CN106936112B - Combiner box protection device - Google Patents

Abstract

The invention discloses a combiner box protection device, wherein the combiner box includes a photovoltaic cable and a circuit breaker, and the combiner box protection device includes an acquisition unit, a logic unit and an execution unit. The acquisition unit is electrically connected to the photovoltaic cable, and is used to acquire the voltage signal of the photovoltaic cable; the logic unit is electrically connected to the acquisition unit to receive the voltage signal transmitted from the acquisition unit, and then compares the electrical signal with the comparison voltage, when the voltage When the absolute value of the difference between the signal and the comparison voltage is greater than or equal to the set value, the logic unit sends an instruction to the execution unit; and the execution unit is electrically connected to the logic unit and controls the circuit breaker to open according to the instruction transmitted from the logic unit. The combiner box protection device of the present invention can effectively control the opening of the circuit breaker when the photovoltaic cable is directly grounded, thereby solving a series of problems caused by the grounding of the photovoltaic cable.

Description

Combiner box protection device

technical field

The invention relates to the field of photovoltaic power generation, in particular to a combiner box protection device.

Background technique

A combiner box is an electrical device used in a photovoltaic power generation system. It is responsible for transferring the direct current generated by photovoltaic modules to the photovoltaic inverter after its primary confluence. In order to ensure the reliability and safety of power generation, the combiner box is equipped with lightning protection, overcurrent and overload protection. However, the highest failure rate of photovoltaic cables and photovoltaic cables connected to the combiner box is single-phase ground fault (positive ground or negative ground). The case was broken down, causing a fire. When this kind of fault occurs, the existing protection in the combiner box cannot operate, so this is a kind of defect in the design of the combiner box.

Contents of the invention

The purpose of the present invention is to provide a combiner box protection device to solve the above-mentioned problems in the prior art.

In order to solve the above problems, the present invention provides a combiner box protection device, the combiner box includes a photovoltaic cable and a circuit breaker, the combiner box protection device includes an acquisition unit, a logic unit and an execution unit; the acquisition unit and the The photovoltaic cable is electrically connected and used to collect the voltage signal of the photovoltaic cable; the logic unit is electrically connected to the collection unit to receive the voltage signal transmitted from the collection unit, and then compares the voltage signal with the comparison voltage, When the absolute value of the difference between the voltage signal and the comparison voltage is greater than or equal to the set value, the logic unit sends an instruction to the execution unit; and the execution unit is electrically connected to the logic unit and according to the logic unit The incoming command controls the opening of the circuit breaker.

Preferably, the comparison voltage is equal to 1.25-2 times the set value.

Preferably, the logic unit includes a comparator, and the comparator is electrically connected to the acquisition unit and the execution unit respectively.

Preferably, the logic unit further includes a first resistor and a second resistor, the first resistor and the second resistor are respectively connected to the positive and negative input terminals of the comparator through wires, and the first resistor and The resistance values of the second resistors are equal.

Preferably, the execution unit includes a first relay, and the first relay is in electrical communication with the logic unit and the circuit breaker, so as to control the opening of the circuit breaker according to an instruction transmitted from the logic unit.

Preferably, the execution unit further includes a second relay, the second relay is in electrical communication with the logic unit and the circuit breaker, so as to control the circuit breaker to close according to an instruction transmitted from the logic unit.

Preferably, the acquisition unit is configured to perform step-down processing on the voltage collected from the photovoltaic cable, and transmit the voltage value after step-down processing to the logic unit.

Preferably, the combiner box protection device further includes a secondary power supply, the secondary power supply is electrically connected to the acquisition unit, the logic unit and the execution unit to provide electric energy for the acquisition unit, the logic unit and the execution unit.

Preferably, the comparison voltage is equal to 17/41-20/41 of the open circuit voltage of the photovoltaic string branch.

Preferably, the comparison voltage is equal to 380V-400V, and the set value is equal to 190V-320V.

