Frequency converter and current sampling circuit thereof, and three-phase current sampling method for motor

Abstract

A frequency converter and a current sampling circuit thereof, and a three-phase current sampling method for a motor. The frequency converter (1000) is suitable for driving a motor (M) in a compressor. The current sampling circuit comprises: a single-resistor sampling unit (10) configured to perform current sampling at a voltage effective vector moment to obtain three-phase currents of the motor (M); a multi-resistor sampling unit (20) configured to perform current sampling at a voltage zero vector moment to obtain three-phase currents of the motor (M); and a switching control unit (30) configured to acquire a parameter of the motor (M), determine a switching index on the basis of the parameter of the motor (M), and select one of the single-resistor sampling unit (10) and the multi-resistor sampling unit (20) on the basis of the switching index to perform current sampling.

Description

Frequency converter and current sampling circuit thereof, and three-phase current sampling method of motor

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application number 202311526796.X filed on November 13, 2023, entitled “Frequency converter, current sampling circuit thereof, and three-phase current sampling method of motor”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present disclosure relates to the technical field of motor control, and in particular to a frequency converter and a current sampling circuit thereof, and a three-phase current sampling method of a motor. Background Art

[0004] Permanent magnet synchronous motors (PMSMs) offer advantages such as high efficiency, high power density, and simple structure, making them widely used in industries such as industry, home appliances, and automobiles. Current sampling is crucial for motor control, and common current sampling methods include current sensors and resistors. Resistor sampling, due to its low cost, is widely used in cost-sensitive applications. Resistor sampling solutions include single-resistor, dual-resistor, and triple-resistor sampling.

[0005] The principle of dual-resistor sampling is similar to that of three-resistor sampling. The sampling resistor is located on the lower side of the inverter and current sampling is performed at the voltage zero vector. Therefore, the modulation ratio cannot be too high, and the voltage zero vector time must be greater than the minimum current sampling time. Therefore, dual-resistor sampling suffers from low voltage utilization in high-speed applications. Single-resistor sampling uses a sampling resistor located on the DC bus and samples current at the voltage valid vector time. However, at low speeds and in sector transition regions, the voltage valid vector time can be less than the minimum current sampling time. PWM (Pulse Width Modulation) phase shifting is typically used to ensure sufficient voltage valid vector time for current sampling. However, this PWM phase shifting can cause current distortion and lead to high motor noise. Summary of the Invention

[0006] The present disclosure aims to address, at least to some extent, one of the technical problems in the related art. To this end, a first objective of the present disclosure is to provide a current sampling circuit for an inverter that switches between single-resistor sampling and multi-resistor sampling based on motor parameters. This circuit can address the issues of high motor noise caused by using only a single-resistor sampling circuit and the degraded motor performance caused by using only multi-resistor sampling circuit, thereby improving motor performance.

[0007] A second objective of the present disclosure is to provide a frequency converter.

[0008] The third objective of the present disclosure is to provide a three-phase current sampling method for a motor.

[0009] A fourth object of the present disclosure is to provide a computer-readable storage medium.

[0010] A fifth objective of the present disclosure is to provide another frequency converter.

[0011] A sixth object of the present disclosure is to provide a compressor.

[0012] A seventh object of the present disclosure is to provide a vehicle.

[0013] To achieve the above-mentioned purpose, according to an embodiment of the first aspect of the present disclosure, a current sampling circuit of an inverter is proposed. The inverter is suitable for driving a motor in a compressor. The current sampling circuit includes: a single-resistance sampling unit, configured to perform current sampling at the moment of a voltage effective vector to obtain the three-phase current of the motor; a multi-resistance sampling unit, configured to perform current sampling at the moment of a voltage zero vector to obtain the three-phase current of the motor; a switching control unit, configured to obtain parameters of the motor, determine a switching index based on the parameters of the motor, and select one of the single-resistance sampling unit and the multi-resistance sampling unit for current sampling based on the switching index.

[0014] According to an embodiment of the present disclosure, the current sampling circuit of the frequency converter includes a single-resistance sampling unit, a multi-resistance sampling unit, and a switching control unit. The switching control unit is configured to obtain motor parameters, determine a switching index based on the motor parameters, and select one of the single-resistance sampling unit and the multi-resistance sampling unit for current sampling based on the switching index. Thus, the switching control unit switches between single-resistance sampling and multi-resistance sampling based on the motor parameters and in combination with the application scenarios of single-resistance sampling and multi-resistance sampling. This solves the problem of high motor noise caused by using only single-resistance sampling and the problem of degraded motor performance caused by using only multi-resistance sampling, broadens the motor's speed regulation range, and thus improves the motor's performance.

[0015] According to an embodiment of the present disclosure, the parameters of the motor include a voltage operating range and a maximum torque of the motor, wherein the switching control unit is further configured to determine the switching rotation speed according to the voltage operating range and the maximum torque.

[0016] According to one embodiment of the present disclosure, the switching control unit is further configured to determine the maximum speed of the motor without entering weak magnetic control when the motor operates at the lower limit value of the voltage operating range and the maximum torque, and determine the switching speed based on the maximum speed.

[0017] According to one embodiment of the present disclosure, the switching control unit is further configured to obtain the current speed of the motor, wherein, when the current speed is greater than the switching speed, a single resistor sampling unit is selected for current sampling; when the current speed is less than or equal to the switching speed, a multi-resistance sampling unit is selected for current sampling.

[0018] According to an embodiment of the present disclosure, the parameters of the motor include a modulation period and a minimum current sampling time of the motor, and the switching control unit is further configured to determine a switching modulation ratio according to the modulation period and the minimum current sampling time.

[0019] According to one embodiment of the present disclosure, the switching control unit is further configured to calculate the difference between the modulation period and four times the minimum current sampling time, divide the difference by the modulation period to obtain the maximum modulation ratio, and determine the switching modulation ratio according to the maximum modulation ratio.

