Current sampling circuit and compressor surge monitoring system

Abstract

The utility model discloses a current sampling circuit and a compressor surge monitoring system. The current sampling circuit comprises an instantaneous current sampling module and a current determining module. The instantaneous current sampling module is connected with the current determination module and is used for acquiring an instantaneous current value of a motor of the compressor driven by the frequency converter to rotate; the current determination module is used for determining a current sampling value according to a preset algorithm and the instantaneous current value, and the current sampling value is used for monitoring whether the compressor surges or not. According to the current sampling circuit, in the surge monitoring process of rotation of the compressor motor driven by the frequency converter, a special current effective value sensor does not need to be additionally arranged, and an instantaneous current value is obtained by directly sampling instantaneous current through an instantaneous current sensor of the frequency converter; and then the effective current value for preventing the compressor from surging is determined according to the preset algorithm and the instantaneous current value, redundancy of sensor configuration is not generated, and the cost of compressor surging monitoring is reduced.

Description

Technical Field

[0001] This utility model relates to the field of compressor operation status monitoring technology, and in particular to a current sampling circuit and a compressor surge monitoring system. Background Technology

[0002] The surge monitoring method for compressors in related technologies uses the changing trends of parameters such as compressor vibration characteristics, surge pressure ratio, discharge pressure fluctuations, and motor operating current fluctuations, along with compressor fluid dynamics data, to jointly determine whether surge characteristics have occurred. When the compressor meets the preset judgment rules, the compressor controller eliminates surge by adjusting the motor speed setpoint and changing the opening degree of the compressor inlet and outlet valves.

[0003] In related technologies, compressor controllers typically acquire motor current data using a current RMS sensor. When a current below the rated current is applied, the sensor automatically calculates the RMS value of the current and converts it into a 4-20mA signal. 4mA corresponds to 0A, and 20mA corresponds to the sensor's rated current. When measuring motor current, the selected sensor has a 50%-100% margin to ensure that even with slight overcurrent, the motor remains within the linear range of the current RMS sensor. The measured current RMS signal is transmitted to the compressor controller via the 4-20mA interface. The controller then combines this signal with other surge detection rules to assess the surge situation and adjusts the inverter's setpoint and control valve opening in real time to eliminate surge.

[0004] Currently, when using frequency converters to drive compressors, the acquisition of motor operating current data still follows the old method of using RMS current sensors when driven by mains frequency grids. However, in this method, the frequency converter must be equipped with an output current sensor to ensure its own stable operation and protect against abnormal conditions. Since the frequency converter control uses a current sensor that samples instantaneous values, while compressor surge monitoring requires a current sensor that outputs RMS values, the two have different functions. This leads to redundancy in sensor configuration and increases costs. Utility Model Content

[0005] In view of this, the present invention aims to at least partially solve one of the problems in the related art. Therefore, the purpose of the present invention is to provide a current sampling circuit and a compressor surge monitoring system.

[0006] This application provides a current sampling circuit. The current sampling circuit includes an instantaneous current sampling module and a current determination module, wherein the instantaneous current sampling module is connected to the current determination module; the instantaneous current sampling module is used to acquire the instantaneous current value of the motor driving the compressor via a frequency converter; the current determination module is used to determine a current sampling value according to a preset algorithm and the instantaneous current value, and the current sampling value is used to monitor whether the compressor experiences surge.

[0007] In some implementations, the instantaneous current sampling module is used to acquire the instantaneous current value output from the inverter output terminal that drives the motor of the compressor to rotate.

[0008] In some implementations, the instantaneous current sampling module is used to acquire the instantaneous current value input at the inverter input terminal that drives the motor of the compressor to rotate.

[0009] In some embodiments, the current determination module includes a calculation unit electrically connected to the instantaneous current sampling module. The instantaneous current sampling module is used to acquire the first-phase instantaneous current value and the second-phase instantaneous current value of the motor driving the compressor via the frequency converter. The calculation unit is used to calculate the third-phase instantaneous current value based on the first-phase instantaneous current value, the second-phase instantaneous current value, and a first formula. The current sampling value is calculated based on the first-phase instantaneous current value, the second-phase instantaneous current value, the third-phase instantaneous current value, and the second formula.

[0010] In some embodiments, the current determination module includes an amplification unit connected between the instantaneous current sampling module and the calculation unit; the amplification unit is used to amplify the first phase instantaneous current value and the second phase instantaneous current value to obtain amplified first phase instantaneous current value and second phase instantaneous current value.

