Overcurrent protection circuit

Abstract

The utility model provides an over-current protection circuit, which comprises a current sampling circuit, the input end of the current sampling circuit is connected with the current output end of APF / SVG equipment, and the current sampling circuit is used for monitoring the working current of the APF / SVG equipment in real time; the input end of the hysteresis protection circuit is connected with the output end of the current sampling circuit, and the hysteresis protection circuit is used for receiving a monitoring signal of the current sampling circuit, judging according to a preset threshold value and starting an overcurrent protection mechanism; and the protection execution circuit is connected with the hysteresis protection circuit and is used for adjusting the running state of the APF / SVG equipment according to the received signal of the hysteresis protection circuit. The hysteresis protection circuit is additionally arranged in the equipment overcurrent protection circuit, so that equipment shutdown caused by overcurrent can be avoided to a certain extent, and the running state of the equipment can be adjusted according to the real-time current condition to achieve the optimal compensation effect.

Description

Technical Field

[0001] The utility model belongs to the technical field of power electronics, and particularly relates to an overcurrent protection circuit for an active power filter (APF) and a static var generator (SVG). Background Art

[0002] In a power system, an active power filter (APF) and a static var generator (SVG) are two commonly used power electronic devices, which are of great significance for improving the power quality and stability of the power system. However, in actual operation, due to the complex and changeable on-site operation environment, when the machine is running, the load current suddenly changes, and the compensated current also changes accordingly. The machine may experience hardware overcurrent. Most machines on the market will directly stop running in case of overcurrent, thus affecting the compensation effect.

[0003] If the on-site operation environment is relatively harsh, the frequency of load mutation is too high, and the number of times of overcurrent of the machine is too many, the machine will be in a continuous restart state. This will not only result in a poor compensation effect, but seriously cause damage to the machine components; if the number of times of overcurrent that occurs occasionally is relatively high, the machine will keep stopping, affecting the performance of the equipment. Summary of the Invention

[0004] To solve the above problems, the utility model proposes an improved overcurrent protection circuit, which can not only effectively prevent the equipment from directly stopping when detecting overcurrent, but also adjust the operation state of the equipment according to the degree of overcurrent to ensure the continuous operation and compensation effect of the equipment to the greatest extent.

[0005] The technical solution of this application is: an overcurrent protection circuit, characterized in that the overcurrent protection circuit includes:

[0006] The input end of the current sampling circuit is connected to the current output end of the APF / SVG device, and is used for real-time monitoring of the working current of the APF / SVG device;

[0007] The input end of the hysteresis protection circuit is connected to the output end of the current sampling circuit, and is used for receiving the monitoring signal of the current sampling circuit and judging according to a preset threshold to start the overcurrent protection mechanism;

[0008] The protection execution circuit is connected to the hysteresis protection circuit, and is used for adjusting the operation state of the APF / SVG device after receiving the signal of the hysteresis protection circuit.

[0009] Further, the overcurrent protection circuit further includes: an input end of an amplifying circuit is connected to an output end of the current sampling circuit for amplifying a current signal collected by the current sampling circuit, and an output end of the amplifying circuit is connected to an input end of the hysteresis protection circuit.

[0010] Further, the current sampling circuit includes a first resistor R36. One end of the first resistor R36 is connected to a current output end of the APF / SVG device, and the other end is grounded for converting the current signal of the APF / SVG device into a voltage signal.

[0011] Further, the amplifying circuit includes an operational amplifier U3A. A positive output end of the operational amplifier U3A is grounded. A negative output end of the operational amplifier U3A is connected to an output end of the current sampling circuit through a second resistor R3. An output end of the operational amplifier U3A is connected to a negative input end through a third resistor R41 to form a feedback loop.

