Leakage current detection circuit and inverter

Abstract

The application provides a leakage current detection circuit and an inverter. The leakage current detection circuit comprises a leakage current sensor and a self-excitation circuit. The leakage current sensor comprises a magnetic core and an excitation coil wound on the magnetic core, and the magnetic core is used for sleeving on a measured circuit. The self-excitation circuit comprises a comparator, a voltage dividing circuit and a first resistor. A power supply connected to a power supply end of the comparator is a power supply of the self-excitation circuit, and a voltage of an inverting input end of the comparator is related to a current in the excitation coil. The comparator is used for determining a voltage in a voltage signal output by a comparison output end according to a voltage of a non-inverting input end and the voltage of the inverting input end. The leakage current detection circuit provided by the application realizes single power supply of the self-excitation circuit by taking the power supply connected to the power supply end of the single power supply comparator as the power supply of the self-excitation circuit, simplifies the leakage current detection circuit, and reduces the power consumption of the leakage current detection circuit.

Description

Technical Field

[0001] This application relates to the field of power supply protection technology, and in particular to a leakage current detection circuit and an inverter. Background Technology

[0002] When electrical devices in a power supply network system generate leakage current, it can easily cause electric shock injuries or fires. For example, when the leakage current exceeds 25 milliamps, it exceeds the human body's safe current of 10 milliamps, making it difficult for anyone who comes into contact with it to break free, thus posing a danger. Alternatively, if the insulation of electrical devices in the power grid is poor, leakage current may also exist between the live wire and the neutral wire, causing a short circuit and potentially leading to a fire.

[0003] Currently, leakage current detection circuits can detect leakage current, enabling the control circuit to promptly cut off the power supply when leakage occurs, ensuring personal and property safety and preventing accidents. However, leakage current detection circuits require dual power supplies, resulting in complex circuitry, space constraints, and high power consumption. Summary of the Invention

[0004] This application provides a leakage current detection circuit and an inverter to simplify the circuit and save space.

[0005] In a first aspect, this application provides a leakage current detection circuit, including a leakage current sensor and a self-excited circuit;

[0006] The leakage current sensor includes a magnetic core and an excitation coil wound on the magnetic core. The magnetic core is used to mount the circuit under test. The self-excited circuit includes a comparator, a voltage divider circuit, and a first resistor. The comparator includes a non-inverting input terminal, an inverting input terminal, a power supply terminal, a ground terminal, and a comparison output terminal. The voltage divider circuit includes a first input terminal, a second input terminal, a first voltage divider resistor, a second voltage divider resistor, and a voltage divider output terminal. The voltage at the first input terminal is less than the voltage at the power supply terminal. One end of the first voltage divider resistor is the first input terminal, and the other end is the voltage divider output terminal. One end of the second voltage divider resistor is the second input terminal, and the other end is connected to the voltage divider output terminal. The non-inverting input of the comparator... The input terminal is connected to the voltage divider output terminal, the inverting input terminal is connected to the first input terminal through a first resistor, the power supply terminal is used to connect to the power supply, which is the power supply for the self-excited circuit, and the comparator output terminal is connected to the second input terminal of the voltage divider circuit. One end of the excitation coil is connected to the inverting input terminal through the first resistor, and the other end is connected to the comparator output terminal. The voltage at the inverting input terminal of the comparator is related to the current in the excitation coil. The comparator is used to determine the voltage in the voltage signal output by the comparator based on the voltage at the non-inverting input terminal and the voltage at the inverting input terminal. The voltage signal output by the comparator is used to detect the leakage current of the circuit under test. The leakage current detection circuit embodiment provided in this application uses the power supply connected to the power supply terminal of the comparator, which is powered by a single power supply, as the power supply for the self-excited circuit, thus realizing a single power supply for the self-excited circuit. This simplifies the leakage current detection circuit, reduces one power supply compared to dual power supply, and saves space. Furthermore, single power supply also reduces the power consumption of the leakage current detection circuit, which is beneficial for energy conservation.

[0007] In one possible implementation, the comparator is used to determine the voltage in the voltage signal output by the comparison output terminal based on the voltage at the non-inverting input terminal and the voltage at the inverting input terminal, including: in response to the voltage at the inverting input terminal being greater than the voltage at the non-inverting input terminal, the comparison output terminal outputs a first voltage value, the first voltage value being equal to the voltage at the ground terminal; in response to the voltage at the inverting input terminal being less than the voltage at the non-inverting input terminal, the comparison output terminal outputs a second voltage value, the second voltage value being equal to the voltage at the power supply terminal.

[0008] In one possible implementation, the circuit further includes a second resistor, through which the inverting input of the comparator is connected to the first resistor.

[0009] In one possible implementation, the self-excited circuit further includes a driving circuit; the comparison output terminal of the comparator is connected to the first terminal of the excitation coil through the driving circuit.

[0010] In one possible implementation, the drive circuit includes a selection switch; the first end of the excitation coil is connected to the power supply and ground respectively through the selection switch; in response to the output of the comparator outputting a low level, the first end of the excitation coil is connected to ground through the selection switch; in response to the output of the comparator outputting a high level, the first end of the excitation coil is connected to the power supply through the selection switch.

[0011] In one possible implementation, the driving circuit includes an NPN transistor and a PNP transistor. The bases of the NPN transistor and the PNP transistor are connected to the output of the comparator, the emitters of the NPN transistor and the PNP transistor are connected to the first end of the excitation coil, the collector of the NPN transistor is connected to the power supply, and the collector of the PNP transistor is grounded.

[0012] In one possible implementation, the leakage current detection circuit further includes a signal adjustment circuit connected to the output of the comparator, used to adjust at least one of the amplitude and pulse slope of the voltage signal output from the output.

[0013] In one possible implementation, the function of the comparator described above can be implemented using an operational amplifier.

