Impedance detection circuit and photovoltaic inverter
By using an impedance detection circuit with switching transistors and optocouplers, the problem of low relay reliability in photovoltaic inverters is solved, achieving high-precision and high-reliability impedance detection.
Patent Information
- Application Number
- CN202422699492.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-06
- Publication Date
- 2025-10-28
- Estimated Expiration
- 2034-11-06
AI Technical Summary
The impedance detection circuit in existing photovoltaic inverters uses relays, which are prone to mechanical failure and sticking, resulting in low reliability.
An impedance detection circuit based on first and second switching transistors (such as MOSFETs) and an optocoupler is used. By controlling the on and off states of the switching transistors and utilizing the strong and weak electrical isolation effect of the optocoupler, the impedance to ground is measured, and the detection accuracy and reliability are improved through a feedback circuit.
This improves the reliability and accuracy of impedance detection, avoids mechanical failures and sticking problems of relays, and enhances safety and stability.
Smart Images
Figure CN223486074U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of energy storage technology, and more specifically, to an impedance detection circuit and a photovoltaic inverter. Background Technology
[0002] In related technical solutions, relays are often used in the impedance detection circuit of photovoltaic inverters.
[0003] The impedance value in the circuit is different when the relay is in different open and closed states, so the impedance in the circuit can be detected.
[0004] However, relays are prone to mechanical failures and sticking, so the reliability of using relays for impedance measurement is relatively low. Utility Model Content
[0005] The present invention aims to at least solve the technical problem that relays in the prior art or related technologies are prone to mechanical failures and adhesion, and obviously, the reliability of the impedance measurement scheme using relays is relatively low.
[0006] Therefore, the first aspect of this utility model is to provide an impedance detection circuit.
[0007] The second aspect of this utility model is that it provides a photovoltaic inverter.
[0008] In view of the above, according to a first aspect of the present invention, the present invention provides an impedance detection circuit, comprising: a first controllable branch, the first controllable branch including a first switching transistor; a second controllable branch, the second controllable branch including a second switching transistor, the output terminal of the second controllable branch being connected to the output terminal of the first controllable branch and then connected to a first ground point; a detection resistor, the first end of the detection resistor being connected to the output terminal of the first controllable branch, and the second end of the detection resistor being connected to a first power supply; a feedback circuit, the first end of the feedback circuit being connected to the first end of the detection resistor; a first optocoupler, the first end of the first optocoupler being connected to the first power supply, the second end of the first optocoupler being connected to the second end of the feedback circuit, the third end of the first optocoupler being connected to the first end of the feedback circuit, and the fourth end of the first optocoupler being connected to the third end of the feedback circuit; wherein, the ground impedance of the first controllable branch and the second controllable branch is determined by the ground-to-ground signal values output by the fifth and sixth ends of the first optocoupler according to the first switching transistor and the second switching transistor being in different conduction states.
[0009] This invention proposes an impedance detection circuit, which includes a first controllable branch, a second controllable branch, a detection resistor, a feedback circuit, and a first optocoupler. The first switching transistor in the first controllable branch, the second switching transistor in the second controllable branch, and the first optocoupler can be used in combination to replace a relay.
[0010] In this process, the first and second switching transistors, as devices that can switch between the on and off states, do not have the mechanical faults of relays, nor the sticking problems that are prone to occur in relays. Therefore, the impedance detection circuit using the first and second switching transistors can not only achieve impedance detection, but also improve the reliability of the impedance detection circuit.
[0011] The impedance detection circuit proposed in this utility model is based on the following principle: Specifically, when the first switch is switching between the on and off states, the circuit connected to the first ground point in the first controllable branch will change, and therefore, the impedance to ground of the first controllable branch will also change.
[0012] Similarly, when the second switch switches between the on and off states, the circuit connected to the first ground point in the second controllable branch will change, and therefore, the impedance to ground of the second controllable branch will also change.
[0013] Therefore, when the first and second switches are in the off state, the ground signals output from the fifth and sixth terminals of the first optocoupler can be collected and used as the first ground signal; when the first switch is in the on state and the second switch is in the off state, the ground signals output from the fifth and sixth terminals of the first optocoupler can be collected and used as the second ground signal; when the first switch is in the off state and the second switch is in the on state, the ground signals output from the fifth and sixth terminals of the first optocoupler can be collected and used as the third ground signal; after obtaining the first, second, and third ground signals, the ground impedances of the first and second controllable branches can be obtained by solving the first, second, and third ground signals.
[0014] In the technical solution of this utility model, the ground impedance is determined by the ground signal values output from the fifth and sixth terminals of the first optocoupler. The isolation effect of the strong and weak currents of the first optocoupler can be used to reduce the influence of the BOOST circuit on the impedance detection result, thereby improving the accuracy of impedance detection.
[0015] In addition, the impedance detection circuit proposed in this application has the following additional technical features.
[0016] In some technical solutions, optionally, the first controllable branch further includes: a first driving circuit, the first terminal of which is used to receive a first signal, the second terminal of which is grounded, the third terminal of which is connected to the control terminal of the first switching transistor, the fourth terminal of which is connected to the second terminal of the first switching transistor, the fifth terminal of which is connected to the second power supply, and the sixth terminal of which is connected to the first power supply; a first resistor, the first terminal of which is used to receive a first voltage signal, and the second terminal of which is connected to the first terminal of the first switching transistor; and a second resistor, the first terminal of which is connected to the second terminal of the first resistor, and the second terminal of which is connected to the first power supply. The location connection and / or the second controllable branch further includes: a second driving circuit, the first terminal of which is used to receive a second signal, the second terminal of which is grounded, the third terminal of which is connected to the control terminal of the second switching transistor, the fourth terminal of which is connected to the second terminal of the second switching transistor, the fifth terminal of which is connected to the second power supply, and the sixth terminal of which is connected to the first power supply; a third resistor, the first terminal of which is used to receive a second voltage signal, and the second terminal of which is connected to the first terminal of the second switching transistor; and a fourth resistor, the first terminal of which is connected to the second terminal of the third resistor, and the second terminal of which is connected to the first grounding point.
