A bus protection device, method and frequency converter for a frequency converter

Abstract

The present invention discloses a bus protection device, method and frequency converter for a frequency converter. The device includes: a sampling unit and a control unit; wherein, the sampling unit is configured to sample the bus voltage of the frequency converter to obtain a bus voltage sampling value and a common-mode voltage sampling value; the control unit is configured to determine the state of the bus voltage of the frequency converter according to the bus voltage sampling value and the common-mode voltage sampling value; and to protect the bus voltage of the frequency converter according to the state of the bus voltage of the frequency converter. The solution of the present invention can solve the problem of inaccurate bus voltage sampling resulting in mis-triggering of energy feedback, and achieve the effect of improving the accuracy of bus voltage sampling to avoid mis-triggering of energy feedback.

Description

Technical Field

[0001] The present invention belongs to the technical field of compressors, and particularly relates to a bus protection device, method and frequency converter for a frequency converter, and more particularly to a bus voltage undervoltage detection and protection device, method and frequency converter for a frequency converter. Background Art

[0002] In the bus protection of the frequency converter of a magnetic levitation centrifuge, when an abnormality occurs in a certain link of the bus voltage sampling, such as poor contact of the sampling line, it will erroneously trigger energy feedback, resulting in a bus voltage pump-up, causing the magnetic levitation bearing to directly drop and hit the shaft under the high-speed rotation state.

[0003] The above content is only used to assist in understanding the technical solution of the present invention, and does not represent an admission that the above content is prior art. Summary of the Invention

[0004] The purpose of the present invention is to provide a bus protection device, method and frequency converter for a frequency converter, so as to solve the problem of inaccurate bus voltage sampling leading to erroneous triggering of energy feedback, and achieve the effect of improving the accuracy of bus voltage sampling to avoid erroneous triggering of energy feedback.

[0005] The present invention provides a bus protection device for a frequency converter, including: a sampling unit and a control unit; wherein, the sampling unit is configured to sample the bus voltage of the frequency converter to obtain a bus voltage sampling value and a common-mode voltage sampling value; the control unit is configured to determine the state of the bus voltage of the frequency converter according to the bus voltage sampling value and the common-mode voltage sampling value; and, protect the bus voltage of the frequency converter according to the state of the bus voltage of the frequency converter.

[0006] In some embodiments, the sampling unit includes: a first differential sampling circuit and a second differential sampling circuit; the sampling unit samples the bus voltage of the frequency converter, including: the first differential sampling circuit is configured to sample the positive pole and the negative pole of the bus voltage of the frequency converter to obtain a bus voltage sampling value; the second differential sampling circuit is configured to sample the positive pole of the bus voltage of the frequency converter and the chassis ground voltage to obtain a common-mode voltage sampling value.

[0007] In some embodiments, the first differential sampling circuit and the second differential sampling circuit have the same structure; the first differential sampling circuit includes: a differential sampling circuit body, a clamping module and a feedforward module; wherein, the number of the clamping modules is two, and one of the two clamping modules is arranged at the inverting input end of the differential sampling circuit body; the other of the two clamping modules is arranged at the non-inverting input end of the differential sampling circuit body; the feedforward module is connected across the inverting input end and the non-inverting input end of the differential sampling circuit body.

[0008] In some embodiments, the control unit determines the state of the bus voltage of the frequency converter according to the bus voltage sampling value and the common-mode voltage sampling value, including: determining whether the bus voltage sampling value is greater than a first reference voltage, and determining whether the common-mode voltage sampling value is greater than a second reference voltage; if the bus voltage sampling value is less than or equal to the first reference voltage and the common-mode voltage sampling value is less than or equal to the second reference voltage, determining that the state of the bus voltage of the frequency converter is a first state; if the bus voltage sampling value is greater than the first reference voltage and / or the common-mode voltage sampling value is greater than the second reference voltage, determining that the state of the bus voltage of the frequency converter is a second state.

[0009] In some embodiments, the control unit protects the bus voltage of the frequency converter according to the state of the bus voltage of the frequency converter, including: when the state of the bus voltage of the frequency converter is the first state, controlling the frequency converter to enter an energy feedback process; when the state of the bus voltage of the frequency converter is the second state, if the bus voltage sampling value is greater than the first reference voltage, reporting that the bus voltage sampling of the frequency converter is abnormal and stopping the machine; if the common-mode voltage sampling value is greater than the second reference voltage, reporting that the bus voltage of the frequency converter is grounded abnormally and stopping the machine.

[0010] Matched with the above device, on the other hand, the present invention provides a frequency converter, including: the bus protection device of the frequency converter described above.

[0011] Matched with the above frequency converter, on the other hand, the present invention provides a method for protecting the bus of a frequency converter, including: sampling the bus voltage of the frequency converter to obtain a bus voltage sampling value and a common-mode voltage sampling value; determining the state of the bus voltage of the frequency converter according to the bus voltage sampling value and the common-mode voltage sampling value; and protecting the bus voltage of the frequency converter according to the state of the bus voltage of the frequency converter.

[0012] In some embodiments, sampling the bus voltage of the frequency converter to obtain a bus voltage sampling value and a common-mode voltage sampling value includes: sampling the positive pole and the negative pole of the bus voltage of the frequency converter to obtain a bus voltage sampling value; sampling the positive pole of the bus voltage of the frequency converter and the chassis ground voltage to obtain a common-mode voltage sampling value.

