CN103986192B - A kind of non-isolated photovoltaic grid-connected inverter and grid-connected photovoltaic system - Google Patents

Abstract

The embodiment of the invention discloses a kind of non-isolated photovoltaic grid-connected inverter, comprising: inversion unit; Be positioned at the leakage current sensor of the AC of described inversion unit; Connect the control module of described inversion unit and described leakage current sensor; The DC side of non-isolated photovoltaic grid-connected inverter described in one termination, the other end pass the passive device of ground connection after described leakage current sensor by wire, this passive device comprises equivalent resistance; And the gate-controlled switch being in series with described passive device, the control signal input of described gate-controlled switch connects described control module, to ensure that non-isolated photovoltaic grid-connected inverter still possesses leakage current troubleshooting capability in the situation that exchanging side joint isolating transformer. In addition, the invention also discloses a kind of isolated form grid-connected photovoltaic system.

Description

A non-isolated photovoltaic grid-connected inverter and photovoltaic grid-connected power generation system

technical field

The invention relates to the technical field of photovoltaic power generation, and more specifically, to a non-isolated photovoltaic grid-connected inverter and a photovoltaic grid-connected power generation system.

Background technique

Referring to Figure 1a, the non-isolated photovoltaic grid-connected inverter is an energy conversion device of a photovoltaic power generation system, which is used to convert the direct current generated by the photovoltaic module PV into alternating current and then send it to the grid. The components of the inverter include at least an inverter unit 10, a control unit 20, and a leakage current sensor 30; when the DC side of the inverter unit 10 is short-circuited to ground or the impedance is small, a great The leakage current flows to the AC side of the inverter unit 10, and the function of the control unit 20 is to control the inverter to handle the fault when it detects that the leakage current measured by the leakage current sensor 30 exceeds the preset value. (including controlling the switch tube in the inverter unit 10 to be turned off).

However, when the AC side of the non-isolated photovoltaic grid-connected inverter is connected to the isolation transformer 40 (see Figure 1b), the leakage current will not flow to the AC side, so the leakage current sensor 30 on the AC side cannot The magnitude of the leakage current is measured, so that the non-isolated photovoltaic grid-connected inverter loses the ability to handle leakage current faults, and is extremely prone to electric shock hazards.

Contents of the invention

In view of this, the present invention provides a non-isolated photovoltaic grid-connected inverter and an isolated photovoltaic grid-connected power generation system to ensure that the non-isolated photovoltaic grid-connected inverter is still connected to the isolation transformer on the AC side. Capable of handling leakage current faults.

A non-isolated photovoltaic grid-connected inverter, comprising an inverter unit, a leakage current sensor located on the AC side of the inverter unit, and a control unit connecting the inverter unit and the leakage current sensor, in addition It includes: a passive device with one end connected to the DC side of the non-isolated photovoltaic grid-connected inverter, and the other end passing through the leakage current sensor through a wire and then grounded. The passive device includes an equivalent resistance; and the A controllable switch connected in series with passive components, the control signal input end of the controllable switch is connected to the control unit.

Wherein, the controllable switch includes: a crystal controllable switch tube, an isolation controllable switch or a relay.

Optionally, the non-isolated photovoltaic grid-connected inverter further includes: a diode connected in series with the passive device.

Wherein, when the non-isolated photovoltaic grid-connected inverter is an inverter that requires no high-intensity negative voltage between the negative pole and the ground, the anode of the diode is connected to the leakage current sensor, and the cathode is connected to the leakage current sensor through the passive device. into the negative pole of the non-isolated photovoltaic grid-connected inverter.

Wherein, when the non-isolated photovoltaic grid-connected inverter is an inverter that requires no high-strength positive voltage between the positive pole and the ground, the cathode of the diode is connected to the leakage current sensor, and the anode is connected to the leakage current sensor through the passive device. into the positive pole of the non-isolated photovoltaic grid-connected inverter.

