which issued on Sep. 11, 2018. 
     U.S. patent application Ser. No. 15/263,234 claims benefit of U.S. Provisional Patent Application Ser. No. 62/217,958 filed Sep. 13, 2015. 
     The contents of the related application(s) listed above are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to systems and methods for the control of energy production, storage, consumption, and export management, and more particularly, to a power control system for supplying power to a load based on at least one of at least one DC power source and at least one AC power source. 
     BACKGROUND 
     Modern concerns for the environment have driven consumer demand for sustainable renewable energy production and storage technologies. For example, renewable energy sources such as wind and solar have resulted in increased demand for wind-powered turbine and photovoltaic (PV) array consumer technologies. Such demand has driven the availability and advancement in efficiency of sustainable renewable energy solutions, providing the consumer market with a multiplicity of technology options. Additionally, recent advancements in energy storage technology have presented the consumer market with a multiplicity of energy storage solutions for storing power generated from renewable energy sources and/or other sources. 
     Due to the dynamic nature of these emerging markets and the lack of standardization of renewable power generation and storage systems, consumers are left with a multiplicity of non-standardized renewable power generation technologies and non-standardized power storage technologies. As such, consumers are left without a simple, cost effective means to integrate consumer operated power generation systems, consumer operated energy storage systems, and/or the utility power grid. 
     Accordingly, there exists a need for a power control system capable of integrating one or more of renewable energy generation technologies, energy storage technologies, and/or the utility power grid. 
     SUMMARY 
     The present invention may be embodied as a power supply configured to operatively connect at least one load to at least one DC power source comprising an AC bus, a DC bus, a DC/AC converter, and a load balancer. The AC bus is adapted to be operatively connected to the load. The DC/AC converter is operatively connected between the DC bus and the AC bus. The load balancer is adapted to be operatively connected to the at least one DC power source and operatively connected to the DC bus. The power supply supplies power to the load from the first DC power source through the load balancer, the DC bus, the DC/AC converter, and the AC bus. 
     The present invention may also be embodied as a power supply configured to operatively connect at least one load to a plurality of DC power sources comprising an AC bus, a DC bus, a DC/AC converter, a first DC/DC converter, a second DC/DC converter, and a load balancer. The AC bus is adapted to be operatively connected to the load. The DC/AC converter is operatively connected between the DC bus and the AC bus. The first DC/DC converter is operatively connected between a first DC power source and the DC bus. The second DC/DC converter is operatively connected to a second DC power source. The load balancer is operatively connected between the second DC/DC converter and the DC bus. The power supply supplies power to the load from the first DC power source through the first DC/DC converter, the DC bus, the DC/AC converter, and the AC bus and from the second DC power source through the second DC/DC converter, the load balancer, the DC bus, the DC/AC converter, and the AC bus. 
     The present invention may also be embodied as a method of operatively connecting at least one load to at least one DC power source comprising the following steps. An AC bus is operatively connected to the load. A DC/AC converter is operatively connected between a DC bus and the AC bus. A load balancer is operatively connected between at least one DC power source and the DC bus. Power is supplied to the load from the first DC power source through the load balancer, the DC bus, the DC/AC converter, and the AC bus. 
     The present invention may be implemented as a power control system comprising a multiplicity of integrated circuit controlled DC and AC components which control the flow, inversion, storage, consumption and export of power. The power control system comprises of a neutral point clamping DC to AC inverter that inverts AC power signals being supplied by a plurality of AC power sources into a DC power signal and inverts DC power signals being supplied by a plurality of DC power sources into an AC power signal. A load balancing circuit is incorporated into the power control system to balance loads of unknown characteristics that are connected to the power control system. A plurality of DC converters are used to generate a plurality of output DC power signals from a plurality of DC power sources, before the DC to AC inverter inverts the DC power signal into an AC power signal to supply power to one or more loads. Converted DC power signals may also be used to supply power to at least one or more connected DC energy storage device. A plurality of AC power supplies, inclusive of the utility power grid or another AC power generator may be connected to the power control system to supply an AC power signal for supplying the one or more loads directly, or for inversion into a DC power signal to supply power to at least one or more connected DC energy storage device. One or more relay switches is provided to operatively connect one or more of the attached AC power supplies to the power control system and to operatively connect the DC stage of the power control system to the AC stage of the power control system. 
     A power control system implementing the present invention may further comprise control software for controlling which of the integrated circuit controlled DC components of the power control system shall assert control over the DC bus and for controlling which of the relay switches are closed to operatively connect one or more of the attached AC power supplies and/or to operatively connect the DC stage of the power control system to the AC stage of the power control system. 
     A power control system implementing the present invention may further comprise control software for controlling the output AC power signal of the power control system for synchronizing the subject output AC power signal of the power control system with AC power signal of one of the operatively connected AC power supplies. 
     A power control system implementing the present invention may further comprise another layer of logic based on consumer use model scenarios to determine which AC or DC power sources to operatively connect to provide optimal production, storage, consumption and exportation of energy in compliance with the consumer&#39;s desires. Such logic may be based upon environmental, economic, power control system component status and other factors including, but not limited to: renewable energy source output, life cycle of DC energy storage device, cost of utility power grid consumption, AC power supply generator fuel, size and/or capacity of various components of the power control system and time of year and/or day. 
     The present system is designed to provide efficient uninterrupted transition from multiple DC and AC inputs to supply power to one or more loads of unknown characteristics, to charge one or more DC energy storage devices, such as batteries, and to export energy to the utility power grid. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a highly schematic block diagram representation of the scalability and modularity of the present invention, depicting the attachment of a plurality of AC power sources, a plurality of DC power sources, and a load; 
         FIG. 2  is a three dimensional (3D) representation of an example environment in which a power control system constructed in accordance with the present invention may be used; 
         FIG. 3  is a schematic block diagram depicting an example power control system configured in accordance with the present invention; 
         FIG. 4  is a detailed circuit diagram depicting the details of the DC stage of the example power control system shown in  FIG. 3 ; 
         FIG. 5  is a detailed circuit diagram depicting the details of the AC stage of the example power control system shown in  FIG. 3 ; 
         FIG. 6  is a detailed circuit diagram depicting the details of the example load balancer  54  shown in  FIGS. 3 and 4 ; 
         FIG. 7  is a schematic block diagram depicting a second example power control system configured in accordance with the present invention and to include the communications network between the integrated circuit controllers and to represent the analog and digital output signals of the example power control system; 
         FIG. 8  is a highly schematic flow chart representing an example of logic used to implement a method of selecting which integrated circuit controller shall assert control over the DC bus depicted in  FIGS. 3 and 4 ; and 
         FIG. 9  is a highly schematic flow chart representing an example of logic used to implement a method of synchronizing the output AC power signal from the present invention with external AC power supplies and/or a load. 
     