[0014] Secondly, this application provides a leakage current detection circuit, including a leakage current sensor, a self-excited circuit, and a signal adjustment circuit. The leakage current sensor includes a magnetic core and an excitation coil wound on the magnetic core, the magnetic core being used to be fitted onto the circuit under test. The self-excited circuit is connected to the excitation coil and is used to output a voltage signal. The duty cycle of the voltage signal is related to the leakage current detected by the leakage current sensor. The signal adjustment circuit is used to receive the voltage signal output by the self-excited circuit and adjust at least one of the amplitude and pulse slope of the voltage signal to suit the processor to obtain the duty cycle of the voltage signal, so that the processor can determine whether the circuit under test is leaking current based on the duty cycle of the voltage signal, thereby achieving the purpose of detecting leakage current. The leakage current detection circuit provided in this application does not require a low-pass filter, reducing the space occupied by the low-pass filter. Furthermore, the leakage current detection circuit does not require adjustment of the low-pass filter parameters during use, effectively reducing the complexity of using the leakage current detection circuit and improving the convenience of detecting leakage current.

[0015] In one possible implementation, the signal adjustment circuit includes at least one of a shaping circuit and a level conversion circuit; the level conversion circuit is used to adjust the amplitude of the voltage signal to meet the processor's amplitude requirements for the input signal; the shaping circuit is used to adjust the pulse slope of the voltage signal to meet the processor's pulse slope requirements for the input signal.

[0016] In one possible implementation, the self-excited circuit described above is powered by a single power supply.

[0017] Thirdly, this application provides an inverter, including: a switching circuit, a control circuit, and a leakage current detection circuit; the leakage current detection circuit includes a leakage current sensor and a self-excited circuit; the self-excited circuit includes a comparator, a voltage divider circuit, and a first resistor; the comparator includes a non-inverting input terminal, an inverting input terminal, a power supply terminal, a ground terminal, and a comparison output terminal; the voltage divider circuit includes a first input terminal, a second input terminal, a first voltage divider resistor, a second voltage divider resistor, and a voltage divider output terminal, wherein the voltage at the first input terminal is less than the voltage at the power supply terminal, one end of the first voltage divider resistor is the first input terminal, and the other end is the voltage divider output terminal; one end of the second voltage divider resistor is the second input terminal, and the other end is connected to the voltage divider output terminal; the non-inverting input terminal of the comparator is connected to the voltage divider output terminal. The inverting input terminal is connected to the first input terminal through a first resistor. The power supply terminal is used to connect to the power supply, which is the power supply of the self-excited circuit. The comparison output terminal is connected to the second input terminal of the voltage divider circuit. In the leakage current sensor, one end of the excitation coil is connected to the inverting input terminal through the first resistor, and the other end is connected to the comparison output terminal. The voltage at the inverting input terminal of the comparator is related to the current in the excitation coil. The comparator is used to determine the voltage in the voltage signal output by the comparison output terminal based on the voltage at the non-inverting input terminal and the voltage at the inverting input terminal. The control circuit is used to receive the voltage signal output by the comparison output terminal of the comparator and determine whether the circuit detected by the leakage current detection circuit is leaking current based on the voltage signal. In the case of leakage current, the control circuit controls the switching circuit to turn off the circuit.

[0018] Fourthly, this application provides an inverter, including: a switching circuit, a control circuit, and a leakage current detection circuit; the switching circuit is used to be installed in the circuit under test; the control circuit includes a processor; the leakage current detection circuit includes a leakage current sensor, a self-excited circuit, and a signal adjustment circuit; the leakage current sensor includes a magnetic core and an excitation coil wound on the magnetic core, the magnetic core being used to be fitted onto the circuit under test; the self-excited circuit is connected to the excitation coil and the signal adjustment circuit, and the self-excited circuit is used to output a voltage signal; wherein, the duty cycle of the voltage signal is related to the leakage current detected by the leakage current sensor; the signal adjustment circuit is used to receive the voltage signal output by the self-excited circuit, and adjust at least one of the amplitude and pulse slope of the voltage signal to obtain an input signal that meets the requirements of the processor; the processor is used to obtain the duty cycle of the voltage signal using the input signal, determine whether the circuit under test is leaking current based on the duty cycle of the voltage signal, and control the switching circuit to turn off the circuit under test when the circuit under test is leaking current.

[0019] In one possible implementation, the processor is further configured to obtain the leakage current value of the circuit under test based on the duty cycle, and control the switching circuit to turn off the circuit under test if the leakage current value is greater than a first threshold or less than a second threshold; wherein the first threshold is greater than the second threshold.

[0020] In one possible implementation, the circuit under test is a DC circuit, and the inverter also includes a DC input circuit; the DC input circuit is connected to the DC side of the inverter circuit in the inverter through a switching circuit.

[0021] In one possible implementation, the circuit under test is an AC circuit, and the switching circuit is connected to the AC side of the inverter circuit in the inverter.

[0022] Fifthly, this application provides a charging device including the inverter described in any one of the third and fourth aspects above.

[0023] Sixthly, this application provides an electric device including the charging device of any one of the fifth aspects above. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of an existing leakage current detection circuit;

[0025] Figure 2 This is a schematic diagram of a leakage current detection circuit provided in an embodiment of this application;

[0026] Figure 3 A schematic block diagram of another optical inverter provided in this application embodiment;

[0027] Figure 4 This is a schematic diagram of the structure of an optical inverter provided in an embodiment of this application;

[0028] Figure 5 This is a schematic diagram of a leakage current detection circuit provided in an embodiment of this application;

[0029] Figure 6 This is a schematic diagram of another leakage current detection circuit provided in an embodiment of this application;

[0030] Figure 7 This is a schematic diagram of another leakage current detection circuit provided in an embodiment of this application;

[0031] Figure 8 This is a schematic diagram of another leakage current detection circuit provided in an embodiment of this application;

[0032] Figure 9 This is a schematic diagram of another leakage current detection circuit provided in an embodiment of this application. Detailed Implementation

[0033] The terminology used in the implementation section of this application is for the purpose of explaining specific embodiments of this application only, and is not intended to limit this application.

