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

Abstract

The invention discloses a frequency converter, a current sampling circuit thereof and a three-phase current sampling method of a motor, the frequency converter is suitable for driving the motor in a compressor, and the current sampling circuit comprises a single-resistance sampling unit configured to perform current sampling at a voltage effective vector moment so as to obtain three-phase current of the motor; the multi-resistance sampling unit is configured to perform current sampling at a voltage zero vector moment so as to obtain three-phase current of the motor; and the switching control unit is configured to acquire parameters of the motor, determine a switching index according to the parameters of the motor, and select one of the single-resistor sampling unit and the multi-resistor sampling unit to perform current sampling based on the switching index. The current sampling circuit can solve the problems that the noise of the motor is large due to single-resistor sampling and the performance of the motor is reduced due to multi-resistor sampling, so that the performance of the motor is improved.

Description

Technical Field

[0001] The present application 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

[0002] Permanent magnet synchronous motors have the advantages of high efficiency, high power density, and simple structure, and are widely used in industries, home appliances, automobiles, and other fields. Current sampling is the key to motor control. Common current sampling methods include current sensor sampling and resistor sampling. Resistor sampling is widely used in situations with high cost requirements due to its low cost advantage. Resistor sampling solutions include single resistor sampling, dual resistor sampling, and three resistor sampling.

[0003] The principle of dual-resistance sampling is similar to that of three-resistance sampling. The sampling resistor is located in the lower bridge of the inverter, and current sampling is performed at the voltage zero vector moment. Therefore, the modulation ratio cannot be too high, and the voltage zero vector time is required to be greater than the minimum sampling time for current sampling. Therefore, in high-speed situations, dual-resistance sampling has the disadvantage of low voltage utilization. The sampling resistor of single-resistance sampling is located on the DC bus, and current sampling is performed at the voltage effective vector moment. However, in the low-speed and sector transition area, the voltage effective vector time will be lower than the minimum sampling time for current sampling. PWM (Pulse Width Modulation) phase shifting method is usually used to ensure that there is enough voltage effective vector time for sampling current. This PWM phase shifting will cause current distortion and lead to high motor noise. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the first purpose of the present invention is to provide a current sampling circuit of a frequency converter, which switches between single-resistance sampling and multi-resistance sampling according to the parameters of the motor, thereby solving the problem of high motor noise caused by only single-resistance sampling and the problem of motor performance degradation caused by only multi-resistance sampling, thereby improving the performance of the motor.

[0005] A second object of the present invention is to provide a frequency converter.

[0006] The third object of the present invention is to provide a three-phase current sampling method for a motor.

[0007] A fourth object of the present invention is to provide a computer-readable storage medium.

[0008] A fifth object of the present invention is to provide another frequency converter.

[0009] A sixth object of the present invention is to provide a compressor.

[0010] A seventh object of the present invention is to provide a vehicle.

[0011] To achieve the above-mentioned purpose, according to an embodiment of the first aspect of the present invention, a current sampling circuit of an inverter is proposed, and the inverter is suitable for driving a motor in a compressor. The current sampling circuit includes: a single resistor 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 according to the parameters of the motor, and select one of the single resistor sampling unit and the multi-resistance sampling unit for current sampling based on the switching index.

[0012] According to the current sampling circuit of the frequency converter of the embodiment of the present invention, it includes a single resistor 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 the switching index according to the parameters of the motor, and select one of the single resistor sampling unit and the multi-resistance sampling unit for current sampling based on the switching index. Thus, the switching control unit switches between single resistor sampling and multi-resistance sampling according to the parameters of the motor and in combination with the application scenarios of single resistor sampling and multi-resistance sampling, thereby solving the problem of high motor noise caused by only single resistor sampling and the problem of motor performance degradation caused by only multi-resistance sampling, broadening the speed regulation range of the motor, and thus improving the performance of the motor.

[0013] According to an embodiment of the present invention, 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.

[0014] According to one embodiment of the present invention, the switching control unit is also 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.

[0015] According to one embodiment of the present invention, 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.