[0017] In this technical solution, the first controllable branch also includes a first driving circuit, a first resistor, and a second resistor. The first driving circuit can switch the first switching transistor between its on and off states. The first resistor is used to connect the first voltage signal to the first switching transistor and also forms a loop with the first grounding point through the second resistor. During this process, as the first switching transistor switches between its on and off states, the impedance at the second end of the first resistor changes, so as to measure the impedance to ground based on the ground signal value measured by the first switching transistor in different states.
[0018] Similarly, the second controllable branch also includes a second driving circuit, a third resistor, and a fourth resistor. The second driving circuit can switch the second switching transistor between its on and off states. The third resistor is used to connect the second voltage signal to the second switching transistor and also forms a loop with the first grounding point through the fourth resistor. During this process, as the second switching transistor switches between its on and off states, the impedance at the second end of the third resistor changes, so as to measure the impedance to ground based on the ground signal value measured by the second switching transistor in different states.
[0019] In the above technical solution, the first voltage signal and the second voltage signal can be understood as the high voltage power connected to the first controllable branch and the second controllable branch.
[0020] In the above technical solution, the first signal can be understood as a signal used to drive the first switch to be turned on and off by the first driving circuit. If the first driving circuit receives the first signal, the first switch is in the on state; otherwise, if the first driving circuit does not receive the first signal, the first switch is in the off state.
[0021] Similarly, the second signal can be understood as a signal used to drive the second switch to be turned on and off using the second driving circuit. If the second driving circuit receives the second signal, the second switch is in the on state; otherwise, if the second driving circuit does not receive the second signal, the second switch is in the off state.
[0022] In this technical solution, the impedance between the first resistor and the second resistor can be adjusted by controlling the first switch to turn on and off using the first signal. At the same time, the impedance between the third resistor and the fourth resistor can be adjusted by controlling the second switch to turn on and off using the second signal, thereby realizing the ground impedance of the first controllable branch and the second controllable branch.
[0023] In this process, the impedance detection circuit using the first and second switching transistors can not only achieve impedance detection, but also improve the reliability of the impedance detection circuit.
[0024] In some technical solutions, optionally, the first driving circuit includes: a second optocoupler, the first end of which is used to receive a first signal, the second end of which is grounded, the third end of which is connected to a first power supply, and the fourth end of which is connected to the control terminal of a first switching transistor; and a first current-limiting resistor, the first end of which is connected to a second power supply, and the second end of which is connected to the fourth end of the second optocoupler.
[0025] In this technical solution, the second optocoupler can isolate the first signal and the first voltage signal, thereby improving the safety of the impedance detection circuit.
[0026] Specifically, the first signal is used to drive the first switching transistor to turn on and off. It is a weak current signal, while the first voltage signal is a strong voltage signal. By using the second optocoupler, the weak current and the strong current signal can be isolated, thereby improving the safety of the impedance detection circuit while realizing the driving control of the first switching transistor.
[0027] In the above technical solution, by setting a first current-limiting resistor, the current flowing into the fourth terminal of the second optocoupler is limited, thereby reducing the probability of the second optocoupler being damaged due to overcurrent, and thus improving the reliability of the impedance detection circuit.
[0028] In the above technical solution, the resistance value of the first current-limiting resistor can be selected according to actual usage needs, and its specific value will not be elaborated here.
[0029] In some technical solutions, the first driving circuit may optionally include: a fifth resistor located between the fourth terminal of the second optocoupler and the control terminal of the first switching transistor; and a first capacitor, with its first terminal connected to the control terminal of the first switching transistor and its second terminal connected to the second terminal of the first switching transistor.
[0030] In this technical solution, the fifth resistor and the first capacitor can form an RC filter circuit. During this process, the RC filter circuit can be used to filter out the harmonics in the signal output from the fourth terminal of the second optocoupler, so that the first switching transistor can be stably turned on and off, thereby improving the reliability of the impedance detection circuit.
[0031] In some technical solutions, optionally, the second driving circuit includes: a third optocoupler, the first end of which is used to receive the second signal, the second end of which is grounded, the third end of which is connected to the first power supply, and the fourth end of which is connected to the control terminal of the second switching transistor; and a second current-limiting resistor, the first end of which is connected to the second power supply, and the second end of which is connected to the fourth end of the third optocoupler.
[0032] In this technical solution, the third optocoupler can isolate the second signal and the second voltage signal, thereby improving the safety of the impedance detection circuit.
[0033] Specifically, the second signal is used to drive the second switch to turn on and off. It is a weak current signal, while the second voltage signal is a strong voltage signal. By using a third optocoupler, the weak current and the strong current can be isolated, thereby improving the safety of the impedance detection circuit while realizing the driving control of the second switch.
[0034] In the above technical solution, by setting a second current-limiting resistor, the current flowing into the fourth terminal of the second optocoupler is limited, thereby reducing the probability of the third optocoupler being damaged due to overcurrent, and thus improving the reliability of the impedance detection circuit.
[0035] In the above technical solution, the resistance value of the second current-limiting resistor can be selected according to actual usage needs, and its specific value will not be elaborated here.
[0036] In some technical solutions, the second driving circuit may optionally include: a sixth resistor located between the fourth terminal of the third optocoupler and the control terminal of the second switching transistor; and a second capacitor, the first terminal of which is connected to the control terminal of the second switching transistor, and the second terminal of which is connected to the second terminal of the second switching transistor.
[0037] In this technical solution, the sixth resistor and the second capacitor can form an RC filter circuit. During this process, the RC filter circuit can be used to filter out the harmonics in the signal output from the fourth terminal of the third optocoupler, so that the second switching transistor can be stably turned on and off, thereby improving the reliability of the impedance detection circuit.
[0038] In some technical solutions, the feedback circuit may optionally include: a first comparator, the non-inverting input terminal of the first comparator being connected to the first terminal of the sensing resistor and the third terminal of the first optocoupler, the negative input terminal of the first comparator being connected to the first power supply and the fourth terminal of the first optocoupler, and the output terminal of the first comparator being connected to the second terminal of the first optocoupler; and a third capacitor, the first terminal of the third capacitor being connected to the negative input terminal of the first comparator, and the second terminal of the third capacitor being connected to the output terminal of the first comparator.