[0034] Leakage current detection devices can be used not only in electrical devices in power supply systems, but also in charging equipment, uninterruptible power supplies (UPS), photovoltaic inverters, etc.

[0035] The inverter provided in this application embodiment includes an inverter circuit, a switching circuit, a control circuit, and a leakage current detection circuit. The leakage current detection circuit can be located on the DC side of the inverter circuit to detect whether leakage occurs in the DC-transmitting line. Alternatively, the leakage current detection circuit can be located on the AC side of the inverter circuit to detect whether leakage occurs in the AC-transmitting line. The inverter circuit typically includes a bridge circuit composed of switching transistors to convert DC to AC. The switching circuit is connected to the line under test and includes at least one switch. When the line under test is used to transmit DC or single-phase AC, it consists of two cables; correspondingly, the switching circuit includes two controlled switches, each connected to one of the cables. When the line under test is three-phase AC, it consists of three or four cables; correspondingly, the switching circuit includes three controlled switches (e.g., ...). Figures 5 to 8 The switch circuit shown is 131) or four controlled switches (such as...). Figure 9 The switch circuit 132 shown is connected to one of the cables. Alternatively, each tested line or cable has a controlled switch connected to it. The controlled switch can be a circuit breaker, relay, or other switching component.

[0036] Existing leakage current detection circuits such as Figure 1 As shown, the circuit includes a leakage current sensor 1, a self-excited circuit 2, and a low-pass filter 3. The magnetic core of the leakage current sensor 1 is located outside the circuit under test 6, and the two ends of the excitation coil in the leakage current sensor 1 are connected to the self-excited circuit 2. The current signal collected by the leakage current sensor 1 is converted into a voltage signal by the self-excited circuit 2. The self-excited circuit 2 is connected to the low-pass filter 3 and outputs a leakage current signal representing the magnitude of the leakage current and an oscillator frequency signal. The control module 4 judges based on the leakage current signal and the oscillator frequency signal, and outputs a control signal according to the judgment result to control the on / off state of the switching circuit 5. However, in existing leakage current detection circuits, the self-excited circuit is powered by dual power supplies (VDD and VCC), making the leakage current detection circuit complex, not conducive to saving space, and with high power consumption.

[0037] In one embodiment of this application, the leakage current detection circuit is powered by a single power supply. Specifically, the self-oscillating circuit may include an operational amplifier / comparator (such as...). Figure 2 U1 shown), voltage divider circuit, first resistor (as shown) Figure 2 The resistor R3 shown) and the second resistor (as shown) Figure 2 The resistor R1 is shown. Here, "first" and "second" are used to distinguish different resistors. One power supply terminal of the operational amplifier / comparator is connected to the power supply (e.g., ...). Figure 2The VCC power supply shown is connected to ground (as indicated by the figure). Figure 2 (GND as shown). The first input terminal of the voltage divider circuit (as shown). Figure 2 The voltage at the upper end of resistor R4 (as shown) is less than the power supply voltage (VCC as shown in the figure), and the voltage at the second input terminal (as shown in the figure) is less than the power supply voltage. Figure 2 The left end of resistor R2 (as shown) is connected to the first end of the excitation coil (e.g., Figure 2 The left end of the excitation coil in the leakage current sensor 1 shown) and the output terminal of the operational amplifier / comparator (as shown) Figure 2 The Vo terminal shown), the voltage divider output terminal (as shown) Figure 2 The connection point of resistors R2 and R4 shown is connected to the non-inverting input of the operational amplifier / comparator (e.g., Figure 2 The "+" terminal of U1 is shown. One end of the first resistor is connected to the first input terminal of the voltage divider circuit, and the other end is connected to the second terminal of the excitation coil in the leakage current sensor (as shown). Figure 2 The right end of the excitation coil in the leakage current sensor 1 shown) and one end of the second resistor (as shown) Figure 2 The left end of resistor R1 (as shown); the other end of the second resistor (as shown) Figure 2 The right end of resistor R1 (as shown) is connected to the inverting input of the operational amplifier / comparator (e.g., Figure 2 (The "-" terminal of U1 shown). The operational amplifier / comparator is used to determine the voltage in the voltage signal output by the comparison output terminal based on the voltage at the non-inverting input terminal and the voltage at the inverting input terminal, wherein the voltage signal output by the comparison output terminal is used to detect the leakage current of the circuit under test. In some embodiments, the operational amplifier / comparator is used to determine the voltage in the voltage signal output by the comparison output terminal based on the voltage at the non-inverting input terminal and the voltage at the inverting input terminal, including: in response to the voltage at the inverting input terminal being greater than the voltage at the non-inverting input terminal, the comparison output terminal outputs a first voltage value, the first voltage value being equal to the voltage at the ground terminal; in response to the voltage at the inverting input terminal being less than the voltage at the non-inverting input terminal, the comparison output terminal outputs a second voltage value, the second voltage value being equal to the voltage at the power supply terminal.

[0038] In some embodiments where noise interference requirements are low, the second resistor may be omitted.

[0039] Preferably, the voltage divider circuit described above may include two voltage divider resistors connected in series. For example... Figure 2As shown, in the self-oscillating circuit 22, the voltage divider circuit includes voltage divider resistors R2 and R4 connected in series. The end where voltage divider resistors R2 and R4 are connected is the output terminal of the voltage divider circuit. In some embodiments, when the voltage Vin+ at the non-inverting input terminal of the operational amplifier / comparator is less than the voltage Vin- at the inverting input terminal, the high level (voltage at the first input terminal) of the voltage divider circuit is V (V is less than VCC), the low level (voltage at the second input terminal) is 0, and the voltage at its output terminal is V×R2 / (R2+R4); when the voltage Vin+ at the non-inverting input terminal of the operational amplifier / comparator is greater than the voltage Vin- at the inverting input terminal, the low level (voltage at the first input terminal) of the voltage divider circuit is V (V is less than VCC), the high level (voltage at the second input terminal) is VCC, and the voltage at its output terminal is V+(VCC-V)×R4 / (R2+R4).