Wherein, the DC side of the non-isolated photovoltaic grid-connected inverter includes: the DC side or the DC bus of the inverter unit.

An isolated photovoltaic grid-connected power generation system, comprising: a photovoltaic module, any of the above-mentioned non-isolated photovoltaic grid-connected inverters, and an isolation transformer connecting the power grid and each of the non-isolated photovoltaic grid-connected inverters.

It can be seen from the above technical solutions that the present invention introduces passive devices and controllable switches into the existing non-isolated photovoltaic grid-connected inverter, one end of the passive device is connected to the DC side of the inverter, One end is grounded after passing through the leakage current sensor through a wire, and the controllable switch is connected to the control unit and connected in series with the passive device; thus, when the inverter is connected to the isolation transformer, it is only necessary to make the controllable switch When the switch is turned on, the leakage current generated on the DC side of the inverter can be directly introduced into the leakage current sensor for detection, so that the control unit can control the inverter to handle the leakage current fault according to the detection result of the leakage current sensor , to avoid the risk of electric shock.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1a is a schematic structural diagram of a photovoltaic grid-connected power generation system disclosed in the prior art;

Fig. 1b is a structural schematic diagram of another photovoltaic grid-connected power generation system disclosed in the prior art;

Fig. 2 is a schematic structural diagram of a non-isolated photovoltaic grid-connected inverter disclosed in Embodiment 1 of the present invention;

3a-3b are schematic structural diagrams of a non-isolated photovoltaic grid-connected inverter disclosed in Embodiment 2 of the present invention;

Fig. 4 is a schematic structural diagram of another non-isolated photovoltaic grid-connected inverter disclosed in Embodiment 2 of the present invention;

Fig. 5 is a schematic structural diagram of an isolated photovoltaic grid-connected power generation system disclosed in Embodiment 3 of the present invention.

detailed description

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Embodiment one:

Referring to Figure 2, Embodiment 1 of the present invention discloses a non-isolated photovoltaic grid-connected inverter to ensure that the non-isolated photovoltaic grid-connected inverter still has leakage current fault handling capabilities when the AC side is connected to an isolation transformer , including an inverter unit 10, a control unit 20, a leakage current sensor 30, a passive device 40 and a controllable switch K, wherein:

The leakage current sensor 30 is located on the AC side of the inverter unit 10; the control unit 20 is respectively connected to the inverter unit 10 and the leakage current sensor 30;

One end of the passive device 40 is connected to the DC side of the non-isolated photovoltaic grid-connected inverter, and the other end is grounded after passing through the leakage current sensor 30 through a wire, and the passive device 40 includes an equivalent resistance;

The controllable switch K is connected in series with the passive device 40 , and the control signal input end of the controllable switch K is connected to the control unit 20 (the connection relationship is not shown in FIG. 2 ).

Regarding this embodiment, there are 5 points that need to be explained (hereinafter referred to as the DC side and AC side of the non-isolated photovoltaic grid-connected inverter are "A side" and "B side", referred to as "A side" positive , the negative poles are PV ⁺ and PV ^- respectively):

1) The resistance value of the passive device 40 described in this embodiment is preferably 5KΩ-100KΩ, and its circuit structure may be one resistor, or a series-parallel combination of multiple resistors, etc., and is not limited thereto.

2) The direction and manner of the wire passing through the leakage current sensor 30 (such as a single-turn passing manner or a multi-turn passing manner) are not limited.

3) The controllable switch K can adopt a crystal controllable switch tube, an isolation controllable switch or a relay, etc.

4) The DC side of the non-isolated photovoltaic grid-connected inverter includes: the DC side or the DC bus bar of the inverter unit 10, and FIG. 2 only takes the passive device 40 connected to the DC side of the inverter unit 10 as an example; wherein , the non-isolated photovoltaic grid-connected inverter usually also includes a boost circuit arranged on the DC side of the inverter unit 10, and the outgoing line of the boost circuit is the DC bus.