Preferably, the comparison voltage is equal to 400V, and the set value is equal to 200V.

In summary, through the combiner box protection device of the present invention, when the photovoltaic cable is directly grounded, the circuit breaker can be effectively controlled to open, thereby solving a series of problems caused by the grounding of the photovoltaic cable, and the ground fault of the photovoltaic cable through the transition resistance occurs in the combiner box , the combiner box protection device of the present invention will effectively control the opening of the circuit breaker when the damage is large, and will not operate when the damage is not large, so as to prevent economic losses caused by shutdown.

Description of drawings

Figure 1 is a schematic diagram of a photovoltaic power generation system;

Figure 2 shows the photovoltaic cable grounding in the combiner box;

Figure 3 is a schematic diagram of a photovoltaic module;

Fig. 4 is a schematic diagram of unit connections of a combiner box protection device according to an embodiment of the present invention;

5A-5B show the main circuit diagram of the logic unit of the present invention; and

Fig. 6 is a schematic diagram of connection of units of a combiner box protection device according to another embodiment of the present invention.

Detailed ways

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, so as to better understand the purpose, features and advantages of the present invention. It should be understood that the embodiments shown in the drawings are not intended to limit the scope of the present invention, but only to illustrate the essence of the technical solutions of the present invention.

Glossary

Combiner box: The main function of the combiner box is to combine the input of the photovoltaic array at the first level to reduce the connection between the photovoltaic array and the inverter. At the same time, it provides lightning protection function, detects the operating status of the photovoltaic panel, and collects the DC flow status. and circuit breaker status, etc.

Photovoltaic inverter: Photovoltaic inverter connects resistors and capacitors through power electronic devices (MOSFET, IGBT, etc.), controls the on-off of the device in the form of pulse width modulation, converts the direct current transmitted by the combiner box into alternating current, and completes the photovoltaic inverter at the same time. Maximum Power Point Tracking (MPPT) of components, guaranteed functional control and anti-islanding effects, etc.

Circuit breaker: The designed opening and closing device can close, break and carry the current in normal state; and it can also perform closing, breaking and conducting and breaking within a certain period of time under abnormal operating conditions.

Photovoltaic power generation system, its electrical schematic diagram is shown in 1. As can be seen from Figure 1, photovoltaic cables and DC cables are connected to the combiner box. Photovoltaic cables are used to connect photovoltaic module strings. DC cables are used for the connection between the combiner box and the PV inverter.

Fig. 2 shows the situation that a ground fault occurs during the actual operation of the photovoltaic power generation system. As shown in Figure 2, during the actual operation of the photovoltaic power station, the probability of a ground fault at a certain point of the photovoltaic cable is the highest.

When sunlight irradiates the surface of the photovoltaic module, it absorbs photons with a certain energy, and generates electron-hole pairs in an unbalanced state inside the module; under the action of the electric field in the P-N junction, the electrons and holes are respectively tended to N and P junctions, so that a photogenerated electric field opposite to the built-in electric field is formed near the P-N junction; the excess part of the photogenerated electric field offsets the built-in electric field of the P-N junction, making the P and N regions respectively bring positive and negative points, so that the N region is generated The photo-generated electromotive force pointing to the P area, that is, the voltage of the photovoltaic module in Figure 1; when the external load is connected, the current flows from the P area, and flows into the photovoltaic cell from the N area through the load. The schematic diagram is shown in Figure 3. Due to the influence of the P-N junction as a zero reference point, under normal operating conditions, the amplitude of the positive and negative voltages is equal, which is half of the voltage of the photovoltaic module.

In Figure 2, when a ground fault occurs at point A, the voltage on the positive copper bar side of the combiner box is close to zero. Since the P-N junction is an ungrounded reference point, the voltage on the negative copper side of the combiner box is the voltage of the photovoltaic module. The sharp rise of the voltage on the negative copper side will cause the devices inside the combiner box to be broken down under high voltage, thus causing a fire. However, the current, overload and other protections equipped with circuit breakers at this stage cannot operate and disconnect the circuit breaker. For this reason, the inventor invented the combiner box protection device of the present invention.

