A protection circuit for overcurrent and short circuit of an inverter
By combining a two-stage active low-pass filter and a dual-threshold high-speed comparator, the inverter protection circuit solves the noise interference and response delay problems of traditional inverter overcurrent and short-circuit protection circuits, and achieves fast and accurate fault detection and protection control.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- QINGDAO SKYWISE TECH
- Filing Date
- 2025-06-19
- Publication Date
- 2026-05-29
AI Technical Summary
Traditional inverter overcurrent and short-circuit protection circuits are sensitive to noise interference, have high response delays and malfunction rates, and cannot effectively cope with sudden load changes and line faults.
The inverter adopts an overcurrent and short-circuit protection circuit, including a switching transistor, filter capacitor, safety capacitor, bleeder resistor, varistor, current transformer, rectifier bridge, operational amplifier and microcontroller. It achieves accurate noise filtering and dynamic threshold judgment through a combination of a two-stage active low-pass filter and a dual-threshold high-speed comparator, and combines hardware isolation with software collaborative control.
It significantly improves the inverter's response speed and detection accuracy, reduces the false alarm rate, and enhances the system's anti-interference capability and safety.
Smart Images
Figure CN224305404U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of electronic circuit application technology, and in particular to a protection circuit for overcurrent and short circuit of an inverter. Background Technology
[0002] Inverters, as the core equipment for power conversion, are widely used in photovoltaic power generation, electric vehicle drive and other fields. They achieve DC to AC conversion by controlling the on and off of power switching transistors. However, during operation, overcurrent and short circuits may occur due to sudden load changes, device breakdown or line faults. This can lead to overheating and damage of switching transistors, or even system-level failures or safety accidents. Therefore, the overcurrent and short circuit protection circuit of inverters has become a key safety module. Traditional technology often uses a single-stage RC filter combined with a fixed threshold comparator for current detection.
[0003] However, in current technology, single-stage RC filtering combined with a fixed threshold comparator suffers from problems such as sensitivity to noise interference, response delay, and high false alarm rate. Utility Model Content
[0004] To overcome the above shortcomings, this utility model provides an inverter overcurrent and short circuit protection circuit, which aims to improve the problems of noise interference sensitivity, response delay and high malfunction rate.
[0005] To achieve the above objectives, the present invention provides the following technical solution:
[0006] An inverter overcurrent and short-circuit protection circuit includes:
[0007] The inverter output unit includes a switching transistor, a filter capacitor, a safety capacitor, a discharge resistor, and a varistor. The output terminal of the switching transistor is connected in sequence to the filter capacitor, the safety capacitor, and the discharge resistor. The varistor is connected in parallel to the inverter output terminal.
[0008] The current sampling unit includes a current transformer and a rectifier bridge. The primary winding of the current transformer is connected in series in the inverter output circuit, and the secondary winding is connected to the input terminal of the rectifier bridge.
[0009] The overcurrent and short-circuit analysis unit includes a two-stage active low-pass filter composed of operational amplifiers U2A and U2B and a high-speed comparator. The output of the rectifier bridge is connected to the input of the two-stage active low-pass filter through a voltage divider resistor network. The output of the two-stage active low-pass filter is connected to the non-inverting input of the high-speed comparator, and the inverting input of the high-speed comparator is connected to the high threshold voltage and the low threshold voltage, respectively.
[0010] The protection execution unit includes an optocoupler and a microcontroller. The output of the high-speed comparator is connected to the input pin of the microcontroller after being isolated by the optocoupler.
[0011] The above technical solution involves an inverter output unit composed of a switching transistor, a filter capacitor, a safety capacitor, a discharge resistor, and a varistor, which are used for filtering, suppressing interference, discharging charge, and absorbing surges, respectively.
[0012] The current sampling unit samples the magnetic induction current of the main circuit through a current transformer and converts it into a DC signal through a rectifier bridge.
[0013] The analysis unit uses a two-stage active filter to filter noise and a dual-threshold high-speed comparator to synchronously determine overload and short circuit.
