Active Active Suppression Method for Motor Bearing Voltage Based on Software-Hardware Combined Strategy

Abstract

The present invention relates to an active suppression method for motor bearing voltage based on a software-hardware combination strategy, belonging to the technical field of motor bearing voltage suppression. The active suppression method for motor bearing voltage based on a software-hardware combination strategy includes the following steps: constructing a common-mode equivalent circuit of the internal capacitance of the motor; calculating the bearing voltage division ratio of the motor according to the common-mode equivalent circuit; adopting the AZSPWM strategy for motor control, and injecting voltage at both ends of the bearing by using the principle of the common-mode transformer to cancel the bearing voltage. The invention saves volume, has a simple method, does not need to suppress the common-mode voltage from the source, only needs to suppress the bearing voltage with a small amplitude, the power of the four-leg transistors required is small, and can completely eliminate the bearing voltage and suppress the bearing electro-corrosion phenomenon.

Description

Technical Field

[0001] The present invention relates to an active suppression method for motor bearing voltage, belonging to the technical field of motor bearing voltage suppression. Background Art

[0002] With the rapid development of power electronic devices, high-switching-frequency speed regulation technology has been maturely applied in motor drive systems, which has the advantages of effectively reducing the slope in the output waveform and suppressing torque ripple. However, the high-speed and frequent switching of the switching tubes results in a dv / dt as high as several kV / us, and the asymmetry of the output three-phase voltage will generate a high-frequency common-mode voltage at the neutral point of the motor. Under the excitation of the high-frequency common-mode voltage, the impedance characteristic of the motor is capacitive, and the common-mode voltage forms a common-mode loop through the coupling of the stray capacitance inside the motor after being transmitted through the cable, and induces a high-frequency bearing voltage between the inner and outer raceways of the motor bearing. When the bearing voltage exceeds the maximum withstand voltage of the lubricating oil film, partial discharge will occur on the surface of the motor bearing to generate an EDM shaft current. When the bearing voltage breaks down the oil film, the breakdown point area is very small, resulting in a large shaft current density, generating an extremely high temperature locally at the breakdown point to melt or evaporate metal molecules. Long-term accumulation will lead to aggravated bearing electrical corrosion, forming large-area indentations and washboard patterns, shortening the service life of the motor, and seriously affecting the normal operation of the motor.

[0003] At present, the suppression schemes for bearing voltage are mainly divided into software suppression and hardware suppression. In terms of software suppression, modulation methods such as near state pwm (NSPWM) and active zero state pwm (AZSPWM) are mainly used to suppress bearing voltage, but the bearing voltage cannot be completely eliminated, and there is still a possibility that the bearing oil film will be broken down; in terms of hardware suppression, insulated bearings are mainly used in combination with carbon brushes. However, ceramic bearings are expensive and prone to failure, and the conductor carbon brushes must be replaced and maintained regularly. The effects of both suppression schemes are not ideal enough. In the prior art, the publication number is CN117526792A, and the invention creation name is a common-mode voltage suppression method for a permanent magnet synchronous motor. In its technical solution, an additional bridge arm is added in parallel on the basis of a three-phase three-bridge-arm inverter, the sector where the reference voltage vector is located is judged, the switching vector is selected, and the action sequence and action time of the switching vector are confirmed, so as to control the switching states of the four bridge arms, which can not only avoid using zero vectors, but also minimize the common-mode voltage of the system to the greatest extent, thereby improving the performance and service life of the motor. However, its modulation strategy is relatively complex, and it suppresses the common-mode voltage from the source, and the power of the switching tubes is relatively large.

[0004] Therefore, there is an urgent need to propose an active suppression method for motor bearing voltage based on a combination of software and hardware strategies to solve the above technical problems. Summary of the Invention

[0005] To solve the above problems, an active suppression method for motor bearing voltage based on a combination of software and hardware strategies is provided. A brief overview of the present invention is given below to provide a basic understanding of certain aspects of the present invention. It should be understood that this overview is not an exhaustive overview of the present invention. It is not intended to identify the key or important parts of the present invention, nor is it intended to limit the scope of the present invention.

