A frequency converter bus overcurrent protection circuit

Abstract

The application belongs to the technical field of power electronics, and is especially a frequency converter bus overcurrent protection circuit; comprising sampling module, comparison and judgment module and signal shaping module which are electrically connected in sequence; the sampling module is used for collecting the frequency converter DC bus current and converting it into voltage sampling signal output; the comparison and judgment module is built-in fixed voltage reference threshold, receives the voltage sampling signal and compares it with the reference threshold in real time, and outputs the isolated fault level signal when the bus overflows; the signal shaping module receives the fault level signal, shapes the waveform, and then outputs the standard protection trigger signal to the frequency converter main control unit. The whole circuit is composed of three modules of sampling, comparison and shaping, the device selection is all conventional general devices, without complex control program and additional power supply, which reduces the design and manufacturing cost, realizes the real-time monitoring and fast protection trigger of the DC bus current through the hardware circuit, and has the advantages of real-time detection, fast response, compact structure and low cost.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, specifically to an overcurrent protection circuit for a frequency converter bus. Background Technology

[0002] In the actual operating environment of frequency converters, DC bus overcurrent faults are a frequent and highly destructive abnormal condition, with diverse triggering factors. On the one hand, when power semiconductor devices such as the inverter bridge arm IGBT module experience a short circuit, the DC bus current can surge rapidly to several times its rated value within microseconds, far exceeding the system's capacity. This not only causes fuse failure but also affects critical components such as bus connecting wires, rectifier bridge structure, and filter capacitor banks. In severe cases, it can lead to catastrophic consequences such as permanent breakdown of the IGBT module, carbonization of the printed circuit board substrate, or even open flame combustion. On the other hand, external load surges (such as mechanical transmission system jamming or conveyor belt slippage), internal motor faults (including short circuits caused by broken inter-turn insulation in the windings), aging power supply lines (such as leakage current caused by deteriorated cable insulation), and defects in the control system itself (including inaccurate current detection circuitry and disordered drive signal timing) can all trigger abnormal increases in bus current, thereby activating the overcurrent protection mechanism. The consequences of such faults vary significantly. In mild cases, they can force the inverter to shut down and interrupt the production line. In severe cases, they can damage core power devices, paralyze the electrical system, and even threaten the safety of operators. The resulting equipment replacement costs and production stoppage losses are considerable. Therefore, building an efficient and reliable bus overcurrent protection mechanism has become a core aspect of inverter product development.

[0003] In current industrial applications, inverter bus overcurrent protection mainly employs two technical approaches: software protection and hardware protection. However, both have inherent drawbacks that are difficult to reconcile, failing to simultaneously meet the comprehensive requirements of protection performance, economy, and structural compactness. Software protection schemes rely on the computing power of the main control chip, periodically acquiring analog signals output from the current detection circuit via an analog-to-digital converter. After digital processing, these signals are logically compared with preset thresholds to ultimately determine the triggering of protection actions. The fatal flaw of this method lies in the time delay introduced by the signal processing flow. In extreme fault scenarios with a sudden surge in bus current, the protection response lags behind the fault development speed, failing to promptly stop the continuous expansion of the fault current, causing vulnerable power devices such as IGBTs to lose effective protection. Simultaneously, software protection continuously consumes the main control chip's computing resources, potentially interfering with the real-time execution of the inverter's core control algorithm under complex operating conditions, reducing the overall system stability.

[0004] While hardware protection solutions offer advantages such as fast response speed and independence from main control resources, current implementations still face multiple technical bottlenecks. The primary issue lies in the selection of detection components. Most solutions rely on DC current sensors as the front-end sampling unit. These sensors not only have high procurement costs, but their physical dimensions (especially the magnetic aperture) must increase with the expansion of the detection current range, directly restricting the miniaturization design of the overall inverter structure and contradicting the urgent market demand for compact, low-cost products in the low-voltage inverter market. Secondly, some hardware circuit topologies are overly complex, involving additional control logic units and high-power switching devices, significantly increasing circuit design difficulty and material costs, while also increasing potential failure points. Thirdly, some protection circuits require independent auxiliary power supplies to maintain operation, which not only complicates the power supply architecture but also introduces the risk of protection function failure due to power supply anomalies. Fourthly, some solutions use fuses connected in series with the bus or dedicated IGBT protection modules. The former requires manual replacement after a fault to restore operation, significantly increasing maintenance cycles and costs, while the latter increases overall size and price due to the need for drive circuits and cooling systems, and cannot cover short-circuit faults in the inverter's standby state. Furthermore, protection circuits based on inverse time-limit characteristics are implemented using Hall elements in conjunction with operational amplifiers and rectifier circuits, requiring a large number of components, resulting in a crowded circuit layout, reduced reliability, and further increased manufacturing costs.

[0005] As industrial automation equipment continues to evolve towards miniaturization, cost-effectiveness, and high robustness, the shortcomings of existing frequency converter bus overcurrent protection technology in terms of dynamic response characteristics, circuit integration, cost control capabilities, physical space occupation, and fault coverage are becoming increasingly prominent. It is difficult to meet the stringent requirements of modern industrial scenarios for protection systems in terms of instantaneous response capability, accurate judgment level, and economic efficiency throughout the entire life cycle.

[0006] Therefore, we propose an inverter bus overcurrent protection circuit to solve the above problems. Summary of the Invention

[0007] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a frequency converter bus overcurrent protection circuit, which has the advantages of real-time detection, fast response, compact structure, and low cost, thus solving the problems mentioned in the background art.

[0008] (II) Technical Solution To achieve the above objectives, the present invention specifically adopts the following technical solution: A frequency converter bus overcurrent protection circuit includes a sampling module, a comparison and judgment module and a signal shaping module connected in sequence. The sampling module is used to collect the DC bus current of the frequency converter and convert it into a voltage sampling signal output. The comparison and judgment module has a built-in fixed voltage reference threshold, receives the voltage sampling signal and compares it with the reference threshold in real time, and outputs an isolated fault level signal when the bus is overcurrent. The signal shaping module receives the fault level signal, shapes the waveform, and outputs a standard protection trigger signal to the inverter main control unit.

[0009] Furthermore, the sampling module includes multiple parallel sampling resistors, a clamping protection diode D2, and an operational amplifier unit; multiple sets of sampling resistors are connected in series in the DC bus circuit of the frequency converter to collect the bus current, and the clamping protection diode is connected in parallel at the output terminal of the sampling resistor to limit the sampling voltage amplitude. The current signal output by the sampling resistor is proportionally amplified by the operational amplifier unit to output a voltage sampling signal.

[0010] Furthermore, the multi-parallel sampling resistors include RA1, RA2, RA3, and RA4, which are connected in parallel to form an equivalent sampling resistor R; the operational amplifier unit adopts a dual-channel operational amplifier U4B, and the output voltage of the operational amplifier unit satisfies the relationship: Vout=I×R×(R11 / R9), where I is the actual DC bus current, and R9 and R11 are the voltage divider feedback resistors matched to the operational amplifier unit.

[0011] Furthermore, the clamping protection diode is an LBAV99 high-speed diode. The bidirectional clamping of the diode limits the sampling input voltage to ±0.7V, blocks instantaneous overvoltage surges, and prevents the subsequent operational amplifier from being damaged. The sampling module is also equipped with filter capacitors C6, C7, and C12 to filter out high-frequency noise interference from the bus.

[0012] Furthermore, the comparison and judgment module includes a reference voltage generation unit, a voltage comparison unit, a voltage regulation clamping unit, and a high-speed isolation optocoupler unit; the reference voltage generation unit outputs a constant threshold voltage to supply the voltage comparison unit, the voltage comparison unit compares the sampled voltage with the threshold voltage and outputs a comparison level, the voltage regulation clamping unit limits the output level of the comparison unit, and the high-speed isolation optocoupler unit isolates the transmission of the comparison level and outputs a fault level signal.