[0016] According to an embodiment of the present invention, 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.

[0017] According to one embodiment of the present invention, 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.

[0018] According to one embodiment of the present invention, 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.

[0019] To achieve the above objective, a frequency converter is provided according to a second aspect of the present invention, comprising a current sampling circuit according to any one of the above embodiments.

[0020] According to the inverter of the embodiment of the present invention, by adopting the above-mentioned current sampling circuit, 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 only single-resistance sampling and the problem of reduced motor performance caused by only multi-resistance sampling, thereby improving the performance of the motor.

[0021] To achieve the above-mentioned purpose, according to an embodiment of the third aspect of the present invention, 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 resistor sampling unit and a multi-resistance sampling unit. The three-phase current sampling method includes: obtaining parameters of the motor and determining a switching index according to the parameters of the motor; based on the switching index, selecting one of the single resistor sampling unit and the multi-resistance sampling unit to perform current sampling to obtain the three-phase current of the motor.

[0022] According to the three-phase current sampling method of the motor of the embodiment of the present invention, the parameters of the motor are obtained, and the switching index is determined according to the parameters of the motor, and one of the single resistor sampling unit and the multi-resistance sampling unit is selected for current sampling based on the switching index, wherein the frequency converter includes a single resistor 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 resistor sampling and multi-resistance sampling, the single resistor sampling or multi-resistance sampling is switched, which solves the problem of high motor noise caused by only single resistor sampling and the problem of motor performance degradation caused by only multi-resistance sampling, broadens the speed regulation range of the motor, and thus improves the performance of the motor.

[0023] According to one embodiment of the present invention, 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 is operating at the lower limit value of the voltage operating range and the maximum torque, determining the maximum speed of the motor without entering the weak magnetic control, and determining the switching speed according to the maximum speed.

[0024] According to one embodiment of the present invention, 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.

[0025] According to one embodiment of the present invention, the parameters of the motor include a modulation period and a minimum current sampling time of the motor, wherein a 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 a switching modulation ratio based on the maximum modulation ratio.

[0026] According to one embodiment of the present invention, 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 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 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.

[0027] To achieve the above-mentioned purpose, according to the fourth aspect of the present invention, 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.

[0028] According to the computer-readable storage medium of an embodiment of the present invention, by executing a computer program of the above-mentioned three-phase current sampling method of the motor, 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 only single-resistance sampling and the problem of reduced motor performance caused by only multi-resistance sampling, thereby improving the performance of the motor.

[0029] To achieve the above-mentioned purpose, another inverter is proposed according to the fifth aspect embodiment of the present invention, including: a memory, a processor, and a three-phase current sampling program of the motor stored in the memory and executable on the processor. When the processor executes the program, the three-phase current sampling method of the motor of any of the aforementioned embodiments is implemented.

[0030] According to the inverter of the embodiment of the present invention, 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 reduced motor performance caused by using only multi-resistance sampling, thereby improving the performance of the motor.

[0031] To achieve the above-mentioned object, a compressor is proposed according to a sixth aspect of the present invention, comprising: a motor; and the aforementioned inverter, wherein the inverter is suitable for driving the motor.

[0032] According to the compressor of the embodiment of the present invention, 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 only single-resistance sampling and the problem of reduced motor performance caused by only multi-resistance sampling, thereby improving the performance of the motor.

[0033] To achieve the above objective, a vehicle is provided according to a seventh aspect of the present invention, comprising the aforementioned compressor.

[0034] According to the vehicle of the embodiment of the present invention, by adopting the above-mentioned compressor, 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 only single-resistance sampling and the problem of reduced motor performance caused by only multi-resistance sampling, thereby improving the performance of the motor.

