A three-phase common-mode filter for brushless motors

Abstract

The utility model relates to the technical field of motor EMI noise suppression, and more specifically to a three-phase common-mode filter of a brushless motor, comprising a three-phase common-mode inductor and a common-mode capacitor, wherein the three-phase common-mode inductor is fixed on a lower partition plate, the three-phase common-mode inductor is fixed on a PCB board through the lower partition plate, the common-mode capacitor is arranged in the PCB board, the PCB board is fixed on the bottom of an outer shell, the upper part of the outer shell is buckled and fixed on the bottom of the outer shell, and the three-phase common-mode inductor is arranged in the upper part of the outer shell through the lower partition plate and the PCB board; the three-phase common-mode inductor comprises a magnetic ring and an inner partition plate, the magnetic ring is plugged and provided with the inner partition plate, and the inner partition plate divides the inner part of the magnetic ring into three spaces; the beneficial effect of the utility model is that the electromagnetic noise generated by the switch tube of the driving module of the three-phase brushless motor can be solved, and the switching noise, in addition to the common-mode noise, will also drive the equivalent antenna to be emitted outward in the form of differential mode; thereby solving the problem that the common-mode and differential-mode noises cannot be effectively suppressed at the same time.

Description

Technical Field

[0001] The utility model relates to the technical field of motor EMI noise suppression, in particular to a three-phase common mode filter of a brushless motor. Background Art

[0002] Due to its special structure, the three-phase common-mode inductor can use one device to realize common-mode filtering on three signals at the same time. Compared with the traditional two-phase common-mode inductor, three signals require three two-phase common-mode inductors, which saves the number of devices, space and cost. It has good application value in the filtering of three-phase brushless motor drives.

[0003] However, the three-phase common mode is ultimately a common mode inductor, which mainly filters the common mode noise. In order to adapt to the non-directionality and easy installation of the device, the symmetry and consistency of the three sets of coils are strived for when making the three-phase common mode, so the leakage inductance will be relatively small, and the corresponding differential mode filtering effect will be almost non-existent. The main noise source of the three-phase brushless motor drive generally includes the switching noise of the switching power supply, and these switching noises will also drive the equivalent antenna to emit outward in the form of differential mode. Therefore, when designing the product, not only common mode filtering but also differential mode filtering should be considered;

[0004] A high-voltage and high-current three-phase common-mode filter similar to patent number CN202321313471.9 comprises a housing, the housing comprises a base, a filter assembly is fixedly mounted on the inner wall of the base, the filter assembly comprises an annular core, winding one, winding two and winding three are wound and mounted on the outer wall of the annular core, the winding one and winding three are symmetrically distributed, the winding two is located at the right center of the annular core, the winding one, winding two and winding three are isolated and distributed from each other, the winding one, winding two and winding three are used to cooperate and connect a high-voltage and high-current three-phase circuit, an upper cover is detachably fixedly mounted on the top of the base, a buckle cover is fixedly mounted on the bottom of the upper cover, the outer wall of the buckle cover is plugged in with the inner wall of the top of the base, and a partition is fixedly mounted on the outer wall of the bottom of the buckle cover, which is convenient for limiting the three windings, so that the three windings can avoid accidental touch under vibration, thereby improving the stability between the windings;

[0005] However, the device cannot effectively filter the differential mode noise generated by the motor drive module. Utility Model Content

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the problem in the prior art that the generated common mode filtering and differential mode filtering cannot be filtered.

[0007] To this end, the technical solution adopted is that the utility model is a three-phase common-mode filter for a brushless motor, including a three-phase common-mode inductor and a common-mode capacitor, the three-phase common-mode inductor is fixed on the lower partition, the three-phase common-mode inductor is fixed on the PCB board through the lower partition, the common-mode capacitor is arranged in the PCB board, the PCB board is fixed to the bottom of the shell, the upper part of the shell is buckled and fixed on the bottom of the shell, and the three-phase common-mode inductor is arranged in the upper part of the shell through the lower partition and the PCB board.

[0008] Preferably, the three-phase common-mode inductor comprises a magnetic ring and an inner partition, and the magnetic ring is plugged with the inner partition, and the inner partition divides the magnetic ring into three spaces.

