Three-phase current sampling device and method of frequency converter, frequency converter and magnetic suspension unit

Abstract

The invention discloses a three-phase current sampling device and method of a frequency converter, the frequency converter and a magnetic levitation unit, and the device comprises a first-phase current sampling circuit which processes a sensing value of a first-phase current to obtain a sampling value of the first-phase current of the frequency converter; the second phase current sampling circuit is used for processing the sensing value of the second phase current to obtain a sampling value of the second phase current of the frequency converter; the third-phase current calculation circuit is used for performing hardware calculation based on a process value when the sensing value of the first-phase current is converted to the sampling value of the first-phase current of the frequency converter and a process value when the sensing value of the second-phase current is converted to the sampling value of the second-phase current of the frequency converter, so as to obtain a sampling value of a third-phase current of the frequency converter; sampling of three-phase current of the frequency converter is realized. According to the scheme, the current calculation circuit is used for calculating the third-phase current sampling value based on the two-phase current sampling value output by the two-phase current sampling circuit, the cost is low, and the error is small.

Description

Technical Field

[0001] The present invention belongs to the technical field of inverter control, and specifically relates to a three-phase current sampling device, method, inverter and magnetic levitation unit of an inverter, and more particularly to a three-phase current sampling device, method, inverter and magnetic levitation unit of a high-power inverter of a magnetic levitation unit. Background Art

[0002] In response to the green and environmental protection theme of the new era, oil-free and frictionless high-speed magnetic levitation centrifuges have developed rapidly. As one of the core components of the magnetic levitation centrifuge unit, the magnetic levitation centrifuge inverter needs to stably adjust the speed of the magnetic bearing of the magnetic levitation centrifuge, and its reliability is particularly important.

[0003] Since the inverters used in the magnetic levitation units are all high-power inverters, their input and output currents often reach several hundred amperes. If a fault occurs inside the inverter, its input and output currents can even reach higher. As the main switching device of the diode inverter inverter circuit and the four-quadrant inverter rectifier and inverter circuit, the switching state of IGBT is particularly important to the system where the inverter is located. If the input and output currents of the inverter are too large, it is easy to burn out the power devices (such as IGBT) and cause unit failure. Therefore, the detection of the input and output currents of the inverter is particularly important. In the related scheme, when sampling the three-phase current of the inverter, the three-phase current of the inverter can be directly sampled, but the cost of the inverter will increase.

[0004] The above contents are only used to assist in understanding the technical solution of the present invention and do not constitute an admission that the above contents are prior art. Summary of the invention

[0005] The purpose of the present invention is to provide a three-phase current sampling device, method, inverter and magnetic levitation unit of a frequency converter to solve the problem that directly sampling the three-phase current of the frequency converter will increase the cost of the frequency converter, so as to achieve the effect of low cost and small error by using a current calculation circuit to calculate the third-phase current sampling value based on the two-phase current sampling values ​​output by the two-phase current sampling circuit.

[0006] The present invention provides a three-phase current sampling device for a frequency converter, wherein the frequency converter has an IGBT module and a main control unit; comprises: a current sensor unit and a three-phase current sampling unit; the current sensor unit comprises: a first-phase current sensor and a second-phase current sensor; the three-phase current sampling unit comprises: a first-phase current sampling circuit, a second-phase current sampling circuit, and a third-phase current calculation circuit; wherein the first-phase current sensor is used to sample the first-phase current of the three-phase current of the frequency converter to obtain the sensing value of the first-phase current; the first-phase current sampling circuit is used to process the sensing value of the first-phase current to obtain the sampling value of the first-phase current of the frequency converter; the second-phase current sensor is used to sample the second-phase current of the three-phase current of the frequency converter , obtain the sensing value of the second phase current; the second phase current sampling circuit is used to process the sensing value of the second phase current to obtain the sampling value of the second phase current of the inverter; the third phase current calculation circuit is used to perform hardware calculation based on the process value when the sensing value of the first phase current is converted to the sampling value of the first phase current of the inverter, and the process value when the sensing value of the second phase current is converted to the sampling value of the second phase current of the inverter, to obtain the sampling value of the third phase current of the inverter, so as to realize the sampling of the three-phase current of the inverter; the main control unit of the inverter is used to control the IGBT module based on the sampling value of the first phase current of the inverter, the sampling value of the second phase current of the inverter, and the sampling value of the third phase current of the inverter.

[0007] In some embodiments, the first phase current sampling circuit processes the sensing value of the first phase current to obtain the sampling value of the first phase current of the inverter, specifically: the first phase current sampling circuit is specifically used to process the sensing value of the first phase current to sequentially obtain the first analog value of the first phase current, the second analog value of the first phase current, and the third analog value of the first phase current, so as to use the third analog value of the first phase current as the sampling value of the first phase current of the inverter; the second phase current sampling circuit processes the sensing value of the second phase current to obtain the sampling value of the second phase current of the inverter, specifically: the second phase current sampling circuit is specifically used to process the sensing value of the second phase current to sequentially obtain the first analog value of the second phase current, the second analog value of the second phase current , and a third analog value of the second phase current; using the third analog value of the second phase current as the sampling value of the second phase current of the inverter; the third phase current calculation circuit is used to perform hardware calculation based on the process value when the sensor value of the first phase current is converted to the sampling value of the first phase current of the inverter, and the process value when the sensor value of the second phase current is converted to the sampling value of the second phase current of the inverter, to obtain the sampling value of the third phase current of the inverter, specifically: the third phase current calculation circuit is specifically used to perform hardware calculation based on the second analog value of the first phase current and the second analog value of the second phase current, to successively obtain the first analog value of the third phase current and the second analog value of the third phase current, so as to use the second analog value of the third phase current as the sampling value of the third phase current of the inverter.

[0008] In some embodiments, it also includes: an overcurrent protection unit; wherein the overcurrent protection unit is used to determine whether the three-phase current of the inverter is overcurrent based on the first analog value of the first phase current, the first analog value of the second phase current, and the first analog value of the third phase current; if it is determined that the three-phase current of the inverter is overcurrent, an overcurrent protection signal is output; the main control unit of the inverter is also used to control the IGBT module to shut down according to the overcurrent protection signal.

[0009] In some embodiments, the structures of the first phase current sampling circuit and the second phase current sampling circuit are the same; the first phase current sampling circuit includes: a first sampling processing module, a second sampling processing module, a third sampling processing module, and a sampling output module; wherein, the first phase current sampling circuit processes the sensing value of the first phase current to obtain the sampling value of the first phase current of the inverter, including: the first sampling processing module, which is used to process based on the sensing value of the first phase current to obtain the conversion value of the first phase current; the second sampling processing module, which is used to process based on a preset reference voltage and the conversion value of the first phase current to obtain the first analog value of the first phase current; the third sampling processing module, which is used to process based on the first analog value of the first phase current to obtain the second analog value of the first phase current; the sampling output module, which is used to process based on the second analog value of the first phase current to obtain the third analog value of the first phase current.

[0010] In some embodiments, the first sampling processing module includes: a first operational amplifier module; the second sampling processing module includes: a second operational amplifier module; the third sampling processing module includes: a third operational amplifier module; the sampling output module includes: a first RC module; wherein the first phase current sampling circuit processes the sensing value of the first phase current to specifically obtain the sampling value of the first phase current of the inverter, specifically including: the first operational amplifier module, used to process the sensing value of the first phase current to obtain the conversion value of the first phase current; the second operational amplifier module, used to process the processed value of the first phase current based on a preset reference voltage to obtain the first analog value of the first phase current; the third operational amplifier module, used to process the first analog value of the first phase current to obtain the second analog value of the first phase current; the first RC module, used to process the second analog value of the first phase current to obtain the third analog value of the first phase current, so as to use the third analog value of the first phase current as the sampling value of the first phase current of the inverter.