[0006] Technical solution of the present invention:

[0007] An active suppression method for motor bearing voltage based on a combination of software and hardware strategies includes the following steps:

[0008] Step 1: Construct a common-mode equivalent circuit composed of the internal capacitors of the motor;

[0009] Step 2: Calculate the bearing voltage division ratio of the motor according to the common-mode equivalent circuit;

[0010] Step 3: Adopt the AZSPWM strategy for motor control, and use the principle of the common-mode transformer to inject voltage at both ends of the bearing to cancel the bearing voltage.

[0011] Preferably: In step 1, the capacitors include the parasitic capacitance C ws between the stator winding and the machine shell, the parasitic capacitance C rs between the machine shell and the rotating shaft, the parasitic capacitance C wr between the stator winding and the rotating shaft, the capacitance C b,d at the bearing drive end, and the capacitance C b,nd at the non-drive end of the bearing; The high-frequency common-mode voltage is used as the circuit excitation source, and after passing through the internal parasitic coupling capacitance loop of the motor, starting from the stator winding of the motor, it forms a common-mode loop with the stator, rotor, machine shell, and the ground;

[0012] In a three-phase PMSM drive system, the common-mode voltage V com is defined as the voltage between the midpoint of the DC side and the neutral point of the motor; The common-mode voltage under different switch states can be expressed by the following formula (1) (1 means the upper switch of the switch tube is turned on and the lower switch is turned off, and 0 vice versa);

[0013]

[0014] Among them, V com is the common-mode voltage output by the inverter (abbreviation: common-mode voltage).

[0015] Preferably: In step 2, according to the Figure 2 shown common-mode equivalent circuit, the BVR calculation formula is derived as shown in formula (2):

[0016]

[0017] By extracting the parameters of the motor capacitor, the calculation formula for the bearing voltage can be determined as follows:

[0018]

[0019] Among them, the bearing voltage ratio (BVR) of the motor is the bearing voltage V b to the common-mode voltage V com ratio.

[0020] Preferably: In step three, it includes the following steps:

[0021] Step 3.1: Design the motor system structure;

[0022] Step 3.2: The fourth bridge arm synchronously controls the on or off of the switching tubes according to the switching states of the first three bridge arms, realizes the neutral point potential balance strategy of the three-phase four-bridge arm inverter and the common-mode voltage suppression, and improves the stability and efficiency of the system through decoupling and optimal configuration;

[0023] Step 3.3: Balance the voltage and eliminate the bearing current;

[0024] Step 3.4: By optimizing the AZSPWM strategy and combining with a common-mode filter, the V b voltage can be effectively adjusted to cancel the bearing voltage.

[0025] Preferably: In step 3.1, the motor adopts a permanent magnet synchronous motor (PMSM). The motor system includes: a stator core, a stator housing (motor housing), a rotor core, a rotating shaft, a common-mode magnetic ring (magnetic ring or common-mode transformer magnetic ring), and a four-bridge arm inverter. Three bridge arms of the four-bridge arm inverter are used to control the motor, that is, by using two basic non-zero vectors with equal amplitudes and opposite directions acting for the same time to replace the effect of the zero vector, the common-mode voltage amplitude is attenuated from V dc / 2 to V dc / 6. It can be seen from equation (2) that the bearing voltage is also attenuated by one-third in proportion. The bearing voltage waveform after changing the modulation strategy is as Figure 4 shown; Two common-mode transformers with a turn ratio of n:1 are fixed at both ends of the rotating shaft inside the motor. The rotating shaft passes through the two common-mode transformer magnetic rings, and the common-mode transformer uses the rotating shaft as the secondary side; One end of the primary winding of the common-mode transformer is connected to the midpoint of the fourth bridge arm, the other end of the primary winding is connected to the midpoint of the bus capacitor, and is controlled by the fourth bridge arm. The rotating shaft is regarded as a secondary winding with 1 turn.