[0009] Preferably, three coils are evenly wound on the magnetic ring.

[0010] Preferably, the three coils are evenly arranged in three spaces separated by the inner partition.

[0011] Preferably, the coil is in the shape of a flat wire structure.

[0012] Preferably, the coil is fixed on the PCB board by welding.

[0013] Preferably, the PCB board is electrically connected to the bottom of the housing by welding; and a common-mode capacitor is fixed in the PCB board by welding.

[0014] Preferably, a capacitor is provided on the line of the driving signal connected to the bottom of the housing.

[0015] Preferably, the bottom of the housing fixes the entire three-phase common-mode filter on the PCB of the motor by welding.

[0016] Preferably, the bottom of the housing is fixed to a small plate by welding to form a filter element with three inputs and three outputs.

[0017] The beneficial effects of this device are:

[0018] 1. It can solve the problem of driving three-phase brushless motors. The main noise source generally includes the switching noise of the switching power supply. These switching noises will also drive the equivalent antenna to emit outward in the form of differential mode; thus solving the problem of being unable to filter the common mode filtering and differential mode filtering generated;

[0019] 2. Use three-phase common-mode inductors to replace traditional two-phase common-mode inductors, and use the characteristics of common-mode capacitors to filter out both differential and common-mode noises, using as few components and space as possible to achieve high common-mode and differential-mode filtering performance for three-phase motors;

[0020] 3. The entire filter module can be directly welded on the PCB of the motor as an on-board device, or it can be welded and assembled on a small board to form an independent filter device with three inputs and outputs and the installation position can be changed at will.

[0021] Other features and advantages of the utility model will be described in the following description, and partly become apparent from the description, or understood by implementing the utility model. The purpose and other advantages of the utility model can be realized and obtained by the structure specifically pointed out in this application document.

[0022] The technical solution of the utility model is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0024] Figure 1 It is a schematic diagram of the overall structure of the actual product of the utility model;

[0025] Figure 2 It is a schematic diagram of the insertion loss curve of the three-phase common mode inductor + ordinary capacitor of the utility model;

[0026] Figure 3 It is a topological diagram of a three-phase common mode inductor + ordinary capacitor circuit of the utility model;

[0027] Figure 4 It is a schematic diagram of the insertion loss curve of the three-phase common-mode inductor + common-mode capacitor of the utility model;

[0028] Figure 5 It is a topological schematic diagram of a three-phase common-mode inductor + common-mode capacitor circuit of the utility model;

[0029] Figure 6 It is a structural schematic diagram of the three-phase common-mode inductor of the utility model;

[0030] Figure 7 This is an exploded view of the overall structure of the actual product of the utility model;

[0031] Figure 8 It is a side view of the exploded view of the overall structure of the actual product of the utility model;

[0032] Fig. 9 The RE test fails before adding the filtering solution;

[0033] Fig.10 It is the RE test Pass after loading the filtering solution of the utility model.

[0034] In the figure: upper part of the shell 1; magnetic ring 2; inner partition 3; coil 4; lower partition 5; PCB board 6; bottom of the shell 7. DETAILED DESCRIPTION

[0035] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0036] In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "middle", "top", "bottom", "inside", "outside", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. The terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0037] In addition, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0038] In the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature. Specific implementation method one:

[0040] like Figure 1 and Figure 7As shown, a three-phase common-mode filter for a brushless motor includes a three-phase common-mode inductor and a common-mode capacitor. The three-phase common-mode inductor is fixed on a lower partition plate 5, and the three-phase common-mode inductor is fixed on a PCB board 6 through the lower partition plate 5. The common-mode capacitor is arranged in the PCB board 6. The PCB board 6 is fixed on a shell bottom 7, and a shell upper part 1 is fastened and fixed on the shell bottom 7. The three-phase common-mode inductor is arranged in the shell upper part 1 through the lower partition plate 5 and the PCB board 6.