[0040] Preferably, the voltage divider resistors R2 and R4 have equal resistance.

[0041] Preferably, the voltage at the first input terminal of the voltage divider circuit is equal to or close to half of the power supply voltage VCC of the self-excited circuit 22.

[0042] Preferably, the resistance of the second resistor R1 is equal to the resistance of the voltage divider resistor R2 or R4.

[0043] Preferably, R1 >> R3.

[0044] Preferably, the self-excited circuit further includes a driving circuit (such as...) Figure 7 The 241 shown and Figure 8 As shown in 242), it is used to improve the load-carrying capacity of the output signal of the operational amplifier / comparator. The output of the operational amplifier / comparator is connected to the first end of the excitation coil through a drive circuit.

[0045] Preferably, the drive circuit includes a selection switch. The first end of the excitation coil is connected to the power supply (e.g., [power supply]) via the selection switch. Figure 8 The VCC power supply and ground are shown; when the output of the operational amplifier / comparator is low, the first end of the excitation coil (that is, connected to the second input of the voltage divider circuit) is connected to ground through a selection switch; when the output of the operational amplifier / comparator is high, the first end of the excitation coil (that is, connected to the second input of the voltage divider circuit) is connected to the power supply through a selection switch.

[0046] The aforementioned selection switch is activated by a transistor.

[0047] Preferably, the driving circuit includes switching transistors NPN and PNP (such as...) Figure 8As shown in 242), the base of the NPN and PNP is connected to the output of the operational amplifier / comparator, the emitter of the NPN and PNP is connected to the first end of the excitation coil (that is, connected to the second input of the voltage divider circuit), the collector of the NPN is connected to the power supply, and the collector of the PNP is grounded.

[0048] Furthermore, existing leakage current detection circuits are complex to operate and inconvenient to use. When using existing leakage current detection circuits, the filter parameters of the low-pass filter need to be adjusted so that the filter cutoff frequency is greater than the frequency of the detected leakage current to ensure accuracy is not compromised, and less than the oscillation frequency of the self-excited circuit. Therefore, debugging and selecting filter parameters is relatively difficult, reducing the ease of use of the leakage current detection circuit.

[0049] To address this issue, another leakage current detection circuit provided in this application includes a leakage current sensor, a self-excited circuit, and a signal adjustment circuit. The signal adjustment circuit outputs a signal containing leakage current duty cycle characteristics suitable for processor processing, achieving the purpose of detecting leakage current. This eliminates the need for a low-pass filter, reducing the complexity and space required for use and improving the convenience of leakage current detection. In some embodiments, the leakage current sensor includes a magnetic core and an excitation coil wound on the magnetic core, which is used to be mounted on the circuit under test. The self-excited circuit is connected to the excitation coil and the signal adjustment circuit, outputting a voltage signal whose duty cycle is related to the leakage current detected by the leakage current sensor. The signal adjustment circuit receives the voltage signal output by the self-excited circuit and adjusts at least one of the voltage signal's amplitude and pulse slope.

[0050] The material of the leakage current sensor can be cobalt-based amorphous material; this is only for illustrative purposes and not a limitation. The leakage current sensor may include a magnetic core and an excitation coil wound around the magnetic core. The magnetic core is used to sense the magnetic field generated by the leakage current in the circuit under test. In use, the magnetic core is placed around the circuit under test. According to the fluxgate principle, the leakage current detection circuit uses a self-excited circuit to apply an alternating current of fixed frequency and waveform to the excitation coil of the leakage current sensor, causing the magnetic core to reciprocate until saturation. If there is no leakage current in the circuit under test within the magnetic core of the leakage current sensor (i.e., the excitation coil is in operation when there is no leakage current in the circuit under test), then there is no magnetic field generated by the leakage current within the magnetic core, and the signal waveform output by the excitation coil is symmetrical in both positive and negative directions. When leakage occurs in the circuit under test, the leakage current generates an external DC magnetic field. At the same time, there is a DC magnetic field and an excitation alternating magnetic field in the magnetic core. The DC magnetic field causes the magnetic core to reach saturation in advance in the first half or the second half of the cycle, while it causes the magnetic core to reach saturation with a delay in the second half or the first half of the cycle. This causes the duration of the excitation current rising (or increasing) and the duration of the excitation current falling (or decreasing) in the excitation coil to be unequal in the excitation cycle. This makes the voltage signal waveform output by the self-excited circuit asymmetrical in the positive and negative half cycles, thereby generating a voltage signal with a duty cycle greater than 50% or less than 50%.

[0051] Specifically, the self-excited circuit outputs a rectangular wave voltage signal that alternates between high and low levels and applies it to the excitation coil of the leakage current sensor, thereby providing excitation current in different directions to the excitation coil.