[0011] In some embodiments, the current determination module includes an analog-to-digital converter, a digital signal processor, a digital-to-analog converter, and a voltage-to-current converter; a first terminal of the analog-to-digital converter is connected to the computing unit, and a second terminal of the analog-to-digital converter is connected to a first terminal of the digital signal processor; a second terminal of the digital signal processor is connected to a first terminal of the digital-to-analog converter; a second terminal of the digital-to-analog converter is connected to the voltage-to-current converter; the analog-to-digital converter performs analog-to-digital conversion on the current sample value output by the computing unit to obtain a converted digital signal; the digital signal processor performs calculations on the digital signal to obtain a processed digital signal; the digital-to-analog converter performs digital-to-analog conversion on the processed digital signal to obtain a converted voltage signal; and the voltage-to-current converter converts the voltage signal into a current signal corresponding to the current sample value.

[0012] In some embodiments, the current determination module further includes an adjustment unit connected between the digital signal processor and the digital-to-analog converter. The adjustment unit is used to adjust the current signal to a range of [4mA, 20mA] according to the range corresponding to the rated current of the motor.

[0013] In some embodiments, the current determination module further includes a filter connected between the digital signal processor and the digital-to-analog converter, and the filter is positioned before the adjustment unit; the filter is used to filter the digital signal calculated by the digital signal processor according to a digital low-pass filter function, and output the filtered digital signal to the digital-to-analog converter.

[0014] In some implementations, the function expression of the digital low-pass filter function is: Yn=a*Y(n-1)+(1-a)*Xn; where Y(n) represents the output value of the filtered digital signal at the current time, Y(n-1) represents the output value of the filtered digital signal at the previous time, X(n) represents the original data at the current time without filtering, a represents the filtering coefficient, and 0<a<1.

[0015] This application also provides a compressor surge monitoring system. The compressor surge monitoring system includes a frequency converter, a compressor, and a compressor surge monitoring module. The frequency converter includes a current sampling circuit as described in any of the above embodiments. The frequency converter is electrically connected to the compressor and the compressor surge monitoring module, respectively. The compressor surge monitoring module is used to: collect operating data of the compressor; receive the current sampling value output by the current sampling circuit; and determine whether the compressor is experiencing surge based on the operating data and the current sampling value.

[0016] Thus, this application uses a current sampling circuit to determine the current sampling value for monitoring whether the compressor is experiencing surge. During the surge monitoring process of the compressor motor driven by the frequency converter, there is no need to add an additional dedicated current RMS sensor. The instantaneous current sensor built into the frequency converter is used directly to sample the instantaneous current. Then, the effective current value that prevents the compressor from experiencing surge is determined according to the preset algorithm and the instantaneous current value. This avoids redundancy in sensor configuration and reduces the cost of compressor surge monitoring.

[0017] Additional aspects and advantages of this invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0018] The above and / or additional aspects and advantages of this utility model will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, in which:

[0019] Figure 1 This is a schematic diagram of the structure of a compressor surge monitoring system in related technologies;

[0020] Figure 2 This is a schematic diagram of the current sampling circuit according to some embodiments of this application;

[0021] Figure 3 This is a schematic diagram of the structure of a compressor surge monitoring system according to certain embodiments of this application;

[0022] Figure 4 This is a schematic diagram of the current sampling circuit according to some embodiments of this application;

[0023] Figure 5 This is a schematic diagram illustrating the working principle of the calculation unit in the current sampling circuit of some embodiments of this application;

[0024] Figure 6 This is a schematic diagram of the current sampling circuit according to some embodiments of this application;

[0025] Figure 7 This is a schematic diagram of the current sampling circuit according to some embodiments of this application;

[0026] Figure 8 This is a schematic diagram of the current sampling circuit according to some embodiments of this application;

[0027] Figure 9 This is a schematic diagram illustrating the working principle of the filter in the current sampling circuit of some embodiments of this application.

[0028] Main component reference numerals:

[0029] Compressor surge monitoring system 1000;

[0030] The system includes: a current sampling circuit 100, an instantaneous current sampling module 10, a current determination module 20, a calculation unit 21, an amplification unit 22, an analog-to-digital converter 23, a digital signal processor 24, a digital-to-analog converter 25, a voltage-to-current converter 26, an adjustment unit 27, and a filter 28.

[0031] Inverter 200, compressor 300, compressor surge monitoring module 400. Detailed Implementation

[0032] The embodiments of this utility model are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this utility model, and should not be construed as limiting this utility model.

[0033] In the description of this utility model, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance, or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this utility model, "a plurality of" means two or more, unless otherwise explicitly specified.

