CN117833166A

CN117833166A - Inverter and control method

Info

Publication number: CN117833166A
Application number: CN202410005820.3A
Authority: CN
Inventors: 王中武; 吴凡
Original assignee: Sungrow Power Supply Co Ltd
Current assignee: Sungrow Power Supply Co Ltd
Priority date: 2024-01-02
Filing date: 2024-01-02
Publication date: 2024-04-05

Abstract

The application discloses an inverter and a control method, the inverter includes: the control module, the controllable switch, the first switch module, the second switch module, the third switch module, the fourth switch module, the positive bus and the negative bus; the first end and the second end of the first switch module are respectively connected with the positive bus and the first end of the second switch module; the second end of the second switch module is connected with the output end of the inverter and the first end of the third switch module; the second end of the third switch module is connected with the first end of the fourth switch module; the second end of the fourth switch module is connected with a negative bus; the controllable switch is arranged in a first loop of the inverter, and the first loop is a current loop when the negative bus is short-circuited to the ground; the control module is used for controlling the controllable switch to be disconnected when the negative bus is short-circuited to the ground. According to the embodiment of the application, the controllable switch arranged on the first loop formed when the negative bus is short-circuited to the ground is controlled to be disconnected, so that the first loop can be disconnected, the inverter or the alternating current relay is protected, and the safety is improved.

Description

Inverter and control method

Technical Field

The present disclosure relates to the field of power electronics, and in particular, to an inverter and a control method thereof.

Background

Because the thunderstorm in summer is more, the photovoltaic system equipment is easy to be hit by thunder, thereby causing the damage of components and parts of the photovoltaic system equipment, in order to prevent the damage of the thunder to the photovoltaic system equipment, the photovoltaic system equipment is generally required to be grounded so as to lead the thunder to the earth, and the normal operation of the photovoltaic system equipment is protected.

Currently, a TN (terra neutral) system is generally adopted to realize the grounding of photovoltaic system equipment. The TN system is a system in which the power supply neutral point is directly grounded, and the exposed electrically conductive portion of the apparatus is directly electrically connected to the power supply neutral point.

However, PV cables connected to photovoltaic power systems may have a problem of short-circuiting to ground due to long-term insolation, resulting in damage to the inverter or ac relay.

Disclosure of Invention

Based on the above problems, the present application provides an inverter and a control method, so as to protect the inverter or the ac relay and improve the safety.

The embodiment of the application discloses the following technical scheme:

in a first aspect, an embodiment of the present application provides an inverter, including a control module, a controllable switch, a first switch module, a second switch module, a third switch module, a fourth switch module, a positive bus, and a negative bus; the first end and the second end of the first switch module are respectively connected with the positive bus and the first end of the second switch module; the second end of the second switch module is connected with the output end of the inverter, and the first end of the third switch module; the second end of the third switch module is connected with the first end of the fourth switch module; the second end of the fourth switch module is connected with the negative bus;

the controllable switch is arranged in a first loop of the inverter; the first loop is a current loop when the negative bus is short-circuited to the ground;

and the control module is used for controlling the controllable switch to be disconnected when the negative bus is short-circuited to the ground.

Optionally, the control module is configured to obtain a detection current, and determine that the negative bus is shorted to ground when the detection current is greater than a preset current value, and control the controllable switch to be turned off.

Optionally, the inverter is a three-phase inverter; the detection current is three-phase current; the control module is used for:

sequentially judging whether a first phase current, a second phase current and a third phase current in the three-phase current are larger than zero or not;

and if the first phase current, the second phase current and the third phase current are all larger than zero, determining that the negative bus is short-circuited to ground, and controlling the controllable switch to be disconnected.

Optionally, the inverter is a three-phase inverter; the detection current is three-phase current and/or leakage current; the control module is further configured to:

adding the first phase current, the second phase current and the third phase current in the three-phase current to obtain a target current value; judging whether the target current value is larger than zero or not; if the target current value is greater than zero, determining that the negative bus is short-circuited to ground; and/or the number of the groups of groups,

judging whether the leakage current is larger than a preset leakage current value or not; and if the leakage current is larger than the preset leakage current value, determining that the negative bus is short-circuited to ground.