[0026] Preferably: In step 3.2, the fourth bridge arm synchronously controls the on or off of the switching tubes according to the switching states of the first three bridge arms. If the switching states of the first three bridge arms are (110, 101, 011), the upper tube of the fourth bridge arm conducts and the lower tube turns off, that is, the switching state is "1", injecting an amplitude of V into the two common-mode magnetic rings on the primary side dcVoltage V of / 2 choke When the switching states of the first three bridge arms are (100, 010, 001), the upper transistor of the fourth bridge arm is turned off and the lower transistor is turned on, that is, the switching state is "0", and the voltage V injected into the two common-mode magnetic rings on the primary side choke The amplitude becomes -V dc / 2.

[0027] Preferably: In step 3.3, the voltage V choke Induces two injection voltages V at both ends of the bearing of the rotating shaft inj , by designing the number of turns n of the two magnetic rings, so that V inj Is equal in magnitude and opposite in phase to the bearing voltage V b After adding the common-mode transformer, the common-mode equivalent circuit is as shown in Figure 5 Shown;

[0028] The injection voltage V inj And the bearing voltage V b The superposition is equal to zero, completely eliminating the bearing voltage, and the effect diagram is as shown in Figure 6 Shown, thereby eliminating the bearing current and effectively suppressing the bearing electro-corrosion phenomenon.

[0029] Preferably: In step 3.4, the method for determining the number of turns n of the common-mode magnetic ring is as follows. According to the transformer principle, the ratio of the primary side of the magnetic ring to the injection voltage as the secondary side is shown in formula (4):

[0030]

[0031] Where V choke The magnitude is shown in formula (5):

[0032]

[0033] After adopting the AZSPWM strategy, the V b Voltage is shown in formula (6):

[0034]

[0035] In order to offset the bearing voltage, it is required that the voltage be equal in magnitude and opposite in phase to the bearing voltage as shown in formula (7):

[0036] V inj = V b (7)

[0037] Finally, the expression of n is derived as shown in formula (8):

[0038]

[0039] The present invention has the following beneficial effects:

[0040] 1. Based on the transformer principle, the present invention controls the magnetic ring through the fourth bridge arm to synchronously induce an injection voltage equal in magnitude and opposite in direction to the bearing voltage at both ends of the bearing, achieving complete elimination of the bearing voltage and suppressing the bearing electro-corrosion phenomenon;

[0041] 2. Regarding the rotating shaft of the present invention as the secondary side of the transformer, only a single-sided coil needs to be provided, saving volume, with a simple method and a simplified circuit structure;

[0042] 3. The present invention does not need to suppress the common-mode voltage from the source, only needs to suppress the relatively small-amplitude bearing voltage, and the power of the four bridge arm tubes required is small;

[0043] 4. Different from the traditional common-mode transformer that inserts the secondary side into the circuit, the present invention uses the rotating shaft as the secondary side of the common-mode transformer, which belongs to a non-contact suppression method, reducing wear, improving safety, being reliable in operation, avoiding errors and noise caused by mechanical contact from affecting the effect, having strong adaptability and low cost. Description of the Drawings

[0044] Figure 1 is a schematic structural diagram of an active and active suppression method for motor bearing voltage based on a software and hardware combination strategy;

[0045] Figure 2 is a high-frequency common-mode equivalent circuit diagram;

[0046] Figure 3 is a bearing voltage waveform diagram;

[0047] Figure 4 is the effect diagram of the bearing voltage after adopting AZSPWM;

[0048] Figure 5 is the common-mode equivalent circuit after adding a common-mode transformer;

[0049] Figure 6 is the effect diagram of the bearing voltage after adopting the active and active suppression method for motor bearing voltage based on a software and hardware combination strategy. Detailed Embodiments

[0050] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be described below through specific embodiments shown in the drawings. However, it should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0051] Detailed Embodiment 1: Combined with Figure 1-6 To illustrate this embodiment, the active and active suppression method for motor bearing voltage based on a software and hardware combination strategy in this embodiment includes the following steps:

[0052] Step 1: Construct a common-mode equivalent circuit composed of the internal capacitance of the motor; an equivalent circuit of the motor bearing used to calculate the shaft voltage. Through this circuit, a proportional relationship between the bearing voltage and the common-mode voltage is obtained, so that subsequent compensation can be performed according to the specific value of the bearing voltage.