[0013] Furthermore, the reference voltage generating unit includes a TL431 reference chip U3, a current-limiting resistor R1, and an anti-surge fast recovery diode D1; the current-limiting resistor R1 is connected in series between the power supply terminal and the input terminal of U3 to limit the operating current of the reference branch; the anti-surge fast recovery diode D1 is connected in reverse parallel to the power supply input terminal of U3 to suppress the +VNP high voltage surge at the moment of power-on, and U3 stably outputs a 2.5V reference voltage as the overcurrent judgment threshold; The voltage comparison unit uses a dual-channel operational amplifier U4A to form a voltage comparator; the voltage regulation clamping unit uses a 5.1V Zener diode Z1, the Zener diode Z1 model is LMBZ5231BLTIG, Z1 is connected in parallel to the output terminal of U4A, and clamps the output voltage of U4A to 5.1V under normal bus current conditions. The high-speed isolation optocoupler unit is a 6N137 high-speed optocoupler U1. The primary end of the optocoupler is connected to the output of U4A and the reference ground respectively. The secondary end of the optocoupler is equipped with a pull-up resistor R3 connected to a +5V power supply. When the sampling module outputs Vout > 2.5V, U4A outputs a low level, the primary end of the optocoupler forms a voltage difference and conducts, and the secondary end outputs a low-level fault signal. When Vout < 2.5V, the output of U4A is clamped to 5.1V by Z1, the primary end of the optocoupler is cut off without voltage difference, and the secondary end maintains a high-level normal signal. The comparison and judgment module is also equipped with filter capacitors C1, C2, and C5 to stabilize the reference voltage and the comparison input signal.

[0014] Furthermore, the signal shaping module includes a Schmitt trigger, an input current-limiting resistor, and a filter capacitor; the current-limiting resistor is connected in series at the input of the shaping module to receive the fault level signal output by the comparison and judgment module; the Schmitt trigger shapes the output waveform of the optocoupler that has jitter and edge distortion, and outputs a regular rectangular wave standard protection trigger signal.

[0015] Furthermore, the Schmitt trigger U2 adopts a dual-channel inverting Schmitt chip AIP74LVC2G14; the current-limiting resistor is R6, and the filter capacitors include C3 and C4 connected in parallel between the input pin of the trigger and ground; the Vo level output by the optocoupler is current-limited by R6 and sent to the input terminal of the Schmitt trigger, and the output terminal of the trigger outputs the shaped VCE level to the main control DSP of the frequency converter.

[0016] Furthermore, the circuit is suitable for detecting and protecting against various bus overcurrent faults, including inverter standby short circuit, IGBT shoot-through short circuit, motor load jamming, and winding inter-turn short circuit. The circuit adopts a layout of small SOT23 packaged devices and has no large-aperture current sensors, thus reducing the overall installation size of the inverter.

[0017] (III) Beneficial Effects Compared with the prior art, the present invention provides an inverter bus overcurrent protection circuit, which has the following advantages: This invention includes a sampling module, a comparison and judgment module, and a signal shaping module connected in sequence. The sampling module is used to collect the DC bus current of the frequency converter and convert it into a voltage sampling signal output. The comparison and judgment module has a built-in fixed voltage reference threshold, receives the voltage sampling signal and compares it with the reference threshold in real time, and outputs an isolated fault level signal when the bus is overcurrent. The signal shaping module receives the fault level signal, shapes the waveform and outputs a standard protection trigger signal to the main control unit of the frequency converter. The real-time monitoring and rapid protection triggering of the DC bus current are realized through hardware circuitry, which has the advantages of real-time detection, fast response, compact structure and low cost. Attached Figure Description

[0018] Figure 1 This is the circuit schematic diagram of the present invention; Figure 2 This is a schematic diagram of the sampling circuit of the present invention; Figure 3 This is a schematic diagram of the comparator circuit of the present invention; Figure 4 This is a schematic diagram of the shaping circuit of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example Traditional overcurrent protection solutions for frequency converter buses, whether software-based or hardware-based, suffer from problems such as insufficient response speed, high consumption of main control resources, high hardware costs, large structural size, complex circuit design, and the need for auxiliary power supplies. These shortcomings make it difficult to meet the multiple demands of industrial production for frequency converter protection performance, cost control, and miniaturization.

[0021] In this regard, such as Figure 1-4 As shown, this application proposes a bus overcurrent protection circuit for a frequency converter, which includes a sampling module, a comparison and judgment module, and a signal shaping module connected in sequence. The sampling module is used to collect the DC bus current of the frequency converter and convert it into a voltage sampling signal output. The comparison and judgment module has a built-in constant voltage reference threshold, receives the voltage sampling signal and compares it with the reference threshold in real time, and outputs an isolated fault level signal when the bus is overcurrent. The signal shaping module receives the fault level signal, shapes the waveform and outputs a standard protection trigger signal to the main control unit of the frequency converter.

[0022] The core of the inverter bus overcurrent protection circuit in this embodiment lies in the sequentially electrically connected sampling module, comparison and judgment module, and signal shaping module. This modular design ensures the logicality and efficiency of signal processing, and the smooth transmission of signals between the modules through electrical connections, working together to complete the overcurrent protection function.

[0023] The sampling module is used to acquire the DC bus current of the frequency converter and convert it into a voltage sampling signal output. One implementation method is to connect a small-value sampling resistor in series in the DC bus circuit. When current flows through this resistor, a voltage drop proportional to the current is generated across it. This voltage drop can be directly output as a voltage sampling signal, or buffered by a voltage follower before output. Another implementation method is to use a current transformer or Hall element (not involving a Hall current sensor) to sense the bus current and convert it into a voltage signal.

[0024] The comparison and judgment module has a built-in constant voltage reference threshold. It receives the voltage sampling signal and compares it with the reference threshold in real time. When there is an overcurrent on the bus, it outputs an isolated fault level signal. Specifically, a conventional voltage comparator can be used. One input is connected to the voltage sampling signal output by the sampling module, and the other input is connected to a constant reference voltage generated by a Zener diode or a voltage divider resistor network. When the amplitude of the voltage sampling signal exceeds the constant reference voltage, the comparator output state flips, indicating an overcurrent event. To achieve electrical isolation, the comparator's output signal can drive the input of a conventional optocoupler, transmitting the fault information to the optocoupler's output via optical signal transmission, thereby generating an isolated fault level signal.

[0025] The signal shaping module receives the fault level signal, shapes the waveform, and outputs a standard protection trigger signal to the inverter's main control unit.

[0026] The inverter bus overcurrent protection circuit in this embodiment, through a hardware-based modular design, achieves rapid, real-time monitoring and judgment of the inverter's DC bus current. This solution effectively avoids the response lag problem of software protection and eliminates the need for complex current sensors or power switching devices, effectively reducing hardware costs and circuit size. Simultaneously, it simplifies the circuit topology, eliminates the need for auxiliary power supplies, improves system stability, and enables rapid response to various bus overcurrent faults, providing immediate protection for the inverter's core power devices.

[0027] This application further proposes a sampling module for an inverter bus overcurrent protection circuit, which includes multiple parallel sampling resistors, a clamping protection diode D2, and an operational amplifier unit. Specifically, multiple sets of sampling resistors are connected in series in the inverter DC bus circuit to collect the bus current, and the clamping protection diode D2 is connected in parallel at the output terminal of the sampling resistor to limit the sampling voltage amplitude. The current signal output by the sampling resistor is proportionally amplified by the operational amplifier unit to output a voltage sampling signal.

[0028] Among them, the multi-parallel sampling resistor is a key component used to convert the current signal flowing through the DC bus of the frequency converter into a voltage signal. Its resistance accuracy, temperature stability, and power handling capacity directly affect the sampling accuracy. The multi-parallel structure aims to distribute the current flowing through individual resistors, thereby reducing the power consumption and temperature rise of individual resistors and improving the overall power capacity and long-term stability of the sampling resistors. Furthermore, the parallel structure provides redundancy; even if one resistor fails, the others can continue to operate, ensuring sampling reliability. In practical applications, multiple low-resistance, high-precision surface-mount resistors (e.g., 0.01 ohms, 1% accuracy) can be connected in parallel to achieve the required equivalent sampling resistance value; for example, two, three, or more resistors can be connected in parallel. Alternatively, a specially designed current sampling resistor array can be used, which integrates multiple parallel resistors and optimizes heat dissipation and matching characteristics to provide a more compact and stable sampling solution.

