Systems and methods for photovoltaic direct current (DC) bus control
Solar power systems and methods utilize DC power transmission and centralized power inversion. The solar power systems include a photovoltaic (PV) bus system and a fixed bus system. The PV system utilizes a control mode handoff control method, which includes determining that a local maximum power point tracking (MPPT) control is enabled; in response to determining that the local MPPT control is enabled, starting an MPPT mode timer; performing local MPPT; determining that the MPPT mode timer is greater than a predetermined period; and, in response to determining that the MPPT mode timer is greater than a predetermined period, handing off MPPT control to the next MPPT controller. The distributed MPPT control method may include sequential MPPT control, adaptive ΔV MPPT control, and/or power limiting control. The fixed bus system includes PV string-level MPPT controllers and a fixed DC input central inverter or multiple fixed DC modular inverters.
1. A method comprising:
determining, at a current DC/DC controller, that a maximum power point tracking (MPPT) control is enabled;
in response to determining that the MPPT control is enabled, allowing a single voltage perturbation for a distributed energy resource connected to the current DC/DC controller; and
handing off MPPT control mode to a next DC/DC controller.
2. The method of claim 1 , further comprising scaling the magnitude of the voltage perturbation based on a local device metric.
3. The method of claim 1 , wherein the local device metric is based on an output power.
4. The method of claim 1 , wherein the local device metric is based on a battery state of charge.
5. The method of claim 1 , further comprising:
in response to determining that the MPPT control is enabled, starting an MPPT mode timer; and
handing off MPPT control mode to the next DC/DC controller after the single voltage perturbation and in response to determining the MPPT mode timer exceeds a predetermined period.
6. The method of claim 5 , further comprising:
determining that the MPPT mode timer is not greater than the predetermined period;
in response to determining that the MPPT mode timer is not greater than the predetermined period, further determining that the MPPT control is enabled; and
in response to further determining that the MPPT control is enabled, starting the MPPT mode timer.
7. The method of claim 1 , further comprising:
determining that the MPPT control is not enabled; and
in response to determining that the MPPT control is not enabled, holding a previous duty cycle at the current DC/DC controller's last known MPPT setpoint.
8. The method of claim 1 , further comprising:
measuring local voltage and current; and
determining MPPT ΔV based on the local voltage.
9. The method of claim 8 , further comprising:
determining that a power limit is enabled; and
in response to determining that the power limit is enabled:
determining output power based on the local voltage and current; and
determining that the output power is greater than a power threshold; and
in response to determining that the output power is greater than the power threshold, performing MPPT.
10. The method of claim 9 , further comprising:
determining that the output power is not greater than a power threshold; and
in response to determining that the output power is not greater than the power threshold, performing reverse MPPT.
11. A PV bus system, comprising:
a central inverter unit;
a plurality of PV buses coupled to the central inverter unit;
a plurality of PV strings coupled to the central inverter unit via the plurality of PV buses, respectively;
a plurality of batteries coupled to the plurality of PV buses, respectively; and
a plurality of DC/DC controllers coupled between the plurality of batteries and the plurality of PV buses, respectively, each of the plurality of DC/DC controllers comprising:
a processor; and
a memory having stored thereon instructions, which, when executed by the processor, cause a DC/DC controller to:
determine that a local maximum power point tracking (MPPT) control is enabled;
in response to determining that the local MPPT control is enabled, allowing a single voltage perturbation for a distributed energy resource connected to the DC/DC controller; and
handing off MPPT control mode to a next DC/DC controller.
12. The PV bus system of claim 11 , wherein each DC/DC controller of the plurality of DC/DC controllers includes an MPPT controller and a DC/DC converter, and wherein each of the plurality of PV strings includes at least one PV panel.
13. The PV bus system of claim 11 , wherein the instructions, when executed by the processor, further cause the DC/DC controller to:
determine that the MPPT control is not enabled; and
in response to determining that the MPPT control is not enabled, hold a previous duty cycle at the current DC/DC controller's last known MPPT setpoint.
14. The PV bus system of claim 11 , wherein the instructions, when executed by the processor, further cause the DC/DC controller to:
measure local voltage and current;
determine MPPT ΔV based on the measured local voltage;
determine that a power limit is enabled; and
in response to determining that the power limit is enabled:
determine output power based on the measured local voltage and current; and
determine that the output power is greater than a power threshold; and
in response to determining that the output power is greater than the power threshold, perform MPPT.
15. The PV bus system of claim 11 , wherein the instructions, when executed by the processor, further cause the DC/DC controller to:
determine that output power is not greater than a power threshold; and
in response to determining that the output power is not greater than the power threshold, perform reverse MPPT.
16. A method comprising:
determining, at a current DC/DC controller, that a maximum power point tracking (MPPT) control is enabled;
in response to determining MPPT control is enabled:
determining that a power threshold is enabled;
measuring a local voltage and local current at the current DC/DC controller;
determining output power is greater than the power threshold based on the measured local voltage and local current;
in response to determining that the output power is greater than the power threshold, performing MPPT; and
handing off MPPT control to a next DC/DC controller.
17. The method of claim 16 , further comprising determining MPPT ΔV based on the measured local voltage.
18. The method of claim 16 , further comprising:
determining that the output power is not greater than the power threshold; and
in response to determining that the output power is not greater than the power threshold, performing reverse MPPT.
19. The method of claim 16 , further comprising:
in response to determining that the local MPPT control is enabled, starting an MPPT mode timer;
determining the MPPT mode timer exceeds a predetermined threshold; and
handing off MPPT control to the next DC/DC controller after performing MPPT and in response to determining the MPPT mode timer exceeds the predetermined threshold.
20. The method of claim 16 , further comprising:
determining that the MPPT control is not enabled; and
in response to determining that the MPPT control is not enabled, holding a previous duty cycle at the current DC/DC controller's last known MPPT setpoint.