Frequency converter output voltage early warning system

Abstract

The invention discloses a frequency converter output voltage early warning system which comprises a resistance voltage reduction module, a high-speed isolator module, a high-speed acquisition module, a low-speed acquisition module and an acquisition early warning module. Three-phase voltage output by the frequency converter is connected with the input of the resistance voltage reduction module, three-phase attenuation voltage and zero sequence voltage at the output end of the resistance voltage reduction module are isolated through a Hall PT and then connected with the input of the low-speed acquisition module, and the low-speed acquisition module transmits processed voltage data to the acquisition early warning module through the communication board. The acquisition and early warning module extracts voltage data of the low-speed acquisition module according to a preset low-speed sampling frequency and is used for performing low-frequency monitoring and early warning; the three-phase attenuation voltage of the output end of the resistance voltage reduction module is connected with the input ends of the three high-speed isolator modules respectively, the output ends of the high-speed isolator modules are connected with the input end of the high-speed acquisition module, and the high-speed acquisition module transmits processed voltage data to the acquisition early warning module through the communication board. The acquisition and early warning module extracts voltage data of the high-speed acquisition module according to a preset high-speed sampling frequency and is used for performing high-frequency monitoring and early warning on the output voltage of the frequency converter; therefore, high-frequency and low-frequency monitoring and early warning are carried out on the output voltage of the frequency converter in real time, and fault occurrence or fault expansion of the frequency converter is avoided through timely early warning.

Description

Technical Field

[0001] This invention relates to the field of frequency converter technology, and in particular to a frequency converter output voltage early warning system. Background Technology

[0002] Low-voltage AC / DC / AC voltage-type frequency converters generally use IGBT power devices, and the converter output voltage is a PWM pulse voltage. There are two types of detection for the converter output voltage: low-frequency detection, which only detects the effective value when the converter output voltage is a sine wave, mainly used for converter and motor control and status monitoring; and high-frequency detection, which detects each PWM pulse voltage at the converter output, mainly used for the research and development and performance testing of converter PWM control, as well as for trigger testing, fault diagnosis, and analysis when the converter malfunctions.

[0003] Currently, inverter output voltage detection is mostly done at low frequencies. There are generally two methods for low-frequency detection: Method one, used by some inverter manufacturers, involves configuring Hall effect voltage sensors to detect the inverter output voltage; Method two does not use a voltage sensor, but instead calculates the inverter output voltage using the PWMT modulation rate of the output voltage and the actual DC circuit voltage of the inverter. Method two usually meets the requirements for motor speed control performance and eliminates the need for a voltage sensor, but it cannot accurately reflect the actual output voltage of the inverter when there is an abnormality. Hall effect voltage sensors are characterized by accuracy and stability, but their bandwidth is generally low, making them unable to accurately detect high-frequency signals.

[0004] As the requirements of smart manufacturing technology applications increase, there is a need for online status monitoring of medium and large capacity frequency converters with incomplete protection functions, as well as those operating in harsh environments. These frequency converters are prone to failure, leading to abnormal voltage or current. However, due to the numerous factors involved, troubleshooting and locating these frequency converters is very difficult. When troubleshooting the trigger circuits or replacing power devices of these frequency converters, a low-voltage power-on test is required. In existing technologies, this is generally done by temporarily testing the output PWM pulse voltage of the frequency converter using tools such as oscilloscopes to determine if there are faults such as missing pulses, erroneous pulses, or narrow pulses. However, oscilloscopes can only be used temporarily for short periods.

[0005] Therefore, how to perform real-time high and low frequency monitoring and early warning of the inverter output voltage is a problem we need to solve. Summary of the Invention

[0006] In view of the above problems, the present invention provides an inverter output voltage early warning system, which realizes real-time high-frequency and low-frequency monitoring and early warning of inverter output voltage, and avoids inverter failure or failure expansion through timely early warning.

[0007] According to a first aspect of the present invention, an inverter output voltage early warning system is provided, comprising:

[0008] Resistor step-down module, high-speed isolator module, high-speed data acquisition module, low-speed data acquisition module, and data acquisition and early warning module;

[0009] The three-phase voltages output by the frequency converter are connected to the input terminals of the resistor step-down module. The three-phase attenuation voltage and zero-sequence voltage output by the resistor step-down module are isolated by four Hall voltage sensors and then connected to the input terminal of the low-speed acquisition module. The low-speed acquisition module transmits the processed voltage data to the acquisition and early warning module through the communication board. The acquisition and early warning module extracts the voltage data from the low-speed acquisition module according to a preset low-speed sampling frequency, compresses and stores it, and uses LABview to perform waveform creation, measurement, Fourier transform, and calculation processing on the extracted voltage data to achieve low-frequency monitoring and early warning of the frequency converter output voltage.