[0012] Further, the hysteresis protection circuit includes a first comparator U4A. A positive input end of the first comparator U4A is connected to an output end of the amplifying circuit through a fourth resistor R34. A negative input end of the first comparator U4A receives a first reference voltage signal which is set according to a preset first threshold. When a voltage signal at the positive input end is greater than the reference voltage signal at the negative input end, the first comparator U4A outputs a high-level signal.

[0013] Further, the hysteresis protection circuit includes a second comparator U4B. A negative input end of the second comparator U4B is connected to an output end of the amplifying circuit through a fifth resistor R51. A positive input end of the second comparator U4B receives a second reference voltage signal which is set according to a preset second threshold. When a voltage signal at the negative input end is less than the second reference voltage signal at the positive input end, the second comparator U4B outputs a high-level signal.

[0014] Further, the protection execution circuit includes a triode Q1. A base of the triode Q1 is connected to an output end of the hysteresis protection circuit, its emitter is grounded, and its collector is connected to a control element for controlling an operating state of the APF / SVG device.

[0015] Further, the control element is a CPLD.

[0016] Further, an input end of the control element CPLD receives a signal from the triode Q1, and an output end of the control element CPLD is electrically connected to an IGBT drive board.

[0017] Further, the control element CPLD controls the IGBT drive board through PWM waves.

[0018] The beneficial effects of the present utility model are as follows:

[0019] A hysteresis protection circuit is added to the overcurrent protection circuit of the device, and two thresholds are set. When the machine experiences overcurrent, instead of immediately shutting down, it is adjusted according to the degree of overcurrent. Specifically, when the current exceeds the first threshold, the hysteresis protection circuit triggers a protection action, such as reducing the output power of the device to reduce the current. This processing method can effectively prevent the device from directly shutting down due to overcurrent and ensure the continuous operation of the device under overcurrent conditions. When it is monitored that the current is less than the second threshold, it indicates that the device is operating normally. At this time, the hysteresis protection circuit will no longer trigger a protection action, and the APF / SVG device will resume its normal compensation function. Through such a design, not only can the device shutdown caused by overcurrent be avoided to a certain extent, but also the operating state of the device can be adjusted according to the real-time current situation to achieve the best compensation effect. Description of the Drawings

[0020] Figure 1 : Schematic diagram of the connection between the overcurrent protection circuit of the present application and the APF / SVG device;

[0021] Figure 2 : Schematic diagram of an embodiment of an overcurrent protection circuit of the present application;

[0022] Figure 3 : Schematic diagram of another embodiment of an overcurrent protection circuit of the present application;

[0023] Figure 4 : Circuit diagram of an embodiment of an overcurrent protection circuit of the present application; Detailed Embodiments

[0024] The following embodiments further illustrate the content of the present utility model, but should not be construed as a limitation to the present utility model. Without departing from the spirit and essence of the present utility model, any modification or replacement made to the methods, steps or conditions of the present utility model falls within the scope of the present utility model.

[0025] The present utility model will be described in detail below with reference to the drawings and embodiments.

[0026] Such as Figure 1As shown in the figure, it is the schematic diagram of SVG (Static Var Generator). SVG is an important power electronic device in modern power systems. SVG is mainly used for dynamically compensating reactive power, improving the power factor of the power system, reducing line losses, and stabilizing the grid voltage; while APF is mainly used for filtering harmonics in the power system, improving power quality, and protecting electrical equipment. However, since SVG and APF need to handle a large number of power conversion and filtering tasks during operation, the design of their overcurrent protection circuits and protection mechanisms is particularly important.

[0027] The input end of an overcurrent protection circuit of the present application is connected to the current output end of the APF / SVG device, and the output end of an overcurrent protection circuit of the present application is electrically connected to the control module of the APF / SVG device.

