Method and apparatus for time-domain droop control with integrated phasor current control

Patent metadata

Field	Value
Publication number	US-2016248253-A1
Application number	US-201615048651-A
Country	US
Kind code	A1
Filing date	Feb 19, 2016
Priority date	Feb 19, 2015
Publication date	Aug 25, 2016
Grant date	—

Abstract

A method and apparatus for power converter current control. In one embodiment, the method comprises controlling an instantaneous current generated by a power converter such that that power converter appears, from the perspective of an AC line coupled to the power converter, as a virtual AC voltage source in series with a virtual impedance, wherein real and reactive phasor currents for the power converter are indirectly controlled by modifying amplitude and phase of a virtual AC voltage waveform that defines the virtual AC voltage source.

First claim

1 . A method for power converter current control, comprising:
controlling an instantaneous current generated by a power converter such that that power converter appears, from the perspective of an AC line coupled to the power converter, as a virtual AC voltage source in series with a virtual impedance, wherein real and reactive phasor currents for the power converter are indirectly controlled by modifying amplitude and phase of a virtual AC voltage waveform that defines the virtual AC voltage source.

2 . The method of claim 1 , wherein the instantaneous current is determined by:
determining a desired real phasor current value and a desired reactive phasor current value by a droop control technique; generating a controlled real phasor current value based on a comparison between the desired real phasor current value and a real phasor current threshold; generating a controlled reactive phasor current value based on a comparison between the desired reactive phasor current value and a reactive phasor current threshold; computing the virtual AC voltage waveform based on the controlled real and reactive phasor current values; and determining an instantaneous current value for driving the power converter to emulate the virtual impedance in the time domain while generating an amount of real and reactive current equal to the controlled real and reactive phasor current values.

3 . The method of claim 2 , wherein the real and reactive phasor current thresholds are determined using one or more current limiting techniques.

4 . The method of claim 3 , wherein the current limiting techniques comprise one or more of maximum power point tracking (MPPT), economic optimization, charge control, advanced grid functions, or demand response.

5 . The method of claim 2 , wherein the droop technique is a phase-shifted virtual voltage-virtual impedance droop technique, wherein the virtual AC voltage waveform is a sinusoidal waveform having a constant amplitude and a phase shifted from the frequency of the AC line by an amount proportional to the difference between a measured frequency of the AC line and a nominal frequency of the AC line.

6 . The method of claim 4 , wherein:
if the desired real phasor current value is greater than the real phasor current threshold, the controlled real phasor current value is set equal to the real phasor current threshold; if the desired real phasor current value is less than the negative of the real phasor current threshold, the controlled real phasor current value is set equal to the negative of the real phasor current threshold; if the desired reactive phasor current value is greater than the reactive phasor current threshold, the controlled reactive phasor current value is set equal to the reactive phasor current threshold; and if the desired reactive phasor current value is less than the negative of the reactive phasor current threshold, the controlled reactive phasor current value is set equal to the negative of the reactive phasor current threshold.

7 . The method of claim 3 , wherein the instantaneous current is controlled such that the power converter appears as the virtual AC voltage source when the power converter is grid-connected and when the power converter is islanded to enable a seamless transition between operating in a grid-connected state and operating in an islanded state.

8 . An apparatus for power converter current control, comprising:
a controller for controlling an instantaneous current generated by a power converter such that that power converter appears, from the perspective of an AC line coupled to the power converter, as a virtual AC voltage source in series with a virtual impedance, wherein real and reactive phasor currents for the power converter are indirectly controlled by modifying amplitude and phase of a virtual AC voltage waveform that defines the virtual AC voltage source.

9 . The apparatus of claim 8 , wherein the instantaneous current is determined by:
determining a desired real phasor current value and a desired reactive phasor current value by a droop control technique; generating a controlled real phasor current value based on a comparison between the real phasor current value and a real current threshold; generating a controlled reactive phasor current value based on a comparison between the reactive phasor current value and a reactive current threshold; computing the virtual AC voltage waveform based on the controlled real and reactive phasor current values; and determining an instantaneous current value for driving the power converter to emulate the virtual impedance in the time domain while generating an amount of real and reactive current equal to the controlled real and reactive phasor current values.

10 . The apparatus of claim 9 , wherein the real and reactive phasor current thresholds are determined using one or more current limiting techniques.

11 . The apparatus of claim 10 , wherein the current limiting techniques comprise one or more of maximum power point tracking (MPPT), economic optimization, charge control, advanced grid functions, or demand response.

12 . The apparatus of claim 9 , wherein the droop technique is a phase-shifted virtual voltage-virtual impedance droop technique, wherein the virtual AC voltage waveform is a sinusoidal waveform having a constant amplitude and a phase shifted from the frequency of the AC line by an amount proportional to the difference between a measured frequency of the AC line and a nominal frequency of the AC line.

13 . The apparatus of claim 11 , wherein:
if the desired real phasor current value is greater than the real phasor current threshold, the controlled real phasor current value is set equal to the real phasor current threshold; if the desired real phasor current value is less than the negative of the real phasor current threshold, the controlled real phasor current value is set equal to the negative of the real phasor current threshold; if the desired reactive phasor current value is greater than the reactive phasor current threshold, the controlled reactive phasor current value is set equal to the reactive phasor current threshold; and if the desired reactive phasor current value is less than the negative of the reactive phasor current threshold, the controlled reactive phasor current value is set equal to the negative of the reactive phasor current threshold.

14 . The apparatus of claim 10 , wherein the instantaneous current is controlled such that the power converter appears as the virtual AC voltage source when the power converter is grid-connected and when the power converter is islanded to enable a seamless transition between operating in a grid-connected state and operating in an islanded state.

15 . A system for generating power, comprising:
a plurality of power sources; and a plurality of power converters, coupled to one another via an AC line and coupled to the plurality of power sources in a one-to-one correspondence, wherein each power converter of the plurality of power converters comprises a controller for controlling an instantaneous current generated by the power converter such that that power converter appears, from the perspective of the AC line coupled to the power converter, as a virtual AC voltage source in series with a virtual impedance, wherein real and reactive phasor currents for the power converter are indirectly controlled by modifying amplitude and phase of a virtual AC voltage waveform that defines the virtual AC voltage source.

16 . The system of claim 15 , wherein the instantaneous current is determined by:
determining a des

Assignees

• Enphase Energy Inc

Inventors

• Zimmanck Donald Richard

Classifications

• H02M5/02

  without intermediate conversion into DC · CPC title

• H02J2101/20

  Dispersed power generation using renewable energy sources · CPC title

• H02J3/382 Primary

  Electricity · mapped topic

• H02J3/50

  Controlling the sharing of reactive power · CPC title

• H02J3/48

  Controlling the sharing of active power · CPC title