[0011] In some embodiments, the third phase current calculation circuit includes: a calculation input module, a first calculation processing module, a second calculation processing module, a third calculation processing module, and a calculation output module; the process value when the sensor value of the first phase current is converted to the sampling value of the first phase current of the inverter includes: the second analog value of the first phase current; the process value when the sensor value of the second phase current is converted to the sampling value of the second phase current of the inverter includes: the second analog value of the second phase current; wherein, the third phase current calculation circuit performs hardware calculation based on the process value when the sensor value of the first phase current is converted to the sampling value of the first phase current of the inverter and the process value when the sensor value of the second phase current is converted to the sampling value of the second phase current of the inverter to obtain the sampling value of the third phase current of the inverter, including: the calculation input module, using The first calculation processing module is used for performing summation calculation on the second analog value of the first phase current and the second analog value of the second phase current to obtain a calculated value of the two-phase current; the first calculation processing module is used for performing processing based on the calculated value of the two-phase current to obtain a first processed value of the two-phase current; the second calculation processing module is used for performing processing based on the first processed value of the two-phase current to obtain a second processed value of the two-phase current; the third calculation processing module is used for performing processing based on a preset reference voltage and the second processed value of the two-phase current to obtain a third processed value of the two-phase current, so as to use the third processed value of the two-phase current as the first analog value of the third phase current; the calculation output module is used for performing processing based on the first analog value of the third phase current to obtain a second analog value of the third phase current, so as to use the second analog value of the third phase current as the sampling value of the third phase current of the inverter.

[0012] In some embodiments, the calculation input module includes: a summing circuit; the first calculation processing module includes: a fourth operational amplifier module; the second calculation processing module includes: a fifth operational amplifier module; the third calculation processing module includes: a sixth operational amplifier module; the calculation output module includes: a second RC module; wherein the third phase current calculation circuit performs hardware calculation based on the process value when the sensing value of the first phase current is converted to the sampling value of the first phase current of the inverter, and the process value when the sensing value of the second phase current is converted to the sampling value of the second phase current of the inverter, to obtain the sampling value of the third phase current of the inverter, specifically including: the summing circuit is used to calculate the second analog value of the first phase current and the second analog value of the second phase current The analog values ​​are summed up to obtain the calculated values ​​of the two-phase current; the fourth operational amplifier module is used to process based on the calculated values ​​of the two-phase current to obtain the first processed value of the two-phase current; the fifth operational amplifier module is used to process based on the first processed value of the two-phase current to obtain the second processed value of the two-phase current; the sixth operational amplifier module is used to process based on a preset reference voltage and the second processed value of the two-phase current to obtain the third processed value of the two-phase current, so as to use the third processed value of the two-phase current as the first analog value of the third phase current; the second RC module is used to process based on the first analog value of the third phase current to obtain the second analog value of the third phase current, so as to use the second analog value of the third phase current as the sampling value of the third phase current of the inverter.

[0013] Matching the above device, the present invention provides a frequency converter on another aspect, including: the three-phase current sampling device of the frequency converter described above.

[0014] Matching the above-mentioned device, the present invention provides a magnetic levitation unit on another aspect, including: the three-phase current sampling device of the frequency converter mentioned above, or the frequency converter mentioned above.

[0015] Matching the above-mentioned frequency converter, the present invention provides a three-phase current sampling method of the frequency converter on another aspect, comprising: sampling the first phase current of the three-phase current of the frequency converter through the first phase current sensor to obtain the sensing value of the first phase current; processing the sensing value of the first phase current through the first phase current sampling circuit to obtain the sampling value of the first phase current of the frequency converter; sampling the second phase current of the three-phase current of the frequency converter through the second phase current sensor to obtain the sensing value of the second phase current; processing the sensing value of the second phase current through the second phase current sampling circuit to obtain the The sampling value of the second phase current of the inverter is obtained by hardware calculation based on the process value when the sensor value of the first phase current is converted to the sampling value of the first phase current of the inverter and the process value when the sensor value of the second phase current is converted to the sampling value of the second phase current of the inverter through the third phase current calculation circuit, so as to realize the sampling of the three-phase current of the inverter; based on the sampling value of the first phase current of the inverter, the sampling value of the second phase current of the inverter and the sampling value of the third phase current of the inverter, the IGBT module is controlled.

[0016] In some embodiments, it also includes: judging whether the three-phase current of the inverter is overcurrent based on the first analog value of the first phase current, the first analog value of the second phase current, and the first analog value of the third phase current through the overcurrent protection unit; if it is determined that the three-phase current of the inverter is overcurrent, outputting an overcurrent protection signal; and controlling the IGBT module to shut down according to the overcurrent protection signal.

[0017] Therefore, the scheme of the present invention, for the three-phase current of the inverter (such as the three-phase input current of the inverter or the three-phase output current of the inverter), sets two current sensors to respectively sample two-phase currents (such as U-phase current and V-phase current) of the three-phase current of the inverter, sets two current sampling circuits to respectively process the two-phase currents sampled by the two current sensors to obtain two-phase current sampling values, and sets a current calculation circuit to calculate the third-phase current (such as W-phase current) according to the two-phase current sampling values; thereby, the third-phase current sampling value is calculated by using the current calculation circuit based on the two-phase current sampling values ​​output by the two-phase current sampling circuit, with low cost and small error.

[0018] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present invention.

[0019] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of an embodiment of a three-phase current sampling device for a frequency converter of the present invention;

[0021] Figure 2 It is a structural diagram of the current sampling and overcurrent protection device of the frequency converter;

[0022] Figure 3 It is a circuit principle schematic diagram of the U-phase current sampling circuit;

[0023] Figure 4 It is a circuit principle schematic diagram of the V-phase current sampling circuit;

[0024] Figure 5 It is the circuit principle diagram of the W-phase current hardware calculation circuit;

[0025] Figure 6 A schematic flow chart of an embodiment of a three-phase current sampling method for a frequency converter of the present invention;

[0026] Figure 7 The present invention is a flow chart of an embodiment of overcurrent protection for the frequency converter in the method of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] Considering that, in the relevant schemes, most inverters adopt two current sampling methods: one is to directly install a current sensor in each phase of the three-phase circuit to sample the current of each phase. Although this scheme can achieve current sampling, it also significantly increases the cost of the inverter itself; the other is to only sample two-phase currents and calculate the third-phase current value through the software. Although this sampling method reduces a current sensor, the third-phase current calculated by the software has a delay problem. As the frequency increases, the error between the calculated third-phase current value and the actual value will become larger and larger.

[0029] Therefore, the solution of the present invention proposes a three-phase current sampling device for a frequency converter, specifically a three-phase current sampling device for a high-power frequency converter of a magnetic levitation unit. By sampling two-phase current and then using a hardware circuit to calculate the third-phase current, not only can the use of a current sensor be reduced and the cost of the frequency converter itself be reduced; and the third-phase current sampling analog value is calculated by the hardware circuit, and the error of the third-phase current value calculated by software is much smaller, which can reduce the error of the third-phase current calculation.

[0030] According to an embodiment of the present invention, a three-phase current sampling device for a frequency converter is provided. Figure 1 The inverter has an IGBT module (such as an IGB in a controlled rectifier of the inverter, an IGB in an inverter of the inverter), and a main control unit (such as Figure 2 The DSP main chip and main control part shown in the figure); including: a current sensor unit, and a three-phase current sampling unit; the current sensor unit includes: a first-phase current sensor (such as a U-phase current sensor), a second-phase current sensor (such as a V-phase current sensor); the three-phase current sampling unit includes: a first-phase current sampling circuit (such as a U-phase current sampling circuit), a second-phase current sampling circuit (such as a V-phase current sampling circuit), and a third-phase current calculation circuit (such as a W-phase current hardware calculation circuit).