[0014] The execution unit transmits signals to the microcontroller via optocoupler isolation, triggering the switching transistor to turn off.
[0015] By employing precise noise filtering and dynamic threshold design, combined with hardware isolation and software collaborative control, the system achieves rapid response, low false alarm rate, and intelligent recovery mechanism, significantly improving system security and anti-interference capabilities.
[0016] Preferably, one end of the bleeder resistor in the inverter output unit is connected to the common node of the filter capacitor and the safety capacitor, and the other end is grounded;
[0017] The two ends of the varistor are respectively connected to the positive and negative busbars of the inverter output terminal.
[0018] The above technical solution involves connecting one end of the bleed resistor to the common node of the filter capacitor and the safety capacitor, and grounding the other end. This structure provides a charge discharge path for the filter capacitor when power is off, avoiding the risk of residual voltage. The varistor is connected between the positive and negative buses of the inverter output terminal, and its nonlinear characteristics are used to absorb surge voltage. This forms a hardware protection layer from the two dimensions of energy discharge and transient suppression, ensuring that the inverter quickly enters a safe state when there is an abnormality.
[0019] Preferably, the secondary winding of the current transformer is connected in series with the input terminal of the rectifier bridge via a resistor.
[0020] The above technical solution involves connecting the secondary winding of the current transformer to the input terminal of the rectifier bridge via a series resistor. This resistor limits the secondary circuit current to prevent overload of the rectifier bridge and achieves impedance matching to optimize signal transmission.
[0021] Preferably, the first stage filter in the second-stage active low-pass filter includes an operational amplifier U2A, a resistor three, a resistor four, and a capacitor. The resistor three is connected to the output terminal of the rectifier bridge and the non-inverting input terminal of the operational amplifier U2A. The resistor four and the capacitor are connected in parallel and then connected across the output terminal and the inverting input terminal of the operational amplifier U2A.
[0022] The above technical solution involves the first-stage active low-pass filter transmitting the rectified pulsating signal to the non-inverting input of the operational amplifier via an input resistor. The feedback network filters out high-frequency noise and adjusts the gain through a parallel structure, generating a smooth DC signal at the output.
[0023] Preferably, the second-stage filter in the secondary active low-pass filter comprises an operational amplifier U2B, resistor five, resistor six, and a capacitor, and the connection method is the same as that of the first-stage filter.
[0024] The above technical solution involves the second-stage filter employing the same operational amplifier and RC network structure as the first stage. The second-stage operational amplifier performs secondary processing on the filtered signal from the previous stage, further filtering out residual high-frequency noise and improving signal smoothness.
[0025] Preferably, the voltage divider resistor network includes resistors seven and eight connected in series. One end of resistor seven is connected to the output terminal of the rectifier bridge, and the other end is connected to resistor eight and the non-inverting input terminal of the operational amplifier. The other end of resistor eight is grounded.
[0026] The above technical solution attenuates the high-amplitude signal after rectification to the range that the operational amplifier can handle by using resistor voltage division. This not only prevents signal overload from causing device saturation, but also provides an impedance matching interface for subsequent filtering circuits, ensuring that the current sampling signal is accurately matched to the threshold judgment range, thereby improving the reliability of overcurrent and short circuit detection.
[0027] Preferably, the output terminal of the high-speed comparator is connected to the positive terminal of the light-emitting diode of the optocoupler via current-limiting resistor nine and resistor ten, and the collector of the output transistor of the optocoupler is connected to the input pin of the microcontroller, while the emitter is grounded.
[0028] The above technical solution achieves full isolation protection control from fault detection to execution by matching the optocoupler drive requirements with a current-limiting resistor, blocking electrical interference between the main circuit and the control terminal, and converting the logic signal output by the comparator into a clean level that the microcontroller can recognize. The microcontroller then judges and triggers the switching transistor to turn off in real time, effectively improving the system's anti-interference capability and protection reliability.
[0029] Preferably, the first bleeder resistor has a resistance of 10kΩ-100kΩ and is connected in parallel across the filter capacitor.