    
    
     DETAILED DESCRIPTION 
     The basic concept of the present invention may be embodied in any one of a number of configurations. An example embodiment of the present invention will be described below, with the understanding that this embodiment illustrates the scope of the present invention but is not intended to be an exhaustive description of all scenarios in which the present invention may be used. In addition, not all components of the example embodiment described below are needed to implement the present invention in a more basic form. 
     Referring initially to  FIG. 1 , depicted therein is a first power supply system  20  constructed in in accordance with, and embodying, the principles of the present invention. The example power supply system  20  supplies a load power signal to a load  22 . The example power supply system  20  contains at least one electrical component that consumes electric power operated based at least in part on the load power signal generated by the power supply system  20 . 
     The characteristics of at least some of the electric components forming the example load  22  are typically unknown, the load  22  may be imbalanced. In particular, in a single phase electric power signal a load is considered balanced when the current flowing through each conductor is approximately equal. A load is considered imbalanced when the current flowing through one conductor is greater than the current flowing through the other conductor. When a load is unbalanced, power transmission can be inefficient under certain circumstances. 
     As represented in  FIG. 1 , the example power supply system  20  comprises a power control system  30  and at least one AC power source  24   a ,  24   b , through  24   n  and/or at least one DC power source  26   a ,  26   b , and  26   n.    
     The example power control system  30  is configured to generate the load  22  power signal based on at least one of the AC power sources  24   a ,  24   b , through  24   n  and/or at least one of the DC power sources  26   a ,  26   b , through  26   n . Furthermore, the power control system  30  is configured to transfer energy from at least one of a multiplicity of AC power sources  24  and/or DC power sources  26  for storage in at least one DC power sources  26 , as represented in the bi-directional power flow arrow associated with the first DC power source  26   a . Finally, the power control system  30  is configured to export energy from at least one of a multiplicity of DC power sources  26  to at least one of a multiplicity of AC power sources, as represented by the bi-directional power flow arrow associated with the first AC power source  24   a.    
     Referring now to  FIG. 2 , a specific example of the example power supply system  20  constructed in accordance with, and embodying, the principles of the present invention will now be described. As depicted in  FIG. 2 , the load  22  to which the first example power supply system  20  supplies a load power signal is represented by a house. When the load  22  is formed by a house as shown in  FIG. 2 , the load  22  will contain numerous electronic devices that operate at least in part based on the load power signal generated by the power supply system  20 . Further, at least some of the electronic devices forming the load  22  may result in the load being imbalanced. 
     As depicted in  FIG. 2 , the example power control system  30  is connected to a utility grid  32  (depicted in  FIG. 2  as utility power lines) forming a first AC power source, an energy storage system  34  forming a first DC power source, an AC power system  36  formed by a second AC power source, and a DC power generation system  38  forming a second DC power source. The example energy storage system  34  comprises at least one battery and will also be referred to herein as the battery  34 . The example second AC power system  36  is or may be a conventional AC generator having an internal combustion engine and will be referred to herein as the generator  36 . The example DC power generation system  38  is a photovoltaic array and will also be referred to herein as the PV system  38 . Other types of energy storage systems, AC power systems, and/or DC power systems may be used instead of or in addition to the utility grid  32  and example power storage and generation systems  34 ,  36 , and  38  described herein. 
     The example power control system  30  is configured to generate the load power signal based on at least one of the utility power grid  32 , the battery  34 , the generator  36 , and the PV system  38 . In addition, the power control system  30  may charge the battery from at least one of the utility power grid  32 , the generator  36 , and the PV system  38 . The example power control system  30  may further be optimized to select an appropriate one of the first and second AC power sources  32  and  36  and DC power sources  34  and  38  based on factors such as availability and cost. 
     Referring now to  FIG. 3 , depicted therein at  30  is a block diagram depicting an example of the power control system  30  generally described above.  FIG. 3  illustrates that the example power control system  30  comprises a DC stage  40  and an AC stage  42 . The DC stage  40  comprises a DC bus  50 , a first DC/DC converter  52 , a load balancer  54 , a second DC/DC converter  56 , and a DC/AC converter  58 . The first DC/DC converter  52  is connected between the PV system  38  and the load balancer  54 . The load balancer  54  connects the first DC/DC converter  52  to the DC bus  50 . The second DC/DC converter  56  is connected between the battery  32  and the DC bus  50 . The AC stage  42  comprises an AC bus  60 , a first control switch  62 , a second control switch  64 , and a third control switch  66 . The first control switch  62  is operatively connected between the DC/AC converter  58  of the DC stage  40  and the AC bus  60  of the AC stage  42 . The second control switch  64  is operatively connected between the grid  32  and the AC bus  60 . The third control switch  66  is operatively connected between the generator  36  and the AC bus  60 . 
     The example first DC/DC converter  52 , second DC/DC converter  56 , and DC/AC converter  58  all are or may be conventional and will not be described herein in detail beyond what is necessary for a complete understanding of the present invention. In particular, the DC/DC converters  52  and  56  each convert a DC power signal from one DC voltage to another DC voltage. The DC/AC converter  58  converts an AC signal into a DC voltage. The example second DC/DC converter  56  and the example DC/AC converter  58  are both bidirectional. 
