Overcurrent protection circuit and overcurrent protection method

Abstract

The present invention relates to an overcurrent protection circuit and an overcurrent protection method, wherein the existing ground voltage sampling circuit, output voltage sampling circuit and CMU management unit in the PID repair circuit are utilized, and a differential circuit, i.e., an overcurrent protection circuit, is constructed by adding an operational amplifier and a comparator, and the output signals of the output voltage sampling circuit and the ground voltage sampling circuit are multiplexed to this differential circuit to generate a voltage difference signal, wherein the voltage difference signal is the voltage difference between the output voltage and the ground voltage, and the CMU management unit determines whether the PID repair circuit has an overcurrent according to the change of the voltage difference signal. The present application has a fast response speed for overcurrent protection, better meets safety regulations, and can reduce the cost invested.

Description

Technical Field

[0001] The present invention relates to the technical field of protection circuits, and in particular to a circuit and method for overcurrent protection during a PID repair process. Background Art

[0002] Solar cell modules are the most expensive part of the entire photovoltaic system. Failure of solar cell modules directly affects the power generation income of the entire project cycle. The PID effect of solar cell modules is a failure that affects power generation efficiency and can be prevented and repaired. The PID effect is that the solar cell module is exposed to high voltage on the DC side system for a long time, which leads to leakage current between the glass and the packaging material. A large amount of charge accumulates on the surface of the battery, which deteriorates the passivation effect on the surface of the solar cell module, reduces the fill factor, open circuit voltage, and short circuit current of the solar cell module, and causes the battery performance to decay. In extreme cases, the PID effect will cause more than 50% power loss of the solar cell module, affecting the power output of the entire string.

[0003] In response to the above problems, the existing technical means use a PID repair power supply to raise the PV- or PV+ potential to half the BUS voltage, that is, half the bus voltage, so that the bus side connected to the PID repair power supply (hereinafter referred to as the PID repair connection side) is reversed relative to the PE voltage, thereby performing nighttime repair. The existing method of PID repair power supply mainly performs overvoltage protection by sampling the output voltage of the PID repair power supply, sampling the ground voltage of the PID repair connection side to PE, performing closed-loop control based on these two sampled voltages, and adding a current limiting loop on this basis. However, in the event of an unexpected moment such as a short circuit between the PID repair connection side and PE in the inverter, the secondary current of the PID repair power supply will be too large. In this case, even if the software current limiting loop is activated, due to its long response time, the electrical components may still be damaged, and even more serious failures or losses may occur, resulting in the same failure to meet safety regulations.

[0004] Therefore, how to optimize the overcurrent protection during the PID repair process and shorten the response time of the overcurrent protection is the technical problem that this application aims to solve. Summary of the invention

[0005] A main purpose of the present invention is to overcome at least one of the above-mentioned defects, and to provide an overcurrent protection circuit and an overcurrent protection method, which can realize overcurrent protection based on hardware circuits, have a fast response speed, better meet safety requirements, and reduce the investment cost.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: The present invention provides an overcurrent protection circuit for overcurrent protection of a PID repair circuit. The PID repair circuit comprises a direct current power supply, an isolation circuit, a ground voltage sampling circuit, an output voltage sampling circuit and a CMU management unit. The direct current power supply is connected to the positive terminal PV+ or the negative terminal PV- of a solar cell module to be PID repaired after being processed by the isolation circuit, and is used to output a repair voltage to perform PID repair on the solar cell module. The ground voltage sampling circuit is used to collect the ground voltage between the positive terminal PV+ or the negative terminal PV- and the PE terminal, and the output voltage sampling circuit is used to collect the output voltage of the isolation circuit. The overcurrent protection circuit comprises a third operational amplifier and a second comparator. The output signals of the ground voltage sampling circuit and the output voltage sampling circuit are connected to the input terminal of the third operational amplifier, the output terminal of the third operational amplifier is connected to the second comparator, and the output terminal of the second comparator is further connected to the CMU management unit.

[0007] According to one embodiment of the present invention, the output end of the output voltage sampling circuit is divided into at least two outputs, including a first output and a second output, wherein the first output is connected to the CMU management unit, and the second output is connected to an input end of the third operational amplifier; The output end of the ground voltage sampling circuit is divided into at least two outputs, including a fourth output and a fifth output, wherein the fourth output is connected to the CMU management unit, and the fifth output is connected to another input end of the third operational amplifier.