[0041] The working principle and beneficial effects of this embodiment are as follows: since the device adds the upper shell 1 and the bottom shell 7, the entire filter can be directly mounted on the circuit board of the product as a patch device, and based on the actual needs of different usage scenarios, devices of different sizes and packages will be designed for use in the device;

[0042] Three-phase common-mode filters are usually installed on the power supply line of the motor or the output line of the driver, but their filtering effect is relatively weak and cannot be completely filtered;

[0043] Through on-site analysis and positioning, the main source of noise is the switching noise of the motor drive module, and the noise includes not only common-mode noise, but also a large proportion of differential-mode noise. Therefore, when designing the filter, it is necessary to consider not only common-mode filtering, but also to strengthen differential-mode filtering. Combined with the structural characteristics of the product, adding common-mode filtering measures to the motor drive cable is not feasible and is not conducive to its mechanical reliability. Therefore, it is considered to add filtering measures directly to the PCB.

[0044] Based on theoretical calculation and analysis, common-mode inductors can be added to the output end of the motor drive signal to address the common-mode noise problem. However, considering that there are three groups of motor drive signals, if two groups of common-mode inductors are added, at least three devices are required, and the three devices cannot be placed in parallel. The signal lines will be limited by the routing requirements of the common-mode inductor devices, resulting in additional coupling between each other, reducing the filtering effect of the common-mode inductor. Therefore, it is necessary to consider a three-phase common-mode inductor with a symmetrical structure and easy wiring, which can also save the number of devices and layout space, thereby reducing costs. Figure 6 As shown in FIG. 1 , a three-phase common-mode inductor is shown, in which three sets of coils 4 are wound around the same magnetic ring 2 ; this is to reduce the device size and improve the common-mode filtering effect. Specific implementation method 2:

[0046] like Figure 1 and Figure 6 , Figure 7 and Figure 8 As shown, a three-phase common-mode filter of a brushless motor, the three-phase common-mode inductor includes a magnetic ring 2 and an inner partition 3, the magnetic ring 2 is plugged with the inner partition 3, the inner partition 3 divides the magnetic ring 2 into three spaces; three coils 4 are evenly wound on the magnetic ring 2; the three coils 4 are evenly arranged in the three spaces separated by the inner partition 3.

[0047] The working principle and beneficial effects of this embodiment are as follows: a three-phase common-mode inductor is used, and three sets of coils are wound on the same magnetic ring 2; at the same time, the entire filter module can be directly welded on the PCB of the motor as an on-board device, or it can be welded and assembled on a small board to form an independent filter device with three inputs and outputs, and the installation position can be changed at will. The filter can filter out the problems of differential mode noise and common mode noise. Specific implementation method three:

[0049] like Figure 1 and Figure 6 , Figure 7 and Figure 8 As shown, a three-phase common-mode filter of a brushless motor, the coil 4 is in the shape of a flat wire structure.

[0050] The working principle and beneficial effects of this embodiment are as follows: the coil with a flat wire structure is adopted to reduce the size of the device; at the same time, the common mode filtering effect is conveniently improved. Specific implementation method four:

[0052] like Figure 1 and Figure 6 , Figure 7 and Figure 8 As shown, a three-phase common-mode filter of a brushless motor, the coil 4 is fixed on the PCB board 6 by welding; the PCB board 6 is electrically connected to the bottom 7 of the shell by welding; and a common-mode capacitor is fixed in the PCB board 6 by welding.

[0053] The working principle and beneficial effects of this embodiment are as follows: through the welding connection points on the bottom 7 of the shell, current can flow through the PCB board 6 and the three groups of coils 4, and then filtering is performed through the magnetic induction effect of the magnetic ring 2 in the three-phase common mode inductor. Specific implementation method five:

[0055] like Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown, a three-phase common mode filter of a brushless motor is provided with a capacitor on the line of the driving signal connected to the bottom 7 of the housing.