[0031] The first-phase current sensor is used to sample the first-phase current of the three-phase current of the inverter to obtain a sensing value of the first-phase current (such as a current analog value I_U_OUT corresponding to the U-phase current).

[0032] The first-phase current sampling circuit is used to process the sensing value of the first-phase current to obtain the sampling value of the first-phase current of the inverter, thereby realizing the sampling of the first-phase current of the three-phase current of the inverter.

[0033] The second-phase current sensor is used to sample the second-phase current of the three-phase current of the inverter to obtain a sensing value of the second-phase current (such as a current analog value I_V_OUT corresponding to the V-phase current);

[0034] The second-phase current sampling circuit is used to process the sensing value of the second-phase current to obtain the sampling value of the second-phase current of the inverter, thereby realizing the sampling of the second-phase current of the three-phase current of the inverter.

[0035] The third phase current calculation circuit is used to perform hardware calculation based on the process value when the sensor value of the first phase current is converted to the sampling value of the first phase current of the inverter, and the process value when the sensor value of the second phase current is converted to the sampling value of the second phase current of the inverter, to obtain the sampling value of the third phase current of the inverter, thereby sampling the third phase current of the three-phase current of the inverter, thereby sampling the three-phase current of the inverter.

[0036] The main control unit of the inverter is used to control the IGBT module based on the sampling value of the first phase current of the inverter, the sampling value of the second phase current of the inverter, and the sampling value of the third phase current of the inverter, for example: controlling the turning on or off of the IGBT module, and controlling the duty cycle of the PWM drive signal of the IGBT module when the IGBT module is turned on.

[0037] The solution of the present invention proposes a three-phase current sampling scheme for a high-power inverter of a magnetic levitation unit, which only samples current of any two phases of the inverter output current, converts current and voltage by using a current sensor, outputs two-phase current sampling analog values, and calculates the third-phase current sampling analog value through a hardware circuit. The error of the third-phase current value calculated by software is much smaller, and the use of one current sensor is reduced, thereby reducing the cost of the inverter itself.

[0038] In some embodiments, the first-phase current sampling circuit processes the sensing value of the first-phase current to obtain the sampling value of the first-phase current of the inverter, thereby sampling the first-phase current among the three-phase current of the inverter. Specifically, the first-phase current sampling circuit is specifically used to process the sensing value of the first-phase current to sequentially obtain the first analog value of the first-phase current (such as the current analog value I_U.P of the U phase), the second analog value of the first-phase current (such as the current analog value I_U of the U phase), and the third analog value of the first-phase current (such as the current analog value I_U.DSP of the U phase), so as to use the third analog value of the first-phase current as the sampling value of the first-phase current of the inverter, thereby sampling the first-phase current among the three-phase current of the inverter.

[0039] The second-phase current sampling circuit processes the sensing value of the second-phase current to obtain the sampling value of the second-phase current of the inverter, thereby sampling the second-phase current in the three-phase current of the inverter. Specifically, the second-phase current sampling circuit is used to process the sensing value of the second-phase current to sequentially obtain the first analog value of the second-phase current (such as the current analog value I_V.P of the V phase), the second analog value of the second-phase current (such as the current analog value I_V of the V phase), and the third analog value of the second-phase current (such as the current analog value I_V.DSP of the V phase); the third analog value of the second-phase current is used as the sampling value of the second-phase current of the inverter, thereby sampling the second-phase current in the three-phase current of the inverter.

[0040] The process value when the sensing value of the first phase current is converted to the sampling value of the first phase current of the inverter includes: the second analog value of the first phase current (such as the current analog value I_U of the U phase); the process value when the sensing value of the second phase current is converted to the sampling value of the second phase current of the inverter includes: the second analog value of the second phase current (such as the current analog value I_V of the V phase). The third-phase current calculation circuit is used to perform hardware calculation based on the process value when the sensor value of the first-phase current is converted to the sampling value of the first-phase current of the inverter, and the process value when the sensor value of the second-phase current is converted to the sampling value of the second-phase current of the inverter, to obtain the sampling value of the third-phase current of the inverter, and to implement the sampling of the third-phase current in the three-phase current of the inverter. Specifically, the third-phase current calculation circuit is specifically used to perform hardware calculation based on the second analog value of the first-phase current and the second analog value of the second-phase current, and sequentially obtain the first analog value of the third-phase current (such as the current analog value I_W.P of the W phase) and the second analog value of the third-phase current (the current analog value I_W.DSP of the W phase), so as to use the second analog value of the third-phase current as the sampling value of the third-phase current of the inverter, to implement the sampling of the third-phase current in the three-phase current of the inverter, thereby implementing the sampling of the three-phase current of the inverter.

[0041] Figure 2 The figure is a schematic diagram of the structure of the current sampling and overcurrent protection device of the inverter. Figure 2As shown, the current sampling and overcurrent protection device of the frequency converter includes: a current sensor unit, a three-phase current sampling part, a DSP main chip, an overcurrent protection part, and a main control part. The current sensor unit includes: a U-phase current sensor and a V-phase current sensor. The current sampling part includes: a U-phase current sampling circuit, a V-phase current sampling circuit, and a W-phase current calculation circuit. In order to solve the problem that there is a large error in the current analog value of the third phase calculated by the software and the problem that the cost of the frequency converter increases due to sampling of all three phases, the solution of the present invention proposes a three-phase current sampling device for a high-power frequency converter of a magnetic levitation unit.

[0042] exist Figure 2 In the example shown, the solution of the present invention uses only two current sensors to perform sampling work for the three-phase input current and / or the three-phase output current of the inverter. When the inverter is working, the three-phase circuit of the inverter (such as the input circuit of the inverter or the output circuit of the inverter) will generate AC current, and the current sensor only samples the current values ​​of the U phase and the V phase, and then outputs the corresponding current analog values ​​I_U_OUT (i.e. the current analog value I_U_OUT corresponding to the U phase current) and I_V_OUT (i.e. the current analog value I_V_OUT corresponding to the V phase current) respectively and enters the current sampling circuit (i.e. Figure 2 The current sampling section shown in FIG.

[0043] The current sampling analog value input into the inverter mainboard (i.e., the current analog value I_U_OUT corresponding to the U-phase current, the current analog value I_V_OUT corresponding to the V-phase current) is converted and output through the internal circuit to output the U-phase current analog value I_U and the V-phase current analog value I_V into the W-phase current calculation circuit. The W-phase current calculation circuit converts and outputs the W-phase current analog value I_W.DSP through the internal circuit into the DSP main chip. Therefore, the DSP main chip samples the W-phase current (i.e., the W-phase current analog value I_W.DSP) in this way.

[0044] While the current sampling circuits of the U phase and the V phase output the current analog value I_U of the U phase and the current analog value I_V of the V phase, the current analog value I_U.DSP of the U phase and the current analog value I_V.DSP of the V phase are also input into the DSP main chip. The current analog value I_U.DSP of the U phase and the current analog value I_V.DSP of the V phase are exactly the current sampling analog values ​​of the U phase and the V phase. After the DSP main chip samples the current analog values ​​of each phase, it is converted by the internal software and sent to the main control part in the form of data communication.

[0045] In the solution of the present invention, the number of current sensors used is reduced by sampling the current, thereby reducing the unit cost. In the solution of the present invention, the method of sampling only any two-phase current output by the frequency converter and then using an operational amplifier circuit to calculate the third-phase current is used to reduce the problem of large errors in the current simulation value of the third phase calculated by software.