[0013] In some embodiments, determining the state of the bus voltage of the frequency converter based on the sampled value of the bus voltage and the sampled value of the common-mode voltage includes: determining whether the sampled value of the bus voltage is greater than a first reference voltage, and determining whether the sampled value of the common-mode voltage is greater than a second reference voltage; if the sampled value of the bus voltage is less than or equal to the first reference voltage and the sampled value of the common-mode voltage is less than or equal to the second reference voltage, determining that the state of the bus voltage of the frequency converter is a first state; if the sampled value of the bus voltage is greater than the first reference voltage and / or the sampled value of the common-mode voltage is greater than the second reference voltage, determining that the state of the bus voltage of the frequency converter is a second state.

[0014] In some embodiments, protecting the bus voltage of the frequency converter according to the state of the bus voltage of the frequency converter includes: when the state of the bus voltage of the frequency converter is the first state, controlling the frequency converter to enter an energy feedback process; when the state of the bus voltage of the frequency converter is the second state, if the sampled value of the bus voltage is greater than the first reference voltage, reporting an abnormal sampled value of the bus voltage of the frequency converter and stopping the machine; if the sampled value of the common-mode voltage is greater than the second reference voltage, reporting an abnormal grounding of the bus voltage of the frequency converter and stopping the machine.

[0015] Thus, the solution of the present invention, by differentially sampling the bus voltage and the common-mode voltage of the bus, determines the actual operating condition of the frequency converter unit according to the states of the bus voltage and the common-mode voltage of the bus, so as to perform protection in a timely manner when the actual operating condition of the frequency converter unit is abnormal, solve the problem of inaccurate sampling of the bus voltage leading to mis-triggering of energy feedback, and achieve the effect of improving the accuracy of bus voltage sampling to avoid mis-triggering of energy feedback.

[0016] Other features and advantages of the present invention will be described in the following specification, and some of them will become obvious from the specification or be understood by implementing the present invention.

[0017] The technical solution of the present invention will be further described in detail below with reference to the drawings and embodiments. Description of the Drawings

[0018] Figure 1 It is a schematic structural diagram of an embodiment of the bus protection device of the frequency converter of the present invention;

[0019] Figure 2 It is a schematic structural diagram of an embodiment of the bus voltage sampling module in the frequency converter system;

[0020] Figure 3 It is a schematic structural diagram of another embodiment of the bus voltage sampling module in the frequency converter system;

[0021] Figure 4Schematic structural diagram of an embodiment of a voltage differential sampling circuit;

[0022] Figure 5 Schematic structural diagram of another embodiment of a voltage differential sampling circuit;

[0023] Figure 6 Schematic structural and truth value diagrams of an embodiment of an undervoltage detection and protection circuit;

[0024] Figure 7 Schematic truth value diagram of an embodiment of an undervoltage detection and protection circuit;

[0025] Figure 8 Schematic flowchart of an embodiment of a bus voltage undervoltage protection process;

[0026] Figure 9 Schematic flowchart of an embodiment of a bus protection method for an inverter of the present invention;

[0027] Figure 10 Schematic flowchart of an embodiment of determining the state of the bus voltage of the inverter in the method of the present invention;

[0028] Figure 11 Schematic flowchart of an embodiment of protecting the bus voltage of the inverter in the method of the present invention. Detailed implementation manners

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0030] According to an embodiment of the present invention, a bus protection device for an inverter is provided. Refer to Figure 1 Schematic structural diagram of an embodiment of the device of the present invention shown. The bus protection device for the inverter can be applied in a motor system such as a compressor system. The bus protection device for the inverter of the motor system such as a compressor system can include: a sampling unit and a control unit.

[0031] Specifically, the sampling unit can be configured to sample the bus voltage of the inverter to obtain a bus voltage sampling value and a common-mode voltage sampling value.

[0032] In some embodiments, the sampling unit can include: a first differential sampling circuit and a second differential sampling circuit.

[0033] The sampling unit samples the bus voltage of the frequency converter, including:

[0034] The first differential sampling circuit can be configured to sample the positive pole of the bus voltage and the negative pole of the bus voltage of the frequency converter to obtain a bus voltage sampling value.

[0035] The second differential sampling circuit can be configured to sample the positive pole of the bus voltage of the frequency converter and the chassis ground voltage to obtain a common-mode voltage sampling value.

[0036] For example: increasing the common-mode protection of the bus of the frequency converter of the positive pole DC+ of the bus voltage to the chassis ground PE enables the detection of the grounding state, can realize the detection of the grounding state of the frequency converter, solves the problem of faults caused by the unreliable grounding of the frequency converter; when the sampling line of the positive pole DC+ or the negative pole DC- of the bus voltage is inaccurate due to poor contact, the actual bus voltage state can be judged by detecting the potential difference between the positive pole DC+ of the bus voltage and the chassis ground PE, preventing mis-triggering of energy feedback, resulting in system failure, improving the accuracy of the sampling circuit, and preventing mis-triggering of energy feedback.

[0037] Thus, through the differential sampling design of the bus voltage and the bus common-mode voltage, the differential sampling design of the bus voltage and the bus common-mode voltage is adopted to ensure the accuracy of sampling and prevent mis-triggering of energy feedback.

[0038] In some embodiments, the structures of the first differential sampling circuit and the second differential sampling circuit are the same. The first differential sampling circuit can include: a differential sampling circuit body, a clamping module, and a feedforward module. The differential sampling circuit body can include: a comparator, an in-phase sampling module such as two resistors R1 disposed at the inverting input terminal of the comparator, an in-phase sampling module such as another two resistors R1 disposed at the non-inverting input terminal of the comparator, an output resistor R disposed at the output terminal of the comparator, and the output resistor R can output the sampled bus voltage sampling value and the common-mode voltage sampling value. The output resistor R is also grounded through a capacitor C. A resistor R2 is disposed between the inverting input terminal and the output terminal of the comparator, and the non-inverting input terminal of the comparator is also grounded through another resistor R2. Among them,

[0039] The number of the clamping modules is two. One of the two clamping modules is disposed at the inverting input terminal of the differential sampling circuit body; the other of the two clamping modules is disposed at the non-inverting input terminal of the differential sampling circuit body. Preferably, the two clamping modules can be symmetrically disposed at the inverting input terminal and the non-inverting input terminal of the differential sampling circuit body.