[0035] Additional aspects and advantages of the present invention 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 invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a structural schematic diagram of a current sampling circuit of a frequency converter according to an embodiment of the present invention;

[0037] Figure 2 is a circuit diagram of a current sampling circuit according to an embodiment of the present invention;

[0038] Figure 3 is a schematic diagram of a flow chart of switching a sampling mode according to a motor speed according to an embodiment of the present invention;

[0039] Figure 4 is a schematic diagram of a sector according to an embodiment of the present invention;

[0040] Figure 5 is a waveform diagram of a driving signal of a first sector according to an embodiment of the present invention;

[0041] Figure 6 is a waveform diagram of a driving signal of a fourth sector according to an embodiment of the present invention;

[0042] Figure 7 is a schematic diagram of a flow chart of switching a sampling mode according to a motor modulation ratio according to an embodiment of the present invention;

[0043] Figure 8 is a schematic flow chart of a three-phase current sampling method for a motor according to an embodiment of the present invention;

[0044] Fig. 9 is a system schematic diagram of a frequency converter according to an embodiment of the present invention;

[0045] Fig.10 is a schematic structural diagram of a compressor according to an embodiment of the present invention;

[0046] Fig.11 is a schematic structural diagram of a vehicle according to an embodiment of the present invention. DETAILED DESCRIPTION

[0047] Embodiments of the present invention are described in detail below, 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 invention, and should not be construed as limiting the present invention.

[0048] The following describes a frequency converter and a current sampling circuit thereof, a three-phase current sampling method of a motor, a storage medium, a compressor, and a vehicle according to embodiments of the present invention with reference to the accompanying drawings.

[0049] Figure 1 is a circuit diagram of a current sampling circuit of a frequency converter according to an embodiment of the present invention. Figure 1 As shown, the frequency converter 1000 is suitable for driving the motor M in the compressor, and the current sampling circuit includes: a single resistor sampling unit 10 , a multi-resistance sampling unit 20 and a switching control unit 30 .

[0050] Among them, the single resistor 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, and determine the switching index according to the parameters of the motor M, and select one of the single resistor sampling unit 10 and the multi-resistance sampling unit 20 for current sampling based on the switching index.

[0051] Specifically, Figure 1As shown, the inverter 1000 includes 6 switch tubes Q1-Q6, the first switch tube Q1 and the second switch tube Q2 form a U-phase bridge arm, the third switch tube Q3 and the fourth switch tube Q4 form a V-phase bridge arm, and the fifth switch tube Q5 and the sixth switch tube Q5 form a 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. Figure 2 As shown in the example, the single resistor sampling unit 10 includes a first sampling resistor R1, and the first sampling resistor R1 is arranged on the DC bus DC. The multi-resistance sampling unit 20 includes a second sampling resistor R2 and a third sampling resistor R3, the second sampling resistor R2 is arranged on the lower bridge arm of the U phase, and the third sampling resistor R3 is arranged on the lower bridge arm of the V phase. Single resistor current sampling and multi-resistance current sampling are suitable for different application scenarios. In different application scenarios, the parameters of the motor M are different. Therefore, the switching control unit 30 can determine when to switch the current sampling mode according to the parameters of the motor M, that is, determine the switching index, determine the current sampling mode applicable to the motor M according to the switching index and the current parameters of the motor M, and then switch the corresponding sampling unit to perform current sampling.

[0052] It should be noted that the second sampling resistor R2 and the third sampling resistor R3 in the multi-resistance sampling unit 20 of this embodiment are not limited to Figure 2 In the connection mode shown, the second sampling resistor R2 and the third sampling resistor R3 can be set on any two phase lower bridge arms. The multi-resistance sampling unit 20 is not limited to two sampling resistors, but can also be three sampling resistors, with one sampling resistor set on each phase lower bridge arm. Figure 2 The multi-resistance sampling unit 20 shown is exemplary and is not intended to limit the present application.

[0053] In an optional embodiment, if Figure 2 As shown, the single resistor sampling unit 10 further includes a first operational amplifier module 11, which is arranged at both ends of the first sampling resistor R1 to sample the voltage at both ends of 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 arranged at both ends of the second sampling resistor R2 to sample the voltage at both ends of 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 arranged at both ends of the third sampling resistor R3 to sample the voltage at both ends of 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.

