A photovoltaic grid-connected inverter

Abstract

The application provides a photovoltaic grid-connected inverter. The photovoltaic grid-connected inverter comprises a current sensor and a first relay; the first relay is installed at an output end of the photovoltaic grid-connected inverter, a first end point of the first relay is connected with a zero line, a second end point of the first relay is grounded, and the first relay is used for being attracted when the photovoltaic grid-connected inverter is off-grid; the current sensor is installed at the output end of the photovoltaic grid-connected inverter, and the current sensor is used for determining a value of a leakage current; when the value of the leakage current is greater than or equal to a preset leakage current threshold value, the photovoltaic grid-connected inverter is disconnected with a load. Since the output end of the existing photovoltaic grid-connected inverter is provided with the current sensor, the embodiment of the application can realize the leakage current detection of the load side when the inverter is off-grid based on the current sensor and an additional low-cost relay, and does not need to separately configure a high-cost RCD device at the load side, thereby reducing the system cost.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic inverter grid connection technology, and in particular to a photovoltaic grid-connected inverter. Background Technology

[0002] When configuring photovoltaic inverters for grid connection, grid connection standards require the ability to detect leakage current at the load end to ensure personnel safety from electric shock. To this end, existing technologies typically add an RCD (Residual Current Device) at the load end. When this RCD detects a large leakage current, it initiates circuit breaking protection to ensure personnel safety. However, RCD devices are expensive, increasing the overall system cost and making on-site configuration more complex for customers. Summary of the Invention

[0003] This invention provides a photovoltaic grid-connected inverter to solve the problem of high cost caused by the need to configure an RCD to detect leakage current in existing photovoltaic grid-connected inverters during grid connection.

[0004] In a first aspect, embodiments of the present invention provide a photovoltaic grid-connected inverter, including a current sensor and a first relay;

[0005] The first relay is installed at the output terminal of the photovoltaic grid-connected inverter. The first terminal of the first relay is connected to the neutral line, and the second terminal of the first relay is grounded. The first relay is used to activate when the photovoltaic grid-connected inverter is disconnected from the grid.

[0006] The current sensor is installed at the output terminal of the photovoltaic grid-connected inverter. The current sensor is used to determine the value of leakage current. When the value of leakage current is greater than or equal to the preset leakage current threshold, the photovoltaic grid-connected inverter is disconnected from the load.

[0007] In one possible implementation, the first terminal of the first relay is located between the output terminal of the photovoltaic grid-connected inverter and the current sensor. The live wire and the neutral wire are wound with the same number of turns around the current sensor. When there is no leakage current, the current in the neutral wire and the live wire are equal in magnitude and opposite in direction, and the current sensor has no electrical signal output. When there is leakage current, the current sensor outputs an electrical signal, which is used to indicate the magnitude of the leakage current.

[0008] In one possible implementation, the current sensor further includes an amplification module for amplifying the electrical signal.

[0009] In one possible implementation, the photovoltaic grid-connected inverter further includes a second relay, which is a voltage relay. The electrical signal is a voltage signal determined by the current sensor based on the leakage current value. The input terminal of the second relay is connected to the signal output terminal of the current sensor to receive the voltage signal. The second relay includes a first contact switch and a second contact switch. The first contact switch is connected to the live wire, and the second contact switch is connected to the neutral wire. When the absolute value of the voltage corresponding to the voltage signal is greater than or equal to a preset voltage threshold, the first contact switch and the second contact switch are simultaneously disconnected to control the photovoltaic grid-connected inverter to disconnect from the load. When the absolute value of the voltage corresponding to the voltage signal is equal to the voltage threshold, the leakage current value is equal to the leakage current threshold.

[0010] In one possible implementation, the photovoltaic grid-connected inverter further includes a second relay, which is a current relay. The electrical signal is a current signal. The input terminal of the second relay is connected to the signal output terminal of the current sensor to receive the current signal. The second relay includes a first contact switch and a second contact switch. The first contact switch is connected to the live wire, and the second contact switch is connected to the neutral wire. When the absolute value of the current value corresponding to the current signal is greater than or equal to the leakage current threshold, the first contact switch and the second contact switch are simultaneously disconnected to control the photovoltaic grid-connected inverter to disconnect from the load.

[0011] In one possible implementation, the first relay includes at least two single-contact relays connected in series, and the first relay is disconnected when the photovoltaic grid-connected inverter is connected to the grid.

[0012] In one possible implementation, the current sensor is a Hall current sensor.

[0013] In one possible implementation, the Hall current sensor further includes a temperature compensation module, which includes a compensation resistor and a constant voltage power supply, wherein the constant voltage power supply, the compensation resistor, and the Hall current sensor are connected in series.