[0029] The main function of the clamping protection diode D2 is to limit the voltage signal at the output of the sampling resistor, preventing its amplitude from exceeding the safe range. When an overcurrent or transient surge occurs on the inverter bus, the voltage across the sampling resistor may rise instantaneously, far exceeding the input withstand voltage range of the subsequent operational amplifier unit. By connecting the clamping diode D2 in parallel, the excessively high voltage can be clamped to a preset safe level, effectively protecting the sensitive subsequent operational amplifier unit from overvoltage damage and ensuring the long-term reliability of the circuit. For example, a pair of anti-parallel ordinary Schottky diodes or fast recovery diodes can be used. These have low forward conduction voltages and can quickly conduct when the voltage exceeds a certain threshold, clamping the voltage within the range of approximately ±0.3V to ±0.7V. Alternatively, transient voltage suppressors (TVS diodes) or Zener diodes can be selected. These devices have faster response speeds and higher energy absorption capabilities, more effectively absorbing transient overvoltage spikes and clamping the voltage near a specific Zener voltage or breakdown voltage.

[0030] The operational amplifier unit (OAB) amplifies the weak current signal output from the sampling resistor, converting it into a standard voltage sampling signal suitable for processing by the subsequent comparison and judgment module. Since the sampling resistor typically has a very small resistance, the voltage signal across it may be too weak to directly drive the comparator. The OAB, with its high input impedance, low output impedance, and controllable gain, not only amplifies the signal to a usable level but also provides good signal isolation and driving capability, while effectively suppressing common-mode noise and improving the signal-to-noise ratio and stability.

[0031] Through the above technical solutions, the sampling module can efficiently, safely, and accurately acquire the DC bus current of the frequency converter. The design of multiple parallel sampling resistors effectively disperses the current, reduces the power consumption and thermal drift of individual resistors, significantly improves the stability and long-term reliability of current sampling, and provides redundant protection. The introduction of clamping protection diode D2 can quickly limit the sampling voltage to a safe range when the bus current fluctuates abnormally or there is a momentary overvoltage, thereby effectively protecting the subsequent operational amplifier unit from damage caused by overvoltage surges and greatly enhancing the robustness and shock resistance of the circuit. The operational amplifier unit accurately amplifies the weak sampling signal and converts it into a standard voltage sampling signal. This not only achieves signal level matching but also provides accurate and reliable input to the subsequent comparison and judgment module through its excellent driving capability and anti-interference characteristics, ensuring the accuracy and fast response of the entire overcurrent protection logic. This effectively solves the technical challenges of accurate bus current acquisition, overvoltage protection, and signal stability.

[0032] This application further proposes that the multi-parallel sampling resistors include RA1, RA2, RA3, and RA4, which are connected in parallel to form an equivalent sampling resistor R; the operational amplifier unit adopts a dual-channel operational amplifier U4B, and the output voltage of the operational amplifier unit satisfies the relationship: Vout=I×R×(R11 / R9), where I is the actual DC bus current, and R9 and R11 are the voltage divider feedback resistors matched to the operational amplifier unit.

[0033] Specifically, the design of multiple parallel sampling resistors aims to effectively reduce the power loss and temperature rise of individual resistors by distributing the current paths, thereby improving the overall power handling capacity and long-term stability of the sampling resistors. Furthermore, by connecting multiple resistors in parallel, a finer equivalent resistance value can be achieved, improving the accuracy of current sampling.

[0034] The operational amplification unit plays a key role in the sampling module by amplifying weak current sampling signals and performing impedance transformation. The use of the dual-channel operational amplifier U4B not only integrates two independent amplification channels in a single chip, thus saving circuit board space and simplifying power management, but also allows one channel to be used for precise amplification of current signals, while the other channel can be used for other auxiliary functions, such as buffering, filtering, or constructing a differential amplifier. In addition to dual-channel operational amplifiers, single-channel or four-channel operational amplifiers can also be selected according to design requirements, or dedicated current sense amplifiers with specific low-noise, high-precision or wide-bandwidth characteristics can be adopted to meet performance requirements in different application scenarios.

[0035] The output voltage of the operational amplification unit satisfies the relational expression: Vout=I×R×(R11 / R9), where I is the actual current of the DC bus, and R9 and R11 are the voltage division feedback resistors supporting the operational amplification unit. This relational expression clarifies the linear proportional relationship by which the operational amplification unit converts the actual DC bus current I into the voltage sampling signal Vout. Here, I×R represents the voltage drop generated when current flows through the equivalent sampling resistor R, which is the original current sampling signal. Through the operational amplifier U4B and its supporting voltage division feedback resistors R9 and R11, this voltage drop is precisely amplified, and the amplification factor is determined by the ratio of R11 / R9. This configuration is usually implemented by constructing a non-inverting amplifier or differential amplifier circuit, ensuring a high degree of linearity between the output voltage Vout and the input current I. By precisely selecting the resistance values of R9 and R11, the amplification factor can be flexibly adjusted so that the amplitude of Vout can adapt to the input range of the subsequent comparison and judgment module, while maintaining high precision and low drift.

[0036] Through the above technical solutions, the present application adopts multiple parallel sampling resistors RA1, RA2, RA3, RA4 to form the equivalent sampling resistor R, which effectively disperses the thermal effect of current, improves the power withstand capability and stability of the sampling resistors, and ensures the accuracy of the sampling resistors. On this basis, the dual-channel operational amplifier U4B is used as the operational amplification unit, combined with the precisely configured voltage division feedback resistors R9 and R11, to realize linear proportional amplification of the sampling signal. This design makes the output voltage Vout of the operational amplification unit and the actual DC bus current I strictly follow the linear relationship of Vout=I×R×(R11 / R9). This precise current-voltage conversion mechanism not only solves the problem of realizing high-precision current signal conversion through discrete components, but also ensures the linearity and accuracy of the sampling signal, provides a reliable and stable voltage sampling signal for the subsequent comparison and judgment module, thereby significantly improving the detection accuracy and response reliability of the entire frequency converter bus overcurrent protection circuit.

[0037] This application further proposes that the clamping protection diode is selected as the LBAV99 high-speed diode. The bidirectional clamping of the diode limits the sampling input voltage to ±0.7V, blocks instantaneous overvoltage surges, and prevents the subsequent operational amplifier from being damaged. The sampling module is also equipped with filter capacitors C6, C7, and C12 to filter out high-frequency noise interference from the bus.

[0038] Specifically, in this application, the clamping protection diode D2 is an LBAV99 high-speed diode, a small-signal Schottky diode with extremely fast switching speed and low forward voltage drop. Its high-speed response characteristics enable it to react quickly to transient overvoltage pulses, effectively suppressing voltage spikes. Furthermore, its bidirectional clamping capability means it can limit the voltage in both forward and reverse directions, ensuring that the sampled input voltage does not exceed the safe range in either direction. Bidirectional clamping means the diode can limit the voltage in both forward and reverse directions. When the input voltage exceeds the forward conduction voltage (typically around 0.7V), the diode conducts forward, clamping the voltage to approximately 0.7V; when the input voltage is below the reverse breakdown voltage (or conducts forward through a diode connected in reverse parallel), the voltage is clamped to approximately -0.7V. This ±0.7V limiting range effectively protects the subsequent operational amplifier, as most operational amplifiers typically allow a voltage range between the power rails at their inputs and have limited tolerance to transient overvoltages. Transient overvoltage surges refer to short-duration high-voltage pulses generated in circuits due to switching actions, inductive load switching, or external interference. The amplitude of these pulses may far exceed the normal operating voltage. If applied directly to the input of sensitive devices such as operational amplifiers, it can cause internal PN junction breakdown, resulting in permanent damage. By clamping the voltage within a safe range using the protection diode D2, these overvoltage energies can be effectively absorbed and dissipated, thus protecting the operational amplifier.

[0039] Meanwhile, filter capacitors C6, C7, and C12 are passive devices used to filter out high-frequency noise and ripple in the circuit. They are usually connected in parallel on the signal path or power line, utilizing their capacitive reactance to decrease with increasing frequency to provide a low-impedance path for high-frequency signals, allowing them to flow to ground or bypass, thus enabling low-frequency or DC signals to pass. In addition to single capacitors, composite filter networks such as LC filters and RC filters can be used, or combinations of capacitors with different media (such as ceramic capacitors and electrolytic capacitors) and capacitances can be used to achieve a wider frequency range or higher filtering efficiency. During the operation of the inverter's DC bus, the high-frequency switching action of power devices such as IGBTs generates a large amount of high-frequency harmonics and electromagnetic interference. These high-frequency noises are superimposed on the DC bus current signal, causing distortion and fluctuation in the sampling signal, which in turn affects the accuracy of subsequent comparison and judgment modules. By configuring filter capacitors C6, C7, and C12, these high-frequency noises can be effectively bypassed, ensuring that the sampling signal entering the operational amplifier unit is purer and more stable.