5) The connection point between the passive device 40 and the "side ^A " can be PV ⁺ or PV-;

The non-isolated photovoltaic grid-connected inverter with PV ^- as the connection point is used to match the photovoltaic module that requires no high-intensity negative voltage between the negative pole and the ground, that is, the non-isolated photovoltaic grid-connected inverter is required to be connected between PV ^- and the ground. Inverters without high-intensity negative voltage, hereinafter referred to as Class 1 inverters;

The non-isolated photovoltaic grid-connected inverter with PV ⁺ as the connection point is used to match photovoltaic modules that require no high-intensity positive voltage between the positive pole and the ground, that is, the non-isolated photovoltaic grid-connected inverter is required to be connected between PV ⁺ and the ground. Inverters without high-intensity positive voltages are referred to as Type 2 inverters hereinafter.

In the following, the advantages of the solution described in this embodiment will be described in detail by analyzing the defects of existing non-isolated photovoltaic grid-connected inverters.

First of all, for the existing non-isolated photovoltaic grid-connected inverters, when the "B side" is not connected to the isolation transformer, the "A side" has a direct electrical connection with the grid, and the leakage current generated by the "A side" will flow to The "B side" is directly measured by the leakage current sensor 30 located on the "B side". After the introduction of the isolation transformer, due to the electrical isolation between the "A side" and the power grid, the leakage current can no longer flow from the "A side" to the "B side", resulting in the leakage current sensor 30 and the control unit 20 being idle, non-isolated The type photovoltaic grid-connected inverter loses the ability to handle leakage current faults, and if the operator accidentally touches the "A side" at this time, it is easy to cause an electric shock hazard.

For the non-isolated photovoltaic grid-connected inverter described in this embodiment, regardless of whether an isolation transformer is introduced into the photovoltaic power generation system, the detection of leakage current and fault handling can be realized without additional leakage current sensors. . It works as follows:

When the B side is not connected to the isolation transformer, the controllable switch K is turned off, then the working principle of the non-isolated photovoltaic grid-connected inverter described in this embodiment is consistent with that of the existing non-isolated photovoltaic grid-connected inverter ;

When the B side is connected to the isolation transformer, the controllable switch K is turned on. Since one end of the passive device 40 is connected to the A side, and the other end passes through the leakage current sensor 30 through a wire and then grounded, the leakage current generated on the A side can directly flow into the drain. The current sensor 30 realizes the detection of the leakage current;

The superiority of this embodiment in handling leakage current faults will be described below by taking a class 1 inverter as an example. When the A side of the type 1 inverter is short-circuited to the ground or the impedance to the ground is extremely small (that is, the PV ⁺ of the type 1 inverter is short-circuited to the ground or the impedance of the PV ⁺ to the ground is extremely small), the PV ^- and PV ⁺ to the ground The impedances are all very small ^, PV- and PV ⁺ all have higher ground voltage and can output a large leakage current, and the leakage current sensor 30 can detect a large leakage current and send the measurement result to the control unit 20, this The timing control unit 20 can perform leakage current fault processing when the measurement result exceeds the preset value, thereby avoiding the danger of electric shock. Wherein compared with the prior art, the leakage current fault handling described in this embodiment further includes: controlling the controllable switch K to be turned off.

That is to say, no matter whether the "B side" is connected to the isolation transformer or not, the leakage current generated by the "A side" can be reflected to the leakage current sensor 30 only by controlling the on and off of the controllable switch K, and the control unit 20 When it is detected that the measured value of the leakage current sensor 30 exceeds the preset value, the non-isolated photovoltaic grid-connected inverter can be controlled to handle the leakage current fault, thereby avoiding the risk of electric shock and solving the problems existing in the prior art .