[0034] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation" and "connection" should be interpreted broadly, referring to fixed connections, detachable connections, or integral connections; mechanical connections, electrical connections, or connections capable of communication; direct connections or indirect connections through an intermediate medium; and connections within two components or interactions between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0035] The following disclosure provides many different embodiments or examples for implementing various structures of the present invention. To simplify the disclosure, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the scope of the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed.

[0036] The embodiments of this utility model are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this utility model, and should not be construed as limiting this utility model.

[0037] Figure 1 This is a compressor surge monitoring system for compressor motors driven by frequency converters. For example... Figure 1 As shown, the two instantaneous current sensors inside the frequency converter are used for the converter's own control and protection. The two instantaneous current sensors are used to collect the instantaneous current of the two phases driving the motor. From... Figure 1 As can be seen, when sampling the current of the motor driving the compressor, the compressor surge monitoring module needs to be equipped with an additional current RMS sensor to transmit the effective current sampling data corresponding to the two-phase instantaneous current to the compressor surge monitoring module through a 4-20mA signal format.

[0038] In other words, when a frequency converter controls the compressor, it needs to be equipped with an instantaneous current sensor that can sample instantaneous values. However, when the compressor surge monitoring module monitors the compressor's operating status, it also needs to be equipped with an RMS current sensor that outputs the RMS current value. The instantaneous current sensor and the RMS current sensor have different functions, which leads to redundancy in the sensor configuration of current compressor surge monitoring systems, increasing costs.

[0039] In view of this, please refer to Figure 2 This application discloses a current sampling circuit 100. The current sampling circuit 100 includes an instantaneous current sampling module 10 and a current determination module 20. The instantaneous current sampling module 10 is connected to the current determination module 20. The instantaneous current sampling module 10 is used to acquire the instantaneous current value of the motor driving the compressor via a frequency converter. The current determination module 20 is used to determine the current sampling value according to a preset algorithm and the instantaneous current value. The current sampling value is used to monitor whether the compressor experiences surge.

[0040] Specifically, the instantaneous current sampling module 10 may include the instantaneous current sensor mentioned above, which can collect the instantaneous current value at a certain moment when the motor of the inverter drives the compressor to rotate.

[0041] The current determination module 20 can calculate and determine the current sampling value based on a preset algorithm and the instantaneous current value collected by the instantaneous current sampling module 10. The preset algorithm can be a pre-defined program algorithm. That is to say, the current determination module 20 of this application can calculate or process the instantaneous current value using a preset algorithm to obtain a current sampling value that can effectively monitor compressor surge.

[0042] The current sampling value is used to monitor whether the compressor is experiencing surge. That is to say, the current determination module 20 can output the current sampling value to the compressor surge monitoring module 30, and combine it with other monitoring data inside the compressor surge monitoring module 30 to monitor whether the compressor is experiencing surge.

[0043] Please refer to Figure 3 Both the instantaneous current sampling module 10 and the current determination module 20 can be structural components within the inverter's internal controller. For example, the instantaneous current sampling module 10 can be an instantaneous current sensor within the inverter's internal controller, and the current determination module 20 can be a control module within the inverter's internal controller. That is to say, the current sampling circuit 100 of this application can be a circuit formed by adding a preset algorithm to the existing instantaneous current sensor in the inverter's internal controller and the existing control module.

[0044] Thus, this application uses a current sampling circuit 100 to determine the current sampling value for monitoring whether the compressor is experiencing surge. During the surge monitoring process of the compressor motor driven by the frequency converter, there is no need to add an additional dedicated current RMS sensor. The instantaneous current sensor built into the frequency converter is used directly to sample the instantaneous current. Then, the effective current value that prevents the compressor from experiencing surge is determined according to the preset algorithm and the instantaneous current value. This avoids redundancy in sensor configuration and reduces the cost of compressor surge monitoring.

[0045] In some implementations, the instantaneous current sampling module 10 is used to acquire the instantaneous current value output from the inverter output terminal that drives the motor of the compressor to rotate.

[0046] In other words, the instantaneous current sampling module 10 of this application can be set in the output circuit of the motor of the compressor from the output current of the frequency converter, so as to collect the instantaneous current value of the output of the frequency converter and obtain the instantaneous current value relatively quickly.

[0047] In some implementations, the instantaneous current sampling module 10 is used to acquire the instantaneous current value input at the inverter input terminal that drives the motor of the compressor to rotate.