[0040] For example: the sampling circuit performs differential sampling, and the voltage sampling value is:

[0041]

[0042] Among them, D1 and D2 are clamping diodes that clamp the voltage between U+ and U-, where U+ and U- are the supply voltage ranges of the operational amplifier. For the voltage differential sampling circuit, adding D1 and D2 as clamping diodes is to clamp the voltage between U+ and U-, where U+ and U- are the supply voltage ranges of the operational amplifier. The clamping diodes are used to prevent the voltage from exceeding the chip supply voltage.

[0043] The feedforward module is connected across the inverting input terminal and the non-inverting input terminal of the differential sampling circuit body. Specifically, the feedforward module can be connected across the input side of the inverting input terminal of the differential sampling circuit body (i.e., the side of the inverting sampling module away from the inverting input terminal of the comparator) and the input side of the non-inverting input terminal of the differential sampling circuit body (i.e., the side of the non-inverting sampling module away from the non-inverting input terminal of the comparator).

[0044] For example: when the sampling circuit performs differential sampling, the function of connecting a resistor R0 across the non-inverting input terminal and the inverting input terminal of the operational amplifier is to provide a feedforward signal, suppress signal overshoot, and improve the anti-interference ability of the sampling circuit. Adding a resistor R0 across the non-inverting input terminal and the inverting input terminal of the operational amplifier serves to provide a feedforward signal, suppress signal overshoot, and improve the anti-interference ability of the sampling circuit. The anti-interference ability of the sampling circuit is improved through the resistor R0.

[0045] Therefore, by adopting the clamping diodes and the cross-connected resistor for the sampling feedforward design, the abnormal phenomenon of the bus voltage pumping up caused by energy feedback can be solved, and the sampling anti-interference performance can be improved.

[0046] Specifically, the control unit can be configured to determine the state of the bus voltage of the frequency converter according to the bus voltage sampling value and the common-mode voltage sampling value; and protect the bus voltage of the frequency converter according to the state of the bus voltage of the frequency converter.

[0047] Therefore, by judging the states of the bus voltage and the bus common-mode voltage to determine the actual operating condition of the unit and realizing the design of the abnormal state diagnosis and protection circuit, the accuracy of the sampling circuit can be improved, and the mis-triggering of energy feedback can be prevented.

[0048] In some embodiments, the control unit determining the state of the bus voltage of the frequency converter according to the bus voltage sampling value and the common-mode voltage sampling value can include:

[0049] The control unit is specifically further configured to determine whether the bus voltage sampling value is greater than a first reference voltage and determine whether the common-mode voltage sampling value is greater than a second reference voltage. Among them, the first reference voltage is such as the threshold voltage U REF1 and the second reference voltage is such as the threshold voltage UREF2 。

[0050] The control unit is specifically further configured to determine that the state of the bus voltage of the frequency converter is the first state if the sampled value of the bus voltage is less than or equal to the first reference voltage and the sampled value of the common-mode voltage is less than or equal to the second reference voltage. The first state is the state in which the frequency converter can normally enter the energy feedback process.

[0051] The control unit is specifically further configured to determine that the state of the bus voltage of the frequency converter is the second state if the sampled value of the bus voltage is greater than the first reference voltage and / or the sampled value of the common-mode voltage is greater than the second reference voltage. The second state is the fault state of the frequency converter.

[0052] For example, in the under-voltage protection of the bus voltage, when it is set that the bus voltage is lower than 400V, it is in the under-voltage state, and its threshold voltage is U REF1 。The sampled value of the bus voltage is compared with the threshold voltage U REF1 and then the level signal FO.DC is sent to the main control chip of the frequency converter for processing. When the sampled value of the bus voltage U DC is greater than the threshold voltage U REF1 , the output signal FO.DC is at a high level; when the sampled value of the bus voltage U DC is less than the threshold voltage U REF1 , the output signal FO.DC is at a low level.

[0053] When it is set that the common-mode voltage of the bus is lower than 200V, it is in the under-voltage state, and its threshold voltage is U REF2 。The sampled value of the common-mode voltage is compared with the threshold voltage U REF2 and then the level signal FO.PE is sent to the main control chip of the frequency converter for processing. When the sampled value of the common-mode voltage U DC-PE is greater than the threshold voltage U REF2 , the output signal FO.PE is at a high level; when the sampled value of the bus voltage U DC-PE is less than the threshold voltage U REF2 , the output signal FO.PE is at a low level.

[0054] Thus, through the under-voltage detection protection circuit and the truth table, the state of the bus voltage and the state of the common-mode voltage of the bus are judged, and after the "OR" logic, it is sent to the main control chip for processing; through the combination of the comparison circuit and the truth table operation circuit, the under-voltage protection function is realized according to the operation result of the truth table.

[0055] In some embodiments, the control unit protects the bus voltage of the frequency converter according to the state of the bus voltage of the frequency converter, which can include:

[0056] The control unit is specifically further configured to control the frequency converter to enter an energy feedback process when the bus voltage state of the frequency converter is in the first state, so that the motor stops rotating and the magnetic suspension bearing stably drops onto the shaft.

