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A reactive power compensation system includes a distributed energy resource situated at a local location configured to also receive power from a remote location by a distribution feeder line. The distributed energy resource includes an inverter including power semiconductor switching devices and an

A reactive power compensation system includes a distributed energy resource situated at a local location configured to also receive power from a remote location by a distribution feeder line. The distributed energy resource includes an inverter including power semiconductor switching devices and an inverter controller configured for controlling the power semiconductor switching devices so as to provide reactive power support to the distribution feeder line.

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The invention claimed is: 1. A reactive power compensation system comprising: a distributed energy resource situated at a local location, the local location being configured to also receive power from a remote location by a distribution feeder line, the distributed energy resource comprising an inv

The invention claimed is: 1. A reactive power compensation system comprising: a distributed energy resource situated at a local location, the local location being configured to also receive power from a remote location by a distribution feeder line, the distributed energy resource comprising an inverter; wherein the inverter comprises power semiconductor switching devices and an inverter controller configured for controlling the power semiconductor switching devices so as to provide reactive power support to the distribution feeder line; and a distribution management system configured for providing a reactive power command and a communication link configured for providing the reactive power command to the inverter such that reactive power is adjusted in a predetermined manner to maintain voltage stability associated with the distribution feeder line. 2. The compensation system of claim 1 wherein the inverter further comprises a sensor configured for sensing voltage on the feeder line, and wherein the inverter controller is further configured for using the sensed voltage to calculate an inverter output voltage adjustment designed to provide the reactive power support. 3. The compensation system of claim 1 wherein the distributed energy resource comprises a plurality of distributed energy resources, and wherein the distribution management system is configured for providing a plurality of respective reactive power commands. 4. The compensation system of claim 3 wherein the communication link comprises a unidirectional communication link. 5. The compensation system of claim 3 wherein the distribution management system is further configured for establishing the plurality of reactive power commands. 6. The compensation system of claim 5 wherein the communication link comprises a bi-directional communication link. 7. The compensation system of claim 6 wherein the inverters each are configured to supply an operational status signal to the distribution management system. 8. The compensation system of claim 7 wherein the distribution management system is further configured for using the operational status signals to establish the plurality of reactive power commands. 9. The compensation system of claim 1 wherein the compensation system is further configured with a processor for: using instantaneous feeder line voltage and phase angle measurements to obtain a voltage phasor magnitude and an estimated voltage phase; dividing the reactive power command by the voltage phasor magnitude to obtain a reactive current command; dividing a real power command by the voltage phasor magnitude to obtain a real current command; calculating an inverter current magnitude command from the reactive current command and the real current command; calculating an estimated current phase from the reactive current command and the real current command; adding the estimated current phase to the estimated voltage phase to obtain an inverter current phase angle command. 10. The compensation system of claim 9 wherein the inverter controller comprises the processor. 11. The compensation system of claim 9 wherein the processor is situated outside of the inverter. 12. The compensation system of claim 9 further comprising a distribution management system configured for providing a reactive power command and a communication link configured for providing the reactive power command to the inverter, and wherein the processor is further configured for using a power distribution system frequency in addition to the instantaneous feeder line voltage and phase angle signals to obtain the voltage phasor magnitude and the estimated voltage phase. 13. The compensation system of claim 12 wherein the distribution management system is configured to supply the power distribution system frequency to the inverter controller through the communication link. 14. The compensation system of claim 12 wherein the inverter controller is further configured to derive the power system frequency using two consecutive voltage phasor estimates. 15. The compensation system of claim 1 further comprising a low pass filter for obtaining a voltage phasor magnitude estimate from an instantaneous feeder line voltage measurement; a phase locked loop for obtaining an estimated voltage phase from an instantaneous feeder line voltage phase angle measurement; a divider for dividing the reactive power command by the voltage phasor magnitude to obtain a reactive current command; a divider for dividing a real power command by the voltage phasor magnitude to obtain a real current command; a current magnitude command calculator for calculating an inverter current magnitude command from the reactive current command and the real current command; a current phase command calculator for calculating an estimated current phase from the reactive current command and the real current command; a summation element for adding the estimated current phase to the estimated voltage phase to obtain an inverter current phase angle command. 16. The compensation system of claim 1 wherein the distributed energy resource comprises a photovoltaic system comprising a photovoltaic array. 17. The compensation system of claim 16 wherein the local location comprises a building and wherein the photovoltaic array and the inverter are situated outside the building. 18. The compensation system of claim 17 further comprising a distribution panel and a lockable disconnect, wherein the lockable disconnect is situated outside of the building and configured for coupling to inverter to the distribution panel. 19. The compensation system of claim 16 wherein the local location comprises a building, and wherein the inverter is situated inside to building. 20. The compensation system of claim 19 further comprising a distribution panel and a lockable disconnect wherein the lockable disconnect is situated outside of the building and configured for coupling the inverter to the distribution panel. 21. The compensation system of claim 20 further comprising an additional lockable disconnect situated inside of the building and configured for coupling the lockable disconnect to the distribution panel. 22. The compensation system of claim 16 wherein the local location comprises a building, wherein the photovoltaic array and the inverter are situated outside the building; and further comprising an energy storage device configured for supplying power to the inverter when power from the photovoltaic system is insufficient to meet building load demands. 23. The compensation system of claim 16 wherein the local location comprises a building, wherein the inverter is situated inside the building; and further comprising an energy storage device configured for supplying power to the inverter when power from the photovoltaic system is insufficient to meet building load demands. 24. A reactive power compensation method comprising: providing a distributed energy resource at a local location configured to also receive power from a remote location by a distribution feeder line, the distributed energy resource comprising an inverter; and using the inverter to provide reactive power support to the distribution feeder line such that reactive power is adjusted in a predetermined manner to maintain voltage stability associated with the distribution feeder line.