阅读说明：本技术 一种光伏发电系统和光伏组件的保护电路 (Photovoltaic power generation system and photovoltaic module's protection circuit ) 是由 李运生 于 2021-08-12 设计创作，主要内容包括：本发明提供一种光伏发电系统和光伏组件的保护电路；该保护电路,包括：反向过压检测单元和保护支路单元；反向过压检测单元、电流支路和旁路二极管并联连接；反向过压检测单元,用于检测光伏组件是否存在反向过压故障；并在检测到存在反向过压故障时,触发保护支路单元对旁路二极管进行分流；其中,反向过压故障为光伏组件出现反向过压；进而在光伏组件出现反向过压时,触发保护支路单元对旁路二极管进行分流、以保持旁路二极管对光伏组件的保护,从而保护旁路二极管不被损坏；同时,保护方式为分流,并不是直接将该旁路二极管进行断路,保持旁路二极管的功能,提高旁路二极管所在电路的安全性。(The invention provides a photovoltaic power generation system and a protection circuit of a photovoltaic module; the protection circuit includes: the device comprises a reverse overvoltage detection unit and a protection branch unit; the reverse overvoltage detection unit, the current branch and the bypass diode are connected in parallel; the reverse overvoltage detection unit is used for detecting whether a photovoltaic module has a reverse overvoltage fault; when the reverse overvoltage fault is detected, the protection branch unit is triggered to shunt the bypass diode; the photovoltaic module is connected with the power supply, wherein the photovoltaic module is connected with the power supply through the power supply line; when the photovoltaic module is in reverse overvoltage, the protection branch unit is triggered to shunt the bypass diode so as to keep the bypass diode protecting the photovoltaic module, and therefore the bypass diode is protected from being damaged; meanwhile, the protection mode is shunting, the bypass diode is not directly broken, the function of the bypass diode is kept, and the safety of a circuit where the bypass diode is located is improved.)

1. The protection circuit of the photovoltaic module is characterized in that the photovoltaic module comprises N photovoltaic cell substrings which are sequentially connected in series; two ends of each photovoltaic cell sub-string are reversely connected with a bypass diode in parallel; the protection circuit includes: the device comprises a reverse overvoltage detection unit and a protection branch unit;

the protection branch unit and the bypass diode are directly or indirectly connected in parallel;

the reverse overvoltage detection unit is connected with the bypass diode in series or in parallel;

the reverse overvoltage detection unit is used for detecting whether a reverse overvoltage fault exists in the photovoltaic module; when the reverse overvoltage fault is detected, the protection branch circuit unit is triggered to shunt the bypass diode; wherein the reverse overvoltage fault is the occurrence of reverse overvoltage of the photovoltaic module.

2. The protection circuit of a photovoltaic module according to claim 1, wherein the reverse overvoltage detection unit comprises: the first resistor and the voltage stabilizing switch are connected in series;

and a connection point between the first resistor and the voltage stabilizing switch is used as an output end of the reverse overvoltage detection unit.

3. The protection circuit of the photovoltaic module according to claim 2, wherein the zener switch is a zener diode.

4. The protection circuit of the photovoltaic module according to claim 3, wherein the zener diode is the bypass diode, or is a zener diode independent of the bypass diode.

5. The protection circuit of the photovoltaic module according to claim 3, wherein the first resistor and the voltage stabilizing switch are sequentially connected in series between the positive electrode and the negative electrode of the photovoltaic module; alternatively, the first and second electrodes may be,

the first resistor and the voltage stabilizing switch are sequentially connected in series between the negative electrode and the positive electrode of the photovoltaic module.

6. The protection circuit of a photovoltaic module according to any one of claims 1 to 5, wherein the protection branching unit comprises: a first controllable switch;

two ends of the first controllable switch are used as two ends of the protection branch unit;

and the control end of the first controllable switch is used as the control end of the protection branch unit.

7. The protection circuit of a photovoltaic module according to claim 6, wherein the first controllable switch comprises at least one of a relay and a switch tube.

8. The protection circuit of claim 7, wherein if the first controllable switch is the relay, the reverse overvoltage detection unit is a secondary side of a coil of the relay.

9. The protection circuit of a photovoltaic module according to claim 6, wherein the protection branching unit further comprises a second resistor connected in series with the first controllable switch.

10. A protection circuit of a photovoltaic module is characterized in that the photovoltaic module comprises N photovoltaic cell substrings which are sequentially connected in series; the output end of each photovoltaic cell sub-string is reversely connected with a bypass diode in parallel; the protection circuit includes: the device comprises a forward overcurrent detection unit and a bypass shunt unit;

the forward overcurrent detection unit is connected with the bypass diode in series;

the bypass shunt unit is connected with the bypass diode in parallel;

the forward overcurrent detection unit is used for detecting whether a forward overcurrent fault exists in the photovoltaic assembly; when the forward overcurrent fault is detected, the bypass shunt unit is triggered to shunt the bypass diode; and the forward overcurrent fault is that the photovoltaic module has forward overcurrent.

11. The protection circuit of a photovoltaic module according to claim 10, wherein the forward overcurrent detection unit includes: a second resistor and a third resistor;

the second resistor and the third resistor are connected in series and then are connected in series with the bypass diode;

and a connection point between the second resistor and the third resistor is connected with the output end of the forward overcurrent detection unit.

12. The protection circuit of a photovoltaic module according to claim 11, wherein the forward overcurrent detection unit further comprises: a first switch tube;

the control end of the first switch tube is connected with a connection point between the second resistor and the third resistor;

the first end of the first switch tube is connected with one end, far away from the third resistor, of the second resistor;

and the second end of the first switching tube is connected with the output end of the forward overcurrent detection unit.

13. The protection circuit of a photovoltaic module according to claim 11, wherein the third resistor is a thermistor;

the thermistor is disposed proximate to the bypass diode.