[0053] In step 1, the capacitance includes the parasitic capacitance C between the stator winding and the casing. ws , parasitic capacitance C between the housing and the shaft rs , parasitic capacitance C between stator winding and shaft wr , the capacitance C at the bearing drive end b,d and the capacitance C at the non-drive end of the bearing b,nd ; High frequency common mode voltage V com As the circuit excitation source, it passes through the parasitic coupling capacitor loop (common-mode equivalent circuit) inside the motor, starting from the motor stator winding, and forms a common-mode loop with the stator, rotor, housing and the earth;

[0054] In a three-phase PMSM drive system, the common-mode voltage V com It is defined as the voltage between the midpoint of the DC side and the neutral point of the motor. The common-mode voltage under different switch states can be expressed as the following formula (1) (1 means the upper switch is on and the lower switch is off, 0 means the opposite). The common-mode voltage is coupled to the shaft through the parasitic capacitance between the stator winding and the motor housing, the stator winding and the rotor, and the rotor and the motor housing inside the motor, inducing a high-frequency bearing voltage V between the inner and outer raceways of the motor bearing. b The waveform of the bearing voltage is as follows: Figure 3 As shown, EDM shaft current is then generated, and the EDM shaft current forms a circulation loop between the rotating shaft, the inner and outer rings of the bearing, and the bearing chamber, causing electrical corrosion damage to the motor bearings;

[0055]

[0056] Among them, V com is the common mode voltage output by the inverter (referred to as common mode voltage), V dc is the DC bus voltage;

[0057] Step 2: Calculate the bearing voltage divider ratio of the motor according to the common-mode equivalent circuit;

[0058] In step 2, according to Figure 2 The common-mode equivalent circuit shown in the figure is used to derive the BVR calculation formula as shown in formula (2):

[0059]

[0060] By extracting the parameters of the motor parasitic capacitance, the calculation formula for the bearing voltage can be determined as:

[0061]

[0062] Among them, the bearing voltage division ratio (BVR) of the motor is the bearing voltage V b to the common-mode voltage V com ratio;

[0063] Step 3: Adopt the AZSPWM strategy for motor control, and use the principle of the common-mode transformer to inject a voltage across the bearings to cancel the bearing voltage, that is, to achieve common-mode cancellation;

[0064] In Step 3, AZSPWM is adopted for the first three phase legs, and the fourth phase conducts the switch according to the signals of the first three phases, greatly simplifying the modulation strategy and improving the efficiency. The shaft voltage suppressed by the present invention is smaller than the amplitude of the common-mode voltage. A voltage opposite to the shaft voltage is directly injected from the bearing end according to the principle of the transformer, and the shaft voltage can be completely eliminated, suppressing the phenomenon of bearing electro-corrosion. Therefore, the power of the switch tube of the fourth leg will be smaller, including the following steps:

[0065] Step 3.1: Design the motor system structure;

[0066] In Step 3.1, a permanent magnet synchronous motor (PMSM) is adopted for the motor. The motor system includes: a stator core (excluding windings), a stator housing (motor housing), a rotor core (excluding windings), a rotating shaft, a common-mode magnetic ring (magnetic ring or common-mode transformer magnetic ring), and a four-leg inverter. Three legs of the four-leg inverter are used to control the motor, that is, two basic non-zero vectors with equal amplitudes and opposite directions act for the same time to replace the effect of the zero vector, and the amplitude of the common-mode voltage is attenuated from V dc / 2 to V dc / 6. It can be seen from Equation (2) that the bearing voltage is also attenuated by one-third in proportion. The waveform of the bearing voltage after changing the modulation strategy is as Figure 4 shown; Two common-mode transformers with a turn ratio of n:1 are fixed at both ends of the rotating shaft inside the motor. The rotating shaft passes through the two common-mode transformer magnetic rings, and the common-mode transformer uses the rotating shaft as the secondary side; One end of the primary winding of the common-mode transformer is connected to the midpoint of the fourth leg, and the other end of the primary winding is connected to the midpoint of the bus capacitor and is controlled by the fourth leg. The rotating shaft is regarded as a secondary winding with 1 turn;