[0052] Preferably, the self-excited circuit may include a comparator (or an operational amplifier used as a comparator), a third resistor (such as...) Figure 5 The resistor R5 shown (the term "third" is used only to distinguish it from the voltage divider resistor) and two voltage divider resistors (such as...) Figure 5(See the voltage divider resistors R6 and R7 shown). The inverting input of the comparator is connected to the third resistor and one end of the excitation coil. The non-inverting input is connected to one end of the two voltage divider resistors, the other end of which has a voltage lower than the power supply voltage. The other end of the other voltage divider resistor is connected to the output of the comparator. The output of the comparator (i.e., the output of the self-excited circuit) is also connected to the other end of the excitation coil. When the voltage at the non-inverting input of the comparator is higher than the voltage at the inverting input, the comparator outputs a high level, which is applied to the excitation coil. The excitation coil generates an excitation current under the combined action of the third resistor and the high level output of the comparator. The excitation current begins to increase after the comparator outputs a high level. Simultaneously, the voltage at the inverting input of the comparator increases with the increase of the excitation current. When the voltage at the inverting input is higher than the voltage at the non-inverting input, the comparator outputs a low level, the polarity of the excitation current in the excitation coil reverses, and the excitation current begins to decrease. The voltage at the inverting input of the comparator also begins to decrease. When the voltage at the inverting input of the comparator decreases to below the voltage at the non-inverting input, the comparator outputs a high level, the excitation current in the excitation coil begins to increase again, and the voltage at the inverting input of the comparator increases accordingly. This process repeats repeatedly, causing the comparator to output a rectangular square wave voltage signal.

[0053] When there is no leakage current in the tested circuit, the duration of the increase in excitation current in the excitation coil is equal to the duration of the decrease in excitation current, resulting in a duty cycle of approximately 50% for the rectangular square wave voltage signal output by the comparator. When leakage current occurs in the tested circuit, it accelerates core saturation in one direction, causing the duration of the increase in excitation current to be less than the duration of the decrease, or vice versa. This results in a higher percentage of high-level signals or a higher percentage of low-level signals in each cycle of the comparator output signal. Experiments have shown that when the leakage current detection circuit provided in this embodiment detects leakage in the tested circuit, the duty cycle of the voltage signal output by the self-excited circuit is linearly related to the actual leakage current value. For example, when the duty cycle is greater than 0.5, the larger the duty cycle, the larger the leakage current value; when the duty cycle is less than 0.5, the smaller the duty cycle, the larger the reverse leakage current value. Furthermore, the method of detecting leakage current based on duty cycle meets the accuracy judgment criteria.

[0054] The signal adjustment circuit is used to adjust the voltage signal output by the self-oscillating circuit (i.e., the voltage signal output by the comparator). For example, it adjusts at least one of the voltage signal's amplitude and pulse slope (i.e., the slope of the signal's rising or falling edge) to obtain an input signal that meets the processor's requirements (i.e., the voltage signal output by the leakage current detection circuit). For instance, if the comparator's output voltage amplitude is large, the signal adjustment circuit can reduce it to meet the processor's amplitude requirements, such as a high level of 3 volts and a low level of 0 volts. Alternatively, if the signal output by the self-oscillating circuit is a non-standard square wave, such as a trapezoidal wave, its pulse slope can be adjusted so that its rising or falling edge is parallel to the y-axis, thus becoming a standard square wave. This is merely an example and not a limitation; the goal is simply to meet the processor's requirements for the processed signal.

[0055] The signal adjustment circuit may include at least one of a shaping circuit and a level conversion circuit. When the voltage signal output by the self-excited circuit needs to have its amplitude adjusted, the signal adjustment circuit includes a level conversion circuit; when the voltage signal output by the self-excited circuit needs to have its pulse slope adjusted, the signal adjustment circuit includes a shaping circuit.

[0056] The control circuit includes a processor and a memory. The memory stores the computer program (which can also be instructions or code). The memory can be set up separately, integrated with the processor, or the computer program stored in the memory can be stored inside the processor, thus eliminating the need for a separate memory. The processor is connected to the memory and the output of the self-oscillating circuit. This processor can be a central processing unit (CPU), a microcontroller (MCU), a digital signal processor (DSP), etc. When the processor runs the computer program, it performs the following: analyzes and calculates the input signal to obtain the duty cycle of the voltage signal output by the self-oscillating circuit, and determines whether the tested circuit is leaking current based on the duty cycle. As mentioned above, when the tested circuit has no leakage current, the duty cycle of this signal is equal to or close to 50%; when the duty cycle is greater than 50% or less than 50%, the tested circuit may have leakage current.

[0057] It is understandable that the control circuit can also control the switching transistors in the inverter circuit, and adjust the operating frequency of the switching transistors, etc., which will not be elaborated here.

[0058] Take photovoltaic inverters as an example.

[0059] like Figure 3As shown, the photovoltaic inverter includes a leakage current detection circuit 110, a control circuit 120, a switching circuit 130, and an inverter circuit 140. The leakage current detection circuit 110, control circuit 120, and switching circuit 130 are located on the DC side of the inverter circuit 140. The DC side line (i.e., the DC line) includes two cables. The switching circuit 130 includes two controlled switches, with each cable connected to one controlled switch. The two controlled switches can be closed or opened simultaneously, causing both cables to be simultaneously energized or de-energized. In the event of leakage current on the DC side, the control circuit 120 controls the switching circuit 130 to open, thereby stopping the photovoltaic inverter from operating. The control circuit 120 includes a processor. When the processor runs a computer program (instructions or code), it analyzes and calculates the voltage signal output by the received leakage current detection circuit 110 to obtain the duty cycle of the voltage signal (i.e., the duty cycle of the voltage signal output by the self-excited circuit). Based on the duty cycle, it determines whether the DC line is leaking current. If leakage is detected in the DC line, it controls the switch circuit 130 to open, thereby cutting off the power to the DC line and achieving the purpose of protection. The photovoltaic inverter provided in this application embodiment achieves the purpose of detecting whether the line is leaking current by controlling the duty cycle of the output signal of the detection and adjustment circuit, and has the advantages of small size and convenient use.

[0060] Preferably, the processor can obtain the leakage current value based on the duty cycle and its linear relationship with the leakage current value.

[0061] Preferably, the processor can control the switch circuit 130 to turn off when the leakage current value is greater than a first threshold (e.g., 25 mA), or when the leakage current value is less than a second threshold (e.g., -25 mA).