[0020] According to one embodiment of the present disclosure, the switching control unit is further configured to obtain the current modulation ratio of the motor, wherein, when the current modulation ratio is greater than the switching modulation ratio, a single resistor sampling unit is selected for current sampling; when the current modulation ratio is less than or equal to the switching modulation ratio, a multi-resistance sampling unit is selected for current sampling.

[0021] To achieve the above-mentioned objective, according to a second aspect of the present disclosure, an inverter is provided, comprising the current sampling circuit of any of the aforementioned embodiments.

[0022] According to the inverter of the embodiment of the present disclosure, by adopting the above-mentioned current sampling circuit, single-resistor sampling or multi-resistor sampling is switched according to the parameters of the motor, which can solve the problem of high motor noise caused by using only single-resistor sampling and the problem of degraded motor performance caused by using only multi-resistor sampling, thereby improving the performance of the motor.

[0023] To achieve the above-mentioned purpose, according to an embodiment of the third aspect of the present disclosure, a three-phase current sampling method for a motor is proposed. The motor is arranged in a compressor, and the three-phase current sampling method is applied to a frequency converter. The frequency converter is suitable for driving the motor and includes a single-resistance sampling unit and a multi-resistance sampling unit. The three-phase current sampling method includes: obtaining the parameters of the motor and determining a switching index based on the parameters of the motor; selecting one of the single-resistance sampling unit and the multi-resistance sampling unit based on the switching index to perform current sampling to obtain the three-phase current of the motor.

[0024] According to the three-phase current sampling method for a motor in an embodiment of the present disclosure, motor parameters are obtained, a switching index is determined based on the motor parameters, and based on the switching index, one of a single-resistance sampling unit and a multi-resistance sampling unit is selected for current sampling. The frequency converter includes a single-resistance sampling unit, a multi-resistance sampling unit, and a switching control unit. Thus, based on the motor parameters and in combination with the application scenarios of single-resistance sampling and multi-resistance sampling, switching between single-resistance sampling and multi-resistance sampling is performed, solving the problem of high motor noise caused by using only single-resistance sampling and the problem of degraded motor performance caused by using only multi-resistance sampling, broadening the motor's speed regulation range, and thereby improving motor performance.

[0025] According to one embodiment of the present disclosure, the parameters of the motor include the voltage operating range and maximum torque of the motor, wherein the switching index is determined based on the parameters of the motor, including: when the motor operates at the lower limit value of the voltage operating range and the maximum torque, determining the maximum speed of the motor without entering weak magnetic control, and determining the switching speed based on the maximum speed.

[0026] According to one embodiment of the present disclosure, one of a single-resistance sampling unit and a multi-resistance sampling unit is selected for current sampling based on a switching index, including: obtaining the current speed of the motor; when the current speed is greater than the switching speed, selecting the single-resistance sampling unit for current sampling; when the current speed is less than or equal to the switching speed, selecting the multi-resistance sampling unit for current sampling.

[0027] According to one embodiment of the present disclosure, the parameters of the motor include a modulation period and a minimum current sampling time of the motor, wherein the switching index is determined based on the parameters of the motor, including: calculating the difference between the modulation period and four times the minimum current sampling time, and dividing the difference by the modulation period to obtain a maximum modulation ratio, and determining the switching modulation ratio based on the maximum modulation ratio.

[0028] According to one embodiment of the present disclosure, one of a single-resistance sampling unit and a multi-resistance sampling unit is selected for current sampling based on a switching index, including: obtaining a current modulation ratio of the motor; when the current modulation ratio is greater than the switching modulation ratio, selecting the single-resistance sampling unit for current sampling; when the current modulation ratio is less than or equal to the switching modulation ratio, selecting the multi-resistance sampling unit for current sampling.

[0029] To achieve the above-mentioned purpose, according to the fourth aspect of the present disclosure, a computer-readable storage medium is proposed, on which a three-phase current sampling program of a motor is stored. When the program is executed by a processor, the three-phase current sampling method of the motor of any of the aforementioned embodiments is implemented.

[0030] According to the computer-readable storage medium of the embodiment of the present disclosure, by executing a computer program of the above-mentioned three-phase current sampling method of the motor, switching between single-resistance sampling and multi-resistance sampling according to the parameters of the motor can solve the problem of high motor noise caused by using only single-resistance sampling and the problem of degraded motor performance caused by using only multi-resistance sampling, thereby improving the performance of the motor.

[0031] To achieve the above-mentioned purpose, according to the fifth aspect embodiment of the present disclosure, another inverter is proposed, including: a memory, a processor, and a three-phase current sampling program of the motor stored in the memory and runnable on the processor. When the processor executes the program, the three-phase current sampling method of the motor of any of the above-mentioned embodiments is implemented.

[0032] According to the inverter of the embodiment of the present disclosure, the computer program of the three-phase current sampling method of the above-mentioned motor is executed by the processor, and single-resistance sampling or multi-resistance sampling is switched according to the parameters of the motor. This can solve the problem of high motor noise caused by using only single-resistance sampling and the problem of degraded motor performance caused by using only multi-resistance sampling, thereby improving the performance of the motor.

[0033] To achieve the above-mentioned purpose, according to a sixth aspect of the present disclosure, a compressor is proposed, comprising: a motor; and the aforementioned inverter, wherein the inverter is suitable for driving the motor.

[0034] According to the compressor of the embodiment of the present disclosure, by adopting the above-mentioned inverter, single-resistance sampling or multi-resistance sampling is switched according to the parameters of the motor, which can solve the problem of high motor noise caused by using only single-resistance sampling and the problem of motor performance degradation caused by using only multi-resistance sampling, thereby improving the performance of the motor.

[0035] To achieve the above-mentioned objectives, according to a seventh aspect of the present disclosure, a vehicle is proposed, comprising the aforementioned compressor.

[0036] According to the vehicle of the embodiment of the present disclosure, by adopting the above-mentioned compressor, switching between single-resistance sampling and multi-resistance sampling according to the parameters of the motor can solve the problem of high motor noise caused by using only single-resistance sampling and the problem of degraded motor performance caused by using only multi-resistance sampling, thereby improving the performance of the motor.