14. The protection circuit of claim 12, wherein the first switch tube is a voltage-driven low-impedance switch tube.

15. The protection circuit of a photovoltaic module according to any one of claims 11 to 14, wherein the bypass shunt unit comprises: a second controllable switch and a fourth resistor;

the second controllable switch is indirectly connected in parallel with the bypass diode;

the control end of the second controllable switch is connected with one end of the fourth resistor;

and the first end of the second controllable switch is connected with the other end of the fourth resistor, and the connection point is used as the control end of the bypass shunt unit.

16. The protection circuit of a photovoltaic module according to claim 15, wherein when the forward overcurrent detecting unit includes the first switching tube:

a connecting point between the third resistor and the fourth resistor is connected with the second end of the first switching tube;

a second terminal of the second controllable switch is connected to the cathode of the bypass diode.

17. The protection circuit of claim 15, wherein the second controllable switch is an NPN transistor.

18. A photovoltaic power generation system, comprising: an inverter unit, at least one photovoltaic module, and at least one protection circuit of a photovoltaic module according to any one of claims 1 to 9 or a protection circuit of a photovoltaic module according to any one of claims 10 to 17; wherein:

the photovoltaic modules are connected in series to form photovoltaic string, and the output end of each photovoltaic string is connected in parallel and then connected to the direct current side of the inverter unit;

and the alternating current side of the inversion unit is connected to a power grid.

19. The photovoltaic power generation system of claim 18, wherein the protection circuit in the photovoltaic module is disposed in a junction box of the photovoltaic module.

Technical Field

The invention belongs to the technical field of photovoltaic module protection, and particularly relates to a photovoltaic power generation system and a photovoltaic module protection circuit.

Background

At present, a photovoltaic module is formed by connecting dozens of silicon wafers in series, and then the silicon wafers connected in series are divided into three photovoltaic cell sub-strings, namely, a plurality of photovoltaic cell sub-strings are connected, and if one of the photovoltaic cell sub-strings fails, other photovoltaic cell sub-strings are affected.

As shown in fig. 1, each of the sub-strings of the photovoltaic cell in the prior art is connected in parallel with a bypass diode, but when the bypass diode fails once, particularly when the photovoltaic module is in reverse overvoltage, the bypass diode cannot work normally, and then the bypass diode cannot bypass the faulty sub-string of the photovoltaic cell shielded by the shadow, and the faulty sub-string of the photovoltaic cell still affects the stability of other sub-strings of the photovoltaic cell and the system.

Disclosure of Invention

In view of the above, the present invention provides a photovoltaic power generation system and a protection circuit of a photovoltaic module, which are used to maintain the function of a bypass diode and improve the safety and stability of the photovoltaic module and the system thereof.

The invention discloses a protection circuit of a photovoltaic module, wherein the photovoltaic module comprises N photovoltaic cell sub-strings which are sequentially connected in series; two ends of each photovoltaic cell sub-string are reversely connected with a bypass diode in parallel; the protection circuit includes: the device comprises a reverse overvoltage detection unit and a protection branch unit;

the protection branch unit and the bypass diode are directly or indirectly connected in parallel;

the reverse overvoltage detection unit is connected with the bypass diode in series or in parallel;

the reverse overvoltage detection unit is used for detecting whether a reverse overvoltage fault exists in the photovoltaic module; when the reverse overvoltage fault is detected, the protection branch circuit unit is triggered to shunt the bypass diode; wherein the reverse overvoltage fault is the occurrence of reverse overvoltage of the photovoltaic module.

Optionally, the reverse overvoltage detection unit includes: the first resistor and the voltage stabilizing switch are connected in series;

and a connection point between the first resistor and the voltage stabilizing switch is used as an output end of the reverse detection unit.

Optionally, the voltage stabilizing switch is a voltage stabilizing diode.

Optionally, the zener diode is the bypass diode, or is a zener diode independent of the bypass diode.

Optionally, the first resistor and the voltage stabilizing switch are sequentially connected in series between the positive electrode and the negative electrode of the photovoltaic module; alternatively, the first and second electrodes may be,

the first resistor and the voltage stabilizing switch are sequentially connected in series between the negative electrode and the positive electrode of the photovoltaic module.

Optionally, the protection branch unit includes: a first controllable switch;

two ends of the first controllable switch are used as two ends of the protection branch unit;

and the control end of the first controllable switch is used as the control end of the protection branch unit.

Optionally, the first controllable switch includes at least one of a relay and a switch tube.

Optionally, if the first controllable switch is the relay, the reverse overvoltage detection unit is a coil secondary side of the relay.

Optionally, the protection branch unit further includes a second resistor connected in series with the first controllable switch.

The invention discloses a protection circuit of a photovoltaic module, wherein the photovoltaic module comprises N photovoltaic cell sub-strings which are sequentially connected in series; the output end of each photovoltaic cell sub-string is reversely connected with a bypass diode in parallel; the protection circuit includes: the device comprises a forward overcurrent detection unit and a bypass shunt unit;

the forward overcurrent detection unit is connected with the bypass diode in series;

the bypass shunt unit is connected with the bypass diode in parallel;

the forward overcurrent detection unit is used for detecting whether a forward overcurrent fault exists in the photovoltaic assembly; when the forward overcurrent fault is detected, the bypass shunt unit is triggered to shunt the bypass diode; and the forward overcurrent fault is that the photovoltaic module has forward overcurrent.

Optionally, the forward overcurrent detection unit includes: a second resistor and a third resistor;

the second resistor and the third resistor are connected in series and then are connected in series with the bypass diode;

and a connection point between the second resistor and the third resistor is connected with the output end of the forward overcurrent detection unit.

Optionally, the forward overcurrent detection unit further includes: a first switch tube;

the control end of the first switch tube is connected with a connection point between the second resistor and the third resistor;

the first end of the first switch tube is connected with one end, far away from the third resistor, of the second resistor;

and the second end of the first switching tube is connected with the output end of the forward overcurrent detection unit.

Optionally, the third resistor is a thermistor;

the thermistor is disposed proximate to the bypass diode.

Optionally, the first switch tube is a low-impedance switch tube driven by a voltage type.