[0048] In other words, the instantaneous current sampling module 10 of this application can also be set in the input circuit of the inverter input current, and the collected current value is used as the instantaneous current value. This method of collecting the instantaneous current value of the motor driving the compressor at the input of the inverter can be applied when the current harmonics of the compressor motor are large or the fluctuation period is short, and it can also be applied to the scenario when the surge oscillation period is long, which can ensure the accuracy of the instantaneous current value.

[0049] Please see Figure 4 In some embodiments, the current determination module 20 includes a calculation unit 21. The calculation unit 21 is electrically connected to the instantaneous current sampling module 10, which acquires the first-phase instantaneous current value and the second-phase instantaneous current value of the motor driving the compressor via the frequency converter. The calculation unit 21 calculates the third-phase instantaneous current value based on the first-phase instantaneous current value, the second-phase instantaneous current value, and a first formula; and calculates the current sampling value based on the first-phase instantaneous current value, the second-phase instantaneous current value, the third-phase instantaneous current value, and the second formula.

[0050] Specifically, such as Figure 4 As shown, the instantaneous current sampling module 10 may include an A-phase instantaneous current sensor and a C-phase instantaneous current sensor. The A-phase instantaneous current sensor is used to acquire the first-phase instantaneous current value Ia of the motor driving the compressor to rotate, and the C-phase instantaneous current sensor is used to acquire the second-phase instantaneous current value Ia of the motor driving the compressor to rotate.

[0051] The first formula can be Ib = -(Ia + Ic), where Ia is the instantaneous current value of the first phase, Ic is the instantaneous current value of the second phase, and Ib is the instantaneous current value of the third phase. That is, the calculation unit 21 of this application can calculate the instantaneous value of the third phase current Ib based on the fact that the vector sum of the three-phase currents in a three-phase system without a neutral wire is zero.

[0052] The second formula can be Irms = sqrt((Ia*Ia+Ib*Ib+Ic*Ic) / 3), where Irms is the current sampling value.

[0053] In detail, such as Figure 3 and Figure 5 As shown, the frequency converter detects the instantaneous values ​​of two phase currents in the three wires connected to the motor. Based on the fact that the instantaneous sum of the three phase currents is zero, the instantaneous value of Ib = -(Ia + Ic) is obtained. Then, the instantaneous value of the motor sample value is calculated according to the general formula for calculating the effective value of current of the frequency converter, Irms = sqrt((Ia*Ia + Ib*Ib + Ic*Ic) / 3).

[0054] Understandably, if single-phase current sampling is used to calculate the effective value, then because the single-phase sinusoidal current is symmetrical within one cycle, it is necessary to continuously sample for at least half a cycle in order to obtain a relatively accurate current sample value through integration or averaging. This is because if only a very short time period is sampled, the obtained current value may only be a peak or trough of the sine wave, which cannot represent the thermal effect within the entire cycle.

[0055] In the current sampling circuit 100 of this application, when the frequency converter detects the three-phase current connected to the motor, it can simultaneously obtain the instantaneous values ​​of the three-phase current. Therefore, the calculation formula for the effective value of the three-phase current can be directly applied to calculate the current sampling value. This eliminates the need to wait at least half a cycle to calculate the current sampling value, as is required for single-phase current sampling, resulting in a faster response speed. This is because the simultaneous sampling of the three-phase current already contains sufficient information to reflect the thermal effects throughout the entire cycle.

[0056] Thus, the current determination module 20 in the current sampling circuit 100 of this application can calculate the third phase instantaneous current value through the calculation unit 21 based on the first phase instantaneous current value, the second phase instantaneous current value, and the first formula, and simultaneously obtain the instantaneous values ​​of the three phase currents. Then, the instantaneous value of the motor sampling value can be calculated more quickly through the instantaneous values ​​of the three phase currents.

[0057] Please see Figure 6 In some embodiments, the current determination module 20 includes an amplification unit 22. The amplification unit 22 is connected between the instantaneous current sampling module 10 and the calculation unit 21. The amplification unit 22 is used to amplify the instantaneous current values ​​of the first phase and the second phase to obtain amplified instantaneous current values ​​of the first phase and the second phase.

[0058] Specifically, the amplification unit 22 can be an amplification circuit composed of operational amplifiers. An operational amplifier is a circuit unit with very high amplification, mainly composed of three parts: an input stage, an intermediate stage, and an output stage. The input stage typically uses a differential amplifier circuit to effectively suppress zero-point drift and temperature drift, and improve the circuit's input impedance and common-mode rejection ratio. The intermediate stage is mostly a common-emitter (or common-collector) amplifier circuit to obtain higher voltage gain and power gain. The output stage is usually a high-power common-collector amplifier circuit (emitter follower) to reduce output resistance and improve the circuit's load-driving capability.

