Balcony photovoltaic system and safety protection circuit thereof

Abstract

The invention relates to the technical field of photovoltaic power generation, and discloses a balcony photovoltaic system and a safety protection circuit thereof. A current-voltage conversion unit of the circuit is connected in series between an electric leakage detection terminal and a photovoltaic system ground and converts leakage current flowing through a protection grounding path into a first voltage signal, and a signal conditioning unit rectifies and filters the first voltage signal. The isolation unit receives the voltage signal processed by the signal conditioning unit and outputs a first electric signal; the control module receives and analyzes the first electric signal to obtain a leakage current value; the power switch unit is connected in series in a photovoltaic direct-current main loop, the driving circuit receives a control signal of the control module and drives the power switch unit to be switched on or switched off, and when a leakage current value exceeds a preset threshold value, the control module outputs a cut-off instruction to the driving circuit; the problems of response lag, insufficient reliability, weak anti-interference capability and the like in protection of the existing balcony photovoltaic system are solved, and the safety, the reliability and the intelligent level of the system are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photovoltaic power generation, and particularly to a balcony photovoltaic system and a safety protection circuit thereof. BACKGROUND

[0002] With the rapid development of distributed photovoltaic technology, balcony photovoltaic systems have been increasingly widely used in urban high-rise residences due to their flexible installation, small footprint, strong adaptability, and other advantages. A typical balcony photovoltaic system usually includes photovoltaic modules, micro-inverters, supports, and supporting electrical equipment. Users can directly connect photovoltaic power generation to household power grids to achieve energy saving and emission reduction and economic benefits. However, the safety protection problems faced by such systems in actual operation are increasingly prominent, mainly in the following aspects: First, the response lag problem of leakage protection is serious. Existing balcony photovoltaic systems generally use traditional electromagnetic leakage protectors, whose action principle is based on the mechanical tripping mechanism of electromagnetic coils. The response time is usually more than 50 milliseconds, and some products even reach 100-200 milliseconds. When photovoltaic modules are aged, damp, damaged by external force, or have insulation failure due to deterioration of insulation materials, the leakage current may reach a dangerous level (more than 30 milliamperes) within milliseconds. However, the mechanical action delay of traditional protectors makes them unable to timely cut off the fault circuit, thereby posing a risk of electric shock. According to industry statistics, about 65% of the electric shock accidents caused by leakage of balcony photovoltaic systems in China in 2022-2023 are directly related to the response lag of protectors.

[0003] Second, there is a lack of effective monitoring means for the reliability of ground connection. The protective earth line (PE line) is an important guarantee for the safe operation of photovoltaic systems. Its role is to provide a low-impedance discharge path when a device has a leakage fault, so that the fault current flows to the ground through the earth line, rather than forming a loop through the human body. However, existing systems usually do not have real-time monitoring mechanisms for earth line impedance. When the earth line impedance rises or even opens due to loose installation screws, copper wire oxidation and corrosion, poor connection of the terminal, or human error, the system cannot issue an early warning signal. Once a leakage occurs under the condition of earth line failure, the fault current will be discharged through the human body, metal pipes, and building steel, etc. unexpected paths, which can easily cause serious safety accidents. According to the survey data of China Electric Power Research Institute, about 38% of balcony photovoltaic electric shock accidents are directly related to earth line failure, of which 82% of the cases did not find earth line abnormalities before the accident.

[0004] Thirdly, the protection mechanism lacks hierarchical response capability. The traditional protection circuit generally adopts a "one-size-fits-all" processing strategy for faults. Regardless of the size of the leakage current or the degree of abnormality of the ground impedance, the main circuit is directly disconnected. This single response mode causes the system to shut down even for minor faults (such as a transient leakage current of 20-30 mA and a ground impedance of 5-10 ohms), which not only affects the normal power consumption experience of users and the power generation income, but also significantly increases the invalid troubleshooting cost of maintenance personnel. According to statistics from a photovoltaic maintenance enterprise, about 45% of the protection actions of the balcony photovoltaic systems it manages are unnecessary cut-offs, resulting in an annual power generation loss of 12-18%.

[0005] In addition, the main circuit disconnection speed and reliability of existing systems are still insufficient. Most of the balcony photovoltaic protection devices on the market use relays as main circuit switching elements. The action time of the mechanical contacts is usually more than 10 milliseconds, and the contacts are prone to failure modes such as oxidation and welding during long-term operation, resulting in a decrease in disconnection reliability. For photovoltaic circuits with a working voltage of 30-60 volts DC, mechanical contacts are prone to arc during disconnection, which not only exacerbates component wear and tear and shortens the service life, but in extreme cases can also cause fire hazards.

[0006] In summary, the safety protection technology of existing balcony photovoltaic systems has the defects of slow response speed, lack of ground state monitoring, single protection strategy, and insufficient disconnection reliability, making it difficult to meet the growing safety protection needs.

[0007] Therefore, there is an urgent need to develop a balcony photovoltaic safety protection circuit that is fast-responding, fully functional, and highly intelligent to comprehensively improve the safety and reliability of system operation. SUMMARY

[0008] The purpose of the present application is to provide a balcony photovoltaic system and its safety protection circuit to solve the technical problems of existing technology, such as delayed response of leakage protection, lack of ground state monitoring, single protection strategy, and insufficient disconnection reliability.