[0037] Additional aspects and advantages of the present disclosure will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG1 is a schematic structural diagram of a current sampling circuit of an inverter according to an embodiment of the present disclosure;

[0039] FIG2 is a circuit diagram of a current sampling circuit according to an embodiment of the present disclosure;

[0040] FIG3 is a flow chart of switching sampling modes according to motor speed according to an embodiment of the present disclosure;

[0041] FIG4 is a schematic diagram of a sector according to an embodiment of the present disclosure;

[0042] FIG5 is a waveform diagram of a driving signal of a first sector according to an embodiment of the present disclosure;

[0043] FIG6 is a waveform diagram of a driving signal of a fourth sector according to one embodiment of the present disclosure;

[0044] FIG7 is a flow chart of switching sampling modes according to a motor modulation ratio according to an embodiment of the present disclosure;

[0045] FIG8 is a flow chart of a method for sampling three-phase current of a motor according to an embodiment of the present disclosure;

[0046] FIG9 is a system schematic diagram of a frequency converter according to an embodiment of the present disclosure;

[0047] FIG10 is a schematic structural diagram of a compressor according to an embodiment of the present disclosure;

[0048] FIG11 is a schematic structural diagram of a vehicle according to an embodiment of the present disclosure. Modes for Carrying Out the Invention

[0049] The following describes in detail embodiments of the present disclosure, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present disclosure, and should not be construed as limiting the present disclosure.

[0050] The following describes an inverter and a current sampling circuit thereof, a three-phase current sampling method for a motor, a storage medium, a compressor, and a vehicle according to embodiments of the present disclosure with reference to the accompanying drawings.

[0051] Figure 1 is a circuit diagram of a current sampling circuit for an inverter according to one embodiment of the present disclosure. As shown in Figure 1 , an inverter 1000 is suitable for driving a motor M in a compressor. The current sampling circuit includes a single-resistance sampling unit 10, a multi-resistance sampling unit 20, and a switching control unit 30.

[0052] Among them, the single-resistance sampling unit 10 is configured to perform current sampling at the voltage effective vector moment to obtain the three-phase current of the motor M; the multi-resistance sampling unit 20 is configured to perform current sampling at the voltage zero vector moment to obtain the three-phase current of the motor M; the switching control unit 30 is configured to obtain the parameters of the motor M, determine the switching index according to the parameters of the motor M, and select one of the single-resistance sampling unit 10 and the multi-resistance sampling unit 20 for current sampling based on the switching index.

[0053] Specifically, as shown in FIG1 , the inverter 1000 includes six switching transistors Q1-Q6. The first and second switching transistors Q1 and Q2 form the U-phase bridge arm, the third and fourth switching transistors Q3 and Q4 form the V-phase bridge arm, and the fifth and sixth switching transistors Q5 and Q6 form the W-phase bridge arm, which are connected to the U-phase, W-phase, and V-phase of the motor M. The upper bridge arms of the three-phase bridge arms are all connected to the positive pole of the DC bus DC. Taking FIG2 as an example, the single-resistance sampling unit 10 includes a first sampling resistor R1, which is disposed on the DC bus DC. The multi-resistance sampling unit 20 includes a second sampling resistor R2 and a third sampling resistor R3, which are disposed on the U-phase lower bridge arm and the V-phase lower bridge arm. Single-resistor current sampling and multi-resistor current sampling are suitable for different application scenarios. In different application scenarios, the parameters of motor M are different. Therefore, the switching control unit 30 can determine when to switch the current sampling mode according to the parameters of motor M, that is, determine the switching index, determine the current sampling mode applicable to motor M according to the switching index and the current parameters of motor M, and then switch the corresponding sampling unit to perform current sampling.

[0054] It should be noted that the second sampling resistor R2 and the third sampling resistor R3 in the multi-resistor sampling unit 20 of this embodiment are not limited to the connection method shown in FIG2 . The second sampling resistor R2 and the third sampling resistor R3 can be arranged on the lower bridge arms of any two phases. The multi-resistor sampling unit 20 is also not limited to two sampling resistors and can also include three sampling resistors, with one sampling resistor arranged on the lower bridge arm of each phase. The multi-resistor sampling unit 20 shown in FIG2 is exemplary and does not limit the present application.

[0055] In an optional embodiment, as shown in FIG2 , the single-resistance sampling unit 10 further includes a first operational amplifier module 11, which is disposed across the first sampling resistor R1 to sample the voltage across the first sampling resistor R1 to obtain a first voltage sampling value, amplify the first voltage sampling value, and input the amplified first voltage sampling value to the switching control unit 30. The multi-resistance sampling unit 20 further includes a second operational amplifier module 21 and a third operational amplifier module 22. The second operational amplifier module 21 is disposed across the second sampling resistor R2 to sample the voltage across the second sampling resistor R2 to obtain a second voltage sampling value, amplify the second voltage sampling value, and input the amplified second voltage sampling value to the switching control unit 30. The third operational amplifier module 22 is disposed across the third sampling resistor R3 to sample the voltage across the third sampling resistor R3 to obtain a third voltage sampling value, amplify the third voltage sampling value, and input the amplified third voltage sampling value to the switching control unit 30.

[0056] In the above embodiment, because single-resistor current sampling and multi-resistor current sampling are applicable to different scenarios, the switching control unit can determine the current sampling method applicable to the motor according to the parameters of the motor, and then switch the corresponding sampling unit to perform current sampling, which solves the problems existing in single-resistor current sampling and multi-resistor current sampling in different application scenarios, broadens the speed regulation range of the motor, and thus improves the performance of the motor.

[0057] In some embodiments, the parameters of the motor M include a voltage operating range and a maximum torque of the motor M, wherein the switching control unit 30 is further configured to determine the switching speed according to the voltage operating range and the maximum torque.