[0039] In this technical solution, the first comparator can compare the signals input to the negative input terminal and the positive input terminal, and then output the corresponding comparison result. Since the positive input terminal of the first comparator is also connected to the third terminal of the first optocoupler, and the negative input terminal of the first comparator is also connected to the fourth terminal of the first optocoupler, the signals output from the third terminal and the fourth terminal of the first optocoupler will also act on the first comparator, thereby realizing closed-loop negative feedback. In this process, the input between the first terminal and the second terminal of the first optocoupler and the output between the third terminal and the fourth terminal of the first optocoupler tend to be 1:1, thereby realizing the detection of insulation resistance.
[0040] In the above technical solution, the third capacitor can be configured and used with the first comparator to achieve negative feedback drive control.
[0041] In some technical solutions, the feedback circuit may optionally include a seventh resistor connected in series between the output of the first comparator and the second terminal of the first optocoupler.
[0042] In this technical solution, by setting a seventh resistor, the current value of the signal output by the first comparator can be limited. In this process, the current value of the signal input to the second terminal of the first optocoupler can be reduced, thereby reducing the probability of the first optocoupler being damaged due to overcurrent, and thus improving the reliability of the impedance detection circuit.
[0043] In the above technical solution, the resistance value of the seventh resistor can be selected according to actual usage needs, and its specific value will not be elaborated here.
[0044] In some technical solutions, the impedance detection circuit may optionally include: a second comparator connected in series between the non-inverting input of the first comparator and the first end of the detection resistor; the non-inverting input of the second comparator is connected to the first end of the detection resistor; the output of the second comparator is connected to the non-inverting input of the first comparator; and the negative input of the second comparator is connected to the output of the second comparator.
[0045] In this technical solution, a second comparator is set up so that the voltage drop at the first terminal of the sensing resistor can be output by the comparator. In this process, the second comparator can output a signal that follows the voltage drop at the first terminal of the sensing resistor. In this process, the setting of the second comparator can meet the input requirements of the feedback circuit.
[0046] In some technical solutions, the impedance detection circuit may optionally include a third current-limiting resistor located between the output of the second comparator and the non-inverting input of the first comparator.
[0047] In this technical solution, by setting a third current-limiting resistor, the current value of the input signal of the first comparator can be limited. In this process, the probability of the first comparator being damaged due to overcurrent can be reduced, thereby improving the reliability of the impedance detection circuit.
[0048] In the above technical solution, the resistance value of the third current-limiting resistor can be selected according to actual usage needs, which will not be elaborated here.
[0049] In some technical solutions, the impedance detection circuit may optionally further include: a third comparator, the non-inverting input of which is connected to the fifth terminal of the first optocoupler, the negative input of which is connected to the sixth terminal of the first optocoupler, and the output of which is used to output a signal to ground; an eighth resistor, the first terminal of which is connected to the non-inverting input of the third comparator, and the second terminal of which is grounded; a ninth resistor, the first terminal of which is connected to the negative input of the third comparator, and the second terminal of which is connected to the output of the third comparator; and a fourth capacitor, the first terminal of which is connected to the first terminal of the ninth resistor, and the second terminal of which is connected to the second terminal of the ninth resistor.
[0050] In this technical solution, a third comparator is set up so that it can be used in conjunction with an eighth resistor, a ninth resistor and a fourth capacitor to realize the acquisition and output of ground signals. In this process, the eighth resistor enables the fifth terminal of the first optocoupler to be grounded and forms a voltage on the eighth resistor. The voltage on the eighth resistor can be used as the input of the non-inverting input terminal of the third comparator.
[0051] In the above technical solution, by setting a ninth resistor, the ninth resistor can be used as the feedback resistor of the third comparator, thereby realizing the adjustment of the amplification factor. In this process, the signals at the fifth and sixth terminals of the first optocoupler can be amplified and output, thereby realizing the measurement of the impedance to ground.
[0052] In the above technical solution, by setting a fourth capacitor, interference can be eliminated, thereby improving the reliability of the signal output by the third comparator.
[0053] In some technical solutions, the impedance detection circuit may optionally include: a fifth capacitor, the first terminal of the fifth capacitor being connected to the first terminal of the detection resistor, and the second terminal of the fifth capacitor being connected to the second terminal of the detection resistor.
[0054] In this technical solution, by setting a fifth capacitor, the voltage drop across the sensing resistor can be stored in the fifth capacitor as energy. In this process, the fluctuation of the voltage drop across the sensing resistor can be reduced, thereby improving the stability of the feedback circuit during operation.
[0055] Specifically, when the first and second switching transistors are in different conduction states, a stable voltage can be formed on the fifth capacitor, which makes the voltage input to the second comparator more stable, thereby improving the stability of the feedback circuit during operation.
[0056] According to a second aspect of the present invention, the present invention provides a photovoltaic inverter, comprising: an impedance detection circuit as described in any one of the above.
[0057] Additional aspects and advantages of this invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description
[0058] The above and / or additional aspects and advantages of this utility model will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:
[0059] Figure 1 A schematic diagram of the topology of an impedance detection circuit according to an embodiment of the present invention is shown.
[0060] in, Figure 1 The correspondence between the reference numerals and component names in the attached drawings is as follows:
[0061] 100 Impedance detection circuit, 102 First controllable branch, 1022 First drive circuit, 104 Second controllable branch, 1042 Second drive circuit, Q1 First switching transistor, Q2 Second switching transistor, GND First ground point, Rs Detection resistor, 106 Feedback circuit, G1 First optocoupler, G2 Second optocoupler, G3 Third optocoupler, R1 First resistor, R2 Second resistor, R3 Third resistor, R4 Fourth resistor, R5 Fifth resistor, R6 Sixth resistor, R7 Seventh resistor, R8 Eighth resistor, R9 Ninth resistor, Rx1 First current limiting resistor, Rx2 Second current limiting resistor, Rx3 Third current limiting resistor, C1 First capacitor, C2 Second capacitor, C3 Third capacitor, C4 Fourth capacitor, C5 Fifth capacitor, B1 First comparator, B2 Second comparator, B3 Third comparator, BUS - First power supply, BUSH Second power supply. Detailed Implementation
[0062] To better understand the above aspects, features, and advantages of this utility model, the present utility model will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.
[0063] Many specific details are set forth in the following description in order to provide a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.