[0030] The above technical solution provides a controllable discharge path for the charge stored in the filter capacitor when the system is powered off, avoiding the risk of electric shock caused by residual voltage. At the same time, it works in conjunction with the safety capacitor to maintain the filtering efficiency during normal operation and quickly release energy under abnormal conditions, forming a hardware-level safety protection mechanism. This ensures the stability of the inverter output and prevents the capacitor charge from causing potential damage to the switching transistors and subsequent circuits after power failure.
[0031] This utility model has the following beneficial effects:
[0032] 1. In this utility model, a combination of a two-stage active low-pass filter and a dual-threshold comparator is used to filter out high-frequency noise in the current sampling signal step by step using two-stage operational amplifiers. Then, a high-speed comparator is used to synchronously compare the high and low thresholds to accurately distinguish between short circuits and overloads, thereby significantly improving detection accuracy and response speed and ensuring signal reliability.
[0033] 2. In this utility model, the current transformer T7, optocoupler U5 / U6 and microcontroller MCU work together to block the transmission of high voltage interference to the control terminal. At the same time, it supports automatic overload reset and short-circuit hard latch, enhances the circuit's anti-interference capability, optimizes the fault handling process, and reduces the frequency of manual maintenance. Attached Figure Description
[0034] Figure 1 This is a schematic diagram of the overcurrent and short-circuit protection circuit for an inverter proposed in this utility model.
[0035] Figure 2 This is a schematic diagram of the inverter output current sampling unit circuit structure proposed in this utility model.
[0036] Figure 3 A schematic diagram of the overcurrent and short-circuit analysis unit structure proposed in this utility model;
[0037] Figure 4 This is a schematic diagram of the overcurrent and short-circuit analysis unit structure proposed in this utility model - B. Detailed Implementation
[0038] The technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.
[0039] Reference Figures 1-4 One embodiment of this utility model provides: an inverter overcurrent and short circuit protection circuit, comprising:
[0040] The inverter output unit includes a switching transistor, a filter capacitor C1, a safety capacitor C2, C3, a bleeder resistor R1, and a varistor RP1. The output terminal of the switching transistor is connected in sequence to the filter capacitor C1, the safety capacitor C2, C3, and the bleeder resistor R1. The varistor RP1 is connected in parallel to the inverter output terminal.
[0041] The current sampling unit includes a current transformer T7 and a rectifier bridge U1. The primary winding of the current transformer T7 is connected in series in the inverter output circuit, and the secondary winding is connected to the input terminal of the rectifier bridge U1.
[0042] The overcurrent and short-circuit analysis unit includes a two-stage active low-pass filter composed of operational amplifiers U2A and U2B and high-speed comparators U3 and U4. The output of rectifier bridge U1 is connected to the input of the two-stage active low-pass filter through a voltage divider resistor network. The output of the two-stage active low-pass filter is connected to the non-inverting input of high-speed comparators U3 and U4 respectively. The inverting input of high-speed comparators U3 and U4 is connected to the high threshold voltage V1 and the low threshold voltage V2 respectively.
[0043] The protection execution unit includes optocouplers U5 and U6 and a microcontroller MCU. The outputs of high-speed comparators U3 and U4 are isolated by optocouplers U5 and U6 and then connected to the input pins of the microcontroller MCU.
[0044] Specifically, the inverter output unit outputs an AC signal through an internal switching transistor. A filter capacitor C1 is connected to the output terminal of the switching transistor to filter out high-frequency ripple and stabilize the output voltage. Safety capacitors C2 and C3 are connected between the output terminal and ground to improve the electromagnetic compatibility of the system by suppressing common-mode interference. A discharge resistor R1 is connected in parallel across the filter capacitor C1 to quickly release residual charge when the power is off to avoid the risk of electric shock. Then, a varistor RP1 is directly connected across the positive and negative buses of the inverter output. Through its nonlinear resistance characteristics, it absorbs transient overvoltage energy to prevent voltage spikes from damaging the switching transistor, ensuring the stability of the inverter output and achieving hardware-level protection against overcurrent, short circuit and surge impact.