Optionally, the third switch module comprises a third switch tube and third unidirectional current passing devices connected in parallel to two ends of the third switch tube; the fourth switching module comprises a fourth switching tube and fourth unidirectional current passing devices connected in parallel at two ends of the fourth switching tube; and the current of the third unidirectional current passing device and the current of the fourth unidirectional current passing device are led to the positive bus direction from the negative bus direction.

Optionally, the third unidirectional current device is the controllable switch, and/or the fourth unidirectional current device is the controllable switch;

the current of the first loop sequentially flows through the negative bus, the fourth unidirectional current passing device, the third unidirectional current passing device, the output end, the power grid and the protection grounding wire PE of the power grid.

Optionally, the control module includes a controller or control circuit;

the control circuit comprises a current detection circuit and a comparison circuit; the current detection circuit is used for detecting loop current of the first loop; the comparison circuit is used for determining a comparison result according to the loop current; the controllable switch is turned off when the comparison result indicates that the loop current is greater than a preset current value.

Optionally, the inverter further includes: a fifth switch module and a sixth switch module;

the first end and the second end of the fifth switch module are respectively connected with the first node and the neutral point; the first end and the second end of the sixth switch module are respectively connected with the neutral point and the second node; the first node is a common end of the first switch module and the second switch module; the second node is a common end of the third switch module and the fourth switch module.

Optionally, the inverter further includes: a first diode and a second diode;

the first end and the second end of the first diode are respectively connected with a first node and a neutral point; the first end and the second end of the second diode are respectively connected with the neutral point and the second node; the first node is a common end of the first switch module and the second switch module; the second node is a common end of the third switch module and the fourth switch module.

In a second aspect, an embodiment of the present application provides a control method of an inverter, where the inverter includes: the control module, the controllable switch, the first switch module, the second switch module, the third switch module, the fourth switch module, the positive bus and the negative bus; the first end and the second end of the first switch module are respectively connected with the positive bus and the first end of the second switch module; the second end of the second switch module is connected with the output end of the inverter, and the first end of the third switch module; the second end of the third switch module is connected with the first end of the fourth switch module; the second end of the fourth switch module is connected with the negative bus;

the control method comprises the following steps:

and when the negative bus is short-circuited to the ground, the controllable switch is controlled to be disconnected.

In a third aspect, embodiments of the present application provide a photovoltaic system, including: a string of photovoltaic strings and an inverter as described in the first aspect;

the input side of the inverter is connected with the photovoltaic group string.

Compared with the prior art, the application has the following beneficial effects:

the inverter provided by the embodiment of the application comprises a control module, a controllable switch, a first switch module, a second switch module, a third switch module, a fourth switch module, a positive bus and a negative bus; the first end and the second end of the first switch module are respectively connected with the positive bus and the first end of the second switch module; the second end of the second switch module is connected with the output end of the inverter and the first end of the third switch module; the second end of the third switch module is connected with the first end of the fourth switch module; the second end of the fourth switch module is connected with a negative bus; the controllable switch is arranged in a first loop of the inverter, and the first loop is a current loop when the negative bus is short-circuited to the ground; the control module is used for controlling the disconnection of the controllable switch when the negative bus is short-circuited to the ground. According to the embodiment of the application, the controllable switch is arranged on the first loop formed when the negative bus is short-circuited to the ground, and the controllable switch is controlled to be disconnected when the negative bus is short-circuited to the ground, so that the first loop is disconnected, the inverter or the alternating current relay is protected, and the safety is improved.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive faculty for a person skilled in the art.

FIG. 1 is a schematic diagram of a negative bus-to-ground short circuit provided in the related art;

fig. 2 is a schematic structural diagram of an inverter according to an embodiment of the present disclosure;

fig. 3a is a schematic first structural diagram of another inverter according to an embodiment of the present disclosure;

fig. 3b is a second schematic structural diagram of another inverter according to an embodiment of the present disclosure;

fig. 3c is a schematic third structural diagram of another inverter according to an embodiment of the present disclosure;

fig. 4a is a schematic first structural diagram of yet another inverter according to an embodiment of the present disclosure;

fig. 4b is a second schematic structural diagram of yet another inverter according to an embodiment of the present disclosure;

fig. 5a is a schematic diagram of a first structure of a further inverter according to an embodiment of the present disclosure;

fig. 5b is a second schematic structural diagram of still another inverter according to an embodiment of the present disclosure;

fig. 6 is a flowchart of a control method of an inverter according to an embodiment of the present application.

