An overcurrent protection circuit and method for an external fan of a photovoltaic inverter

Abstract

The present invention discloses an overcurrent protection circuit for an external fan of a photovoltaic inverter. The circuit comprises a power supply circuit for supplying power to the fan. The overcurrent protection circuit includes a first switch connected in series with the power supply circuit to turn the fan on or off, and a control signal input terminal for receiving a control signal from the control system of the photovoltaic inverter. The first switch is controlled to turn on or off by the control signal. The overcurrent protection circuit also includes: a sampling unit for generating a voltage sampling value based on the fan current; a comparison unit for receiving the voltage sampling value and comparing it with a protection threshold value to output a low or high level accordingly; and a second switch for pulling down the control signal to turn off the first switch upon receiving the high level output by the comparison unit. When an overcurrent or short circuit fault occurs in the external fan, the present invention can quickly cut off the power supply circuit, preventing circuit damage and improving the reliability of the photovoltaic inverter while maintaining a low cost.

Description

Technical Field

[0001] The invention relates to an overcurrent protection circuit and method for an external fan of a photovoltaic inverter. Background Art

[0002] Since the external fan of the photovoltaic inverter is exposed outside the chassis, it may cause overcurrent or short circuit in the fan power supply circuit due to damage or aging of the power supply line. The existing traditional solutions mainly include: no protection, or adding current limiting resistors or fuses, such as Figure 1 As shown in the figure. In the event of a short circuit, excessive current may blow components such as fuses, current-limiting resistors, or circuit switches. This passive defense is rigid and lacks control over response time. Even after the external fan fault clears, damaged circuit components will cause the circuit to cease operation. To maintain continued operation, damaged components must be frequently replaced, increasing operational costs. Summary of the Invention

[0003] In response to the above problems, an object of the present invention is to provide an overcurrent protection device for an external fan of a photovoltaic inverter, which can quickly cut off the power supply circuit when an overcurrent or short circuit fault occurs in the external fan, and has low cost.

[0004] Another object of the present invention is to provide an overcurrent protection method for an external fan of a photovoltaic inverter, which can quickly cut off the power supply circuit when an overcurrent or short circuit fault occurs in the external fan, while having low cost.

[0005] To achieve the above object, the present invention provides an overcurrent protection circuit for an external fan of a photovoltaic inverter, comprising:

[0006] An overcurrent protection circuit for an external fan of a photovoltaic inverter includes a power supply circuit for supplying power to the fan, the overcurrent protection circuit comprising a first switching tube connected in series with the power supply circuit to switch the circuit on or off, and a control signal input terminal for receiving a control signal from a control system of the photovoltaic inverter, the first switching tube being capable of being switched on or off by control of the control signal. The overcurrent protection circuit further comprises:

[0007] a sampling unit, configured to generate a voltage sampling value according to the fan current;

[0008] a comparing unit having a first input terminal for electrically connecting to the sampling unit, a second input terminal for obtaining the protection threshold, and an output terminal, the comparing unit being configured to receive the voltage sampling value and compare it with the protection threshold value and then output a low level or a high level accordingly;

[0009] The second switch tube has a control terminal electrically connected to the output terminal of the comparison unit, so as to pull the control signal low to turn off the first switch tube after receiving the high level output by the comparison unit.

[0010] Preferably, the overcurrent protection circuit also includes a control signal pull-up resistor, the power supply circuit has a positive power supply electrode and a negative power supply electrode, the control signal pull-up resistor and the second switch tube are connected in series to form a first branch, the first branch is connected between the positive power supply electrode and the negative power supply electrode, and the control signal input terminal is electrically connected to the midpoint between the control signal pull-up resistor and the second switch tube and then connected to the control end of the first switch tube.

[0011] More preferably, the first switch tube and the second switch tube are transistors, including but not limited to field effect tubes, and the control end is the gate of the field effect tube.

[0012] Preferably, the overcurrent protection circuit further includes a protection signal pull-up resistor, one end of the protection signal pull-up resistor is electrically connected between the control signal pull-up resistor and the positive pole of the power supply, and the other end is electrically connected to the output end of the comparison unit.

[0013] Preferably, the overcurrent protection circuit further comprises a protection hysteresis circuit electrically connected between the output terminal and the first input terminal of the comparison unit, so that the hysteresis time of circuit protection and recovery can be set.

[0014] Preferably, the protection hysteresis circuit includes a diode and a hysteresis resistor connected in series between the output terminal and the first input terminal. By adjusting the diode and the protection resistor, the hysteresis time of each protection and recovery of the circuit can be set.