[0058] It is understood that since multi-resistor current sampling is suitable for applications with lower motor speeds, and single-resistor current sampling is suitable for applications with higher motor speeds, the motor speed can be used to determine when to switch the current sampling mode. The switching control unit 30 obtains the voltage operating range and maximum torque of the motor M, determines the switching speed based on the voltage operating range and maximum torque, and switches the current sampling mode when the motor speed reaches the switching speed.

[0059] In some embodiments, the switching control unit 30 is further configured to determine the maximum speed at which the motor M does not enter magnetic weakening control when the motor M operates at the lower limit of the voltage operating range and the maximum torque, and determine the switching speed based on the maximum speed.

[0060] Specifically, the motor M is controlled to operate at the lower limit of the voltage operating range and the maximum torque. As the speed of the motor M increases, when the speed reaches a certain value, the speed cannot continue to increase because the operating voltage and maximum speed of the motor M remain unchanged. It is necessary to weaken the magnetic field of the motor M to reduce the back electromotive force, thereby increasing the speed. Without weakening the magnetic field of the motor M, the speed of the motor M is sampled, and the sampled speed of the motor M is the maximum speed. Since a certain margin must be retained for switching speeds, the switching speed is the product of the maximum speed and a preset proportional coefficient, which is between 0.3 and 0.9.

[0061] For example, assume the voltage operating range is 200V-490V and the maximum torque is 7Nm. Motor M is controlled to operate at 200V and 7Nm. The speed of motor M before entering field weakening is sampled and the maximum speed is determined to be 4600 rpm. Since the preset proportional coefficient is between 0.3 and 0.9 and the switching speed is between 1380 rpm and 4140 rpm, 4100 rpm can be selected as the switching speed.

[0062] It should be noted that since dual-resistance sampling is suitable for low-speed scenarios and single-resistance sampling is suitable for high-speed scenarios, the higher the switching speed, the better, the more accurate the current sampling, and the better the performance of the motor M. The best switching speed is the maximum speed * 0.9.

[0063] In some embodiments, as shown in FIG3 , the switching control unit 30 is further configured to obtain the current speed of the motor M, wherein when the current speed is greater than the switching speed, the single-resistance sampling unit 10 is selected for current sampling; and when the current speed is less than or equal to the switching speed, the multi-resistance sampling unit 20 is selected for current sampling.

[0064] Specifically, because multi-resistor current sampling is performed at the voltage zero vector moment, time for the voltage zero vector moment must be reserved. Therefore, multi-resistor current sampling is suitable for applications with low motor speeds. Since single-resistor current sampling is performed at the voltage valid vector moment, single-resistor current sampling is suitable for applications with high motor speeds. Therefore, when the current speed is greater than the switching speed, it indicates that the current speed is high and the time when the voltage space vector is a valid vector is longer, so the single-resistor sampling unit 10 is selected for current sampling. When the current speed is less than or equal to the switching speed, it indicates that the current speed is low and the time when the voltage space vector is a zero vector is longer, so the multi-resistor sampling unit 20 is selected for current sampling.

[0065] In some embodiments, the parameters of the motor M include a modulation period and a minimum current sampling time of the motor M. The switching control unit 30 is further configured to determine a switching modulation ratio according to the modulation period and the minimum current sampling time.

[0066] It can be understood that the modulation ratio is the duty cycle of the drive signals for the six switching transistors generated using SVPWM (Space Vector Pulse Width Modulation). Because multi-resistor current sampling is performed at the voltage zero vector moment, it is suitable for applications with relatively low modulation. Because single-resistor current sampling is performed at the voltage valid vector moment, it is suitable for applications with relatively high modulation. Therefore, the modulation ratio can be used to determine when to switch the current sampling mode. The switching control unit 30 determines the switching modulation ratio based on the modulation period and the minimum current sampling time. When the motor modulation ratio reaches the switching modulation ratio, the current sampling mode is switched.

[0067] In some embodiments, the switching control unit 30 is further configured to calculate the difference between the modulation period and four times the minimum current sampling time, divide the difference by the modulation period to obtain the maximum modulation ratio, and determine the switching modulation ratio according to the maximum modulation ratio.

[0068] Specifically, the maximum modulation ratio is calculated according to the following formula (1):

[0069] (1)

[0070] Where Mmax is the maximum modulation ratio, T is the modulation period, and Tmin is the minimum current sampling time.

[0071] Since the switching modulation ratio needs to retain a certain margin, the switching modulation ratio is the product of the maximum modulation ratio and the Mmax preset proportional coefficient, and the preset proportional coefficient is between 0.3-0.9.

[0072] The derivation process of formula (1) is as follows:

[0073] Taking Figure 4 as an example, the motor M is in the first sector. Figure 5 is a driving signal waveform corresponding to the first sector obtained based on the 7-segment SVPWM algorithm. The 7-segment voltage space vector includes 3 zero voltage space vectors and 4 basic voltage space vectors. The order of action of the 7-segment voltage space vector is (0,0,0), (1,0,0), (1,1,0), (1,1,1), (1,1,0), (1,0,0), (0,0,0). Therefore, the 3 zero voltage space vectors are located at the beginning, middle, and end of the driving signal waveform, respectively. As can be seen from Figure 5, the first switch tube Q1 switches from off to on at time T0, the third switch tube Q3 switches from off to on at time T0+T1 / 2, and the fifth switch tube Q5 switches from off to on at time T0+T1 / 2+T2 / 2, where T=T1+T2+4T0, so the modulation ratio of the first switch tube Q1 is the largest. The modulation ratio of the first switch tube Q1 is calculated according to the following formula (2):

[0074] (2)

[0075] When the multi-resistance sampling unit 20 is used for current sampling, as shown in formula (3), the time T0 of the zero voltage space vector needs to be greater than the minimum current sampling time Tmin:

[0076] (3)

[0077] Substituting formula (2) into formula (3), we can obtain formula (4):

[0078] (4)

[0079] According to formula (4), the maximum modulation ratio formula (1) can be obtained.