Detailed Description

As described above, in the research on the inverter, it was found that the photovoltaic system apparatus is easily hit by lightning due to a lot of thunderstorm in summer, thereby causing damage to components of the photovoltaic system apparatus, in order to prevent damage of the photovoltaic system apparatus by the lightning, it is generally necessary to ground the photovoltaic system apparatus to introduce the lightning into the ground, thereby protecting the photovoltaic system apparatus from normal operation.

Referring to fig. 1, a schematic diagram of a negative bus to ground short circuit is provided in the related art.

Referring to fig. 1, when the negative bus is shorted to ground, the lower half-bridge diode of the power grid forms a loop, that is, when the negative bus PV-is shorted to ground, the short-circuit current loop is: PV-D4-D3-L1-K1-Van-PE-PV-, that is to say, when the negative bus is shorted to ground, it can be understood that PE is connected to PV, since the loop does not pass through the IGBT, the IGBT turn-off does not create an impedance effect on the current path, further resulting in inverter or relay damage.

In order to solve the above problems, an embodiment of the present application provides an inverter and a control method, where the inverter includes a control module, a controllable switch, a first switch module, a second switch module, a third switch module, a fourth switch module, a positive bus, and a negative bus; the first end and the second end of the first switch module are respectively connected with the positive bus and the first end of the second switch module; the second end of the second switch module is connected with the output end of the inverter and the first end of the third switch module; the second end of the third switch module is connected with the first end of the fourth switch module; the second end of the fourth switch module is connected with a negative bus; the controllable switch is arranged in a first loop of the inverter, and the first loop is a current loop when the negative bus is short-circuited to the ground; the control module is used for controlling the disconnection of the controllable switch when the negative bus is short-circuited to the ground.

Therefore, according to the embodiment of the application, the controllable switch is arranged at any position of the first loop formed by the negative bus ground short circuit, and the first loop can be disconnected by controlling the controllable switch to be disconnected when the negative bus ground short circuit occurs, so that the inverter or the alternating current relay is protected, and the safety is improved.

In order to make the present application solution better understood by those skilled in the art, the following description will clearly and completely describe the technical solution in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are only some embodiments of the present application, not all embodiments. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present disclosure.

Referring to fig. 2, the structure of an inverter according to an embodiment of the present application is shown.

As shown in fig. 2, the inverter 200 provided in the embodiment of the present application may include: the control module, the controllable switch Tx, the first switch module Q1, the second switch module Q2, the third switch module Q3, the fourth switch module Q4, the positive BUS BUS+ and the negative BUS BUS-.

Wherein, the first end and the second end of the first switch module Q1 are respectively connected with the positive bus+ and the first end of the second switch module Q2; the second end of the second switch module Q2 is connected with the output end of the inverter, and the first end of the third switch module Q3; the second end of the third switch module Q3 is connected with the first end of the fourth switch module Q4; the second end of the fourth switch module Q4 is connected with the negative BUS BUS-.

Wherein the controllable switch Tx is arranged in a first loop of the inverter; the first loop is a current loop when the negative bus is short-circuited to ground. In the embodiment of the present application, the first loop refers to a loop formed by bus→the fourth switch module q4→the third switch module q3→the output terminal→the power grid van→pe→bus-. That is, a current loop is formed when the negative bus is shorted to the ground, which may cause damage to components on the loop, i.e., damage to the inverter or the relay.

As shown in fig. 2, the controllable switch Tx may be disposed between the negative bus bar and the fourth switch module, or may be disposed between the output terminal and the power grid, which is not particularly limited herein, and fig. 2 is merely an exemplary illustration.