[0010] The three-phase attenuated voltage at the output of the resistor step-down module is connected to the input of each of the three high-speed isolator modules. After signal impedance transformation, isolation, and differential amplification, the output of the high-speed isolator module is connected to the input of the high-speed acquisition module. The high-speed acquisition module transmits the processed voltage data to the acquisition and early warning module via a communication board. The acquisition and early warning module extracts the voltage data from the high-speed acquisition module according to a preset high-speed sampling frequency, compresses and stores it, and uses LABview to create, measure, and calculate the extracted voltage data to achieve high-frequency monitoring and early warning of the inverter output voltage.

[0011] Optionally, the resistor step-down module includes three first non-inductive resistor units and a second non-inductive resistor unit. The input terminal of each first non-inductive resistor unit is connected to the single-phase voltage of the inverter output terminal. The output terminals of the three first non-inductive resistor units are connected in parallel to obtain the simulated neutral point C. The output terminal of the simulated neutral point C is connected to the input terminal of the second non-inductive resistor unit, and the output terminal of the second non-inductive resistor unit is grounded to E.

[0012] The first non-inductive resistor unit includes a first resistor, a second resistor, a third resistor, and a fourth resistor connected in series. The voltage between the input terminal of the fourth resistor and the analog center point C is used as the single-phase attenuation voltage.

[0013] Optionally, the second non-inductive resistor unit includes four non-inductive resistors connected in series, and the voltage across the fourth non-inductive resistor is used as the zero-sequence voltage.

[0014] Optionally, the three-phase attenuation voltage and the zero-sequence voltage are respectively connected to four Hall voltage sensors. After isolation and voltage transformation by the Hall voltage sensors, they are respectively connected to four analog channels at the input end of the low-speed acquisition module.

[0015] Optionally, the selection range of the high-speed sampling frequency includes 50KHz, 100KHz, 200KHz and 300KHz.

[0016] Optionally, the selection range of the low-speed sampling frequency includes 1KHz, 2KHz, 4KHz, 6KHz, 10KHz and 20KHz.

[0017] Optionally, the high-frequency and low-frequency monitoring and early warning of the inverter output voltage includes:

[0018] The data acquisition and early warning module extracts the voltage data and uses LABview to create, measure, and perform Fourier transform on the waveform to obtain the effective value, peak-to-peak value, distortion, DC component, zero-sequence voltage, and the number of PWM pulses during the positive and negative half-wave time of each phase attenuation voltage.

[0019] Based on the high-frequency and low-frequency early warning methods for inverter output voltage, mathematical and logical operations are performed on the effective value, peak-to-peak value, distortion, DC component, zero-sequence voltage, and the number of PWM pulses during the positive and negative half-wave time of each phase attenuation voltage of the obtained three-phase attenuation voltage to monitor and warn whether there is a fault in the inverter output voltage.

[0020] Optionally, the faults include pulse loss, pulse error, overvoltage, three-phase voltage imbalance, excessive voltage harmonic components, excessive DC components, and excessive zero-sequence voltage.

[0021] Optionally, the types of faults include minor faults and major faults;

[0022] If a minor fault is detected, an early warning message will be sent to the staff, and the frequency converter will continue to operate without shutting down.

[0023] If a serious fault is detected, equipment inspection information is sent to staff for inspection of the frequency converter.

[0024] Optionally, the high-speed isolator module includes an operational amplifier U1 unit for impedance attenuation of the three-phase attenuated voltage, a signal isolation U2 unit for electrical isolation of AC voltage, an operational amplifier U3 unit for signal amplification and zeroing, and two DC / DC isolated power supplies.

[0025] One DC / DC isolated power supply powers the input side of the operational amplifier U1 unit and the signal isolation U2 unit respectively, and the other DC / DC isolated power supply powers the output side of the signal isolation U2 unit and the operational amplifier U3 unit respectively.