[0062] The inverter circuit 140 may include switching transistors (such as insulated gate bipolar transistors (IGBTs)) and their control circuits, inverter-side capacitors and inductors, etc.

[0063] Preferably, the photovoltaic inverter may further include a photovoltaic panel input circuit (i.e., a DC input circuit). For example, the photovoltaic panel input circuit can be configured as follows: Figure 3 The DC transmission line shown is connected to the switching circuit 130.

[0064] Preferably, the photovoltaic inverter may further include a DC boost circuit. For example, the boost circuit may be located between the photovoltaic panel input circuit and the DC side of the inverter circuit 140.

[0065] Preferably, the leakage current detection circuit 110 can be located between the photovoltaic panel input circuit and the boost circuit.

[0066] In another embodiment, the photovoltaic inverter is as follows: Figure 4As shown, the leakage current detection circuit 110, the control circuit 120, and the switch circuit 130 are provided on the AC side of the inverter circuit 140 to disconnect the AC line on the AC side of the inverter circuit 140 in the case of leakage on the AC side. The AC line may include two cables, three cables, or four cables (such as Figure 9 the measured line 62 shown), and so on.

[0067] An embodiment of a leakage current detection circuit provided by this application is as Figure 5 shown. The leakage current detection circuit 110 includes a leakage current sensor 1, a self-excitation circuit 21, and a shaping circuit 411. The leakage current sensor 1 includes a magnetic core and an exciting coil. The self-excitation circuit 21 includes an operational amplifier / comparator U1, a resistor R5, voltage-dividing resistors R6 and R7.

[0068] The magnetic core in the leakage current sensor 1 is sleeved outside the measured line 6. One end of the exciting coil in the leakage current sensor 1 is connected to the inverting input terminal of the operational amplifier / comparator U1 in the self-excitation circuit 21, and the other end is connected to the output terminal of the operational amplifier / comparator U1 to form a loop. The operational amplifier / comparator U1 is powered by a dual power supply, and the power supply voltage connected to its negative power supply terminal is VDD, and the power supply voltage connected to its positive power supply terminal is VCC.

[0069] The self-excitation circuit 21 has two operating states:

[0070] State 1: When the voltage Vin- at the inverting input terminal of the operational amplifier / comparator U1 is greater than the voltage Vin+ at the non-inverting input terminal, the output signal Vo of the operational amplifier / comparator U1 is the low level VDD, Vin+ = VDD×R6 / (R6 + R7), VDD is applied to the exciting coil, and the current I direction of the exciting coil is the same as the Figure 5 arrow direction shown, and the current (exciting current) I of the exciting coil gradually increases. Since Vin- = -R5×I, when the current I gradually increases, Vin- continues to decrease until it is less than Vin+, and then it enters State 2.

[0071] State 2: When Vin- < Vin+, the output signal Vo of the self-excitation circuit 21 is the high level VCC, Vin+ = VCC×R6 / (R6 + R7), the current I gradually decreases, and Vin- gradually increases. As time goes by, the current I changes from positive to negative (that is, the current I direction of the exciting coil is opposite to the Figure 5 arrow direction shown), Vin- = -R5×I, the current I gradually increases, causing Vin- to continue to increase until it is greater than Vin+, and then it re-enters State 1.

[0072] Therefore, the output signal Vo of the self-excited circuit 21 is a square wave signal with alternating high level VCC and low level VDD, that is, a pulse width modulation (PWM) signal or an input / output (IO) signal.

[0073] In this embodiment, the slope of the voltage signal pulse wave output by the operational amplifier / comparator U1 is too small. Therefore, the voltage signal Vo pulse slope is adjusted by the shaping circuit 411 to obtain a standard square wave input signal V that meets the requirements of the processor 420. AD This is to suit the processing of the processor 420. The shaping circuit 411 can be an RC circuit, a Schmitt trigger, etc., which is only an example and is not limited, as long as it can correct the voltage signal output by the self-excited circuit 21 and shape the distorted waveform into a standard square wave waveform.

[0074] Processor 420 receives input signal V AD After that, V can be calculated. AD Duty cycle (V) AD The duty cycle of the signal is equal to the duty cycle of Vo. Since Vo is a square wave signal with a duty cycle of 50% (or close to 50%) when there is no leakage current in the tested circuit 6, when a reverse leakage current occurs in the tested circuit 6, the duty cycle of Vo is lower than 50%, and the larger the reverse leakage current value, the smaller the corresponding duty cycle of Vo; when a forward leakage current occurs in the tested circuit 6, the duty cycle of Vo is higher than 50%, and the larger the forward leakage current value, the larger the corresponding duty cycle. Therefore, the processor 420 can also obtain the corresponding leakage current value based on the calculated duty cycle and the linear relationship between the duty cycle and the leakage current value. After obtaining the corresponding leakage current value, the processor 420 determines whether it exceeds a threshold (e.g., greater than the first threshold or less than the second threshold). If it exceeds the threshold, it controls the switching circuit 131 to disconnect (e.g., disconnect the relay) the power supply to achieve the purpose of protection. For example, the processor 420 can run a computer program (instructions or code) to perform the above operations.

[0075] As a variation of this embodiment, when the slope of the voltage signal pulse output by the self-excited circuit meets the processor's requirements for the input signal, but its amplitude does not meet the processor's requirements, the level conversion circuit can replace the shaping circuit 411. When the self-excited circuit is powered by a dual power supply (e.g., Figure 5In the illustrated embodiment, the low level of the output voltage signal Vo is negative. Therefore, the level conversion circuit may include a voltage boosting circuit to boost the low level of the voltage signal Vo to 0 volts that meets the requirements of the processor. If the high level of the voltage signal Vo is too high and does not meet the requirements of the processor, the level conversion circuit may include a voltage dividing circuit to make the high level of the voltage signal Vo meet the requirements of the processor (such as 3 volts). If both the high and low levels of the voltage signal Vo output by the self-exciting circuit do not meet the requirements of the processor, the level conversion circuit may include a voltage boosting circuit and a voltage dividing circuit.