The controllable switch Tx means a switch that can be controlled to be turned on or off by a controller or a control circuit, etc., such as an insulated gate bipolar transistor IGBT, an insulated gate field effect MOS transistor, etc., and is not particularly limited herein.

In one possible implementation manner, the third switching module comprises a third switching tube T3 and third unidirectional current passing devices connected in parallel to two ends of the third switching tube T3; the fourth switching module comprises a fourth switching tube T4 and fourth unidirectional current passing devices connected in parallel to two ends of the fourth switching tube T4.

And the current of the third unidirectional current passing device and the current of the fourth unidirectional current passing device are led to the positive bus direction from the negative bus direction.

The unidirectional current device means a unidirectional current device, such as a diode, and the like, and is not particularly limited herein.

In this embodiment of the present application, the controllable switch Tx may be disposed at any position of the first loop, and in one implementation manner, the controllable switch Tx may be disposed between the output end and the power grid, between the negative bus and the fourth switching tube, where the third unidirectional current device and the fourth unidirectional current device are diodes, as shown in fig. 2 specifically.

In another implementation, the third unidirectional current device in the third switch module may be the controllable switch Tx, and the fourth unidirectional current device in the fourth switch module is a diode, that is, the third unidirectional current device in the third switch module is replaced by the diode with the controllable switch Tx, as shown in fig. 3 a.

In one implementation, the third unidirectional current device in the third switch module may be a diode, and the fourth unidirectional current device of the fourth unidirectional current device in the fourth switch module may be a controllable switch Tx, that is, the fourth unidirectional current device in the fourth switch module is replaced by the diode with the controllable switch Tx, as shown in fig. 3 b.

In yet another implementation, the third unidirectional current device and the fourth unidirectional current device are both controllable switches Tx, i.e. the third unidirectional current device and the fourth unidirectional current device are replaced by diodes with controllable switches Tx, as shown in fig. 3 c.

It should be noted that, replacing the third unidirectional current device or the fourth unidirectional current device with the diode with the controllable switch Tx may save cost.

It should be noted that, when the third unidirectional current device and the fourth unidirectional current device are both replaced by the controllable switch Tx, and the negative bus is shorted to the ground, the control module may control at least one of the two controllable switches to be turned off, i.e. the first loop may be turned off.

It should be noted that, because the third switch module includes the third switch tube and the third unidirectional current device, the fourth switch module includes the fourth switch tube and the fourth unidirectional current device, when the negative bus is shorted to the ground, the third switch tube and the fourth switch tube are disconnected, but the short-circuit current will form a loop through the third unidirectional current device and the fourth unidirectional current device, that is, a first loop is formed, the first loop is the negative bus, the fourth unidirectional current device, the third unidirectional current device, the output end, the power grid, the PE, and the negative bus. The third unidirectional current passing device and/or the fourth unidirectional current passing device can be replaced by a diode to be a controllable switch, and when the negative bus is short-circuited to the ground, the current of the first loop can flow through the controllable switch Tx, at the moment, the first loop can be disconnected by controlling the controllable switch Tx to be disconnected, so that the damage of the inverter or the relay is avoided, and the safety is improved.

When the third unidirectional current device and/or the fourth unidirectional current device are/is controllable switches Tx, the current of the controllable switches Tx is led from the negative BUS-direction to the positive bus+ direction. As an example, it is assumed that the controllable switch Tx is an IGBT which is connected in anti-parallel across the third switching tube, i.e. the current of the third switching tube leads from the positive bus direction to the negative bus direction, and the current of the IGBT leads from the negative bus direction to the positive bus direction. In this embodiment, when the inverter is operating normally, the controllable switch Tx is in a closed state.

And the control module is used for controlling the controllable switch Tx to be disconnected when the negative bus is short-circuited to the ground.

The control module may be a controller or a control circuit. The controller can directly control the controllable switch to be disconnected when the negative bus is determined to be short-circuited to the ground. The control circuit comprises a current detection circuit and a comparison circuit; the current detection circuit is used for detecting loop current of the first loop; the comparison circuit is used for determining a comparison result according to the loop current; the controllable switch is turned off when the comparison result indicates that the loop current is greater than a preset current value.