[0059] Understandably, instantaneous current is often very weak, and the directly acquired current value may be affected by noise and interference, resulting in inaccurate values. This application uses the amplification unit 22 to amplify the instantaneous current value, which can convert the small input current into a larger output current, thereby increasing the strength of the instantaneous current signal and making the acquired instantaneous current value more accurate.

[0060] Thus, before calculating the current sampling value using the instantaneous current values ​​of the first and second phases, the current determination module 20 of this application can first amplify the instantaneous current values ​​of the first and second phases to obtain amplified instantaneous current values ​​of the first and second phases. This facilitates improving the strength of the instantaneous current signal and obtaining a more accurate instantaneous current value, making the current sampling value calculated subsequently more accurate.

[0061] Please see Figure 4 or Figure 6 In some embodiments, the current determination module 20 includes an analog-to-digital converter 23, a digital signal processor 24, a digital-to-analog converter 25, and a voltage-to-current converter 26. A first terminal of the analog-to-digital converter 23 is connected to the computing unit 21, and a second terminal of the analog-to-digital converter 23 is connected to a first terminal of the digital signal processor 24. A second terminal of the digital signal processor 24 is connected to a first terminal of the digital-to-analog converter 25. A second terminal of the digital-to-analog converter 25 is connected to the voltage-to-current converter 26. The analog-to-digital converter 23 performs analog-to-digital conversion on the amplified instantaneous current value to obtain a converted digital signal. The digital signal processor 24 performs calculations on the digital signal to obtain a processed digital signal. The digital-to-analog converter 25 performs digital-to-analog conversion on the processed digital signal to obtain a converted voltage signal. The voltage-to-current converter 26 converts the voltage signal into a current signal corresponding to the current sampling value.

[0062] Specifically, the analog-to-digital converter 23 (ADC) is an electronic component that can convert analog signals into digital signals. The ADC 23 first receives the current sample values ​​input from the computing unit 21, and then performs analog-to-digital conversion on the analog signal composed of the current sample values ​​to obtain the converted digital signal. The digital signal converted by the ADC is usually represented in binary form. Binary is a counting system based on 0s and 1s, which is very suitable for the processing of electronic devices because electronic devices typically have only two stable states (such as on and off). That is to say, a digital signal can be a sequence of "0"s or "1"s.

[0063] Furthermore, the analog-to-digital converter 23 can also be a "Σ-Δ (Delta Sigma) converter," or, when the analog-to-digital converter 23 is a "Σ-Δ converter," it can be integrated with the instantaneous current sensor of the instantaneous current sampling module 10, forming an integrated device of the "Σ-Δ converter" and the instantaneous current sensor, making the structure of the current sampling circuit 100 of this application more compact. A "Σ-Δ converter" refers to a converter that performs analog-to-digital conversion using a sigma-delta modulation sampling processing method.

[0064] The digital signal processor 24 can perform various operations and processes on the converted digital signal, such as filtering, transformation, detection, modulation, and demodulation, to extract useful information or change the properties of the signal. The digital signal processor 24 can be a device composed of components such as a digital signal processor (DSP), a field-programmable gate array (FPGA), or a microcontroller unit (MCU), and there are no limitations on its capabilities.

[0065] Then, the digital-to-analog converter 25 (DAC) performs digital-to-analog conversion on the processed digital signal, that is, converts the digital signal processed by the digital signal processor 24 back into an analog signal, which can be output in the form of a voltage signal. In other words, this application can integrate peripheral analog circuits such as ADC and amplifier circuits with MCU, DSP, and FPGA into a single chip to form an integrated chip for determining the current sampling value, making the structure of the current sampling circuit 100 of this application more compact and simpler.

[0066] Finally, the voltage-to-current converter 26 converts the voltage signal output by the digital-to-analog converter 25 into a current signal with the current sample value, so that the current signal can be output to the compressor surge monitoring module for compressor surge monitoring.

[0067] In other words, this application uses the inverter's original instantaneous current sensor, along with related hardware circuits, to perform data acquisition and transformation, thereby outputting current sampling values ​​that can be used by the compressor surge monitoring module to monitor the compressor's surge.

[0068] like Figure 4 As shown, the current signals sampled by the A-phase instantaneous current sensor and the C-phase instantaneous current sensor are amplified and adjusted by the amplification unit 22, and the B-phase instantaneous current and the current sample value are calculated by the calculation unit 21. Then, the current sample value from the calculation unit 21 is transmitted to the ADC inside the inverter controller for analog-to-digital conversion. After ADC conversion, the current data is further processed digitally by the DSP, FPGA, MCU, etc., inside the inverter controller, and then output to the DAC inside the inverter controller for digital-to-analog conversion. The voltage signal output by the DAC is then converted into a current signal by the voltage-to-current converter inside the inverter controller. This current signal is transmitted to the compressor surge monitoring module for surge detection.

