# US 11,907,000 B2 · Systems and methods for photovoltaic direct current (DC) bus control

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- Number: US 11,907,000 B2
- Document ID: US11907000B2
- Status: Granted
- Kind: B2
- Application number: 17/601,921
- Filed: 2020-05-04
- Published: 2022-05-12
- Granted: 2024-02-20
- Earliest claimed: 2019-05-03
- Assignees: Nextracker LLC
- Applicants: NEXTracker LLC
- Inventors: Yang Liu; Alexander W. Au; Fei Gu
- Web page: https://patentgrep.com/patent/US11907000B2

## CPC

- G05F 1/67: to the maximum power available from a generator, e.g. from solar cell
- H02J 3/381: {Dispersed generators}
- H02J 7/35: with light sensitive cells
- H02J 2101/24: Photovoltaics
- H02J 2101/25: {involving maximum power point tracking control for photovoltaic sources}
- H02J 2207/20: Charging or discharging characterised by the power electronics converter
- Y02E 10/56: Power conversion systems, e.g. maximum power point trackers
- G05F: SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
- H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

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.

## Claims

### Claim 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, starting an MPPT mode timer;
performing 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 mode to a next DC/DC controller.

### Claim 2 (depends on 1)

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.

### Claim 3 (depends on 1)

The method of claim 1, further comprising:
measuring local voltage and current; and
determining MPPT ΔV based on the local voltage.

### Claim 4 (depends on 3)

The method of claim 3, 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.

### Claim 5 (depends on 4)

The method of claim 4, 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.

### Claim 6 (depends on 1)

The method of claim 1, further comprising:
determining that a power limit is not enabled; and
in response to determining that the power limit is not enabled, performing MPPT.

### Claim 7 (depends on 1)

The method of claim 1, 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.

### Claim 8 (depends on 1)

The method of claim 1, 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 not enabled; and
in response to further determining that the MPPT control is not enabled, further holding a previous duty cycle at the current DC/DC controller's last known MPPT setpoint.

### Claim 9 (depends on 1)

The method of claim 1, further comprising in response to determining that the MPPT mode timer is greater than a predetermined period, allowing a voltage perturbation for a distributed energy resource before handing off MPPT control mode to the next DC/DC controller.

### Claim 10 (depends on 9)

The method of claim 9, further comprising scaling a magnitude of the voltage perturbation based on a local device metric,
wherein the local device metric is an output power or a battery state of charge.

### Claim 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, start an MPPT mode timer;
perform MPPT;
determine 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, hand off MPPT control mode to a next DC/DC controller.

### Claim 12 (depends on 11)

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.

### Claim 13 (depends on 11)

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.

### Claim 14 (depends on 11)

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.

### Claim 15 (depends on 11)

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.

### Claim 16

A fixed DC bus system, comprising:
a plurality of modular inverters;
a fixed DC bus coupled to the plurality of modular inverters;
a plurality of PV strings coupled to the plurality of modular inverters via the fixed DC bus;
a plurality of MPPT controllers coupled to the plurality of PV strings, respectively, each MPPT controller of the plurality of MPPT controllers including a PID control stage and a droop stage having a droop gain;
a plurality of batteries coupled to the fixed DC bus; and
a plurality of DC/DC controllers coupled between the plurality of batteries and the fixed DC bus.

### Claim 17 (depends on 16)

The fixed DC bus system of claim 16, wherein the PID control stage includes:
a first voltage gain block; and
a first PI controller coupled to an output of the first voltage gain block.

### Claim 18 (depends on 17)

The fixed DC bus system of claim 17, wherein the droop stage includes:
a droop gain block configured to apply a droop gain to an input voltage to obtain a droop gain voltage; and
a first subtraction block coupled to an output of the droop gain block and configured to subtract the droop gain voltage from an output of the first PI controller to obtain an adjusted PI controller output.

### Claim 19 (depends on 18)

The fixed DC bus system of claim 18, wherein the droop stage further includes:
an addition block coupled to an output of the first subtraction block and configured to add the adjusted PI controller output to a reference power to obtain a further adjusted PI controller output; and
a second subtraction block coupled to the addition block and configured to subtract the input voltage from the further adjusted PI controller output.

### Claim 20 (depends on 19)

The fixed DC bus system of claim 19, wherein the droop stage further includes:
a second voltage gain block coupled to an output of the second subtraction block; and
a second PI controller coupled to an output of the second voltage gain block.