OPTIMIZER, CONTROL METHOD AND PARALLEL ARRANGEMENT FOR PHOTOVOLTAIC SYSTEM

• US 20190326758A1
• Filed: 03/22/2019
• Published: 10/24/2019
• Est. Priority Date: 04/23/2018
• Status: Active Grant

• Current Assignee: Delta Electronics Incorporated
• Original Assignee: Delta Electronics Incorporated
• Inventors: ZHU, Xuancai, WENG, Bingwen, ZHANG, Jiao, LI, Yanlong, ZHANG, Jinfa
• Granted Patent: US 11,005,268 B2
• Time in Patent Office: Days
• CPC Class Codes: H02J 2300/26 involving maximum power point tracking control for photovoltaic sources maximum power point systems in particular G05F1/67
• CPC Class Codes: H02J 3/38 Arrangements for parallely feeding a single network by two or more generators, converters or transformers
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02M 1/0003 Details of control, feedback or regulation circuits
• CPC Class Codes: H02M 1/0058 by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero using an auxiliary actively switched resonant commutation circuit connected to an intermediate DC voltage or between two push-pull branches of an inverter bridge H02M7/4811; in resonant inverters H02M7/4815; in inverters operating from a resonant DC source H02M7/4826
• CPC Class Codes: H02M 1/08 Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 3/01 Resonant DC/DC converters
• CPC Class Codes: H02M 3/285 Single converters with a plurality of output stages connected in parallel parallel operation of a plurality of converters in dc distribution networks H02J1/10
• CPC Class Codes: H02M 3/33573 Full-bridge at primary side of an isolation transformer
• CPC Class Codes: H02M 7/493 the static converters being arranged for operation in parallel
• CPC Class Codes: H02S 40/32 comprising DC/AC inverter means associated with the PV module itself, e.g. AC modules
• CPC Class Codes: H02S 50/00 Monitoring or testing of PV systems, e.g. load balancing or fault identification
• CPC Class Codes: H02S 50/10 Testing of PV devices, e.g. of PV modules or single PV cells testing of semiconductor devices during manufacturing H01L22/00
• CPC Class Codes: Y02B 10/10 Photovoltaic [PV]
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

The present disclosure provides an optimizer for a photovoltaic system, a control method for an optimizer, and an optimizer parallel arrangement thereof. In the method, a DC bus voltage output by the optimizer is acquired; and the optimizer is controlled to switch among an MPPT mode, a limited power mode and a fast shutdown mode based on the DC bus voltage.

Claims

1. A control method for an optimizer, which is applied for a photovoltaic system, an input terminal of the optimizer being connected to an output terminal of a photovoltaic panel, and an output terminal of the optimizer being connected to an input terminal of an inverter by a DC bus, the control method comprising:

acquiring a DC bus voltage output by the optimizer; and

controlling the optimizer to switch among an MPPT mode, a limited power mode and a fast shutdown mode based on the DC bus voltage.

2. The control method for the optimizer according to claim 1, further comprising:

when the DC bus voltage is lower than a first voltage limit or higher than a third voltage limit, controlling the optimizer to operate in the fast shutdown mode.

3. The control method for the optimizer according to claim 2, wherein in the fast shutdown mode, a PWM pulse signal for turning off the optimizer is generated to disconnect the optimizer from the DC bus.

4. The control method for the optimizer according to claim 1, further comprising:

when the DC bus voltage is higher than a first voltage limit and lower than a second voltage limit, controlling the optimizer to operate in the MPPT mode, wherein the second voltage limit is lower than a third voltage limit.

5. The control method for the optimizer according to claim 4, further comprising, in the MPPT mode:

determining a reference voltage based on the DC bus voltage;

acquiring an input voltage of the optimizer;

determining a reference current based on a comparison result between the input voltage and the reference voltage;

acquiring an input current of the optimizer; and

determining a duty ratio of a PWM pulse signal for driving the optimizer based on a comparison result between the input current and the reference current.

6. The control method for the optimizer according to claim 1, further comprising:

when the DC bus voltage is higher than a second voltage limit and lower than a third voltage limit, controlling the optimizer to operate in the limited power mode.

7. The control method for the optimizer according to claim 6, further comprising, in the limited power mode:

determining a reference current based on the DC bus voltage;

acquiring an input current of the optimizer; and

determining a duty ratio of a PWM pulse signal for driving the optimizer based on a comparison result between the input current and the reference current.

8. The control method for the optimizer according to claim 1, wherein outputs of a plurality of the optimizers are connected in parallel to the DC bus.