[0057] The control unit is specifically further configured to, when the bus voltage state of the frequency converter is in the second state, if the sampled value of the bus voltage is greater than the first reference voltage, report an abnormal sampled value of the bus voltage of the frequency converter and stop the machine; if the sampled value of the common-mode voltage is greater than the second reference voltage, report an abnormal grounding of the bus voltage of the frequency converter and stop the machine.

[0058] For example: The level signal FO.TZ output after the "OR" operation of FO.DC and FO.PE is sent to the main control chip of the frequency converter for processing. When both FO.DC and FO.PE are at low level, the output signal FO.TZ is at low level, triggering energy feedback. Otherwise, the level signal FO.TZ is at high level, and energy feedback is not triggered. Through the "OR" operation, energy feedback is entered only when FO.TZ is at low level, reducing the probability of mis-triggering energy feedback.

[0059] Thus, the bus voltage and the bus common-mode voltage are collected by the bus voltage sampling module, and the bus voltage sampling module is a sampling resistor board; only when the sampling results of both the bus voltage and the bus common-mode voltage are in an undervoltage state at the same time, the frequency converter controller determines that the unit is undervoltage, immediately enters energy feedback and stops due to a fault; when an abnormality occurs in the sampling of either the bus voltage or the bus common-mode voltage, the frequency converter controller determines that the sampling is abnormal, and the unit stops due to a fault but does not trigger energy feedback; it is possible to avoid inaccurate sampling caused by poor contact of the sampling wire, thus achieving improved accuracy of the sampling circuit.

[0060] After a large number of experimental verifications, by adopting the technical solution of the present invention, through differential sampling of the bus voltage and the bus common-mode voltage, and determining the actual operating condition of the frequency converter unit according to the states of the bus voltage and the bus common-mode voltage, protection can be provided in a timely manner when an abnormality occurs in the actual operating condition of the frequency converter unit, which can improve the system reliability of the magnetic suspension centrifuge.

[0061] According to an embodiment of the present invention, there is also provided a frequency converter corresponding to the bus protection device of the frequency converter. This frequency converter can include: the bus protection device of the above-mentioned frequency converter.

[0062] In response to the call of the era of green, intelligent, and energy-saving, magnetic levitation centrifuges have reached a peak of development with characteristics such as oil-free, frictionless, and high efficiency. Magnetic levitation centrifuges adopt advanced magnetic levitation bearing technology, with no contact friction during operation, greatly increasing the motor speed. To meet the special requirements of high speed and stable floating and dropping of the shaft of magnetic levitation centrifuges, a dedicated frequency converter for magnetic levitation centrifuges needs to be developed. During the normal operation of a magnetic levitation centrifuge, if the three-phase input power is cut off or the bus voltage drops below the voltage thresholds of the frequency converter power supply and the bearing controller power supply due to other abnormal conditions, it will cause the power loss of the frequency converter power supply and the bearing controller power supply, and the magnetic levitation bearing will directly drop and hit the shaft under the high-speed rotation state. Therefore, the dedicated frequency converter for magnetic levitation centrifuges needs to have an energy feedback function to ensure that in case of an abnormal situation, the energy of the motor coasting is fed back to the bus, maintaining the bus voltage above 400V until the magnetic levitation bearing stops rotating and stably drops the shaft.

[0063] Figure 2 It is a schematic structural diagram of an embodiment of the bus voltage sampling module in the frequency converter system. Figure 2 In the rectification module, IGBT controlled rectification can be used, or a diode uncontrolled rectification module can also be used. In the frequency converter system as shown in Figure 2 The bus voltage is detected by the bus voltage sampling module. When the bus voltage is lower than 400V, the energy feedback function is triggered. When an abnormality occurs in a certain link of the bus voltage sampling, such as poor contact of the sampling line, resulting in the sampling value of the bus voltage being 0 while the actual bus voltage is 670V, it will mis-trigger the energy feedback and cause the bus voltage to pump up. When the bus voltage pumps up higher than the voltage thresholds of the frequency converter power supply and the bearing controller power supply, it will also cause the power loss of the frequency converter power supply and the bearing controller power supply, and the magnetic levitation bearing will directly drop and hit the shaft under the high-speed rotation state. Therefore, bus voltage sampling is a crucial link, and it is necessary to ensure the accuracy of bus voltage sampling.

[0064] In some embodiments, to solve the problem of mis-triggering the energy feedback caused by inaccurate bus voltage sampling, the solution of the present invention provides a method for detecting and protecting the under-voltage of the bus voltage for a frequency converter, which can improve the system reliability of the magnetic levitation centrifuge and is applicable to the field of magnetic levitation centrifuge frequency converter control.

[0065] The solution of the present invention ensures the accuracy of sampling through the differential sampling design of the bus voltage and the bus common-mode voltage. In this way, by adopting the differential sampling design of the bus voltage and the bus common-mode voltage, the abnormal phenomenon of inaccurate bus voltage sampling caused by factors such as poor contact is solved, that is, the problem of inaccurate sampling caused by poor contact of the sampling line is solved, thus achieving the improvement of the accuracy of the sampling circuit and preventing the mis-triggering of the energy feedback.

[0066] The solution of the present invention adopts a clamping diode and a shunt resistor for pre-sampling feedforward design, which can solve the abnormal phenomenon of bus voltage pumping caused by energy feedback and improve the anti-interference ability of sampling.

[0067] The solution of the present invention determines the actual operating condition of the unit by judging the states of the bus voltage and the bus common-mode voltage, and realizes the diagnosis of abnormal states and the design of the protection circuit. In this way, a logic for triggering energy feedback is provided. Through the differential sampling design of the bus common-mode voltage, the grounding state of the frequency converter can be detected, the fault caused by the unreliable grounding of the frequency converter is solved, and the grounding state can be detected.