[0026] The input terminal of the operational amplifier U1 unit is connected to a single-phase attenuated voltage, and the output terminal is connected to the input terminal of the signal isolation unit U2; the output terminal of the signal isolation unit U2 unit is connected to the input terminal of the operational amplifier U3 unit, and the output terminal of the operational amplifier U3 unit is connected to the analog channel of the high-speed acquisition module.

[0027] The above-described one or more technical solutions in the embodiments of this specification have at least the following technical effects:

[0028] This specification provides an inverter output voltage early warning system. By simply modifying an existing inverter, it can achieve real-time high-frequency and low-frequency monitoring and early warning of the inverter's output voltage. It can predict whether the inverter's output PWM pulse voltage has lost or erroneous pulses, and whether the three-phase voltage is symmetrical, or whether harmonics, DC components, and zero-sequence voltage exceed limits. Through timely warnings, it reminds staff to strengthen inspections or take necessary measures to prevent inverter failures from occurring or escalating.

[0029] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0030] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0031] Figure 1 A schematic diagram of an inverter output voltage early warning system according to an embodiment of the present invention is shown.

[0032] Figure 2 A schematic diagram of a resistor-based voltage reduction module according to an embodiment of the present invention is shown.

[0033] Figure 3 A schematic diagram of a high-speed isolator module according to an embodiment of the present invention is shown. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0035] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0036] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0037] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0038] In existing technologies, most frequency converters calculate their output voltage using the frequency converter's PWM modulation rate and the actual DC circuit voltage. However, this method cannot accurately reflect the actual output voltage of the frequency converter when it malfunctions, nor can it detect the motor's zero-sequence voltage in real time. Some frequency converters use Hall voltage sensors for voltage detection, but Hall voltage sensors cannot acquire the frequency converter's output PWM pulse voltage in real time, nor can they detect the motor's zero-sequence voltage.

[0039] Based on the above situation, combined with Figure 1 As shown, the present invention provides an inverter output voltage early warning system, including a resistor step-down module, a high-speed isolator module, a high-speed acquisition module, a low-speed acquisition module, and an acquisition and early warning module.

[0040] The three-phase voltages output from the frequency converter are connected to the input terminals of the resistor step-down module. After passing through the resistor step-down module, four sets of voltages are obtained: the three-phase attenuated voltages U1C, V1C, W1C, and zero-sequence voltage C1E at the output terminals of the resistor step-down module. These four sets of voltages are divided into two paths. One path is isolated by four Hall voltage sensors (Hall voltage PTs) and then connected to the input terminal of the low-speed acquisition module. The low-speed acquisition module transmits the processed voltage data to the acquisition and early warning module through the communication board. The acquisition and early warning module extracts the voltage data from the low-speed acquisition module according to a preset low-speed sampling frequency, compresses and stores the acquired voltage data, and uses LABview to perform waveform creation, measurement, Fourier transform, and mathematical and logical operations on the acquired data to realize low-frequency monitoring and early warning of the frequency converter output voltage.

[0041] On the other side, the three-phase attenuated voltages U1C, V1C, and W1C from these four voltage groups are connected to the input terminals of three high-speed isolator modules respectively. After signal impedance transformation, isolation, and differential amplification, the output terminal of the high-speed isolator module is connected to the input terminal of the high-speed acquisition module. The high-speed acquisition module transmits the processed voltage data to the acquisition and early warning module through the communication board. The acquisition and early warning module extracts the voltage data from the high-speed acquisition module according to a preset high-speed sampling frequency, compresses and stores the acquired voltage data, and uses LABview to create waveforms, measure, and perform mathematical and logical operations on the acquired data to achieve high-frequency monitoring and early warning of the inverter output voltage.

[0042] Specifically, the resistor step-down module includes three first non-inductive resistor units and a second non-inductive resistor unit.

[0043] In this configuration, the input terminal of each first non-inductive resistor unit is connected to a single-phase voltage at the output terminal of the frequency converter, and the output terminals of the three first non-inductive resistor units are connected in parallel to form a simulated neutral point C; the other end of the simulated neutral point C is connected to the input terminal of the second non-inductive resistor unit, and the output terminal of the second non-inductive resistor unit is grounded.

[0044] Specifically, the first non-inductive resistor unit includes a first resistor, a second resistor, a third resistor, and a fourth resistor connected in series. The voltage between the input terminal of the fourth resistor and the analog center point C is the single-phase attenuation voltage (U1C, V1C, or W1C).