Optionally, the bypass shunt unit includes: a second controllable switch and a fourth resistor;

the second controllable switch is indirectly connected in parallel with the bypass diode;

the control end of the second controllable switch is connected with one end of the fourth resistor;

and the first end of the second controllable switch is connected with the other end of the fourth resistor, and the connection point is used as the control end of the bypass shunt unit.

Optionally, when the forward overcurrent detection unit includes the first switching tube:

a connecting point between the third resistor and the fourth resistor is connected with the second end of the first switching tube;

a second terminal of the second controllable switch is connected to the cathode of the bypass diode.

Optionally, the second controllable switch is an NPN type triode.

A third aspect of the present invention discloses a photovoltaic power generation system, including: an inverter unit, at least one photovoltaic module, and at least one protection circuit of the photovoltaic module according to any one of the first aspect of the present invention or the second aspect of the present invention; wherein:

the photovoltaic modules are connected in series to form photovoltaic string, and the output end of each photovoltaic string is connected in parallel and then connected to the direct current side of the inverter unit;

and the alternating current side of the inversion unit is connected to a power grid.

Optionally, the protection circuit in the photovoltaic module is disposed in a junction box of the photovoltaic module.

From the above technical solution, the protection circuit of a photovoltaic module provided by the present invention includes: the device comprises a reverse overvoltage detection unit and a protection branch unit; the reverse overvoltage detection unit, the current branch and the bypass diode are connected in parallel; the reverse overvoltage detection unit is used for detecting whether a photovoltaic module has a reverse overvoltage fault; when the reverse overvoltage fault is detected, the protection branch unit is triggered to shunt the bypass diode; the photovoltaic module is connected with the power supply, wherein the photovoltaic module is connected with the power supply through the power supply line; when the photovoltaic module is in reverse overvoltage, the protection branch unit is triggered to shunt the bypass diode so as to keep the bypass diode protecting the photovoltaic module, and therefore the bypass diode is protected from being damaged; meanwhile, the protection mode is shunting, the bypass diode is not directly broken, the function of the bypass diode is kept, and the safety of a circuit where the bypass diode is located is improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a schematic view of a photovoltaic module provided by the prior art;

fig. 2 is a schematic diagram of a protection circuit of a photovoltaic module according to an embodiment of the present invention;

fig. 3 is a schematic diagram of a protection circuit of another photovoltaic module provided by the embodiment of the invention;

fig. 4 is a schematic diagram of a protection circuit of another photovoltaic module provided by the embodiment of the invention;

FIG. 5 is a schematic diagram of another photovoltaic module and its protection circuit provided by embodiments of the present invention;

FIG. 6 is a timing diagram of the current of a photovoltaic module according to an embodiment of the present invention;

fig. 7 is a schematic diagram of a protection circuit of another photovoltaic module provided by an embodiment of the invention;

fig. 8 is a schematic diagram of a protection circuit of another photovoltaic module provided by an embodiment of the invention;

fig. 9 is a schematic diagram of another photovoltaic module and its protection circuit provided by the embodiment of the invention;

FIG. 10 is a timing diagram of the current flow of another photovoltaic module provided by embodiments of the present invention;

fig. 11 is a schematic diagram of a protection circuit of another photovoltaic module provided by an embodiment of the invention;

fig. 12 is a schematic diagram of another photovoltaic module and a protection circuit thereof according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In this application, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The embodiment of the invention provides a protection circuit of a photovoltaic assembly, which is used for solving the problems that in the prior art, each photovoltaic cell sub-string is connected with a bypass diode in parallel, once the bypass diode fails, particularly when the photovoltaic assembly is in reverse overvoltage, the bypass diode cannot work normally, further the bypass diode cannot bypass a fault photovoltaic cell sub-string shielded by a shadow, and the fault photovoltaic cell sub-string still influences the stability of other photovoltaic cell sub-strings and a system.

Referring to fig. 2, the photovoltaic module includes N photovoltaic cell sub-strings, and specifically, the N photovoltaic cell sub-strings are sequentially connected in series. And the output end of each photovoltaic cell sub-string is reversely connected with a bypass diode in parallel.

This photovoltaic module's protection circuit includes: a reverse overvoltage detection unit 10 and a protection bypass unit 20.

The protection branching unit 20 and the bypass diode DP are directly or indirectly connected in parallel.

The reverse overvoltage detection unit 10 is connected in series with the bypass diode DP, or the reverse overvoltage detection unit 10 is connected in parallel with the bypass diode DP; the specific structure thereof is not described herein any more and is within the scope of the present application.

The reverse overvoltage detection unit 10 is used for detecting whether a photovoltaic module has a reverse overvoltage fault; when detecting that a reverse overvoltage fault exists, triggering the protection branch unit 20 to shunt the bypass diode DP; wherein, reverse overvoltage fault appears reverse overvoltage for photovoltaic module.

That is, if the photovoltaic module has a reverse overvoltage, the reverse overvoltage detection unit 10 can detect the reverse overvoltage, and when a reverse overvoltage fault is detected, the protection branch unit 20 is triggered to protect the photovoltaic module. Specifically, the protection branch unit 20 branches the bypass diode DP to protect the photovoltaic module.

That is, the protection of the photovoltaic module by the protection branch unit 20 is to shunt the bypass diode DP, and the bypass diode DP is not directly switched out, so that the bypass diode DP can continue to operate.

Specifically, protection branch unit 20 shunts bypass diode DP, and then makes the electric current that originally flows through bypass diode DP reduce, avoids bypass diode DP to become invalid and lead to the unable protected problem of photovoltaic module when photovoltaic module reverse overvoltage appears, improves photovoltaic module's security and stability.

In this embodiment, when a reverse overvoltage occurs to the photovoltaic module, the protection branch unit 20 is triggered to shunt the bypass diode DP to keep the photovoltaic module protected by the bypass diode DP, so as to protect the bypass diode DP from being damaged; meanwhile, the protection mode is shunting, the bypass diode DP is not directly broken, the function of the bypass diode DP is kept, and the safety of a circuit where the bypass diode DP is located is improved.