[0068] Figure 3 Schematic structural diagram of another embodiment of the bus voltage sampling module in the frequency converter system. As Figure 3 shown, the bus voltage and the bus common-mode voltage are collected by the bus voltage sampling module, and the bus voltage sampling module is a sampling resistor board. When an abnormality occurs in the sampling of either the bus voltage or the bus common-mode voltage, the frequency converter controller determines that the sampling is abnormal, and the unit shuts down due to a fault but does not trigger energy feedback. Only when the sampling results of both the bus voltage and the bus common-mode voltage are in an undervoltage state at the same time, the frequency converter controller determines that the unit is undervoltage, immediately enters energy feedback and shuts down due to a fault. This method can avoid the problem of inaccurate sampling caused by poor contact of the sampling line, and thus improves the accuracy of the sampling circuit.

[0069] In the frequency converter system as Figure 3 shown, the common-mode protection of the bus of the common-mode frequency converter from the positive pole DC+ of the bus voltage to the chassis ground PE is increased, so that the grounding state can be detected, the grounding state of the frequency converter can be detected, and the problem of the fault caused by the unreliable grounding of the frequency converter is solved; when the positive pole DC+ of the bus voltage or the negative pole DC- of the bus voltage has inaccurate sampling due to poor contact of the sampling line, the actual bus voltage state can be judged by detecting the potential difference between the positive pole DC+ of the bus voltage and the chassis ground PE, preventing mis-triggering of energy feedback, resulting in system failure, improving the accuracy of the sampling circuit, and preventing mis-triggering of energy feedback.

[0070] Figure 4 and Figure 5 is a schematic structural diagram of an embodiment of a voltage differential sampling circuit. Through Figure 4 and Figure 5 shown in the sampling circuit for differential sampling, the voltage sampling value is:

[0071]

[0072] Among them, D1 and D2 are clamping diodes, whose purpose is to clamp the voltage between U+ and U-, where U+ and U- are the power supply voltage ranges of the operational amplifier. The function of the resistor R0 connected across the non-inverting input terminal and the inverting input terminal of the operational amplifier is to provide a feedforward signal, suppress signal overshoot, and improve the anti-interference ability of the sampling circuit.

[0073] In Figure 4 and Figure 5 In the example shown, for the voltage differential sampling circuit, adding D1 and D2 as clamping diodes is to clamp the voltage between U+ and U-, where U+ and U- are the power supply voltage ranges of the operational amplifier, and prevent the voltage from exceeding the chip power supply voltage through the clamping diodes.

[0074] In Figure 4 and Figure 5 In the example shown, adding a resistor R0 connected across the non-inverting input terminal and the inverting input terminal of the operational amplifier, its function is to provide a feedforward signal, suppress signal overshoot, and improve the anti-interference ability of the sampling circuit. The anti-interference ability of the sampling circuit is improved through the resistor R0.

[0075] Figure 6 and Figure 7 And are the schematic diagrams of the structure and truth table of an embodiment of the undervoltage detection protection circuit. See the bus voltage undervoltage protection circuit in Figure 6 and Figure 7 , when it is set that the bus voltage is lower than 400V, it is in an undervoltage state, and its threshold voltage is U REF1 . After comparing the sampled value of the bus voltage with the threshold voltage U REF1 , the level signal FO.DC is sent to the main control chip of the frequency converter for processing. When the sampled value U DC of the bus voltage is greater than the threshold voltage U REF1 , the output signal FO.DC is at a high level; when the sampled value U DC of the bus voltage is less than the threshold voltage U REF1 , the output signal FO.DC is at a low level.

[0076] When it is set that the bus common-mode voltage is lower than 200V, it is in an undervoltage state, and its threshold voltage is U REF2 . After comparing the sampled value of the common-mode voltage with the threshold voltage U REF2 , the level signal FO.PE is sent to the main control chip of the frequency converter for processing. When the sampled value U DC-PE of the common-mode voltage is greater than the threshold voltage U REF2 , the output signal FO.PE is at a high level; when the sampled value U DC-PE of the bus voltage is less than the threshold voltage U REF2 , the output signal FO.PE is at a low level.

[0077] The level signal FO.TZ output after the "OR" operation between FO.DC and FO.PE is sent to the main control chip of the frequency converter for processing. When both FO.DC and FO.PE are at low levels, the output signal FO.TZ is at a low level, triggering energy feedback. Otherwise, the level signal FO.TZ is at a high level, and energy feedback is not triggered. Through the "OR" operation, only when FO.TZ is at a low level can energy feedback be entered, reducing the probability of false triggering of energy feedback.

[0078] In Figure 6 and Figure 7 In the example shown, the bus voltage status and the bus common-mode voltage status are judged through the undervoltage detection protection circuit and the truth table, and after the "OR" logic, it is sent to the main control chip for processing. Through the combination of the comparison circuit and the truth table operation circuit, the undervoltage protection function is realized according to the result of the truth table operation.

[0079] In the above embodiment, whether the bus voltage undervoltage actually occurs is judged by detecting the bus voltage sampling signal and the bus common-mode voltage sampling signal, or it can be replaced by detecting the two-way bus voltage sampling values. If both two-way bus voltage sampling values are lower than the threshold voltage, it is determined that the bus voltage actually has an undervoltage fault, and energy feedback is immediately entered.