[0015] Preferably, the overcurrent protection circuit further comprises a filtering circuit for filtering the sampled values ​​of the sampling unit, so as to prevent high-frequency interference from causing erroneous protection.

[0016] Preferably, the filtering circuit includes a capacitor and a filtering resistor, a branch formed by the capacitor and the filtering resistor connected in series is connected in parallel to both ends of the sampling unit, and the first input end is electrically connected to the middle point of the capacitor and the filtering resistor.

[0017] Preferably, the sampling unit is a sampling resistor connected in series in the power supply circuit; and / or the comparison unit is a comparator. Specifically, the comparator is an operational amplifier, and the first input terminal, the second input terminal, and the output terminal are the non-inverting input terminal, the inverting input terminal, and the output terminal of the operational amplifier, respectively.

[0018] Preferably, the overcurrent protection circuit further includes a first voltage-dividing resistor and a second voltage-dividing resistor, wherein a branch formed by the first and second voltage-dividing resistors being connected in series is connected in parallel to both ends of the power supply of the power supply circuit, and the preset protection threshold can be adjusted by changing the parameters of the first and second voltage-dividing resistors. The second input terminal of the comparison unit is electrically connected to a midpoint between the first and second voltage-dividing resistors.

[0019] The present invention also adopts the following technical solutions:

[0020] An overcurrent protection method, using the overcurrent protection circuit as described above, comprises the following steps:

[0021] Controlling the first switch tube by a control signal;

[0022] The current flowing through the fan is sampled to obtain a sample value, and the sample value is compared with a protection threshold. When the sample value is less than the protection threshold, the second switch tube is disconnected, the control signal controls the first switch tube to be closed, and the power supply circuit of the fan is turned on; when the sample value is equal to or greater than the protection threshold, the second switch tube is closed, the control signal is pulled low, the first switch tube is disconnected, and the power supply circuit of the fan is cut off.

[0023] The present invention adopts the above solution and has the following advantages compared with the prior art:

[0024] The present invention provides an overcurrent protection circuit and overcurrent protection method for an external fan of a photovoltaic inverter. A sampling unit generates a voltage sampling value, a comparison unit receives the voltage sampling value and compares it with a protection threshold value, and then outputs a low level or a high level accordingly. When the sampling voltage exceeds the protection threshold value, a second switch tube is turned on to lower a control signal, and a first switch tube controlled by the control signal is turned off, thereby cutting off the power supply circuit of the fan. When an overcurrent or short circuit fault occurs in the external fan, the power supply circuit can be quickly cut off to prevent circuit damage, thereby improving the reliability of the photovoltaic inverter and reducing the cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solution of the present invention, the following is a brief introduction to the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 It is a structural diagram of an overcurrent protection circuit in the prior art;

[0027] Figure 2The figure is a schematic structural diagram of an overcurrent protection circuit for an external fan of a photovoltaic inverter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings to make the advantages and features of the present invention more easily understood by those skilled in the art. It should be noted that the description of these embodiments is intended to facilitate understanding of the present invention and does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0029] Reference Figure 2 As shown, according to this embodiment, an overcurrent protection circuit for an external fan of a photovoltaic inverter is provided, comprising a power supply circuit 10 for supplying power to a fan 1. The overcurrent protection circuit includes a first switch Q1 connected in series with the power supply circuit 10 to turn it on or off, and a control signal input terminal E for receiving a control signal from the photovoltaic inverter control system. The first switch Q1 is controlled to turn on or off by the control signal. The overcurrent protection circuit also includes a sampling unit for generating a voltage sample value based on the fan current; a comparison unit having a first input terminal a1 electrically connected to the sampling unit, a second input terminal a2 for obtaining a protection threshold, and an output terminal a3. The comparison unit is configured to receive the voltage sample value, compare it with the protection threshold, and output a low or high level accordingly; and a second switch Q2, whose control terminal is electrically connected to the output terminal a3 of the comparison unit. Upon receiving the high level output from the comparison unit, the control signal is pulled low, thereby turning off the first switch Q1.

[0030] Specifically, the overcurrent protection circuit also includes a control signal pull-up resistor R6. The power supply circuit 10 includes a power supply 100 having a positive power supply electrode 101 and a negative power supply electrode 102. The control signal pull-up resistor R6 and the second switch transistor Q2 are connected in series to form a first branch 20. The first branch 20 is connected between the positive power supply electrode 101 and the negative power supply electrode 102. One end of the control signal input terminal E is electrically connected to the control system of the photovoltaic inverter (specifically, the DSP chip of the photovoltaic inverter), and the other end is electrically connected to the midpoint between the control signal pull-up resistor R6 and the second switch transistor Q2, and then to the control terminal of the first switch transistor Q1.