       FIG. 4-6  illustrate an example circuit capable of implementing the functionality of the example power control system  30  described herein.  FIG. 4  illustrates an example of the DC stage  40 , while  FIG. 5  illustrates an example of the AC stage  42 .  FIG. 6  is a detailed view of a portion of the example DC stage  40 . 
     As depicted in  FIG. 4 , the example DC/DC converter  52  converts a PV output voltage associated with the example PV system  38  into a DC bus voltage. In particular, the example PV system  38  generates a PV output voltage within a first range, and the example first DC/DC converter  52  converts this PV output voltage to positive and negative DC voltages relative to a ground. The positive DC signal is connected to the DC bus  50  through the load balancer  54 . The output of the PV system  38  is thus effectively converted to the DC bus voltage on the DC bus  50 . As depicted in  FIG. 4 , the example first DC/DC converter  52  is a BB component  252  converter. 
     The example DC/DC converter converts a battery voltage associated with the example battery  34  into the DC bus voltage. As depicted in  FIG. 4 , the example battery  34  generates a battery DC signal of a first DC value, and the DC/DC converter  56  converts the battery DC signal into the DC bus voltage. The DC/DC converter applies this voltage to the DC bus  50 . The example DC/DC converter  56  is bidirectional and is capable of converting the DC bus voltage to a DC battery voltage appropriate for charging the example battery  34 . As depicted in  FIG. 4 , the example second DC/DC converter  56  is a dual active bridge (DAB). 
     The example DC/AC converter  58  converts a DC voltage on the DC bus  50  into an AC power signal appropriate for powering the load  22 . As shown in  FIG. 4 , the DC/AC converter  58  is capable of converting the DC bus voltage present on the example DC bus  50  into an AC power signal that is applied to the AC bus  60 . The example DC/AC converter  58  is bidirectional. Accordingly, the DC/AC converter may convert a AC bus voltage present on the AC bus  60  to the DC bus voltage and supply this DC bus voltage to the DC bus  50 . 
       FIGS. 4 and 5  illustrates that the example DC/AC converter  58  may be operatively connected to the AC bus  60  when the example first control switch  62  is in a closed configuration and is disconnected from the AC bus  60  when the example first control switch is in an open configuration. The example first control switch  62  as depicted in  FIG. 5  is formed by one or more electromechanical relays, but other switch circuits may be used in addition or instead. 
       FIG. 5  also illustrates that the AC bus  60  may be operatively connected to the utility power grid  32  when the example second control switch  64  is in a closed configuration and is disconnected from the power grid  32  when the example second control switch  64  is in an open configuration.  FIG. 5  further illustrates that the example second control switch  64  is formed by one or more electromechanical relays, but other switch circuits may be used in addition or instead. 
       FIG. 5  further illustrates that the example AC power source generator  36  is operatively connected to the AC bus  60  when the example third control switch  66  is in a closed configuration and is disconnected from the AC bus  60  when the example third control switch  66  is in an open configuration. As shown in  FIG. 5 , the example third control switch  66  is formed by one or more electromechanical relays, but other switch circuits may be used in addition or instead. 
       FIG. 5  further illustrates that the example power control system  30  defines load terminals  70   a ,  70   b , and  70   c . The load terminals  70   a ,  70   b , and  70   c  are operatively connected to the AC bus  60 . The load terminals  70   a ,  70   b , and  70   c  allow the AC bus  60  of the example power control system  30  to be connected to the load  22  and thus allow a load power signal output from the example power control system  30  to be supplied to the load  22 . 
     When the example first control switch  62  is in its closed configuration, the DC/AC converter  58  is operatively connected to the AC bus  60 . With the DC/AC converter  58  is operatively connected to the AC bus  60 , power may be transferred in either direction between the DC bus  50  and the AC bus  60  through the example bidirectional DC/AC converter  58 . With the example second control switch  64  is in its closed configuration, the grid  32  is operatively connected to the AC bus  60 . When the grid  32  is operatively connected to the AC bus, power from the grid  32  can be transferred from the grid  32  to the load  22  or to the battery  34 , or power from the battery  34 , the generator  36 , and/or the PV system  38  can be transferred to the grid  32 . When the example third control switch  64  is in its closed configuration, the generator  36  is operatively connected to the AC bus  60 . When the generator  36  is operatively connected to the AC bus  60 , power from the generator  36  can be transferred from the generator  36  to the load  22 , to the grid  32 , and/or to the battery  34 . 
       FIG. 4  further illustrates that the output of the PV system  38  is connected to the first DC/DC converter  52  at a first DC input terminal  80   aa  and a second DC input terminal  80   b . The first DC/DC converter  52  is in turn connected to the load balancer  54  at a first DC intermediate terminal  82   a  and a second DC intermediate terminal  82   b . The load balancer  54  is in turn connected to the DC bus  50  at a first DC bus terminal  84   a  and a second DC bus terminal  84   b.    
     The battery  34  is connected to the second DC/DC converter  56  at a first battery terminal  86   a  and a second battery terminal  86   b . The second DC/DC converter  56  is connected to the DC bus  50  at the first DC bus terminal  84   a  and the second DC bus terminal  84   b.    
     The example DC/AC converter  58  is connected between the first DC bus terminal  84   a  and the second DC bus terminal  84   b  and a first intermediate AC terminal  90   a  and a second intermediate AC terminal  90   b . The second DC bus terminal  84   b  is connected to an intermediate reference terminal  92 . As shown in  FIG. 5 , the intermediate AC terminals  90   a ,  90   b , and  92  are connected to the AC bus  60  through the first control switch  62 . 
     The load  22 , the grid  32 , the generator  36 , and the DC/AC converter  58  are all connected to one another by their respective line  1 , line  2  and neutral wires to form the example AC bus  60 . In particular, line  1  of the load  22 , line  1  of the grid  32 , line  1  of the generator  36  and the first intermediate AC terminal  90   a  are all connected to each other. Line  2  of the load  22 , line  2  of the grid  32 , line  2  of the generator  36  and the second intermediate AC terminal  90   b  are all connected to each other. The neutral of the load  22 , the neutral of the grid  32 , the neutral of the generator  36 , and the intermediate reference terminal  92  are all connected to each other. 