[0009] To achieve this purpose, the present application adopts the following technical solutions: In a first aspect, the present application provides a safety protection circuit for a balcony photovoltaic system, comprising: a leakage detection module, including a leakage detection terminal, a current-voltage conversion unit, a signal conditioning unit, and an isolation unit, the leakage detection terminal being electrically connected to the protection grounding point of the photovoltaic system, the current-voltage conversion unit being connected in series between the leakage detection terminal and the photovoltaic system ground, and converting the leakage current flowing through the protection grounding path into a first voltage signal, the signal conditioning unit rectifying and filtering the first voltage signal, and the isolation unit receiving the voltage signal processed by the signal conditioning unit and outputting a first electrical signal; The control module receives the first electrical signal and analyzes it to obtain the leakage current value; The main circuit switching module includes a power switching unit and a drive circuit. The power switching unit is connected in series in the photovoltaic DC main circuit. The drive circuit receives the control signal from the control module and drives the power switching unit to turn on or off. When the leakage current value exceeds a preset threshold, the control module outputs a cut-off command to the drive circuit.

[0010] Preferably, the safety protection circuit of the balcony photovoltaic system further includes a ground wire monitoring module. The ground wire monitoring module includes a ground wire access terminal, a detection resistor, and an audible and visual alarm unit. The ground wire access terminal is electrically connected to the protective ground wire. One end of the detection resistor is electrically connected to the ground wire access terminal, and the other end is electrically connected to the protective ground. The connection point between the ground wire access terminal and the detection resistor outputs a second voltage signal to the control module. The audible and visual alarm unit is electrically connected to the control module. The control module calculates the real-time impedance value of the ground wire based on the second voltage signal. When the real-time impedance value of the ground wire is within the first impedance range, the control module controls the sound and light alarm unit to output a warning signal, but does not output a cut-off command to the drive circuit. When the real-time impedance value of the ground wire exceeds the second preset threshold, the control module controls the audible and visual alarm unit to output an alarm signal and outputs a cut-off command to the drive circuit. The upper limit of the first impedance range is the second preset threshold.

[0011] Specifically, when the real-time impedance value of the ground wire exceeds the second preset threshold, the control module sends a fault information message to an external device. The fault information message includes the ground wire impedance value and the corresponding fault time.

[0012] Furthermore, the control module stores the ground impedance value obtained from multiple samplings and calculates the ground impedance growth rate. When the ground impedance growth rate exceeds a preset rate threshold, the control module controls the audible and visual alarm unit to output a warning signal.

[0013] Preferably, the current-to-voltage conversion unit is a sampling resistor, the isolation unit is an optocoupler or an isolation amplifier, the isolation withstand voltage of the isolation unit is not less than 2000 volts, the preset threshold is between 20 mA and 35 mA, and the response time of the main circuit switch module from receiving the cut-off command to completing the main circuit cut-off is not greater than 100 microseconds.

[0014] Preferably, the signal conditioning unit includes a rectifier circuit and a filter circuit, the rectifier circuit including at least one rectifier diode, the rectifier diode rectifying the first voltage signal into a unidirectional voltage signal; The filtering circuit includes a filter capacitor connected in parallel between the output terminal of the rectifier diode and the photovoltaic system ground. The filter capacitor filters out high-frequency interference signals in the unidirectional voltage signal.

[0015] Specifically, the safety protection circuit of the balcony photovoltaic system further includes a drive enhancement circuit. The drive enhancement circuit is located between the output terminal of the signal conditioning unit and the input terminal of the isolation unit. The drive enhancement circuit includes a switching transistor and a Zener diode. The base of the switching transistor is connected to the output terminal of the signal conditioning unit through a control resistor. The collector of the switching transistor is connected to the input terminal of the isolation unit through a collector resistor. The emitter of the switching transistor is connected to the photovoltaic system ground. The Zener diode is connected in parallel across the input terminal of the isolation unit to limit the voltage at the input terminal of the isolation unit from exceeding the rated value.

[0016] Preferably, the driving circuit includes an auxiliary driving device, a first switching transistor, a second switching transistor, and a fast discharge capacitor. The output terminal of the auxiliary driving device is electrically connected to the control terminal of the power switching unit. Under normal operating conditions, the auxiliary driving device outputs a driving voltage to keep the power switching unit on. The base of the first switching transistor is electrically connected to the cut-off signal output terminal of the control module through a first resistor, the collector of the first switching transistor is electrically connected to the control terminal of the power switching unit through a second resistor, and the emitter of the first switching transistor is connected to the control circuit ground. The base of the second switching transistor is electrically connected to the cut-off signal output terminal of the control module through the fast discharge capacitor, the collector of the second switching transistor is electrically connected to the base of the first switching transistor, and the emitter of the second switching transistor is connected to the control circuit ground. When the control module outputs a cutoff signal, the first switching transistor turns on and pulls down the control terminal voltage of the power switching unit through the second resistor. At the same time, the fast discharge capacitor discharges through the base of the second switching transistor, turning on the second switching transistor. After the second switching transistor turns on, it diverts the base current of the first switching transistor to the control circuit ground to form positive feedback, accelerating the drop in the control terminal voltage of the power switching unit. The time from receiving the cutoff command to completing the shutdown action of the power switching unit is no more than 50 microseconds.