[0054] In the above embodiment, because single-resistance current sampling and multi-resistance 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-resistance current sampling and multi-resistance current sampling in different application scenarios, broadens the speed regulation range of the motor, and thus improves the performance of the motor.

[0055] 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 a switching rotation speed according to the voltage operating range and the maximum torque.

[0056] It is understandable that, since multi-resistance current sampling is suitable for application scenarios with lower motor speeds, and single-resistance current sampling is suitable for application scenarios with higher motor speeds, it is possible to determine when to switch the current sampling mode according to the motor speed. The switching control unit 30 obtains the voltage operating range and maximum torque of the motor M, determines the switching speed according to the voltage operating range and the maximum torque, and switches the current sampling mode when the motor speed reaches the switching speed.

[0057] In some embodiments, the switching control unit 30 is further configured to determine the maximum speed at which the motor M does not enter weak magnetic 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.

[0058] 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 speed of the motor M obtained by sampling is the maximum speed. Since a certain margin needs to be retained for switching the speed, the switching speed is the product of the maximum speed and a preset proportional coefficient, and the preset proportional coefficient is between 0.3-0.9.

[0059] For example, assuming that the voltage operating range is 200V-490V and the maximum torque is 7N.m. Control the motor M to work at 200V and 7N.m, sample the speed of the motor M before it enters weak magnetic field, and determine that the maximum speed is 4600rpm. Since the preset proportional coefficient is between 0.3-0.9 and the switching speed is between 1380rpm-4140rpm, 4100rpm can be selected as the switching speed.

[0060] 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.

[0061] In some embodiments, Figure 3 As shown, the switching control unit 30 is also configured to obtain the current speed of the motor M, wherein when the current speed is greater than the switching speed, the single resistor sampling unit 10 is selected for current sampling; when the current speed is less than or equal to the switching speed, the multi-resistance sampling unit 20 is selected for current sampling.

[0062] Specifically, since multi-resistance current sampling is performed at the voltage zero vector moment, it is necessary to reserve the time for the voltage zero vector moment, so multi-resistance current sampling is suitable for application scenarios with low motor speeds, and since single-resistance current sampling is performed at the voltage effective vector moment, single-resistance current sampling is suitable for application scenarios 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 moment when the voltage space vector is a valid vector is longer, so the single-resistance 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 moment when the voltage space vector is a zero vector is longer, so the multi-resistance sampling unit 20 is selected for current sampling.

[0063] In some embodiments, the parameters of the motor M include a modulation period and a minimum current sampling time of the motor M, and 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.

[0064] It can be understood that the modulation ratio is the duty cycle of the drive signal for the six switch tubes generated by SVPWM (Space Vector Pulse Width Modulation). Since the multi-resistor current sampling is sampled at the voltage zero vector moment, it is suitable for application scenarios with relatively low modulation. Since the single-resistor current sampling is sampled at the voltage effective vector moment, it is suitable for application scenarios with relatively high modulation. Therefore, according to the modulation ratio, it can be determined when to switch the current sampling mode. The switching control unit 30 modulates the cycle and the minimum current sampling time, determines the switching modulation ratio according to the modulation cycle and the minimum current sampling time, and switches the current sampling mode when the motor modulation ratio reaches the switching modulation ratio.

[0065] 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.

[0066] Specifically, the maximum modulation ratio is calculated according to the following formula (1):

[0067]

[0068] Where Mmax is the maximum modulation ratio, T is the modulation period, and Tmin is the minimum current sampling time.

[0069] 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.

[0070] The derivation process of formula (1) is as follows:

[0071] by Figure 4 As shown in the example, the motor M is in the first sector. Figure 5 This is the drive 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 action order 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 drive signal waveform respectively. Figure 5 It can be seen that 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):

[0072]

[0073] 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:

[0074]

[0075] Substituting formula (2) into formula (3), we can obtain formula (4):

[0076]

[0077] According to formula (4), the formula (1) of the maximum modulation ratio can be obtained.