[0040] By introducing the LBAV99 high-speed diode D2 for bidirectional clamping protection, the sampling input voltage can be precisely limited to a safe range of ±0.7V. This mechanism can quickly respond to and effectively block instantaneous overvoltage surges generated on the inverter bus during switching or faults, physically protecting the downstream operational amplifier unit from breakdown damage and significantly improving the sampling module's withstand voltage and long-term operational stability. Simultaneously, by configuring filter capacitors C6, C7, and C12 in the sampling module, high-frequency noise interference generated by IGBT high-frequency switching on the DC bus can be effectively filtered out. This ensures that the current sampling signal entering the operational amplifier unit is pure and stable, avoiding sampling signal fluctuations and distortions caused by noise, thereby improving the accuracy of the overcurrent judgment threshold. In summary, the inverter bus overcurrent protection circuit of this application exhibits stronger robustness and reliability in complex electromagnetic environments, ensuring timely and accurate triggering of protection actions under real overcurrent conditions, effectively preventing false triggering or protection failure, and thus ensuring the safe operation of the inverter and related equipment.

[0041] This application further proposes that the comparison and judgment module includes a reference voltage generation unit, a voltage comparison unit, a voltage stabilization clamping unit, and a high-speed isolation optocoupler unit; the reference voltage generation unit outputs a constant threshold voltage to supply the voltage comparison unit, the voltage comparison unit compares the sampled voltage with the threshold voltage and outputs a comparison level, the voltage stabilization clamping unit limits the output level of the comparison unit, and the high-speed isolation optocoupler unit isolates the transmission of the comparison level and outputs a fault level signal.

[0042] The reference voltage generation unit provides a stable and accurate reference voltage as a threshold for determining whether the bus is overcurrent. Its implementation can include, but is not limited to: using a high-precision reference voltage chip, such as TL431 or LM4040, to generate a stable output voltage through an internal voltage regulator circuit; or using a Zener diode in conjunction with a resistor divider network to provide a relatively stable reference voltage even when the power supply voltage fluctuates.

[0043] The voltage comparison unit receives the voltage sampling signal from the sampling module and compares it in real time with the threshold voltage provided by the reference voltage generation unit. This unit is typically implemented by configuring an operational amplifier in comparator mode.

[0044] The voltage clamping unit limits the output level of the voltage comparator unit to prevent it from becoming too high or too low, thereby protecting subsequent circuits from overvoltage surges and ensuring signal level compatibility. This unit can be implemented using a Zener diode, a transient voltage suppressor diode (TVS), or a clamping circuit composed of ordinary diodes and resistors.

[0045] The high-speed isolation optocoupler unit is used to achieve electrical isolation transmission of the comparison level, effectively isolating the high-voltage circuit on the DC bus side of the frequency converter from the low-voltage control circuit of the main control unit.

[0046] Through the above technical solution, the comparison and judgment module constructs a complete logic link including reference generation, comparison and judgment, amplitude limiting protection, and electrical isolation, achieving accurate capture and safe reporting of bus overcurrent status. The reference voltage generation unit provides a constant threshold voltage, providing a stable judgment benchmark for the voltage comparison unit, ensuring the accuracy of overcurrent judgment and avoiding malfunctions caused by reference voltage drift. The voltage comparison unit receives the sampled voltage and compares it with the reference voltage in real time, converting the analog current sampling signal into a logic level signal, thereby achieving rapid response to overcurrent status. The voltage clamping unit limits the output level of the comparison unit, effectively preventing excessively high comparator output voltage from damaging subsequent circuits, ensuring signal level compatibility and safety during transmission. The high-speed isolation optocoupler unit transmits the comparison level through electrical isolation, cutting off the electrical connection between the power circuit and the control circuit, effectively blocking high-voltage interference or transient impacts on the bus side, ensuring that fault level signals can be stably and reliably transmitted to the inverter main control unit, thereby improving the anti-interference capability and system safety of the entire protection circuit. Overall, this comparison and judgment module significantly enhances the stability and reliability of the circuit while ensuring a fast response, effectively avoiding the risks of false triggering and protection failure, and providing safe and accurate overcurrent fault information for the inverter's main control unit.

[0047] This application further proposes an overcurrent protection circuit for a frequency converter bus, wherein the reference voltage generation unit of the comparison and judgment module includes a TL431 reference chip U3, a current-limiting resistor R1, and an anti-surge fast recovery diode D1. The reference voltage generation unit is a circuit module used to provide a stable and accurate voltage reference, its function being to provide a reliable reference point for subsequent voltage comparison, ensuring the accuracy of overcurrent judgment. Besides using a precision shunt reference source such as the TL431, it can also be implemented using a Zener diode with resistor voltage division, or an integrated voltage regulator outputting a fixed voltage. The TL431 reference chip U3 is a programmable precision parallel voltage regulator, which internally contains a high-precision voltage reference and comparator, capable of providing a stable output voltage. The current-limiting resistor R1 is connected in series between the power supply terminal and the input terminal of U3 to limit the operating current flowing through the reference branch, protecting the reference chip U3 from excessive current surges and ensuring its operation within the normal operating current range. Besides a fixed resistor, an adjustable resistor can be used for fine-tuning, or a constant current source circuit can be used to provide a stable operating current. A fast recovery diode D1 is connected in reverse parallel to the power supply input of U3 to suppress the high voltage surge at +VNP during power-on, protecting the reference chip U3 from transient overvoltage damage. Besides the fast recovery diode, a transient voltage suppressor diode (TVS) or an RC snubber circuit can also be used to achieve similar protection. With this configuration, U3 can stably output a 2.5V reference voltage as the overcurrent detection threshold.

[0048] The voltage comparator unit uses a dual-channel operational amplifier U4A to construct a voltage comparator. A voltage comparator unit is a circuit used to compare the magnitudes of two input voltages and output corresponding logic levels. Its core function is to determine whether an overcurrent event has occurred based on the relative magnitude of the sampled voltage and the reference voltage. Besides using an operational amplifier configured in comparator mode, a dedicated voltage comparator integrated circuit can also be used. Operational amplifier U4A can be used as a voltage comparator in open-loop or high-gain closed-loop states. When there is a slight difference between its two input voltages, the output quickly switches to the power rail or ground level, thus achieving the voltage comparison function. The voltage clamping unit uses a 5.1V Zener diode Z1, connected in parallel to the output of U4A, clamping the U4A output voltage to 5.1V under normal bus current conditions. A voltage clamping unit is a circuit used to limit the voltage in a circuit within a specific range. Its function is to prevent excessively high or low voltages, protect subsequent circuits, and ensure signal level stability. Besides using Zener diodes, limiting diodes, TVS diodes, or active clamping circuits can also be used. The 5.1V Zener diode Z1 is a diode that uses the Zener breakdown effect to maintain a relatively constant voltage across its terminals. When the reverse voltage reaches its Zener voltage, it will conduct and maintain that voltage, thereby achieving voltage regulation or clamping function.

[0049] The high-speed isolation optocoupler unit is the 6N137 high-speed optocoupler U1. A high-speed isolation optocoupler unit is a device that achieves electrical signal isolation transmission through optical signals. Its function is to transmit fault signals from the high-voltage side to the low-voltage side under the premise of electrical isolation, protecting the main control unit from high-voltage surges and preventing common-mode interference. Besides optocouplers, digital isolators can also be used to achieve high-speed isolation transmission. The 6N137 high-speed optocoupler U1 is an optocoupler with high transmission rate and good common-mode rejection ratio. It uses a combination of light-emitting diodes and phototransistors to convert the input electrical signal into an optical signal, and then back into an electrical signal, achieving electrical isolation between input and output. The primary terminals of the optocoupler are connected to the output terminal of U4A and the reference ground, respectively. The secondary terminal of the optocoupler is equipped with a pull-up resistor R3 connected to a +5V power supply. The pull-up resistor R3 is a resistor connected to the power supply voltage, used to pull the signal line to a high level when there is no other driving source, ensuring that the secondary terminal of the optocoupler outputs a high level when not conducting, meeting the logic level requirements. When the sampling module outputs Vout > 2.5V, U4A outputs a low level, the primary side of the optocoupler forms a voltage difference and conducts, and the secondary side outputs a low-level fault signal. When Vout < 2.5V, the U4A output is clamped to 5.1V by Z1, the primary side of the optocoupler is cut off due to no voltage difference, and the secondary side maintains a high-level normal signal. In addition, the comparison and judgment module is equipped with filter capacitors C1, C2, and C5 to stabilize the reference voltage and the comparison input signal. These filter capacitors are used to filter out high-frequency noise and ripple in the circuit, stabilize the power supply voltage and signal input, and prevent interference-induced misjudgments. Besides ordinary ceramic capacitors, electrolytic capacitors, tantalum capacitors, or film capacitors can also be used, and different capacitance values ​​and quantities can be configured according to filtering requirements.