In addition, when the controllable switch K is turned on, the non-isolated photovoltaic grid-connected inverter described in this embodiment can also suppress the PID (potential Induced Degradation, potential potential induced degradation) effect, the analysis is as follows:

The PID effect refers to the phenomenon that the performance level of the photovoltaic module is greatly reduced when it operates under a high voltage condition of a specific polarity; when the connection point between the passive device 40 and the A side is PV ^- , the impedance of PV ^- to the ground is much higher. Less than the ground impedance of PV ⁺ , so the ground voltage of PV ^- is very small, which avoids the PID effect caused by the existence of high voltage between PV- ^and the earth; in the same way, when the passive device 40 is connected to the A side When the point is PV ⁺ , the PID effect caused by the high voltage between PV ⁺ and the earth can also be avoided.

It can be seen from the above description that based on the non-isolated photovoltaic grid-connected inverter described in the first embodiment, only the controllable switch K is turned on and off, so that the leakage current generated on the "A side" can reflect The leakage current sensor 30 is used to detect the leakage current and handle the fault; in addition, when the controllable switch K is turned on, the inverter can effectively suppress the PID effect.

Embodiment two:

In order to reduce the current flowing through the branch where the passive device 40 is located, another non-isolated photovoltaic grid-connected inverter disclosed in Embodiment 2 further includes a diode connected in series with the passive device 40 . The conduction direction of this diode in the inverter is determined by the type of inverter. The specific analysis is as follows:

Referring to Fig. 3a, the non-isolated photovoltaic grid-connected inverter disclosed in the second embodiment based on the type 1 inverter includes: an inverter unit 10, a control unit 20, a leakage current sensor 30, a passive device 40, and a controllable switch K , and the anode is connected to the leakage current sensor 30 , and the cathode is connected to the cathode diode D of the non-isolated photovoltaic grid-connected inverter through the passive device 40 .

When the isolation transformer needs to be connected, it is only necessary to turn on the controllable switch K. At this time, the negative pole of the non-isolated photovoltaic grid-connected inverter can always maintain no high-intensity negative bias voltage to the ground, and the distance between the negative pole and the ground The PID effect is effectively suppressed due to the absence of a high negative bias voltage.

In addition, the non-isolated photovoltaic grid-connected inverter shown in Figure 3a (or Figure 2) can not only operate alone, but also can be used in parallel in multiple photovoltaic power generation systems, as shown in Figure 3b with two inverters The photovoltaic power generation system (including inverter 1 and inverter 2) is taken as an example (for the convenience of description, the branch where the controllable switch K, diode D and passive device 40 are located is defined as the PID suppression branch) for analysis:

If the PV ⁺ on the "A side" of inverter 1 is short-circuited to ground or the impedance to ground is extremely small, part of the current flowing from PV ⁺ to the ground will flow through the PID suppression branch of inverter 1, and the other part will flow through the inverter 2 PID suppression branch. At the same time, there will be circulating current between inverter 1 and inverter 2 due to parallel output; in inverter 1, the current flowing through the PID suppression branch is in the same direction as the circulating current, so they will strengthen each other, and the leakage current sensor will A large current value is detected, and when the current value is greater than a preset value, inverter 1 performs leakage current fault processing; while in inverter 2, the current flowing through the PID suppression branch is opposite to the direction of the circulating current , and thus cancel each other out, the current value detected by the leakage current sensor is too small to reach the preset value, and the inverter 2 does not perform leakage current fault processing. In this way, it is ensured that when one inverter fails, only the failed inverter performs leakage current fault treatment, while other unfailed inverters still operate normally in grid connection.

Referring to Fig. 4, the non-isolated photovoltaic grid-connected inverter disclosed in the second embodiment based on the 2 types of inverters includes: inverter unit 10, control unit 20, leakage current sensor 30, passive device 40, and cathode leakage The anode of the current sensor 30 is connected to the positive diode D of the non-isolated photovoltaic grid-connected inverter through the passive device 40 .

Similarly, when the inverter is connected to the isolation transformer, it is only necessary to turn on the controllable switch K. At this time, the PID effect is effectively suppressed because there is no high positive bias voltage between the positive pole of the inverter and the ground; Moreover, the inverter can be operated independently, and multiple units can be connected in parallel and applied in a photovoltaic power generation system.