[0078] The modulation ratios of other sectors are calculated in the same way as the first sector. For example, Figure 6 As shown in the figure, when the motor M is in the fourth sector, the modulation ratio of the fifth switch Q5 is the largest, and the modulation ratio of the fifth switch Q5 is also calculated according to formula (2). Therefore, the maximum modulation ratio calculated by formula (1) is applicable to all sectors.

[0079] For example, assuming that the switching frequency of motor M is 16kHz, the control period T=1 / 16kHz=62.5us, the minimum current sampling time Tmin is 3us (including current oscillation time and sampling time), and the control period T=62.5us and the minimum current sampling time of 3us are substituted into formula (1), and the maximum modulation ratio Mmax=0.808 can be calculated. Considering that a certain margin is reserved, the switching modulation ratio is 0.7.

[0080] It should be noted that the motor of this embodiment is not limited to using the 7-segment SVPWM algorithm, and can also use the 5-segment SVPWM algorithm. However, when using the 5-segment SVPWM algorithm, it is necessary to distinguish whether the upper bridge arm of a certain phase is always 0 or always 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 more complicated.

[0081] In some embodiments, Figure 7 As shown, the switching control unit 30 is also configured to obtain the 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; 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.

[0082] Specifically, since multi-resistance current sampling is performed at the voltage zero vector moment, it is necessary to reserve time for the voltage zero vector moment, so multi-resistance current sampling is suitable for application scenarios with relatively low modulation. Since single-resistance current sampling is performed at the voltage effective vector moment, single-resistance 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. When the current modulation ratio is greater than the switching modulation ratio, it indicates that the current modulation is relatively high, and the moment when the voltage space vector is an effective vector is longer, so the single-resistance sampling unit 10 is selected for current sampling; when 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 moment when the voltage space vector is a zero vector is longer, so the multi-resistance sampling unit 20 is selected for current sampling.

[0083] In summary, the current sampling circuit of the frequency converter according to the embodiment of the present invention includes a single resistor 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 the switching index according to the parameters of the motor, and select one of the single resistor sampling unit and the multi-resistance sampling unit for current sampling based on the switching index. Thus, the switching control unit switches between single resistor sampling and multi-resistance sampling according to the parameters of the motor and in combination with the application scenarios of single resistor sampling and multi-resistance sampling, thereby solving the problem of high motor noise caused by only single resistor sampling and the problem of decreased motor performance caused by only multi-resistance sampling, broadening the speed regulation range of the motor, and thus improving the performance of the motor.

[0084] Corresponding to the above embodiment, the embodiment of the present invention further provides a frequency converter. Figure 1 As shown, the frequency converter 1000 includes the current sampling circuit 100 of any of the aforementioned embodiments.

[0085] According to the inverter of the embodiment of the present invention, by adopting the above-mentioned current sampling circuit, 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 only single-resistance sampling and the problem of reduced motor performance caused by only multi-resistance sampling, thereby improving the performance of the motor.

[0086] Corresponding to the above embodiment, the embodiment of the present invention further provides a three-phase current sampling method for a motor. The motor M is arranged in a compressor, and the three-phase current sampling method for the motor is applied to Figure 1 The inverter 1000 shown in FIG. 1 is suitable for driving a motor M and includes a single resistor sampling unit 10 and a multi-resistance sampling unit 20. Figure 8 As shown, the three-phase current sampling method of the motor includes:

[0087] S101, obtaining parameters of a motor, and determining a switching index according to the parameters of the motor.

[0088] 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.

[0089] S102 , selecting one of a single resistor sampling unit and a multi-resistance sampling unit to perform current sampling based on a switching index to obtain a three-phase current of the motor.

[0090] 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.

[0091] When a single resistor current sampling method is adopted, when the voltage space vector is the first effective vector, a first current value sampled by the single resistor sampling unit is obtained, and when the voltage space vector is the 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.

[0092] In adopting Figure 2 In the dual-resistance current sampling method shown, 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.