[0014] In one possible implementation, the resistance value of the compensation resistor is determined by the internal resistance value of the Hall current sensor, the potential stability coefficient of the Hall current sensor, the semiconductor temperature coefficient of the Hall current sensor, and the temperature coefficient of the compensation resistor.

[0015] In one possible implementation, the resistance value of the compensation resistor is determined by a preset formula, wherein the preset formula is:

[0016]

[0017] Wherein, R is the resistance value of the compensation resistor, r is the internal resistance value of the Hall current sensor, α is the potential stability coefficient of the Hall current sensor, β is the semiconductor temperature coefficient of the Hall current sensor, and δ is the temperature coefficient of the compensation resistor.

[0018] This invention provides a photovoltaic grid-connected inverter, including a current sensor and a first relay. When the photovoltaic grid-connected inverter changes from a grid-connected state to an off-grid state, the first relay is activated and grounded, forming a grounding loop between the live wire, neutral wire, and load. The current sensor detects leakage current. When the leakage current value is greater than or equal to a preset leakage current threshold, the photovoltaic grid-connected inverter is disconnected from the load, thereby achieving leakage current protection. Since existing photovoltaic grid-connected inverters are equipped with current sensors at their output terminals, this invention can achieve leakage current detection on the load side when the inverter is off-grid based on this current sensor and by adding a low-cost relay, eliminating the need for a separate, expensive RCD device on the load side, thus reducing system costs. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the structure of a photovoltaic grid-connected inverter provided in an embodiment of the present invention;

[0021] Figure 2 This is a schematic diagram of another photovoltaic grid-connected inverter provided in an embodiment of the present invention;

[0022] Figure 3 This is a schematic diagram of the structure of another photovoltaic grid-connected inverter provided in an embodiment of the present invention;

[0023] Figure 4 This is a schematic diagram of the structure of a Hall current sensor provided in an embodiment of the present invention. Detailed Implementation

[0024] To enable those skilled in the art to better understand this solution, the technical solutions in the embodiments of this solution will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this solution, not all of them. Based on the embodiments of this solution, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this solution.

[0025] The term "comprising" and any other variations thereof in the specification, claims, and accompanying drawings of this invention mean "including but not limited to," and are intended to cover a non-exclusive inclusion, not limited to the examples listed herein. Furthermore, the terms "first" and "second," etc., are used to distinguish different objects, not to describe a specific order.

[0026] The implementation of the present invention will be described in detail below with reference to the accompanying drawings:

[0027] Figure 1 This is a schematic diagram of a photovoltaic grid-connected inverter provided in an embodiment of the present invention. (Refer to...) Figure 1 The photovoltaic grid-connected inverter includes a current sensor and a first relay;

[0028] The first relay is installed at the output terminal of the photovoltaic grid-connected inverter. The first terminal of the first relay is connected to the neutral line, and the second terminal of the first relay is grounded. The first relay is used to activate when the photovoltaic grid-connected inverter is disconnected from the grid.

[0029] The current sensor is installed at the output terminal of the photovoltaic grid-connected inverter. The current sensor is used to determine the value of leakage current. When the value of leakage current is greater than or equal to the preset leakage current threshold, the photovoltaic grid-connected inverter is disconnected from the load.

[0030] like Figure 1 As shown, when a photovoltaic grid-connected inverter changes from grid-connected to off-grid mode, it supplies power to the load instead of the grid. To detect leakage current after grid disconnection, existing technologies typically add a separate RCD at the inverter's output. However, RCDs are expensive, increasing the overall system cost. In this embodiment, existing photovoltaic grid-connected inverters are equipped with current sensors at their output, or the cost of adding a separate current sensor is much lower than that of an RCD. Furthermore, a relatively inexpensive first relay is added. When the photovoltaic grid-connected inverter changes from grid-connected to off-grid mode, the first relay is grounded, creating a grounding loop between the live wire, neutral wire, and load. Leakage current is detected by the current sensor. When the leakage current value is greater than or equal to a preset leakage current threshold, the photovoltaic grid-connected inverter disconnects from the load, thus achieving leakage protection and reducing system cost.

[0031] In one possible implementation, combining Figure 1 The first terminal of the first relay is located between the output terminal of the photovoltaic grid-connected inverter and the current sensor. The number of turns of the live wire and the neutral wire wound around the current sensor is the same. When there is no leakage current, the current in the neutral wire and the live wire is equal in magnitude and opposite in direction, and the current sensor has no electrical signal output. When there is leakage current, the current sensor outputs an electrical signal, which is used to indicate the magnitude of the leakage current.