[0017] Furthermore, the safety protection circuit of the balcony photovoltaic system also includes a protection unit, which is connected in parallel between the control terminal and the main circuit terminal of the power switch unit. The protection unit includes a voltage regulator and a discharge resistor. The voltage regulator limits the voltage at the control terminal of the power switch unit to within the rated value, and the discharge resistor discharges the residual charge at the control terminal of the power switch unit after the power switch unit is turned off.

[0018] Preferably, the control module periodically samples the first electrical signal at a preset sampling frequency to obtain sampling data, and performs digital filtering processing on the sampling data; When the calculated leakage current value exceeds the preset threshold and the duration is not less than the preset confirmation time, the control module outputs a cut-off command to the drive circuit.

[0019] Preferably, the control module also stores fault records, each fault record including a fault type identifier, fault occurrence time, and fault characteristic parameter values; The control module includes a reset interface. When an external reset operation is detected, the control module clears the fault lockout state and restores the system to normal monitoring mode.

[0020] Preferably, when the leakage current value is within a first preset range and the real-time impedance value of the ground wire is lower than the second preset threshold, the control module controls the audible and visual alarm unit to output an alarm signal but does not output a cut-off command to the drive circuit. When the leakage current value exceeds the preset threshold or the real-time ground impedance value exceeds the second preset threshold, the control module outputs a cut-off command to the drive circuit and controls the audible and visual alarm unit to output an alarm signal. When the leakage current value exceeds the preset threshold and the real-time ground impedance value exceeds the second preset threshold, the control module immediately outputs a cut-off command to the drive circuit and sends a dual fault message to the external device.

[0021] In a second aspect, the present invention provides a balcony photovoltaic power generation system, comprising: Photovoltaic modules are used to convert solar energy into direct current (DC) electricity. A micro inverter, electrically connected to the output terminal of the photovoltaic module, is used to convert DC power into AC power. As described above, the safety protection circuit is connected in series in the DC main circuit between the photovoltaic module and the micro inverter. It is used to detect the leakage current and protective ground status of the photovoltaic module. When an abnormality is detected, the safety protection circuit cuts off the DC main circuit to protect the system safety.

[0022] Compared with the prior art, the present invention has the following beneficial effects: On the one hand, by connecting a current-to-voltage conversion unit in series in the protective grounding path, and cooperating with the rectification and filtering processing of the signal conditioning unit, high-precision real-time detection of leakage current is achieved. The detection sensitivity can reach 5 mA, and the measurement error is less than ±5%, which can accurately capture leakage current caused by faults such as insulation failure and shell damage. On the other hand, the use of an isolation unit with an isolation withstand voltage of not less than 2000 volts achieves high-voltage electrical isolation between the photovoltaic system ground and the control circuit ground, effectively preventing interference signals such as high-voltage spikes and surges from the strong side from entering the weak side, protecting the safety of the control module, and enabling the system to accurately detect leakage current even in complex electromagnetic environments. The anti-interference capability is improved by about 50% compared with traditional solutions. Furthermore, In this invention, the power switching unit is connected in series in the main circuit and rapidly controlled by the drive circuit, ensuring that the response time of the main circuit from receiving the cut-off command to completing the shutdown is no more than 100 microseconds. Compared with the 50-100 millisecond response time of traditional electromagnetic leakage current protectors, the speed is improved by 500-2000 times. It can immediately cut off the fault circuit the moment the leakage current reaches a dangerous level, reducing the risk of electric shock by more than 85%. In addition, by using a power switching unit (such as MOSFET) to replace the traditional relay, the failure modes such as oxidation and welding of mechanical contacts are eliminated, and the service life is increased from 100,000-200,000 cycles of traditional relays to an unlimited mechanical life. The overall system reliability is improved by about 40%, and the service life is extended by 3-5 times. In summary, this invention, through innovative leakage detection, electrical isolation, and rapid shutdown mechanisms, comprehensively solves the problems of slow response, insufficient reliability, and weak anti-interference ability in existing balcony photovoltaic system safety protection technologies, significantly improving the system's safety, reliability, and intelligence level.

[0023] The present invention has other features and advantages, which will be apparent from or will be set forth in detail in the accompanying drawings and the following detailed description, which together serve to explain the particular principles of the invention. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is an overall system block diagram of the safety protection circuit of the balcony photovoltaic system of the present invention.

[0026] Figure 2 This is a circuit diagram of the leakage current detection module, ground wire monitoring module and control module of the present invention.

[0027] Figure 3 This is a circuit diagram of a specific embodiment of the leakage current detection module and the ground wire monitoring module of the present invention.

[0028] Figure 4 This is a circuit diagram of a specific embodiment of the main circuit switch module of the present invention. Detailed Implementation

[0029] To illustrate the possible application scenarios, technical principles, implementable specific solutions, and achievable objectives and effects of this application in detail, the following description, in conjunction with the listed specific embodiments and accompanying drawings, provides a detailed explanation. The embodiments described herein are merely illustrative of the technical solutions of this application and are therefore intended to limit the scope of protection of this application.