[0028] In some embodiments, as Figure 2 shown, an overcurrent protection circuit, the overcurrent protection circuit includes:

[0029] Current sampling circuit The input end of the current sampling circuit is connected to the current output end of the APF / SVG device, and is used for real-time monitoring of the operating current of the APF / SVG device;

[0030] Hysteresis protection circuit The input end of the hysteresis protection circuit is connected to the output end of the current sampling circuit, and is used for receiving the monitoring signal of the current sampling circuit and making a judgment according to a preset threshold to start the overcurrent protection mechanism;

[0031] Protection execution circuit The protection execution circuit is connected to the hysteresis protection circuit, and is used for adjusting the operating state of the APF / SVG device after receiving the signal of the hysteresis protection circuit.

[0032] In some embodiments, as Figure 3 shown, the overcurrent protection circuit further includes: Amplification circuit The input end of the amplification circuit is connected to the output end of the current sampling circuit, and is used for amplifying the current signal collected by the current sampling circuit. The output end of the amplification circuit is connected to the input end of the hysteresis protection circuit.

[0033] Specifically, in some embodiments, as Figure 4 shown, the current sampling circuit 1 includes a first resistor R36. One end of the first resistor R36 is connected to the current output end of the APF / SVG device, and the other end is grounded, and is used for converting the current signal of the APF / SVG device into a voltage signal.

[0034] The voltage signal is connected to the inverting input terminal of the operational amplifier U3A through R35. The non-inverting input terminal of the operational amplifier U3A is grounded, forming a voltage follower structure. By adjusting the resistance value of the first resistor R36, the amplitude of the sampled voltage can be changed to adapt to different ranges of current monitoring requirements. At the same time, in order to ensure the stability of the sampled voltage, a small capacitor C1 is connected in parallel across R35, and the other end of the capacitor C1 is grounded to filter out high-frequency noise.

[0035] To increase the stability of the circuit, the amplifier circuit 2 adopts a feedback loop design. Specifically, the output terminal of the operational amplifier U3A is connected to the inverting input terminal through the third resistor R41, forming a negative feedback loop. Such a design can reduce the fluctuation of the output signal and improve the stability of the circuit. At the same time, by adjusting the resistance value of the third resistor R41, the gain of the amplifier circuit can be changed to adapt to the amplification requirements of different current signals.

[0036] The voltage signal Vout is sent into the hysteresis protection circuit. The hysteresis protection circuit includes a first comparison circuit 301 and a second comparison circuit 302. Further, the hysteresis protection circuit realizes the accurate judgment and processing of the overcurrent signal through the first comparator U4A and the second comparator U4B. In the circuit design, in the first comparison circuit 301, the fourth resistor R34 connects the voltage signal Vout to the non-inverting input terminal of the first comparator U4A, and the first reference voltage signal is connected to the inverting input terminal of the first comparator U4A through a stable voltage source and the resistor R37. A resistor R39 and a capacitor C2 are also connected in parallel across the inverting output terminal, forming a simple RC circuit for generating an appropriate delay to prevent instantaneous overcurrent signals from triggering false protection.

[0037] The output terminal 1 of the first comparator U4A is connected to the non-inverting terminal through the diode D3 and the resistor R31. The diode D3 and the resistor R31 constitute the positive feedback part of the hysteresis loop, enabling the circuit to respond quickly and output stably when detecting an overcurrent signal.

[0038] When the voltage signal Vout exceeds the first reference voltage signal, that is, when the current exceeds the preset first threshold, the first comparator U4A outputs a high-level signal. This signal is transmitted to the subsequent hysteresis logic circuit to trigger a protection action, such as reducing the output power of the device.

[0039] Similarly, in the second comparison circuit 302, the voltage signal Vout is connected to the inverting input terminal of the second comparator U4B through the fifth resistor R51, while the second reference voltage signal is connected to the non-inverting input terminal of the second comparator U4B through a stable voltage source, resistor R44, and resistor R45. The output terminal of the second comparator U4B is connected to the non-inverting terminal through the diode D7 and resistor R46. When the voltage signal Vout is lower than the second reference voltage signal, that is, when the current is lower than the preset second threshold, the second comparator U4B outputs a high-level signal.