In practical applications, as shown in fig. 3, the reverse overvoltage detection unit 10 includes: a first resistor R1 and a voltage stabilizing switch (D1 shown in fig. 3) connected in series.

The connection point between the first resistor R1 and the voltage stabilizing switch is used as the output end of the reverse overvoltage detection unit 10; that is, the voltage at the connection point between the first resistor R1 and the zener switch is used as the output signal of the reverse overvoltage detection unit 10 to control the protection branch unit 200, and the specific control process may be: when the voltage at the connection point between the first resistor R1 and the zener switch is higher than the threshold value, the protection bypass unit 20 is triggered to bypass the bypass diode DP. Of course, other modes are also possible, and are not described in detail herein, and all are within the scope of protection of the present application.

The first resistor R1 and the voltage stabilizing switch are sequentially connected in series between the anode and the cathode of the photovoltaic module; or the first resistor R1 and the voltage stabilizing switch are sequentially connected in series between the negative electrode and the positive electrode of the photovoltaic module.

Specifically, one end of the first resistor R1 is connected with the battery anode of the photovoltaic battery sub-string, the other end of the first resistor R1 is connected with one end of the voltage stabilizing switch, and the other end of the voltage stabilizing switch is connected with the cathode of the photovoltaic battery sub-string. Or one end of the first resistor R1 is connected with the negative electrode of the photovoltaic cell sub-string, the other end of the first resistor R1 is connected with one end of the voltage stabilizing switch, and the other end of the voltage stabilizing switch is connected with the positive electrode of the photovoltaic cell sub-string. The connection position between the first resistor R1 and the voltage regulator switch is not specifically limited herein, and is within the protection scope of the present application.

The first resistor R1 may be a thermistor or a common resistor, and is not limited herein, and is within the scope of the present application.

In practical applications, the voltage stabilizing switch is a voltage stabilizing diode D1.

Specifically, the direction of the anode of the zener diode D1 pointing to the cathode is opposite to the direction from the positive electrode to the negative electrode of the photovoltaic cell sub-string; that is, the pass of zener diode D1 is connected in anti-parallel with the output of the photovoltaic cell sub-string.

Note that the zener diode D1 may be a zener diode D1 independent of the bypass diode DP; that is, there are two diodes in the photovoltaic string (as shown in fig. 3) at this time. The zener diode D1 may be a bypass diode DP in a photovoltaic module; i.e. there is only one diode in the photovoltaic cell sub-string (as shown in fig. 4).

In practical applications, the protection branching unit 20 includes: a first controllable switch S1.

Both ends of the first controllable switch S1 serve as both ends of the protection branching unit 20; the control terminal of the first controllable switch S1 serves as the control terminal of the protection branching unit 20.

Specifically, as shown in fig. 3, the control terminal of the first controllable switch S1 is connected to the anode of the zener diode D1 and one terminal of the first resistor R1, respectively; one end of the first controllable switch S1 is respectively connected with the other end of the first resistor R1 and the battery cathode of the photovoltaic battery sub-string; the other end of the first controllable switch S1 is connected to the cathode of the zener diode D1 and the battery anode of the photovoltaic battery sub-string, respectively.

It should be noted that, when the positions of the first resistor R1 and the zener diode D1 are exchanged, the connection relationship of the first controllable switch S1 is similar to the connection relationship shown in fig. 3, and details are not repeated here and are within the protection scope of the present application.

When the photovoltaic cell sub-string is reversely over-voltage, the voltage difference between the two ends of the first resistor R1 reaches the threshold value, and then the first controllable switch S1 is triggered to be switched on, so that the first controllable switch S1 shunts the bypass diode DP, and the photovoltaic cell sub-string is protected.

In this embodiment, the protection circuit can realize protection of the photovoltaic module by adding the first resistor R1 and the first controllable switch S1.

It should be noted that the first controllable switch S1 includes at least one of a relay and a switch tube.

If the first controllable switch S1 is a relay, the reverse overvoltage detection unit 10 is a coil secondary of the relay. The structure of the device is not described in detail herein, and is within the scope of the present application depending on the actual situation.

In practical applications, the protection branch unit 20 further comprises a second resistor R2 connected in series with the first controllable switch S1.

The second resistor R2 is used to limit the current flowing through the first controllable switch S1. The purpose of limiting the first controllable switch S1 is to avoid overcurrent damage of the first controllable switch S1.

As shown in fig. 5, taking the number of the sub-strings of the photovoltaic cells equal to 3 as an example, one photovoltaic module is formed by connecting dozens of silicon wafers in series, and then dividing the silicon wafers connected in series into three sub-strings of the photovoltaic cells, wherein each sub-string of the photovoltaic cells is reversely connected with a bypass diode DP in parallel; three protection circuits and three bypass diodes DP (shown as DP, DP2 and DP2 in fig. 5) are provided accordingly.

Wherein, in the first protection circuit: r11, S11 are reverse overvoltage conditions for protection of bypass diode DP 1. In the second protection circuit: r12, S12 are reverse overvoltage conditions for protection of bypass diode DP 2. In the third protection circuit: r13, S13 are reverse overvoltage conditions for protection of bypass diode DP 3.

The source electrode S of the switching tube S11 is respectively connected with the first resistor R11 and the battery cathode of the corresponding photovoltaic battery sub-string; the grid G of the switch tube S11 is connected with the anode of the bypass diode DP 1; the drain D of the switching tube S11 is connected to the cell anode of the corresponding photovoltaic cell sub-string. The source electrode S of the switching tube S12 is respectively connected with the first resistor R12 and the battery cathode of the corresponding photovoltaic battery sub-string; the grid G of the switch tube S12 is connected with the anode of the bypass diode DP 2; the drain D of the switching tube S12 is connected to the cell anode of the corresponding photovoltaic cell sub-string. The source electrode S of the switching tube S13 is respectively connected with the first resistor R13 and the battery cathode of the corresponding photovoltaic battery sub-string; the grid G of the switch tube S13 is connected with the anode of the bypass diode DP 3; the drain D of the switching tube S13 is connected to the cell anode of the corresponding photovoltaic cell sub-string.