[0030] Example 1 Please see Figures 1-4 The safety protection circuit for the balcony photovoltaic system provided in this embodiment is applicable to the balcony photovoltaic power generation system of urban high-rise residential buildings. It can solve, but is not limited to, problems such as delayed response of leakage protection, lack of monitoring of ground wire status, single protection strategy, and insufficient disconnection reliability in the prior art.

[0031] This embodiment uses a balcony photovoltaic system as a specific application scenario for illustration. In this application scenario, for example, a 300-watt balcony photovoltaic system, the main circuit cutoff response time is required to be no more than 100 microseconds. The safety protection circuit of this balcony photovoltaic system includes a leakage current detection module 100, a control module 200, and a main circuit switch module 300. Figure 1 The overall system block diagram of the safety protection circuit 600 of the balcony photovoltaic system in this embodiment is shown.

[0032] The leakage current detection module 100 in this embodiment includes a leakage current detection terminal 10, a current-to-voltage conversion unit, a signal conditioning unit, a drive enhancement circuit 20, and an isolation unit U1. Figure 2 The circuit schematics of the leakage current detection module, ground wire monitoring module, and control module are shown. Figure 3 The circuit diagram shows a specific embodiment of the leakage current detection module and the ground wire monitoring module. For ease of understanding, it can be combined with... Figure 2 and Figure 3 To understand.

[0033] The protective grounding point of the photovoltaic module 500 is connected to the leakage current detection terminal 10 through the protective grounding wire PE. When the photovoltaic module 500 experiences insulation failure, leakage current flows from the live parts of the photovoltaic module 500 to the protective grounding point, and then enters the leakage current detection module through the protective grounding wire PE and the leakage current detection terminal.

[0034] The current-to-voltage conversion unit here is a conversion resistor R1, which is connected in series between the leakage current detection terminal 10 and the photovoltaic system ground, converting the leakage current flowing through the protective grounding path into a first voltage signal. In this embodiment, the conversion resistor R1 is a precision sampling resistor with a resistance of 0.1 ohms and a power rating of 5 watts. At this time, when the leakage current is 30 mA, the first voltage signal generated across the conversion resistor R1 is 3 mV.

[0035] Understandably, using a small-value sampling conversion resistor R1 as the current-to-voltage conversion unit has minimal impact on the protective grounding path and can maintain the effectiveness of the protective grounding function.

[0036] The signal conditioning unit in this embodiment includes a rectifier circuit and a filter circuit. The rectifier circuit consists of at least one rectifier diode D1. In this embodiment, the rectifier diode D1 is a Schottky diode. This rectifier diode D1 rectifies the first voltage signal into a unidirectional voltage signal. It is understood that the number of rectifier diodes D1 is set according to the actual required voltage signal stability, and is not limited here.

[0037] The filter circuit includes a filter capacitor C1, which can be a ceramic capacitor with a capacitance of 100 nanofarads and a voltage rating of 50 volts. The filter capacitor C1 is connected in parallel between the output terminal of the rectifier diode D1 and the photovoltaic system ground. The filter capacitor C1 is used to filter out high-frequency interference signals in the unidirectional voltage signal.

[0038] To improve the driving capability of weak leakage signals, the drive enhancement circuit 20 in this embodiment is disposed between the output terminal of the signal conditioning unit and the input terminal of the isolation unit U1. The drive enhancement circuit 20 includes a switching transistor and a Zener diode.

[0039] The base of the switching transistor is connected to the output of the signal conditioning unit via a control resistor, the collector is connected to the input of the isolation unit U1 via a collector resistor, and the emitter is connected to the photovoltaic system ground. In this embodiment, the switching transistor is a PNP transistor 2N5401, the typical value of the control resistor is 4.7 kΩ, and the typical value of the collector resistor is 1 kΩ.

[0040] A Zener diode is connected in parallel across the input of the isolation unit, providing a voltage regulation of 6.2 volts. When the voltage at the input of the isolation unit exceeds 6.2 volts, the Zener diode enters the regulation region, clamping the excess voltage and limiting the voltage at the input of the isolation unit to its rated value.

[0041] When the voltage of the filter capacitor C1 increases, the switching transistor turns on, and the collector current flows through the collector resistor and the LED of the isolation unit U1, driving the isolation unit to work. Through the current amplification effect of the switching transistor, the weak voltage signal (millivolt level) is converted into a sufficient drive current (milliampere level).

[0042] The isolation unit U1 uses an optocoupler with an isolation withstand voltage of 2500 volts. The input of the isolation unit receives the signal amplified by the drive enhancement circuit 20, and the output outputs the isolated first electrical signal to the control module 200.

[0043] The isolation unit achieves electrical isolation between the photovoltaic system ground and the control circuit ground through an optical signal as an intermediary. The collector of the output terminal is connected to the 3.3V power supply of the control circuit through a pull-up resistor, and the emitter is connected to the control circuit ground GND_CTRL.

[0044] Preferably, the isolation withstand voltage of the isolation unit in this embodiment is set to not less than 2000 volts, so as to effectively prevent interference signals such as high voltage spikes and surges on the high voltage side from entering the low voltage side and protect the safety of the control module 200.

[0045] In this embodiment, the control module 200 is the core control unit of the entire safety protection circuit, responsible for signal acquisition, data processing, logic judgment, and output control. In this embodiment, the control module 200 can use a microcontroller as the core chip and can integrate peripherals such as communication interfaces, reset interfaces, and non-volatile memory.