9. The control method for the optimizer according to claim 1, wherein the first voltage limit is a lowest voltage of an operating voltage range of the optimizer, and the second voltage limit is a highest voltage at which the optimizer operates in the MPPT mode, and the third voltage limit is a highest voltage of the operating voltage range of the optimizer.

10. An optimizer applied in a photovoltaic system, an input terminal of the optimizer being connected a power output terminal of a photovoltaic panel, an output terminal of the optimizer being connected to an input terminal of an inverter via a DC bus, wherein the optimizer comprises:

a converter configured to convert electric power of the photovoltaic panel to DC electric power, an input terminal of the converter being connected to an input terminal of the optimizer, an output terminal of the converter being connected to an output terminal of the optimizer; and

a controller configured to acquire a DC bus voltage output by the optimizer, and control the optimizer to switch among an MPPT mode, a limited power mode and a fast shutdown mode based on the DC bus voltage.

11. The optimizer according to claim 10, wherein the controller comprises:

a first voltage detection unit configured to acquire the DC bus voltage;

a second voltage detection unit configured to acquire an input voltage of the optimizer;

a first current detection unit configured to acquire an input current of the optimizer;

a mode selection unit configured to control the optimizer to switch among the MPPT mode, the limited power mode and the fast shutdown mode based on the DC bus voltage;

a pulse generation unit configured to generate a PWM pulse signal for turning off or on the optimizer; and

a drive unit configured to turn off or drive the optimizer based on the PWM pulse signal.

12. The optimizer according to claim 11, wherein the mode selection unit is further configured to:

control the optimizer to operate in the fast shutdown mode when the DC bus voltage is lower than a first voltage limit or higher than a third voltage limit;

control the optimizer to operate in the MPPT mode when the DC bus voltage is higher than the first voltage limit and lower than a second voltage limit; and

control the optimizer to operate in the limited power mode when the DC bus voltage is higher than the second voltage limit and lower than the third voltage limit.

13. The optimizer according to claim 11, wherein the controller further comprises:

a current reference generation unit configured to generate a reference current based on the DC bus voltage and the input voltage in the MPPT mode and the power limited mode; and

a second regulator configured to generate a PWM pulse signal for driving the optimizer based on the reference current and the input current.

14. The optimizer according to claim 13, wherein the current reference generation unit comprises:

an MPPT control unit configured to generate a reference voltage based on the DC bus voltage in the MPPT mode; and

a first regulator configured to generate a reference current based on a comparison result between the input voltage and the reference voltage in the MPPT mode.

15. The optimizer according to claim 13, wherein the current reference generation unit comprises:

a reference setting unit configured to generate a reference current based on the DC bus voltage in the limited power mode.

16. The optimizer according to claim 11, wherein the mode selection unit is further configured to generate a PWM pulse signal for turning off the optimizer in the fast shutdown mode.

17. The optimizer according to claim 10, wherein

the first voltage limit is a lowest voltage of an operating voltage range of the optimizer, and the second voltage limit is a highest voltage at which the optimizer operates in the MPPT mode and the third voltage limit is a highest voltage of the operating voltage range of the optimizer.

18. An optimizer parallel arrangement applied in a photovoltaic system, comprising a plurality of optimizers according to claim 10, wherein outputs of the plurality of optimizers are connected to the DC output bus.

19. The optimizer parallel arrangement according to claim 18, wherein

each of the plurality of optimizers includes a first positive terminal, a second positive terminal, a first negative terminal and a second negative terminal, wherein the first positive terminal of each optimizer is connected to a positive output bus of the DC output bus, the first negative terminal is connected to a negative output bus of the DC output bus, the first positive terminal is connected to the first positive terminal of another optimizer via the second positive terminal inside the optimizer, and the first negative terminal is connected to the first negative terminal of another optimizer via the second negative terminal inside the optimizer.

20. A photovoltaic system, at least comprising an optimizer and a photovoltaic panel, an input terminal of the optimizer being connected a power output terminal of the photovoltaic panel, an output terminal of the optimizer being connected to an input terminal of an inverter via a DC bus, wherein the optimizer comprises:

a converter configured to convert electric power of the photovoltaic panel to DC electric power, an input terminal of the converter being connected to an input terminal of the optimizer, an output terminal of the converter being connected to an output terminal of the optimizer; and

a controller configured to acquire a DC bus voltage output by the optimizer, and control the optimizer to switch among an MPPT mode, a limited power mode and a fast shutdown mode based on the DC bus voltage.