[0069] Thus, the current determination module 20 of this application can process the instantaneous current value according to a preset algorithm using the existing analog-to-digital converter, digital signal processor, digital-to-analog converter and voltage-to-current converter in the controller of the frequency converter to obtain a current signal that can be used for surge determination.

[0070] Please see Figure 7 In some embodiments, the current determination module 20 further includes an adjustment unit 27. The adjustment unit 27 is connected between the digital signal processor 24 and the digital-to-analog converter 25. The adjustment unit 27 is used to adjust the current signal to a range of [4mA, 20mA] according to the range corresponding to the rated current of the motor.

[0071] In other words, after the instantaneous current sampling module 10 acquires the instantaneous current signals of phases A and C, the amplification unit 22 amplifies and adjusts them, and the calculation unit 21 calculates the initial current sampling value. Then, the calculation unit 21 transmits the initial current sampling value without digital filtering to the ADC inside the inverter controller for analog-to-digital conversion. The converted data is then processed by DSP, FPGA, MCU, etc., to obtain a digital signal.

[0072] The adjustment unit 27 can adjust the digital signal according to the range corresponding to the rated current of the compressor motor so that the final output current signal is within the range of [4mA, 20mA]. Then, the adjustment unit 27 can output the adjusted digital signal to the DAC for digital-to-analog conversion. After conversion, the voltage signal output by the DAC is processed by the voltage-to-current converter 26 and the adjustment unit 27 into a 4-20mA range current signal compatible with the interface form in related technologies. This current signal is transmitted to the compressor surge monitoring module for surge detection.

[0073] Please see Figure 8 In some embodiments, the current determination module 20 further includes a filter 28. The filter 28 is connected between the digital signal processor 24 and the digital-to-analog converter 25, and is positioned before the adjustment unit 27. The filter 28 is used to filter the digital signal calculated by the digital signal processor 24 according to a digital low-pass filter function, and outputs the filtered digital signal to the digital-to-analog converter 25.

[0074] That is to say, such as Figure 8As shown, the digital signal processor 24 of this application can output the digital signal corresponding to the calculated current sampling value to the filter 28. After filtering by the digital low-pass filter function in the filter 28, and then by digital-to-analog conversion methods such as DAC conversion and PWM modulation output filtering, a voltage signal is obtained. Finally, the voltage signal output by the DAC is processed by the voltage-to-current converter 26 and the adjustment unit 27 and becomes a current signal with a range of 4-20mA that is compatible with the interface form in related technologies.

[0075] Thus, by setting a filter 28 between the digital signal processor 24 and the digital-to-analog converter 25 to filter the digital signal, this application can reduce the interference of instantaneous current value sampling on the current signal finally output to the compressor surge monitoring module.

[0076] Specifically, in some implementations, the functional expression of the digital low-pass filter function is as follows:

[0077] Yn=a*Y(n-1)+(1-a)*Xn

[0078] Where Y(n) represents the filtered digital signal output value at the current time, Y(n-1) represents the filtered digital signal output value at the previous time, X(n) represents the unfiltered raw data at the current time, and a represents the filtering coefficient, 0 < a < 1.

[0079] Specifically, such as Figure 9 As shown, Figure 9 The flowchart illustrates the internal working principle of filter 28. First, the filtered digital signal output value Y(n-1) from the previous moment is read. Then, the unfiltered raw data X(n) of the current moment, calculated from the root mean square of the three-phase current, is substituted into the formula Yn=a*Y(n-1)+(1-a)*Xn to calculate the filtered digital signal output value Yn at the current moment. Finally, Yn is adjusted according to the measurement range and output to the DAC for digital-to-analog conversion. After digital-to-analog conversion by the DAC, the voltage signal output by the DAC is converted into a current signal by the voltage-to-current converter inside the inverter controller. This current signal is transmitted to the compressor surge monitoring module for surge detection.

[0080] Understandably, commonly used RMS current sensors in engineering have a test bandwidth (-1dB) range of DC or 20Hz-6000Hz, and a response speed to step signals of no more than 150ms@0-90% of the target value. 20Hz is the lower limit of the sensor's effective bandwidth; lower frequencies will affect calculation accuracy. For compressor drive motors, the operating frequency range under normal conditions is between 25Hz and 125Hz, and RMS current sensors can effectively meet the bandwidth requirements of the test signal. The step signal response speed represents the delay between the sensor's output and input; RMS current sensor parameters include a requirement for an output change rate of "0-90% response speed less than 150ms".