[0080] Among them, when only one-way bus voltage is detected, false alarms may occur due to reasons such as loose wiring. Therefore, one more bus voltage sampling signal is led out as a redundant design, and the two-way bus voltage sampling points are the same. For example: collecting two-way bus voltages as a redundant design, the two-way bus voltage sampling points are the same. When any one of the two-way bus voltage samplings is abnormal and the other is normal, a bus voltage sampling abnormal fault is reported, and energy feedback is not triggered. At this time, it should be checked whether the bus voltage sampling module of the frequency converter is abnormal or whether the bus voltage sampling line is in poor contact; only when the two-way bus voltage sampling signals are both lower than the set threshold can energy feedback be entered, reducing the probability of false triggering of energy feedback.

[0081] Figure 8 It is a schematic diagram of the bus voltage undervoltage protection process. As Figure 8 shown, a software processing logic flow of a method for detecting and protecting the bus voltage undervoltage of a frequency converter can include:

[0082] Step 1: During the operation of the unit, the bus voltage and the bus common-mode voltage are detected in real time and sent to the main control chip of the frequency converter for processing.

[0083] Step 2: Determine whether the FO.TZ signal is equal to 0. If the FO.TZ signal is equal to 0, the main control chip determines that the bus voltage is in an undervoltage state and immediately enters energy feedback to ensure that the bus voltage is stably maintained above 400V until the motor stops rotating, the magnetic levitation bearing stably drops the shaft, and the unit makes an emergency stop. If FO.TZ is equal to 1, the main control chip determines that the bus voltage is not undervoltage and does not trigger energy feedback.

[0084] Step 3: Determine whether the FO.DC signal is equal to 0. If FO.DC is equal to 0, the main control chip determines that the bus voltage is abnormal, reports abnormal protection for bus voltage sampling, and the unit stops, but does not trigger energy feedback. If FO.DC is equal to 1, then detect the FO.PE signal.

[0085] Step 4: Determine whether FO.PE is equal to 0. If FO.PE is equal to 0, the main control chip determines that the grounding is abnormal, reports grounding abnormal protection, and the unit stops, but does not trigger energy feedback. If FO.PE is equal to 1, then the unit is in a normal operation state, and continuously detects the bus voltage and the sampled value of the bus common-mode voltage.

[0086] In the above embodiments, the demonstration of the parameters containing specific values does not need to be exactly equal to the corresponding values, and should be determined according to the actual situation.

[0087] In the above embodiments, the IGBT controllable rectification module adopted can be replaced with a diode uncontrolled rectification module.

[0088] Since the processing and functions implemented by the frequency converter in this embodiment are basically corresponding to the Figure 1 embodiment, principle and example of the device shown above, for the parts not detailed in the description of this embodiment, reference can be made to the relevant descriptions in the foregoing embodiments, and details will not be repeated here.

[0089] Through a large number of experimental verifications, by adopting the technical solution of the present invention, through differential sampling of the bus voltage and the bus common-mode voltage, and determining the actual operating conditions of the frequency converter unit according to the states of the bus voltage and the bus common-mode voltage, so as to perform protection in a timely manner when the actual operating conditions of the frequency converter unit are abnormal, solve the abnormal phenomenon that the bus voltage sampling is inaccurate caused by factors such as poor contact, that is, solve the problem of inaccurate sampling caused by poor contact of the sampling line, thus achieving the improvement of the accuracy of the sampling circuit and preventing mis-triggering of energy feedback.

[0090] According to an embodiment of the present invention, there is also provided a bus protection method for a frequency converter corresponding to the frequency converter, as Figure 9 shown in the flowchart of an embodiment of the method of the present invention. This bus protection method for the frequency converter can be applied in a motor system such as a compressor system. The bus protection method for the frequency converter in a motor system such as a compressor system can include: step S110 and step S120.

[0091] At step S110, sample the bus voltage of the frequency converter to obtain a bus voltage sampling value and a common-mode voltage sampling value.

[0092] In some embodiments, the specific process of sampling the bus voltage of the frequency converter in step S110 to obtain a bus voltage sampling value and a common-mode voltage sampling value may include: sampling the positive pole and the negative pole of the bus voltage of the frequency converter to obtain a bus voltage sampling value; sampling the positive pole of the bus voltage of the frequency converter and the chassis ground voltage to obtain a common-mode voltage sampling value.

[0093] For example: increasing the common-mode protection of the bus of the frequency converter of the positive pole DC+ of the bus voltage to the chassis ground PE enables the detection of the grounding state, and the grounding state of the frequency converter can be detected, solving the problem of faults caused by the unreliable grounding of the frequency converter; when the sampling of the positive pole DC+ or the negative pole DC- of the bus voltage is inaccurate due to poor contact of the sampling line, the actual bus voltage state can be judged by detecting the potential difference between the positive pole DC+ of the bus voltage and the chassis ground PE, preventing the mis-triggering of energy feedback, resulting in system failure, improving the accuracy of the sampling circuit, and preventing the mis-triggering of energy feedback.

[0094] Thus, through the differential sampling design of the bus voltage and the bus common-mode voltage, the differential sampling design of the bus voltage and the bus common-mode voltage is adopted to ensure the accuracy of sampling and prevent the mis-triggering of energy feedback.

[0095] At step S120, determine the state of the bus voltage of the frequency converter according to the bus voltage sampling value and the common-mode voltage sampling value; and protect the bus voltage of the frequency converter according to the state of the bus voltage of the frequency converter.

[0096] Thus, by judging the states of the bus voltage and the bus common-mode voltage, the actual operating condition of the unit is determined, and the diagnosis of the abnormal state and the design of the protection circuit are realized, which can improve the accuracy of the sampling circuit and prevent the mis-triggering of energy feedback.

[0097] In some embodiments, the specific process of determining the state of the bus voltage of the frequency converter in step S120 according to the bus voltage sampling value and the common-mode voltage sampling value can be seen in the following exemplary description.

