Photovoltaic system, inverter, and control method

Patent metadata

Field	Value
Publication number	US-12418248-B2
Application number	US-202318463399-A
Country	US
Kind code	B2
Filing date	Sep 8, 2023
Priority date	Mar 10, 2021
Publication date	Sep 16, 2025
Grant date	Sep 16, 2025

Abstract

A three-level neutral point clamped inverter includes four switch units. When an average value of an output current of the three-level neutral point clamped inverter is greater than a first current threshold or less than a second current threshold, only one of the four switch units is controlled to perform a high-frequency operation, to reduce power consumption caused by a high-frequency operation. The average value of the output current is an average value of the output current of the three-level neutral point clamped inverter in a switching cycle. The first current threshold is a positive number, and the second current threshold is a negative number. Power consumption caused by the high-frequency operation of the switch unit in the inverter may be reduced, and electric energy conversion efficiency of the inverter may be improved. A time period in which two switch units perform complementary operations at high frequency is very small.

First claim

The invention claimed is:

1. A photovoltaic system, comprising:
a three-level neutral point clamped inverter, comprising a first switch unit, a second switch unit, a third switch unit, and a fourth switch unit; and
a controller,
wherein a first end of the first switch unit is connected to a positive direct current bus, a second end of the first switch unit is connected to a first end of the second switch unit, a second end of the second switch unit is connected to a first end of the third switch unit, a second end of the third switch unit is connected to a first end of the fourth switch unit, a second end of the fourth switch unit is connected to a negative direct current bus, and the second end of the second switch unit is an output end of the three-level neutral point clamped inverter; and
the controller is configured to:
in response to an average value of an output current of the three-level neutral point clamped inverter is greater than a first current threshold or less than a second current threshold, control only one of the four switch units to perform a high-frequency operation, to reduce power consumption caused by a high-frequency operation, wherein the average value of the output current is an average value of the output current of the three-level neutral point clamped inverter in a switching cycle, the output current of the inverter is positive in response to flowing out of the inverter, and is negative in response to flowing into the inverter, the first current threshold is a positive number, and the second current threshold is a negative number.

2. The photovoltaic system according to claim 1 , wherein the controller is further configured to:
in response to the average value of the output current is greater than the second current threshold and less than the first current threshold, control two of the four switch units to perform high-frequency operations.

3. The photovoltaic system according to claim 1 , wherein
in a positive half cycle of an output voltage of the three-level neutral point clamped inverter, the controller is further configured to: control the second switch unit to be turned on, and control the fourth switch unit to be turned off; in response to the average value of the output current is greater than the first current threshold, control the third switch unit to be turned off, and control the first switch unit to perform a high-frequency operation; and in response to the average value of the output current is less than the second current threshold, control the first switch unit to be turned off, and control the third switch unit to perform a high-frequency operation; and
in a negative half cycle of the output voltage, the controller is further configured to: control the third switch unit to be turned on, and control the first switch unit to be turned off; in response to the average value of the output current is greater than the first current threshold, control the fourth switch unit to be turned off, and control the second switch unit to perform a high-frequency operation; and in response to the average value of the output current is less than the second current threshold, control the second switch unit to be turned off, and control the fourth switch unit to perform a high-frequency operation.

4. The photovoltaic system according to claim 1 , wherein
in response to a minimum value of the output current in one switching cycle is 0, the first current threshold is greater than or equal to an average value of the output current corresponding to the switching cycle; and
in response to a maximum value of the output current in one switching cycle is 0, the second current threshold is less than or equal to an average value of the output current corresponding to the switching cycle.

5. The photovoltaic system according to claim 1 , wherein the controller is further configured to:
obtain a total harmonic current distortion of the output current; and in response to the total harmonic current distortion increases, increase the first current threshold; or
in response to the total harmonic current distortion decreases, decrease the first current threshold.

6. The photovoltaic system according to claim 1 , wherein the controller is further configured to:
obtain a modulation ratio of the three-level neutral point clamped inverter; and in response to the modulation ratio decreases, increase the first current threshold; or
in response to the modulation ratio increases, decrease the first current threshold, wherein the modulation ratio is a ratio of an output phase voltage peak of the three-level neutral point clamped inverter to a half direct current bus voltage.

7. The photovoltaic system according to claim 1 , wherein the controller is further configured to:
obtain a power factor of the three-level neutral point clamped inverter; and in response to an absolute value of the power factor decreases, increase the first current threshold; or
in response to an absolute value of the power factor increases, decrease the first current threshold.

8. The photovoltaic system according to claim 1 , wherein the controller is further configured to:
obtain an output power of the three-level neutral point clamped inverter; and in response to the output power decreases, increase the first current threshold; or
in response to the output power increases, decrease the first current threshold.

9. The photovoltaic system according to claim 1 , wherein the controller is further configured to:
obtain the total harmonic current distortion of the output current; and in response to the total harmonic current distortion increases, decrease the second current threshold; or
in response to the total harmonic current distortion decreases, increase the second current threshold.

10. The photovoltaic system according to claim 1 , wherein the controller is further configured to:
obtain the modulation ratio of the three-level neutral point clamped inverter; and in response to the modulation ratio decreases, decrease the second current threshold; or
in response to the modulation ratio increases, increase the second current threshold, wherein the modulation ratio is the ratio of the output phase voltage peak of the three-level neutral point clamped inverter to the half direct current bus voltage.

11. The photovoltaic system according to claim 1 , wherein the controller is further configured to:
obtain the power factor of the three-level neutral point clamped inverter; and in response to the absolute value of the power factor decreases, decrease the second current threshold; or
in response to the absolute value of the power factor increases, increase the second current threshold.

12. The photovoltaic system according to claim 1 , wherein the controller is further configured to:
obtain the output power of the three-level neutral point clamped inverter; and in response to the output power decreases, decrease the second current threshold; or
in response to the output power increases, increase the second current threshold.

13. The photovoltaic system according to claim 1 , wherein the three-level neutral point clamped inverter is a central inverter, a string inverter, or a household single-phase inverter.

14. The photovoltaic system according to claim 1 , wherein the three-level neutral point clamped inverter further comprises: a first capacitor, a second capacitor, a first diode, and a second diode;
a first end of the first capacitor is connected to the positive direct current bus, a second end of the first capacitor is connected to a first end of the second capacitor, and a second end of the second capacitor is connected to the neg

Assignees

• Huawei Digital Power Tech Co Ltd

Inventors

• Yu Xinyu
• Wang Xudong
• Xin Kai
• Shi Lei

Classifications

• H02M1/12

  Arrangements for reducing harmonics from AC input or output · CPC title

• H02M7/5395

  by pulse-width modulation · CPC title

• H02M1/0054

  Transistor switching losses (periodically suspending operation of switching converter in low power mode H02M1/0035) · CPC title

• H02M7/487 Primary

  Neutral point clamped inverters · CPC title

• Y02E10/56

  Power conversion systems, e.g. maximum power point trackers · CPC title