As shown in Figure 1, the combiner box usually includes photovoltaic cables, combiner box fuses, copper bars and circuit breakers. Among them, the photovoltaic cable is connected to the photovoltaic string, the photovoltaic string is connected in parallel through the photovoltaic cable, and then connected in series with the circuit breaker through the copper bar, and the combiner box fuse is set on the photovoltaic cable.

The combiner box protection device of the present invention generally includes an acquisition unit, a logic unit and an execution unit. The collection unit is electrically connected with the photovoltaic cable, so as to collect the voltage value of the photovoltaic cable. The logic unit is electrically connected to the acquisition unit, and receives the voltage value transmitted from the acquisition unit, and then compares the voltage value with the reference voltage value, and when the absolute value of the difference between the voltage value and the reference voltage value is greater than or equal to the set value , send instructions to the execution unit. The execution unit controls the opening of the circuit breaker according to the instruction sent from the logic unit, so that the combiner box will not be damaged due to the grounding of the photovoltaic cable.

The combiner box protection device of the present invention will be described in detail below in conjunction with the accompanying drawings.

Example 1

Fig. 4 is a schematic diagram of connection of units of the combiner box protection device according to this embodiment. As shown in FIG. 4 , the combiner box protection device 100 includes an acquisition unit 10 , a logic unit 20 and an execution unit 30 . Wherein, the collection unit 10 is electrically communicated with the positive electrode 41 of the photovoltaic cable and the negative electrode 42 of the photovoltaic cable respectively through wires. The logic unit 20 is in electrical communication with the acquisition unit 10 through wires. The execution unit 30 is in electrical communication with the logic unit 20 through wires.

As shown in Figure 4, the acquisition unit 10 of this embodiment is a voltage system measurement device, which can be a VSM or a DC/DC step-down component, which collects the voltage U ₊ and U _- of the positive pole 41 and negative pole 42 of the photovoltaic cable, and The collected voltages U ₊ and U- are subjected to step _- down processing, and after the collected voltages U ₊ and U- are subjected to step _- down processing, the processed voltage values are then passed to the logic unit, which will be described in detail below. In FIG. 4 , PE represents the zero reference point, GND represents the protective ground, and the secondary power supply 50 supplies power to the acquisition unit 10 .

5A and 5B are main circuit diagrams of the logic unit. As shown in Figures 5A and 5B, the logic unit mainly includes comparators 21 and 22, wherein Figure 5A shows the comparator 21 connected to the positive pole of the photovoltaic cable, and Figure 5B shows the comparator 22 connected to the negative pole of the photovoltaic cable.

Figure 5A shows comparator ₂₁ , resistors R1, R2 and _R3 , wherein, _one end of resistor R1 is connected to the positive input terminal of comparator ₂₁ through _a wire, and the other end of resistor R1 is connected to acquisition unit 10 through a wire , and receive the reduced voltage U ₊ from the acquisition unit 10 . One end of R ₂ is connected to the negative input end of the comparator 21 through a wire, and the other end receives the comparison voltage U _N through a wire. The output terminal of the comparator 21 is electrically connected to the execution unit 30, so as to send instructions to the execution unit.

FIG. 5B is similar to FIG. 5A except that the positive input end of the comparator 22 is connected to the acquisition unit 10 through wires, and receives the voltage U ₋ from the acquisition unit 10 after voltage reduction. As shown in Figure 5B, one end of the resistor R4 is connected to the positive input terminal of the comparator ₂₂ through a wire, and the other end of the resistor R4 is connected to the acquisition unit ₁₀ through a wire, and receives the voltage after the step-down process from the acquisition unit 10 _{U_} . One end of R ₅ is connected to the negative input terminal of the comparator 22 through a wire, and the other end receives a comparison voltage U _N through a wire, and the comparison voltage U _N is determined according to the open circuit voltage of the photovoltaic string branch. It will be described in detail below. The output end of the comparator 22 is electrically connected to the execution unit 30 , so as to send an instruction to the execution unit 30 .