Next, the working principle process of the protection circuit of one group of independent photovoltaic modules is analyzed, and the normal illumination working condition of the photovoltaic modules, the shadow shielding working condition of the photovoltaic modules in which the photovoltaic cell substrings appear, and the reverse overvoltage short circuit working condition of the bypass diode DP are analyzed.

Firstly, when the photovoltaic module is illuminated normally, the photovoltaic cell sub-string is used as output power, the direction of the generated voltage U1 at the output end is consistent with the voltage direction of the photovoltaic cell sub-string, and at the moment, the bypass diode DP1 is disconnected, namely i2 is equal to 0; at this time, VT > VSG is 0, and the switching tube S11 is in an off state, where the voltage U _ S1 across the switching tube S11 is U1< 0. At the moment, the bypass diode DP1 is disconnected, the switch tube S11 is disconnected, and the photovoltaic module is in normal power generation.

Secondly, a shadow shielding working condition occurs on a battery sub-string in the photovoltaic module, when an internal resistor formed by shielding is larger than an external load resistor, the direction of the generated voltage U1 at the output end is inconsistent with the voltage direction of the photovoltaic battery sub-string, the specific value is as formula (1), a bypass diode DP1 is conducted to shunt, and a second resistor R2 generates voltage drop; the shunt current i2>0, and the voltage drop at the source S and the gate G of the switch transistor S11 is formula (2).

U1＝i2×(R1+R2+R4)+V_D1Formula (1)

0＜V_SG＝i2×R2＝-V_GSFormula (2)

Wherein, V_DPIs the voltage across bypass diode DP1, V_SGThe source-gate voltage of the corresponding switch tube.

The driving voltage VGS <0 of the switching tube S11 is obtained from formula (1), and the switching tube S11 is in an off state. At this time, the bypass diode DP1 is in the normal conducting state, and the switching tube S11 is turned off, thereby not playing the protection role.

When the photovoltaic module is subjected to a reverse voltage of the bypass diode DP1 exceeding the withstand reverse voltage, the bypass diode DP1 will be short-circuited by a reverse overvoltage.

The reverse overvoltage can be classified into two types, one is electric breakdown that can be recovered, and the other is thermal breakdown that can not be recovered. The breakdown process can be divided into two stages, namely a dynamic stage of diode breakdown caused by external reverse voltage; the second stage is a steady state stage after breakdown, and the steady state stage has two states, one is that the short circuit can not be recovered after the breakdown of the diode, and the other is that the short circuit can be recovered after the breakdown of the diode.

Stage one: and (4) dynamic process.

Since the direction of the external reverse overvoltage voltage, i.e. the voltage direction of U1, is not consistent with the direction of the photovoltaic cell sub-string, the bypass diode DP1 breaks down and conducts when bearing the reverse withstand voltage, the current i2 flows from bottom to top, the voltage VGS across the gate G and the source S of the switching tube S11 is generated by the second resistor R2, the resistance of the first resistor R1 increases along with the heat generation of the bypass diode DP1 along with the heat generation caused by the reverse overvoltage of the bypass diode DP1, if the first resistor R1 is a thermistor. As shown in equation (3), when VGS is greater than the threshold voltage VT of the switch transistor S11, the switch transistor S11 is turned on. At this time, the switch tube S11 shunts the bypass diode DP1 to reduce the thermal loss of the bypass diode DP1, so as to protect the bypass diode DP1 from thermal breakdown.

V_T＜V_GSI2 xr 2 formula (3)

When the temperature of the bypass diode DP1 decreases or the current decreases, the voltage across the second resistor R2 decreases. As shown in formula (4), when the voltage drop of the second resistor R2 is lower than the turn-on voltage of the switching tube S11, the switching tube S11 is turned off; the bypass diode DP1 continues to carry the full current at this point. When the temperature or the current of the bypass diode DP1 rises to a certain degree, the voltage across the second resistor R2 increases to a level that the switch tube S11 is turned on, the switch tube S11 is turned on to shunt the bypass diode DP1, the current on the switch tube S1 is i3, and the current on the bypass diode DP is i 4. The formula adopted for each current is formula (5).

V_T＞V_GSI2 xr 2 formula (4)

i2 ═ i3+ i4 formula (5)

And a second stage: a steady state process.

The recoverable steady state is taken as an example for explanation:

when the bypass diode DP1 returns to normal after passing through the reverse overvoltage, the bypass diode DP1 returns to off under normal illumination, and at this time, the current i2 of the branch where the bypass diode DP1 is located is 0, VGS of the switching tube S11 is 0, and the switching tube S1 is off.

When the photovoltaic cell sub-string is shielded by a shadow, the bypass diode DP1 is turned on in the forward direction after shielding to a certain degree, and specific analysis shows that the above is not repeated here, and the details are all within the protection range of the present application, and specifically, at this time, the current timing sequence in the protection circuit and the bypass diode DP1 is as shown in fig. 6, that is, the value of each current in the above description is repeated.

In this embodiment, when the bypass diode DP is in a reverse overvoltage condition, the protection circuit protects the photovoltaic module through an automatic shunting mechanism, so that an unrecoverable thermal breakdown of the bypass diode DP is avoided. Meanwhile, when the photovoltaic module and the inverter are connected for normal power generation, a single photovoltaic cell sub-string subjected to reverse overvoltage is automatically protected, namely, other photovoltaic modules are not influenced, the module with reverse overvoltage voltage is also protected, and the power generation of a photovoltaic system is not influenced in the whole process.

The invention also provides a protection circuit of the photovoltaic module; the photovoltaic module comprises N photovoltaic cell sub-strings which are sequentially connected in series; and the output end of each photovoltaic cell sub-string is reversely connected with a bypass diode DP in parallel.

As shown in fig. 7, the protection circuit of the photovoltaic module includes: a forward overcurrent detecting unit 30 and a bypass shunt unit 40.

