A method and system for suppressing common mode voltage of a frequency converter

Abstract

The present invention provides a method and system for suppressing the common-mode voltage of a frequency converter. The suppression method is used to control the suppression system. A three-phase motor has a set speed. The three-phase motor is connected to the frequency converter. The inverter is connected to the frequency converter. The inverter is provided with a three-phase bridge arm switch. The three-phase bridge arm switch controls the frequency converter. The suppression method comprises: controlling the three-phase motor to run at the set speed; obtaining a reference current of the three-phase motor and obtaining a current operating current of the three-phase motor; controlling a current regulator to adjust the current operating current so that the current operating current is equal to the reference current; obtaining a reference voltage according to the reference current; obtaining the action time of a reference vector; and controlling a suppression module to output a control instruction according to the reference voltage and the action time. The control instruction is used to control the on and off of the three-phase bridge arm switch, thereby suppressing the common-mode voltage of the frequency converter and reducing the number of changes in the common-mode voltage.

Description

Technical Field

[0001] The present invention relates to the technical field, and in particular to a method and system for suppressing common-mode voltage of a frequency converter. Background Art

[0002] As PWM inverters are widely used in various industrial occasions, some negative effects have also emerged. The high-frequency common-mode voltage generated by the PWM inverter is added to the motor shaft, inducing a high shaft voltage. When this shaft voltage exceeds the critical voltage of the bearing, a shaft current will be formed, causing the motor bearing to be damaged by electrical reasons in a short period of time, shortening the service life of the motor; in the high-speed switching device of the IGBT, the charging and discharging current will flow through the parasitic capacitance inside the motor, thereby generating leakage current flowing into the earth. Excessive leakage current will cause the motor protection circuit to malfunction. The high-frequency leakage current will flow back to the three-phase power supply of the system through the ground wire to generate electromagnetic interference; when the inverter is connected to the motor using a cable, an overvoltage will be generated at the motor end due to voltage reflection.

[0003] In the prior art, in order to solve the common-mode voltage problem of the frequency converter, a common-mode filter solution and an advanced software modulation strategy are usually adopted, wherein the advanced software modulation strategies mainly include AZPWM, NSPWM and RSPWM. Installing a common-mode voltage filter to suppress the common-mode voltage and overvoltage in the frequency conversion system will bring about problems such as complex filter topology and large volume; conventional advanced software modulation strategies have complex calculation steps. Therefore, it is very necessary to provide a method and system for suppressing the common-mode voltage of the frequency converter, simplify the suppression method, facilitate implementation, and reduce the number of changes in the common-mode voltage. Summary of the invention

[0004] Therefore, the present invention provides a method and system for suppressing the common-mode voltage of a frequency converter, aiming to simplify the suppression method and reduce the number of changes in the common-mode voltage for easy implementation.

[0005] To solve the above problems, the present invention provides a method and system for suppressing the common-mode voltage of a frequency converter. The suppression method is used to control the suppression system. The suppression system includes: a three-phase motor, a frequency converter, an inverter, a current regulator and a suppression module. The three-phase motor has a set speed. The three-phase motor is connected to the frequency converter. The inverter is connected to the frequency converter. The inverter is provided with a three-phase bridge arm switch. The three-phase bridge arm switch controls the frequency converter. The suppression method includes: controlling the three-phase motor to run at a set speed; obtaining a reference current of the three-phase motor, wherein the reference current is the current when the three-phase motor runs at the set speed; obtaining the current running current of the three-phase motor; controlling the current regulator to adjust the current running current so that the current running current is equal to the reference current; obtaining a reference voltage according to the reference current; obtaining the action time of a reference vector, wherein the reference vector is obtained by synthesizing the basic vector inherent to the three-phase motor; and controlling the suppression module to output a control instruction according to the reference voltage and the action time. The control instruction is used to control the on and off of the three-phase bridge arm switch, thereby suppressing the common-mode voltage of the frequency converter.