[0045] Specifically, combining Figure 2 As shown, three 1KV / 1mm wires are led out from the inverter output terminals U, V, and W respectively. 2The circuit consists of resistors R1, R2, R3, and R4 forming a first non-inductive resistor unit, whose input is connected to a single-phase voltage U of the frequency converter. R5, R6, R7, and R8 form another first non-inductive resistor unit, whose input is connected to a single-phase voltage V of the frequency converter. R9, R10, R11, and R12 form yet another first non-inductive resistor unit, whose input is connected to a single-phase voltage W of the frequency converter. R1, R2, and R3 are 51KΩ / 10W non-inductive resistors; R5, R6, and R7 are 51KΩ / 10W non-inductive resistors; and R9, R10, and R11 are 51KΩ / 10W non-inductive resistors. R4, R8, and R12 serve as the fourth resistor in each first non-inductive resistor unit, and are 5KΩ / 2W non-inductive resistors. The outputs of R4, R8, and R12 are connected in parallel, serving as the analog center point C. The voltages across R4, R8, and R12 are the three single-phase attenuation voltages U1C, V1C, and W1C.

[0046] The simulation center point C is connected in series with the second non-inductive resistor. The second non-inductive resistor unit includes four non-inductive resistors connected in series in sequence, namely R13, R14, R15 and R16. Among them, R16 serves as the fourth resistor in the second non-inductive resistor unit, and the voltage across R16 serves as the attenuated zero-sequence voltage C1E.

[0047] It should be noted that although these four voltage levels have low amplitudes, their potential to ground is still very high, posing a risk of electric shock to personnel and insulation breakdown of low-voltage electronic circuits.

[0048] Therefore, these four voltages are then connected to two separate paths: one path connects to a high-speed isolator module, and then to a high-speed data acquisition card; the other path connects to a Hall voltage sensor (i.e., Hall PT), and then to a low-speed data acquisition card.

[0049] Specifically, these four voltage sets are grouped into one channel: the three-phase attenuated voltages U1C, V1C, W1C, and the zero-sequence voltage. Each channel is connected to one of four Hall effect voltage sensors. After isolation and voltage conversion by the Hall effect sensors, the voltages are then connected to the four analog channels of the low-speed acquisition module. The low-speed acquisition module is equipped with an FPGA chip. After isolation and voltage conversion by the Hall effect sensors, the four voltage sets undergo internal A / D conversion and digital isolation within the low-speed acquisition module. The FPGA chip then synchronously reads and stores the voltage data from these four channels according to the low-speed sampling frequency set by the acquisition and warning module. Communication with the low-speed communication board is then established via the backplane bus, and the acquired voltage data is transmitted to the acquisition and warning module via Ethernet. The selectable low-speed sampling frequency range includes 1kHz, 2kHz, 4kHz, 6kHz, 10kHz, and 20kHz.

[0050] The other path involves transmitting the three-phase attenuated voltages U1C, V1C, and W1C through three high-speed isolator modules, and then via shielded cables to three analog channels on a high-speed acquisition card. After high-frequency filtering, A / D conversion, and digital isolation within the high-speed acquisition module, the FPGA chip on the high-speed acquisition card synchronously reads and stores these three analog channels via the SPI bus according to the high-speed sampling frequency set by the acquisition and early warning module. Then, it communicates with the high-speed communication board via the backplane bus, and finally transmits the acquired voltage data to the acquisition and early warning module via Ethernet. The high-speed sampling frequency selection range includes 50kHz, 100kHz, 200kHz, and 300kHz.

[0051] It should be noted that, in order to acquire the three-phase voltage (PWM pulse voltage) output by the frequency converter without distortion, this embodiment includes a high-speed isolator module, such as... Figure 3 As shown, the high-speed isolator module includes an operational amplifier U1 unit for impedance attenuation of each phase attenuation voltage, a signal isolation unit U2 unit for electrical isolation of AC voltage, an operational amplifier U3 unit for signal amplification and zeroing, and two DC / DC isolation power supplies. The two DC / DC isolation power supplies isolate the input and output signals, and are also mutually isolated. The first DC / DC isolation power supply outputs ±15V (V1+, V1-) to power the input side of the operational amplifier U1 unit and the signal isolation unit U2 unit. The second DC / DC isolation power supply outputs ±15V (V2+, V2-) to power the output side of the signal isolation unit U2 unit and the operational amplifier U3 unit. The input of the operational amplifier U1 unit is connected to a single-phase attenuation voltage (U1C, V1C, or W1C), and its output is connected to the input of the signal isolation unit U2 unit. The output of the signal isolation unit U2 unit is connected to the input of the operational amplifier U3 unit, and the output of the operational amplifier U3 unit is connected to the analog channel of the high-speed acquisition module.