[0050] Through the above technical solutions, the comparison and judgment module of this application can effectively solve key technical challenges such as reference voltage stability, power-on surge suppression, fault signal isolation transmission, and accurate output level switching. Specifically, the reference voltage generation unit uses a TL431 reference chip U3, combined with a current-limiting resistor R1 and a surge-resistant fast recovery diode D1, ensuring the long-term stability and high accuracy of the overcurrent judgment threshold of 2.5V. Simultaneously, D1 effectively suppresses the high-voltage surge that may be generated by the +VNP bus voltage at the moment of inverter power-on, protecting the reliability of the reference circuit. The voltage comparison unit uses a dual-channel operational amplifier U4A as a comparator, which can quickly respond to the comparison result between the voltage sampling signal Vout output by the sampling module and the 2.5V reference voltage. The 5.1V Zener diode Z1 in the voltage clamping unit accurately clamps the output voltage of U4A to 5.1V under normal bus current conditions, avoiding output level drift or uncertainty and ensuring stable output of normal signals. The high-speed isolation optocoupler unit uses a 6N137 high-speed optocoupler U1, achieving electrical isolation between the fault signal and the inverter main control unit. When an overcurrent occurs (Vout > 2.5V), U4A outputs a low level, the primary winding of optocoupler U1 conducts, and the secondary winding outputs a low-level fault signal. When there is no overcurrent (Vout < 2.5V), the output of U4A is clamped to 5.1V by Z1, the primary winding of optocoupler U1 is cut off, and the secondary winding maintains a high-level normal signal. This isolated transmission method effectively blocks interference and potential damage risks from the high-voltage side, greatly improving the safety and reliability of the entire protection circuit. Furthermore, the configured filter capacitors C1, C2, and C5 further stabilize the reference voltage and comparison input signal, effectively filtering out high-frequency noise interference and ensuring the accuracy and anti-interference capability of the comparison judgment. Overall, this comparison judgment module, through ingenious component combination and circuit design, achieves fast, accurate, safe, and highly reliable hardware judgment and signal output for inverter bus overcurrent faults without the need for complex software logic. It provides timely and effective protection trigger signals for the inverter's main control unit, significantly improving the inverter's operational stability and safety.

[0051] This application further proposes an inverter bus overcurrent protection circuit, wherein the signal shaping module includes a Schmitt trigger, an input current limiting resistor and a filter capacitor; the current limiting resistor is connected in series at the input terminal of the shaping module to receive the fault level signal output by the comparison and judgment module; the Schmitt trigger shapes the output waveform of the optocoupler that has jitter and edge distortion, and outputs a regular rectangular wave standard protection trigger signal.

[0052] Specifically, in this application, the signal shaping module aims to receive the fault level signal from the comparison and judgment module, process it to eliminate noise, jitter, and distortion in the signal, and finally output a standard and regular protection trigger signal. Besides a Schmitt trigger, the signal shaping module can also employ a comparator-based shaping circuit, which converts the analog signal into a digital signal using a high-precision comparator and sets an appropriate threshold to eliminate noise; or it can employ a digital logic gate-based shaping circuit, which combines logic gates with a delay circuit to achieve sharpening of signal edges and suppression of jitter.

[0053] In this application, a Schmitt trigger is used to shape the optocoupler output waveform, which may contain jitter and edge distortion, from the comparison and judgment module, converting it into a regular rectangular wave. The Schmitt trigger can be constructed using discrete components such as transistors, resistors, and capacitors, or it can utilize various commercially available integrated Schmitt trigger chips, such as CMOS or TTL series Schmitt inverters.

[0054] In this application, an input current-limiting resistor is connected in series at the input terminal of the shaping module to limit the current entering the shaping module from the fault level signal output by the comparison and judgment module, thereby protecting subsequent circuit components such as the Schmitt trigger from excessive current surges. The input current-limiting resistor can be a fixed value resistor, or, in scenarios requiring debugging or adaptation to different input sources, an adjustable resistor can be used to precisely adjust the current-limiting value.

[0055] In this application, the filter capacitor works in conjunction with the input current-limiting resistor to filter out high-frequency noise interference that may be mixed into the fault level signal, providing a cleaner input signal for the Schmitt trigger and improving the shaping effect. The filter capacitor can be a ceramic capacitor, suitable for high-frequency filtering, or an electrolytic capacitor or tantalum capacitor, suitable for low-frequency filtering or power supply decoupling.

[0056] A current-limiting resistor is connected in series at the input of the shaping module to receive the fault level signal output by the comparison and judgment module. This connection method ensures that the current is effectively limited before the fault level signal enters the shaping module. This not only protects the sensitive components inside the shaping module from overcurrent damage but also provides stable input conditions for subsequent filtering and shaping. The current-limiting resistor can be directly connected in series between the output pin of the comparison and judgment module and the input pin of the shaping module, or in a modular design, it can be integrated into the connector or interface circuit.

[0057] Schmitt triggers shape the output waveform of optocouplers that suffer from jitter and edge distortion. As isolation devices, optocouplers are susceptible to interference during transmission, resulting in jitter and edge distortion, which degrades signal quality. Schmitt triggers, utilizing their inherent hysteresis characteristics, effectively "clean up" these irregular signals. When the input signal changes slowly or contains noise, the Schmitt trigger does not repeatedly toggle around its threshold; instead, it only transitions when the signal amplitude clearly crosses its upper and lower thresholds. This eliminates jitter and steepens the signal edges, resulting in a clear digital waveform. For general jitter and distortion, a single-stage Schmitt trigger is sufficient for shaping. In cases of extremely poor signal quality or requiring higher shaping accuracy, multiple Schmitt triggers can be connected in series to further enhance the shaping effect.

[0058] After being shaped by a Schmitt trigger, the output signal has clear logic high and low levels, steep rising and falling edges, and a stable pulse width, forming a standard rectangular wave—the standard protection trigger signal with a well-defined rectangular wave output. This well-defined signal is crucial for the inverter's main control unit, as it ensures accurate identification of fault signals, avoiding misjudgments or missed judgments due to signal quality issues, thus enabling timely activation of protection actions and ensuring equipment safety. The output of the Schmitt trigger can be directly connected to the input pin of the inverter's main control unit, or, to enhance drive capability or further isolate the signal, a buffer can be added to the output before connecting it to the main control unit.

[0059] This application further proposes that the Schmitt trigger uses a dual-channel inverting Schmitt chip AIP74LVC2G14; the current-limiting resistor is R6, and the filter capacitors, including C3 and C4, are connected in parallel between the input pin of the trigger and ground; the Vo level output by the optocoupler is current-limited by R6 and sent to the input terminal of the Schmitt trigger, and the output terminal of the trigger outputs the shaped VCE level to the main control DSP of the frequency converter.