[0008] According to one embodiment of the present invention, the output end of the output voltage sampling circuit has a third output, the third output is connected to the input end of the first comparator, and the output end of the first comparator is connected to the CMU management unit.

[0009] According to one embodiment of the present invention, the output end of the third operational amplifier is divided into two outputs, including a sixth output and a seventh output, wherein the sixth output is connected to the CMU management unit, and the seventh output is connected to the second comparator.

[0010] According to one embodiment of the present invention, the overcurrent protection circuit includes a current limiting protection resistor, and the current limiting protection resistor is connected in series at the output side of the isolation circuit.

[0011] According to one embodiment of the present invention, the DC power supply is connected to the input side of the isolation circuit, a control switch is provided in the connection path between the DC power supply and the isolation circuit, the control switch is connected to the CMU management unit, and is turned on or off according to a control signal output by the CMU management unit.

[0012] According to one embodiment of the present invention, the isolation circuit includes an isolation transformer, wherein a primary side of the isolation transformer is connected to the DC power supply, and a secondary side of the isolation transformer is connected to the solar cell module.

[0013] According to one embodiment of the present invention, the control switch is arranged in series in a connection path between the DC power supply and the primary side of the isolation transformer.

[0014] In particular, the present invention provides an overcurrent protection method for overcurrent protection of a PID repair circuit, wherein the PID repair circuit is connected to the positive terminal PV+ or the negative terminal PV- of the solar cell module, and outputs a repair voltage to perform PID repair on the solar cell module, and the ground voltage between the positive terminal PV+ or the negative terminal PV- and the PE terminal is collected through a ground voltage sampling circuit, and the output voltage output by the PID repair circuit to the solar cell module is collected through an output voltage sampling circuit, wherein the output signals of the output voltage sampling circuit and the ground voltage sampling circuit are multiplexed to a differential circuit to generate a voltage difference signal, and the voltage difference signal is the voltage difference between the output voltage and the ground voltage, and the CMU management unit determines whether there is an overcurrent in the PID repair circuit according to the change of the voltage difference signal.

[0015] According to one embodiment of the present invention, when the CMU management unit determines that the PID repair circuit has an overcurrent, it either issues an alarm or controls the PID repair circuit to stop supplying power.

[0016] Compared with the prior art, the advantages and beneficial effects of the overcurrent protection circuit and overcurrent protection method of the patent application of the present invention are: The present application utilizes the existing ground voltage sampling circuit, output voltage sampling circuit and CMU management unit in the PID repair circuit, and constructs a differential circuit, i.e., an overcurrent protection circuit, through a newly added operational amplifier and comparator. The output signals of the output voltage sampling circuit and the ground voltage sampling circuit are multiplexed to this differential circuit to generate a voltage difference signal, which is the voltage difference between the output voltage and the ground voltage. The CMU management unit determines whether the PID repair circuit has an overcurrent according to the change of the voltage difference signal. The present application has a fast response speed for overcurrent protection, better meets safety regulations, and can reduce the cost of investment. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Hereinafter, some specific embodiments of the present invention will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings: Figure 1 is a circuit structure diagram of an overcurrent protection circuit and a PID repair circuit according to an embodiment of the present invention; Figure 2 4 is a schematic diagram of the working process of an overcurrent protection method according to another embodiment of the present invention. DETAILED DESCRIPTION

[0018] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0020] Embodiment 1: like Figure 1 As shown, the PID repair circuit includes a DC power supply, an isolation circuit, a ground voltage sampling circuit, an output voltage sampling circuit and a CMU management unit, the DC power supply is connected to the input side of the isolation circuit, and the solar cell module to be PID repaired is connected to the output side of the isolation circuit. In this embodiment, the DC power supply is connected to the negative terminal PV- of the solar cell module as a load after being processed by the isolation circuit, and is used to output a repair voltage to perform PID repair on the solar cell module.

[0021] The isolation circuit includes an isolation transformer, wherein a primary side of the isolation transformer is connected to the DC power supply, and a secondary side of the isolation transformer is connected to the solar cell module.

