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US-12627139-B2 - Systems and methods of power-voltage droop control for a direct current (DC) microgrid

US12627139B2US 12627139 B2US12627139 B2US 12627139B2US-12627139-B2

Abstract

A direct current (DC) microgrid is provided. The microgrid includes a power converter, a power-voltage (PV) droop control loop, and an inner current control loop of the power converter. The PV droop control loop is configured to receive measurements of a droop current quantity that is not a DC bus current of the DC microgrid. The droop current quantity is used to determine a droop power quantity selected as a power quantity in a PV relationship. The PV droop control loop is further configured to derive a current reference based on droop in the droop power quantity. The inner current control loop is configured to control operation of the power converter by deriving a measured current corresponding to the control quantity based on the measurements of the droop current quantity, directly comparing the current reference with the measured current, and generating switching signals of switches in the power converter.

Inventors

  • Govind Sahadeo Chavan
  • Li Qi
  • Samy Gamal Faddel Mohamed

Assignees

  • ABB SCHWEIZ AG

Dates

Publication Date
20260512
Application Date
20231213

Claims (20)

  1. 1 . A direct current (DC) microgrid comprising: a power converter; a power-voltage (PV) droop control loop electrically coupled with the power converter, the PV droop control loop configured to: receive measurements of a droop current quantity that is a current quantity other than a DC bus current of a DC microgrid, wherein the droop current quantity is used to determine a droop power quantity selected as a power quantity in a PV relationship between the power quantity and a DC bus voltage of the DC microgrid in a PV droop control of the DC microgrid; and derive a current reference based on droop in the droop power quantity, the current reference corresponding to a control quantity of an inner current control loop of the power converter; the inner current control loop of the power converter electrically coupled with the power converter and the PV droop control loop, the inner current control loop configured to control operation of the power converter by: deriving a measured current corresponding to the control quantity based on the measurements of the droop current quantity; directly comparing the current reference with the measured current; and generating switching signals of switches in the power converter based on the comparing.
  2. 2 . The DC microgrid of claim 1 , wherein the droop power quantity is a fictitious power including a product of multiplication of the DC bus voltage and the droop current quantity.
  3. 3 . The DC microgrid of claim 2 , wherein the droop current quantity is an input current of the power converter.
  4. 4 . The DC microgrid of claim 3 , wherein the power converter is an alternate current (AC) to DC converter and/or a DC to DC boost converter.
  5. 5 . The DC microgrid of claim 2 , wherein the power converter is a DC to DC buck converter, and the droop current quantity is an output current of the power converter.
  6. 6 . The DC microgrid of claim 2 , wherein a droop gain of the PV droop control increases as a loading level of the DC microgrid increases.
  7. 7 . The DC microgrid of claim 1 , wherein a droop gain of the PV droop control is a function of time.
  8. 8 . The DC microgrid of claim 1 , wherein a droop gain of the PV droop control is a function of a variable in the power converter and/or in the DC microgrid.
  9. 9 . The DC microgrid of claim 1 , wherein the DC microgrid comprises a plurality of power converters.
  10. 10 . The DC microgrid of claim 1 , wherein the droop power quantity is an input power of the power converter.
  11. 11 . A method of power-voltage (PV) droop control in a direct current (DC) microgrid, the method comprising: selecting a droop power quantity as a power quantity in a PV relationship between the power quantity and a DC bus voltage of a DC microgrid in a PV droop control of the DC microgrid, wherein the droop power quantity is based on a droop current quantity that is a current quantity other than a DC bus current of the DC microgrid; deriving a current reference based on droop in the droop power quantity, the current reference corresponding to a control quantity of an inner current control loop of a power converter; deriving a measured current corresponding to the control quantity based on measurements of the droop current quantity; and controlling operation of the power converter by: in the inner current control loop, directly comparing the current reference with the measured current; and generating switching signals of switches in the power converter based on the comparing.
  12. 12 . The method of claim 11 , wherein selecting the droop power quantity further comprises selecting the droop power quantity as a fictitious power including a product of multiplication of the DC bus voltage and the droop current quantity.
  13. 13 . The method of claim 12 , wherein the droop current quantity is an input current of the power converter.
  14. 14 . The method of claim 13 , wherein the power converter is an alternate current (AC) to DC converter and/or a DC to DC boost converter.
  15. 15 . The method of claim 12 , wherein the power converter is a DC to DC buck converter, and the droop current quantity is an output current of the power converter.
  16. 16 . The method of claim 12 , further comprising selecting a droop gain of the PV droop control, wherein the droop gain increases as a loading level of the DC microgrid increases.
  17. 17 . The method of claim 11 , further comprising selecting a droop gain of the PV droop control as a function of time.
  18. 18 . The method of claim 11 , further comprising selecting a droop gain of the PV droop control as a function of a variable in the power converter and/or in the DC microgrid.
  19. 19 . The method of claim 11 , wherein the DC microgrid includes a plurality of power converters.
  20. 20 . The method of claim 11 , wherein selecting the droop power quantity further comprises selecting the droop power quantity as an input power of the power converter.