[0031] The overcurrent protection circuit further includes a protection signal pull-up resistor R5 , one end of which is electrically connected between the control signal pull-up resistor R6 and the positive electrode of the power supply, and the other end of which is electrically connected to the output terminal a3 of the comparison unit.

[0032] The overcurrent protection circuit also includes a protection hysteresis circuit 40 electrically connected between the output terminal a3 of the comparison unit and the first input terminal a1. When overcurrent protection occurs, it generates positive feedback to the sampling terminal, increases the protection hysteresis time, and can adjust the response time of the overcurrent protection accordingly. Specifically, the protection hysteresis circuit 40 includes a diode D1 and a hysteresis resistor R7 for increasing the hysteresis time when performing protection. One end of the branch formed by the diode D1 and the hysteresis resistor R7 in series is connected to the output terminal a3 of the comparison unit U1, and the other end is connected to the first input terminal a1 of the comparison unit. The overcurrent protection circuit also includes a filter circuit 30 for filtering the sampled value of the sampling unit to prevent high-frequency interference. It can filter the sampled value to prevent high-frequency interference from causing false protection. The filter circuit 30 includes a capacitor C1 and a filter resistor R4. The branch formed by the capacitor C1 and the filter resistor R4 in series is connected in parallel to the two ends of the sampling unit. The first input terminal a1 is electrically connected to the midpoint between the capacitor C1 and the filter resistor R4. By adjusting the values ​​of diode D1, hysteresis resistor R7, capacitor C1 and filter resistor R4, the hysteresis time of each protection and recovery of the circuit can be set.

[0033] Specifically in this embodiment, the sampling unit is a sampling resistor R3 connected in series in the power supply circuit. The comparison unit U1 is a comparator. Specifically, the comparator U1 is an operational amplifier, and the first input terminal a1, the second input terminal a2, and the output terminal a3 are the non-inverting input terminal, the inverting input terminal, and the output terminal of the operational amplifier, respectively.

[0034] The overcurrent protection circuit also includes a first voltage-dividing resistor R1 and a second voltage-dividing resistor R2. The first and second voltage-dividing resistors R1 and R2 are connected in series to form a branch circuit connected in parallel to both ends of the power supply 100 of the power supply circuit. The second input terminal a2 of the comparison unit U1 is electrically connected to the midpoint between the first and second voltage-dividing resistors R1 and R2. The preset protection threshold can be adjusted by changing the parameters of the first and second voltage-dividing resistors R1 and R2.

[0035] This embodiment further provides an overcurrent protection method, which uses the above overcurrent protection circuit and includes the following steps:

[0036] A. When the circuit operates normally, the sampling unit samples the current flowing through fan 1 and filters it through filter circuit 30, obtaining a sampled value at point C. Comparison unit U1 compares the sampled value at point C with a preset protection threshold at point B. If the sampled value is less than the protection threshold, the comparison unit outputs a low level from output terminal a3 to point D, turning off second switch Q2 and closing first switch Q1 with a control signal, turning on the power supply circuit of fan 1.

[0037] B. When a circuit abnormality occurs, i.e., a short circuit or overcurrent occurs in the circuit, the current I in the circuit increases, generating a larger sampling voltage at point A. The sampling unit samples the current flowing through fan 1 and filters it through filter circuit 30 to obtain a sampled value at point C. The comparison unit compares the sampled value at point C with the preset protection threshold at point B. When the sampled value is equal to or greater than the protection threshold, the comparison unit outputs a high level from output terminal a3 to point D, closing the second switch Q2, pulling the control signal low, disconnecting the first switch Q1, and cutting off the power supply circuit of fan 1.

[0038] C. Since Q1 is disconnected, the current I in the circuit decreases, and the potential at point A becomes lower. The sampling unit samples the current flowing through fan 1 and filters it through filtering circuit 30, obtaining a sampled value at point C. The comparison unit compares the sampled value at point C with the preset protection threshold at point B. When the sampled value is less than the protection threshold, the comparison unit outputs a low level from output terminal a3 to point D, turning off the second switch Q2. The control signal turns on the first switch Q1, and the power supply circuit of fan 1 is turned on again.