[0093] It should be noted that the second sampling resistor R2 and the third sampling resistor R3 in the multi-resistance sampling unit 20 of this embodiment are not limited to Figure 2 In the connection mode shown, the second sampling resistor R2 and the third sampling resistor R3 can be set on any two phase lower bridge arms. The multi-resistance sampling unit 20 is not limited to two sampling resistors, but can also be three sampling resistors, with one sampling resistor set on each phase lower bridge arm. Figure 2 The multi-resistance sampling unit shown is exemplary and is not intended to limit the present application.

[0094] In the above embodiment, because single-resistance current sampling and multi-resistance 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-resistance current sampling and multi-resistance current sampling in different application scenarios, broadens the speed regulation range of the motor, and thus improves the performance of the motor.

[0095] 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.

[0096] Specifically, the motor is controlled to operate at the lower limit of the voltage operating range and the maximum torque. As the speed of the motor increases, when the speed reaches a certain value, the speed cannot continue to rise because the operating voltage and maximum speed of the motor remain unchanged. It is necessary to weaken the motor magnetic field to reduce the back electromotive force, thereby increasing the speed. Without weakening the motor 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 0.3-0.9.

[0097] For example, assuming the voltage operating range is 200V-490V and the maximum torque is 7N.m. The motor is controlled to work at 200V and 7N.m, and the speed of the motor before entering weak magnetic field is sampled to determine the maximum speed is 4600rpm. Since the preset proportional coefficient is between 0.3-0.9 and the switching speed is between 1380rpm-4140rpm, 4100rpm can be selected as the switching speed.

[0098] 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. The best switching speed is maximum speed * 0.9.

[0099] 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.

[0100] Specifically, since multi-resistor current sampling is performed at the voltage zero vector moment, it is necessary to reserve the time for the voltage zero vector moment, so multi-resistor current sampling is suitable for application scenarios with low motor speeds. Since single-resistor current sampling is performed at the voltage effective vector moment, single-resistor current sampling is suitable for application scenarios 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 a 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 a multi-resistor sampling unit is selected for current sampling.

[0101] In some embodiments, the parameters of the motor include a modulation period and a minimum current sampling time of the motor, wherein a 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, dividing the difference by the modulation period to obtain a maximum modulation ratio, and determining a switching modulation ratio based on the maximum modulation ratio.

[0102] 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 Mmax preset proportional coefficient, and the preset proportional coefficient is between 0.3-0.9.

[0103] 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 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 reserved, the switching modulation ratio is 0.7.

[0104] It should be noted that the motor of this embodiment is not limited to using the 7-segment SVPWM algorithm, and can also use the 5-segment SVPWM algorithm. However, when using the 5-segment SVPWM algorithm, it is necessary to distinguish whether the upper bridge arm of a certain phase is always 0 or always 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 more complicated.

[0105] 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 a current modulation ratio of the motor; when the current modulation ratio is greater than the switching modulation ratio, selecting a single resistor sampling unit for current sampling; when the current modulation ratio is less than or equal to the switching modulation ratio, selecting a multi-resistance sampling unit for current sampling.

[0106] Specifically, since multi-resistance current sampling is performed at the voltage zero vector moment, it is necessary to reserve time for the voltage zero vector moment, so multi-resistance current sampling is suitable for application scenarios with relatively low modulation. Since single-resistance current sampling is performed at the voltage effective vector moment, single-resistance current sampling is suitable for application scenarios with relatively high modulation. Obtain the modulation ratio of each phase bridge arm, and take the largest modulation ratio among the modulation ratios as the current modulation ratio. When 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 a single-resistance sampling unit is selected for current sampling; when 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 a multi-resistance sampling unit is selected for current sampling.

[0107] In summary, according to the three-phase current sampling method of the motor according to the embodiment of the present invention, the parameters of the motor are obtained, and the switching index is determined according to the parameters of the motor, and one of the single resistor sampling unit and the multi-resistance sampling unit is selected for current sampling based on the switching index, wherein the frequency converter includes a single resistor 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 resistor sampling and multi-resistance sampling, switching between single resistor sampling and multi-resistance sampling solves the problem of high motor noise caused by only single resistor sampling and the problem of decreased motor performance caused by only multi-resistance sampling, broadens the speed regulation range of the motor, and thus improves the performance of the motor.