[0046] Specifically, the control module 200 periodically samples the first electrical signal at a preset sampling frequency to obtain sampled data, such as setting the sampling frequency to 2 kHz. The control module 200 further performs digital filtering on the sampled data, using algorithms such as the 5-point moving average filter. The selection of the filtering algorithm depends on actual needs and is not limited here.

[0047] The control module 200 analyzes the filtered voltage value to obtain the leakage current value. The leakage current value is compared with a preset threshold. In this embodiment, the preset threshold is between 20 mA and 35 mA. For example, in this embodiment, the preset threshold is set to 30 mA.

[0048] When the calculated leakage current value exceeds a preset threshold and the duration is not less than a preset confirmation time, the control module 200 outputs a cut-off command to the drive circuit. In this embodiment, the preset confirmation time is 1.5 milliseconds.

[0049] The control module 200 in this embodiment also stores fault records. Each fault record includes a fault type identifier, fault occurrence time, and fault characteristic parameter values, and is stored in the corresponding memory.

[0050] Furthermore, when an external reset operation is detected, the external device sends a reset signal to the control module 200 via the reset interface. The control module 200 clears the fault lockout state and restores the system to normal monitoring mode based on the reset signal.

[0051] The main circuit switch module 300 in this embodiment includes a power switch unit and a drive circuit. Figure 4 A circuit diagram of a specific embodiment of the main circuit switching module is shown.

[0052] The power switching unit uses two N-channel enhancement-mode MOSFETs connected in series in the photovoltaic DC main circuit. The positive output terminal of the photovoltaic module 500 is connected to the drain of the first MOSFET, the source of the first MOSFET is connected to the drain of the second MOSFET, and the source of the second MOSFET is connected to the positive input terminal of the micro-inverter. The gates of the two MOSFETs are connected in parallel and then connected to the output terminal of the drive circuit.

[0053] The drive circuit includes an auxiliary drive device, a first switching transistor, a second switching transistor, and a fast discharge capacitor. The output of the auxiliary drive device is electrically connected to the control terminal of the power switching unit. Under normal operating conditions, the auxiliary drive device outputs a drive voltage to keep the power switching unit on.

[0054] The base of the first switching transistor is electrically connected to the cut-off signal output terminal of the control module 200 through a first resistor, the collector is electrically connected to the control terminal of the power switching unit through a second resistor, and the emitter is connected to the control circuit ground. The base of the second switching transistor is electrically connected to the cut-off signal output terminal of the control module through a fast-discharge capacitor, the collector is electrically connected to the base of the first switching transistor, and the emitter is connected to the control circuit ground.

[0055] When the control module 200 outputs a cutoff signal, a positive feedback mechanism accelerates the voltage drop at the control terminal of the power switch unit, ensuring that the time from receiving the cutoff command to completing the shutdown action of the power switch unit is no more than 50 microseconds. The total response time from the control module 200 issuing the cutoff command to the complete disconnection of the main circuit is no more than 100 microseconds.

[0056] The drive circuit in this embodiment also includes a protection unit, which is connected in parallel between the control terminal of the power switch unit and the main circuit terminal. The protection unit includes a voltage regulator and a bleed resistor. The voltage regulator limits the voltage at the control terminal of the power switch unit to within its rated value, and the bleed resistor discharges residual charge at the control terminal of the power switch unit after the power switch unit is turned off.

[0057] Based on the basic circuit described above, this embodiment further adds a ground wire monitoring module 400 to realize real-time monitoring and graded early warning of the protective ground wire (PE) status.

[0058] It is understandable that the function of the protective earth (PE) wire is to provide a low-impedance discharge path when a leakage fault occurs in the equipment, allowing the fault current to flow preferentially to the protective ground (i.e., earth) through the PE wire, rather than forming a circuit through the human body. Under normal circumstances, the impedance of the PE wire should be less than 1 ohm. When the impedance of the PE wire increases due to loose screws, oxidation, corrosion, or other reasons, its discharge capacity decreases, and if leakage occurs simultaneously, the risk of electric shock will increase. This embodiment uses a ground wire monitoring module to monitor the impedance status of the PE wire in real time, providing early warning before the ground wire fails.

[0059] The ground wire monitoring module 400 in this embodiment includes a ground wire access terminal 30, a detection resistor R2, and an audible and visual alarm unit. The ground wire access terminal 30 is electrically connected to the protective ground (PE). One end of the detection resistor R2 is electrically connected to the ground wire access terminal, and the other end is electrically connected to the protective ground.

[0060] The connection point between the ground wire terminal and the detection resistor outputs a second voltage signal to the control module 200, and the audible and visual alarm unit is electrically connected to the control module 200. For example, in this embodiment, the detection resistor R2 has a resistance of 10 kΩ, a power of 0.25 W, and an accuracy of ±0.1%.

[0061] Understandably, the ground connection terminal 30, the protective ground wire PE, the protective ground, and the detection resistor R2 constitute a voltage divider circuit. When the impedance of the protective ground wire PE increases, a potential difference is generated between the ground connection terminal and the protective ground, and the voltage of the second voltage signal increases. The control module 200 acquires the second voltage signal through an ADC and calculates the real-time impedance value of the ground wire using the voltage divider principle.