[0064] In one embodiment of this application, such as Figure 1 As shown, an impedance detection circuit 100 is provided, including: a first controllable branch 102, which includes a first switching transistor Q1; a second controllable branch 104, which includes a second switching transistor Q2, the output terminal of which is connected to the output terminal of the first controllable branch 102 and then connected to a first ground point GND; a detection resistor Rs, the first end of which is connected to the output terminal of the first controllable branch 102, and the second end of which is connected to a first power supply BUS-; and a feedback circuit 106, the first end of which is connected to... The first terminal of the detection resistor Rs is connected to; the first optocoupler G1, the first terminal of the first optocoupler G1 is connected to the first power supply BUS-, the second terminal of the first optocoupler G1 is connected to the second terminal of the feedback circuit 106, the third terminal of the first optocoupler G1 is connected to the first terminal of the feedback circuit 106, and the fourth terminal of the first optocoupler G1 is connected to the third terminal of the feedback circuit 106; wherein, based on the different conduction states of the first switch Q1 and the second switch Q2, the ground impedance of the first controllable branch 102 and the second controllable branch 104 is determined by the ground signal values output from the fifth and sixth terminals of the first optocoupler G1.
[0065] This invention proposes an impedance detection circuit 100, which includes a first controllable branch 102, a second controllable branch 104, a detection resistor Rs, a feedback circuit 106, and a first optocoupler G1. The first switch Q1 in the first controllable branch 102, the second switch Q2 in the second controllable branch 104, and the first optocoupler G1 can be used in combination to replace a relay.
[0066] In this process, the first switch Q1 and the second switch Q2 are devices that can switch between the on and off states. They do not have the mechanical faults that exist in relays, nor do they have the problem of sticking that is prone to occur in relays. Therefore, the impedance detection circuit 100 using the first switch Q1 and the second switch Q2 can not only realize impedance detection, but also improve the reliability of the impedance detection circuit 100.
[0067] The impedance detection circuit 100 proposed in this utility model is based on the following principle: Specifically, when the first switch Q1 switches between the on state and the off state, the circuit connected to the first ground point GND in the first controllable branch 102 will change, and therefore, the impedance to ground of the first controllable branch 102 will also change.
[0068] Similarly, when the second switch Q2 switches between the on and off states, the circuit in the second controllable branch 104 connected to the first ground point GND will change, and therefore, the impedance to ground of the second controllable branch 104 will also change.
[0069] Therefore, when the first switch Q1 and the second switch Q2 are in the off state, the ground signals output from the fifth and sixth terminals of the first optocoupler G1 can be collected and used as the first ground signal; when the first switch Q1 is in the on state and the second switch Q2 is in the off state, the ground signals output from the fifth and sixth terminals of the first optocoupler G1 can be collected and used as the second ground signal; when the first switch Q1 is in the off state and the second switch Q2 is in the on state, the ground signals output from the fifth and sixth terminals of the first optocoupler G1 can be collected and used as the third ground signal; after obtaining the first, second, and third ground signals, the ground impedances of the first controllable branch 102 and the second controllable branch 104 can be obtained by solving the first, second, and third ground signals.
[0070] Specifically, the impedance to ground of the first controllable branch 102 is determined to meet the requirements based on the first grounding signal and the second grounding signal, and the impedance to ground of the second controllable branch 104 is determined to meet the requirements based on the first grounding signal and the third grounding signal.
[0071] In the above implementation, after the third grounding signal is measured, the first switch Q1 and the second switch Q2 are controlled to be turned off.
[0072] In some embodiments, the first switch Q1 and the second switch Q2 may optionally be metal-oxide-semiconductor field-effect transistors (MOSFETs).
[0073] In the above embodiment, a light-emitting diode is connected in series between the first end and the second end of the first optocoupler G1. When the first switch Q1 and the second switch Q2 are in different conduction states, the voltage drop across the detection resistor Rs is also different. The first end of the feedback circuit 106 is connected to the first end of the detection resistor Rs. Therefore, the changing voltage drop across the detection resistor Rs will be detected by the feedback circuit 106 and then fed back to the second end of the first optocoupler G1 using the second end of the feedback circuit 106. The light-emitting diode located between the first end and the second end of the first optocoupler G1 will emit light of different intensities according to the changing voltage drop across the detection resistor Rs.
[0074] Simultaneously, the photosensitive device located between the third and fourth terminals of the first optocoupler G1 will conduct according to the luminous intensity of the light-emitting diode. Utilizing the connection between the first optocoupler G1 and the feedback circuit 106, the signal on the photosensitive device is fed as input to the feedback circuit 106, thereby achieving closed-loop negative feedback regulation. During this process, the input between the first and second terminals of the first optocoupler G1, the output between the third and fourth terminals of the first optocoupler G1, and the output between the fifth and sixth terminals of the first optocoupler G1 can approach a 1:1 ratio, thus achieving insulation resistance detection.
[0075] In the above embodiment, by setting the first optocoupler G1, the high voltage and low voltage outputs on the first controllable branch 102 and the second controllable branch 104 can be isolated, thereby enabling the impedance detection circuit 100 to meet the safety requirements of insulation.
[0076] In addition, in related embodiments, impedance detection points are often set in the first controllable branch 102 and the second controllable branch 104 when performing impedance detection. However, the first controllable branch 102 and / or the second controllable branch 104 are affected by the BOOST circuit, which makes the impedance detection results inaccurate.
[0077] Among them, the BOOST circuit is a boost circuit.
[0078] In the embodiments of this utility model, the ground impedance is determined by the ground signal values output from the fifth and sixth terminals of the first optocoupler G1. The isolation effect of the strong and weak currents of the first optocoupler G1 can be used to reduce the influence of the BOOST circuit on the impedance detection result, thereby improving the accuracy of impedance detection.
[0079] Furthermore, in the technical solution proposed in this utility model, the ground impedance of the first controllable branch 102 and the second controllable branch 104 can be calculated. Therefore, it is possible to accurately determine which branch of the first controllable branch 102 and the second controllable branch 104 has a ground impedance that does not meet the requirements, thereby enabling targeted detection of the ground impedance of the controllable branch.