[0045] The current sampling unit is connected in series with the primary winding of the current transformer T7 to the inverter output circuit. Through electromagnetic induction, the main circuit current is proportionally converted into a secondary low-voltage signal. The AC signal output from the secondary winding is rectified by the input of the rectifier bridge U1 to generate a pulsating DC signal, which is then transmitted to the subsequent analysis unit through the output. This achieves electrical isolation between the high-voltage main circuit and the low-voltage sampling circuit, and at the same time converts the AC current signal into a processable DC signal, providing an accurate current sampling reference for subsequent overcurrent and short-circuit protection.
[0046] In the overcurrent and short-circuit analysis unit, the pulsating DC signal output by the rectifier bridge U1 is adjusted in amplitude by a voltage divider resistor network and then input to a two-stage active low-pass filter composed of operational amplifiers U2A and U2B. The two-stage filtering eliminates high-frequency noise and outputs a smooth DC signal to the non-inverting input of high-speed comparators U3 and U4. The high threshold voltage V1 and the low threshold voltage V2 are connected to the inverting input of comparators U3 and U4, respectively. When the filtered signal exceeds the threshold, the comparator outputs a switching signal to realize dynamic threshold judgment of the current signal and provide interference-free triggering logic for the subsequent protection execution unit.
[0047] In the protection execution unit, the logic signals output by high-speed comparators U3 and U4 are input through the LED terminals of optocouplers U5 and U6. After opto-isolation, the signals are transmitted to the input pins of the microcontroller MCU via the transistors at the output terminals of the optocouplers, achieving electrical isolation between the high-voltage side signals and the low-voltage control circuit. Optocouplers U5 and U6 block the influence of common-mode interference on the MCU. At the same time, the MCU drives the turn-off control terminal of the inverter switching transistor based on the high / low level of the isolated signal state, forming a closed-loop protection mechanism from fault detection to execution action, ensuring that the main circuit is quickly cut off and the fault state is locked in case of overcurrent or short circuit.
[0048] Reference Figure 1 In the inverter output unit, one end of the bleeder resistor R1 is connected to the common node of the filter capacitor C1 and the safety capacitors C2 and C3, and the other end is grounded.
[0049] The two ends of the varistor RP1 are connected to the positive and negative busbars of the inverter output terminal, respectively;
[0050] Specifically, one end of the bleeder resistor R1 is connected to the common node of the filter capacitor C1 and the safety capacitors C2 and C3, and the other end is grounded. This ensures that the charge stored in the filter capacitor C1 is discharged when the system is powered off, avoiding the risk of electric shock caused by residual voltage. The varistor RP1 is connected across the positive and negative buses of the inverter output. Through its nonlinear impedance characteristics, it absorbs voltage surges and suppresses the impact of abnormal high voltage on the switching transistors at the output. Thus, a hardware protection layer is constructed from the two dimensions of energy discharge and transient suppression to ensure that the inverter unit quickly enters a safe state in the event of overcurrent or short circuit.
[0051] Reference Figure 1 The secondary winding of current transformer T7 is connected in series with the input terminal of rectifier bridge U1 through resistor R2. Specifically, resistor R2 limits the amplitude of the secondary current and achieves impedance matching to prevent rectifier bridge U1 from being damaged due to overload. After the secondary AC signal is adjusted by resistor R2, it is rectified by full wave at the input terminal of rectifier bridge U1, generating a pulsating DC signal at the output terminal. That is, resistor R2 balances the output characteristics of the transformer and converts the AC signal into a DC signal, providing a stable and processable current sampling reference for the subsequent overcurrent and short-circuit analysis unit.
[0052] Reference Figures 2-4 The first stage of the two-stage active low-pass filter includes an operational amplifier U2A, resistors R3 and R4, and capacitor C4. Resistor R3 connects the output of rectifier bridge U1 to the non-inverting input of operational amplifier U2A. Resistor R4 and capacitor C4 are connected in parallel and then connected across the output and inverting input of operational amplifier U2A.