[0098] The following combines Figure 10 The schematic flow diagram of an embodiment for determining the state of the bus voltage of the frequency converter in the method of the present invention shown, and further illustrates the specific process of determining the state of the bus voltage of the frequency converter in step S120, which may include: step S210 to step S230.

[0099] Step S210, determine whether the sampled value of the bus voltage is greater than a first reference voltage, and determine whether the sampled value of the common-mode voltage is greater than a second reference voltage. Among them, the first reference voltage is such as the threshold voltage U REF1 ), and the second reference voltage is such as the threshold voltage U REF2 .

[0100] Step S220, if the sampled value of the bus voltage is less than or equal to the first reference voltage and the sampled value of the common-mode voltage is less than or equal to the second reference voltage, then determine that the state of the bus voltage of the frequency converter is the first state.

[0101] Step S230, if the sampled value of the bus voltage is greater than the first reference voltage and / or the sampled value of the common-mode voltage is greater than the second reference voltage, then determine that the state of the bus voltage of the frequency converter is the second state.

[0102] For example: in the under-voltage protection of the bus voltage, when it is set that the bus voltage is lower than 400V, it is in the under-voltage state, and its threshold voltage is U REF1 . The sampled value of the bus voltage is compared with the threshold voltage U REF1 , and then the level signal FO.DC is sent to the main control chip of the frequency converter for processing. When the sampled value of the bus voltage U DC is greater than the threshold voltage U REF1 , the output signal FO.DC is at a high level; when the sampled value of the bus voltage U DC is less than the threshold voltage U REF1 , the output signal FO.DC is at a low level.

[0103] When it is set that the common-mode voltage of the bus is lower than 200V, it is in the under-voltage state, and its threshold voltage is U REF2 . The sampled value of the common-mode voltage is compared with the threshold voltage U REF2 , and then the level signal FO.PE is sent to the main control chip of the frequency converter for processing. When the sampled value of the common-mode voltage U DC-PE is greater than the threshold voltage U REF2 , the output signal FO.PE is at a high level; when the sampled value of the bus voltage U DC-PE is less than the threshold voltage U REF2 , the output signal FO.PE is at a low level.

[0104] Thus, through the under-voltage detection protection circuit and the truth table, the states of the bus voltage and the common-mode voltage of the bus are judged, and after the "OR" logic, they are sent to the main control chip for processing; through the combination of the comparison circuit and the truth table operation circuit, the under-voltage protection function is realized according to the operation result of the truth table.

[0105] In some embodiments, for the specific process of protecting the bus voltage of the frequency converter according to the status of the bus voltage of the frequency converter in step S120, the following exemplary description can be referred to.

[0106] The following combines Figure 11 FIG. 3 is a schematic flowchart of an embodiment of protecting the bus voltage of the frequency converter in the method of the present invention, further illustrating the specific process of protecting the bus voltage of the frequency converter in step S120, which can include: step S310 and step S320.

[0107] Step S310, when the bus voltage status of the frequency converter is in the first state, control the frequency converter to enter the energy feedback process to stop the motor and make the magnetic levitation bearing stably drop the shaft.

[0108] Step S320, when the bus voltage status of the frequency converter is in the second state, if the sampled value of the bus voltage is greater than the first reference voltage, report that the sampled value of the bus voltage of the frequency converter is abnormal and stop the machine; if the sampled value of the common-mode voltage is greater than the second reference voltage, report that the bus voltage of the frequency converter is grounded abnormally and stop the machine.

[0109] For example: After the "OR" operation of FO.DC and FO.PE, the output level signal FO.TZ is sent to the main control chip of the frequency converter for processing. When both FO.DC and FO.PE are at low level, the output signal FO.TZ is at low level, triggering energy feedback. Otherwise, the output level signal FO.TZ is at high level, and energy feedback is not triggered. Through the "OR" operation, energy feedback is entered only when FO.TZ is at low level, reducing the probability of mis-triggering energy feedback.

[0110] Thus, the bus voltage and the bus common-mode voltage are collected by the bus voltage sampling module, and the bus voltage sampling module is a sampling resistor board; only when the sampling results of the bus voltage and the bus common-mode voltage both show an undervoltage state, the frequency converter controller determines that the unit is undervoltage, immediately enters the energy feedback and faults to stop the machine; when an abnormality occurs in the sampling of either the bus voltage or the bus common-mode voltage, the frequency converter controller determines that the sampling is abnormal, the unit faults to stop the machine but does not trigger energy feedback; it is possible to avoid the problem of inaccurate sampling caused by poor contact of the sampling line, thus achieving improved accuracy of the sampling circuit.

[0111] Since the processing and functions implemented by the method of this embodiment are basically corresponding to the foregoing embodiments, principles and examples of the frequency converter, for the parts not detailed in the description of this embodiment, reference can be made to the relevant descriptions in the foregoing embodiments and will not be elaborated herein.

[0112] After a large number of experimental verifications, by adopting the technical solution of this embodiment, differential sampling is performed on the bus voltage and the bus common-mode voltage, and the actual operating condition of the frequency converter unit is determined according to the states of the bus voltage and the bus common-mode voltage, so as to perform protection in time when the actual operating condition of the frequency converter unit is abnormal. It is possible to detect the grounding state of the frequency converter, solve the faults caused by the unreliable grounding of the frequency converter, make the grounding state detectable, and improve the detection reliability of the bus voltage.

[0113] In summary, it is easy for those skilled in the art to understand that, on the premise of no conflict, the above-mentioned advantageous ways can be freely combined and superimposed.

[0114] The above are only the embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of the claims of the present invention.