The logic unit 20 is used to compare the voltages U ₊ , U ₋ with the reference voltage _UN . Wherein, the comparator 21 is used to compare the magnitude of the voltage U ₊ and U _N , and the comparator 22 is used to compare the magnitude of the voltage U ₋ and the comparison voltage U _N. When the expression ∣U _N -U ₊ ∣≥ε or ∣U _N -U _- ∣≥ε (ε is the set value) is satisfied, it can be determined that the photovoltaic cable is grounded, and of course, the DC cable is also grounded.

The execution unit 30 mainly includes a relay J1, which is electrically connected to the logic unit 20 and the circuit breaker 60. When the logic unit 20 sends an opening command to the relay J1, the relay J1 controls the switch 31 to close, thereby controlling the circuit breaker 60 to open.

The photovoltaic cable grounding or DC cable grounding of the combiner box includes direct grounding and transition resistance grounding. Direct grounding means that the photovoltaic cable is directly connected to the ground, and transition resistance grounding means that the photovoltaic cable is grounded again through a resistor. Therefore, the photovoltaic cable The collected voltage of the photovoltaic cable is 0 when it is directly grounded, and the value of the collected voltage when the photovoltaic cable is grounded through a transition resistance also depends on the magnitude of the resistance grounded through the resistance.

However, after a large amount of engineering practice, the inventor found that, in the case of grounding through a transition resistance, if the resistance to grounding through the transition resistance is large enough, the danger caused is extremely small. Therefore, the present invention is based on the actual situation of engineering practice.

Setting U _N to be equal to 17/41-20/41 of the open circuit voltage of the photovoltaic group transmission branch, and setting ε to be equal to 0.4U _N -0.8U _N , can achieve good results. For example, when the open circuit voltage of the branch circuit of the photovoltaic string is equal to 820V, U _N is equal to 380V-400V, and ε is equal to 0.4U _N -0.8U _N . Preferably, when the open circuit voltage of the photovoltaic string branch is equal to 820V, U _N is set to 400V, and ε is set to 200V.

During the working process of the combiner box, if the photovoltaic cable is directly grounded, since the photovoltaic cable is directly grounded, the voltage at the ground point is 0, so the U ₊ or U _- collected by the acquisition unit is equal to 0, at this time, the logic The unit judges ∣U _N -U ₊ ∣≥ε or ∣U _N -U _- ∣≥ε, thus, the logic unit sends an opening command to the execution unit, and after receiving the opening command, the logic unit controls the switch 31 through the relay J1 Closed, thereby controlling the opening of the circuit breaker. Therefore, serious consequences caused by the grounding of the combiner box are avoided.

If the photovoltaic cable is grounded through the transition resistance, at this time, if ∣U _N -U ₊ ∣≥ε or ∣U _N -U _- ∣≥ε, the logic unit sends an opening command to the execution unit, and the logic unit receives After receiving the opening command, the relay J1 controls the switch 31 to close, thereby controlling the opening of the circuit breaker of the combiner box, thereby avoiding serious consequences caused by the grounding of the combiner box. However, if ∣U _N -U ₊ ∣≥ε or ∣U _N -U _- ∣≥ε is not satisfied, it is not necessary to deal with it, because this situation will not cause major damage, thereby minimizing the damage caused by downtime Loss.

Example 2

Fig. 6 is a schematic diagram of connection of units of the combiner box protection device according to this embodiment. The combiner box protection device 200 of this embodiment will be described below with reference to FIG. 6 . The difference between Embodiment 2 and Embodiment 1 is mainly that the execution unit 30 also includes a relay J2, and the relay J2 is electrically connected to the logic unit through a wire, so as to receive the closing instruction sent by the logic unit. When receiving the closing instruction sent by the logic unit , the control circuit breaker is closed.