     Referring now to  FIG. 6  is an example of a detailed circuit diagram of the example load balancer  54 . In the example depicted in  FIG. 6 , the example load balancer  54  comprises a balance circuit  120 . The balance circuit  120  is configured across a portion of a switch circuit  122  and first and second split rail capacitors  124  and  126  of the first DC/DC converter  52 . The example balance circuit  120  is an inductor-capacitor (LC) resonant charge pump circuit comprising a resonant capacitor  130  and a resonant inductor  132 . The example switch circuit  120  comprises a first transistor  140 , a second transistor  142 , a third transistor  144 , and a fourth transistor  146 . 
     The example first DC/DC converter  52  formed by the switch circuit  122  and the split rail capacitors  124  and  126  is or may be conventional and will not be described herein beyond that extend necessary for a complete understanding of the present invention. In particular, the first transistor  140  is connected to the DC bus  50  and to the second transistor  142 . The second transistor  142  is connected to the third transistor  144 . The fourth transistor  146  is connected to the second transistor  144  and the DC bus  50 . The first rail capacitor  124  is connected to the DC bus  50  and between the second and third transistors  142  and  144 . The second rail capacitor  126  is connected between the second and third transistors  142  and  144  and to the DC bus  50 . The juncture of the first and second rail capacitors  124  and  126  is also connected to the DC bus. 
     The example balance circuit  120  is connected to the example first DC/DC converter  52  as follows. The resonant capacitor  130  and resonant inductor  132  are connected in series with the resonant capacitor  130  connected to a point between the first and second transistors  140  and  142  and the resonant inductor  132  connected to a point between the third and fourth transistors  144  and  146 . When the example switch circuit  120  is operated in a conventional manner such that the example first DC/DC converter  52  functions as a buck-boost converter, the switches  140 ,  142 ,  144 , and  146  forming example first DC/DC converter  52  are operated at predetermined inverter switching frequency, typically at or near a duty cycle of 50% during normal operation. With the balance circuit  120  connected to the example first DC/DC converter  52  as described above, the values of the resonant capacitor  130  and resonant inductor  132  will determine a balancer frequency and a balancer duty cycle associated with the balance circuit  120 . 
     In operation, the example load balancer  54  effectively maintains an equal voltage across the first split rail capacitor  124  and the second split rail capacitor  126 . In particular, the balance circuit  120  is sequentially connected in parallel across the split rail capacitors  124  and  126  during normal operation of the example first DC/DC converter  52 . The balance circuit  120  will, effectively, take energy from either of the capacitors  124  and  126  at a higher voltage and give energy to either of the capacitors  124  and  126  at a lower voltage. By maintaining substantially equal voltages across the first split rail capacitor  150  and the second split rail capacitor  152 , the example load balancer  54  substantially compensates for imbalances in the load  22 . 
     In the example balance circuit  120 , the values of the resonant capacitor  130  and the resonant inductor  132  are selected such that the balancer frequency and balancer duty cycle substantially match the inverter frequency and inverter duty cycle. The balance circuit  120  thus allows the load balancer  54  to operate with the example first DC/DC converter  52  at nearly zero voltage switching, rendering the operation of the balance circuit  120  highly efficient. 
     The switches  62 ,  64 , and  66  of the example power control system  30  may be operated in different switch configurations. In a first example switch configuration, the second control switch  64  is in the open configuration, the third control switch  66  is in the open configuration, and the first control switch  62  is in the closed configuration. When the switches  62 ,  64 , and  66  are in this first example switch configuration, the power control system  30  is operating in an off-grid mode in which the grid  32  and the generator  36  are disconnected from the AC bus  60  and the DC/AC converter  58  is operatively connected to the AC bus  60  In the off-grid mode, one or both of the PV system  38  and the battery  34  may supply power to the load  22 . Should the power output from the PV system  38  exceed the power demands of the load  22 , power from the PV system  38  may be used to charge the battery  34 . 
     In a second switch configuration, the second control switch  64  is closed and the third control switch  66  is open. In this second switch configuration, the example power control system  30  operates in a grid-tied mode in which the grid  32  is operatively connected to the AC bus  60  and the power supply generator  36  is disconnected from the AC bus  60 . In the grid-tied mode, the power control system  30 , can either supply the power demands of the load  22  directly where the first control switch  62  is open, or, where the first control switch  62  is closed and the DC/AC converter  58  is thereby operatively connected to the AC bus  60 , either the grid  32  can supply power to, and thereby charge, the example battery  34 , or the example PV system  38  can export power to the grid  32 . 
     In a third switch configuration, the second control switch  64  is open and the third control switch  66  closed. As such, the grid  32  is not operatively connected to the AC bus  60 , but the power supply generator  36  is operatively connected to the AC bus  60 , and the power control system  30  is operating in a generator mode. In a generator mode, as in this example, the power control system  30 , can either supply the demands of the load  22  directly where the first control switch  62  is open, or, where the electromechanical relay switch  62  is closed and the DC/AC converter  58  is thereby operatively connected to the AC bus  60 , the generator  36  can supply power to, and thereby charge, the example battery  34 . 
     Referring now to  FIG. 7  of the drawing, depicted therein is a second example power system  220  of the present invention. The example power system  220  is configured to provide power to a load  222 . 