The current detection circuit may be a current sensor or a circuit composed of a plurality of components, and is not particularly limited herein.

It should be noted that, in the embodiment of the present application, by setting the controllable switch at any position of the first loop formed by the negative bus ground short circuit, and controlling the controllable switch to be turned off when the negative bus ground short circuit occurs, the first loop can be turned off, so as to protect the inverter or the ac relay, and improve the safety.

Based on the inverter provided in the foregoing embodiment, in order to further explain how the control module controls the on or off of the controllable switch, the control module may be configured to obtain the detection current, determine that the negative bus is shorted to the ground when the detection current is greater than a preset current value, and control the controllable switch to be turned off.

The detection current means a current for determining whether the negative bus is shorted to the ground, such as a three-phase current, a leakage current, and the like, and is not particularly limited herein.

In one implementation manner, when the inverter in the embodiment of the present application is a three-phase inverter, the detected current is a three-phase current; the control module is used for judging whether the first phase current, the second phase current and the third phase current in the three-phase current are larger than zero or not in sequence; and if the first phase current, the second phase current and the third phase current are all larger than zero, determining that the negative bus is short-circuited to ground, and controlling the controllable switch to be disconnected.

That is, when the inverter of the embodiment of the present application is a three-phase inverter, it is possible to determine whether the negative bus is shorted to the ground by sequentially detecting whether the first phase current, the second phase current, and the third phase current among the three-phase currents are greater than zero.

In another implementation manner, when the inverter provided in the embodiments of the present application is a three-phase inverter; the detection current is three-phase current; the control module is used for adding the first phase current, the second phase current and the third phase current in the three-phase current to obtain a target current value; judging whether the target current value is larger than zero or not; and if the target current value is larger than zero, determining that the negative bus is short-circuited to ground.

That is, when the inverter in the embodiment of the present application is a three-level inverter, three-phase currents may be obtained first, and the first phase current, the second phase current, and the third phase current in the three-phase currents are added, and whether the target current value obtained after the addition is greater than zero is determined, so as to determine whether the negative bus is shorted to the ground.

In still another implementation manner, when the inverter provided in the embodiment of the present application is a three-phase inverter; the detection current is leakage current; the control module is used for judging whether the leakage current is larger than a preset leakage current value or not; and if the leakage current is larger than the preset leakage current value, determining that the negative bus is short-circuited to ground.

Leakage current means current caused by leakage of current into the ground due to problems with negative bus insulation.

That is, when the inverter of the embodiment of the present application is a three-level inverter, it is also possible to determine whether the negative bus is shorted to the ground by detecting whether the leakage current is greater than a preset leakage current value.

In yet another implementation, when the inverter provided in the embodiments of the present application is a single-phase inverter; the detection current is leakage current; and the control module is used for judging whether the leakage current is larger than a preset leakage current value, and if the leakage current is larger than the preset leakage current value, determining that the negative bus is short-circuited to ground.

The leakage current means a current generated by the leakage current, that is, when the inverter is a single-phase inverter, whether the leakage current exists or not can be determined by determining whether the leakage current exists, and whether the negative bus is short-circuited to ground or not can be further determined by the leakage current.

In yet another implementation, when the inverter provided in the embodiments of the present application is a three-phase inverter; the control module is also used for receiving the short-circuit signal to ground and controlling the disconnection of the controllable switch according to the short-circuit signal to ground; the short circuit signal to ground is obtained by a current detection circuit.

In the embodiment of the present application, the detection current may be obtained through a current detection circuit, and the current detection circuit may be a current sensor or may be a detection circuit formed by other components, which is not specifically limited herein.

Referring to fig. 4a, a first schematic structural diagram of yet another inverter according to an embodiment of the present application is shown.

As shown in conjunction with fig. 4a, an inverter 401 provided in an embodiment of the present application may include: the control module, the controllable switch Tx, the first switch module Q1, the second switch module Q2, the third switch module Q3, the fourth switch module Q4, the positive BUS bar BUS+, the negative BUS bar BUS-, the fifth switch module Q5 and the sixth switch module Q6.