[0022] The isolation circuit also includes an RCD absorption circuit composed of a capacitor C1, a resistor R3, and a diode D1. The capacitor C1 is connected in parallel with the primary coil of the isolation transformer and then connected in series with the DC power supply. The capacitor C1 is connected in parallel with the resistor R3 and then connected in series with the diode D1 to form the RCD absorption circuit. Due to the presence of the diode D1, the capacitor C1 will not generate LC oscillation with the inductance of the primary coil. The function of the RCD absorption circuit is mainly to absorb the peak when the control switch Q is turned on or off. The setting of the RCD absorption circuit can be determined according to design requirements.

[0023] A control switch is provided in the connection path between the DC power supply and the isolation circuit. The control switch is provided in series in the connection path between the DC power supply and the primary side of the isolation transformer. The control switch is connected to the CMU management unit and is turned on or off according to a control signal output by the CMU management unit.

[0024] The ground voltage sampling circuit is used to collect the ground voltage between the positive terminal PV+ or the negative terminal PV- and the PE terminal, and the output voltage sampling circuit is used to collect the output voltage of the isolation circuit. The overcurrent protection circuit of this embodiment is used for overcurrent protection of the PID repair circuit, wherein the overcurrent protection circuit includes a third operational amplifier U3 and a second comparator, the output signals of the ground voltage sampling circuit and the output voltage sampling circuit are connected to the input end of the third operational amplifier U3, the output end of the third operational amplifier U3 is connected to the second comparator, and the output end of the second comparator is connected to the CMU management unit.

[0025] Figure 1 The resistors with the same resistor number have the same resistance value. The output voltage sampling circuit and the ground voltage sampling circuit both use differential amplifier circuits, and the output voltage sampling circuit and the ground voltage sampling circuit have the same amplification ratio. The overcurrent protection circuit is also a differential amplifier circuit constructed using the third operational amplifier, but the resistors used at the in-phase input terminal and the reverse input terminal are equal, so the overcurrent protection circuit constitutes a subtractor, that is, the output voltage of the third operational amplifier is the input voltage of its in-phase input terminal minus the input voltage of the reverse input terminal.

[0026] The output end of the output voltage sampling circuit is divided into three outputs, including a first output, a second output and a third output, wherein the first output is connected to the CMU management unit, the second output is connected to the non-inverting input end of the third operational amplifier, the third output is connected to the input end of the first comparator, and the output end of the first comparator is connected to the CMU management unit.

[0027] The output end of the ground voltage sampling circuit is divided into at least two outputs, including a fourth output and a fifth output, wherein the fourth output is connected to the CMU management unit, and the fifth output is connected to the inverting input end of the third operational amplifier.

[0028] The output end of the third operational amplifier in the overcurrent protection circuit is divided into two outputs, including a sixth output and a seventh output, wherein the sixth output is connected to the CMU management unit, and the seventh output is connected to the second comparator.

[0029] In addition, it should be noted that the non-inverting input terminal of the third operational amplifier can be connected to the output of the ground voltage sampling circuit, and the inverting input terminal of the third operational amplifier is connected to the output of the output voltage sampling circuit. Overcurrent protection can be achieved by making slight adjustments to the judgment logic, and should also be included in the protection of this application, so it will not be elaborated here.

[0030] When the inverter is PID repaired at night or connected to the grid during the day, the CMU management unit performs closed-loop feedback control on the voltage sampled by the ground voltage sampling circuit composed of the second operational amplifier U2, power supply V2, resistors R and R1 and the voltage error given by the system, controls the on and off of the NMOS tube as the control switch to convert the DC power supply V into the required voltage, and further raises the PV-to-PE voltage to above half the bus voltage to achieve the effect of nighttime repair and daytime grid connection prevention. When the CMU management unit controls the control switch Q to turn on, the primary coil of the isolation transformer T is used as an inductor to store energy. When the CMU management unit controls the control switch Q to turn off, the secondary coil on the secondary side of the isolation transformer T releases energy, and the diode D2 on the secondary side rectifies the voltage across the secondary coil into a DC voltage, i.e., the output voltage. The primary side of the isolation transformer is composed of a diode D1, a capacitor C1, and a resistor R3, and an RCD absorption circuit is formed. The RCD absorption circuit is the primary inductor continuous current, and at the same time weakens the turn-off voltage spike of the control switch Q.