[0108] Corresponding to the above embodiments, an embodiment of the present invention further provides a computer-readable storage medium 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 a motor in any of the above embodiments is implemented.

[0109] According to the computer-readable storage medium of an embodiment of the present invention, by executing a computer program of the above-mentioned three-phase current sampling method of the motor, 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 only single-resistance sampling and the problem of reduced motor performance caused by only multi-resistance sampling, thereby improving the performance of the motor.

[0110] Corresponding to the above embodiment, the embodiment of the present invention also provides another frequency converter. Fig. 9 As shown, the inverter 1000 includes: a memory 1100, a processor 1200, and a three-phase current sampling program of the motor stored in the memory 1100 and executable on the processor 1200. When the processor 1200 executes the program, the three-phase current sampling method of the motor of any of the aforementioned embodiments is implemented.

[0111] According to the inverter of the embodiment of the present invention, 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 reduced motor performance caused by using only multi-resistance sampling, thereby improving the performance of the motor.

[0112] Corresponding to the above embodiment, the embodiment of the present invention further provides a compressor. Fig.10 As shown, the compressor 2000 includes: a motor M and the aforementioned inverter 1000 , wherein the inverter 1000 is suitable for driving the motor M.

[0113] According to the compressor of the embodiment of the present invention, 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 only single-resistance sampling and the problem of reduced motor performance caused by only multi-resistance sampling, thereby improving the performance of the motor.

[0114] Corresponding to the above embodiment, an embodiment of the present invention further provides a vehicle. Fig.11 As shown, vehicle 3000 includes compressor 2000 .

[0115] The vehicle according to the embodiment of the present invention 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 a 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 a motor as the main driving force. Regarding the internal combustion engine and the 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 motor can use power batteries, hydrogen fuel cells, etc., which are not specifically limited 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 invention.

[0116] According to the vehicle of the embodiment of the present invention, 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 only single-resistance sampling and the problem of reduced motor performance caused by only multi-resistance sampling, thereby improving the performance of the motor.

[0117] It should be noted that the logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be specifically implemented in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in combination with these instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in combination with these instruction execution systems, devices or apparatuses. More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection portion with one or more wirings (electronic device), a portable computer disk box (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, 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 in other suitable ways if necessary, and then stored in a computer memory.

[0118] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0119] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0120] In addition, the terms "first", "second", etc. used in the embodiments of the present invention 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 present embodiment. Therefore, the features defined by the terms "first", "second", etc. in the embodiments of the present invention can explicitly or implicitly indicate that the embodiment includes at least one of the features. In the description of the present invention, the word "multiple" means at least two or two or more, such as two, three, four, etc., unless otherwise clearly and specifically defined in the embodiments.

[0121] In the present invention, unless otherwise clearly specified or limited in the embodiments, the terms "installed", "connected", "connected" and "fixed" etc. in the embodiments should be understood in a broad sense. For example, the connection can be a fixed connection, a detachable connection, or an integrated connection. It can be understood that 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 connection of two elements, or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific implementation situation.

[0122] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A current sampling circuit for a frequency converter, characterized in that: The frequency converter is suitable for driving the motor in the compressor, and the current sampling circuit includes: 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, characterized in that: 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, characterized in that: 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, characterized in that: 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, characterized in that: 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, characterized in that: 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, characterized in that: 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, characterized in that: The invention comprises a current sampling circuit according to any one of claims 1 to 7.

9. A three-phase current sampling method for a motor, characterized in that: 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 includes a single resistor sampling unit and a multi-resistance sampling unit, and the three-phase current sampling method includes: 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, characterized in that 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, characterized in that 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, characterized in that 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, characterized in that 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, characterized in that: A three-phase current sampling program of the motor is stored thereon, and when the program is executed by the processor, the three-phase current sampling method of the motor according to any one of claims 9-13 is implemented.

15. A frequency converter, characterized in that: include: 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, characterized in that: include: 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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