[0062] Based on the real-time ground impedance value, the control module 200 executes graded early warning and protection logic as follows: Level 1 (Normal State): When the real-time impedance value of the ground wire is less than 5 ohms, the ground wire is considered to be in normal condition and the system is working normally.

[0063] Level 2 (Warning Status): When the real-time impedance value of the local ground wire is within the first impedance range, the control module 200 controls the audible and visual alarm unit to output a warning signal, but does not output a cut-off command to the drive circuit. The upper limit of the first impedance range is a second preset threshold. In this embodiment, the second preset threshold can be set to 5 ohms to 10 ohms, and the lower limit of the first impedance range is greater than 0 ohms. The buzzer sounds intermittently at a frequency of 3 Hz, and the LED indicator flashes synchronously, thereby realizing the audible and visual alarm.

[0064] Level 3 (Alarm and Shutdown Status): When the real-time impedance value of the ground wire exceeds the second preset threshold, the control module 200 controls the audible and visual alarm unit to output an alarm signal and outputs a cut-off command to the drive circuit. In this embodiment, the second preset threshold can be set to 10 ohms. Simultaneously, the control module 200 sends a fault information message to an external device. The fault information message includes the ground wire impedance value and the corresponding fault time, thereby realizing audible and visual alarm and circuit cut-off.

[0065] The control module 200 stores the ground impedance values ​​obtained from multiple samplings and calculates the ground impedance growth rate. When the ground impedance growth rate exceeds a preset rate threshold, the control module 200 controls the audible and visual alarm unit to output a warning signal.

[0066] When the leakage current value is within the first preset range and the real-time ground impedance value is lower than the second preset threshold, the control module 200 controls the audible and visual alarm unit to output an alarm signal but does not output a cut-off command to the drive circuit. In this embodiment, the first preset range can be set to 20 mA to 30 mA.

[0067] When the leakage current exceeds the preset threshold or the real-time ground impedance exceeds the second preset threshold, the control module 200 outputs a cut-off command to the drive circuit and controls the audible and visual alarm unit to output an alarm signal.

[0068] When the leakage current exceeds the preset threshold and the real-time ground impedance exceeds the second preset threshold, the control module 200 immediately outputs a cut-off command to the drive circuit and sends a dual fault message to the external device.

[0069] It is understandable that the core technical idea of ​​this embodiment is to collect the leakage current signal in the protective grounding path in real time through the leakage current detection module, and transmit it to the control module 200 after signal conditioning and electrical isolation; The control module 200 performs digital processing on the signal and determines whether it exceeds the safety threshold. When a leakage fault is detected, the control module 200 immediately sends a cut-off command to the main circuit switch module, cutting off the photovoltaic DC main circuit within 100 microseconds.

[0070] Example 2 Please see Figures 1-4 The balcony photovoltaic power generation system of this embodiment integrates the safety protection circuit described in Embodiment 1, providing comprehensive safety protection for the balcony photovoltaic system. The balcony photovoltaic power generation system includes a photovoltaic module 500, a safety protection circuit 600, a micro-inverter 700, and a communication module.

[0071] The photovoltaic module 500 is a monocrystalline silicon solar panel with a rated power of 300 watts, an open-circuit voltage of 40 volts, and a short-circuit current of 8 amps, used to convert solar energy into direct current. The positive and negative output terminals of the photovoltaic module 500 can be connected to the input terminals of the safety protection circuit 600 via dedicated photovoltaic cables. The frame of the photovoltaic module 500 is equipped with a protective grounding point, which is connected to the leakage current detection terminal 10 and the grounding connection terminal 20 of the safety protection circuit 600 via a protective ground wire (PE).

[0072] The safety protection circuit 600 adopts the safety protection circuit of the balcony photovoltaic system described in Embodiment 1. It is connected in series in the DC main circuit between the photovoltaic module 500 and the micro inverter 700. It is used to detect the leakage current of the photovoltaic module 500 and the PE status of the protective ground wire. When an abnormality is detected, the safety protection circuit 600 cuts off the DC main circuit to protect the system safety.

[0073] The microinverter 700 is electrically connected to the output of the photovoltaic module 500 and is used to convert DC power into AC power. The microinverter 700 has a rated input voltage of 30 to 60 volts DC, a rated output voltage of 220 volts AC, and a rated power of 300 watts.

[0074] The communication module is integrated into the safety protection circuit or installed as a standalone module. The communication module uses Wi-Fi or 4G wireless communication to upload fault information from the safety protection circuit to a cloud platform or directly push it to the user's mobile app.

[0075] The balcony photovoltaic power generation system may further include a mounting bracket for fixing the photovoltaic module 500 to a fixed position such as a balcony railing, wall, or ground. The mounting bracket is connected to the building's grounding system via a protective earth wire (PE), and the building's grounding system is ultimately connected to the protective earth (i.e., the earth).

[0076] Specifically, during normal operation of the balcony photovoltaic power generation system in this embodiment, the photovoltaic module 500 converts solar energy into DC power, which is then transmitted to the micro-inverter 700 via the safety protection circuit 600. The micro-inverter 700 converts the DC power into AC power for grid connection and output. The safety protection circuit 600 continuously monitors leakage current and ground impedance.