[0031] The output voltage sampling circuit of the PID repair circuit is composed of the first operational amplifier U1, power supply V1, resistors R and R1. The output signal of the first operational amplifier U1 is transmitted to the CMU management unit in real time to calculate the output voltage of the PID repair power supply. At the same time, the output signal is transmitted to the first comparator for comparison. If the output voltage is too large, the CMU management unit will detect that the output signal level of the first comparator is reversed, so that the CMU management unit issues an instruction to control the switch Q to block the wave and protect the circuit. The output voltage sampling circuit has the same transformation ratio as the ground voltage sampling circuit.

[0032] The output signals of the first operational amplifier U1 and the second operational amplifier U2 are used as the input signals of the third operational amplifier U3, and form a sampling circuit of the voltage difference between the output voltage and the voltage to ground with the power supply V3 and the resistor R2. It should be noted here that the voltage difference between the output voltage and the voltage to ground acts on the line impedance between the output voltage sampling circuit and the voltage to ground sampling circuit in the figure at the bus connection point. This line impedance is basically a certain value, which can be recorded as resistor R4. Therefore, after calculating and obtaining the voltage difference between the output voltage and the voltage to ground, the current on the bus can be obtained by dividing it by the resistance value of this resistor R4. Of course, a current limiting protection resistor can also be set, which can play a role of current limiting protection when necessary, and can also be used as a basis for calculating the bus current (that is, the current limiting protection resistor is used as the aforementioned resistor R4, or added to the aforementioned line impedance as the aforementioned resistor R4), and the current limiting protection resistor is connected in series on the output side of the isolation circuit, and is set on the connection path between the output voltage sampling circuit and the voltage to ground sampling circuit at the bus connection point. The output signal of the third operational amplifier U3 in the overcurrent protection circuit is transmitted to the CMU management unit to calculate the repair current when the PID repair circuit is working, and is also transmitted to the second comparator for comparison. When the PID repair circuit is working normally, the current of the PID repair circuit will not exceed the software given value under the action of the software current limiting loop, so that the output signal of the second operational comparator will not be reversed in level and will not trigger the overcurrent protection circuit. If the inverter has a fault such as PV- to PE short circuit, PV- to PE is 0, which causes the output voltage of the PID repair circuit to act on the resistor R4 and overcurrent instantaneously. At this time, the output signal of the third operational amplifier U3 will instantly increase, and the comparison with the second comparator causes the output signal transmitted to the CMU management unit to be reversed in level, and then the CMU management unit issues an instruction to control the switch Q to seal the wave, which plays a role in protecting the circuit and the inverter. According to the aforementioned resistor R4, the CMU management unit can also calculate the bus current at this time for feedback.

[0033] When the CMU management unit determines that the PID repair circuit has an overcurrent, it either issues an alarm or controls the PID repair circuit to stop supplying power.

[0034] Embodiment 2: This embodiment describes an overcurrent protection method, based on the overcurrent protection circuit described in Example 1, the PID repair circuit is connected to the positive terminal PV+ or the negative terminal PV- of the solar cell module, and outputs a repair voltage to perform PID repair on the solar cell module. Figure 2As shown, the ground voltage between the positive terminal PV+ or the negative terminal PV- and the PE terminal is collected through the ground voltage sampling circuit, and the output voltage output by the PID repair circuit to the solar cell module is collected through the output voltage sampling circuit, wherein the output signals of the output voltage sampling circuit and the ground voltage sampling circuit are multiplexed to the differential circuit to generate a voltage difference signal, and the voltage difference signal is the voltage difference between the output voltage and the ground voltage, and the CMU management unit determines whether the PID repair circuit has an overcurrent according to the change of the voltage difference signal.

[0035] When the CMU management unit determines that the PID repair circuit has an overcurrent, it either issues an alarm or controls the PID repair circuit to stop supplying power.