[0046] In some implementations, the three-phase current sampling device for the frequency converter described in the solution of the present invention further includes: an overcurrent protection unit, such as an overcurrent protection circuit, for performing overcurrent protection on the frequency converter.

[0047] Among them, the overcurrent protection unit is used to determine whether the three-phase current of the inverter is overcurrent based on the first analog value of the first phase current, the first analog value of the second phase current, and the first analog value of the third phase current; if it is determined that the three-phase current of the inverter is overcurrent, an overcurrent protection signal (such as signal TZ) is output.

[0048] The main control unit of the frequency converter is also used to control the IGBT module to shut down according to the overcurrent protection signal.

[0049] exist Figure 2 In the example shown, when the three-phase current sampling circuit of the inverter is working, the overcurrent protection circuit of the inverter (such as Figure 2 The overcurrent protection part shown in the figure is also in operation at all times, because only the existence of the overcurrent protection circuit can ensure that the three-phase circuit can take timely action to protect the internal devices when there is an overcurrent. The current sampling circuit of the U phase and the V phase will output the current analog value I_U.P (i.e. the current analog value I_U.P of the U phase) and I_V.P (i.e. the current analog value I_V.P of the V phase) after internal conversion of the sampled current analog value into the overcurrent protection circuit, and then the overcurrent protection circuit will process the internal circuit to distinguish whether the current is overcurrent. At the same time, in the entire sampling circuit, when the calculated current analog value I_W.P of the W phase is also input into the overcurrent protection circuit for processing to distinguish whether the current is overcurrent. If the overcurrent protection circuit determines that there is an overcurrent, it will output the protection signal TZ to the DSP main chip in time, thereby driving the DSP main chip to control the IGBT to turn off and protect the safety of the internal devices of the inverter. In the case of sampling the three-phase input current of the frequency converter, the IGBT is a power device in the rectifier of the frequency converter; in the case of sampling the three-phase output current of the frequency converter, the IGBT is a power device in the inverter of the frequency converter.

[0050] In some implementations, the first phase current sampling circuit and the second phase current sampling circuit have the same structure; the first phase current sampling circuit includes: a first sampling processing module, a second sampling processing module, a third sampling processing module, and a sampling output module.

[0051] The first phase current sampling circuit processes the sensing value of the first phase current to obtain the sampling value of the first phase current of the inverter, including:

[0052] The first sampling processing module is used to perform processing based on the sensing value of the first phase current to obtain a conversion value of the first phase current.

[0053] The second sampling processing module is used to perform processing based on a preset reference voltage and the converted value of the first phase current to obtain a first analog value of the first phase current (such as the current analog value I_U.P of the U phase).

[0054] The third sampling and processing module is used to process the first analog value of the first phase current to obtain the second analog value of the first phase current (such as the current analog value I_U of the U phase).

[0055] The sampling output module is used to process the second analog value of the first phase current to obtain a third analog value of the first phase current (such as the current analog value I_U.DSP of the U phase).

[0056] Figure 3 It is the circuit principle diagram of the U phase current sampling circuit. Figure 4 The schematic diagram of the circuit principle of the V-phase current sampling circuit is shown in Figure 2. Figure 3 As shown, the V phase sampling circuit is as follows Figure 4 As shown, the U phase and V phase are the same sampling circuit.

[0057] In the scheme of the present invention, a two-phase current sampling circuit with the same structure is used. The current value detected by the current sensor can be sampled and processed based on the same current sampling circuit to obtain the required current sampling value, which can ensure that the sampling and processing method and structure for the two-phase current are consistent, which is beneficial to improving the accuracy of the three-phase current sampling for the inverter.

[0058] In some embodiments, the first sampling processing module includes: a first operational amplifier module, such as Figure 3 The operational amplifier U1 and its peripheral circuits in the second sampling processing module include: a second operational amplifier module, such as Figure 3 The operational amplifier U2 and its peripheral circuits in the third sampling processing module include: a third operational amplifier module, such as Figure 3 The operational amplifier U3 and its peripheral circuits in the sampling output module include: a first RC module, such as Figure 3 The resistor R13 and the capacitor C7 in it.

[0059] The first phase current sampling circuit processes the sensing value of the first phase current to obtain the sampling value of the first phase current of the inverter, which specifically includes:

[0060] The first operational amplifier module is used to process the sensing value of the first phase current to obtain a conversion value of the first phase current.

[0061] The second operational amplifier module is used to process the processed value of the first phase current based on a preset reference voltage to obtain a first analog value of the first phase current (such as the current analog value I_U.P of the U phase).

[0062] The third operational amplifier module is used to process the first analog value of the first phase current to obtain the second analog value of the first phase current (such as the U-phase current analog value I_U).

[0063] The first RC module is used to process the second analog value of the first phase current to obtain the third analog value of the first phase current (such as the current analog value I_U.DSP of the U phase), so as to use the third analog value of the first phase current as the sampling value of the first phase current of the inverter, thereby realizing the sampling of the first phase current among the three-phase current of the inverter.

[0064] like Figure 3As shown, the U-phase current sampling circuit includes: resistor R1, resistor R2, resistor R3, resistor R4, resistor R5, resistor R6, resistor R7, resistor R8, resistor R9, resistor R10, resistor R11, resistor R12, resistor R13, capacitor C1, capacitor C2, capacitor C3, capacitor C4, capacitor C5, capacitor C6, capacitor C7, operational amplifier U1, operational amplifier U2, operational amplifier U3. Signal I_U_OUT is input to the non-inverting input terminal of the operational amplifier U1 after passing through the resistor R1; the non-inverting input terminal of the operational amplifier U1 is also connected to the analog ground AGND after passing through the parallel resistor R3 and capacitor C1; the inverting input terminal of the operational amplifier U1 is connected to the analog ground AGND after passing through the resistor R2; the inverting input terminal of the operational amplifier U1 is also connected to the output terminal of the operational amplifier U1 after passing through the parallel resistor R4 and capacitor C2. The output end of the operational amplifier U1 is connected to the inverting input end of the operational amplifier U2 via a resistor R6; the preset reference voltage VREF is connected to the inverting input end of the operational amplifier U2 via a resistor R7 and a capacitor C3 connected in parallel; the non-inverting input end of the operational amplifier U2 is connected to the analog ground ANGND via a resistor R5; the non-inverting input end of the operational amplifier U2 is also connected to the output end of the operational amplifier U2 via a resistor R8 and a capacitor C4 connected in parallel; the output end of the operational amplifier U2 outputs the current analog value I_U.P of the U phase. The output end of the operational amplifier U2 is connected to the inverting input end of the operational amplifier U3 through the resistor R10; the inverting input end of the operational amplifier U3 is connected to the analog ground ANGND through the parallel resistor R11 and capacitor C5; the non-inverting input end of the operational amplifier U3 is connected to the analog ground AGND through the resistor R9; the non-inverting input end of the operational amplifier U3 is also connected to the output end of the operational amplifier U3 through the parallel capacitor C6 and resistor R12; the output end of the operational amplifier U3 outputs the current analog value I_U of the U phase. The output end of the operational amplifier U3 is connected to the analog ground AGND through the resistor R13 and capacitor C7. The common end of the resistor R13 and the capacitor C7 outputs the current analog value I_U.DSP of the U phase.