[0053] Specifically, the pulsating DC signal output from rectifier bridge U1 is input to the non-inverting input of operational amplifier U2A via resistor R3. Through the parallel feedback network of resistor R4 and capacitor C4, an adjustable cutoff frequency filter path is formed to attenuate high-frequency noise in the rectified signal. At the same time, the amplitude of the low-frequency signal is increased by the amplification effect of operational amplifier U2A, and a smooth DC signal is generated at the output to ensure the accuracy of overcurrent and short-circuit detection.
[0054] Reference Figure 3 The second stage of the two-stage active low-pass filter consists of an operational amplifier U2B, resistor R5, resistor R6, and capacitor C5, and the connection method is the same as that of the first stage filter.
[0055] Specifically, the signal output from the first-stage filter is input to the non-inverting input of operational amplifier U2B via resistor R5. Through the parallel feedback network of resistor R6 and capacitor C5, a filtering path symmetrical to the first-stage filter is formed, which performs secondary attenuation on the residual high-frequency noise in the previous stage filtered signal. At the same time, the gain compensation of operational amplifier U2B improves the signal-to-noise ratio of the low-frequency signal, and a cleaner DC signal is generated at the output, providing a stable and reliable input reference for the subsequent high-speed comparators U3 and U4, ensuring that the threshold judgment of overcurrent and short-circuit detection is not affected by high-frequency interference.
[0056] Reference Figures 1-4 The voltage divider resistor network includes resistors R7 and R8 connected in series. One end of resistor R7 is connected to the output of rectifier bridge U1, and the other end is connected to resistor R8 and the non-inverting input of operational amplifier U2A. The other end of resistor R8 is grounded.
[0057] Specifically, the pulsating DC signal output from rectifier bridge U1 is divided by resistors R7 and R8 in series, forming a voltage signal with appropriate amplitude at their connection point, which is then input to operational amplifier U2A. This prevents the operational amplifier from saturating due to signal overload and provides an impedance-matched input interface for the two-stage active low-pass filters U2A / U2B, ensuring that the amplitude of the current sampling signal is accurately matched to the threshold judgment range of the subsequent comparators U3 / U4, thereby improving the reliability of overcurrent and short-circuit detection.
[0058] Reference Figure 4 The output terminals of high-speed comparators U3 and U4 are connected to the positive terminals of the LEDs of optocouplers U5 and U6 via current-limiting resistor R9 and resistor R10. The collectors of the output transistors of optocouplers U5 and U6 are connected to the input pins of the microcontroller MCU, and the emitters are grounded.
[0059] Specifically, the output signals of high-speed comparators U3 and U4, after having their drive current adjusted by current-limiting resistors R9 and R10, are input to the positive terminals of the LEDs of optocouplers U5 and U6. Through photoelectric conversion, the logic signal is isolated and transmitted to the collector of the transistor at the output of the optocoupler, and then connected to the input pin of the microcontroller MCU. Thus, the current-limiting resistor R9 and resistor R10 match the drive requirements of the optocouplers. The electrical isolation characteristics of optocouplers U5 / U6 are used to block the transmission of interference from the main circuit to the MCU side. At the same time, the high / low level of the fault status signal output by the comparator is converted into a clean logic signal that the MCU can recognize. This allows the MCU to quickly turn off the switching transistor through the drive terminal, realizing fully isolated protection control from fault detection to action execution, improving the system's anti-interference capability and response reliability.
[0060] Reference Figure 2 The bleeder resistor R1 has a resistance of 10kΩ-100kΩ and is connected in parallel across the filter capacitor C1. Specifically, by setting the resistance range of R1, a controllable discharge path is provided for the energy stored in the filter capacitor C1 when the system is powered off, avoiding safety hazards caused by residual charge in capacitor C1 leading to voltage stagnation at the output terminal. Together with safety capacitors C2 and C3, it forms a safety redundancy protection layer for the output unit.
[0061] Table 1 shows the overcurrent and short-circuit protection logic.