[0060] The Schmitt trigger is a comparator with hysteresis characteristics. Its output state depends not only on the current input signal but also on the previous output state. It has two different threshold voltages, effectively eliminating noise and jitter in the input signal, converting slowly changing analog signals into steep-edge digital signals, thereby improving signal anti-interference capability and stability. Besides using dual-channel inverting Schmitt chips, other types of Schmitt trigger integrated circuits can be used, such as single-channel or multi-channel Schmitt trigger chips, or a comparator circuit with hysteresis characteristics can be built using discrete components (such as operational amplifiers, resistors, and capacitors). The current-limiting resistor is mainly used in the circuit to limit the current magnitude, protecting subsequent circuits from excessive current surges, or to adjust signal levels. Here, it works in conjunction with the filter capacitor to form an RC filter network for preprocessing the input signal. The current-limiting resistor can be a standard resistor with different resistance values, such as carbon film resistors or metal film resistors, depending on the specific requirements of the circuit. The resistance value selection needs to comprehensively consider the output capability of the optocoupler, the input impedance of the Schmitt trigger, and the required filtering effect. In circuits, filter capacitors are primarily used to remove high-frequency noise and ripple from signals, making them smoother and more stable. By connecting a capacitor in parallel between the signal path and ground, a low-impedance path can be provided for high-frequency noise, bypassing it to ground and thus purifying the signal. Different types of filter capacitors can be selected, such as ceramic capacitors, electrolytic capacitors, and tantalum capacitors. Their capacitance and voltage ratings need to be selected based on the circuit's operating frequency and voltage range. The Vo level output of the optocoupler is an isolated fault signal, but it may contain noise and jitter. The current-limiting resistor R6 can provide initial current limiting and level adjustment for this signal, and together with filter capacitors C3 and C4, it forms an RC low-pass filter to filter out high-frequency interference, providing a relatively clean input signal for the Schmitt trigger. In addition to current limiting with a current-limiting resistor, a buffer or level shifting circuit can be added to further optimize the signal input characteristics to ensure that the signal received by the Schmitt trigger meets its input specifications. The shaped VCE level output from the trigger's output terminal is sent to the inverter's main control DSP. This process describes the output of the Schmitt trigger after signal shaping and its target. Schmitt triggers utilize their hysteresis characteristic to convert noisy and jittery input signals into rectangular wave signals with steep edges and clear logic levels, i.e., shaped VCE levels. This regularized digital signal is sent to the inverter's main control DSP as a precise protection trigger signal. Besides direct output to the DSP, the shaped signal can also be processed through a logic gate (such as a NOT gate or AND gate), or its driving capability can be enhanced by a driver before being sent to the main control unit, to adapt to different interface requirements or implement more complex protection logic.

[0061] Through the above technical solution, this application introduces a Schmitt trigger and a matching current-limiting filter circuit into the signal shaping module, effectively solving the non-ideal states such as jitter and edge distortion that may occur in the transmission of fault level signals from the optocoupler. Specifically, the current-limiting resistor R6 and the parallel filter capacitors C3 and C4 work together to efficiently filter out high-frequency noise and glitches mixed in the optocoupler output signal before the signal enters the Schmitt trigger, providing a cleaner input level for subsequent shaping processing, thereby avoiding erroneous switching of the Schmitt trigger due to noise interference. On this basis, a dual-channel inverting Schmitt chip AIP74LVC2G14 is used as the core shaping device. Utilizing its inherent hysteresis characteristics, it can forcibly convert analog level signals that have undergone preliminary filtering but may still have jitter or slow edges into rectangular wave signals with steep edges and regular logic levels. This deep shaping process eliminates the uncertainty of the signal during transmission, enabling the inverter's main control DSP to receive clear, stable, and rapidly responsive logic trigger levels. Therefore, this application can ensure that the main control unit can quickly and accurately execute the protection logic when it receives an overcurrent fault signal, which significantly improves the accuracy and timeliness of the inverter bus overcurrent protection action, effectively avoids protection failure or maloperation caused by signal quality problems, and further enhances the reliability and safety of the inverter system.

[0062] This application proposes an inverter bus overcurrent protection circuit, which does not require an external independent auxiliary power supply. Instead, it relies on the inverter's internal +VNP bus voltage and onboard +5V logic voltage to power all modules. At the same time, all components in the circuit are general-purpose discrete devices and standard integrated circuits, without high-power dedicated switching devices or DC Hall current sensors.

[0063] Through the above technical solutions, the inverter bus overcurrent protection circuit of this application has been optimized in terms of power supply and component selection, achieving a highly simplified circuit design. Since the circuit relies on the existing +VNP bus voltage and onboard +5V logic voltage within the inverter for power supply, it fundamentally eliminates the dependence on external independent auxiliary power supplies, avoids the risk of protection failure caused by abnormal auxiliary power supply, and significantly improves the overall reliability of the system. Furthermore, by using all general-purpose discrete components and standard integrated circuits, and abandoning the high-power dedicated switching devices and DC Hall current sensors commonly used in traditional solutions, not only is the hardware procurement cost significantly reduced, but the miniaturized layout of components effectively solves the problem of bulky overall structure caused by the large size of specific sensors or power devices in traditional protection circuits. Therefore, the protection circuit of this application achieves deep optimization of low cost, miniaturization, and high reliability without sacrificing performance, and can better meet the requirements of modern industry for the accuracy, speed, and economy of inverter bus overcurrent protection.

[0064] This application proposes a bus overcurrent protection circuit for frequency converters, which is suitable for detecting and protecting against various types of bus overcurrent faults, including standby short circuits, IGBT shoot-through short circuits, motor load jamming, and winding turn-to-turn short circuits. The circuit adopts a layout of small SOT23 packaged devices and has no large-aperture current sensors, thus reducing the overall installation size of the frequency converter.

[0065] Through the above technical solution, this protection circuit can effectively handle bus overcurrent faults occurring under various complex operating conditions of the frequency converter, such as standby short circuit, IGBT shoot-through short circuit, motor load jamming, and winding turn-to-turn short circuit. This broad fault detection and protection capability ensures the operational safety and reliability of the frequency converter throughout its entire life cycle, avoiding equipment damage or production interruption caused by insufficient protection for a single fault type. Simultaneously, by adopting a small SOT23 packaged device layout and eliminating traditional large-aperture current sensors, the physical size and weight of the protection circuit are significantly reduced. This design not only reduces material costs but also greatly shrinks the overall installation volume of the frequency converter, allowing it to adapt to more compact installation environments and enhancing the product's market competitiveness. This miniaturized, low-cost, and comprehensive protection solution, without sacrificing response speed and protection accuracy, solves the pain points of large size, high cost, and incomplete fault coverage in existing protection circuits, providing strong support for the miniaturization and high reliability development of frequency converters.

[0066] The following example will provide a more detailed explanation of the above technical solution: In an industrial production scenario, a motor driven by a frequency converter suddenly experiences mechanical jamming during operation, causing a sharp increase in motor load and resulting in a momentary surge in the DC bus current of the frequency converter, far exceeding the normal operating range. If this bus overcurrent fault is not handled promptly, it may lead to damage to the IGBT module, blown fuses, or even more serious safety accidents. To quickly and reliably detect and respond to such faults, the frequency converter bus overcurrent protection circuit of this application is integrated into the frequency converter.

[0067] When a motor is stalled and the DC bus current rises abnormally, the sampling module of the inverter bus overcurrent protection circuit functions first. This sampling module includes multiple parallel sampling resistors, such as RA1, RA2, RA3, and RA4, which are connected in series in the DC bus loop of the inverter. These resistors convert the excessive current flowing through the bus into a corresponding voltage signal. Compared with the traditional Hall current sensor, this resistor sampling method has a simple structure and low cost, and does not require a large-aperture design, which is beneficial to the miniaturization of the entire inverter. To prevent the sampling voltage from being too high and damaging the subsequent circuit, the clamp protection diode D2 (for example, the LBAV99 high-speed diode) is connected in parallel at the output end of the sampling resistor, limiting the amplitude of the sampling voltage to ±0.7V and effectively blocking the transient overvoltage shock. Subsequently, the current signal output by the sampling resistor is proportionally amplified by an operational amplification unit (for example, a dual-channel operational amplifier U4B), and a voltage sampling signal Vout is output. The relationship Vout=I×R×(R11 / R9) is satisfied between the voltage sampling signal Vout and the actual DC bus current I, where R is the equivalent sampling resistor, and R9 and R11 are the voltage-dividing feedback resistors matched with the operational amplification unit. At the same time, the sampling module is also equipped with filter capacitors C6, C7, and C12, which are used to filter out high-frequency clutter interference on the bus and ensure the purity of the sampling signal.