[0080] The modulation ratios for other sectors are calculated in the same way as for the first sector. For example, as shown in Figure 6, when the motor M is in the fourth sector, the modulation ratio of the fifth switch Q5 is the largest. The modulation ratio of the fifth switch Q5 is also calculated according to formula (2). Therefore, the maximum modulation ratio calculated using formula (1) is applicable to all sectors.

[0081] For example, assuming that the switching frequency of motor M is 16kHz, the control period T = 1 / 16kHz = 62.5us, and the minimum current sampling time Tmin is 3us (including current oscillation time and sampling time). Substituting the control period T = 62.5us and the minimum current sampling time of 3us into formula (1), the maximum modulation ratio Mmax = 0.808 can be calculated. Considering that a certain margin is retained, the switching modulation ratio is 0.7.

[0082] It should be noted that the motor of this embodiment is not limited to using the 7-segment SVPWM algorithm; a 5-segment SVPWM algorithm can also be used. However, when using the 5-segment SVPWM algorithm, it is necessary to distinguish between cases where the upper bridge arm of a phase is constantly at 0 or constantly at 1. The calculation method of the maximum modulation ratio is different in these two cases. Therefore, when using the 5-segment SVPWM algorithm, the calculation of the maximum modulation ratio is relatively complex.

[0083] In some embodiments, as shown in FIG7 , the switching control unit 30 is further configured to obtain a current modulation ratio of the motor M, wherein when the current modulation ratio is greater than the switching modulation ratio, the single resistor sampling unit 10 is selected for current sampling; and when the current modulation ratio is less than or equal to the switching modulation ratio, the multi-resistance sampling unit 20 is selected for current sampling.

[0084] Specifically, because multi-resistor current sampling is performed at the voltage zero vector moment, time for the voltage zero vector moment must be reserved. Therefore, multi-resistor current sampling is suitable for application scenarios with relatively low modulation. Since single-resistor current sampling is performed at the voltage effective vector moment, single-resistor current sampling is suitable for application scenarios with relatively high modulation. The modulation ratio of each phase bridge arm is obtained, and the largest modulation ratio among the modulation ratios is used as the current modulation ratio. If the current modulation ratio is greater than the switching modulation ratio, it indicates that the current modulation is relatively high and the voltage space vector is a valid vector for a long time, so the single-resistor sampling unit 10 is selected for current sampling. If the current modulation ratio is less than or equal to the switching modulation ratio, it indicates that the current modulation is relatively low and the voltage space vector is a zero vector for a long time, so the multi-resistor sampling unit 20 is selected for current sampling.

[0085] In summary, the current sampling circuit of the inverter according to the embodiment of the present disclosure includes a single-resistance sampling unit, a multi-resistance sampling unit, and a switching control unit, wherein the switching control unit is configured to obtain the parameters of the motor, determine a switching index based on the parameters of the motor, and select one of the single-resistance sampling unit and the multi-resistance sampling unit for current sampling based on the switching index. Thus, the switching control unit switches between single-resistance sampling and multi-resistance sampling based on the parameters of the motor and in combination with the application scenarios of single-resistance sampling and multi-resistance sampling, thereby solving the problem of high motor noise caused by using only single-resistance sampling and the problem of degraded motor performance caused by using only multi-resistance sampling, broadening the speed regulation range of the motor, and thus improving the performance of the motor.

[0086] Corresponding to the above embodiments, the embodiments of the present disclosure further provide a frequency converter. As shown in FIG1 , the frequency converter 1000 includes the current sampling circuit 100 of any of the above embodiments.

[0087] According to the inverter of the embodiment of the present disclosure, by adopting the above-mentioned current sampling circuit, single-resistor sampling or multi-resistor sampling is switched according to the parameters of the motor, which can solve the problem of high motor noise caused by using only single-resistor sampling and the problem of degraded motor performance caused by using only multi-resistor sampling, thereby improving the performance of the motor.

[0088] Corresponding to the above embodiment, an embodiment of the present disclosure further provides a three-phase current sampling method for a motor. The motor M is provided in a compressor, and the three-phase current sampling method for the motor is applied to an inverter 1000 as shown in FIG1 . The inverter 1000 is suitable for driving the motor M and includes a single-resistance sampling unit 10 and a multi-resistance sampling unit 20 . As shown in FIG8 , the three-phase current sampling method for the motor includes:

[0089] S101, obtaining motor parameters and determining a switching index according to the motor parameters.

[0090] Specifically, single-resistance current sampling and multi-resistance current sampling are suitable for different application scenarios. In different application scenarios, the parameters of the motor are different. Therefore, according to the parameters of the motor, it can be determined when to switch the current sampling mode, that is, to determine the switching index.

[0091] S102 : Select one of the single-resistance sampling unit and the multi-resistance sampling unit to perform current sampling based on the switching index to obtain the three-phase current of the motor.

[0092] Specifically, a current sampling method suitable for the motor is determined according to the switching index and the current parameters of the motor, and then the corresponding sampling unit is switched to perform current sampling.

[0093] When a single-resistor current sampling method is adopted, when the voltage space vector is a first effective vector, a first current value sampled by the single-resistor sampling unit is obtained, and when the voltage space vector is a second effective vector, a second current value sampled by the single-resistor sampling unit is obtained, wherein the current phase sampled when the voltage space vector is the first effective vector is different from the current phase sampled when the voltage space vector is the second effective vector. Since the sum of the three-phase currents is 0, the third current value can be calculated based on the first current value and the second current value, thereby obtaining the three-phase current of the motor.

[0094] When adopting the dual-resistance current sampling method shown in Figure 2, when the voltage space vector is a zero vector, the first current value and the second current value sampled by the dual-resistance sampling unit are obtained. Since the sum of the three-phase currents is 0, the third current value can be calculated based on the first current value and the second current value, thereby obtaining the three-phase current of the motor.