[0039] In this embodiment, step BC is a self-checking loop, implemented by the protection hysteresis circuit 40. After the first switch Q1 is turned off, the diode D1 and hysteresis resistor R7 in the protection hysteresis circuit 40 generate a positive feedback signal to the first input terminal a1 of the comparison unit U1, thereby increasing the protection hysteresis time. The protection hysteresis time can be adjusted by changing the parameters of the filter resistor R4, capacitor C1, protection signal pull-up resistor R5, and hysteresis resistor R7. This process protects the circuit from damage caused by a continuous short circuit or overcurrent condition. When a short circuit or overcurrent condition occurs, the circuit will continuously self-check until the fault is repaired.

[0040] When an inverter's external fan fails, this embodiment proactively disconnects the fan circuit by comparing current sampling with protection values, protecting the fan's power supply components from damage. The circuit protection and recovery hysteresis time can be set, improving the reliability of the photovoltaic inverter.

[0041] The above embodiment is intended only to illustrate the technical concepts and features of the present invention and is a preferred embodiment. Its purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. It is not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. An overcurrent protection circuit for an external fan of a photovoltaic inverter, comprising a power supply circuit for supplying power to the fan, the overcurrent protection circuit comprising a first switch connected in series with the power supply circuit to turn the power supply circuit on or off, and a control signal input terminal for receiving a control signal from a control system of the photovoltaic inverter, wherein the first switch can be turned on or off by control of the control signal, and wherein: The overcurrent protection circuit further includes: a sampling unit, configured to generate a voltage sampling value according to the fan current; a comparing unit having a first input terminal for electrically connecting to the sampling unit, a second input terminal for obtaining a protection threshold, and an output terminal, wherein the comparing unit is configured to receive the voltage sampling value and compare it with the protection threshold value and output a low level or a high level accordingly; A second switching tube, whose control end is electrically connected to the output end of the comparison unit, so as to pull down the control signal and disconnect the first switching tube after receiving the high level output by the comparison unit; the overcurrent protection circuit also includes a protection hysteresis circuit electrically connected between the output end and the first input end of the comparison unit, and the protection hysteresis circuit includes a diode and a hysteresis resistor connected in series between the output end and the first input end; the overcurrent protection circuit also includes a filter circuit for filtering the sampled value of the sampling unit, and the filter circuit includes a capacitor and a filter resistor. The branch formed by the series connection of the capacitor and the filter resistor is connected in parallel to the two ends of the sampling unit, and the first input end is electrically connected to the midpoint of the capacitor and the filter resistor. The hysteresis time of each protection and recovery of the circuit is set by adjusting the values ​​of the diode, the hysteresis resistor, the capacitor and the filter resistor.

2. The overcurrent protection circuit according to claim 1, characterized in that: The overcurrent protection circuit also includes a control signal pull-up resistor. The power supply circuit has a positive power supply electrode and a negative power supply electrode. The control signal pull-up resistor and the second switching tube are connected in series to form a first branch. The first branch is connected between the positive power supply electrode and the negative power supply electrode. The control signal input terminal is electrically connected to the midpoint between the control signal pull-up resistor and the second switching tube and then connected to the control end of the first switching tube.

3. The overcurrent protection circuit according to claim 2, characterized in that: The overcurrent protection circuit further includes a protection signal pull-up resistor, one end of which is electrically connected between the control signal pull-up resistor and the positive pole of the power supply, and the other end is electrically connected to the output end of the comparison unit.

4. The overcurrent protection circuit according to any one of claims 1 to 3, characterized in that: The sampling unit is a sampling resistor connected in series in the power supply circuit; and / or the comparing unit is a comparator.

5. The overcurrent protection circuit according to any one of claims 1 to 3, characterized in that: The overcurrent protection circuit also includes a first voltage-dividing resistor and a second voltage-dividing resistor. The branch formed by the first voltage-dividing resistor and the second voltage-dividing resistor in series is connected in parallel to the two ends of the power supply of the power supply circuit, and the second input end of the comparison unit is electrically connected to the midpoint between the first voltage-dividing resistor and the second voltage-dividing resistor.

6. A method for overcurrent protection of an external fan of a photovoltaic inverter, characterized in that: Using the overcurrent protection circuit according to any one of claims 1 to 5, the overcurrent protection method comprises the following steps: Controlling the first switch tube by a control signal; The current flowing through the fan is sampled to obtain a sample value, and the sample value is compared with a protection threshold. When the sample value is less than the protection threshold, the second switch tube is disconnected, the control signal controls the first switch tube to be closed, and the power supply circuit of the fan is turned on; when the sample value is equal to or greater than the protection threshold, the second switch tube is closed, the control signal is pulled low, the first switch tube is disconnected, and the power supply circuit of the fan is cut off.

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