[0052] In detail, since the three-phase attenuation voltages U1C, V1C, and W1C output by the frequency converter are high-impedance signals, while the input to the signal isolator U2 unit is a low-impedance signal, it is necessary to convert the high-impedance signal into a low-impedance signal through the operational amplifier U1 unit. Combined with... Figure 3 As shown, the three-phase attenuated voltage U1C, V1C, or W1C output from the frequency converter is connected to terminals J1 and J2. After being attenuated by resistors R1 and R3, it enters operational amplifier U1 through resistors R4 and R5. Operational amplifier U1 uses differential input. The signal ground at the output of operational amplifier U1 is connected to... Figure 3The 0V terminal (V1_0V) of the DC / DC isolation power supply on the left is connected, and the operational amplifier U1 outputs a low-impedance signal. The signal isolator U2 uses analog signal modulation and demodulation technology, providing 1500V AC voltage isolation between its input and output, with a bandwidth of 300kHz. The input of signal isolator U2 comes from the output of U1, and its output is connected to operational amplifier U3 via resistors R6 and R7. Operational amplifier U3 also uses differential input, primarily for signal amplification and zeroing functions, with the output signal voltage amplitude varying within ±5V. The output signal ground of operational amplifier U3 is connected to... Figure 3 The 0V terminal V2_0V of the DC / DC isolation power supply on the right is connected, and the output terminals of the operational amplifier U3 unit are J3 and J4, which go to the analog channel of the high-speed acquisition module.

[0053] Additionally, it should be noted that this embodiment includes one high-speed acquisition module and one low-speed acquisition module. Each acquisition module has eight analog input channels, and each analog input channel is equipped with an independent DC / DC power supply, a high-frequency filter, a 16-bit A / D converter, and a digital isolator to isolate the signals of each channel and avoid mutual interference between channels. Furthermore, the low-speed acquisition module also features a second-order active filter for each analog input channel to filter the inverter's output voltage (PWM pulse voltage) into an approximate sine wave, facilitating subsequent processing by the low-speed acquisition module.

[0054] Each of the high-speed and low-speed acquisition modules is equipped with an FPGA chip. These FPGA chips synchronously control and read the A / D conversion data of each analog channel via their onboard SPI bus. After digital isolation, the acquired data is stored within their respective FPGAs. The acquired voltage data is then transmitted to their respective communication boards via the backplane bus. Each module also receives different sampling frequency commands set by the acquisition and warning module. For example, the high-speed sampling frequency is 300kHz, and the low-speed sampling frequency is 2kHz.

[0055] Before each data acquisition cycle, the high-speed and low-speed sampling frequencies need to be set on the data acquisition and early warning module. The high-speed sampling frequency is determined based on the PWM pulse frequency and minimum duty cycle, and four levels are available: 50kHz, 100kHz, 200kHz, and 300kHz. The low-speed sampling frequency is selected based on the range of motor operating frequency, and six levels are available: 1kHz, 2kHz, 4kHz, 6kHz, 10kHz, and 20kHz.

[0056] In this embodiment, due to the wide operating speed range of the motor on site, if it exceeds the originally set operating range, the motor voltage frequency may not match the sampling frequency (high-speed sampling frequency, low-speed sampling frequency) of the acquisition and early warning module. This could lead to inaccurate LabVIEW spectrum analysis data and potentially issue incorrect early warning information. Furthermore, once the sampling frequency of the acquisition and early warning module is selected, it cannot be changed after operation begins unless the module is stopped. This prevents real-time monitoring and early warning of the inverter (motor) output voltage. To continuously acquire, monitor, and issue early warnings for the inverter (motor) output voltage, this embodiment provides an adaptive early warning submodule within the acquisition and early warning module. When the motor operating frequency exceeds the target range, the adaptive early warning submodule automatically switches the early warning setting value, thereby avoiding issuing incorrect early warnings.