[0080] In some embodiments, optionally, the first controllable branch 102 further includes: a first driving circuit 1022, the first terminal of the first driving circuit 1022 being used to receive a first signal, the second terminal of the first driving circuit 1022 being grounded, the third terminal of the first driving circuit 1022 being connected to the control terminal of the first switching transistor Q1, the fourth terminal of the first driving circuit 1022 being connected to the second terminal of the first switching transistor Q1, the fifth terminal of the first driving circuit 1022 being connected to the second power supply BUSH, and the sixth terminal of the first driving circuit 1022 being connected to the first power supply BUS-; a first resistor R1, the first terminal of the first resistor R1 being used to receive a first voltage signal V1, and the second terminal of the first resistor R1 being connected to the first terminal of the first switching transistor Q1; a second resistor R2, the first terminal of the second resistor R2 being connected to the second terminal of the first resistor R1, and the second terminal of the second resistor R2 being connected to the first ground point GND; wherein, when the first signal is received, the first switching transistor Q1 is turned on, and when the first signal is not received, the first switching transistor Q1 is turned off. Q1 is off; and / or the second controllable branch 104 further includes: a second driving circuit 1042, the first terminal of which is used to receive a second signal, the second terminal of which is grounded, the third terminal of which is connected to the control terminal of the second switch Q2, the fourth terminal of which is connected to the second terminal of the second switch Q2, the fifth terminal of which is connected to the second power supply BUSH, and the sixth terminal of which is connected to the first power supply BUS-; a third resistor R3, the first terminal of which is used to connect to the second voltage signal V2, and the second terminal of which is connected to the first terminal of the second switch Q2; a fourth resistor R4, the first terminal of which is connected to the second terminal of the third resistor R3, and the second terminal of which is connected to the first ground point GND; wherein, when the second signal is received, the second switch Q2 is turned on, and when the second signal is not received, the second switch Q2 is turned off.
[0081] In this embodiment, the first controllable branch 102 further includes a first driving circuit 1022, a first resistor R1, and a second resistor R2. The first driving circuit 1022 can switch the first switch Q1 between its on and off states. The first resistor R1 is used to connect the first voltage signal to the first switch Q1 and forms a loop with the first ground point GND through the second resistor R2. During this process, as the first switch Q1 switches between its on and off states, the impedance at the second end of the first resistor R1 changes, so as to measure the impedance to ground based on the ground signal value measured by the first switch Q1 in different states.
[0082] Similarly, the second controllable branch 104 also includes a second driving circuit 1042, a third resistor R3, and a fourth resistor R4. The second driving circuit 1042 can switch the second switch Q2 between its on and off states. The third resistor R3 is used to connect the second voltage signal to the second switch Q2 and forms a loop with the first ground point GND through the fourth resistor R4. During this process, as the second switch Q2 switches between its on and off states, the impedance at the second end of the third resistor R3 will change, so as to measure the impedance to ground based on the ground signal value obtained by measuring the second switch Q2 in different states.
[0083] In the above embodiments, the first voltage signal and the second voltage signal can be understood as the high voltage connected to the first controllable branch 102 and the second controllable branch 104.
[0084] In the above embodiments, the first signal can be understood as a signal used to drive the first switch Q1 to be turned on and off by the first driving circuit 1022. If the first driving circuit 1022 receives the first signal, the first switch Q1 is in the on state; otherwise, if the first driving circuit 1022 does not receive the first signal, the first switch Q1 is in the off state.
[0085] Similarly, the second signal can be understood as a signal used to drive the second switch Q2 to be turned on and off using the second driving circuit 1042. If the second driving circuit 1042 receives the second signal, the second switch Q2 is in the on state; otherwise, if the second driving circuit 1042 does not receive the second signal, the second switch Q2 is in the off state.
[0086] In this embodiment, the impedance between the first resistor R1 and the second resistor R2 can be adjusted by controlling the first switch Q1 to turn on and off using the first signal. At the same time, the impedance between the third resistor R3 and the fourth resistor R4 can be adjusted by controlling the second switch Q2 to turn on and off using the second signal, thereby realizing the ground impedance of the first controllable branch and the second controllable branch 104.
[0087] In this process, the impedance detection circuit 100 using the first switch Q1 and the second switch Q2 can not only achieve impedance detection, but also improve the reliability of the impedance detection circuit 100.
[0088] In some embodiments, optionally, the first driving circuit includes: a second optocoupler G2, the first terminal of which is used to receive a first signal, the second terminal of which is grounded, the third terminal of which is connected to a first power supply BUS-, and the fourth terminal of which is connected to the control terminal of a first switching transistor Q1; and a first current-limiting resistor Rx1, the first terminal of which is connected to a second power supply BUSH, and the second terminal of which is connected to the fourth terminal of the second optocoupler G2.
[0089] In this embodiment, the second optocoupler G2 can isolate the first signal and the first voltage signal, thereby improving the safety of the impedance detection circuit 100.
[0090] Specifically, the first signal is used to drive the first switch Q1 to turn on and off. It is a weak current signal, while the first voltage signal is a strong voltage signal. By using the second optocoupler G2, the weak current and the strong current signal can be isolated, thereby improving the safety of the impedance detection circuit 100 while realizing the driving control of the first switch Q1.
[0091] In the above embodiment, by setting a first current-limiting resistor Rx1, the current flowing into the fourth terminal of the second optocoupler G2 is limited, thereby reducing the probability of the second optocoupler G2 being damaged due to overcurrent, and thus improving the reliability of the impedance detection circuit 100.
[0092] In the above embodiments, the resistance value of the first current-limiting resistor Rx1 can be selected according to actual usage needs, and its specific value will not be described in detail here.
[0093] In some embodiments, the first driving circuit may optionally include: a fifth resistor R5, located between the fourth terminal of the second optocoupler G2 and the control terminal of the first switching transistor Q1; and a first capacitor C1, with its first terminal connected to the control terminal of the first switching transistor Q1 and its second terminal connected to the second terminal of the first switching transistor Q1.
[0094] In this embodiment, the fifth resistor R5 and the first capacitor C1 can form an RC filter circuit. During this process, the RC filter circuit can be used to filter out the harmonics in the signal output from the fourth terminal of the second optocoupler G2, so that the first switch Q1 can be stably turned on and off, thereby improving the reliability of the impedance detection circuit 100.
[0095] In some embodiments, the second driving circuit optionally includes: a third optocoupler G3, the first terminal of which is used to receive a second signal, the second terminal of which is grounded, the third terminal of which is connected to a first power supply BUS-, and the fourth terminal of which is connected to the control terminal of the second switching transistor Q2; and a second current-limiting resistor Rx2, the first terminal of which is connected to the second power supply BUSH, and the second terminal of which is connected to the fourth terminal of the third optocoupler G3.
