Electric power distribution methods and apparatus

Abstract

A plurality of end-user locations are served by a commercial utility grid. More than one and less than all of the end-user locations are themselves interconnected by a feeder, the feeder not metallically connected to the utility grid. The end-user locations each have a local AC bus that is not metallically connected to the utility grid or to the feeder, but that is linked by a coupler to both the utility grid and to the feeder. None of the local AC buses or the feeder is required to have the same phase or frequency as the utility grid. Locally generated electric power may be passed by means of the feeder to other end-user locations that are on the feeder. Each local AC bus has two or more inverters powering the bus.

1 . A system for use with AC power at a frequency, the frequency defining a period, the system comprising:
 an AC feeder;   a control path, the control path being separate from the AC feeder, the control path communicating control information with a latency no greater than one-tenth the period of the AC power;   at least two inverters, each inverter receiving DC power from a respective DC power source, each inverter having an AC output metallically connected to the AC feeder, the metallic connection free of any electrical transformer, the respective DC power sources isolated from each other;   each inverter disposed in a first state to generate AC power unsynchronized with any other AC phase, and in said first state to measure its AC output phase and to communicate that phase external to the inverter by means of the control path;   each inverter disposed in a second state to receive an AC phase signal from external to the inverter by means of the control path, and to generate AC power synchronized with the received AC phase signal, said AC power provided to the AC feeder;   control means responsive to a predetermined event causing the first one of the at least two inverters to take said first state and causing any other inverters to take said second state;   said means after said predetermined event responding to failure of the first one of the at least two inverters by causing an inverter other than the first one of the at least two inverters to change to said first state;   said changes of state occurring within an interval less than one-half the period of the AC power;   the AC feeder having loads drawing AC power therefrom.   
     
     
         2 . The system of  claim 1  wherein the number of inverters is at least three. 
     
     
         3 . The system of  claim 1  wherein each inverter generates wye three-phase electrical power. 
     
     
         4 . A method for use with a power system, the power system comprising a utility grid providing AC electric power connectivity and extending geographically to a plurality of first end-user locations and to a plurality of second end-user locations, the first end-user locations comprising more than one and less than all of the end-user locations of the utility grid, each of the first end-user locations comprising a local bus providing AC electric power connectivity, each local bus having associated with it at least one AC load metallically connected thereto and drawing power therefrom, each local bus coupled by means of a respective first at least one coupler to the utility grid, the at least one coupler comprising a first power-supply-inverter and a second power-supply-inverter, each power-supply-inverter having an AC interface and a DC interface and a controller, each power-supply-inverter disposed in a first mode to receive DC power received at the DC interface and to generate AC power delivered at the AC interface, and disposed in a second mode to receive AC power received at the AC interface and to generate DC power delivered at the DC interface, the DC interface of the first power-supply-inverter electrically connected to the DC interface of the second power-supply-inverter, whereby the at least one coupler has a first AC interface defined as the AC interface of the first power-supply-inverter and a second AC interface defined as the AC interface of the second power-supply-inverter, the controller of the first power-supply-inverter and the controller of the second power-supply-inverter coupled so as to prevent the first power-supply-inverter and the second power-supply-inverter from being in the first mode simultaneously for extended intervals, and so as to prevent the first power-supply-inverter and the second power-supply-inverter from being in the second mode simultaneously for extended intervals, each power-supply-inverter disposed when in its first mode to generate its AC power delivered at its AC interface consistent in voltage and phase and frequency with any AC power present external to said AC interface, the power system further comprising a feeder providing AC electric power connectivity and extending geographically to the plurality of first end-user locations, each local bus coupled by means of a respective second at least one coupler to the feeder, the feeder being unsynchronized with the utility grid, the method comprising the steps of:
 at a first time, powering each of the local buses by means of a respective coupler drawing power from the utility grid;   at a second time, generating locally generated electrical power at one of the first end-user locations, and passing some of said locally generated electrical power to others of the first end-user locations by means of the feeder.   
     
     
         5 . A method for use with a system, the system for use with AC power at a frequency, the frequency defining a period, the system comprising an AC feeder;
 a control path, the control path being separate from the AC feeder, the control path communicating control information with a latency no greater than one-tenth the period of the AC power;   at least two inverters, each inverter receiving DC power from a respective DC power source, each inverter having an AC output metallically connected to the AC feeder, the metallic connection free of any electrical transformer, the respective DC power sources isolated from each other;   each inverter disposed in a first state to generate AC power unsynchronized with any other AC phase, and in said first state to measure its AC output phase and to communicate that phase external to the inverter by means of the control path;   each inverter disposed in a second state to receive an AC phase signal from external to the inverter by means of the control path, and to generate AC power synchronized with the received AC phase signal, said AC power provided to the AC feeder;   the AC feeder having loads drawing AC power therefrom;   the method comprising:   at a first time, causing the first one of the at least two inverters to take said first state and causing any other inverters to take said second state;   in response to failure of the first one of the at least two inverters, causing an inverter other than the first one of the at least two inverters to change to said first state, said changes of state occurring within an interval less than one-half the period of the AC power.   
     