The first end and the second end of the fifth switch module Q5 are respectively connected with the first node a and the neutral point N; a first end and a second end of the sixth switch module Q6 are respectively connected to the neutral point N and the second node B; the first node a is a common terminal of the first switch module Q1 and the second switch module Q2; the second node B is a common terminal of the third switch module Q3 and the fourth switch module Q4.

The controllable switch Tx is arranged in a first loop of the inverter; the first loop is a current loop when the negative bus is short-circuited to ground.

It should be understood that the components in the embodiments of the present application that are the same as those in the embodiments described above are given the same reference numerals, and the connection relationships and the explanation of the components that are the same are detailed in the embodiments described above, and are not repeated here.

Referring to fig. 4b, a second schematic structural diagram of yet another inverter according to an embodiment of the present application is shown.

As shown in connection with fig. 4b, the inverter 402 provided in the embodiment of the present application may include: the control module, the controllable switch Tx, the first switch module Q1, the second switch module Q2, the third switch module Q3, the fourth switch module Q4, the positive BUS bar BUS+, the negative BUS bar BUS-, the fifth switch module Q5 and the sixth switch module Q6.

The first switch module Q1 includes a first switch tube T1 and a diode D1, the second switch module Q2 includes a second switch tube T2 and a diode D2, the third switch module Q3 includes a third switch tube T3 and a controllable switch Tx, the fourth switch module Q4 includes a fourth switch tube T4 and a controllable switch Tx, the fifth switch module Q5 includes a fifth switch tube T5 and a diode D5, and the sixth switch module Q6 includes a sixth switch tube T6 and a diode D6.

In this embodiment, by setting the fifth switch module and the sixth switch module, the inverter can obtain more uniform loss distribution, so that thermal management is facilitated, and the on-voltage of the switch can be reduced, thereby improving efficiency and power density.

Referring to fig. 5a, a first schematic structural diagram of still another inverter according to an embodiment of the present application is shown.

As shown in fig. 5a, the inverter 501 provided in the embodiment of the present application may include: the control module, the controllable switch Tx, the first switch module Q1, the second switch module Q2, the third switch module Q3, the fourth switch module Q4, the positive BUS bar BUS+, the negative BUS bar BUS-, the first diode D5 and the second diode D6;

the first end and the second end of the first diode D5 are respectively connected with the first node A and the neutral point N; the first end and the second end of the second diode D6 are respectively connected with the neutral point N and the second node B; the first node a is a common terminal of the first switch module Q1 and the second switch module Q2; the second node B is a common terminal of the third switch module Q3 and the fourth switch module Q4.

Referring to fig. 5b, a second schematic structural diagram of still another inverter according to an embodiment of the present application is shown.

As shown in fig. 5b, the inverter 502 provided in the embodiment of the present application may include: the control module, the controllable switch Tx, the first switch module Q1, the second switch module Q2, the third switch module Q3, the fourth switch module Q4, the positive BUS bar BUS+, the negative BUS bar BUS-, the first diode D5 and the second diode D6.

According to the embodiment of the application, through the added first diode and second diode, the switching loss can be reduced, the efficiency is improved, the caused electromagnetic interference (EMI) is small, the output voltage waveform is three-level, the harmonic content is small, the required filter inductance is small, and the cost and the power loss are reduced.

Referring to fig. 6, a flowchart of a control method of an inverter according to an embodiment of the present application is shown.

As shown in fig. 6, an inverter provided in an embodiment of the present application may include: the control module, the controllable switch, the first switch module, the second switch module, the third switch module, the fourth switch module, the positive bus and the negative bus; the first end and the second end of the first switch module are respectively connected with the positive bus and the first end of the second switch module; the second end of the second switch module is connected with the output end of the inverter, and the first end of the third switch module; the second end of the third switch module is connected with the first end of the fourth switch module; the second end of the fourth switch module is connected with the negative bus;

the controllable switch is arranged in a first loop of the inverter; the first loop is a current loop when the negative bus is short-circuited to ground.

The control method may include:

s601: and judging whether the negative bus is short-circuited to ground.

S602: and when the negative bus is short-circuited to the ground, the controllable switch is controlled to be disconnected.