In addition, in order to play a protective role, a fuse connected in series with the passive device can also be introduced into any of the non-isolated photovoltaic grid-connected inverters disclosed above.

Embodiment three

Referring to Fig. 5, Embodiment 3 of the present invention discloses an isolated photovoltaic grid-connected power generation system, including: a photovoltaic module 1, any of the above-mentioned non-isolated photovoltaic grid-connected inverters 2, and a connection grid and each of the non-isolated Isolation transformer 3 of isolated photovoltaic grid-connected inverter. Wherein, the number of photovoltaic modules 1 (that is, the number of non-isolated photovoltaic grid-connected inverters 2 ) is not limited.

In summary, the present invention introduces passive devices and controllable switches into the existing non-isolated photovoltaic grid-connected inverters, one end of the passive devices is connected to the DC side of the inverter, and the other end is passed through a wire The over-leakage current sensor is grounded after the over-leakage current sensor, and the controllable switch is connected to the control unit and connected in series with the passive device; thus, when the inverter is connected to the isolation transformer, only the controllable switch needs to be turned on, that is The leakage current generated on the DC side of the inverter can be directly introduced into the leakage current sensor for detection, so that the control unit can control the inverter to handle the leakage current fault according to the detection result of the leakage current sensor, so as to avoid electric shock Danger.

Each embodiment in this specification is described in a progressive manner, each embodiment focuses on the difference from other embodiments, and the same and similar parts of each embodiment can be referred to each other.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the embodiments of the present invention . Therefore, the embodiments of the present invention will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims (7)

1. a non-isolated photovoltaic grid-connected inverter, comprises inversion unit, is positioned at described inversion unitThe leakage current sensor of AC, and connect the control of described inversion unit and described leakage current sensorUnit, is characterized in that, described non-isolated photovoltaic grid-connected inverter is common to grid-connected of isolated formElectric system and non-isolation type grid-connected photovoltaic system, described non-isolated photovoltaic grid-connected inverter also comprises:

Described in one termination, the DC side of non-isolated photovoltaic grid-connected inverter, the other end pass institute by wireThe passive device of stating ground connection after leakage current sensor, this passive device comprises equivalent resistance;

And the gate-controlled switch being in series with described passive device, the control signal input of described gate-controlled switchEnd connects described control module.

2. non-isolated photovoltaic grid-connected inverter according to claim 1, is characterized in that, described inGate-controlled switch comprises: crystal controlled tr tube, isolation gate-controlled switch or relay.

3. non-isolated photovoltaic grid-connected inverter according to claim 1, is characterized in that, also bagDraw together: the diode being in series with described passive device.

4. non-isolated photovoltaic grid-connected inverter according to claim 3, is characterized in that, works as instituteWhen stating non-isolated photovoltaic grid-connected inverter and be requirement negative pole and thering is no over the ground the inverter of high strength negative voltage,The anode of described diode connects described leakage current sensor, negative electrode is described non-through described passive device accessThe negative pole of isolated form photovoltaic combining inverter.

5. non-isolated photovoltaic grid-connected inverter according to claim 3, is characterized in that, works as instituteWhen stating non-isolated photovoltaic grid-connected inverter and be requirement positive pole and thering is no over the ground the inverter of high strength positive voltage,The negative electrode of described diode connects described leakage current sensor, anode is described non-through described passive device accessThe positive pole of isolated form photovoltaic combining inverter.

6. non-isolated photovoltaic grid-connected inverter according to claim 1, is characterized in that, described inThe DC side of non-isolated photovoltaic grid-connected inverter comprises: the DC side of described inversion unit or dc bus.

7. an isolated form grid-connected photovoltaic system, is characterized in that, comprising: photovoltaic module, rightRequire the non-isolated photovoltaic grid-connected inverter described in any one in 1-6, and connect electrical network with described in eachThe isolating transformer of non-isolated photovoltaic grid-connected inverter.