Claims

1. A bus protection device for an inverter, characterized in that, it includes: a sampling unit and a control unit; wherein, the sampling unit is configured to sample the bus voltage of the inverter to obtain a bus voltage sampling value and a common-mode voltage sampling value; wherein, the sampling unit samples the positive pole and the negative pole of the bus voltage of the inverter to obtain the bus voltage sampling value; the sampling unit samples the positive pole of the bus voltage of the inverter and the chassis ground voltage to obtain the common-mode voltage sampling value; the control unit is configured to determine the state of the bus voltage of the inverter according to the bus voltage sampling value and the common-mode voltage sampling value; and, determine the actual operating condition of the inverter unit according to the state of the bus voltage of the inverter, so as to perform protection in time when the actual operating condition of the inverter unit is abnormal and protect the bus voltage of the inverter.

2. The bus protection device for an inverter according to claim 1, characterized in that, the sampling unit includes: a first differential sampling circuit and a second differential sampling circuit; the sampling unit samples the bus voltage of the inverter, including: the first differential sampling circuit is configured to sample the positive pole and the negative pole of the bus voltage of the inverter to obtain the bus voltage sampling value; the second differential sampling circuit is configured to sample the positive pole of the bus voltage of the inverter and the chassis ground voltage to obtain the common-mode voltage sampling value.

3. The bus protection device for an inverter according to claim 2, characterized in that, the first differential sampling circuit and the second differential sampling circuit have the same structure; the first differential sampling circuit includes: a differential sampling circuit body, a clamping module and a feedforward module; wherein, the number of the clamping modules is two, and one of the two clamping modules is arranged at the inverting input end of the differential sampling circuit body; the other of the two clamping modules is arranged at the non-inverting input end of the differential sampling circuit body; the feedforward module is connected across the inverting input end and the non-inverting input end of the differential sampling circuit body.

4. The bus protection device for an inverter according to any one of claims 1 to 3, characterized in that, the control unit determines the state of the bus voltage of the inverter according to the bus voltage sampling value and the common-mode voltage sampling value, including: determining whether the bus voltage sampling value is greater than a first reference voltage and determining whether the common-mode voltage sampling value is greater than a second reference voltage; if the bus voltage sampling value is less than or equal to the first reference voltage and the common-mode voltage sampling value is less than or equal to the second reference voltage, then determine that the state of the bus voltage of the inverter is the first state; if the bus voltage sampling value is greater than the first reference voltage and / or the common-mode voltage sampling value is greater than the second reference voltage, then determine that the state of the bus voltage of the inverter is the second state.

5. The bus protection device for an inverter according to claim 4, characterized in that, the control unit protects the bus voltage of the inverter according to the state of the bus voltage of the inverter, including: When the bus voltage state of the frequency converter is in the first state, control the frequency converter to enter the energy feedback process; When the bus voltage state of the frequency converter is in the second state, if the bus voltage sampling value is greater than the first reference voltage, report that the bus voltage sampling of the frequency converter is abnormal and stop the machine; if the common mode voltage sampling value is greater than the second reference voltage, report that the bus voltage grounding of the frequency converter is abnormal and stop the machine.

6. A frequency converter Characterized in that Comprising: The bus protection device of the frequency converter according to any one of claims 1 to 5.

7. A bus protection method for a frequency converter Characterized in that Comprising: Sample the bus voltage of the frequency converter to obtain a bus voltage sampling value and a common mode voltage sampling value; wherein, sample the positive pole and negative pole of the bus voltage of the frequency converter to obtain the bus voltage sampling value; sample the positive pole of the bus voltage of the frequency converter and the chassis ground voltage to obtain the common mode voltage sampling value; According to the bus voltage sampling value and the common mode voltage sampling value, determine the state of the bus voltage of the frequency converter; and, according to the state of the bus voltage of the frequency converter, determine the actual operating condition of the frequency converter unit, so as to perform protection in time when the actual operating condition of the frequency converter unit is abnormal, and protect the bus voltage of the frequency converter.

8. The bus protection method for a frequency converter according to claim 7 Characterized in that Sampling the bus voltage of the frequency converter to obtain a bus voltage sampling value and a common mode voltage sampling value includes: Sampling the positive pole and negative pole of the bus voltage of the frequency converter to obtain the bus voltage sampling value; Sampling the positive pole of the bus voltage of the frequency converter and the chassis ground voltage to obtain the common mode voltage sampling value.

9. The bus protection method for a frequency converter according to claim 7 or 8 Characterized in that According to the bus voltage sampling value and the common mode voltage sampling value, determining the state of the bus voltage of the frequency converter includes: Determine whether the bus voltage sampling value is greater than the first reference voltage, and determine whether the common mode voltage sampling value is greater than the second reference voltage; If the bus voltage sampling value is less than or equal to the first reference voltage and the common mode voltage sampling value is less than or equal to the second reference voltage, determine that the state of the bus voltage of the frequency converter is the first state; If the bus voltage sampling value is greater than the first reference voltage and / or the common mode voltage sampling value is greater than the second reference voltage, determine that the state of the bus voltage of the frequency converter is the second state.

10. The bus protection method for a frequency converter according to claim 9 Characterized in that According to the state of the bus voltage of the frequency converter, protecting the bus voltage of the frequency converter includes: When the bus voltage state of the frequency converter is in the first state, control the frequency converter to enter the energy feedback process; When the bus voltage state of the frequency converter is in the second state, if the bus voltage sampling value is greater than the first reference voltage, report that the bus voltage sampling of the frequency converter is abnormal and stop the machine; if the common mode voltage sampling value is greater than the second reference voltage, report that the bus voltage grounding of the frequency converter is abnormal and stop the machine.

Images