[0006] Compared with the prior art, the technical effect achieved by adopting this technical solution is as follows: the running speed of the three-phase motor is adjusted to reach the set speed, and the set speed corresponds to the current reference value of the three-phase motor under ideal conditions. When the three-phase motor rotates at the set speed, the difference between the current running current of the three-phase motor and the reference current is small. Then, the current running current of the three-phase motor is adjusted by the current regulator to reduce the current error of the three-phase motor, and at the same time, the error between the actual voltage of the three-phase motor and the reference voltage is also reduced, thereby improving the reliability of the control instruction. The basic vector is an inherent vector of the three-phase motor, and each basic vector has a time difference of 60°. The reference vector is synthesized by the basic vector through the parallelogram law. In the process of selecting the basic vector, the sector judgment step is cancelled, and the suppression method is simplified. By controlling the on and off of the three-phase bridge arm switch and the duration of the on and off, the common mode voltage of the inverter is suppressed.

[0007] Furthermore, the suppression system also includes a current distribution device, and the reference current includes: a d-axis reference current and a q-axis reference current. According to the set speed, the reference current of the three-phase motor is obtained, specifically including: controlling the current distribution device to distribute the reference current according to the distribution mode, and obtaining the d-axis reference current and the q-axis reference current; wherein, the first distribution mode is: distribution based on the maximum ratio of the torque of the three-phase motor to the reference current, and the second distribution mode is: distribution based on the ratio of the torque of the three-phase motor to the input voltage of the three-phase motor.

[0008] Compared with the prior art, the technical effect achieved by adopting the technical scheme is as follows: after obtaining the reference current, the current distribution device distributes the reference current to obtain the d-axis reference current and the q-axis reference current, the d-axis and the q-axis are the coordinate axes of the dq coordinate system, the dq-axis coordinate system is a rectangular coordinate system oriented with the direction of the rotor magnetic field and rotating with the rotor, wherein the d-axis is in the same direction as the rotor, the direction of the q-axis is the axis determined by rotating the d-axis by 90° electrical angle along the direction of rotation of the rotor, the d-axis is also called the direct axis, which is highly correlated with the motor magnetic field, the q-axis is also called the quadrature axis, which is highly correlated with the motor torque, and two distribution modes are set to cope with different actual situations, making the current distribution method more reasonable.

[0009] Furthermore, the current distribution device is controlled to distribute the reference current, specifically including: judging the load type of the three-phase motor according to the current operating current; controlling the current distribution device to distribute the reference current according to the load type; when the load type is light load, the current distribution device is controlled to distribute the reference current according to the first distribution mode; when the load type is heavy load, the current distribution device is controlled to distribute the reference current according to the second distribution mode; wherein the three-phase current is provided with a rated current, and the load types include: light load and heavy load, light load means that the current operating current is less than the rated current, and heavy load means that the current operating current is greater than the rated current.

[0010] Compared with the prior art, the technical effect achieved by adopting this technical solution is as follows: the load type of the three-phase motor determines the way in which the current distribution device distributes the current, making the current distribution more reasonable and improving the stability of the suppression method. When the load type is light load, the control current distribution device distributes the reference current according to the first distribution mode; when the load type is heavy load, the control current distribution device distributes the reference current according to the second distribution mode. When the motor is lightly loaded, the current is distributed according to the maximum ratio of torque to reference current, with the purpose of generating the minimum phase current required for the same torque and reducing motor heating and loss; when the motor is heavily loaded and the voltage reaches the limit, the current is distributed according to the maximum ratio of torque to input voltage, the voltage is kept at the maximum value, and a specific set of d-axis reference current and q-axis reference current are selected, the corresponding torque is the largest, and the torque response speed of the motor can be improved.

[0011] Furthermore, the suppression system also includes a conversion device. Before the current regulator is controlled to adjust the current operating current, the suppression method also includes: controlling the conversion device to perform coordinate transformation on the current operating current according to the corresponding relationship of converting the three-phase stationary coordinate system into the two-term rotating coordinate system to obtain the d-axis current and the q-axis current.

[0012] Compared with the prior art, the technical effect achieved by adopting this technical solution is as follows: the coordinate transformation of the current operating current of the six-phase motor is performed from a three-phase stationary coordinate system to a two-phase rotating coordinate system to obtain the d-axis current and the q-axis current.