[0076] Another embodiment of the leakage current detection circuit provided in this application is different from the above-mentioned embodiment of the leakage current detection circuit in that the self-exciting circuit is powered by a single power supply to further simplify the leakage current detection circuit, reduce costs and power consumption, and improve space utilization. As Figure 6 shown, the self-exciting circuit 22 includes an operational amplifier / comparator U1, voltage dividing resistors R2 and R4, a first resistor R3, and a second resistor R1. Among them, R3 << R1 = R2 = R4.

[0077] The negative power supply terminal of the operational amplifier / comparator U1 is grounded, the positive power supply terminal is connected to the VCC power supply, the non-inverting input terminal is connected to the output terminal of the operational amplifier / comparator U1, the first end of the excitation coil, and the lower end of the voltage dividing resistor R4 through the voltage dividing resistor R2, and the inverting input terminal is respectively connected to the second end of the excitation coil and the lower end of the first resistor R3 through the second resistor R1. The upper-end voltages of both the voltage dividing resistor R4 and the first resistor R3 are half of the power supply voltage VCC (VCC / 2). Among them, the voltage VCC / 2 can be obtained by dividing the power supply VCC or other conversion methods. For example, the power supply VCC is grounded through two series-connected resistors with equal resistance values, and the voltage at the connection point of these two series-connected resistors is VCC / 2. This is only an example for illustration and is not limited.

[0078] State 1: Vin -> Vin+, the operational amplifier / comparator U1 outputs Vo = 0V, Vin- = VCC / 2 - R3×I, Vin+ = VCC / 4, and the current I in the excitation coil gradually increases in the reverse direction ( Figure 6 the arrow direction of the current I in the figure is the positive direction), and Vin- decreases accordingly until it is less than Vin+. Then, the self-exciting circuit 22 enters State 2.

[0079] State 2: Vin- < Vin+, the operational amplifier / comparator U1 outputs Vo = VCC, Vin+ = 3 / 4×VCC, the current I in the excitation coil gradually decreases in the reverse direction, and Vin- gradually increases; as time goes by, the current I changes from the reverse direction to the positive direction, Vin- = VCC / 2 + R3×I, and Vin- continues to increase until it is greater than Vin+, and then, the self-exciting circuit 22 returns to State 1 again.

[0080] Another embodiment of leakage current detection circuit provided in this application is similar to Figure 6 The difference in the illustrated embodiment is that the self-oscillating circuit also includes a driving circuit to improve the output driving capability of the operational amplifier / comparator. This driving circuit is connected to the output terminal of the operational amplifier / comparator, and is directly or indirectly connected to the non-inverting input terminal of the operational amplifier / comparator. Figure 7 As shown, in the self-excited circuit 23, the driving circuit 241 is located between the non-inverting input terminal and the output terminal of the operational amplifier / comparator U1. It is connected to the non-inverting input terminal through a voltage divider resistor R2 and is connected to the first end of the excitation coil. It is used to improve the load-carrying capacity (i.e., driving capacity) of the output signal of the operational amplifier / comparator U1.

[0081] The drive circuit may include a selector switch. This selector switch is connected to the first terminal of the excitation coil, a power supply (such as VCC), and ground. When the voltage signal output by the operational amplifier / comparator is 0 volts, the selector switch connects the first terminal of the excitation coil to ground; when the voltage signal output by the operational amplifier / comparator is VCC, the selector switch connects the first terminal of the excitation coil to the VCC power supply. The non-inverting input of the operational amplifier / comparator is directly or indirectly connected to the selector switch.

[0082] The driving circuit may include two switching transistors whose bases and emitters are both connected. Preferably, such as... Figure 8 As shown, in the self-excited circuit 24, the driving circuit 242 includes two switching transistors (upper and lower transistors), the upper transistor being an NPN transistor and the lower transistor being a PNP transistor. The emitters of the upper and lower transistors are connected, and are also connected to one end of the voltage divider resistor R2 and one end of the excitation coil. The bases of the upper and lower transistors are connected, and are also connected to the output of the operational amplifier / comparator U1. The collector of the upper transistor is connected to the power supply VCC, and the collector of the lower transistor is grounded. The upper and lower transistors can be approximated as a selection switch. When Vo = 0V, the upper transistor is cut off and the lower transistor is turned on. The voltage at the end of the voltage divider resistor R2 connected to the emitter of the transistor is 0V + the voltage drop of the lower transistor (PNP transistor) (the voltage drop of the transistor can be ignored). When Vo = VCC, the upper transistor is turned on and the lower transistor is cut off. The voltage at the end of the voltage divider resistor R2 connected to the emitter of the transistor is VCC - the voltage drop of the upper transistor (NPN transistor) (the voltage drop of the transistor can be ignored). Figure 8 The driving circuit shown is for illustrative purposes only and is not a limitation; it is acceptable as long as it fulfills its function.

[0083] It should be noted that the configuration of the self-excited circuits 21 to 24, the shaping circuit 411, and the level conversion circuit 412 in the above-mentioned leakage current detection circuit is not limited to the combinations provided in the above embodiments. They can be freely combined according to actual needs, such as... Figure 9As shown, the leakage current detection circuit includes a self-excited circuit 24 and a level conversion circuit 412 connected to the output terminal of the self-excited circuit 24. The principle is the same as that in the above embodiment, and will not be listed in detail here.

[0084] In the embodiments of the charging device provided in this application, the charging device includes the inverter provided in any of the above embodiments. In addition, it may include more components, such as power supply, which will not be described in detail here.