[0096] In this embodiment, the third optocoupler G3 is configured to isolate the second signal from the second voltage signal, thereby improving the safety of the impedance detection circuit 100.
[0097] Specifically, the second signal is used to drive the second switch Q2 to turn on and off. It is a weak current signal, while the second voltage signal is a strong voltage signal. By using the third optocoupler G3, the weak current and the strong current signal can be isolated, thereby improving the safety of the impedance detection circuit 100 while realizing the driving control of the second switch Q2.
[0098] In the above embodiment, by setting a second current-limiting resistor Rx2, the current flowing into the fourth terminal of the second optocoupler G2 is limited, thereby reducing the probability of the third optocoupler G3 being damaged due to overcurrent, and thus improving the reliability of the impedance detection circuit 100.
[0099] In the above embodiments, the resistance value of the second current-limiting resistor Rx2 can be selected according to actual usage needs, and its specific value will not be described in detail here.
[0100] In some embodiments, the second driving circuit may optionally include: a sixth resistor R6, located between the fourth terminal of the third optocoupler G3 and the control terminal of the second switch Q2; and a second capacitor C2, the first terminal of which is connected to the control terminal of the second switch Q2, and the second terminal of which is connected to the second terminal of the second switch Q2.
[0101] In this embodiment, the sixth resistor R6 and the second capacitor C2 can form an RC filter circuit. During this process, the RC filter circuit can be used to filter out the harmonics in the signal output from the fourth terminal of the third optocoupler G3, so that the second switch Q2 can be stably turned on and off, thereby improving the reliability of the impedance detection circuit 100.
[0102] In some embodiments, the feedback circuit 106 optionally includes: a first comparator B1, the non-inverting input terminal of the first comparator B1 being connected to the first terminal of the detection resistor Rs and the third terminal of the first optocoupler G1, the negative input terminal of the first comparator B1 being connected to the first power supply BUS- and the fourth terminal of the first optocoupler G1, and the output terminal of the first comparator B1 being connected to the second terminal of the first optocoupler G1; and a third capacitor C3, the first terminal of the third capacitor C3 being connected to the negative input terminal of the first comparator B1, and the second terminal of the third capacitor C3 being connected to the output terminal of the first comparator B1.
[0103] In this embodiment, the first comparator B1 compares the signals input to the negative input terminal and the positive input terminal, and outputs the corresponding comparison result. Since the positive input terminal of the first comparator B1 is also connected to the third terminal of the first optocoupler G1, and the negative input terminal of the first comparator B1 is also connected to the fourth terminal of the first optocoupler G1, the signals output from the third and fourth terminals of the first optocoupler G1 will also act on the first comparator B1, thereby realizing closed-loop negative feedback. In this process, the input between the first and second terminals of the first optocoupler G1 and the output between the third and fourth terminals of the first optocoupler G1 tend to be 1:1, thereby realizing the detection of insulation resistance.
[0104] In the above embodiment, the third capacitor C3 can be configured and used with the first comparator B1 to achieve negative feedback drive control.
[0105] In some embodiments, the feedback circuit 106 may optionally include a seventh resistor R7, connected in series between the output of the first comparator B1 and the second terminal of the first optocoupler G1.
[0106] In this embodiment, by setting a seventh resistor R7, the current value of the signal output by the first comparator B1 can be limited. In this process, the current value of the signal input to the second terminal of the first optocoupler G1 can be reduced, thereby reducing the probability of the first optocoupler G1 being damaged due to overcurrent, and thus improving the reliability of the impedance detection circuit 100.
[0107] In the above embodiments, the resistance value of the seventh resistor R7 can be selected according to actual usage needs, and its specific value will not be described in detail here.
[0108] In some embodiments, the impedance detection circuit 100 may optionally include: a second comparator B2 connected in series between the positive input terminal of the first comparator B1 and the first terminal of the detection resistor Rs, the positive input terminal of the second comparator B2 connected to the first terminal of the detection resistor Rs, the output terminal of the second comparator B2 connected to the positive input terminal of the first comparator B1, and the negative input terminal of the second comparator B2 connected to the output terminal of the second comparator B2.
[0109] In this embodiment, by setting a second comparator B2, the voltage drop at the first terminal of the sensing resistor Rs is output using the comparator. During this process, the second comparator B2 can output a signal following the voltage drop at the first terminal of the sensing resistor Rs. In this process, the setting of the second comparator B2 can meet the input requirements of the feedback circuit 106.
[0110] In some embodiments, the impedance detection circuit 100 may optionally include a third current-limiting resistor Rx3 located between the output of the second comparator B2 and the non-inverting input of the first comparator B1.
[0111] In this embodiment, by setting a third current-limiting resistor Rx3, the current value of the input signal to the first comparator B1 is limited. In this process, the probability of the first comparator B1 being damaged due to overcurrent can be reduced, thereby improving the reliability of the impedance detection circuit 100.
[0112] In the above embodiments, the resistance value of the third current-limiting resistor Rx3 can be selected according to actual usage needs, and will not be elaborated here.
[0113] In some embodiments, the impedance detection circuit 100 may optionally further include: a third comparator B3, the positive input terminal of the third comparator B3 being connected to the fifth terminal of the first optocoupler G1, the negative input terminal of the third comparator B3 being connected to the sixth terminal of the first optocoupler G1, and the output terminal of the third comparator B3 being used to output a signal to ground; an eighth resistor R8, the first terminal of the eighth resistor R8 being connected to the positive input terminal of the third comparator B3, and the second terminal of the eighth resistor R8 being grounded; a ninth resistor R9, the first terminal of the ninth resistor R9 being connected to the negative input terminal of the third comparator B3, and the second terminal of the ninth resistor R9 being connected to the output terminal of the third comparator B3; and a fourth capacitor C4, the first terminal of the fourth capacitor C4 being connected to the first terminal of the ninth resistor R9, and the second terminal of the fourth capacitor C4 being connected to the second terminal of the ninth resistor R9.