     The example power system  220  comprises a power control system  230  operatively connected to a utility grid  232 , a battery system  234 , a generator  236 , and a PV array  238 . The example power control system  230  comprises a DC portion  240  and an AC portion  242 . 
     The DC portion  240  comprises a DC bus  250 , a buck-boost (BB) component  252  converter (BB component)  252 , a load balancer  254 , a dual active bridge (DAB component)  256 , and a neutral-point-clamp (NPC)  258 . The example BB component  252  is formed by a non-isolated DC to DC converter for controlling power from, for example, the PV array  238  to the DC bus  250 . The example load balancer  254  is or may be similar to the load balancer  54  described above. The example dual active bridge (DAB)  256  comprises an isolated DC to DC converter that controls power flow between the DC bus  250  and the battery  234 . The example neutral-point-clamp (NPC)  258  comprises an AC inverter that controls power flow between the DC bus  250  and the AC load  222 . 
     The AC portion  242  comprises an AC bus  260  and first, second, and third control switches  262 ,  264 , and  266 . The example power control system  230  further comprises a system controller  270  and a power metering board (PMB)  272 . 
     The example power control system  230  further comprises a system controller (SC)  270  for providing user interface, BMS, and connectivity functionality and a power metering board (PMB)  272  for providing high resolution voltage &amp; current sensors and AC power relay control. 
     All of the controllers are interconnected using a controller area network (CAN)  274 . The example BB component  252 , dual active bridge  256 , neutral-point-clamp  258 , and example power metering board  272  are connected to coordinate operation of the example power control system  230 . In the example power control system  230 , the cabling is daisy chained from example power metering board  272  to example system controller  270  to example dual active bridge  256  to example BB component  252  to example neutral-point-clamp  258 . This cabling also contains two isolated, open-drain signals that may be used to indicate an interprocessor emergency condition. 
     As described herein the example power control system  230  performs, at minimum, the following functions. 
     The neutral-point-clamp  258  provides seamless transition from grid-tied operation to stand-alone mode. Using two different control modes requires a transition time among all three converters (dual active bridge  256 , neutral-point-clamp  258 , buck boost system  252 ) and the AC grid  232 . Transition from grid-tied to stand-alone mode and vice versa requires a very short interrupt to be able to transit from on-grid to off-grid operation. The example power control system  230  uses a droop control method system to operate under the same control mode for both grid-on and grid-off without any need of transitioning between the modes. The neutral-point-clamp  258  can also be configured to transition from synchronous generators. 
     The example power control system  230  employs a minimum loss control algorithm for buck and boost operation of a positive output BB component  252  converter. In particular, the example power control system  230  employs a control method can that allows buck and boost operation to be performed separately while also providing positive output voltage. This control method changes from buck to boost operation and vice versa smoothly to prevent instability in the control loop. Use of this control algorithm improves the efficiency of the BB component  252  at least by 1% and possibly up to 2%. 
     The example power control system  230  employs a battery constant voltage charge algorithm to control a BB component  252  converter. The battery constant voltage charge algorithm is control algorithm that enables the system to charge the batteries  234  when connected to the dual active bridge  256 , under constant voltage mode by controlling the BB component  252  converter connected to PV panels under the off-grid operation. The dual active bridge  256  will be in constant high voltage DC bus control mode and the BB component  252  will inject current to control the battery voltage. The loop can be created in either the BB component  252  to dual active bridge  256  communication or the system controller  270  can run the loop as well. 
     The example power control system  230  employs a control algorithm for pre-charging a common DC bus from multiple sources. The pre-charging control algorithm enables the system  230  to charge a common DC bus from multiple sources. The BB component  252  and the dual active bridge  256  can both pre-charge the DC bus  250 . The algorithm runs the BB component  252  in constant voltage mode at a lower voltage than the dual active bridge  256  constant voltage mode. This allows both the BB component  252  and the dual active bridge  256  to operate together without communication interaction. 
     The example power control system  230  uses PV power to recharge and offset grid consumption and contains an option to cycle the batteries. The example power control system  230  has the ability to not export to the grid under any circumstance, to export only in lieu of curtailment, to export up to a preset output limit, or to export whenever possible, as much as possible. The example power control system  230  uses auto-sensing to pool resources, support shared loads, share surplus, and use power surpluses against battery deficits. The example power control system  230  provide DC coupled generation and AC coupled generation with Frequency-Watt control (e.g., SunSpec) and other advanced grid benefits (var support, power factor correction, ancillary support). Internal communication is automatic and provides presets &amp; custom options. External communication is easily accessible and controlled from Web interface via Ethernet. 
     The example power control system  230  employs frequency-watt control to limit active power generation or consumption when the line frequency deviates from nominal by a specified amount. There are two approaches available for frequency-watt control: the parameter approach and the curve approach. 
     As distributed generation transitions from being an outlier technology to being a key partner in the operation and balance of a well-behaving utility grid, inverters will increasingly be called upon to provide ancillary benefits to the grid—either by mandate, or to support advanced business opportunities. As such, the platform needs to support advanced grid benefit functionalities such as those called out by the Western Utilities Smart Inverter Working Group (SIWG). These functions include VAR support to supply reactive power to the grid, power factor correction (static or active) and other ancillary benefits. 