[0036] In summary, the present application utilizes the existing ground voltage sampling circuit, output voltage sampling circuit and CMU management unit in the PID repair circuit, and constructs a differential circuit, i.e., an overcurrent protection circuit, through the newly added operational amplifier and comparator, and multiplexes the output signals of the output voltage sampling circuit and the ground voltage sampling circuit to this differential circuit to generate a voltage difference signal, which is the voltage difference between the output voltage and the ground voltage. The CMU management unit determines whether there is an overcurrent in the PID repair circuit based on the change of the voltage difference signal. The overcurrent protection has a fast response speed, better meets safety regulations, and can reduce the cost of investment.

[0037] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. An overcurrent protection circuit for overcurrent protection of a PID repair circuit, the PID repair circuit comprising a DC power supply, an isolation circuit, a ground voltage sampling circuit, an output voltage sampling circuit and a CMU management unit, the DC power supply being connected to the positive terminal PV+ or the negative terminal PV- of a solar cell module to be repaired for PID after being processed by the isolation circuit, and being used to output a repair voltage to repair the PID of the solar cell module, the ground voltage sampling circuit being used to collect the ground voltage between the positive terminal PV+ or the negative terminal PV- and the PE terminal, and the output voltage sampling circuit being used to collect the output voltage of the isolation circuit, characterized in that: The overcurrent protection circuit includes a third operational amplifier and a second comparator. The output signals of the ground voltage sampling circuit and the output voltage sampling circuit are connected to the input end of the third operational amplifier. The output end of the third operational amplifier is connected to the second comparator. The output end of the second comparator is then connected to the CMU management unit.

2. The overcurrent protection circuit according to claim 1, characterized in that: The output end of the output voltage sampling circuit is divided into at least two outputs, including a first output and a second output, wherein the first output is connected to the CMU management unit, and the second output is connected to an input end of the third operational amplifier; The output end of the ground voltage sampling circuit is divided into at least two outputs, including a fourth output and a fifth output, wherein the fourth output is connected to the CMU management unit, and the fifth output is connected to another input end of the third operational amplifier.

3. The overcurrent protection circuit according to claim 1 or 2, characterized in that: The output end of the output voltage sampling circuit has a third output, the third output is connected to the input end of the first comparator, and the output end of the first comparator is connected to the CMU management unit.

4. The overcurrent protection circuit according to claim 1 or 2, characterized in that: The output end of the third operational amplifier is divided into two outputs, including a sixth output and a seventh output, wherein the sixth output is connected to the CMU management unit, and the seventh output is connected to the second comparator.

5. The overcurrent protection circuit according to claim 1, characterized in that: The overcurrent protection circuit comprises a current limiting protection resistor, and the current limiting protection resistor is connected in series at the output side of the isolation circuit.

6. The overcurrent protection circuit according to claim 1, characterized in that: The DC power supply is connected to the input side of the isolation circuit. A control switch is provided in the connection path between the DC power supply and the isolation circuit. The control switch is connected to the CMU management unit and is turned on or off according to a control signal output by the CMU management unit.

7. The overcurrent protection circuit according to claim 6, characterized in that: The isolation circuit includes an isolation transformer, wherein a primary side of the isolation transformer is connected to the DC power supply, and a secondary side of the isolation transformer is connected to the solar cell module.

8. The overcurrent protection circuit according to claim 7, characterized in that: The control switch is arranged in series in a connection path between the DC power supply and the primary side of the isolation transformer.

9. An overcurrent protection method, used for overcurrent protection of a PID repair circuit, wherein the PID repair circuit is connected to the positive terminal PV+ or the negative terminal PV- of the solar cell module, outputs a repair voltage to perform PID repair on the solar cell module, collects the ground voltage between the positive terminal PV+ or the negative terminal PV- and the PE terminal through a ground voltage sampling circuit, and collects the output voltage output by the PID repair circuit to the solar cell module through an output voltage sampling circuit, characterized in that: The output signals of the output voltage sampling circuit and the ground voltage sampling circuit are multiplexed to the differential circuit to generate a voltage difference signal, wherein the voltage difference signal is the voltage difference between the output voltage and the ground voltage. The CMU management unit determines whether there is an overcurrent in the PID repair circuit according to the change of the voltage difference signal.

10. The overcurrent protection method according to claim 9, characterized in that: When the CMU management unit determines that the PID repair circuit has an overcurrent, it either issues an alarm or controls the PID repair circuit to stop supplying power.

Images