[0114] In this embodiment, a third comparator B3 is configured to work in conjunction with an eighth resistor R8, a ninth resistor R9, and a fourth capacitor C4 to acquire and output a ground signal. During this process, the eighth resistor R8 enables the fifth terminal of the first optocoupler G1 to be grounded, and a voltage is generated on the eighth resistor R8. The voltage on the eighth resistor R8 can be used as the input to the non-inverting input terminal of the third comparator B3.
[0115] In the above embodiment, by setting a ninth resistor R9, the ninth resistor R9 can be used as the feedback resistor of the third comparator B3, thereby realizing the adjustment of the amplification factor. In this process, the signals at the fifth and sixth terminals of the first optocoupler G1 can be amplified and output, thereby realizing the measurement of the impedance to ground.
[0116] In the above embodiment, by setting a fourth capacitor C4, interference is eliminated, thereby improving the reliability of the signal output by the third comparator B3.
[0117] In some embodiments, the impedance detection circuit 100 may optionally include: a fifth capacitor C5, the first terminal of the fifth capacitor C5 being connected to the first terminal of the detection resistor Rs, and the second terminal of the fifth capacitor C5 being connected to the second terminal of the detection resistor Rs.
[0118] In this embodiment, by setting a fifth capacitor C5, the voltage drop across the sensing resistor Rs is stored in the fifth capacitor C5 as energy. In this process, the fluctuation of the voltage drop across the sensing resistor Rs can be reduced, thereby improving the stability of the feedback circuit 106 during operation.
[0119] Specifically, when the first switch Q1 and the second switch Q2 are in different conduction states, a stable voltage can be formed on the fifth capacitor C5, which makes the voltage input to the second comparator B2 more stable, thereby improving the stability of the feedback circuit 106 during operation.
[0120] In one embodiment, the present invention provides a photovoltaic inverter, including an impedance detection circuit 100 as described above.
[0121] In this embodiment, the photovoltaic inverter includes an impedance detection circuit 100, which includes a first controllable branch 102, a second controllable branch 104, a detection resistor Rs, a feedback circuit 106, and a first optocoupler G1. The first switch Q1 in the first controllable branch 102, the second switch Q2 in the second controllable branch 104, and the first optocoupler G1 can be used in combination to replace the relay.
[0122] In this process, the first switch Q1 and the second switch Q2 are devices that can switch between the on and off states. They do not have the mechanical faults that exist in relays, nor do they have the problem of sticking that is prone to occur in relays. Therefore, the impedance detection circuit 100 using the first switch Q1 and the second switch Q2 can not only realize impedance detection, but also improve the reliability of the impedance detection circuit 100.
[0123] The impedance detection circuit 100 proposed in this utility model is based on the following principle: Specifically, when the first switch Q1 switches between the on state and the off state, the circuit connected to the first ground point GND in the first controllable branch 102 will change, and therefore, the impedance to ground of the first controllable branch 102 will also change.
[0124] Similarly, when the second switch Q2 switches between the on and off states, the circuit in the second controllable branch 104 connected to the first ground point GND will change, and therefore, the impedance to ground of the second controllable branch 104 will also change.
[0125] Therefore, when the first switch Q1 and the second switch Q2 are in the off state, the ground signals output from the fifth and sixth terminals of the first optocoupler G1 can be collected and used as the first ground signal; when the first switch Q1 is in the on state and the second switch Q2 is in the off state, the ground signals output from the fifth and sixth terminals of the first optocoupler G1 can be collected and used as the second ground signal; when the first switch Q1 is in the off state and the second switch Q2 is in the on state, the ground signals output from the fifth and sixth terminals of the first optocoupler G1 can be collected and used as the third ground signal; after obtaining the first, second, and third ground signals, the ground impedances of the first controllable branch 102 and the second controllable branch 104 can be obtained by solving the first, second, and third ground signals.
[0126] In the above embodiment, a light-emitting diode is connected in series between the first end and the second end of the first optocoupler G1. When the first switch Q1 and the second switch Q2 are in different conduction states, the voltage drop across the detection resistor Rs is also different. The first end of the feedback circuit 106 is connected to the first end of the detection resistor Rs. Therefore, the changing voltage drop across the detection resistor Rs will be detected by the feedback circuit 106 and then fed back to the second end of the first optocoupler G1 using the second end of the feedback circuit 106. The light-emitting diode located between the first end and the second end of the first optocoupler G1 will emit light of different intensities according to the changing voltage drop across the detection resistor Rs.
[0127] Simultaneously, the photosensitive device located between the third and fourth terminals of the first optocoupler G1 will conduct according to the luminous intensity of the light-emitting diode. Utilizing the connection between the first optocoupler G1 and the feedback circuit 106, the signal on the photosensitive device is fed as input to the feedback circuit 106, thereby achieving closed-loop negative feedback regulation. During this process, the input between the first and second terminals of the first optocoupler G1, the output between the third and fourth terminals of the first optocoupler G1, and the output between the fifth and sixth terminals of the first optocoupler G1 can approach a 1:1 ratio, thus achieving insulation resistance detection.
[0128] In the above embodiment, by setting the first optocoupler G1, the high voltage and low voltage outputs on the first controllable branch 102 and the second controllable branch 104 can be isolated, thereby enabling the impedance detection circuit 100 to meet the safety requirements of insulation.
[0129] In addition, in related embodiments, impedance detection points are often set in the first controllable branch 102 and the second controllable branch 104 when performing impedance detection. However, the first controllable branch 102 and / or the second controllable branch 104 are affected by the BOOST circuit, which makes the impedance detection results inaccurate.
[0130] Among them, the BOOST circuit is a boost circuit.
[0131] In the embodiments of this utility model, the ground impedance is determined by the ground signal values output from the fifth and sixth terminals of the first optocoupler G1. The isolation effect of the strong and weak currents of the first optocoupler G1 can be used to reduce the influence of the BOOST circuit on the impedance detection result, thereby improving the accuracy of impedance detection.
[0132] In one embodiment of this invention, a photovoltaic inverter (PV inverter or solar inverter) is an inverter that converts the variable DC voltage generated by photovoltaic (PV) solar panels into alternating current (AC) at the mains frequency. This AC voltage can be fed back to a commercial power transmission system or supplied to an off-grid grid. The PV inverter is one of the important system balance (BOS) components in a photovoltaic array system and can be used with general AC-powered equipment. Solar inverters have special functions tailored to photovoltaic arrays, such as maximum power point tracking and islanding protection.