[0095] It should be noted that the second sampling resistor R2 and the third sampling resistor R3 in the multi-resistor sampling unit 20 of this embodiment are not limited to the connection method shown in FIG2 . The second sampling resistor R2 and the third sampling resistor R3 can be arranged on the lower bridge arms of any two phases. The multi-resistor sampling unit 20 is also not limited to two sampling resistors and can also include three sampling resistors, with one sampling resistor arranged on the lower bridge arm of each phase. The multi-resistor sampling unit shown in FIG2 is exemplary and does not limit the present application.

[0096] In the above embodiment, because single-resistor current sampling and multi-resistor current sampling are applicable to different scenarios, the switching control unit can determine the current sampling method applicable to the motor according to the parameters of the motor, and then switch the corresponding sampling unit to perform current sampling, which solves the problems existing in single-resistor current sampling and multi-resistor current sampling in different application scenarios, broadens the speed regulation range of the motor, and thus improves the performance of the motor.

[0097] In some embodiments, the parameters of the motor include the voltage operating range and maximum torque of the motor, wherein the switching index is determined based on the parameters of the motor, including: when the motor operates at the lower limit value of the voltage operating range and the maximum torque, determining the maximum speed of the motor without entering weak magnetic control, and determining the switching speed based on the maximum speed.

[0098] Specifically, the motor is controlled to operate at the lower limit of the voltage operating range and the maximum torque. As the motor speed increases, when the speed reaches a certain value, the speed cannot continue to increase because the motor's operating voltage and maximum speed remain unchanged. It is necessary to weaken the motor's magnetic field to reduce the back electromotive force, thereby increasing the speed. Without weakening the motor's magnetic field, the motor speed is sampled, and the sampled motor speed is the maximum speed. Since a certain margin needs to be retained for switching speeds, the switching speed is the product of the maximum speed and a preset proportional coefficient, and the preset proportional coefficient is between 0.3 and 0.9.

[0099] For example, assume the voltage operating range is 200V-490V and the maximum torque is 7Nm. The motor is controlled to operate at 200V and 7Nm. The motor speed is sampled before entering field weakening, and the maximum speed is determined to be 4600 rpm. Since the preset proportional coefficient is between 0.3 and 0.9, and the switching speed is between 1380 rpm and 4140 rpm, 4100 rpm can be selected as the switching speed.

[0100] It should be noted that since dual-resistance sampling is suitable for low-speed scenarios and single-resistance sampling is suitable for high-speed scenarios, the higher the switching speed, the better, the more accurate the current sampling, and the better the motor performance. The best switching speed is maximum speed * 0.9.

[0101] In some embodiments, one of a single resistor sampling unit and a multi-resistance sampling unit is selected for current sampling based on a switching index, including: obtaining the current speed of the motor; when the current speed is greater than the switching speed, selecting the single resistor sampling unit for current sampling; when the current speed is less than or equal to the switching speed, selecting the multi-resistance sampling unit for current sampling.

[0102] Specifically, because multi-resistor current sampling is performed at the voltage zero vector moment, time for the voltage zero vector moment must be reserved. Therefore, multi-resistor current sampling is suitable for applications with low motor speeds. Since single-resistor current sampling is performed at the voltage valid vector moment, it is suitable for applications with high motor speeds. Therefore, when the current speed is greater than the switching speed, it indicates that the current speed is high and the time when the voltage space vector is a valid vector is longer, so the single-resistor sampling unit is selected for current sampling. When the current speed is less than or equal to the switching speed, it indicates that the current speed is low and the time when the voltage space vector is a zero vector is longer, so the multi-resistor sampling unit is selected for current sampling.

[0103] In some embodiments, the parameters of the motor include a modulation period and a minimum current sampling time of the motor, wherein the switching index is determined based on the parameters of the motor, including: calculating the difference between the modulation period and four times the minimum current sampling time, and dividing the difference by the modulation period to obtain a maximum modulation ratio, and determining the switching modulation ratio based on the maximum modulation ratio.

[0104] Specifically, the maximum modulation ratio is calculated using formula (1). Since the switching modulation ratio needs to retain a certain margin, the switching modulation ratio is the product of the maximum modulation ratio and the preset proportional coefficient Mmax, and the preset proportional coefficient is between 0.3 and 0.9.

[0105] For example, assuming that the switching frequency of the motor is 16kHz, the control period T = 1 / 16kHz = 62.5us, and the minimum current sampling time is 3us (including the current oscillation time and the sampling time). Substituting the control period T = 62.5us and the minimum current sampling time of 3us into formula (1), the maximum modulation ratio Mmax = 0.808 can be calculated. Considering that a certain margin is retained, the switching modulation ratio is 0.7.

[0106] It should be noted that the motor of this embodiment is not limited to using the 7-segment SVPWM algorithm; a 5-segment SVPWM algorithm can also be used. However, when using the 5-segment SVPWM algorithm, it is necessary to distinguish between cases where the upper bridge arm of a phase is constantly at 0 or constantly at 1. The calculation method of the maximum modulation ratio is different in these two cases. Therefore, when using the 5-segment SVPWM algorithm, the calculation of the maximum modulation ratio is relatively complex.

[0107] In some embodiments, one of a single-resistance sampling unit and a multi-resistance sampling unit is selected for current sampling based on a switching index, including: obtaining a current modulation ratio of the motor; when the current modulation ratio is greater than the switching modulation ratio, selecting the single-resistance sampling unit for current sampling; when the current modulation ratio is less than or equal to the switching modulation ratio, selecting the multi-resistance sampling unit for current sampling.

[0108] Specifically, since multi-resistor current sampling is performed at the voltage zero vector moment, time for the voltage zero vector moment needs to be reserved. Therefore, multi-resistor current sampling is suitable for application scenarios with relatively low modulation. Since single-resistor current sampling is performed at the voltage effective vector moment, single-resistor current sampling is suitable for application scenarios with relatively high modulation. The modulation ratio of each phase bridge arm is obtained, and the largest modulation ratio among the modulation ratios is used as the current modulation ratio. If the current modulation ratio is greater than the switching modulation ratio, it indicates that the current modulation is relatively high and the voltage space vector is the effective vector for a long time, so the single-resistor sampling unit is selected for current sampling. If the current modulation ratio is less than or equal to the switching modulation ratio, it indicates that the current modulation is relatively low and the voltage space vector is the zero vector for a long time, so the multi-resistor sampling unit is selected for current sampling.