[0065] like Figure 4As shown, the V-phase current sampling circuit includes: resistor R14, resistor R15, resistor R13, resistor 17, resistor 18, resistor 19, resistor R7, resistor 21, resistor 22, resistor 23, resistor 24, resistor 25, resistor 26, capacitor C8, capacitor C9, capacitor C10, capacitor C11, capacitor C12, capacitor C13, capacitor C14, operational amplifier U4, operational amplifier U5, operational amplifier U6. The signal I_V_OVT is input to the non-inverting input terminal of the operational amplifier U4 after passing through the resistor R14; the non-inverting input terminal of the operational amplifier U4 is also connected to the analog ground AGND after passing through the parallel resistor R13 and capacitor C8; the inverting input terminal of the operational amplifier U4 is connected to the analog ground AGND after passing through the resistor R15; the inverting input terminal of the operational amplifier U4 is also connected to the output terminal of the operational amplifier U4 after passing through the parallel resistor 17 and capacitor C9. The output end of the operational amplifier U4 is connected to the inverting input end of the operational amplifier U5 via a resistor 19; the preset reference voltage VREF is connected to the inverting input end of the operational amplifier U5 via a resistor R7 and a capacitor C10 connected in parallel; the non-inverting input end of the operational amplifier U5 is connected to the analog ground ANGND via a resistor 18; the non-inverting input end of the operational amplifier U5 is also connected to the output end of the operational amplifier U5 via a resistor 21 and a capacitor C11 connected in parallel; the output end of the operational amplifier U5 outputs the V-phase current analog value I_V.P. The output end of the operational amplifier U5 is connected to the inverting input end of the operational amplifier U6 through the resistor 23; the inverting input end of the operational amplifier U6 is connected to the analog ground ANGND through the parallel resistor 24 and the capacitor C12; the non-inverting input end of the operational amplifier U6 is connected to the analog ground AGND through the resistor 22; the non-inverting input end of the operational amplifier U6 is also connected to the output end of the operational amplifier U6 through the parallel capacitor C13 and the resistor 25; the output end of the operational amplifier U6 outputs the current analog value I_V of the V phase. The output end of the operational amplifier U6 is connected to the analog ground AGND through the resistor 26 and the capacitor C14. The common end of the resistor 26 and the capacitor C14 outputs the current analog value I_V.DSP of the V phase.

[0066] Take phase U as an example: Figure 3 In the example shown, resistors R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, and R13 are fixed resistance resistors, and R1 = R2, R3 = R4, R5 = R6 = R7 = R8, R9 = R10, and R11 = R12. All capacitors in the circuit are filter capacitors, and U1, U2, and U3 are operational amplifiers.

[0067] exist Figure 3In the example shown, the signal I_U_OUT is the AC signal collected by the current sensor. Assume that the transformation ratio of the current sensor is N(VΑ), that is, how many V voltages can be converted when 1A current passes through the current sensor; when the current detected by the current sensor is I, the voltage of the signal I_U_OUT is NI. The signal I_U_OUT is first scaled by the operational amplifier U1 and becomes the original The current analog value I_U.P of the U phase is output to the hardware overcurrent protection circuit. At the same time, the current analog value I_U.P of the U phase is further scaled by the operational amplifier U3, and finally the current analog value I_U.DSP of the U phase is output to the DSP main chip. The main purpose of increasing the bias voltage is to eliminate all negative voltages of the current analog value I_U_OUT corresponding to the U phase current, so as to facilitate the subsequent current sampling analog value to be input into the DSP main chip.

[0068] The current sampling output U-phase current analog value I_U. The current value of DSP is:

[0069]

[0070] Similarly, since the V phase and the U phase use the same sampling circuit, the current analog value I_V.DSP of the U phase output by the current sampling is:

[0071]

[0072] Figure 3 and Figure 4 It is a current sampling circuit. The inverter converts the current into voltage through the current sensor, and then goes through a series of voltage conversions in the sampling circuit to become a voltage that can be input into the DSP main chip. If the voltage is too large and exceeds the maximum current value of the DSP main chip, it will burn out the DSP main chip, so it needs to go through a series of voltage conversions in the sampling circuit to become a voltage that can be input into the DSP main chip.

[0073] In some embodiments, the third phase current calculation circuit includes: a calculation input module, a first calculation processing module, a second calculation processing module, a third calculation processing module, and a calculation output module; the process value when the sensing value of the first phase current is converted to the sampling value of the first phase current of the inverter includes: the second analog value of the first phase current (such as the current analog value I_U of the U phase); the process value when the sensing value of the second phase current is converted to the sampling value of the second phase current of the inverter includes: the second analog value of the second phase current (such as the current analog value I_V of the V phase).

[0074] The third phase current calculation circuit performs hardware calculation based on the process value when the sensor value of the first phase current is converted to the sampled value of the first phase current of the inverter, and the process value when the sensor value of the second phase current is converted to the sampled value of the second phase current of the inverter, to obtain the sampled value of the third phase current of the inverter, including:

[0075] The calculation input module is used to perform a sum calculation on the second analog value of the first phase current and the second analog value of the second phase current to obtain a two-phase current calculation value.

[0076] The first calculation and processing module is used to perform processing based on the two-phase current calculation values ​​to obtain first processed values ​​of the two-phase currents.

[0077] The second calculation processing module is used to process the first processed values ​​of the two-phase current to obtain the second processed values ​​of the two-phase current.

[0078] The third calculation and processing module is used to process based on a preset reference voltage and the second processed value of the two-phase current to obtain a third processed value of the two-phase current, so as to use the third processed value of the two-phase current as the first analog value of the third phase current (such as the current analog value I_W.P of the W phase).

[0079] The calculation output module is used to process the first analog value of the third phase current to obtain the second analog value of the third phase current (the current analog value of the W phase I_W.DSP), so as to use the second analog value of the third phase current as the sampling value of the third phase current of the inverter.

[0080] In the solution of the present invention, a third-phase current calculation circuit composed of a calculation input module, a first calculation processing module, a second calculation processing module, a third calculation processing module, and a calculation output module is used. Hardware calculation processing is performed on the two-phase current sampling values ​​obtained by sampling and processing the current value detected by the current sensor by the same two-phase current sampling circuit to obtain the third-phase current sampling value, which has low cost and small error. In the solution of the present invention, the cost of the frequency converter is reduced by using two current sensors for sampling, and the problem of increasing the cost of the frequency converter by directly sampling the three-phase current is solved. In the solution of the present invention, the error of the third-phase current calculation is reduced by sampling the two-phase current and then using the hardware circuit to calculate the third-phase current, and the problem of a large error between the calculated current value and the actual value due to the delay in the software calculation when the third-phase current value is calculated by software is solved.

[0081] In some embodiments, the calculation input module includes: a summing circuit (such as Figure 5The first calculation processing module includes: a fourth operational amplifier module (such as Figure 5 The operational amplifier U7 and its peripheral circuits in the second calculation processing module includes: a fifth operational amplifier module (such as Figure 5 The operational amplifier U8 and its peripheral circuits in the third calculation processing module includes: a sixth operational amplifier module (such as Figure 5 The operational amplifier U9 and its peripheral circuits in the calculation output module includes: a second RC module, such as Figure 5 The resistor R40 and the capacitor C19 in.

[0082] The third phase current calculation circuit performs hardware calculation based on the process value when the sensor value of the first phase current is converted to the sampled value of the first phase current of the inverter, and the process value when the sensor value of the second phase current is converted to the sampled value of the second phase current of the inverter, to obtain the sampled value of the third phase current of the inverter, specifically including:

[0083] The summing circuit is used to sum the second analog value of the first phase current and the second analog value of the second phase current to obtain a two-phase current calculation value.

[0084] The fourth operational amplifier module is used to perform processing based on the two-phase current calculated values ​​to obtain first processed values ​​of the two-phase currents.