[0057] The data acquisition and early warning module is configured with three Ethernet ports. Two of these ports are used for communication with the high-speed and low-speed communication boards, while the third port is used for communication with the host computer at the remote monitoring center. The module extracts voltage data from the high-speed acquisition module at the high-speed acquisition frequency and from the low-speed acquisition module at the low-speed acquisition frequency. The extracted voltage data is then compressed seamlessly in PDA format and stored using time encoding. Simultaneously, the module uses LabVIEW to create, measure, and perform Fourier transforms on the three high-speed acquired three-phase attenuated voltages and the four low-speed acquired three-phase attenuated voltages and zero-sequence voltage. This yields the effective value, peak-to-peak value, distortion, DC component, zero-sequence voltage, and the number of PWM pulses during the positive and negative half-wave times of each phase's attenuated voltage. Then, based on the high-frequency and low-frequency early warning methods of the inverter output voltage, mathematical and logical operations are performed on these data to achieve real-time monitoring and early warning functions for the inverter's three-phase output voltage. Once a fault is detected, such as pulse loss, false pulses, overvoltage, three-phase voltage imbalance, excessive voltage harmonic components, excessive DC components, or excessive zero-sequence voltage, an early warning message is sent to the staff, such as an early warning reminder or equipment inspection information. Furthermore, the IBA analysis software can be used to analyze the voltage data acquired at low speed and high speed offline, thereby providing a detailed analysis of whether there are other abnormalities in the inverter's three-phase output voltage.

[0058] In addition, the types of faults are divided into minor faults and major faults, based on the severity of the fault. If a minor fault is detected, an early warning message will be sent to the staff, reminding them to pay attention to the operating status of the frequency converter, which can continue to operate without shutting down. If a major fault is detected, an equipment inspection message will be sent to the staff, reminding them to immediately inspect the frequency converter and, if necessary, to shut it down urgently.

[0059] In this embodiment, the high-frequency and low-frequency early warning methods for inverter output voltage specifically include:

[0060] Regarding pulse loss monitoring and early warning, the data acquisition and early warning module calculates the number of PWM pulses for each phase voltage within half a cycle in real time, calculates the average number of PWM pulses for the three-phase voltage within half a cycle, and calculates the deviation between the number of PWM pulses for each phase voltage within half a cycle and the average number of PWM pulses for the three-phase voltage within half a cycle. If the absolute value of the deviation between the number of PWM pulses for any phase voltage within half a cycle and the average number of PWM pulses for the three-phase voltage within half a cycle exceeds 5% of the average number of PWM pulses for the three-phase voltage within half a cycle, and this deviation persists for more than 10 seconds, it is judged as a minor pulse loss fault. If the absolute value of the deviation between the number of PWM pulses for any phase voltage within half a cycle and the average number of PWM pulses for the three-phase voltage within half a cycle exceeds 5% of the average number of PWM pulses for the three-phase voltage within half a cycle, and this deviation persists for more than 10 seconds, it is judged as a severe pulse loss fault.

[0061] Regarding false pulse monitoring and early warning, the acquisition and early warning module calculates the number of PWM pulses during the positive half-wave and negative half-wave of each phase voltage in real time, calculates the deviation between the two periods, and calculates the total number of PWM pulses per phase voltage cycle. If the absolute value of the deviation between the positive and negative half-wave of any phase voltage exceeds 5% of the total number of PWM pulses per phase voltage cycle for more than 10 seconds, it is judged as a minor false pulse fault. If the absolute value of the deviation between the positive and negative half-wave of any phase voltage exceeds 10% of the total number of PWM pulses per phase voltage cycle for more than 10 seconds, it is judged as a severe false pulse fault.

[0062] Regarding overvoltage monitoring and early warning, the data acquisition and early warning module will calculate the absolute value of the peak-to-peak value of the three-phase line voltage in real time. When the peak-to-peak value of the line voltage between any two phases exceeds 110% of the peak-to-peak value of the motor's rated voltage and lasts for more than 3 seconds, it is judged as a minor overvoltage fault. When the peak-to-peak value of the line voltage between any two phases exceeds 120% of the peak-to-peak value of the motor's rated voltage and lasts for more than 3 seconds, it is judged as a severe overvoltage fault.

[0063] Regarding the monitoring and early warning of three-phase voltage imbalance, the data acquisition and early warning module will calculate the average value of the effective values ​​of the three-phase line voltages in real time, and calculate the deviation of the effective value of each phase voltage from the average value of the three-phase voltages. If the absolute value of the voltage deviation of any phase exceeds 15% of the average value of the effective values ​​of the three-phase voltages and lasts for more than 10 seconds, it is judged as a minor voltage imbalance fault; if the absolute value of the voltage deviation of any phase exceeds 35% of the average value of the effective values ​​of the three-phase voltages and lasts for more than 10 seconds, it is judged as a severe voltage imbalance fault.