[0067] Step 3.2: The fourth leg synchronously controls the on or off of the switch tube according to the switching states of the first three legs, realizes the neutral point potential balance strategy of the three-phase four-leg inverter and the suppression of the common-mode voltage, and improves the stability and efficiency of the system through decoupling and optimal configuration;

[0068] In step 3.2, the fourth bridge arm synchronously controls the turning on or off of the switching tubes according to the switching states of the first three bridge arms. When the switching states of the first three bridge arms are (110, 101, 011), the upper tube of the fourth bridge arm conducts and the lower tube turns off, that is, the switching state is "1", injecting a voltage V with an amplitude of V dc / 2 to the two common-mode magnetic rings on the primary side choke . When the switching states of the first three bridge arms are (100, 010, 001), the upper tube of the fourth bridge arm turns off and the lower tube conducts, that is, the switching state is "0", injecting a voltage V choke with an amplitude that becomes -V dc / 2 to the two common-mode magnetic rings on the primary side;

[0069] Step 3.3: Balance the voltage and eliminate the bearing current;

[0070] In step 3.3, the voltage V choke induces two injection voltages V inj at both ends of the bearing of the rotating shaft. By designing the number of turns n of the two magnetic rings, V inj is made equal in magnitude and opposite in phase to the bearing voltage V b . After adding the common-mode transformer, the common-mode equivalent circuit is as Figure 5 shown;

[0071] The injection voltage V inj and the bearing voltage V b are superimposed to be equal to zero, completely eliminating the bearing voltage. The effect diagram is as Figure 6 shown, thus eliminating the bearing current and effectively suppressing the bearing electro-corrosion phenomenon;

[0072] Step 3.4: By optimizing the AZSPWM strategy and combining it with a common-mode filter, the V b voltage can be effectively adjusted to cancel out the bearing voltage;

[0073] In step 3.4, the method for determining the number of turns n of the common-mode magnetic ring is as follows. According to the transformer principle, the ratio of the primary side of the magnetic ring to the injection voltage as the secondary side is shown in formula (4):

[0074]

[0075] where the magnitude of V choke is shown in formula (5):

[0076]

[0077] After adopting the AZSPWM strategy, the V b voltage is shown in formula (6):

[0078]

[0079] To counteract the bearing voltage, a large reverse such as voltage and bearing voltage is required as shown in Equation (7):

[0080] V inj = V b (7)

[0081] Finally, the expression of n is derived as shown in Equation (8):

[0082]

[0083] In the present invention, by adopting the AZSPWM modulation algorithm, the bearing voltage is attenuated to a square-wave voltage with 1 / 3 of the original amplitude. And by adding a common-mode transformer at both ends of the rotating shaft inside the motor, the two common-mode transformers pass through the rotating shaft, and the rotating shaft is used as the secondary winding of the common-mode transformer; an additional half-bridge circuit is used to control the primary side of the common-mode transformer, so that the magnetic ring synchronously induces an injection voltage equal in magnitude and opposite in phase to the bearing voltage on both sides of the two bearings, thereby completely eliminating the bearing voltage between the inner and outer rings of the bearing, effectively solving the problem of bearing electro-corrosion. The principle and method are simple, saving volume. It is not necessary to suppress the common-mode voltage from the source, only the bearing voltage with a smaller amplitude needs to be suppressed. The power of the four-leg transistors required is small, achieving complete elimination of the bearing voltage and suppressing the bearing electro-corrosion phenomenon, with a wide range of applications.

[0084] It should be noted that in the above embodiments, as long as the technical solutions are not contradictory, they can be arranged and combined. Those skilled in the art can exhaust all possibilities according to the mathematical knowledge of permutation and combination. Therefore, the present invention will no longer describe the technical solutions after permutation and combination one by one, but it should be understood that the technical solutions after permutation and combination have been disclosed by the present invention.