[0068] The sampled voltage signal Vout is sent to the comparison and judgment module. This module has a built-in fixed voltage reference threshold for real-time comparison of Vout. The comparison and judgment module includes a reference voltage generation unit, a voltage comparison unit, a voltage regulation clamping unit, and a high-speed isolation optocoupler unit. The reference voltage generation unit (including a TL431 reference chip U3, a current-limiting resistor R1, and an anti-surge fast recovery diode D1) stably outputs a 2.5V reference voltage as the overcurrent judgment threshold. Among them, the current-limiting resistor R1 limits the operating current of the reference branch, and the anti-surge fast recovery diode D1 is connected in reverse parallel to the power supply input terminal of U3 to suppress the high voltage surge at the moment of power-on and ensure the stability of the reference voltage. The voltage comparison unit (using a dual-channel operational amplifier U4A to form a voltage comparator) receives Vout and compares it with the 2.5V reference voltage in real time. When the bus current is normal, Vout is lower than 2.5V, and the output voltage of U4A is clamped to 5.1V by the voltage regulation clamping unit (using a 5.1V Zener diode Z1). Once a bus overcurrent occurs, Vout rapidly rises and exceeds the 2.5V threshold, and the output level of U4A immediately flips to low. Compared to software protection schemes that rely on analog-to-digital conversion and algorithmic judgment via the main control chip, this purely hardware-based comparison and judgment response is extremely fast. It can promptly output a fault signal when the bus current surges instantaneously, effectively avoiding protection lag and providing rapid protection for core power devices such as IGBTs. Subsequently, a high-speed isolation optocoupler unit (e.g., 6N137 high-speed optocoupler U1) receives the output level of U4A. When U4A outputs a low level (overcurrent state), a voltage difference is formed in the primary side of the optocoupler, causing it to conduct, and the secondary side outputs a low-level fault signal; when U4A outputs a high level (normal state), the primary side of the optocoupler is cut off without a voltage difference, and the secondary side maintains a high-level normal signal. The introduction of the optocoupler achieves electrical isolation, effectively preventing fault signals from interfering with the inverter's main control unit and improving system reliability. The comparison and judgment module is also equipped with filter capacitors C1, C2, and C5 to stabilize the reference voltage and the comparison input signal.

[0069] Finally, the isolated fault level signal output by the comparison and judgment module is sent to the signal shaping module. This module includes an input current-limiting resistor R6, filter capacitors C3 and C4, and a Schmitt trigger (e.g., a dual-channel inverting Schmitt chip AIP74LVC2G14). The Vo level output from the optocoupler is fed into the input of the Schmitt trigger via the current-limiting resistor R6. Since the waveform output from the optocoupler may have jitter or edge distortion, the Schmitt trigger shapes the waveform, converting the irregular fault signal into a regular rectangular wave standard protection trigger signal VCE. Filter capacitors C3 and C4 are connected in parallel between the trigger input pin and ground to further filter out noise. The shaped VCE signal is output to the inverter's main control unit (e.g., a DSP). Upon receiving this standard protection trigger signal, the main control unit immediately executes the corresponding protection action, such as shutting off the IGBT drive signal, thereby quickly cutting off the bus current, preventing the fault from escalating, and protecting the inverter and related equipment.

[0070] It is worth noting that this circuit requires no external auxiliary power supply. Instead, it relies on the +VNP bus voltage inside the inverter and the onboard +5V logic voltage to power all modules, simplifying the circuit topology and reducing the risk of protection failure due to power supply faults. Furthermore, all components in the circuit are general-purpose discrete devices and standard integrated circuits, without high-power dedicated switching devices or DC Hall current sensors. This results in low cost and compact size. The use of SOT23 small-package devices further reduces the overall installation size of the inverter, meeting the demands of industrial automation for miniaturization, low cost, and high reliability. This circuit can effectively detect and protect the inverter from various bus overcurrent faults, including standby short circuits, IGBT shoot-through short circuits, motor load jamming, and winding turn-to-turn short circuits.

[0071] When using: Refer to Figure 2 As shown, RA1, RA2, RA3, and RA4 are sampling resistors; D2 is a clamping diode that clamps the input signal to approximately ±0.7V, effectively preventing overvoltage surges from damaging the subsequent operational amplifier; the current is converted into a voltage signal after passing through the four sampling resistors, and then amplified by the operational amplifier before being output; assuming the current is I, and the parallel equivalent resistance of RA1, RA2, RA3, and RA4 is R, the output voltage satisfies the formula: Vout = I × R × (R11 / R9).

[0072] The multi-parallel sampling resistor consists of four resistors RA1, RA2, RA3, and RA4 connected in parallel and then in series in the DC bus circuit of the frequency converter. The bus current flows through the multi-parallel sampling resistor to generate a weak sampling voltage. The clamping protection diode D2 is connected in parallel between the output terminal of the sampling resistor group and ground. The output voltage of the sampling resistor group is connected to the non-inverting input terminal of U4B. The inverting input terminal of U4B is grounded through R9. The output terminal of U4B is fed back to the inverting input terminal through R11. The output terminal of U4B is the sampling module output Vout. C6 and C7 are connected in parallel to the input pin of U4B. C12 is connected across +VNP and GND_VNP to form a power supply filter.

[0073] refer to Figure 3As shown: R1 is a current-limiting resistor, used to limit the current flowing through U3 to prevent damage to the device; U3 is a 431 voltage reference chip, whose core function is to provide a stable 2.5V reference voltage for U4 (comparator) as the threshold for overcurrent judgment; D1 is a fast recovery diode, whose function is to prevent the voltage reference chip U3 from being damaged by the +VNP voltage surge at the moment of power-on, ensuring stable startup of the reference circuit; Z1 is a Zener diode, with a nominal Zener voltage of 5.1V, used to clamp the output voltage of U4A; U1 is a high-speed optocoupler, which realizes isolated signal transmission and improves the circuit's anti-interference capability; R3 is a pull-up resistor, which pulls the output terminal of the optocoupler up to 5V to ensure the stability of the output signal; C8, C9, C10, and C11 are filter capacitors, used to filter out noise interference in the circuit and ensure the stability of the reference voltage and comparison signal.

[0074] The operating logic of the comparator circuit is as follows: When the output Vout of the sampling circuit is greater than 2.5V (i.e., the bus current exceeds the preset threshold), the comparator U4A outputs a low level. At this time, a voltage difference is generated between pins 2 and 3 of U1, and current flows through the primary of the optocoupler. The optocoupler U1 is turned on, and the output Vo is low, triggering subsequent protection actions. When Vout is less than 2.5V (i.e., the bus current is within the normal range), U4A outputs a high level. At this time, the Zener diode Z1 clamps the output voltage of U4A at 5.1V. There is no voltage difference or current flowing between pins 2 and 3 of the optocoupler U1. The optocoupler U1 is not turned on, and the output Vo remains high. The circuit is in normal working condition.

[0075] The +VNP power supply terminal is connected to the power supply pin of U3 via R1. D1 is connected in reverse parallel between the power supply input terminal of U3 and ground. U3 outputs a stable 2.5V reference voltage to the non-inverting input terminal of U4A. The voltage comparator unit is composed of a dual-channel operational amplifier U4A. The inverting input terminal of U4A receives the output Vout of the sampling module. Zener diode Z1 is connected in parallel between the output terminal of U4A and ground. The output terminal of U4A is connected to the primary anode of high-speed optocoupler U1 (model 6N137S1), and the primary cathode of optocoupler U1 is grounded. The secondary power supply pin of optocoupler U1 is connected to +5V, and the secondary output pin is pulled up to +5V via pull-up resistor R3. The secondary output terminal of optocoupler is the fault level signal Vo. C1, C2, and C5 are connected in parallel in the reference circuit, the comparator input terminal, and the output terminal of U4A, respectively, to achieve noise filtering.

[0076] refer to Figure 4As shown: R6 is a current-limiting resistor, used to limit the current of the input Schmitt trigger U2 to protect the device; U2 is a Schmitt trigger, primarily used for signal shaping; C3 and C4 are filter capacitors, used to filter out noise in the input signal and improve signal stability. The circuit's operating logic is as follows: when the optocoupler output signal Vo is low, the shaping circuit outputs VCE at a low level; when Vo is high, VCE is high. Because the optocoupler U1 output signal Vo has a certain rise time, it is prone to waveform irregularities and jitter. This shaping circuit can effectively convert such irregular electrical signals into regular rectangular waves, ensuring that the signals received by the subsequent control module are clear and stable, and avoiding false triggering or non-triggering of protection actions due to signal distortion.