[0032] Combination Figure 1 In this embodiment of the invention, IN represents the live wire current, IL represents the neutral wire current, and the number of turns of the live wire and neutral wire through the Hall current sensor are the same. N1 represents the number of turns of the live wire wound around the Hall current sensor, and N2 represents the number of turns of the neutral wire wound around the Hall current sensor. When there is no leakage current, the current through the live wire and the current through the neutral wire are equal in magnitude and opposite in direction, IN*N1 = IL*N2. The magnetic fields generated by the live wire and the neutral wire are equal in magnitude and opposite in direction, canceling each other out. At this time, the Hall current sensor has no electrical signal output, that is, the sum of the live wire current and the neutral wire current is 0. When there is leakage current, due to the formation of the above-mentioned grounding loop, the magnitude of the live wire current at the current sensor is equal to the magnitude of the neutral wire current plus the magnitude of the leakage current. The Hall current sensor outputs an electrical signal to represent the magnitude of the leakage current.

[0033] In one possible implementation, to improve the detection accuracy of leakage current, the current sensor also includes an amplification module for amplifying the electrical signal.

[0034] Figure 2 This is a schematic diagram of another photovoltaic grid-connected inverter provided in an embodiment of the present invention, combined with... Figure 2 The photovoltaic grid-connected inverter also includes a second relay, which is a voltage relay. The electrical signal is a voltage signal determined by a current sensor based on the leakage current value. The input terminal of the second relay is connected to the signal output terminal of the current sensor to receive the voltage signal. The second relay includes a first contact switch and a second contact switch. The first contact switch is connected to the live wire, and the second contact switch is connected to the neutral wire. When the absolute value of the voltage corresponding to the voltage signal is greater than or equal to a preset voltage threshold, the first contact switch and the second contact switch open simultaneously to control the photovoltaic grid-connected inverter to disconnect from the load. When the absolute value of the voltage corresponding to the voltage signal is equal to the voltage threshold, the leakage current value is equal to the leakage current threshold.

[0035] In one possible implementation, the Hall current sensor, after receiving the leakage current signal, generates a voltage signal through a preset resistor. Furthermore, high-order harmonics contained in the current signal can be filtered out using a filter circuit composed of resistors and capacitors to improve the accuracy of relay control.

[0036] In one possible implementation, combining Figure 2 The photovoltaic grid-connected inverter also includes a second relay, which is a current relay. The electrical signal is a current signal. The input terminal of the second relay is connected to the signal output terminal of the current sensor to receive the current signal. The second relay includes a first contact switch and a second contact switch. The first contact switch is connected to the live wire, and the second contact switch is connected to the neutral wire. When the absolute value of the current corresponding to the current signal is greater than or equal to the leakage current threshold, the first contact switch and the second contact switch open simultaneously to control the photovoltaic grid-connected inverter to disconnect from the load.

[0037] Figure 3 This is a structural schematic diagram of another photovoltaic grid-connected inverter provided in an embodiment of the present invention, combined with... Figure 3 The first relay comprises at least two single-contact relays connected in series. When the photovoltaic grid-connected inverter is connected to the grid, the first relay is disconnected. Since the grid neutral wire is already grounded when the photovoltaic grid-connected inverter is connected, the first relay should be disconnected. Setting at least two single-contact relays in series ensures that as long as one single-contact relay is disconnected, the grounding terminal corresponding to the first relay will also be disconnected.

[0038] In one possible implementation, to improve detection accuracy, the current sensor in this embodiment of the invention can be a Hall current sensor.

[0039] In one possible implementation, Figure 4 This is a schematic diagram of a Hall current sensor provided in an embodiment of the present invention. Because Hall current sensors suffer from temperature drift, which affects their detection accuracy, this invention addresses this issue by combining... Figure 4 The Hall current sensor also includes a temperature compensation module, which includes a compensation resistor R and a constant voltage power supply U. The constant voltage power supply, the compensation resistor, and the Hall current sensor are connected in series.

[0040] In one possible implementation, the resistance value of the compensation resistor is determined by the internal resistance value of the Hall current sensor, the potential stability coefficient of the Hall current sensor, the semiconductor temperature coefficient of the Hall current sensor, and the temperature coefficient of the compensation resistor.

[0041] In one possible implementation, the resistance value of the compensation resistor is determined by a preset formula, which is as follows:

[0042]

[0043] Where R is the resistance value of the compensation resistor, r is the internal resistance value of the Hall current sensor, α is the potential stability coefficient of the Hall current sensor, β is the semiconductor temperature coefficient of the Hall current sensor, and δ is the temperature coefficient of the compensation resistor.