The forward overcurrent detection unit 30 is connected in series with the bypass diode DP. That is, the forward overcurrent detecting unit 30 serves to detect the current flowing through the bypass diode DP. When the current of the bypass diode DP is larger than a preset current value, the bypass diode DP has a forward overcurrent fault; when the current of the bypass diode DP is smaller than a preset current value, the bypass diode DP does not have a forward flowing fault; the current of the bypass diode DP may be detected by detecting a temperature condition, or may be detected by detecting a voltage across a series resistor connected to the bypass diode DP.

The bypass shunt unit 40 is connected in parallel with the bypass diode DP; therefore, the bypass shunt unit 40 can shunt the bypass diode DP, thereby protecting the photovoltaic module.

The forward overcurrent detection unit 30 is used for detecting whether a forward overcurrent fault exists in the photovoltaic assembly; and triggers the bypass shunt unit 40 to shunt the bypass diode DP when detecting that there is a forward overcurrent fault.

And the forward overcurrent fault is the forward overcurrent of the photovoltaic module.

That is, if the photovoltaic module has a forward overcurrent, the forward overcurrent detection unit 30 can detect the forward overcurrent and trigger the bypass shunt unit 40 to protect the photovoltaic module when a forward overcurrent fault is detected. Specifically, the bypass shunt unit 40 shunts the bypass diode DP to protect the photovoltaic module.

That is, the bypass shunt unit 40 protects the photovoltaic module by shunting the bypass diode DP, and does not directly switch it out, so that the bypass diode DP can continue to operate.

Specifically, bypass shunting unit 40 shunts bypass diode DP, and then makes the electric current that originally flows through bypass diode DP reduce, avoids when photovoltaic module forward overcurrent appearing, and bypass diode DP became invalid and lead to the unable protected problem of photovoltaic module, improves photovoltaic module's security and stability.

In this embodiment, when the photovoltaic module is subjected to forward overcurrent, the bypass shunt unit 40 is triggered to shunt the bypass diode DP to keep the protection of the photovoltaic module by the bypass diode DP, so as to protect the bypass diode DP from being damaged; meanwhile, the protection mode is shunting, the bypass diode DP is not directly broken, the function of the bypass diode DP is kept, and the safety of a circuit where the bypass diode DP is located is improved.

In practical applications, as shown in fig. 8, the forward overcurrent detecting unit 30 includes: a second resistor R2 and a third resistor R3.

The second resistor R2 and the third resistor R3 are connected in series and then connected in series to the bypass diode DP. And a connection point between the second resistor R2 and the third resistor R3 is connected with the output end of the forward overcurrent detection unit 30.

In practical applications, the third resistor R3 may be a thermistor, or a common resistor, and when the third resistor R3 is a thermistor, the third resistor R3 is disposed close to the bypass diode DP, so that the third resistor R3 can detect the temperature of the bypass diode DP more sharply.

That is, the third resistor R3 is mounted close to the bypass diode DP, and the resistance of the third resistor R3 increases as the temperature of the bypass diode DP increases.

Specifically, one end of the second resistor R2 is used as the input end of the branch where the bypass diode DP is located; the other end of the second resistor R2 is connected to one end of the third resistor R3, and the connection point is used as the output end of the forward overcurrent detection unit 30; the other end of the third resistor R3 is connected with the anode of the bypass diode DP; the cathode of the bypass diode DP serves as the output of the branch in which the bypass diode DP is located.

In practical applications, as shown in fig. 3, the forward overcurrent detecting unit 30 may further include: and the first switching tube Q1 is arranged between the connection point between the second resistor R2 and the third resistor R3 and the output end of the forward overcurrent detection unit 30.

The control end of the first switching tube Q1 is connected with the connection point between the second resistor R2 and the third resistor R3; a first end of the first switch tube Q1 is connected with one end of the second resistor R2 far away from the third resistor R3; a second terminal of the first switching tube Q1 is connected to the output terminal of the forward overcurrent detecting unit 30.

Specifically, one end of the second resistor R2 is connected to the first end of the first switching tube Q1, and the connection point is used as the input end of the branch where the bypass diode DP is located; the other end of the second resistor R2 is respectively connected with one end of the third resistor R3 and the control end of the first switch tube Q1; a second end of the first switching tube Q1 is connected with the output end of the forward overcurrent detection unit 30; the other end of the third resistor R3 is connected with the anode of the bypass diode DP; the cathode of the bypass diode DP serves as the output of the branch in which the bypass diode DP is located.

Specifically, the first switch Q1 is a low-impedance switch driven by a voltage source; for example, the control terminal of the first switch Q1 is the gate of the N MOS, the first terminal of the first switch Q1 is the drain of the N MOS, and the second terminal of the first switch Q1 is the source of the N MOS.

In practical applications, as shown in fig. 8, the bypass shunt unit 40 includes: a second controllable switch S2 and a fourth resistor R4.

The second controllable switch S2 is indirectly connected in parallel with the bypass diode DP; the control terminal of the second controllable switch S2 is connected to one terminal of a fourth resistor R4; a first end of the second controllable switch S2 is connected to the other end of the fourth resistor R4, and the connection point is used as the control end of the bypass shunt unit 40; the connection point also serves as an input of the bypass shunt unit 40; that is, the connection point is connected to the output terminal of the forward overcurrent detecting unit 30; a second terminal of the second controllable switch S2 is connected to the cathode of the bypass diode DP.

In practical applications, when the forward overcurrent detecting unit 30 includes the first switching tube Q1:

a connecting point between the second resistor R2 and the third resistor R3 is connected with the control end of the first switch tube Q1; a first terminal of the second controllable switch S2 is connected to one terminal of the first switching transistor Q1, and a second terminal of the second controllable switch S2 is connected to the cathode of the bypass diode DP.

The second controllable switch S2 may be an NPN transistor; the control terminal of the second controllable switch S2 is a base of an NPN transistor, the first terminal of the second controllable switch S2 is a collector of the NPN transistor, and the second terminal of the second controllable switch S2 is an emitter of the NPN transistor.