During the working process of the combiner box, if the photovoltaic cable is grounded and the circuit breaker is disconnected under the control of the execution unit, after the on-site personnel find out the ground fault and solve the grounding problem, it can be passed in Embodiment 1. Manually close the circuit breaker. In Embodiment 2, the logic unit sends a closing command to the relay J2. After receiving the closing command, the relay J2 controls the switch 32 to close, thereby controlling the closing of the circuit breaker.

In summary, through the combiner box protection device of the present invention, when the photovoltaic cable is directly grounded, the circuit breaker can be effectively controlled to open, thereby solving a series of problems caused by the grounding of the photovoltaic cable, and the ground fault of the photovoltaic cable through the transition resistance occurs in the combiner box , the combiner box protection device of the present invention will effectively control the opening of the circuit breaker when the damage is serious, and will not act when the damage is not serious, so as to prevent economic losses caused by shutdown.

The preferred embodiments of the present invention have been described in detail above, but it should be understood that those skilled in the art can make various changes or modifications to the present invention after reading the above teaching content of the present invention. These equivalent forms also fall within the scope defined by the appended claims of this application.

Claims (10)

1. a kind of header box protective device, the header box include photovoltaic cable and breaker, which is characterized in that the header box Protective device includes acquisition unit, logic unit and execution unit；The acquisition unit is electrically connected with the photovoltaic cable, and For acquiring the voltage signal of the photovoltaic cable；The logic unit is electrically connected to receive and adopt from described with the acquisition unit The positive and negative electrode voltage signal, is then compared by the positive and negative electrode voltage signal that transmits of collection unit with comparison voltage, when this just When the absolute value of the difference of pole tension signal and comparison voltage is greater than or equal to setting value, or the cathode voltage signal is electric compared with When the absolute value of the difference of pressure is greater than or equal to setting value, the logic unit sends to the execution unit and instructs；And it is described Execution unit is electrically connected with the logic unit and controls the breaker open operation according to the instruction transmitted from the logic unit； Wherein, positive and negative anodes are earth-free when the photovoltaic cable works normally；The header box protective device is for solving single-phase earthing event Barrier.

2. header box protective device according to claim 1, which is characterized in that the comparison voltage is equal to the setting value 1.25-2 times.

3. header box protective device according to claim 1, which is characterized in that the logic unit includes comparator, institute Comparator is stated to be electrically connected with the acquisition unit and the execution unit respectively.

4. header box protective device according to claim 3, which is characterized in that the logic unit further includes first resistor And second resistance, the first resistor and second resistance pass through conducting wire respectively and connect with the positive and negative input terminal of the comparator, and The resistance value of the first resistor and the second resistance is equal.

5. header box protective device according to claim 1, which is characterized in that the execution unit includes the first relay Device, first relay be connected to the logic unit and the circuit breaker electric, and according to transmitting from the logic unit Instruction controls the breaker open operation.

6. header box protective device according to claim 5, which is characterized in that the execution unit further includes the second relay Device, second relay is connected to the logic unit and the circuit breaker electric, to transmit according to from the logic unit Instruction control the breaker closing.

7. header box protective device according to claim 1, which is characterized in that the acquisition unit is arranged to from described The voltage of photovoltaic cable acquisition carries out decompression processing, and will treated that voltage value sends the logic unit to by decompression.

8. header box protective device according to claim 1, which is characterized in that the header box protective device further includes two Secondary source, the secondary power supply are electrically connected to adopt to be described respectively with the acquisition unit, logic unit and execution unit Collect unit, logic unit and execution unit and electric energy is provided.

9. header box protective device according to claim 1, which is characterized in that the comparison voltage is equal to photovoltaic group string branch The 17/41-20/41 of the open-circuit voltage on road.

10. header box protective device according to claim 1, which is characterized in that the comparison voltage is equal to 380V- 400V and the setting value are equal to 190V-320V.