[0044] This invention provides a photovoltaic grid-connected inverter. Based on the existing photovoltaic grid-connected inverters, which are equipped with current sensors at their output terminals, or where the cost of adding a separate current sensor is far lower than that of an RCD, a relatively inexpensive first relay is added. When the photovoltaic grid-connected inverter changes from grid-connected to off-grid mode, the first relay is activated and grounded, forming a grounding loop between the live wire, neutral wire, and load. The current sensor detects leakage current; when the leakage current value is greater than or equal to a preset leakage current threshold, the photovoltaic grid-connected inverter is disconnected from the load, thereby achieving leakage protection and reducing system costs.

[0045] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A photovoltaic grid-connected inverter, characterized in that, Includes a current sensor and a first relay; The first relay is installed at the output terminal of the photovoltaic grid-connected inverter. The first terminal of the first relay is connected to the neutral line, and the second terminal of the first relay is grounded. The first relay is used to activate when the photovoltaic grid-connected inverter is in an off-grid state. The current sensor is installed at the output terminal of the photovoltaic grid-connected inverter. The current sensor is used to determine the value of the leakage current. When the value of the leakage current is greater than or equal to the preset leakage current threshold, the photovoltaic grid-connected inverter is disconnected from the load to achieve leakage protection without the need to set up an RCD separately on the load side. The first terminal of the first relay is located between the output terminal of the photovoltaic grid-connected inverter and the current sensor. The number of turns of the live wire and the neutral wire wound around the current sensor is the same. When there is no leakage current, the current in the neutral wire and the live wire is equal in magnitude and opposite in direction, and the current sensor has no electrical signal output. When there is leakage current, the current sensor outputs an electrical signal, which is used to indicate the magnitude of the leakage current. The first relay includes at least two single-contact relays connected in series. When the photovoltaic grid-connected inverter is in grid-connected state, the first relay is disconnected.

2. The photovoltaic grid-connected inverter as described in claim 1, characterized in that, The current sensor also includes an amplification module for amplifying the electrical signal.

3. The photovoltaic grid-connected inverter as described in claim 1 or 2, characterized in that, The photovoltaic grid-connected inverter also includes a second relay, which is a voltage relay. The electrical signal is a voltage signal determined by the current sensor based on the leakage current value. The input terminal of the second relay is connected to the signal output terminal of the current sensor to receive the voltage signal. The second relay includes a first contact switch and a second contact switch. The first contact switch is connected to the live wire, and the second contact switch is connected to the neutral wire. When the absolute value of the voltage corresponding to the voltage signal is greater than or equal to a preset voltage threshold, the first contact switch and the second contact switch open simultaneously to control the photovoltaic grid-connected inverter to disconnect from the load. When the absolute value of the voltage corresponding to the voltage signal is equal to the voltage threshold, the leakage current value is equal to the leakage current threshold.

4. The photovoltaic grid-connected inverter as described in claim 1 or 2, characterized in that, The photovoltaic grid-connected inverter also includes a second relay, which is a current relay. The electrical signal is a current signal. The input terminal of the second relay is connected to the signal output terminal of the current sensor to receive the current signal. The second relay includes a first contact switch and a second contact switch. The first contact switch is connected to the live wire, and the second contact switch is connected to the neutral wire. When the absolute value of the current value corresponding to the current signal is greater than or equal to the leakage current threshold, the first contact switch and the second contact switch are simultaneously disconnected to control the photovoltaic grid-connected inverter to disconnect from the load.

5. The photovoltaic grid-connected inverter as described in claim 1, characterized in that, The current sensor is a Hall current sensor.

6. The photovoltaic grid-connected inverter as described in claim 5, characterized in that, The Hall current sensor also includes a temperature compensation module, which includes a compensation resistor and a constant voltage power supply. The constant voltage power supply, the compensation resistor, and the Hall current sensor are connected in series.

7. The photovoltaic grid-connected inverter as described in claim 6, characterized in that, The resistance value of the compensation resistor is determined by the internal resistance value of the Hall current sensor, the potential stability coefficient of the Hall current sensor, the semiconductor temperature coefficient of the Hall current sensor, and the temperature coefficient of the compensation resistor.

8. The photovoltaic grid-connected inverter as described in claim 7, characterized in that, The resistance value of the compensation resistor is determined by a preset formula, wherein the preset formula is: in, The resistance value of the compensation resistor. Let be the internal resistance value of the Hall current sensor. The potential stability coefficient of the Hall current sensor is given. The semiconductor temperature coefficient of the Hall current sensor. The temperature coefficient of the compensation resistor is denoted as .

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