[0013] Furthermore, controlling the current regulator to adjust the current operating current specifically includes: controlling the current regulator to adjust the d-axis current according to the d-axis reference current so that the d-axis current is equal to the d-axis reference current; controlling the current regulator to adjust the q-axis current according to the q-axis reference current so that the q-axis current is equal to the q-axis reference current.

[0014] Compared with the prior art, the technical effect achieved by adopting this technical solution is as follows: the d-axis current and the q-axis current are adjusted to make the current data of the three-phase motor more accurate, thereby increasing the reliability of the control instructions.

[0015] Furthermore, the suppression system also includes a proportional-integral controller, and the reference voltage includes: a d-axis reference voltage and a q-axis reference voltage. The reference voltage is obtained according to the reference current, specifically including: controlling the proportional-integral controller to obtain the d-axis reference voltage according to the d-axis reference current, and to obtain the q-axis reference voltage according to the q-axis reference current.

[0016] Compared with the prior art, the technical effect achieved by adopting this technical solution is as follows: according to the d-axis reference current and the q-axis reference current, the d-axis reference voltage and the q-axis reference voltage are output, which is convenient for generating control instructions, and then controlling the three-phase bridge arm switches, thereby suppressing the common-mode voltage of the inverter.

[0017] Furthermore, obtaining the action time of the reference vector specifically includes:

[0018] T pwm =T1+T2+T3;

[0019] T1= V α / (2U1)+ ;

[0020] T2=- V α / (4U1)+3V β / (4U1)+ ;

[0021] T3=- V α / (4U1) -3V β / (4U1)+ ;

[0022] Among them, T pwm is the PWM cycle, T1, T2, T3 are the action time of the three basic vectors, U lis the bus voltage amplitude, V α is the α-axis reference voltage vector magnitude, V β is the β-axis reference voltage vector amplitude.

[0023] Compared with the prior art, the technical effect achieved by adopting this technical solution is as follows: a specific calculation method for the action time is given, which is convenient for implementation personnel to check the accuracy of the calculation result of the action time, thereby ensuring the rationality of the control instructions.

[0024] Furthermore, the present invention also provides a suppression system, which executes the suppression method, and the suppression system includes: a three-phase motor; a frequency converter, which is connected to the three-phase motor; an inverter, which is connected to the frequency converter; a speed regulator, which adjusts the running speed of the three-phase motor so that the running speed is equal to the set speed; and a suppression module, which outputs a control instruction.

[0025] Compared with the prior art, the technical effect achieved by adopting this technical solution is as follows: the suppression system of the present invention realizes the suppression method of any technical solution of the present invention, therefore, it has all the beneficial effects of the suppression method of any technical solution of the present invention, which will not be repeated here.

[0026] After adopting the technical solution of the present invention, the following technical effects can be achieved:

[0027] (1) Adjust the running speed of the three-phase motor to reach the set speed. The set speed corresponds to the current reference value of the three-phase motor under ideal conditions. When the three-phase motor rotates at the set speed, the difference between the current running current of the three-phase motor and the reference current is small. Then, the current regulator is used to adjust the current running current of the three-phase motor to reduce the current error of the three-phase motor. At the same time, the error between the actual voltage of the three-phase motor and the reference voltage is also reduced, thereby improving the reliability of the control command. In the process of selecting the basic vector, the sector judgment step is cancelled, and the suppression method is simplified. By controlling the on and off of the three-phase bridge arm switch and the duration of the on and off, the common mode voltage of the inverter is suppressed.

[0028] (2) After obtaining the reference current, the current distribution device distributes the reference current to obtain a d-axis reference current and a q-axis reference current. The d-axis and the q-axis are coordinate axes of a dq coordinate system. The dq-axis coordinate system is a rectangular coordinate system oriented in the direction of the rotor magnetic field and rotating with the rotor. The d-axis is in the same direction as the rotor, and the direction of the q-axis is the axis determined by rotating the d-axis by 90° electrical angle along the direction of rotor rotation. The d-axis is also called the direct axis and has a greater correlation with the motor magnetic field. The q-axis is also called the quadrature axis and has a greater correlation with the motor torque.