[0085] The fifth operational amplifier module is used to perform processing based on the first processed value of the two-phase current to obtain a second processed value of the two-phase current.

[0086] The sixth operational amplifier module is used to process based on a preset reference voltage and the second processed value of the two-phase current to obtain a third processed value of the two-phase current, so as to use the third processed value of the two-phase current as the first analog value of the third phase current (such as the current analog value I_W.P of the W phase).

[0087] The second RC module is used to process the first analog value of the third phase current to obtain the second analog value of the third phase current (the current analog value of the W phase I_W.DSP), so as to use the second analog value of the third phase current as the sampling value of the third phase current of the inverter.

[0088] Figure 5 FIG. 1 is a schematic diagram of the circuit principle of the W-phase current hardware calculation circuit. Figure 5 The schematic diagram of the W-phase current hardware calculation circuit is shown in FIG. The W-phase current sampling value is obtained by calculating the hardware circuit when the U-phase current sampling value and the V-phase current sampling value are determined. Figure 5As shown, the W-phase current hardware calculation circuit includes: resistor R27, resistor R28, resistor R29, resistor R30, resistor R31, resistor R32, resistor R33, resistor R34, resistor R35, resistor R36, resistor R38, resistor R39, resistor R40, capacitor C15, capacitor C16, capacitor C18, capacitor C19, operational amplifier U7, operational amplifier U8, operational amplifier U9.

[0089] like Figure 3 The U-phase current analog value I_U output by the U-phase current sampling circuit shown in FIG. 1 is input to the non-inverting input terminal of the operational amplifier U7 after passing through the resistor R27; Figure 4 The V-phase current analog value I_V output by the V-phase current sampling circuit shown is input to the non-inverting input terminal of the operational amplifier U7 through the resistor R28; the non-inverting input terminal of the operational amplifier U7 is also connected to the analog ground AGND through the parallel resistors R29, R30 and C15; the inverting input terminal of the operational amplifier U7 is connected to the analog ground AGND through the resistor R31; the inverting input terminal of the operational amplifier U7 is also connected to the output terminal of the operational amplifier U7 through the parallel resistor R32 and capacitor C16. The output terminal of the operational amplifier U7 is connected to the inverting input terminal of the operational amplifier U8 through the resistor R33; the non-inverting input terminal of the operational amplifier U8 is connected to the analog ground AGND through the resistor R34; the inverting input terminal of the operational amplifier U8 is also connected to the output terminal of the operational amplifier U8 through the resistor R35. The output end of the operational amplifier U8 is connected to the inverting input end of the operational amplifier U9 through the resistor R36; the preset reference voltage VREF is connected to the inverting input end of the operational amplifier U9 through the parallel resistor R37 and the capacitor C17; the non-inverting input end of the operational amplifier U9 is connected to the analog ground AGND through the resistor R38; the non-inverting input end of the operational amplifier U9 is connected to the output end of the operational amplifier U9 through the resistor R39 and the capacitor C18; the output end of the operational amplifier U9 outputs the current analog value I_W.P of the W phase. The output end of the operational amplifier U9 is connected to the analog ground AGND through the resistor R40 and the capacitor C19; the common end of the resistor R40 and the capacitor C19 outputs the current analog value I_W.DSP of the W phase.

[0090] exist Figure 5In the example shown, resistors R27, R28, R29, R30, R31, R32, R33, R34, R35, R36, R38, R39 and R40 are all fixed resistors, and the resistance is selected according to the actual situation; among them, R27 = R28 = R29 = R30, R31 = R32, R33 = R35, R36 = R37 = R38 = R39 are all voltage divider resistors; resistors R34 and R36 are current limiting resistors, and resistor R40 has a small resistance and forms an RC filter with capacitor C19. U7, U8 and U9 are operational amplifiers, and the capacitors in this circuit are all filter capacitors. After the current analog value I_U.DSP of the U phase and the current analog value I_V.DSP of the V phase are determined, the current analog value I_U.DSP of the U phase and the current analog value I_V.DSP of the V phase are input into the DSP main chip, and the current analog value I_U of the U phase and the current analog value I_V of the V phase are input into the W phase current calculation circuit.

[0091] The current analog value I_U of the U phase and the current analog value I_V of the V phase are input into the W phase current calculation circuit. First, the sum of the current analog value I_U of the U phase and the current analog value I_V of the V phase is obtained through the summing circuit. Since the sum of the three-phase current is zero according to the characteristics of the three-phase current balance, U+V=-W is obtained. Therefore, according to the characteristics of the operational amplifier U8 and the resistor R33=R35, the negative value of the sum of U+V is obtained, which is the W phase current sampling value. Because the calculated W phase current sampling value I_W.DSP may be a negative value, and the input current value of the DSP chip is 0-3.3V, after the calculated W phase sampling value, a bias voltage VREF needs to be applied on this basis and then scaled by the operational amplifier U9 year-on-year to ensure that the W phase current sampling value input into the DSP main chip is always within 0-3.3V.

[0092] The current value of the W phase current sampling output I_W.DSP is:

[0093]

[0094] And because R10=R23, R11=R24, R1=R14, R3=R16, the formulas for the U-phase and V-phase current values ​​and the final W-phase current sampling analog value are obtained through comprehensive calculation as follows:

[0095]

[0096] Among them, I U is the U phase current value (such as the U phase current analog value I_U), I V is the V-phase current value (such as the V-phase current analog value I_V).

[0097] Most frequency converter current sampling only samples two phases of the three-phase current, and then calculates the third phase current through the internal program of the DSP main chip. Although this operation is convenient and cost-saving, this sampling method often increases the deviation of the third phase current value calculated as the frequency converter operating frequency increases. Therefore, the solution of the present invention adopts a hardware circuit to calculate the third phase current value to solve the problem that the error of the calculated third phase current value increases as the operating frequency increases. In the solution of the present invention, the voltage signal collected by the current sensor is scaled, and then a standard bias voltage is added to increase the voltage to a positive value, and then it is scaled by 0 to 3.3V and input to the DSP main chip; by adopting the three-phase current balance U+V=-W characteristics of AC power, the W phase current is calculated through an operational amplifier; by sampling the two-phase current, and then using the hardware circuit to calculate the third phase current, the error of the third phase current calculation is reduced.

[0098] In the scheme of the present invention, the above embodiment only lists some control scenarios of the three-phase current sampling method of a high-power inverter of a magnetic levitation unit. The scheme of the present invention can be modified and applied to other control scenarios according to actual conditions. The scheme of the present invention is not limited to the parameters designed in the example, and the parameters can be adjusted and designed according to actual applications.

[0099] In the scheme of the present invention, current sampling is to sample two phases separately, each phase is scaled and then bias voltage is added, and finally scaled to 0-3.3V and input to the DSP main chip; by sampling the current of two phases and then calculating the third phase current sampling value through hardware circuit, the problem of increasing the unit cost by using current sensors for three-phase current sampling and the problem of using software to calculate the third phase current, which has a large error, can be solved.

[0100] By adopting the technical solution of the present invention, two current sensors are set for sampling two-phase currents (such as U-phase current and V-phase current) of the three-phase current of the inverter (such as the three-phase input current of the inverter or the three-phase output current of the inverter), two current sampling circuits are set to process the two-phase currents sampled by the two current sensors to obtain two-phase current sampling values, and a current calculation circuit is set to calculate the third-phase current (such as W-phase current) according to the two-phase current sampling values; thus, the third-phase current sampling value is calculated by using the current calculation circuit based on the two-phase current sampling values ​​output by the two-phase current sampling circuit, which has low cost and small error.