Specifically, as shown in fig. 8, the operation of the forward overcurrent detecting unit 30 and the bypass shunt unit 40 in the protection circuit will be described:

first, when the bypass diode DP is off, that is, the current i2 flowing through the bypass diode DP becomes 0; the gate-source voltage VGS of the switching tube Q1 is 0. The switching tube Q1 is in an off state. At this time, when the base current ib of the transistor S2 is equal to 0, the transistor S2 is turned off; the diode between the BE end of the transistor S2 and the backward diode of the switch Q1 are in reverse directions, and the switch Q1 and the transistor S2 in the protection circuit are both in an off-state and an inactive state.

Secondly, the bypass diode DP is turned on with a current i2> 0; when i2 is smaller or the temperature of the bypass diode DP is lower and VGS of the switching tube Q1 is smaller than the threshold voltage VT of the switching tube Q1, the switching tube Q1 is in an off state, i.e. 0< VGS < VT. When the temperature of the bypass diode DP is too high or i2 is large, the resistance of the third resistor R3 will increase rapidly with the temperature rise of the bypass diode DP, where VBE of the transistor S2 is 0.7V, and when VGS of the switching transistor Q1 is greater than the turn-on voltage VT of the switching transistor Q1, the switching transistor Q1 is turned on. When the switching tube Q1 is turned on, ib >0 of the rear transistor S2 makes the transistor S2 in a saturation conduction state, and at this time, both the switching tube Q1 and the transistor S2 are in a conduction state.

When the switching tube Q1 and the triode S2 are turned on, the current i2 of the bypass diode DP is shunted, the shunt current is i3, and the current of the bypass diode DP is reduced to i4, so that the switching tube Q1 shares some power on the bypass diode DP to reduce the heat energy on the bypass diode DP, thereby protecting the bypass diode DP.

As the temperature of the bypass diode DP decreases or the current decreases, the resistance of the third resistor R3 decreases; the rate of increase of the resistance value of the third resistor R3 along with temperature rise is greater than the rate of decrease along with temperature drop; as the resistance of the third resistor R3 decreases, the gate VGS <0 of the switch Q1 is turned off. At this time, i3 is equal to 0, the base current ib of the transistor is equal to 0, and the transistor S2 is turned off.

In this embodiment, the third resistor R3 is used to automatically sense and trigger the on/off of the switching tube Q1, and accurately drive the on/off of the switching tube Q1 under different operating conditions, so as to implement shunt protection for the bypass diode DP. Through the series connection of the switching tube Q1 and the triode S2, the problem of forward conduction of a reverse parallel diode of the switching tube Q1 is effectively solved, and the forward conduction overheat protection of the bypass diode DP is realized.

That is to say, according to the operating condition of the bypass diode DP, the on-off of the switching tube is automatically triggered to increase a shunt branch, and the heating power of the bypass diode DP is reduced by reducing the current of the bypass diode DP, so as to protect the abnormal operating condition of the bypass diode DP. Meanwhile, the automatic trigger circuit of the protection circuit is simple and reliable and is effectively triggered through the high-precision third resistor R3.

Specifically, as shown in fig. 9, the operation of the reverse overvoltage detection unit 10 and the bypass shunt unit 40 in the protection circuit will be described:

it should be noted that, as shown in fig. 9, taking N equal to 3 and the third resistor as a thermistor as an example, a photovoltaic module is composed of dozens of silicon wafers connected in series, and then the silicon wafers connected in series are divided into three photovoltaic cell sub-strings, and each photovoltaic cell sub-string is connected with a bypass diode DP (DP 1, DP2 and DP3 shown in fig. 9) in parallel in an inverse manner; three protection circuits are provided correspondingly to protect the respective bypass diodes DP (DP 1, DP2 and DP3 shown in fig. 9).

That is, in the first protection circuit: r21, R31, R41, S21 and Q11 are bypass diodes DP1 used under the protection shading working condition, and a source S of a switch tube Q11 is connected with a triode S21 in series. The drain D of the switch tube Q11 is connected with the upper end of the R21, the grid G thereof is connected with the middle of the resistors R21 and R31, and the source S is connected with the cathode of the bypass diode DP 1.

In the second protection circuit: r22, R32, R42, S22 and Q12 are bypass diodes DP2 used under the protection shading working condition, and a source S of a switch tube Q12 is connected with a triode S22 in series. The drain D of the switch tube Q12 is connected with the upper end of the resistor R22, the grid G thereof is connected with the middle of the resistors R22 and R32, and the source S thereof is connected with the cathode of the bypass diode DP 2.

In the third protection circuit: r23, R33, R43, S23 and Q13 are bypass diodes DP3 used under the protection shading working condition, and a source S of a switch tube Q13 is connected with a triode S23 in series. The drain D of the switch tube Q13 is connected with the upper end of the resistor R23, the grid G thereof is connected with the middle of the resistors R23 and R33, and the source S thereof is connected with the cathode of the bypass diode DP 3.

In practical applications, the respective protection circuits and bypass diodes DP (DP 1, DP2, and DP3 shown in fig. 9) are provided in the junction box. Specifically, the negative terminal output line of the junction box is led out from the connection point between the resistor R21 and the switching tube Q11, and the positive terminal of the junction box is led out from the cathode of the bypass diode DP 3.

The working process of the protection circuit of the photovoltaic module of one group of substrings is analyzed, and the normal illumination working condition of the photovoltaic module and the shadow shielding working condition of the photovoltaic cell substring of the photovoltaic module are analyzed.

Firstly, when the photovoltaic module is illuminated normally, the photovoltaic cell sub-string is used as output power to generate electricity, the direction of the generated voltage U1 at the output end is consistent with the voltage direction of the photovoltaic cell sub-string, and at the moment, the bypass diode DP1 is disconnected, namely the current i2 flowing through the bypass diode DP is 0; the gate-source voltage VGS of the switching tube Q11 is 0, and the switching tube Q11 is off. At this time, when the base current ib of the transistor S21 is equal to 0, the transistor S21 is turned off; the diode between the BE end of the triode S21 and the backward diode of the switch tube Q11 are in the reverse direction, so that photovoltaic power generation is not influenced by the parasitic diode of the switch tube, and the switch tube Q11 and the triode S21 in the protection circuit are in a disconnected and non-operating state under the condition that the photovoltaic component is used as a power supply system when no shading exists. The adopted formula of the gate-source voltage of the switching tube Q11 is formula (6).