     
         6 . A system comprising:
 a three-wire AC power grid;   at least one four-wire wye inverter connected to the AC power grid and serving as a voltage source therefor, the at least one four-wire wye inverter having a respective first power output, any power on the AC power grid having a power quality, the power on the AC power grid defining a voltage and frequency for each phase thereof;   a three-wire inverter connected to the AC power grid and serving as a current source therefor, the three-wire inverter having a respective power output;   the four-wire inverter disposed to sample the voltage on each phase of the AC power grid, and to source or sink power on each phase of the AC power grid so as to dynamically maintain frequency and voltage regulation and improve the power quality of the power on the AC power grid.   
     
     
         7 . A system comprising:
 a three-wire AC power grid;   at least one four-wire wye inverter connected to the AC power grid and serving as a voltage source therefor, the at last one four-wire wye inverter having a respective first power output, any power on the AC power grid having a power quality, the power on the AC power grid defining a voltage for each phase thereof;   an induction generator connected to the AC power grid and serving as a current source therefor, the induction generator having a respective power output;   the four-wire inverter disposed to sample the voltage on each phase of the AC power grid, and to source or sink power on each phase of the AC power grid so as to dynamically maintain frequency and voltage regulation and improve the power quality of the power on the AC power grid.   
     
     
         8 . A method for use with a system comprising a three-wire AC power grid, at least one four-wire wye inverter connected to the AC power grid and serving as a voltage source therefor, the at least one four-wire wye inverter having a respective first power output, any power on the AC power grid having a power quality, the power on the AC power grid defining a voltage for each phase thereof, an additional AC current source connected to the AC power grid and serving as a current source therefor, the additional AC current source having a respective power output, the method comprising the steps of:
 at the four-wire inverter, sampling the voltage on each phase of the AC power grid, and   sourcing or sinking power on each phase of the AC power grid so as to dynamically maintain frequency and voltage regulation and improve the power quality of the power on the AC power grid.   
     
     
         9 . A system comprising:
 a three-wire AC power grid;   a generator connected to the AC power grid and serving as a voltage source therefor, any power on the AC power grid having a power quality, the power on the AC power grid defining a voltage for each phase thereof;   a four-wire wye inverter connected to the AC power grid, the four-wire wye inverter also connected to a DC bus, the DC bus having DC power storage connected thereto;   the four-wire inverter disposed to sample the voltage on each phase of the AC power grid, and to source or sink power on each phase of the AC power grid so as to dynamically maintain frequency and voltage regulation and improve the power quality of the power on the AC power grid.   
     
     
         10 . A method for use with a system comprising a three-wire AC power grid, a first generator connected to the AC power grid and serving as a voltage source therefor, any power on the AC power grid having a power quality, the power on the AC power grid defining a voltage for each phase thereof, a four-wire wye inverter connected to the AC power grid, the four-wire wye inverter also connected to a DC bus, the DC bus having DC power storage connected thereto, the method comprising the steps of:
 at the four-wire inverter, sampling the voltage on each phase of the AC power grid, and   sourcing or sinking power on each phase of the AC power grid so as to dynamically maintain frequency and voltage regulation and improve the power quality of the power on the AC power grid.   
     
     
         11 . A method for use with a first bus and a second bus, the first bus and the second bus connected by a breaker, and with a plurality of inverters, each inverter providing AC power to the first bus at a first voltage, each inverter defining some maximum current associated therewith, the method comprising the steps of:
 sensing a fault on the second bus by means of voltage sensing;   in the event of a sensed fault, releasing each inverter to feed its maximum possible current to the first bus.   
     
     
         12 . The method of  claim 11  further comprising the step, performed after the releasing step, of detecting a return of the first voltage, and thereafter, ceasing the feeding of maximum possible current to the first bus. 
     
     
         13 . A system comprising a first bus and a second bus, the first bus and the second bus connected by a breaker, and a plurality of inverters, each inverter providing AC power to the first bus at a first voltage, each inverter defining some maximum current associated therewith, each inverter responsive to a sensed fault sensed by means of voltage sensing by delivering its maximum possible current to the first bus. 
     
     
         14 . The system of  claim 13  wherein each inverter is further responsive to detection of a return of the first voltage by ceasing the delivery of the maximum possible current to the first bus. 
     
     
         15 . An inverter, the inverter providing AC power at a first voltage, each inverter defining some maximum current associated therewith, each inverter responsive to a sensed fault sensed by means of voltage sensing by delivering its maximum possible current. 
     