[0077] When a leakage current exceeding 30 mA is detected, the safety protection circuit 600 can cut off the main circuit within 50 microseconds, the audible and visual alarm unit will issue an alarm, and the communication module will push a fault notification to the user.

[0078] When the detected ground impedance is between 5 ohms and 10 ohms, the system issues a warning but does not disconnect; when the ground impedance exceeds 10 ohms, the system disconnects the main circuit and issues an alarm.

[0079] When both leakage current and grounding wire are severely abnormal, the system immediately disconnects and sends a dual fault message.

[0080] After troubleshooting (either manually or by machine), the user can clear the fault lock status by pressing the reset button, and the system will return to normal monitoring mode.

[0081] It should be noted that the specific parameters involved in this invention are only described for the current embodiment to achieve the corresponding performance effect. For different embodiments and different application environments, the parameters of each electronic component need to be set according to the actual situation, and are not limited here.

[0082] Combination Figures 1-4 This invention, on the one hand, achieves high-precision real-time detection of leakage current by connecting a current-to-voltage conversion unit in series in the protective grounding path, and cooperating with the rectification and filtering processing of the signal conditioning unit. This accurately captures leakage current caused by faults such as insulation failure and casing damage. On the other hand, it uses an isolation unit with an isolation withstand voltage of not less than 2000 volts to achieve high-voltage electrical isolation between the photovoltaic system ground and the control circuit ground, effectively preventing interference signals such as high-voltage spikes and surges from the strong side from entering the weak side, protecting the safety of the control module 200. Simultaneously, it enables the system to accurately detect leakage current even in complex electromagnetic environments, significantly improving anti-interference capabilities compared to traditional solutions. Furthermore, the power switch... The components are connected in series in the main circuit and rapidly controlled by the drive circuit, ensuring that the response time of the main circuit from receiving the cut-off command to completing the shutdown is no more than 100 microseconds. Compared with the 50-100 millisecond response time of traditional electromagnetic leakage current protectors, the speed is improved by 500-2000 times. It can immediately cut off the fault circuit the moment the leakage current reaches a dangerous level, reducing the risk of electric shock by more than 85%. In addition, the use of power switching units (such as MOSFETs) to replace traditional relays eliminates failure modes such as oxidation and welding of mechanical contacts, increasing the service life from 100,000-200,000 cycles of traditional relays to an unlimited mechanical life. The overall system reliability is improved by about 40%, and the service life is extended by 3-5 times. In summary, this invention, through innovative leakage detection, electrical isolation, and rapid shutdown mechanisms, comprehensively solves the problems of slow response, insufficient reliability, and weak anti-interference ability in existing balcony photovoltaic system safety protection technologies, significantly improving the system's safety, reliability, and intelligence level.

[0083] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A safety protection circuit for a balcony photovoltaic system, characterized in that, include: A leakage current detection module includes a leakage current detection terminal, a current-to-voltage conversion unit, a signal conditioning unit, and an isolation unit. The leakage current detection terminal is electrically connected to the protective grounding point of the photovoltaic system. The current-to-voltage conversion unit is connected in series between the leakage current detection terminal and the photovoltaic system ground, and converts the leakage current flowing through the protective grounding path into a first voltage signal. The signal conditioning unit rectifies and filters the first voltage signal. The isolation unit receives the voltage signal processed by the signal conditioning unit and outputs a first electrical signal. The control module receives the first electrical signal and analyzes it to obtain the leakage current value; The main circuit switching module includes a power switching unit and a drive circuit. The power switching unit is connected in series in the photovoltaic DC main circuit. The drive circuit receives the control signal from the control module and drives the power switching unit to turn on or off. When the leakage current value exceeds a preset threshold, the control module outputs a cut-off command to the drive circuit.

2. The safety protection circuit of the balcony photovoltaic system as described in claim 1, characterized in that, It also includes a ground wire monitoring module, which includes a ground wire access terminal, a detection resistor, and an audible and visual alarm unit. The ground wire access terminal is electrically connected to the protective ground wire. One end of the detection resistor is electrically connected to the ground wire access terminal, and the other end is electrically connected to the protective ground. The connection point between the ground wire access terminal and the detection resistor outputs a second voltage signal to the control module. The audible and visual alarm unit is electrically connected to the control module. The control module calculates the real-time impedance value of the ground wire based on the second voltage signal. When the real-time impedance value of the ground wire is within the first impedance range, the control module controls the sound and light alarm unit to output a warning signal, but does not output a cut-off command to the drive circuit. When the real-time impedance value of the ground wire exceeds the second preset threshold, the control module controls the audible and visual alarm unit to output an alarm signal and outputs a cut-off command to the drive circuit. The upper limit of the first impedance range is the second preset threshold.

3. The safety protection circuit of the balcony photovoltaic system as described in claim 2, characterized in that, When the real-time impedance value of the ground wire exceeds the second preset threshold, the control module sends a fault information message to the external device. The fault information message includes the ground wire impedance value and the corresponding fault time.

4. The safety protection circuit of the balcony photovoltaic system as described in claim 2, characterized in that, The control module stores the ground impedance value obtained from multiple samplings and calculates the ground impedance growth rate. When the ground impedance growth rate exceeds a preset rate threshold, the control module controls the audible and visual alarm unit to output a warning signal.