[0029] (3) When the load type is light load, the control current distribution device distributes the reference current according to the first distribution mode; when the load type is heavy load, the control current distribution device distributes the reference current according to the second distribution mode. When the motor is lightly loaded, the current is distributed according to the maximum ratio of torque to reference current, with the aim of minimizing the phase current required to generate the same torque and reducing motor heating and loss. When the motor is heavily loaded and the voltage reaches the limit, the current is distributed according to the maximum ratio of torque to input voltage, and the voltage is kept at the maximum value. A specific set of d-axis reference current and q-axis reference current are selected, and the corresponding torque is the largest, which can improve the torque response speed of the motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A flowchart of a method for suppressing common-mode voltage of a frequency converter provided by an embodiment of the present invention;

[0031] Figure 2 is the sector distribution map;

[0032] Figure 3 A first voltage vector diagram which is a basic vector;

[0033] Figure 4 A second voltage vector diagram being a basic vector;

[0034] Figure 5 Schematic diagram of the switch state of the three-phase bridge arm switch;

[0035] Figure 6 This is a schematic diagram of the inverter common mode voltage suppression effect;

[0036] Figure 7 Schematic diagram of the inhibition system.

[0037] Description of reference numerals:

[0038] 100: suppression system; 110: three-phase motor; 120: frequency converter; 130: inverter; 140: speed regulator; 150: current regulator; 160: suppression module; 170: current distribution device; 180: conversion device; 190: proportional integral controller. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] The present invention provides a method and system for suppressing common mode voltage of a frequency converter. The suppression method is used to control the suppression system. The suppression system comprises: a three-phase motor, a frequency converter, an inverter, a speed regulator, a current regulator and a suppression module. The three-phase motor has a set speed. The suppression method is as shown in the attached figure. Figure 1 As shown:

[0041] S100, control the three-phase motor to run at a set speed;

[0042] S200, obtaining a reference current of the three-phase motor;

[0043] S300, obtaining the current operating current of the three-phase motor;

[0044] S400, controlling the current regulator to adjust the current operating current so that the current operating current is equal to the reference current;

[0045] S500, obtaining a reference voltage according to the reference current;

[0046] S600, obtaining the action time of a reference vector, where the reference vector is synthesized by synthesizing the basic vectors inherent in the three-phase motor;

[0047] S700, the control inhibition module outputs a control instruction according to the reference voltage and the action time.

[0048] Specifically, when the running speed of the three-phase motor is inconsistent with the set speed, the speed regulator adjusts the running speed of the three-phase motor to reach the set speed. The set speed corresponds to the current reference value of the three-phase motor under ideal conditions. When the three-phase motor rotates at the set speed, the difference between the current running current of the three-phase motor and the reference current is small. Then, the current regulator is used to adjust the current running current of the three-phase motor to reduce the current error of the three-phase motor. At the same time, the error between the actual voltage of the three-phase motor and the reference voltage is also reduced, thereby improving the reliability of the control command. In the process of selecting the basic vector, the sector judgment step is cancelled, the suppression method is simplified, and the common mode voltage of the inverter is suppressed by controlling the on and off of the three-phase bridge arm switch and the duration of the on and off.

[0049] For example, the suppression system also includes a current distribution device, and the reference current includes: a d-axis reference current and a q-axis reference current. According to the set speed, the reference current of the three-phase motor is obtained, specifically including: controlling the current distribution device to distribute the reference current according to the distribution mode, and obtaining the d-axis reference current and the q-axis reference current; wherein, the first distribution mode is: distribution based on the maximum ratio of the torque of the three-phase motor to the reference current, and the second distribution mode is: distribution based on the maximum ratio of the torque of the three-phase motor to the input voltage of the three-phase motor.