[0040] Meanwhile, the inverting input terminal of the second comparator U4B receives the voltage signal Vout through the fifth resistor R51, and its non-inverting input terminal is connected to the voltage source that provides the second reference voltage signal. This second reference voltage signal is set according to the preset second threshold, and usually this threshold is less than the first threshold. When the voltage value of Vout drops below the second threshold set by the second reference voltage signal, the second comparator U4B outputs a low-level signal, indicating that the device has returned to the normal operating state, and at this time the hysteresis protection circuit will no longer trigger the protection action.

[0041] The triode Q1 in the protection execution circuit plays a crucial role. Its base receives the signal from the hysteresis protection circuit. When the first comparator U4A or the second comparator U4B outputs a high-level signal, the triode Q1 conducts accordingly. The collector of the triode Q1 is connected to the control element CPLD. When the triode Q1 conducts, it sends a signal to the CPLD, indicating that the device is currently in an overcurrent state and the operating state needs to be adjusted. After receiving this signal, the CPLD controls the IGBT drive board through the PWM wave, thereby realizing the adjustment of the output power of the APF / SVG device to achieve the purpose of reducing the current and protecting the device.

[0042] Similarly, when the first comparator U4A or the second comparator U4B outputs a low-level signal, when the current drops to a certain value, after Vout is less than the set voltage, U4-1 or U4-7 pin outputs a low level. At this time, the triode Q1 is turned off, and at this time the OC1 signal is pulled high. After the CPLD receives the OC1 pulled high signal, it releases the PWM block, and the machine operates normally.

[0043] The design of the entire overcurrent protection circuit fully considers the actual operating conditions of the device and the requirements of overcurrent protection. By accurately setting two thresholds and adopting the design of the hysteresis protection circuit, the utility model can be flexibly adjusted according to the degree of overcurrent when the device has an overcurrent, which not only ensures the continuous operation of the device but also avoids device damage caused by overcurrent. At the same time, through the introduction of the control element CPLD, the precise control of the device operating state is realized, and the safety and stability of the device are improved.

[0044] In the hysteresis protection circuit, the first comparator U4A and the second comparator U4B play a crucial role. The positive input terminal of the first comparator U4A receives the voltage signal output by the amplifier circuit, and the negative input terminal receives the first reference voltage signal. When the voltage signal is greater than the first reference voltage signal, the first comparator U4A outputs a high-level signal to trigger the protection action. The design of the second comparator U4B is similar to that of the first comparator, but its triggering condition is opposite. When the voltage signal is less than the second reference voltage signal, the second comparator U4B outputs a high-level signal, indicating that the device has returned to normal operation and no longer requires triggering of the protection action.

[0045] In the protection execution circuit, the triode Q1 plays a crucial role. Its base is connected to the output terminal of the hysteresis protection circuit, its emitter is grounded, and its collector is connected to the control element CPLD that controls the operating state of the APF / SVG device. When the hysteresis protection circuit outputs a high-level signal, the triode Q1 conducts, sending a protection signal to the CPLD. After receiving the protection signal, the CPLD adjusts the operating state of the APF / SVG device according to the preset program logic, such as reducing the output power, adjusting the compensation strategy, etc., to cope with the overcurrent situation.

[0046] In a specific embodiment, the CPLD (Complex Programmable Logic Device) programmable logic device controls the IGBT driver board through PWM waves, thereby realizing the adjustment of the operating state of the APF / SVG device. Parameters such as the duty cycle and frequency of the PWM wave can be set according to the actual situation to achieve precise power control and compensation strategy adjustment. Specifically, the IGBT model used in this application is F3L150R07W2E3_B11, and the CPLD model is EF2L15LG100B.