     
         16 . The inverter of  claim 15  wherein the inverter is further responsive to detection of a return of the first voltage by ceasing the delivery of the maximum possible current. 
     
     
         17 . A system comprising a first DC bus, a second DC bus, a feeder, a first AC bus, a second AC bus, and first and second transformers each connected with the feeder;
 the system further comprising a first inverter coupling the first AC bus with the first DC bus, a second inverter coupling the second AC bus with the second DC bus;   a third inverter coupling the first DC bus with the first transformer;   a fourth inverter coupling the second DC bus with the second transformer;   a first load connected with the first AC bus;   a first generator connected with the feeder, the first generator having a power output level;   a second load connected with the feeder;   a second generator connected with the second DC bus and having a power output level;   the second load consuming power amounting to at least the power output of the first generator;   the first load consuming power amounting to at least a portion of the power output of the second generator.   
     
     
         18 . A method for use with system comprising a first DC bus, a second DC bus, a feeder, a first AC bus, a second AC bus, and first and second transformers each connected with the feeder;
 the system further comprising a first inverter coupling the first AC bus with the first DC bus, a second inverter coupling the second AC bus with the second DC bus;   a third inverter coupling the first DC bus with the first transformer;   a fourth inverter coupling the second DC bus with the second transformer;   a first load connected with the first AC bus;   a first generator connected with the feeder, the first generator having a power output level;   a second load connected with the feeder;   a second generator connected with the second DC bus and having a power output level, the method comprising the steps of:   generating power at the first generator at a respective power output level;   generating power at the second generator at a respective power output level;   at the second load, consuming power amounting to at least the power output of the first generator;   and at the first load, consuming power amounting to at least a portion of the power output of the second generator.   
     
     
         19 . A system comprising a first DC bus, a second DC bus, a feeder, a first AC bus, a second AC bus, and first and second transformers each connected with the feeder;
 the system further comprising a first inverter coupling the first AC bus with the first DC bus, a second inverter coupling the second AC bus with the second DC bus;   a third inverter coupling the first DC bus with the first transformer;   a fourth inverter coupling the second DC bus with the second transformer;   a first load connected with the first AC bus;   a first generator connected with the feeder, the first generator having a power output level;   a second load connected with the feeder;   a second generator connected with the second DC bus and having a power output level;   the second load consuming power amounting to at least the power output of the first generator;   the first load consuming power amounting to at least a portion of the power output of the second generator;   the first and second AC buses not synchronized with each other;   the feeder not synchronized with either of the first and second AC buses.   
     
     
         20 . A method for use with system comprising a first DC bus, a second DC bus, a feeder, a first AC bus, a second AC bus, and first and second transformers each connected with the feeder;
 the system further comprising a first inverter coupling the first AC bus with the first DC bus, a second inverter coupling the second AC bus with the second DC bus;   a third inverter coupling the first DC bus with the first transformer;   a fourth inverter coupling the second DC bus with the second transformer;   a first load connected with the first AC bus;   a first generator connected with the feeder, the first generator having a power output level;   a second load connected with the feeder;   a second generator connected with the second DC bus and having a power output level, the method comprising the steps of:   generating power at the first generator at a respective power output level;   generating power at the second generator at a respective power output level, the power generated at the second generator not synchronized with the power generated at the first generator;   at the second load, consuming power amounting to at least the power output of the first generator, the power consumed at the second load not synchronized with the power generated at the first generator and not synchronized with the power generated at the second generator;   and at the first load, consuming power amounting to at least a portion of the power output of the second generator.   
     
     
         21 . A system comprising a first DC bus, a second DC bus, a feeder, a first AC bus, a second AC bus, and first and second transformers each connected with the feeder;
 the system further comprising a first inverter coupling the first AC bus with the first DC bus, a second inverter coupling the second AC bus with the second DC bus;   a third inverter coupling the first DC bus with the first transformer;   a fourth inverter coupling the second DC bus with the second transformer;   a first load connected with the first AC bus;   a second generator connected with the second DC bus and having a power output level;   the first load consuming power amounting to at least a portion of the power output of the second generator.   
     
     
         22 . A method for use with system comprising a first DC bus, a second DC bus, a feeder, a first AC bus, a second AC bus, and first and second transformers each connected with the feeder;
 the system further comprising a first inverter coupling the first AC bus with the first DC bus, a second inverter coupling the second AC bus with the second DC bus;   a third inverter coupling the first DC bus with the first transformer;   a fourth inverter coupling the second DC bus with the second transformer;   a load connected with the first AC bus;   a generator connected with the second DC bus and having a power output level, the method comprising the steps of:   generating power at the generator at a respective power output level;   at the load, consuming power amounting to at least a portion of the power output of the generator.