[0109] In summary, according to the three-phase current sampling method for a motor in an embodiment of the present disclosure, the parameters of the motor are obtained, and a switching index is determined based on the parameters of the motor. Furthermore, based on the switching index, one of a single-resistance sampling unit and a multi-resistance sampling unit is selected for current sampling, wherein the frequency converter includes a single-resistance sampling unit, a multi-resistance sampling unit, and a switching control unit. Thus, according to the parameters of the motor and in combination with the application scenarios of single-resistance sampling and multi-resistance sampling, switching between single-resistance sampling and multi-resistance sampling is performed, thereby solving the problem of high motor noise caused by using only single-resistance sampling and the problem of degraded motor performance caused by using only multi-resistance sampling, broadening the speed regulation range of the motor, and thereby improving the performance of the motor.

[0110] Corresponding to the above embodiments, an embodiment of the present disclosure further provides a computer-readable storage medium on which a three-phase current sampling program for a motor is stored. When the program is executed by a processor, the three-phase current sampling method for a motor of any of the above embodiments is implemented.

[0111] According to the computer-readable storage medium of the embodiment of the present disclosure, by executing a computer program of the above-mentioned three-phase current sampling method of the motor, switching between single-resistance sampling and multi-resistance sampling according to the parameters of the motor can solve the problem of high motor noise caused by using only single-resistance sampling and the problem of degraded motor performance caused by using only multi-resistance sampling, thereby improving the performance of the motor.

[0112] Corresponding to the above embodiments, embodiments of the present disclosure also provide another frequency converter. As shown in FIG9 , frequency converter 1000 includes: a memory 1100 , a processor 1200 , and a three-phase current sampling program for a motor stored in memory 1100 and executable on processor 1200 . When processor 1200 executes the program, it implements the three-phase current sampling method for a motor according to any of the above embodiments.

[0113] According to the inverter of the embodiment of the present disclosure, the computer program of the three-phase current sampling method of the above-mentioned motor is executed by the processor, and single-resistance sampling or multi-resistance sampling is switched according to the parameters of the motor. This can solve the problem of high motor noise caused by using only single-resistance sampling and the problem of degraded motor performance caused by using only multi-resistance sampling, thereby improving the performance of the motor.

[0114] Corresponding to the above embodiment, the embodiment of the present disclosure further provides a compressor. As shown in FIG10 , the compressor 2000 includes: a motor M and the aforementioned inverter 1000 , wherein the inverter 1000 is suitable for driving the motor M.

[0115] According to the compressor of the embodiment of the present disclosure, by adopting the above-mentioned inverter, single-resistance sampling or multi-resistance sampling is switched according to the parameters of the motor, which can solve the problem of high motor noise caused by using only single-resistance sampling and the problem of motor performance degradation caused by using only multi-resistance sampling, thereby improving the performance of the motor.

[0116] Corresponding to the above embodiment, an embodiment of the present disclosure further provides a vehicle. As shown in FIG11 , a vehicle 3000 includes a compressor 2000 .

[0117] The vehicle according to the embodiment of the present disclosure includes the compressor described in any of the above embodiments. Here, the vehicle can be a new energy vehicle. In some embodiments, the new energy vehicle can be a pure electric vehicle with an electric motor as the main driving force. In other embodiments, the new energy vehicle can also be a hybrid vehicle with an internal combustion engine and an electric motor as the main driving force. Regarding the internal combustion engine and the electric motor mentioned in the above embodiments that provide driving power for the new energy vehicle, the internal combustion engine can use gasoline, diesel, hydrogen, etc. as fuel, and the way to provide electrical energy for the electric motor can use power batteries, hydrogen fuel cells, etc., and no special limitation is made here. It should be noted that this is only an exemplary description of the structure of new energy vehicles, etc., and it does not limit the scope of protection of the present disclosure.

[0118] According to the vehicle of the embodiment of the present disclosure, by adopting the above-mentioned inverter, single-resistance sampling or multi-resistance sampling is switched according to the parameters of the motor, which can solve the problem of high motor noise caused by using only single-resistance sampling and the problem of degraded motor performance caused by using only multi-resistance sampling, thereby improving the performance of the motor.

[0119] It should be noted that the logic and / or steps represented in the flowcharts or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing the logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (e.g., a computer-based system, a system including a processor, or other system that can fetch and execute instructions from an instruction execution system, apparatus, or device). For purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transport a program for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (non-exhaustive list) of computer-readable media include the following: an electrical connection with one or more wires (electronic device), a portable computer disk cartridge (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and programmable read-only memory (EPROM or flash memory), fiber optic devices, and a portable compact disc read-only memory (CDROM). Furthermore, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium and then editing, interpreting or processing it in another suitable manner if necessary, and then storing it in a computer memory.

[0120] It should be understood that various parts of the present disclosure can be implemented using hardware, software, firmware, or a combination thereof. In the above-described embodiments, multiple steps or methods can be implemented using software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented using hardware, as in another embodiment, any one of the following technologies known in the art or a combination thereof can be used: a discrete logic circuit having logic gate circuits for implementing logic functions on data signals, an application-specific integrated circuit having suitable combinational logic gate circuits, a programmable gate array (PGA), a field-programmable gate array (FPGA), etc.

[0121] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present disclosure. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0122] In addition, the terms "first" and "second" used in the embodiments of the present disclosure are only used for descriptive purposes and should not be understood as indicating or implying relative importance, or implicitly indicating the number of technical features indicated in the embodiments. Therefore, the features defined in the embodiments of the present disclosure with terms such as "first" and "second" can explicitly or implicitly indicate that the embodiment includes at least one such feature. In the description of the present disclosure, the word "plurality" means at least two or two or more, such as two, three, four, etc., unless otherwise clearly and specifically defined in the embodiments.