[0064] Regarding the monitoring and early warning of excessive harmonic components, if the harmonic distortion of any phase line voltage exceeds 15% and lasts for more than 10 seconds, it is judged as a minor harmonic component excessive fault. If the harmonic distortion of any phase line voltage exceeds 35% and lasts for more than 10 seconds, it is judged as a severe harmonic component excessive fault.

[0065] Regarding the monitoring and early warning of DC component exceeding the limit, the ratio of the DC component to the effective value of the three-phase line voltage can be calculated. If the ratio of the DC component to the effective value of any phase voltage exceeds 25% and lasts for more than 10 seconds, it is judged as a minor DC component exceeding the limit fault; if the ratio of the DC component to the effective value of any phase voltage exceeds 50% and lasts for more than 10 seconds, it is judged as a severe DC component exceeding the limit fault.

[0066] Regarding the monitoring and early warning of zero-sequence voltage exceeding the limit, when the absolute value of the instantaneous value of the three-phase zero-sequence voltage exceeds 250% of the average value of the effective value of the three-phase phase voltage and lasts for more than 20 seconds, it is judged as a minor zero-sequence voltage exceeding the limit fault; when the absolute value of the instantaneous value of the three-phase zero-sequence voltage exceeds 350% of the average value of the effective value of the three-phase phase voltage and lasts for more than 20 seconds, it is judged as a severe zero-sequence voltage exceeding the limit fault.

[0067] The data acquisition and early warning module, based on extracted voltage data, can monitor and warn in real time whether the inverter output voltage is over-voltage, whether the three-phase voltage is symmetrical, and whether voltage harmonics and DC components exceed the limits. It reminds operators to strengthen inspections or take necessary measures, effectively preventing abnormal inverter or motor shutdowns or escalation of faults, thus ensuring stable production. It can also monitor and warn of excessive zero-sequence voltage in the motor, indicating deterioration of the insulation of the inverter, motor, or cables between the inverter and motor. This reminds operators to strengthen inspections of the insulation of the inverter, motor, or cables between the inverter and motor, preventing abnormal inverter or motor shutdowns or escalation of faults. Furthermore, it can provide real-time warnings of missing or erroneous PWM pulses in the inverter output voltage, indicating abnormalities or interference in the inverter trigger circuit. This reminds operators to take immediate action, effectively preventing inverter or motor failures or escalation of faults, thus ensuring stable production. In the event of a fault in the electrical drive system, the IBA can also perform detailed offline analysis of the inverter output voltage, providing effective technical support for fault handlers and significantly reducing fault handling time. Furthermore, when troubleshooting the trigger circuit of a high-capacity frequency converter or replacing power devices, an oscilloscope is not required; the PWM pulse voltage output by the low-voltage power-on warning frequency converter can be directly monitored to determine if it is normal. Simultaneously, this technology allows for a more in-depth understanding of the PWM control characteristics and performance differences of various frequency converters, thus providing a technical basis for frequency converter selection.

[0068] In summary, the inverter output voltage early warning system provided in this specification allows for real-time high-frequency and low-frequency monitoring and early warning of the output voltage of an existing inverter through simple modifications. It can predict whether the inverter's output PWM pulse voltage has lost or erroneous pulses, and whether the three-phase voltage is symmetrical, or whether harmonics, DC components, and zero-sequence voltage exceed limits. Timely warnings remind staff to strengthen inspections or take necessary measures to prevent inverter failures from occurring or escalating.

[0069] The above are merely various embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A frequency converter output voltage early warning system, characterized in that, include: Resistor step-down module, high-speed isolator module, high-speed data acquisition module, low-speed data acquisition module, and data acquisition and early warning module; The three-phase voltages output by the frequency converter are connected to the input terminals of the resistor step-down module. The three-phase attenuation voltage and zero-sequence voltage output by the resistor step-down module are isolated by four Hall voltage sensors and then connected to the input terminal of the low-speed acquisition module. The low-speed acquisition module transmits the processed voltage data to the acquisition and early warning module through the communication board. The acquisition and early warning module extracts the voltage data from the low-speed acquisition module according to a preset low-speed sampling frequency, compresses and stores it, and uses LABview to perform waveform creation, measurement, Fourier transform, and calculation processing on the extracted voltage data to achieve low-frequency monitoring and early warning of the frequency converter output voltage. The three-phase attenuated voltage at the output of the resistor step-down module is connected to the input of each of the three high-speed isolator modules. After signal impedance transformation, isolation, and differential amplification, the output of the high-speed isolator module is connected to the input of the high-speed acquisition module. The high-speed acquisition module transmits the processed voltage data to the acquisition and early warning module via a communication board. The acquisition and early warning module extracts the voltage data from the high-speed acquisition module according to a preset high-speed sampling frequency, compresses and stores it, and uses LABview to create, measure, and calculate the extracted voltage data to achieve high-frequency monitoring and early warning of the inverter output voltage.