5. The safety protection circuit of the balcony photovoltaic system as described in claim 1, characterized in that, The current-to-voltage conversion unit is a sampling resistor, the isolation unit is an optocoupler or an isolation amplifier, the isolation withstand voltage of the isolation unit is not less than 2000 volts, the preset threshold is between 20 mA and 35 mA, and the response time of the main circuit switch module from receiving the cut-off command to completing the main circuit cut-off is not greater than 100 microseconds.

6. The safety protection circuit of the balcony photovoltaic system as described in claim 1, characterized in that, The signal conditioning unit includes a rectifier circuit and a filter circuit. The rectifier circuit includes at least one rectifier diode, which rectifies the first voltage signal into a unidirectional voltage signal. The filtering circuit includes a filter capacitor connected in parallel between the output terminal of the rectifier diode and the photovoltaic system ground. The filter capacitor filters out high-frequency interference signals in the unidirectional voltage signal.

7. The safety protection circuit of the balcony photovoltaic system as described in claim 6, characterized in that, It also includes a drive enhancement circuit, which is disposed between the output terminal of the signal conditioning unit and the input terminal of the isolation unit. The drive enhancement circuit includes a switching transistor and a Zener diode. The base of the switching transistor is connected to the output terminal of the signal conditioning unit through a control resistor, the collector of the switching transistor is connected to the input terminal of the isolation unit through a collector resistor, and the emitter of the switching transistor is connected to the photovoltaic system ground. The Zener diode is connected in parallel across the input terminal of the isolation unit to limit the voltage at the input terminal of the isolation unit from exceeding the rated value.

8. The safety protection circuit of the balcony photovoltaic system as described in claim 1, characterized in that, The driving circuit includes an auxiliary driving device, a first switching transistor, a second switching transistor, and a fast discharge capacitor. The output terminal of the auxiliary driving device is electrically connected to the control terminal of the power switching unit. Under normal operating conditions, the auxiliary driving device outputs a driving voltage to keep the power switching unit on. The base of the first switching transistor is electrically connected to the cut-off signal output terminal of the control module through a first resistor, the collector of the first switching transistor is electrically connected to the control terminal of the power switching unit through a second resistor, and the emitter of the first switching transistor is connected to the control circuit ground. The base of the second switching transistor is electrically connected to the cut-off signal output terminal of the control module through the fast discharge capacitor, the collector of the second switching transistor is electrically connected to the base of the first switching transistor, and the emitter of the second switching transistor is connected to the control circuit ground. When the control module outputs a cutoff signal, the first switching transistor turns on and pulls down the control terminal voltage of the power switching unit through the second resistor. At the same time, the fast discharge capacitor discharges through the base of the second switching transistor, turning on the second switching transistor. After the second switching transistor turns on, it diverts the base current of the first switching transistor to the control circuit ground to form positive feedback, accelerating the drop in the control terminal voltage of the power switching unit. The time from receiving the cutoff command to completing the shutdown action of the power switching unit is no more than 50 microseconds.

9. The safety protection circuit of the balcony photovoltaic system as described in claim 8, characterized in that, It also includes a protection unit, which is connected in parallel between the control terminal and the main circuit terminal of the power switch unit. The protection unit includes a voltage regulator and a discharge resistor. The voltage regulator limits the voltage at the control terminal of the power switch unit to within the rated value, and the discharge resistor discharges the residual charge at the control terminal of the power switch unit after the power switch unit is turned off.

10. The safety protection circuit of the balcony photovoltaic system as described in claim 1, characterized in that, The control module periodically samples the first electrical signal at a preset sampling frequency to obtain sampling data, and performs digital filtering processing on the sampling data. When the calculated leakage current value exceeds the preset threshold and the duration is not less than the preset confirmation time, the control module outputs a cut-off command to the drive circuit.

11. The safety protection circuit of the balcony photovoltaic system as described in claim 1, characterized in that, The control module also stores fault records, each fault record containing a fault type identifier, fault occurrence time, and fault characteristic parameter values. The control module includes a reset interface. When an external reset operation is detected, the control module clears the fault lockout state and restores the system to normal monitoring mode.

12. The safety protection circuit of the balcony photovoltaic system as described in claim 2, characterized in that, When the leakage current value is within the first preset range and the real-time impedance value of the ground wire is lower than the second preset threshold, the control module controls the audible and visual alarm unit to output an alarm signal but does not output a cut-off command to the drive circuit. When the leakage current value exceeds the preset threshold or the real-time ground impedance value exceeds the second preset threshold, the control module outputs a cut-off command to the drive circuit and controls the audible and visual alarm unit to output an alarm signal. When the leakage current value exceeds the preset threshold and the real-time ground impedance value exceeds the second preset threshold, the control module immediately outputs a cut-off command to the drive circuit and sends a dual fault message to the external device.

13. A balcony photovoltaic power generation system, characterized in that, include: Photovoltaic modules are used to convert solar energy into direct current (DC) electricity. A micro inverter, electrically connected to the output terminal of the photovoltaic module, is used to convert DC power into AC power. The safety protection circuit as described in any one of claims 1-12 is connected in series in the DC main circuit between the photovoltaic module and the micro inverter, and is used to detect the leakage current and protective ground status of the photovoltaic module. When an abnormality is detected, the safety protection circuit disconnects the DC main circuit to protect the system safety.

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