[0050] For example, after obtaining the reference current, the current distribution device distributes the reference current to obtain the d-axis reference current and the q-axis reference current. The d-axis and the q-axis are the coordinate axes of the dq coordinate system. The dq-axis coordinate system is a rectangular coordinate system oriented in the direction of the rotor magnetic field and rotating with the rotor, wherein the d-axis is in the same direction as the rotor, and the direction of the q-axis is the axis determined by rotating the d-axis 90° electrical angle along the direction of rotor rotation. The d-axis is also called the direct axis, which is more closely related to the motor magnetic field, and the q-axis is also called the quadrature axis, which is more closely related to the motor torque. Two different distribution modes are set to cope with different operating conditions of the three-phase motor, so that the current distribution is more reasonable.

[0051] Specifically, controlling the current distribution device to distribute the reference current includes: judging the load type of the three-phase motor according to the current operating current; controlling the current distribution device to distribute the reference current according to the load type; when the load type is light load, controlling the current distribution device to distribute the reference current according to the first distribution mode; when the load type is heavy load, controlling the current distribution device to distribute the reference current according to the second distribution mode; the three-phase current is provided with a rated current, and the load types include: light load and heavy load, light load means that the current operating current is less than the rated current, and heavy load means that the current operating current is greater than the rated current.

[0052] Specifically, the load type of the three-phase motor determines the way the current distribution device distributes the current, making the current distribution more reasonable and improving the stability of the suppression method. When the load type is light load, the control current distribution device distributes the reference current according to the first distribution mode; when the load type is heavy load, the control current distribution device distributes the reference current according to the second distribution mode. When the motor is lightly loaded, the current is distributed according to the maximum ratio of torque to reference current, with the purpose of generating the same torque with the minimum phase current required to reduce motor heating and loss; when the motor is heavily loaded and the voltage reaches the limit, the current is distributed according to the maximum ratio of torque to input voltage, the voltage is kept at the maximum value, and a specific set of d-axis reference current and q-axis reference current are selected, the corresponding torque is the largest, and the torque response speed of the motor can be improved.

[0053] Preferably, the present application determines the load type by the current operating current of the three-phase motor. At the same time, a vibration sensor can also be set outside the three-phase motor to determine the load type by the vibration condition of the three-phase motor. When the vibration frequency of the three-phase motor is too large, it can be determined that the load type of the three-phase motor is heavy load, otherwise, it is light load.

[0054] In addition, when the load type is light load, such as the torque is 5Nm, the ratio of the d-axis current to the q-axis current has two combinations: (-3, 4) and (-5, 3). The symbol here indicates the direction, so the corresponding currents are 5 and , where 5 is less than , so choose the combination (-3, 4).

[0055] In addition, when the load type is heavy load, such as the voltage is 200V at this moment, the corresponding ratios of d-axis current and q-axis current are (-10, 12) and (-5, 12). The corresponding torques are 10Nm and 15Nm. Therefore, it is necessary to select the combination of (-5, 12) to make the torque larger.

[0056] Specifically, the suppression system also includes a conversion device. Before controlling the current regulator to adjust the current operating current, the suppression method also includes: controlling the conversion device to perform coordinate transformation on the current operating current according to the corresponding relationship of converting the three-phase stationary coordinate system into the two-phase rotating coordinate system to obtain the d-axis current and the q-axis current.

[0057] Specifically, the coordinate transformation of the current operating current of the six-phase motor is performed from a three-phase stationary coordinate system to a two-phase rotating coordinate system to obtain a d-axis current and a q-axis current.

[0058] For example, controlling the current regulator to adjust the current operating current specifically includes: controlling the current regulator to adjust the d-axis current according to the d-axis reference current so that the d-axis current is equal to the d-axis reference current; controlling the current regulator to adjust the q-axis current according to the q-axis reference current so that the q-axis current is equal to the q-axis reference current.

[0059] For example, by adjusting the d-axis current and the q-axis current, the operating state of the three-phase motor is closer to the set state, so that when obtaining current data, the data is more accurate, the error of data acquisition is reduced, and the reliability of control instructions is increased.

[0060] Specifically, the suppression system also includes a proportional-integral controller, and the reference voltage includes: a d-axis reference voltage and a q-axis reference voltage. The reference voltage is obtained according to the reference current, specifically including: controlling the proportional-integral controller to obtain the d-axis reference voltage according to the d-axis reference current, and to obtain the q-axis reference voltage according to the q-axis reference current.