2. The system according to claim 1, characterized in that, The resistor step-down module includes three first non-inductive resistor units and a second non-inductive resistor unit. The input terminal of each first non-inductive resistor unit is connected to the single-phase voltage output by the frequency converter. The output terminals of the three first non-inductive resistor units are connected in parallel to obtain the simulated neutral point C. The simulated neutral point C is connected to the input terminal of the second non-inductive resistor unit, and the output terminal of the second non-inductive resistor unit is grounded to E. The first non-inductive resistor unit includes a first resistor, a second resistor, a third resistor, and a fourth resistor connected in series. The voltage between the input terminal of the fourth resistor and the analog center point C is used as the single-phase attenuation voltage.

3. The system according to claim 2, characterized in that, The second non-inductive resistor unit includes four non-inductive resistors connected in series, and the voltage across the fourth non-inductive resistor is taken as the zero-sequence voltage.

4. The system according to claim 1, characterized in that, The three-phase attenuation voltage and the zero-sequence voltage are respectively connected to four Hall voltage sensors. After isolation and transformation by the Hall voltage sensors, they are respectively connected to four analog channels at the input end of the low-speed acquisition module.

5. The system according to claim 1, characterized in that, The selection range of the high-speed sampling frequency includes 50KHz, 100KHz, 200KHz and 300KHz.

6. The system according to claim 1, characterized in that, The selection range of the low-speed sampling frequency includes 1KHz, 2KHz, 4KHz, 6KHz, 10KHz and 20KHz.

7. The system according to claim 1, characterized in that, High-frequency and low-frequency monitoring and early warning of inverter output voltage, including: The data acquisition and early warning module extracts the voltage data and uses LABview to create, measure, and perform Fourier transform on the waveform to obtain the effective value, peak-to-peak value, distortion, DC component, zero-sequence voltage, and the number of PWM pulses during the positive and negative half-wave time of each phase attenuation voltage. Based on the high-frequency and low-frequency early warning methods for inverter output voltage, mathematical and logical operations are performed on the effective value, peak-to-peak value, distortion, DC component, zero-sequence voltage, and the number of PWM pulses during the positive and negative half-wave time of each phase attenuation voltage of the obtained three-phase attenuation voltage to monitor and warn whether there is a fault in the inverter output voltage.

8. The system according to claim 7, characterized in that, The faults include pulse loss, pulse error, overvoltage, three-phase voltage imbalance, excessive voltage harmonic components, excessive DC components, and excessive zero-sequence voltage.

9. The system according to claim 7, characterized in that, The types of faults include minor faults and major faults; If a minor fault is detected, an early warning message will be sent to the staff, and the frequency converter will continue to operate without shutting down. If a serious fault is detected, equipment inspection information is sent to staff for inspection of the frequency converter.

10. The system according to claim 1, characterized in that, The high-speed isolator module includes an operational amplifier U1 unit for impedance attenuation of three-phase attenuated voltage, a signal isolation U2 unit for electrical isolation of AC voltage, an operational amplifier U3 unit for signal amplification and zeroing, and two DC / DC isolated power supplies. One of the DC / DC isolated power supplies provides power to the input side of the operational amplifier U1 unit and the signal isolation U2 unit respectively, and the other DC / DC isolated power supply provides power to the output side of the signal isolation U2 unit and the operational amplifier U3 unit respectively. The input terminal of the operational amplifier U1 unit is connected to a single-phase attenuated voltage, and the output terminal is connected to the input terminal of the signal isolation unit U2; the output terminal of the signal isolation unit U2 unit is connected to the input terminal of the operational amplifier U3 unit, and the output terminal of the operational amplifier U3 unit is connected to the analog channel of the high-speed acquisition module.

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