[0062]
[0063] Working principle: The inverter output unit outputs an AC signal through the switching transistor. Filter capacitor C1 and safety capacitors C2 and C3 filter out high-frequency noise. The discharge resistor R1 discharges residual charge, and the varistor RP1 suppresses surge voltage. The current transformer T7 collects the inverter output current in real time. The secondary winding signal is converted into DC voltage by the rectifier bridge U1. After the amplitude is adjusted by the voltage divider resistor network, it is input to the two-stage active low-pass filters U2A and U2B. The two-stage filtering eliminates interference and outputs a smooth DC signal to the high-speed comparators U3 and U4 for comparison with preset thresholds V1 and V2. When overcurrent or short circuit is detected, the comparator outputs a trigger signal, which is transmitted to the microcontroller MCU through optocouplers U5 and U6 for isolation. The MCU controls the switching transistor to turn off, realizing rapid fault cutoff and status locking.
[0064] Finally, it should be noted that the above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Although the present utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.
Claims
1. A protection circuit for overcurrent and short circuit in an inverter, characterized in that: include: The inverter output unit includes a switching transistor, a filter capacitor, a safety capacitor, a discharge resistor, and a varistor. The output terminal of the switching transistor is connected in sequence to the filter capacitor, the safety capacitor, and the discharge resistor. The varistor is connected in parallel to the inverter output terminal. The current sampling unit includes a current transformer and a rectifier bridge. The primary winding of the current transformer is connected in series in the inverter output circuit, and the secondary winding is connected to the input terminal of the rectifier bridge. The overcurrent and short-circuit analysis unit includes a two-stage active low-pass filter composed of operational amplifiers U2A and U2B and a high-speed comparator. The output of the rectifier bridge is connected to the input of the two-stage active low-pass filter through a voltage divider resistor network. The output of the two-stage active low-pass filter is connected to the non-inverting input of the high-speed comparator, and the inverting input of the high-speed comparator is connected to the high threshold voltage and the low threshold voltage, respectively. The protection execution unit includes an optocoupler and a microcontroller. The output of the high-speed comparator is connected to the input pin of the microcontroller after being isolated by the optocoupler.
2. The inverter overcurrent and short circuit protection circuit according to claim 1, characterized in that: In the inverter output unit, one end of the bleeder resistor is connected to the common node of the filter capacitor and the safety capacitor, and the other end is grounded. The two ends of the varistor are respectively connected to the positive and negative busbars of the inverter output terminal.
3. The inverter overcurrent and short circuit protection circuit according to claim 1, characterized in that: The secondary winding of the current transformer is connected in series with the input terminal of the rectifier bridge through resistor two.
4. The inverter overcurrent and short circuit protection circuit according to claim 1, characterized in that: The first stage filter in the two-stage active low-pass filter includes an operational amplifier U2A, resistor three, resistor four, and a capacitor. Resistor three is connected to the output terminal of the rectifier bridge and the non-inverting input terminal of the operational amplifier U2A. Resistor four and capacitor are connected in parallel and then connected across the output terminal and the inverting input terminal of the operational amplifier U2A.
5. The inverter overcurrent and short circuit protection circuit according to claim 4, characterized in that: The second-stage active low-pass filter consists of an operational amplifier U2B, resistors five and six, and a capacitor, and is connected in the same way as the first-stage filter.
6. The inverter overcurrent and short circuit protection circuit according to claim 1, characterized in that: The voltage divider resistor network includes resistors 7 and 8 connected in series. One end of resistor 7 is connected to the output terminal of the rectifier bridge, and the other end is connected to resistor 8 and the non-inverting input terminal of operational amplifier U2A. The other end of resistor 8 is grounded.
7. The inverter overcurrent and short circuit protection circuit according to claim 1, characterized in that: The output of the high-speed comparator is connected to the positive terminal of the LED of the optocoupler via current-limiting resistor 9 and resistor 10. The collector of the output transistor of the optocoupler is connected to the input pin of the microcontroller, and the emitter is grounded.
8. The inverter overcurrent and short circuit protection circuit according to claim 1, characterized in that: The first bleeder resistor has a resistance of 10kΩ-100kΩ and is connected in parallel across the filter capacitor.