[0133] In one embodiment of this utility model, the photovoltaic inverter can be an inverter installed in the photovoltaic system or an inverter installed independently. It can be set according to the actual use scenario, which will not be described in detail here.
[0134] The terms "first" and "second" in the specification and claims of this application may explicitly or implicitly include one or more of the features. In the textual description of this utility model, unless otherwise stated, "multiple" means two or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.
[0135] In the textual description of this utility model, it is understood that, unless explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection between two components or an indirect connection between two components through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.
[0136] In the claims, description, and drawings of this utility model, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this utility model. In the claims, description, and drawings of this utility model, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.
[0137] The above are merely preferred embodiments of this utility model and are not intended to limit the scope of this utility model. Various modifications and variations can be made to this utility model by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this utility model should be included within the protection scope of this utility model.
Claims
1. An impedance detection circuit, characterized in that, include: The first controllable branch includes a first switching transistor; The second controllable branch includes a second switching transistor. The output terminal of the second controllable branch is connected to the output terminal of the first controllable branch and then connected to the first grounding point. A detection resistor, wherein the first end of the detection resistor is connected to the output terminal of the first controllable branch, and the second end of the detection resistor is connected to the first power supply; A feedback circuit, wherein the first terminal of the feedback circuit is connected to the first terminal of the detection resistor; A first optocoupler, wherein a first end of the first optocoupler is connected to the first power supply, a second end of the first optocoupler is connected to the second end of the feedback circuit, a third end of the first optocoupler is connected to the first end of the feedback circuit, and a fourth end of the first optocoupler is connected to the third end of the feedback circuit. Specifically, the ground impedance of the first controllable branch and the second controllable branch is determined by the ground signal values output from the fifth and sixth terminals of the first optocoupler based on the different conduction states of the first and second switching transistors.
2. The impedance detection circuit according to claim 1, characterized in that, The first controllable branch also includes: A first driving circuit, wherein a first terminal of the first driving circuit is used to receive a first signal, a second terminal of the first driving circuit is grounded, a third terminal of the first driving circuit is connected to the control terminal of the first switching transistor, a fourth terminal of the first driving circuit is connected to the second terminal of the first switching transistor, a fifth terminal of the first driving circuit is connected to a second power supply, and a sixth terminal of the first driving circuit is connected to the first power supply. A first resistor, the first end of which is used to receive a first voltage signal, and the second end of which is connected to the first end of the first switching transistor; The second resistor has a first end connected to the second end of the first resistor, and the second end of the second resistor is connected to the first grounding point. and / or The second controllable branch also includes: The second driving circuit has a first terminal for receiving a second signal, a second terminal for grounding, a third terminal for connecting to the control terminal of the second switching transistor, a fourth terminal for connecting to the second terminal of the second switching transistor, a fifth terminal for connecting to the second power supply, and a sixth terminal for connecting to the first power supply. The third resistor has a first end for receiving a second voltage signal and a second end for connecting to the first end of the second switching transistor. The fourth resistor has its first end connected to the second end of the third resistor, and its second end connected to the first grounding point.
3. The impedance detection circuit according to claim 2, characterized in that, The first driving circuit includes: The second optocoupler has a first terminal for receiving the first signal, a second terminal for grounding, a third terminal for connecting to the first power supply, and a fourth terminal for connecting to the control terminal of the first switching transistor. A first current-limiting resistor, the first end of which is connected to the second power supply, and the second end of which is connected to the fourth end of the second optocoupler.
4. The impedance detection circuit according to claim 3, characterized in that, The first driving circuit further includes: The fifth resistor is located between the fourth terminal of the second optocoupler and the control terminal of the first switching transistor; A first capacitor, the first end of which is connected to the control terminal of the first switching transistor, and the second end of which is connected to the second terminal of the first switching transistor.
5. The impedance detection circuit according to claim 2, characterized in that, The second driving circuit includes: The third optocoupler has a first terminal for receiving the second signal, a second terminal for grounding, a third terminal for connecting to the first power supply, and a fourth terminal for connecting to the control terminal of the second switching transistor. The second current-limiting resistor has its first end connected to the second power supply and its second end connected to the fourth end of the third optocoupler.
6. The impedance detection circuit according to claim 5, characterized in that, The second driving circuit also includes: The sixth resistor is located between the fourth terminal of the third optocoupler and the control terminal of the second switching transistor; The second capacitor has its first end connected to the control terminal of the second switching transistor, and its second end connected to the second terminal of the second switching transistor.
7. The impedance detection circuit according to claim 1, characterized in that, The feedback circuit includes: A first comparator, wherein the non-inverting input terminal of the first comparator is connected to the first terminal of the detection resistor and the third terminal of the first optocoupler, the negative-inverting input terminal of the first comparator is connected to the first power supply and the fourth terminal of the first optocoupler, and the output terminal of the first comparator is connected to the second terminal of the first optocoupler; The third capacitor has its first terminal connected to the negative input terminal of the first comparator and its second terminal connected to the output terminal of the first comparator.
8. The impedance detection circuit according to claim 7, characterized in that, The feedback circuit also includes: The seventh resistor is connected in series between the output of the first comparator and the second terminal of the first optocoupler.
9. The impedance detection circuit according to claim 7, characterized in that, The impedance detection circuit further includes: The second comparator is connected in series between the non-inverting input of the first comparator and the first end of the detection resistor. The non-inverting input of the second comparator is connected to the first end of the detection resistor. The output of the second comparator is connected to the non-inverting input of the first comparator. The negative input of the second comparator is connected to the output of the second comparator.
10. The impedance detection circuit according to claim 1, characterized in that, The impedance detection circuit further includes: The third comparator has its positive input terminal connected to the fifth terminal of the first optocoupler, its negative input terminal connected to the sixth terminal of the first optocoupler, and its output terminal used to output the ground signal. The eighth resistor has its first terminal connected to the non-inverting input terminal of the third comparator, and its second terminal grounded. The ninth resistor has its first end connected to the negative input terminal of the third comparator and its second end connected to the output terminal of the third comparator. A fourth capacitor, the first terminal of which is connected to the first terminal of the ninth resistor, and the second terminal of which is connected to the second terminal of the ninth resistor.
11. A photovoltaic inverter, characterized in that, include: The impedance detection circuit as described in any one of claims 1 to 10.