     The example power control system  230  is configured to operate in a diverse set of use-case scenarios simple for each region, language, various utility requirements and different battery technologies. The example control system  230  is an all in one, four port plug and play device utilizing a connectorized installation system. The example control system  230  employs auto-sensing inverters in a parallel system and allows selection of regional grid connection parameters. The example control device includes battery technology presets with full charging algorithms options. 
     With the foregoing general understanding of the example power control system  230  in mind, the details of the example power control system  230  will now be described. 
     The example power control system  230  employs different modes depending upon operating requirements. When the battery is discharging, the inverter performs automatic load management to maximize the run time of critical loads. Without an external critical load panel, the example power control system  230  implements any combination of two modes to increase the available run time by dropping certain loads: drop 240V load mode, protected load mode, or drop 240v mode and protected load mode. 
     The drop 240V load mode occurs while the inverter is operating on battery power and the state-of-charge is sufficient to operate the connected loads in a split-phase configuration (i.e., AC power is produced on two 120v phases 180 degrees out of phase of each other). 120V Loads on L1 and L2 operate from their respective phases and any 240v loads connected between L1 and L2 are powered. Once the battery  234  discharges below a user preset level, or SOC, L1 and L2 phase references, which are normally 180 degrees out of phase, are both connected to L1. That will put both L1 and L2 AC outputs in phase and drop any 240V loads. The phase difference of L2 may be shifted slowly until it is in phase with L1, or it may be done by dropping ½ cycle. 
     Alternatively, in a drop L1 or L2 mode, either L1 or L2 can be designated as the priority phase. In this case, once the battery discharges below user preset level (level2), the priority phase remains on, and the non-priority phase turns off. The priority phase maintains output until the low battery threshold, or minimum State of charge (SOC), is reached, at which point the priority phase is turned off. Once the battery is recharged, normal operation resumes and both phases are reset to their default state. 
     In the protected load mode, the generator input may be used as a load control switched output when an inverter is used without a generator. Critical loads are connected to the LOAD terminals of the inverter. Any other loads are connected to the generator (GEN) terminals. So long as the battery  234  maintains a minimum state of charge, loads connected to the GEN terminals are operated normally. Once the battery level drops below a user preset level, the GEN terminals disconnect, shedding the loads connected thereto. At this point, only critical loads connected to the LOAD terminals will be maintained. 
     In the drop 240v mode and protected load mode, both of these modes are combined to allow loads to be shed depending upon user requirements. 
     Each of the example controllers will now be described in further detail. As example of the logic that may be implemented by the controller portion of the example power control system  230  is depicted in  FIGS. 8 and 9 . 
     The example system controller  270  provides a method to start and stop the example power control system  230 . The example system controller  270  provides the battery management system (state of charge, charging mode, etc.). The example system controller  270  starts and stops the generator  236 . The example system controller  270  acquires data from each of the example power control system  230  controllers connected to the example controller area network  274 . The example system controller  270  provides a method to update the firmware embedded within each of the controllers via the example controller area network  274 . 
     The example power metering board  272  reads high resolution analog voltage and current sensors that are used to measure the power transferred to/from the grid  232  and from the generator  236  and to the load. The example power metering board  272  also outputs four digital zero-cross signals directly to the example neutral-point-clamp  258  that are used to synchronize the off-grid AC output to the grid/generator prior to relay closure. Lastly, the example power metering board  272  controls the AC power interconnection relay (K 15 )  60  for the example neutral-point-clamp  258 , generator  236  (K 3 ,K 6 ), and grid  232  (K 2 ,K 5 ). 
     The example BB component  252  transfers power from the PV array  238  to the DC bus  250 . The example BB component  252  can regulate the DC bus voltage whenever: 
     1. the example power control system  230  is NOT grid-tied, and 
     2. the battery  234  state of charge is insufficient, and 
     3. the available PV power meets or exceeds the load power. 
     The example dual active bridge  256  can transfer power from the battery  234  to the DC bus  250  (discharge), or the example dual active bridge  256  can transfer power to the battery  234  from the DC bus  250  (charge). The example dual active bridge  256  can regulate the DC bus  250  voltage whenever: 
     1. the example power control system  230  is NOT grid-tied, and 
     2. the battery  234  state of charge is sufficient. 
     Depending on the battery  234  state of charge and the grid/generator state, the example system controller  270  determines when and how the example dual active bridge  256  charges the battery  234 . 
     The example neutral-point-clamp  258  can transfer power from an AC source (grid or generator) to the DC bus  250 , or the example neutral-point-clamp  258  can transfer power from the DC bus  250  to the AC grid  232  and load  222 . The example neutral-point-clamp  258  can regulate the DC bus  250  voltage whenever the example power control system  230  is grid-tied. The example neutral-point-clamp  258  can regulate the AC load voltage whenever the example power control system  230  is NOT grid-tied. 
     DC Bus Voltage Control 
     At the heart of the power control system  230  is the high voltage DC bus  250 . The DC bus  250  is used to exchange power between the various sources and loads. Exactly one of the power control system  230  elements may control the DC bus voltage at any given moment. The particular choice is dependent on:
         grid  232  status   generator  236  status   battery  234  state   PV system  238  state       