Description

BACKGROUND The field of the disclosure relates generally to microgrids, and more particularly, to systems and methods of control for a direct current (DC) microgrid. A microgrid is a local electrical grid and may be operated in a grid-connected mode by being connected to the macrogrid and in an island mode by being disconnected from the macrogrid and functioning autonomously. In a DC microgrid, the bus current of the microgrid is DC. One method of controlling the output of a DC microgrid is power-voltage (PV) droop control, which regulates the output DC side power as a function of the DC bus voltage of the microgrid. Known systems and methods of PV droop control are disadvantaged in some aspects and improvements are desired. BRIEF DESCRIPTION In one aspect, a direct current (DC) microgrid is provided. The microgrid includes a power converter, a power-voltage (PV) droop control loop electrically coupled with the power converter, and an inner current control loop of the power converter. The PV droop control loop is configured to receive measurements of a droop current quantity that is a current quantity other than a DC bus current of a DC microgrid. The droop current quantity is used to determine a droop power quantity selected as a power quantity in a PV relationship between the power quantity and a DC bus voltage of the DC microgrid in a PV droop control of the DC microgrid. The PV droop control loop is further configured to derive a current reference based on droop in the droop power quantity, the current reference corresponding to a control quantity of the inner current control loop of the power converter. The inner current control loop of the power converter is electrically coupled with the power converter and the PV droop control loop. The inner current control loop is configured to control operation of the power converter by deriving a measured current corresponding to the control quantity based on the measurements of the droop current quantity, directly comparing the current reference with the measured current, and generating switching signals of switches in the power converter based on the comparing. In another aspect, a method of PV droop control in a DC microgrid is provided. The method includes selecting a droop power quantity as a power quantity in a PV relationship between the power quantity and a DC bus voltage of a DC microgrid in a PV droop control of the DC microgrid. The droop power quantity is based on a droop current quantity that is a current quantity other than a DC bus current of the DC microgrid. The method also includes deriving a current reference based on droop in the droop power quantity, the current reference corresponding to a control quantity of an inner current control loop of a power converter. The method further includes deriving a measured current corresponding to the control quantity based on measurements of the droop current quantity. In addition, the method includes controlling operation of the power converter by in the inner current control loop, directly comparing the current reference with the measured current, and generating switching signals of switches in the power converter based on the comparing. BRIEF DESCRIPTION OF DRAWINGS These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings. FIG. 1A shows a known power-voltage (PV) droop control mechanism. FIG. 1B shows the known PV droop control for an alternate current to direct current (AC/DC) converter. FIG. 1C shows a step response of the known PV droop control for the AC/DC converter shown in FIG. 1B. FIG. 1D shows the known PV droop control for a DC/DC boost converter. FIG. 2A is a schematic diagram of an example microgrid. FIG. 2B is a flow chart of a method of PV droop control. FIG. 3A is an example PV droop control for an AC/DC converter. FIG. 3B is a step response of the control for the AC/DC converter shown in FIG. 3A. FIG. 3C is an example PV droop control for a DC/DC boost converter. FIG. 3D is an example PV droop control for a DC/DC buck converter. FIG. 3E is another example PV droop control for an AC/DC converter. FIG. 4A shows an example microgrid including a plurality of converters. FIG. 4B shows another example microgrid including a plurality of converters. FIG. 5 is a comparison of impedance plots of the PV droop control shown in FIG. 3A with the known PV droop control shown in FIG. 1B. FIG. 6A is a step response of the PV droop control shown in FIG. 3C. FIG. 6B shows impedance plots of the PV droop control shown in FIG. 3C. FIG. 7A shows a step response of the PV droop control shown in FIG. 3E. FIG. 7B shows impedance plots of the PV droop control shown in FIG. 3E. DETAILED DESCRIPTION The disclosure includes power-voltage (PV) droop control for a direct current (DC) microgrid. Method aspects w