[0085] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An active suppression method for motor bearing voltage based on a software and hardware combination strategy, characterized in that: It includes the following steps: Step 1: Construct the common-mode equivalent circuit of the internal capacitance of the motor; Step 2: Calculate the bearing voltage division ratio according to the common-mode equivalent circuit; Step 3: Adopt the AZSPWM strategy for motor control, and use the principle of the common-mode transformer to inject voltage at both ends of the bearing to cancel the bearing voltage; In Step 3, it includes the following steps: Step 3.1: Design the motor system structure; In step 3.1, three arms of the four-arm inverter are used to control the motor, that is, the action effect of the zero vector is replaced by the action of two basic non-zero vectors with equal amplitudes and opposite directions for the same time, and the common-mode voltage amplitude is attenuated from V dc / 2 to V dc / 6. It can be seen from Equation (2) that the bearing voltage is also attenuated by one-third in proportion; two common-mode transformers with a turn ratio of n:1 are fixed at both ends of the inner shaft of the motor, the shaft passes through the magnetic rings of the two common-mode transformers, and the shaft is regarded as the secondary side of the common-mode transformer; one end of the primary winding of the common-mode transformer is connected to the midpoint of the fourth arm, the other end of the primary winding is connected to the midpoint of the bus capacitor, and is controlled by the fourth arm, and the shaft is regarded as the secondary winding with one turn; Step 3.2: The fourth bridge arm synchronously controls the on or off of the switching tube according to the switching states of the first three bridge arms to achieve the neutral point potential balance strategy of the three-phase four-bridge arm inverter and the common-mode voltage suppression; In step 3.2, the fourth bridge arm synchronously controls the turning on or off of the switching tubes according to the switching states of the first three bridge arms. When the switching states of the first three bridge arms are (110, 101, 011), the upper tube of the fourth bridge arm conducts and the lower tube turns off, that is, the switching state is "1", injecting a voltage with an amplitude of V dc / 2 into the two common-mode magnetic rings on the primary side V choke . When the switching states of the first three bridge arms are (100, 010, 001), the upper tube of the fourth bridge arm turns off and the lower tube conducts, that is, the switching state is "0", and the voltage injected into the two common-mode magnetic rings on the primary side V choke has an amplitude that becomes - V dc / 2; Step 3.3: Balance the voltage and eliminate the bearing current; In Step 3.3, the voltage V choke induces two injection voltages at both ends of the bearing of the rotating shaft V inj , and by designing the number of turns n of the two magnetic rings, it is made such that V inj is equal in magnitude and opposite in phase to the bearing voltage V b ; Injected voltage V inj and the bearing voltage V b superimposed is equal to zero, completely eliminating the bearing voltage and thus eliminating the bearing current; Step 3.

4. Adjust the bearing voltage by optimizing AZSPWM the strategy and combining with a common-mode filter V b to cancel out the bearing voltage; In Step 3.4, the determination method of the number of turns n of the common-mode magnetic ring is as follows. According to the transformer principle, the ratio of the primary side of the magnetic ring to the injected voltage as the secondary side is shown in Formula (4): （4） wherein V choke is sized as shown in Equation (5): （5） After adopting the AZSPWM strategy V b The voltage is as shown in Equation (6): （6） To cancel the bearing voltage, it is required that the voltage such as the injection voltage is equal in magnitude and opposite in direction to the bearing voltage as shown in Formula (7): （7） Finally, the expression of n is derived as shown in Formula (8): （8） Among them, BVR is the bearing partial pressure ratio, V com is the common-mode voltage output by the inverter, V dc is the DC bus voltage.

2. The active suppression method for the motor bearing voltage based on the software and hardware combination strategy according to claim 1, wherein: In Step 1, the capacitance includes the parasitic capacitance between the stator winding and the machine housing C ws , the parasitic capacitance between the machine housing and the rotating shaft C rs , the parasitic capacitance between the stator winding and the rotating shaft C wr , the capacitance at the drive end of the bearing C b,d and the capacitance at the non-drive end of the bearing C b,nd ; The common-mode voltage under different switching tube states can be expressed by the following Formula (1): （1）。 3. The method for actively suppressing the motor bearing voltage based on the software and hardware combination strategy according to claim 2, wherein: In step two, use BVR The calculation formula is as shown in formula (2): （2） By extracting the parameters of the motor capacitance, the calculation formula of the bearing voltage can be determined as: （3） Among them, the bearing partial pressure ratio is the bearing voltage V b divided by the common mode voltage V com ratio.

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