[0101] According to an embodiment of the present invention, a frequency converter corresponding to the three-phase current sampling device of the frequency converter is also provided. The frequency converter may include: the three-phase current sampling device of the frequency converter described above.

[0102] Since the processing and functions implemented by the frequency converter of this embodiment basically correspond to the embodiments, principles and examples of the device, for the details not described in this embodiment, please refer to the relevant descriptions in the aforementioned embodiments and will not be repeated here.

[0103] According to an embodiment of the present invention, a magnetic suspension unit corresponding to the three-phase current sampling device of the frequency converter is also provided. The magnetic suspension unit may include: the three-phase current sampling device of the frequency converter described above, or the frequency converter described above.

[0104] Since the processing and functions implemented by the magnetic levitation unit of this embodiment basically correspond to the embodiments, principles and examples of the device, for the details not described in this embodiment, please refer to the relevant descriptions in the aforementioned embodiments and will not be repeated here.

[0105] According to an embodiment of the present invention, a three-phase current sampling method for a frequency converter is also provided, such as Figure 6 The flowchart of an embodiment of the method of the present invention is shown in FIG. The three-phase current sampling method of the frequency converter may include: steps S110 to S160.

[0106] In step S110, the first phase current of the three-phase current of the inverter is sampled by the first phase current sensor to obtain a sensing value of the first phase current (such as a current analog value I_U_OUT corresponding to the U-phase current).

[0107] In step S120, the sensing value of the first phase current is processed by the first phase current sampling circuit to obtain a sampling value of the first phase current of the inverter, thereby implementing sampling of the first phase current of the three-phase current of the inverter.

[0108] In step S130, the second phase current of the three-phase current of the inverter is sampled by the second phase current sensor to obtain a sensing value of the second phase current (such as a current analog value I_V_OUT corresponding to the V phase current).

[0109] In step S140, the sensing value of the second phase current is processed by the second phase current sampling circuit to obtain a sampling value of the second phase current of the inverter, thereby implementing sampling of the second phase current of the three-phase current of the inverter.

[0110] At step S150, the third phase current calculation circuit performs hardware calculation based on the process value when the sensor value of the first phase current is converted to the sampling value of the first phase current of the inverter, and the process value when the sensor value of the second phase current is converted to the sampling value of the second phase current of the inverter, so as to obtain the sampling value of the third phase current of the inverter, thereby sampling the three-phase current of the inverter.

[0111] At step S160, the IGBT module is controlled by the main control unit of the inverter based on the sampling value of the first phase current of the inverter, the sampling value of the second phase current of the inverter, and the sampling value of the third phase current of the inverter, for example: controlling the turning on or off of the IGBT module, and controlling the duty cycle of the PWM drive signal of the IGBT module when the IGBT module is turned on.

[0112] The solution of the present invention proposes a three-phase current sampling scheme for a high-power inverter of a magnetic levitation unit, which only samples current of any two phases of the inverter output current, converts current and voltage by using a current sensor, outputs two-phase current sampling analog values, and calculates the third-phase current sampling analog value through a hardware circuit. The error of the third-phase current value calculated by software is much smaller, and the use of one current sensor is reduced, thereby reducing the cost of the inverter itself.

[0113] In some implementations, the three-phase current sampling method for the inverter described in the solution of the present invention further includes: a process of performing overcurrent protection on the inverter.

[0114] Combine the following Figure 7 The flowchart of an embodiment of over-current protection for the frequency converter in the method of the present invention further illustrates the specific process of over-current protection for the frequency converter, including: step S210 to step S220.

[0115] Step S210, through the overcurrent protection unit, based on the first analog value of the first phase current, the first analog value of the second phase current, and the first analog value of the third phase current, determine whether the three-phase current of the inverter is overcurrent; if it is determined that the three-phase current of the inverter is overcurrent, output an overcurrent protection signal (such as signal TZ).

[0116] Step S220: Controlling the IGBT module to be turned off according to the overcurrent protection signal through the main control unit of the inverter.

[0117] In the solution of the present invention, when the three-phase current sampling circuit of the inverter is working, the overcurrent protection circuit of the inverter (such as Figure 2The overcurrent protection part shown in the figure is also in operation at all times, because only the existence of the overcurrent protection circuit can ensure that the three-phase circuit can take timely action to protect the internal devices when there is an overcurrent. The current sampling circuit of the U phase and the V phase will output the current analog value I_U.P (i.e. the current analog value I_U.P of the U phase) and I_V.P (i.e. the current analog value I_V.P of the V phase) after internal conversion of the sampled current analog value into the overcurrent protection circuit, and then the overcurrent protection circuit will process the internal circuit to distinguish whether the current is overcurrent. At the same time, in the entire sampling circuit, when the calculated current analog value I_W.P of the W phase is also input into the overcurrent protection circuit for processing to distinguish whether the current is overcurrent. If the overcurrent protection circuit determines that there is an overcurrent, it will output the protection signal TZ to the DSP main chip in time, thereby driving the DSP main chip to control the IGBT to turn off and protect the safety of the internal devices of the inverter.

[0118] Since the processing and functions implemented by the method of this embodiment basically correspond to the embodiments, principles and examples of the aforementioned frequency converter, for the details not fully described in the description of this embodiment, please refer to the relevant descriptions in the aforementioned embodiments, and no further elaboration will be made here.

[0119] In summary, it is easy for those skilled in the art to understand that, under the premise of no conflict, the above-mentioned advantageous methods can be freely combined and superimposed.

[0120] The above description is only an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of the claims of the present invention.

Claims

1. A three-phase current sampling device for a frequency converter, characterized in that: The inverter has an IGBT module and a main control unit; includes: a current sensor unit and a three-phase current sampling unit; the current sensor unit includes: a first-phase current sensor and a second-phase current sensor; the three-phase current sampling unit includes: a first-phase current sampling circuit, a second-phase current sampling circuit, and a third-phase current calculation circuit; wherein, The first-phase current sensor is used to sample the first-phase current of the three-phase current of the inverter to obtain a sensing value of the first-phase current; The first phase current sampling circuit is used to process the sensing value of the first phase current to obtain a sampling value of the first phase current of the inverter; The second-phase current sensor is used to sample the second-phase current of the three-phase current of the inverter to obtain a sensing value of the second-phase current; The second phase current sampling circuit is used to process the sensing value of the second phase current to obtain a sampling value of the second phase current of the inverter; The third phase current calculation circuit is used to perform hardware calculation based on the process value when the sensor value of the first phase current is converted to the sampled value of the first phase current of the inverter, and the process value when the sensor value of the second phase current is converted to the sampled value of the second phase current of the inverter, so as to obtain the sampled value of the third phase current of the inverter, thereby realizing the sampling of the three-phase current of the inverter; The main control unit of the inverter is used to control the IGBT module based on the sampled value of the first phase current of the inverter, the sampled value of the second phase current of the inverter, and the sampled value of the third phase current of the inverter.

2. The three-phase current sampling device of the frequency converter according to claim 1, characterized in that: in, The first phase current sampling circuit processes the sensing value of the first phase current to obtain the sampling value of the first phase current of the inverter, specifically: The first phase current sampling circuit is specifically used to process the sensing value of the first phase current to sequentially obtain a first analog value of the first phase current, a second analog value of the first phase current, and a third analog value of the first phase current, so as to use the third analog value of the first phase current as the sampling value of the first phase current of the inverter; The second phase current sampling circuit processes the sensing value of the second phase current to obtain the sampling value of the second phase current of the inverter, specifically: The second phase current sampling circuit is specifically used to process the sensing value of the second phase current to obtain a first analog value of the second phase current, a second analog value of the second phase current, and a third analog value of the second phase current in sequence; and use the third analog value of the second phase current as the sampling value of the second phase current of the inverter; The third phase current calculation circuit is used to perform hardware calculation based on the process value when the sensor value of the first phase current is converted to the sampled value of the first phase current of the inverter, and the process value when the sensor value of the second phase current is converted to the sampled value of the second phase current of the inverter, to obtain the sampled value of the third phase current of the inverter, specifically: The third phase current calculation circuit is specifically used to perform hardware calculation based on the second analog value of the first phase current and the second analog value of the second phase current, and obtain the first analog value of the third phase current and the second analog value of the third phase current in sequence, so as to use the second analog value of the third phase current as the sampling value of the third phase current of the inverter.