[0085] In the embodiments of electric equipment provided in this application, the electric equipment may be an electric vehicle, including the charging equipment provided in the above embodiments. In addition, it may include more components, such as batteries, motors, etc., which will not be elaborated here.

[0086] In this application embodiment, "at least one" refers to one or more, and "more than one" refers to two or more. The character " / " generally indicates that the preceding and following objects are in an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, at least one of a, b, and c can be represented as: a, b, c, a and b, a and c, b and c, or a and b and c, where a, b, and c can be single or multiple.

[0087] The above description is merely a specific embodiment of this application. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the protection scope of this application. The protection scope of this application should be determined by the protection scope of the claims.

Claims

1. A leakage current detection circuit, characterized in that, Includes a leakage current sensor and a self-excited circuit; The leakage current sensor includes a magnetic core and an excitation coil wound on the magnetic core, the magnetic core being used to be fitted onto the circuit under test; the self-excited circuit includes a comparator, a voltage divider circuit and a first resistor; The comparator includes a non-inverting input terminal, an inverting input terminal, a power supply terminal, a ground terminal, and a comparator output terminal; The voltage divider circuit includes a first input terminal, a second input terminal, a first voltage divider resistor, a second voltage divider resistor, and a voltage divider output terminal. The voltage at the first input terminal is less than the voltage at the power supply terminal. One end of the first voltage divider resistor is the first input terminal, and the other end is the voltage divider output terminal. One end of the second voltage divider resistor is the second input terminal, and the other end is connected to the voltage divider output terminal. The non-inverting input terminal of the comparator is connected to the voltage divider output terminal, the inverting input terminal is connected to the first input terminal through the first resistor, the power supply terminal is used to connect to the power supply, the power supply is the power supply of the self-oscillating circuit, and the comparator output terminal is connected to the second input terminal of the voltage divider circuit. The leakage current detection circuit further includes a second resistor, and the inverting input terminal of the comparator is connected to the first resistor through the second resistor; One end of the excitation coil is connected to the inverting input terminal through the second resistor, and the other end is connected to the comparator output terminal. The voltage at the inverting input terminal of the comparator is related to the current in the excitation coil. The comparator is used to determine the voltage in the voltage signal output by the comparator output terminal based on the voltage at the non-inverting input terminal and the voltage at the inverting input terminal, wherein the voltage signal output by the comparator output terminal is used to detect the leakage current of the circuit under test.

2. The circuit according to claim 1, characterized in that, The comparator is used to determine the voltage in the voltage signal output from the comparator output terminal based on the voltage at the non-inverting input terminal and the voltage at the inverting input terminal, including: In response to the voltage at the inverting input terminal being greater than the voltage at the non-inverting input terminal, the comparator output terminal outputs a first voltage value, which is equal to the voltage at the ground terminal; In response to the voltage at the inverting input being less than the voltage at the non-inverting input, the comparator output outputs a second voltage value, which is equal to the voltage at the power supply terminal.

3. The circuit according to any one of claims 1 to 2, characterized in that, The self-excited circuit also includes a driving circuit; the comparison output terminal of the comparator is connected to the first terminal of the excitation coil through the driving circuit.

4. The circuit according to claim 3, characterized in that, The driving circuit includes a selection switch; the first end of the excitation coil is connected to the power supply and ground respectively through the selection switch; in response to the output of the comparator outputting a low level, the first end of the excitation coil is connected to ground through the selection switch; in response to the output of the comparator outputting a high level, the first end of the excitation coil is connected to the power supply through the selection switch.

5. The circuit according to claim 4, characterized in that, The driving circuit includes an NPN transistor and a PNP transistor. The bases of the NPN transistor and the PNP transistor are connected to the output terminal of the comparator. The emitters of the NPN transistor and the PNP transistor are connected to the first terminal of the excitation coil. The collector of the NPN transistor is connected to the power supply, and the collector of the PNP transistor is grounded.

6. The circuit according to any one of claims 1 to 5, characterized in that, It also includes a signal adjustment circuit, which is connected to the output of the comparator and is used to adjust at least one of the amplitude and pulse slope of the voltage signal output from the output.

7. An inverter, characterized in that, include: Switching circuit, control circuit, and leakage current detection circuit; The leakage current detection circuit includes a leakage current sensor and a self-excited circuit. The self-excited circuit includes a comparator, a voltage divider circuit, and a first resistor; The comparator includes a non-inverting input terminal, an inverting input terminal, a power supply terminal, a ground terminal, and a comparator output terminal; The voltage divider circuit includes a first input terminal, a second input terminal, a first voltage divider resistor, a second voltage divider resistor, and a voltage divider output terminal. The voltage at the first input terminal is less than the voltage at the power supply terminal. One end of the first voltage divider resistor is the first input terminal, and the other end is the voltage divider output terminal. One end of the second voltage divider resistor is the second input terminal, and the other end is connected to the voltage divider output terminal. The non-inverting input terminal of the comparator is connected to the voltage divider output terminal, the inverting input terminal is connected to the first input terminal through the first resistor, the power supply terminal is used to connect to the power supply, the power supply is the power supply of the self-oscillating circuit, and the comparator output terminal is connected to the second input terminal of the voltage divider circuit. The leakage current detection circuit further includes a second resistor, and the inverting input terminal of the comparator is connected to the first resistor through the second resistor; In the leakage current sensor, one end of the excitation coil is connected to the inverting input terminal through the second resistor, and the other end is connected to the comparison output terminal. The voltage at the inverting input terminal of the comparator is related to the current in the excitation coil. The comparator is used to determine the voltage in the voltage signal output by the comparator output terminal based on the voltage at the non-inverting input terminal and the voltage at the inverting input terminal; The control circuit is used to receive the voltage signal output from the comparator's comparison output terminal, and determine whether the line detected by the leakage current detection circuit is leaking current based on the voltage signal. If leakage current occurs, the control circuit is used to shut off the line.

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