[0061] Specifically, according to the d-axis reference current and the q-axis reference current, the d-axis reference voltage and the q-axis reference voltage are output, so as to generate control instructions and then control the three-phase bridge arm switches, thereby suppressing the common mode voltage of the inverter.

[0062] Preferably, the d-axis reference voltage and the q-axis reference voltage are obtained by a proportional-integral controller, and the voltage values ​​obtained by the difference between the d-axis reference voltage and the q-axis reference voltage and the input parameters of the proportional-integral controller and the d-axis current and the q-axis current.

[0063] Supplementary explanation: after obtaining the d-axis reference voltage and the q-axis reference voltage, the d-axis reference voltage and the q-axis reference voltage at this moment are voltage values ​​in the two rotating coordinate systems. Therefore, it is necessary to convert the d-axis reference voltage and the q-axis reference voltage into voltage values ​​in the two-phase stationary coordinate system to facilitate the suppression module to output control instructions according to the d-axis reference voltage and the q-axis reference voltage.

[0064] Specifically, when selecting Figure 3 When the basic vectors U4, U2 and U1 shown are combined into a reference vector, the action time of the reference vector is:

[0065] T pwm =T1+T2+T3;

[0066] T1= V α / (2U1)+ ;

[0067] T2=- V α / (4U1)+3V β / (4U1)+ ;

[0068] T3=- V α / (4U1) -3V β / (4U1)+ ;

[0069] Among them, T pwm is the PWM cycle, T1, T2, T3 are the action time of the three basic vectors, U l is the bus voltage amplitude, V α is the α-axis reference voltage vector magnitude, V β is the β-axis reference voltage vector amplitude.

[0070] Specifically, a specific calculation method for the action time is given to facilitate implementation personnel to check the accuracy of the calculation results of the action time, thereby ensuring the rationality of the control instructions.

[0071] Preferably, when Tpwm=1, V α =3, V β =4, U1=20, then according to the calculation formula we can get T1=0.4629, T2=0.4181, T3=0.118.

[0072] Supplementary instructions, as attached Figure 2 As shown, attached Figure 2 is the distribution diagram of the sector, V α is the α-axis reference voltage vector magnitude, V β is the β-axis reference voltage vector amplitude.

[0073] Preferably, in the process of selecting the basic vectors, three basic vectors which differ from each other by 120° are selected to synthesize the reference vector.

[0074] After determining the action time of the reference vectors, the reference vectors are sorted, so the action order is: V1-V2-V3-V2-V1, where the action time of the reference vector V1 is T1, the action time of the reference vector V2 is T2, and the action time of the reference vector V3 is T3, so that the waveform can be centrally symmetrical, thereby suppressing even harmonics, as shown in the attached figure. Figure 5 As shown, the on-off state change waveforms of the three-phase bridge arm switches are centrally symmetrical.

[0075] Preferably, when selecting Figure 4 When the basic vectors U3, U5 and U6 shown are combined into a reference vector, the action time of the reference vector is:

[0076] T pwm =T1+T2+T3;

[0077] T1= V α / (4U1)+3V β / (4U1)+ ;

[0078] T2=- V α / (2U1)+ ;

[0079] T3= V α / (4U1) -3V β / (4U1)+ ;

[0080] Among them, T pwm is the PWM cycle, T1, T2, T3 are the action time of the three basic vectors, U l is the bus voltage amplitude, V α is the α-axis reference voltage vector magnitude, V β is the β-axis reference voltage vector amplitude.

[0081] The present invention also provides a suppression system 100, which executes a suppression method. The suppression system 100 includes: a three-phase motor 110, a frequency converter 120, an inverter 130, a speed regulator 140, a current regulator 150 and a suppression module 160. The frequency converter 120 is connected to the three-phase motor 110; the inverter 130 is connected to the frequency converter 120; the speed regulator 140 adjusts the operating speed of the three-phase motor 110 so that the operating speed is equal to the set speed; the current regulator 150 adjusts the current operating current so that the current operating current is equal to the reference current; and the suppression module 160 outputs a control instruction.