3. The three-phase current sampling device of the frequency converter according to claim 2, characterized in that: Also includes: Overcurrent protection unit; wherein, The overcurrent protection unit is used to determine whether the three-phase current of the inverter is overcurrent based on the first analog value of the first phase current, the first analog value of the second phase current, and the first analog value of the third phase current; if it is determined that the three-phase current of the inverter is overcurrent, output an overcurrent protection signal; The main control unit of the frequency converter is also used to control the IGBT module to shut down according to the overcurrent protection signal.

4. The three-phase current sampling device of the frequency converter according to any one of claims 1 to 3, characterized in that: The first phase current sampling circuit and the second phase current sampling circuit have the same structure; the first phase current sampling circuit includes: a first sampling processing module, a second sampling processing module, a third sampling processing module, and a sampling output module; wherein, The first phase current sampling circuit processes the sensing value of the first phase current to obtain the sampling value of the first phase current of the inverter, including: The first sampling processing module is used to process the sensing value of the first phase current to obtain a conversion value of the first phase current; The second sampling processing module is used to perform processing based on a preset reference voltage and a conversion value of the first phase current to obtain a first analog value of the first phase current; The third sampling processing module is used to process the first analog value of the first phase current to obtain a second analog value of the first phase current; The sampling output module is used to process the second analog value of the first phase current to obtain a third analog value of the first phase current.

5. The three-phase current sampling device for a frequency converter according to claim 4, characterized in that: The first sampling processing module includes: a first operational amplifier module; the second sampling processing module includes: a second operational amplifier module; the third sampling processing module includes: a third operational amplifier module; the sampling output module includes: a first RC module; wherein, The first phase current sampling circuit processes the sensing value of the first phase current to obtain the sampling value of the first phase current of the inverter, specifically including: The first operational amplifier module is used to process the sensing value of the first phase current to obtain a conversion value of the first phase current; The second operational amplifier module is used to process the processed value of the first phase current based on a preset reference voltage to obtain a first analog value of the first phase current; The third operational amplifier module is used to process the first analog value of the first phase current to obtain a second analog value of the first phase current; The first RC module is used to process the second analog value of the first phase current to obtain a third analog value of the first phase current, so as to use the third analog value of the first phase current as a sampled value of the first phase current of the inverter.

6. The three-phase current sampling device of the frequency converter according to any one of claims 1 to 3, characterized in that: The third phase current calculation circuit includes: a calculation input module, a first calculation processing module, a second calculation processing module, a third calculation processing module, and a calculation output module; the process value when the sensor value of the first phase current is converted to the sampling value of the first phase current of the inverter includes: the second analog value of the first phase current; the process value when the sensor value of the second phase current is converted to the sampling value of the second phase current of the inverter includes: the second analog value of the second phase current; wherein, The third phase current calculation circuit performs hardware calculation based on the process value when the sensor value of the first phase current is converted to the sampled value of the first phase current of the inverter, and the process value when the sensor value of the second phase current is converted to the sampled value of the second phase current of the inverter, to obtain the sampled value of the third phase current of the inverter, including: The calculation input module is used to perform a sum calculation on the second analog value of the first phase current and the second analog value of the second phase current to obtain a two-phase current calculation value; The first calculation processing module is used to process based on the two-phase current calculation value to obtain a first processed value of the two-phase current; The second calculation processing module is used to process the first processed value of the two-phase current to obtain a second processed value of the two-phase current; The third calculation processing module is used to process based on a preset reference voltage and the second processed value of the two-phase current to obtain a third processed value of the two-phase current, so as to use the third processed value of the two-phase current as a first analog value of the third-phase current; The calculation output module is used to process the first analog value of the third phase current to obtain a second analog value of the third phase current, so as to use the second analog value of the third phase current as a sampling value of the third phase current of the inverter.

7. The three-phase current sampling device for a frequency converter according to claim 6, characterized in that: The calculation input module includes: a summing circuit; the first calculation processing module includes: a fourth operational amplifier module; the second calculation processing module includes: a fifth operational amplifier module; the third calculation processing module includes: a sixth operational amplifier module; the calculation output module includes: a second RC module; wherein, The third phase current calculation circuit performs hardware calculation based on the process value when the sensor value of the first phase current is converted to the sampled value of the first phase current of the inverter, and the process value when the sensor value of the second phase current is converted to the sampled value of the second phase current of the inverter, to obtain the sampled value of the third phase current of the inverter, specifically including: The summing circuit is used to sum the second analog value of the first phase current and the second analog value of the second phase current to obtain a two-phase current calculation value; The fourth operational amplifier module is used to process based on the two-phase current calculated values ​​to obtain a first processed value of the two-phase current; The fifth operational amplifier module is used to process the first processed value of the two-phase current to obtain a second processed value of the two-phase current; The sixth operational amplifier module is used to process based on a preset reference voltage and the second processed value of the two-phase current to obtain a third processed value of the two-phase current, so as to use the third processed value of the two-phase current as the first analog value of the third-phase current; The second RC module is used to process the first analog value of the third phase current to obtain a second analog value of the third phase current, so as to use the second analog value of the third phase current as a sampling value of the third phase current of the inverter.

8. A frequency converter, characterized in that: include: A three-phase current sampling device for a frequency converter as claimed in any one of claims 1 to 7.

9. A magnetic levitation unit, characterized in that: include: A three-phase current sampling device for a frequency converter as claimed in any one of claims 1 to 7, or a frequency converter as claimed in claim 8.

10. A three-phase current sampling method for a frequency converter corresponding to the three-phase current sampling device for a frequency converter according to any one of claims 1 to 7, characterized in that: include: Sampling a first phase current of the three-phase current of the frequency converter by the first phase current sensor to obtain a sensing value of the first phase current; Processing the sensed value of the first phase current through the first phase current sampling circuit to obtain a sampling value of the first phase current of the inverter; The second phase current sensor is used to sample the second phase current of the three-phase current of the frequency converter to obtain a sensing value of the second phase current. The sensing value of the second phase current is processed by the second phase current sampling circuit to obtain a sampling value of the second phase current of the inverter; The third phase current calculation circuit performs hardware calculation based on the process value when the sensing value of the first phase current is converted to the sampling value of the first phase current of the inverter, and the process value when the sensing value of the second phase current is converted to the sampling value of the second phase current of the inverter, so as to obtain the sampling value of the third phase current of the inverter, thereby realizing the sampling of the three-phase current of the inverter; The IGBT module is controlled based on the sampled value of the first phase current of the inverter, the sampled value of the second phase current of the inverter, and the sampled value of the third phase current of the inverter.

11. The three-phase current sampling method of the frequency converter according to claim 10, characterized in that: Also includes: By means of the overcurrent protection unit, based on the first analog value of the first phase current, the first analog value of the second phase current, and the first analog value of the third phase current, it is determined whether the three-phase current of the inverter is overcurrent; if it is determined that the three-phase current of the inverter is overcurrent, an overcurrent protection signal is output; According to the overcurrent protection signal, the IGBT module is controlled to be turned off.

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