[0081] This application utilizes the current sampling value or effective current value obtained by the current sampling circuit 100. By adjusting the filter coefficient in the digital low-pass filter function, it can also meet the corresponding output change rate of the effective current value change when the compressor surge is determined.

[0082] For example, if the effective value calculation frequency fc of the three-phase current of the motor is 5kHz, and the output data frequency after using a median filter with a filter window size of 5 is 1kHz, according to the formula for calculating the cutoff frequency fc of the low-pass filter, fc = (1-a) / (2π*T*a), it can be calculated that when the constant a in the digital low-pass filter function is adjusted in the range of 0.9 to 0.99, the low-pass frequency fc varies from 17.7Hz to 1.61Hz. In this formula, fc is the cutoff frequency of the low-pass filter, that is, the highest frequency of the signal that the filter allows to pass; signals above this frequency will be significantly attenuated. a is the filter constant or coefficient, which determines the characteristics of the filter, such as the cutoff frequency and the filtering effect. In digital filter design, adjusting this parameter can change the filter response. T is the sampling period, which is the time interval between signal samples. In digital signal processing, the sampling period is fixed and determined by the sampling frequency f, T = 1 / f.

[0083] For conventional low-frequency systems, a Gaussian response characteristic must be met, meaning the bandwidth fc * rise time t = 0.35. Referring to the current RMS sensor used for compressor surge monitoring in related technologies, the rise time t is approximately 0.15s. Using the aforementioned formula for bandwidth fc, the equivalent signal bandwidth of the low-frequency system output is calculated to be fc = 0.35 / 0.15 = 2.33Hz. This frequency fc falls within the adjustable range of the digital low-pass filter (17.7Hz to 1.61Hz), and the filter coefficient a = 0.9856 can be calculated.

[0084] Thus, the filter coefficient 'a' in filter 28 of this application can be flexibly adjusted according to the response speed requirements of the compressor surge monitoring system to meet a wider range of rapid surge monitoring requirements.

[0085] Please see Figure 3 This application also provides a compressor surge monitoring system 1000. The compressor surge monitoring system 1000 includes a frequency converter 200, a compressor 300, and a compressor surge monitoring module 400. The frequency converter 200 includes the current sampling circuit 100 as described in any of the above embodiments. The frequency converter 200 is electrically connected to the compressor 300 and the compressor surge monitoring module 400, respectively. The compressor surge monitoring module 400 is used to collect operating data of the compressor 300; receive current sampling values ​​output by the current sampling circuit 100; and determine whether the compressor 300 has experienced surge based on the operating data and the current sampling values.

[0086] Specifically, the structure and working principle of the current sampling circuit 100 are as described above, and will not be repeated here.

[0087] The operating data collected from compressor 300 can include pressure data and power data. Pressure data includes suction pressure data and discharge pressure data. The operating data of compressor 300 refers to the data required for compressor operation, including: pressure data (including suction pressure data and discharge pressure data), current data, and power data, which respectively characterize the pressure (suction pressure and discharge pressure), current, and power during compressor operation.

[0088] Then, the compressor surge monitoring module 400 can calculate the compressor surge pressure ratio based on pressure data and the compressor fluctuation index based on operating data; the fluctuation index includes: discharge pressure fluctuation index, current fluctuation index, and power fluctuation index. Based on the fluctuation index and surge pressure ratio, the compressor's weighting factor and surge factor are determined, where the weighting factors include discharge pressure weighting factor, current weighting factor, and power weighting factor, and the surge factor includes discharge pressure surge factor, current surge factor, and power surge factor. Finally, based on the weighting factor and surge factor, it is determined whether the compressor has experienced surge.

[0089] Thus, the compressor surge monitoring system 1000 of this application uses a current sampling circuit 100 to determine the current sampling value for monitoring whether the compressor 300 is experiencing surge. During the surge monitoring process of the motor rotation of the compressor 300 driven by the inverter 200, there is no need to add an additional dedicated current RMS sensor. The instantaneous current sensor built into the inverter 200 is used directly to sample the instantaneous current. Then, the effective current value that prevents the compressor 300 from experiencing surge is determined according to the preset algorithm and the instantaneous current value. This avoids redundancy in sensor configuration and reduces the cost of compressor surge monitoring.

[0090] The above embodiments only illustrate several implementation methods of this utility model, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this utility model patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this utility model, and these all fall within the protection scope of this utility model. Therefore, the protection scope of this utility model patent should be determined by the appended claims.