     When grid-tied, the example neutral-point-clamp  258  controls the DC bus  250  by pulling/pushing power from/to the AC grid  232 . 
     When off-grid AND generator  236  is running, the example neutral-point-clamp  258  controls the DC bus  250  by pulling power from the generator  236 . 
     When off-grid AND generator  236  is offline AND the battery  234  contains sufficient charge, the example dual active bridge  256  controls the DC bus  250  by pulling/pushing power from/to the battery  234 . The battery  234  state of charge is determined by the example system controller  270 . 
     When off-grid AND generator  236  is offline AND battery  234  is empty AND the PV system  238  power is insufficient, the power control system  230  is completely shut-down and disconnected until manually reset by the example system controller  270 . 
     Synchronization 
     Grid 
     When K 15   262  is closed AND K 2 +K 5   264  is closed, the example neutral-point-clamp  258  attempts to lock onto the grid 50/60 hz line voltage frequency. If the example neutral-point-clamp  258  has established phase lock with both L1 and L2, the power control system  230  is grid-tied. Otherwise, the power control system  230  is off-grid. The example power metering board  272  controls the relays. 
     Generator 
     When K 15   262  is closed AND K 3 +K 6   266  is closed, the example neutral-point-clamp  258  attempts to lock onto the generator 50/60 hz line voltage frequency. If the example neutral-point-clamp  258  has established phase lock with both L1 and L2, the generator  236  is running. Otherwise, the generator  236  is offline. The example power metering board  272  controls the relays. 
     No AC Source 
     As generally shown in  FIG. 7 , when K 15   262  is closed and K 2 +K 3 +K 5 +K 6  ( 264  and  266 ) are open, the example neutral-point-clamp  258  has no external AC source to lock onto, so the example neutral-point-clamp  258  must generate the AC line voltage and frequency. When either the grid or generator AC sources become available, the example neutral-point-clamp  258  must resynchronize to the AC source before reconnecting it. Only after the example neutral-point-clamp  258  has re-synchronized to the digital sync signals provided by the PMB+relay board can K 3 +K 6   266  or K 2 +K 5   264  be safely closed. 
     PCS Operating Mode 
     Grid-Tied 
     The generator  236  is disconnected (K 3 +K 6   266  open) and the grid is connected (K 2 +K 5   264  closed) in grid-tied mode. While in this mode the example neutral-point-clamp  258  regulates the DC bus voltage by importing/exporting power from/to the grid, and the example BB component  252  injects maximum power from the PV array  238  into the DC bus  250 . The example dual active bridge  256  may consume some of the DC bus  250  power in order to charge the battery  234 . If the net-zero mode is enabled, the example BB component  252  component  252  limits the injected power to match the AC load  222 +battery  234  power so that no power is exported. 
     If/when the grid is lost, the power control system  230  operating mode automatically switches to off-grid with battery mode. 
     Off-Grid with Battery 
     Both AC sources (grid and generator  236 ) are disconnected (K 2 +K 3 +K 5 +K 6   264  and  266  open) in off-grid with battery mode. While in this mode the example dual active bridge  256  regulates the DC bus  250  voltage by either charging or discharging the battery  234 , and the example neutral-point-clamp  258  regulates the load voltage. The example BB component  252  will usually inject maximum power from the PV array  238  into the DC bus  250 . Any PV power in excess of the load  222  demand will be charged into the battery  234 . The example BB component  252  must limit the power injected to the DC bus  250  to be no more than the power demanded by the load  222  plus the power being charged into the battery  234 . 
     If/when the AC grid  232  is restored, the example neutral-point-clamp  258  must synchronize the AC output with the digital sync signals generated by the example power metering board  272  to match the grid  232 . Once the AC output is locked, the example power metering board  272  can reconnect the grid  232  (K 2 +K 5   264  closed). Once the relay is closed, the example neutral-point-clamp  258  will lock onto the actual grid line voltage (analog rather than digital), and the power control system  230  operating mode automatically switches to grid-tied mode. 
     If/when the generator  236  is available, the example neutral-point-clamp  258  must synchronize the AC output with the digital sync signals generated by the example power metering board  272  to match the generator  236 . Once the AC output is locked, the example power metering board  272  can reconnect the generator  236  (K 3 +K 6   266  closed). Once the relay is closed, the example neutral-point-clamp  258  will lock onto the actual generator  236  line voltage (analog rather than digital), and the power control system  230  operating mode automatically switches to generator mode. 
     If/when the battery  234  is depleted and/or cannot support the AC load  222 , the power control system  230  must shutdown and disconnect (K 15   262  open) until manually reset. 
     Generator 
     The grid  232  is disconnected (K 2 +K 5   264  open), and the generator  236  is connected (K 3 +K 6   266  closed) in generator mode. While in this mode the example neutral-point-clamp  258  locks onto the generator line voltage and regulates the DC bus  250  voltage. The generator power is consumed directly by the load  222 , but any excess power available from the generator  236  and PV system  238  can be charged into the battery  234  by the example dual active bridge  256 . The example BB component  252  must limit the PV array  238  power injected such that no power is exported. 
     If/when the battery  234  is fully charged OR if/when the grid  232  is restored OR if the generator  236  is unavailable, the operating mode automatically switches to off-grid with battery mode. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Relay configuration 
               