[0047] Through the above design, the overcurrent protection circuit of the present utility model can monitor the current situation of the device in real time and perform hysteresis protection according to the preset threshold. When the device has an overcurrent, instead of immediately shutting down, it is adjusted according to the degree of overcurrent to ensure the continuous operation of the device. At the same time, this circuit also has the characteristics of high stability and strong reliability, and can adapt to various complex working environments.

[0048] Although the present utility model has been described in detail above with general descriptions, specific embodiments and experiments, based on the present utility model, some modifications or improvements can be made to it, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present utility model all fall within the scope of protection required by the present utility model.

Claims

1. An overcurrent protection circuit is applied to an APF / SVG device, and is characterized in that, The overcurrent protection circuit includes: The input end of the current sampling circuit is connected to the current output end of the APF / SVG device, and is used to monitor the working current of the APF / SVG device in real time; The input end of the hysteresis protection circuit is connected to the output end of the current sampling circuit, and is used to receive the current signal of the current sampling circuit and compare it with a preset threshold. The threshold includes a first threshold and a second threshold. When the current signal is greater than the first threshold, the overcurrent protection mechanism is started, and the output current of the APF / SVG decreases. When the current signal decreases to be less than the second threshold, the overcurrent protection mechanism is released, and the APF / SVG works normally; The protection execution circuit is connected to the hysteresis protection circuit, and is used to adjust the operating state of the APF / SVG device after receiving the signal of the hysteresis protection circuit.

2. The overcurrent protection circuit according to claim 1, wherein The overcurrent protection circuit further includes: The input end of the amplification circuit is connected to the output end of the current sampling circuit, and is used to amplify the current signal collected by the current sampling circuit. The output end of the amplification circuit is connected to the input end of the hysteresis protection circuit.

3. The overcurrent protection circuit according to claim 2, wherein The current sampling circuit includes a first resistor R36. One end of the first resistor R36 is connected to the current output end of the APF / SVG device, and the other end is grounded, and is used to convert the current signal of the APF / SVG device into a voltage signal.

4. The overcurrent protection circuit according to claim 2, wherein The amplification circuit includes an operational amplifier U3A. The positive output end of the operational amplifier U3A is grounded. The negative output end of the operational amplifier U3A is connected to the output end of the current sampling circuit through a second resistor R3. The output end of the operational amplifier U3A is connected to the negative input end through a third resistor R41 to form a feedback loop.

5. The overcurrent protection circuit according to claim 2, wherein The hysteresis protection circuit includes a first comparator U4A. The positive input end of the first comparator U4A is connected to the output end of the amplification circuit through a fourth resistor R34. The negative input end of the first comparator U4A receives a first reference voltage signal. The first reference voltage signal is set according to a preset first threshold. When the voltage signal at the positive input end is greater than the reference voltage signal at the negative input end, the first comparator U4A outputs a high-level signal.

6. The overcurrent protection circuit according to claim 2, wherein The hysteresis protection circuit includes a second comparator U4B. The negative input end of the second comparator U4B is connected to the output end of the amplification circuit through a fifth resistor R51. The positive input end of the second comparator U4B receives a second reference voltage signal. The second reference voltage signal is set according to a preset second threshold. When the voltage signal at the negative input end is less than the second reference voltage signal at the positive input end, the second comparator U4B outputs a low-level signal.

7. The overcurrent protection circuit according to claim 1, wherein The protection execution circuit includes a triode Q1. The base of the triode Q1 is connected to the output end of the hysteresis protection circuit, its emitter is grounded, and its collector is connected to a control element for controlling the operating state of the APF / SVG device.

8. The overcurrent protection circuit according to claim 7, characterized in that, The control element is a CPLD.

9. The overcurrent protection circuit according to claim 8, wherein, The input terminal of the control element CPLD receives a signal from the triode Q1, and the output terminal of the control element CPLD is electrically connected to the IGBT drive board.

10. The overcurrent protection circuit according to claim 9, wherein, The control element CPLD controls the IGBT drive board through a PWM wave.

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