V_GSI2 xr 2 ═ 0 equation (6)

Secondly, a shadow shielding working condition occurs on a photovoltaic cell sub-string in the photovoltaic module, when an internal resistor formed by shielding is larger than an external load resistor, the direction of the generated voltage U1 at the output end is inconsistent with the voltage direction of the photovoltaic cell sub-string, and a bypass diode DP1 is conducted so that the shunt i2 is greater than 0; when i2 is small or the temperature of the bypass diode DP1 is low, the VGS of the switching tube Q11 is smaller than the threshold voltage VT, and the switching tube Q11 is in an off state, i.e. 0< VGS < VT. When the temperature of the bypass diode DP1 is too high, the resistance of the third resistor R31 will increase rapidly with the temperature rise of the bypass diode DP1, where VBE of the transistor S2 is 0.7V, and according to equation (7), the switching tube Q11 is turned on when VGS of the switching tube Q11 is greater than the turn-on voltage VT of the switching tube Q11. The switch Q11 turns on the rear transistor ib >0, so that the transistor S21 is in a saturated conduction state, and at this time, the switch Q11 and the transistor S21 are both in a conduction state.

When the switching tube Q11 and the triode S21 are turned on, the current i2 of the bypass diode DP1 is shunted, the shunt current is i3, and the current of the bypass diode DP1 is reduced to i4, so that the switching tube Q11 shares some power on the bypass diode DP1 to reduce the heat energy on the bypass diode DP1, thereby protecting the bypass diode DP 1. The formula adopted by each current is formula (8).

V_T＜V_GS＝i2×R2-V_BEFormula (7)

i2＝imp-i1

i2 ═ i3+ i4 equation (8)

i3＝imp-i1-i4

Wherein, V_TIs the threshold voltage of the corresponding switch tube, V_GSFor the gate-source voltage, V, of the corresponding switching tube_BEThe voltage between the terminals B and E of the corresponding switch tube.

As the temperature of the bypass diode DP1 decreases, the resistance of the third resistor R3 decreases; the rate of the resistance value of the third resistor R31 increasing with temperature rise is greater than the rate of the resistance value decreasing with temperature drop; the gate VGS <0 of the switching transistor Q11 is turned off as shown in equation (9). At this time, i3 is equal to 0, the base current ib of the transistor S21 is equal to 0, and the transistor S21 is turned off.

0 > VGS ═ i2 × R2-VBE formula (9)

With the switching tube Q11 turned off, if the shadow is blocked, the bypass diode DP1 will bear the i2 again to generate heat, which increases the resistance of the third resistor R31, and will turn on the switching tube Q11 and the transistor S21 to shunt the i3, so that the switching tube Q11 turns on and off back to shunt the protection bypass diode DP1, and at the same time, the switching tube Q11 is not turned on for a long time. Where fig. 10 is a current curve for bypass diode DP1 and the protection circuit in the shadow masking condition.

In this embodiment, this protection circuit can not influence normal photovoltaic module electricity generation, can trigger the protection according to the automatic perception of third resistance R31, and then shelters from at the photovoltaic module shadow and causes under the reverse overvoltage breakdown operating mode, effectively protects photovoltaic module.

It should be noted that the protection circuits of the photovoltaic modules provided in the above two embodiments can be integrated together, and the specific structure thereof is shown in fig. 11, in this case, the two protection circuits can also share a resistor. Specifically, R1, DP1, and S1 collectively constitute one protection circuit, and R1, R2, R4, Q1, and S2 collectively constitute another protection circuit. Referring to fig. 12, a structural diagram of the photovoltaic module is shown, and the specific working principle and the working process of the photovoltaic module are shown by taking the example that the number of the photovoltaic cell substrings in the photovoltaic module is equal to 3, and for details, reference is made to the two protection circuits provided in the above embodiments, which are not described herein again one by one, and are all within the protection scope of the present application.

Another embodiment of the present invention further provides a photovoltaic power generation system, including: the inverter comprises an inverter unit, at least one photovoltaic module and a protection circuit of the at least one photovoltaic module; wherein:

the photovoltaic modules are connected in series to form a photovoltaic string, and the output end of each photovoltaic string is connected in parallel and then connected to the direct current side of the inverter unit.

The protection circuit is used for protecting each photovoltaic cell sub-string in the photovoltaic module; the protection circuit can realize the protection of the corresponding photovoltaic cell sub-string by maintaining the function of the bypass diode of the reverse parallel connection of the photovoltaic cell sub-string.

And the alternating current side of the inversion unit is connected to a power grid.

In practical application, the protection circuit is arranged in a junction box of the photovoltaic module.

The junction box can be arranged on the back of the photovoltaic module, is not specifically limited, and can be determined according to actual conditions, and the junction box is within the protection scope of the application.

The specific structure and the working principle of the protection circuit can be seen in the above embodiments for details, which are not described herein any more and are all within the protection scope of the present application.

It should be noted that, the protection circuits in the prior art are all embedded in the assembly, and the maintainability is poor.

In the embodiment, the protection circuit of the photovoltaic module is placed in the junction box, so that the photovoltaic module is convenient to maintain.

Features described in the embodiments in the present specification may be replaced with or combined with each other, and the same and similar portions among the embodiments may be referred to each other, and each embodiment is described with emphasis on differences from other embodiments. In particular, the system or system embodiments are substantially similar to the method embodiments and therefore are described in a relatively simple manner, and reference may be made to some of the descriptions of the method embodiments for related points. The above-described system and system embodiments are only illustrative, wherein the units described as separate parts may or may not be physically separate, and the parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.

Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative components and steps have been described above generally in terms of their functionality in order to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.