            
           
           
               
               
               
               
            
               
                 Grid 
                 Gen 
                 NPC 
                   
               
               
                 K2, K5 
                 K3, K6 
                 K15 
                 operating mode 
               
               
                   
               
               
                 0 
                 0 
                 0 
                 no power distributed 
               
               
                 0 
                 0 
                 1 
                 offgrid with battery 
               
               
                 0 
                 1 
                 0 
                 generator to load only, PCS off 
               
               
                 0 
                 1 
                 1 
                 generator to battery + load 
               
               
                 1 
                 0 
                 0 
                 bypass: load = grid, PCS off 
               
               
                 1 
                 0 
                 1 
                 grid-tied 
               
               
                 1 
                 1 
                 0 
                 Destructive 
               
               
                 1 
                 1 
                 1 
                 Destructive 
               
               
                   
               
            
           
         
       
     
     There are 8 possible relay configurations. One does not transfer power, two may be destructive, two of the configurations have the power control system  230  disconnected, and the remaining three modes are useful:
         offgrid with battery   generator   grid-tied
 
Inner-Processor Communications
       

     The CAN message (data frame) is defined by the CAN 2.0b specification and contains three main sections: header, payload, and trailer. 
     1. header contains three sections: start, arbitration, and DLC. 
     
         
         
           
             1.1. start 
             1.2. arbitration contains four sections: ID, SRR, IDE and RTR, and uses the extended data frame.
           1.2.1. ID is 29-bit message identifier and contains 5 usable fields, not including reserved bits.
               1.2.1.1. b28-b27: PRIORITY=0 (not currently used).   1.2.1.2. b26-b23: TO=destination ID:
                   {ALL=0,PMB=1,NPC=2,SC=3,DAB=4,BB=5}.   
                   1.2.1.3. b22-b19: FROM=source ID:
                   {ALL=0,PMB=1,NPC=2,SC=3,DAB=4,BB=5}.   
                   1.2.1.4. b18-b17: TYPE   1.2.1.4.1. GET=0: request the value of a parameter.   1.2.1.4.2. SET=1: assign the value of a parameter.   1.2.1.4.3. REPLY=2: report the value of a parameter.   
               1.2.1.5. b16-b9: reserved   1.2.1.6. b8-b0: PARAM
               1.2.1.6.1. 0-0x1F: common to all Sikorsky controllers.   1.2.1.6.2. 0x20-0x1FF: specific to each Sikorsky controller.   
               1.2.2. SRR=Substitute Remote Request (not currently used).   1.2.3. IDE=Identifier Extension (=1:29-bit ID).   1.2.4. RTR=Remote Transmission Request (not currently used).   
         
             1.3. DLC=Data Length Code=number of bytes in payload section.
 
2. payload=0-8 bytes, defined by paramID (see tables 2-5).
 
3. trailer
 
             3.1.1. CRC=Cyclic Redundancy Check 
             3.1.2. ACK=acknowledge 
             3.1.3. end 
           
         
       
    
     Set 
     The SET type message is used by the sender to assign a parameter value on the receiver. 
     Get 
     The GET type message is used by the sender to request the value of a parameter from the receiver. The receiver responds to a GET message with a STATUS message. 
     Reply 
     The REPLY type message is sent in response to a GET message, but it can be sent asynchronously (without a GET message) by the sender to the receiver. 
     Given the foregoing, it should be apparent that the principles of the present invention may be embodied in forms other than those described above. The scope of the present invention should thus be determined by the claims to be appended hereto and not the foregoing detailed description of the invention.