As an example, the control method includes: and obtaining detection current, determining that the negative bus is short-circuited to the ground when the detection current is larger than a preset current value, and controlling the controllable switch to be disconnected.

As an example, the inverter is a three-phase inverter; the detection current is three-phase current; the step S601 includes: sequentially judging whether a first phase current, a second phase current and a third phase current in the three-phase current are larger than zero or not;

step S602 includes: and if the first phase current, the second phase current and the third phase current are all larger than zero, determining that the negative bus is short-circuited to ground, and controlling the controllable switch to be disconnected.

As an example, the inverter is a three-phase inverter; the detection current is three-phase current and/or leakage current; the step S601 includes: adding the first phase current, the second phase current and the third phase current in the three-phase current to obtain a target current value; judging whether the target current value is larger than zero or not; if the target current value is greater than zero, determining that the negative bus is short-circuited to ground;

and/or the number of the groups of groups,

the step S601 includes: judging whether the leakage current is larger than a preset leakage current value or not; and if the leakage current is larger than the preset leakage current value, determining that the negative bus is short-circuited to ground.

The control method of the three-level inverter provided by the embodiment of the present application has the same beneficial effects as the three-level inverter provided by the above embodiment, and therefore will not be described in detail.

The embodiment of the application also provides a photovoltaic system, which comprises: a photovoltaic string and the inverter according to each of the embodiments; the input side of the inverter is connected with the photovoltaic group string.

The photovoltaic system provided in the embodiment of the present application can achieve the beneficial effects achieved in the above embodiments, and will not be described herein.

The "first" and "second" in the names of "first", "second" (where present) and the like in the embodiments of the present application are used for name identification only, and do not represent the first and second in sequence.

The foregoing is merely one specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present application should be covered in the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. An inverter is characterized by comprising a control module, a controllable switch, a first switch module, a second switch module, a third switch module, a fourth switch module, a positive bus and a negative bus; the first end and the second end of the first switch module are respectively connected with the positive bus and the first end of the second switch module; the second end of the second switch module is connected with the output end of the inverter, and the first end of the third switch module; the second end of the third switch module is connected with the first end of the fourth switch module; the second end of the fourth switch module is connected with the negative bus;

2. The inverter of claim 1, wherein the control module is configured to obtain a detected current, determine that the negative bus is shorted to ground, and control the controllable switch to be turned off when the detected current is greater than a preset current value.

3. The inverter of claim 2, wherein the inverter is a three-phase inverter; the detection current is three-phase current; the control module is used for:

4. The inverter of claim 2, wherein the inverter is a three-phase inverter; the detection current is three-phase current and/or leakage current; the control module is further configured to:

5. The inverter of claim 1, wherein the third switching module comprises a third switching tube and a third unidirectional current passing device connected in parallel across the third switching tube; the fourth switching module comprises a fourth switching tube and fourth unidirectional current passing devices connected in parallel at two ends of the fourth switching tube; and the current of the third unidirectional current passing device and the current of the fourth unidirectional current passing device are led to the positive bus direction from the negative bus direction.

6. The inverter of claim 5, wherein the third unidirectional current device is the controllable switch and/or the fourth unidirectional current device is the controllable switch;

7. The inverter of claims 1-6, wherein the control module comprises a controller or a control circuit;

8. The inverter according to any one of claims 1-6, further comprising: a fifth switch module and a sixth switch module;

9. The inverter according to any one of claims 1-6, further comprising: a first diode and a second diode;

10. A control method of an inverter, characterized in that the inverter comprises: the control module, the controllable switch, the first switch module, the second switch module, the third switch module, the fourth switch module, the positive bus and the negative bus; the first end and the second end of the first switch module are respectively connected with the positive bus and the first end of the second switch module; the second end of the second switch module is connected with the output end of the inverter, and the first end of the third switch module; the second end of the third switch module is connected with the first end of the fourth switch module; the second end of the fourth switch module is connected with the negative bus;

the control method comprises the following steps:

11. A photovoltaic system, comprising: a string of photovoltaic strings and an inverter as claimed in any one of claims 1 to 9;

the input side of the inverter is connected with the photovoltaic group string.