[0082] Specifically, as attached Figure 7 As shown, the suppression system 100 is composed of a three-phase motor 110 , a frequency converter 120 , an inverter 130 , a current regulator 150 , a suppression module 160 , a current distribution device 170 and a conversion device 180 .

[0083] First, the running speed W1 of the three-phase motor 110 is obtained. When the running speed W1 is inconsistent with the set speed W, the speed regulator 140 adjusts the running speed W1 so that the running speed W1 is equal to the set speed W. The set speed W corresponds to the reference current I. After determining the load type of the three-phase motor, different load types correspond to different distribution modes. The current distribution device 170 distributes the reference current I according to the corresponding distribution mode to obtain the d-axis reference current I d1 and q-axis reference current I q1 , obtain the current operating current I of each phase of the three-phase motor 110 a ,I b ,I c , the current operating current I at this moment a ,I b ,I c is the current value in the three-phase stationary coordinate system. In order to facilitate current regulation, the current value in the three-phase stationary coordinate system is converted into the current value in the two-phase rotating coordinate system by the conversion device 180, thereby obtaining the d-axis current I d and q-axis current I q , the current regulator 150 adjusts the d-axis current I d , so that I d with I d1 equal, adjust the q-axis current I d , so that I q with I q1 equal.

[0084] The proportional-integral controller 190 is based on the d-axis current I d Output d-axis reference voltage U d , according to the q-axis reference current I q Output q-axis reference voltage Uq ; The suppression module 160 is based on the action time of the reference vector, the q-axis reference current I q Output q-axis reference voltage U q , output the control instruction of the three-phase bridge arm switch, wherein the three-phase bridge arm switch has three phases, and the three-phase motor also has three phases, and the two are connected one by one, so that the three-phase bridge arm switch can control the three-phase motor, the control instruction S1 controls the first phase of the three-phase bridge arm switch, the control instruction S2 controls the second phase of the three-phase bridge arm switch, and the control instruction S3 controls the third phase of the three-phase bridge arm switch. Through the control instruction, the three-phase bridge arm switch is controlled, thereby suppressing the common-mode voltage generated by the inverter 120 and reducing the number of changes in the common-mode voltage.

[0085] The switch status of the three-phase bridge arm switch is shown in the attached figure. Figure 5 As shown, the length of the unit time is determined by the action time, and then the duration of the on-off state of the three-phase bridge arm switch is determined, 1 represents connection, and 0 represents disconnection.

[0086] As attached Figure 5 As shown, the first phase of the three-phase bridge arm switch is first connected and lasts for one unit time, then switched to the disconnected state, lasts for three unit times, and then connected again, lasts for one unit time.

[0087] The second phase of the three-phase bridge arm switch is disconnected first, lasting for one unit time, switched from disconnected to connected state, lasting for one unit time, then switched from connected to disconnected state, lasting for one unit time, then switched to connected state, lasting for one unit time, and finally switched to disconnected state, lasting for one unit time.

[0088] The third phase of the three-phase bridge arm switch is first disconnected for two unit times, switched to a connected state for one unit time, and then switched from a connected state to a disconnected state for two unit times.