Claims

1. A current sampling circuit, characterized in that, The current sampling circuit includes an instantaneous current sampling module and a current determination module, wherein the instantaneous current sampling module is connected to the current determination module; The current determination module includes a calculation unit, which is electrically connected to the instantaneous current sampling module, and the output terminal of the current determination module is electrically connected to the compressor surge monitoring module of the compressor. The instantaneous current sampling module is used to obtain the first-phase instantaneous current value and the second-phase instantaneous current value of the motor that drives the compressor to rotate; The calculation unit is used to calculate the instantaneous current value of the third phase based on the instantaneous current value of the first phase, the instantaneous current value of the second phase, and the fact that the vector sum of the three-phase currents in the three-phase system without a neutral wire is zero; and to calculate the current sampling value based on the instantaneous current value of the first phase, the instantaneous current value of the second phase, the instantaneous current value of the third phase, and the general current effective value calculation formula of the frequency converter. The current sampling value is used to monitor whether the compressor experiences surge. The general formula for calculating the effective value of the current of the frequency converter is: Irms=sqrt((Ia*Ia+Ib*Ib+Ic*Ic) / 3), where Irms is the current sampling value, Ia is the instantaneous current value of the first phase, Ic is the instantaneous current value of the second phase, Ib is the instantaneous current value of the third phase, and sqrt() is the square root function.

2. The current sampling circuit according to claim 1, characterized in that, The instantaneous current sampling module is used to obtain the instantaneous current value output by the inverter output terminal that drives the motor of the compressor to rotate.

3. The current sampling circuit according to claim 1, characterized in that, The instantaneous current sampling module is used to obtain the instantaneous current value input at the input terminal of the frequency converter that drives the motor of the compressor to rotate.

4. The current sampling circuit according to claim 1, characterized in that, The current determination module includes an amplification unit, which is connected between the instantaneous current sampling module and the calculation unit; The amplification unit is used to amplify the instantaneous current values ​​of the first phase and the second phase to obtain amplified instantaneous current values ​​of the first phase and the second phase.

5. The current sampling circuit according to claim 4, characterized in that, The current determination module includes an analog-to-digital converter, a digital signal processor, a digital-to-analog converter, and a voltage-to-current converter; a first terminal of the analog-to-digital converter is connected to the computing unit, a second terminal of the analog-to-digital converter is connected to a first terminal of the digital signal processor, a second terminal of the digital signal processor is connected to a first terminal of the digital-to-analog converter, and a second terminal of the digital-to-analog converter is connected to the voltage-to-current converter. The analog-to-digital converter is used to perform analog-to-digital conversion on the current sample value output by the computing unit to obtain the converted digital signal; The digital signal processor is used to perform calculations on the digital signal to obtain a processed digital signal; The digital-to-analog converter is used to perform digital-to-analog conversion on the processed digital signal to obtain a converted voltage signal; The voltage-to-current converter is used to convert the voltage signal into a current signal corresponding to the current sample value.

6. The current sampling circuit according to claim 5, characterized in that, The current determination module further includes an adjustment unit connected between the digital signal processor and the digital-to-analog converter. The adjustment unit is used to adjust the current signal to the range range of [4mA, 20mA] according to the range corresponding to the rated current of the motor.

7. The current sampling circuit according to claim 6, characterized in that, The current determination module further includes a filter connected between the digital signal processor and the digital-to-analog converter, and the filter is disposed before the adjustment unit. The filter is used to filter the digital signal calculated by the digital signal processor according to the digital low-pass filter function, and the filtered digital signal is output to the digital-to-analog converter.

8. The current sampling circuit according to claim 7, characterized in that, The function expression of the digital low-pass filter function is as follows: Yn = a * Y (n-1) + (1-a) * Xn Where Y(n) represents the filtered digital signal output value at the current time, Y(n-1) represents the filtered digital signal output value at the previous time, X(n) represents the unfiltered raw data at the current time, and a represents the filtering coefficient, 0 < a < 1.

9. A compressor surge monitoring system, characterized in that, The compressor surge monitoring system includes a frequency converter, a compressor, and a compressor surge monitoring module. The frequency converter includes a current sampling circuit as described in any one of claims 1 to 8. The frequency converter is electrically connected to the compressor and the compressor surge monitoring module, respectively. The compressor surge monitoring module is used to: collect the operating data of the compressor; and receive the current sampling value output by the current sampling circuit. The compressor is determined to have experienced surge based on the operating data and the current sampling value.

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