[0077] The optocoupler output signal Vo is connected to the 1A input pin of Schmitt trigger U2 via current-limiting resistor R6. C3 and C4 are connected in parallel between the input pin of U2 and ground. U2 uses an AIP74LVC2G14 dual-channel inverting Schmitt trigger chip, with the VCC pin connected to +5V and the GND pin grounded. The 2A output pin of U2 outputs a shaped standard level VCE, which is directly connected to the protection signal pin of the inverter's main control DSP. Schmitt trigger U2 converts the Vo signal output by the optocoupler, which has rising edge jitter and waveform distortion, into a rectangular wave VCE with regular edges, avoiding misjudgment or protection failure by the main control unit.

[0078] In summary, the sampling circuit converts the bus current into a detectable voltage signal through a parallel sampling resistor, which is then amplified by an operational amplifier before being output, providing both accurate detection and overvoltage protection. The comparator circuit uses a 2.5V threshold provided by the 431 voltage reference chip and achieves signal isolation and level conversion through a high-speed optocoupler, quickly determining whether the bus current exceeds the limit. It has a rapid response and strong anti-interference capability. At the same time, the configuration of fast recovery diodes, Zener diodes, and other components effectively avoids component damage and improves circuit reliability. The shaping circuit eliminates waveform distortion of the optocoupler output signal through a Schmitt trigger, outputting a regular signal to ensure the stable operation of subsequent control modules.

[0079] The circuit has the following core advantages: 1. Simple architecture and low cost: The entire circuit consists of only three modules: sampling, comparison and shaping. The selected components are all conventional general-purpose components (such as 431 reference chip, high-speed optocoupler, Schmitt trigger, etc.), which do not require complex control programs and additional power supplies, thus reducing design and manufacturing costs.

[0080] 2. Rapid response and accurate judgment: The comparator circuit adopts a high-speed optocoupler and a stable 2.5V reference voltage, which can quickly respond to changes in the sampling signal and accurately judge whether the bus is overcurrent, avoiding device damage caused by protection lag; the optocoupler isolation design improves the circuit's anti-interference capability and reduces the impact of noise on the judgment result.

[0081] 3. High reliability and comprehensive protection: Each module is equipped with protection devices (such as clamping diodes, current limiting resistors, fast recovery diodes, etc.) to effectively prevent damage to devices from power-on surges, overvoltages, and overcurrents, and extend the service life of the circuit; the design of the shaping circuit avoids protection abnormalities caused by signal distortion, further improving the reliability of the circuit.

[0082] 4. Strong adaptability: The circuit structure is compact and does not require complex layout. It can be adapted to frequency converters in various industrial scenarios. It can accurately detect the overcurrent status of the bus and provide reliable support for subsequent protection actions. It solves the problems of complex structure, high cost and slow response of existing protection circuits.

[0083] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention 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 invention should be included within the protection scope of the present invention.

Claims

1. A frequency converter bus overcurrent protection circuit, characterized in that, It includes a sampling module, a comparison and judgment module, and a signal shaping module that are electrically connected in sequence; The sampling module is used to collect the DC bus current of the frequency converter and convert it into a voltage sampling signal output. The comparison and judgment module has a built-in fixed voltage reference threshold, receives the voltage sampling signal and compares it with the reference threshold in real time, and outputs an isolated fault level signal when the bus is overcurrent. The signal shaping module receives the fault level signal, shapes the waveform, and outputs a standard protection trigger signal to the inverter main control unit.

2. The inverter bus overcurrent protection circuit according to claim 1, characterized in that: The sampling module includes multiple parallel sampling resistors, a clamping protection diode D2, and an operational amplifier unit. Multiple sets of sampling resistors are connected in series in the DC bus circuit of the frequency converter to collect the bus current. The clamping protection diode is connected in parallel at the output terminal of the sampling resistor to limit the sampling voltage amplitude. The current signal output by the sampling resistor is proportionally amplified by the operational amplifier unit to output a voltage sampling signal.

3. The inverter bus overcurrent protection circuit according to claim 2, characterized in that: The multi-parallel sampling resistors include RA1, RA2, RA3, and RA4, which are connected in parallel to form an equivalent sampling resistor R. The operational amplifier unit adopts a dual-channel operational amplifier U4B, and the output voltage of the operational amplifier unit satisfies the relationship: Vout=I×R×(R11 / R9), where I is the actual DC bus current, and R9 and R11 are the voltage divider feedback resistors matched to the operational amplifier unit.

4. The inverter bus overcurrent protection circuit according to claim 2, characterized in that: The clamping protection diode is an LBAV99 high-speed diode. The bidirectional clamping of the diode limits the sampling input voltage to ±0.7V, blocks instantaneous overvoltage surges, and prevents the subsequent operational amplifier from being damaged. The sampling module is also equipped with filter capacitors C6, C7, and C12 to filter out high-frequency noise interference from the bus.

5. The inverter bus overcurrent protection circuit according to claim 1, characterized in that: The comparison and judgment module includes a reference voltage generation unit, a voltage comparison unit, a voltage stabilization clamping unit, and a high-speed isolation optocoupler unit. The reference voltage generation unit outputs a constant threshold voltage to the voltage comparison unit. The voltage comparison unit compares the sampled voltage with the threshold voltage and outputs a comparison level. The voltage stabilization clamping unit limits the output level of the comparison unit. The high-speed isolation optocoupler unit isolates the transmission of the comparison level and outputs a fault level signal.

6. The inverter bus overcurrent protection circuit according to claim 5, characterized in that: The reference voltage generating unit includes a TL431 reference chip U3, a current-limiting resistor R1, and an anti-surge fast recovery diode D1. The current-limiting resistor R1 is connected in series between the power supply terminal and the input terminal of U3 to limit the operating current of the reference branch. The anti-surge fast recovery diode D1 is connected in reverse parallel to the power supply input terminal of U3 to suppress the +VNP high voltage surge at the moment of power-on. U3 stably outputs a 2.5V reference voltage as the overcurrent judgment threshold. The voltage comparison unit uses a dual-channel operational amplifier U4A to form a voltage comparator; the voltage regulation clamping unit uses a 5.1V Zener diode Z1, which is connected in parallel to the output terminal of U4A to clamp the output voltage of U4A to 5.1V under normal bus current conditions. The high-speed isolation optocoupler unit is a 6N137 high-speed optocoupler U1. The primary end of the optocoupler is connected to the output of U4A and the reference ground respectively. The secondary end of the optocoupler is equipped with a pull-up resistor R3 connected to a +5V power supply. When the sampling module outputs Vout > 2.5V, U4A outputs a low level, the primary end of the optocoupler forms a voltage difference and conducts, and the secondary end outputs a low-level fault signal. When Vout < 2.5V, the output of U4A is clamped to 5.1V by Z1, the primary end of the optocoupler is cut off without voltage difference, and the secondary end maintains a high-level normal signal. The comparison and judgment module is also equipped with filter capacitors C1, C2, and C5 to stabilize the reference voltage and the comparison input signal.

7. The inverter bus overcurrent protection circuit according to claim 1, characterized in that: The signal shaping module includes a Schmitt trigger, an input current-limiting resistor, and a filter capacitor. The current-limiting resistor is connected in series at the input of the shaping module and receives the fault level signal output by the comparison and judgment module. The Schmitt trigger shapes the output waveform of the optocoupler that has jitter and edge distortion, and outputs a regular rectangular wave standard protection trigger signal.

8. The inverter bus overcurrent protection circuit according to claim 7, characterized in that: The Schmitt trigger uses a dual-channel inverting Schmitt chip; the current-limiting resistor is R6, and the filter capacitors, including C3 and C4, are connected in parallel between the input pin of the trigger and ground; the Vo level output by the optocoupler is current-limited by R6 and sent to the input terminal of the Schmitt trigger, and the output terminal of the trigger outputs the shaped VCE level to the main control DSP of the frequency converter.

9. The inverter bus overcurrent protection circuit according to claim 1, characterized in that: The circuit as a whole does not require an external independent auxiliary power supply. It relies on the internal +VNP bus voltage of the frequency converter and the onboard +5V logic voltage to power all modules. All components are general-purpose discrete components and standard integrated circuits, without high-power dedicated switching devices or DC Hall current sensors.

10. The inverter bus overcurrent protection circuit according to claim 1, characterized in that: The circuit is suitable for detecting and protecting against various bus overcurrent faults, including inverter standby short circuit, IGBT shoot-through short circuit, motor load jamming, and winding turn-to-turn short circuit. The circuit adopts a layout of small SOT23 packaged devices and has no large-aperture current sensors, thus reducing the overall installation size of the inverter.

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