[0089] As attached Figure 6 As shown, the common mode voltage of the inverter after suppression is -U dc / 6. It can be clearly judged from the image that the suppression method provided by the present application can effectively suppress the number of changes in the common mode voltage after omitting the sector judgment process.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for suppressing common mode voltage of a frequency converter, characterized in that: The suppression method is used to control a suppression system, which includes: a three-phase motor, a frequency converter, an inverter, a current regulator and a suppression module, wherein the three-phase motor has a set speed, the three-phase motor is connected to the frequency converter, the inverter is connected to the frequency converter, the inverter is provided with a three-phase bridge arm switch, and the three-phase bridge arm switch controls the frequency converter, and the suppression method includes: Controlling the three-phase motor to run at the set speed; Obtaining a reference current of the three-phase motor, wherein the reference current is the current of the three-phase motor when it runs at the set speed; Obtaining the current operating current of the three-phase motor; Controlling the current regulator to adjust the current operating current so that the current operating current is equal to the reference current; deriving a reference voltage according to the reference current; Obtaining an action time of a reference vector, wherein the reference vector is synthesized by synthesizing a basic vector inherent to the three-phase motor; Controlling the suppression module to output a control instruction according to the reference voltage and the action time; Wherein, the control instruction is used to control the on and off of the three-phase bridge arm switch, thereby suppressing the common mode voltage of the inverter; The obtaining of the action time of the reference vector specifically includes: <h2 style=";text-align:left;direction:ltr">T<h2 style=";text-align:left;direction:ltr"> pwm <h2 style=";text-align:left;direction:ltr"> =T1+T2+T3; T1= In α / (2U1)+ ; T2=- V α / (4U1)+3V β / (4U1)+ ; T3=- V α / (4U1)-3V β / (4U1)+ ; Among them, the T pwm is the PWM period, T1, T2, and T3 are the action times of the three basic vectors, and U l is the bus voltage amplitude, the V α is the α-axis reference voltage vector magnitude, the V β is the β-axis reference voltage vector amplitude.

2. The suppression method according to claim 1, characterized in that: The suppression system further includes a current distribution device, wherein the reference current includes: a d-axis reference current and a q-axis reference current, and the reference current of the three-phase motor is obtained according to the set speed, specifically including: Controlling the current distribution device to distribute the reference current according to a distribution mode to obtain the d-axis reference current and the q-axis reference current; Among them, the distribution mode includes: a first distribution mode and a second distribution mode, the first distribution mode is: distribution based on the maximum ratio of the torque of the three-phase motor to the reference current, and the second distribution mode is: distribution based on the maximum ratio of the torque of the three-phase motor to the input voltage of the three-phase motor.

3. The suppression method according to claim 2, characterized in that: The controlling the current distribution device to distribute the reference current according to the distribution mode specifically includes: Determining the load type of the three-phase motor according to the current running current; According to the load type, controlling the current distribution device to distribute the reference current; When the load type is a light load, controlling the current distribution device to distribute the reference current according to the first distribution mode; When the load type is heavy load, controlling the current distribution device to distribute the reference current according to the second distribution mode; Among them, the three-phase motor is provided with a rated current, and the load types include: light load and heavy load, the light load means that the current operating current is less than the rated current, and the heavy load means that the current operating current is greater than the rated current.

4. The suppression method according to claim 3, characterized in that: The suppression system further includes a conversion device, and before controlling the current regulator to adjust the current operating current, the suppression method further includes: The conversion device is controlled to perform coordinate transformation on the current operating current according to the corresponding relationship of converting the three-phase stationary coordinate system into the two-phase rotating coordinate system, so as to obtain the d-axis current and the q-axis current.

5. The suppression method according to claim 4, characterized in that: The controlling the current regulator to adjust the current operating current specifically includes: controlling the current regulator to adjust the d-axis current according to the d-axis reference current so that the d-axis current is equal to the d-axis reference current; The current regulator is controlled to adjust the q-axis current according to the q-axis reference current so that the q-axis current is equal to the q-axis reference current.

6. The suppression method according to claim 5, characterized in that: The suppression system further includes a proportional-integral controller, the reference voltage includes: a d-axis reference voltage and a q-axis reference voltage, and the reference voltage is obtained according to the reference current, specifically including: The proportional-integral controller is controlled to obtain the d-axis reference voltage according to the d-axis reference current, and to obtain the q-axis reference voltage according to the q-axis reference current.

7. A suppression system, the suppression system executing the suppression method according to any one of claims 1 to 6, characterized in that: The suppression system (100) comprises: Three-phase motor (110); A frequency converter (120), the frequency converter (120) being connected to the three-phase motor (110); An inverter (130), the inverter (130) being connected to the frequency converter (120); A current regulator (150), the current regulator (150) regulating the current operating current so that the current operating current is equal to the reference current; A suppression module (160), wherein the suppression module (160) outputs a control instruction.

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