[0123] In this disclosure, unless otherwise clearly specified or limited in the embodiments, the terms "installed," "connected," "connect," and "fixed" appearing in the embodiments should be understood in a broad sense. For example, the connection can be a fixed connection, a detachable connection, or an integral connection. It can also be a mechanical connection, an electrical connection, etc.; of course, it can also be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication between two elements, or the interaction between two elements. For those skilled in the art, the specific meanings of the above terms in this disclosure can be understood based on the specific implementation.

[0124] Although the embodiments of the present disclosure have been shown and described above, it is understood that the above embodiments are illustrative and are not to be construed as limitations on the present disclosure. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present disclosure.

Claims

1. A current sampling circuit of a frequency converter, wherein the frequency converter is suitable for driving a motor in a compressor, and the current sampling circuit comprises: A single resistor sampling unit is configured to perform current sampling at the voltage effective vector moment to obtain the three-phase current of the motor; A multi-resistance sampling unit is configured to perform current sampling at a voltage zero vector moment to obtain a three-phase current of the motor; The switching control unit is configured to obtain the parameters of the motor, determine the switching index according to the parameters of the motor, and select one of the single-resistance sampling unit and the multi-resistance sampling unit to perform current sampling based on the switching index.

2. The current sampling circuit according to claim 1, wherein: The parameters of the motor include a voltage operating range and a maximum torque of the motor, wherein the switching control unit is further configured to determine a switching rotation speed according to the voltage operating range and the maximum torque.

3. The current sampling circuit according to claim 2, wherein: The switching control unit is further configured to determine a maximum speed at which the motor does not enter magnetic field weakening control when the motor operates at a lower limit of the voltage operating range and the maximum torque, and determine the switching speed according to the maximum speed.

4. The current sampling circuit according to claim 2 or 3, wherein: The switching control unit is further configured to obtain a current rotation speed of the motor, wherein: When the current rotation speed is greater than the switching rotation speed, selecting the single resistor sampling unit to perform current sampling; When the current rotation speed is less than or equal to the switching rotation speed, the multi-resistance sampling unit is selected to perform current sampling.

5. The current sampling circuit according to claim 1, wherein: The parameters of the motor include a modulation period and a minimum current sampling time of the motor, and the switching control unit is further configured to determine a switching modulation ratio according to the modulation period and the minimum current sampling time.

6. The current sampling circuit according to claim 5, wherein: The switching control unit is further configured to calculate a difference between the modulation period and four times the minimum current sampling time, divide the difference by the modulation period to obtain a maximum modulation ratio, and determine the switching modulation ratio according to the maximum modulation ratio.

7. The current sampling circuit according to claim 5 or 6, wherein: The switching control unit is further configured to obtain a current modulation ratio of the motor, wherein: When the current modulation ratio is greater than the switching modulation ratio, selecting the single resistor sampling unit to perform current sampling; When the current modulation ratio is less than or equal to the switching modulation ratio, the multi-resistance sampling unit is selected to perform current sampling.

8. A frequency converter, comprising the current sampling circuit according to any one of claims 1 to 7.

9. A three-phase current sampling method for a motor, wherein the motor is arranged in a compressor, the three-phase current sampling method is applied to a frequency converter, the frequency converter is suitable for driving the motor and comprises a single resistor sampling unit and a multi-resistance sampling unit, the three-phase current sampling method comprises: Acquiring parameters of the motor, and determining a switching index according to the parameters of the motor; Based on the switching index, one of the single resistor sampling unit and the multi-resistance sampling unit is selected to perform current sampling to obtain the three-phase current of the motor.

10. The method according to claim 9, wherein: The parameters of the motor include the voltage operating range and the maximum torque of the motor, wherein the switching index is determined according to the parameters of the motor, including: When the motor operates at the lower limit value of the voltage operating range and the maximum torque, a maximum speed of the motor without entering the field weakening control is determined, and a switching speed is determined according to the maximum speed.

11. The method according to claim 10, wherein: Selecting one of the single resistor sampling unit and the multi-resistance sampling unit to perform current sampling based on the switching index includes: Obtaining the current speed of the motor; When the current rotation speed is greater than the switching rotation speed, selecting the single resistor sampling unit to perform current sampling; When the current rotation speed is less than or equal to the switching rotation speed, the multi-resistance sampling unit is selected to perform current sampling.

12. The method according to claim 9, wherein: The parameters of the motor include a modulation period and a minimum current sampling time of the motor, wherein the switching index is determined according to the parameters of the motor, including: The difference between the modulation period and four times the minimum current sampling time is calculated, and the difference is divided by the modulation period to obtain a maximum modulation ratio, and a switching modulation ratio is determined according to the maximum modulation ratio.

13. The method according to claim 12, wherein: Selecting one of the single resistor sampling unit and the multi-resistance sampling unit to perform current sampling based on the switching index includes: Obtaining a current modulation ratio of the motor; When the current modulation ratio is greater than the switching modulation ratio, selecting the single resistor sampling unit to perform current sampling; When the current modulation ratio is less than or equal to the switching modulation ratio, the multi-resistance sampling unit is selected to perform current sampling.

14. A computer-readable storage medium having a three-phase current sampling program of a motor stored thereon, wherein the program, when executed by a processor, implements the three-phase current sampling method of a motor according to any one of claims 9 to 13.

15. A frequency converter, comprising: A memory, a processor, and a three-phase current sampling program of a motor stored in the memory and executable on the processor. When the processor executes the program, a three-phase current sampling method of a motor according to any one of claims 9 to 13 is implemented.

16. A compressor, comprising: Motor; The frequency converter according to claim 8 or 15, wherein the frequency converter is suitable for driving the motor.

17. A vehicle, characterized in that: Comprising a compressor according to claim 16.

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