[0056] The working principle and beneficial effects of this embodiment are as follows: To solve the problem of differential mode noise, a capacitor is connected across the drive signal; the capacitance of the capacitor depends on the specific frequency band to which the noise belongs. In this measured case, the capacitance is 47nF; Figure 2 As shown, it is the common mode and differential mode insertion loss curve after 10mH common mode inductor is matched with 47nF capacitor;

[0057] Considering that common-mode capacitors have better differential-mode characteristics and take into account the effects of differential and common-mode filtering, ordinary capacitors are replaced with common-mode capacitors of the same capacitance, such as Figure 4 As shown in the figure, the same common-mode inductor, when paired with a 47nF common-mode capacitor, not only has a larger differential-mode insertion loss, but also has better common-mode insertion loss characteristics: Figure 2 The common mode insertion loss Scc12 of the common mode inductor + ordinary capacitor can reach -30dB at the strongest, and the -20dB bandwidth is 40MHz~1.8GHz; Figure 4 The common mode insertion loss of the common mode inductor + common mode capacitor is Scc12-80dB, and the -20dB bandwidth is 1.5MHz~3.5GHz, that is, the common mode insertion loss is larger and the bandwidth is wider;

[0058] like Figure 5 It is a circuit topology of common-mode inductance + common-mode capacitance, where L1 is a three-wire common-mode inductance, which is connected in series between the drive signals UVW~U'V'W' of the three-phase motor; C1~C6 are common-mode capacitors, and one common-mode capacitor is connected across every two groups of drive signal lines (such as UV, VW, UW, U'V', V'W', and U'W'). There are three common-mode capacitors before and after L1, which together with L1 form a Π-type filter circuit;

[0059] Since switching noise contains both common-mode noise and differential-mode noise, common-mode noise can be filtered out by common-mode inductors; differential-mode noise can be filtered out by connecting differential-mode capacitors ( Figure 4 C1, C2, C3 between UV, UW, VW, and C4, C5, C6 between U'V', U'W', V'W' in the schematic diagram);

[0060] Compared with ordinary capacitors, common-mode capacitors can be used; common-mode capacitors have the function of common-mode filtering under the premise of differential-mode filtering, which will enhance the common-mode filtering effect of the entire filter device, so it can be seen Figure 4 The Scc12 can reach nearly -80dB, Figure 2 The Scc12 (maximum -30dB) in the XT is nearly 50dB (316 times) stronger, and the bandwidth is wider, which can more effectively filter out noise in the circuit;

[0061] In the past, to achieve a -80dB common-mode filtering effect, you may need to connect two common-mode inductors in series, add a capacitor to each phase line to the ground, and add a differential-mode capacitor between the phase lines, so you will need two three-phase common-mode inductors and at least 18 ordinary capacitors; but after using common-mode capacitors, you can use one three-phase common-mode inductor and six common-mode capacitors to achieve a better filtering effect;

[0062] The inductance and size of the three-phase common-mode inductor of this filter circuit, as well as the capacitance and size of the common-mode capacitor, can be adjusted and selected accordingly based on the actual noise frequency band characteristics. Specific implementation method six:

[0064] like Figure 1 and Figure 6 , Figure 7 and Figure 8 As shown, a three-phase common-mode filter of a brushless motor is provided, wherein the bottom 7 of the housing fixes the entire three-phase common-mode filter on the PCB of the motor by welding.

[0065] The working principle and beneficial effects of this embodiment are as follows: for this case, through on-site analysis and positioning, the main source of noise is the switching noise of the motor drive module, and the noise includes not only common-mode noise but also a large proportion of differential-mode noise. Therefore, when designing the filter, it is necessary to consider not only common-mode filtering but also to strengthen differential-mode filtering. Combined with the structural characteristics of the product, adding common-mode filtering measures to the drive cable of the motor is not easy to implement and is not conducive to its mechanical reliability. Therefore, it is considered to add the filtering measures directly to the PCB. Specific implementation method seven:

[0067] like Figure 1 and Figure 6 , Figure 7 and Figure 8 As shown, a three-phase common mode filter of a brushless motor, the bottom 7 of the housing is fixed on a small plate by welding to assemble into a filter component with three inputs and outputs.

[0068] The working principle and beneficial effects of this embodiment are: it can be welded and assembled on a small board to form an independent filter component with three inputs and outputs and the installation position can be changed at will; the inductance and size of the three-phase common-mode inductor of this filter circuit, as well as the capacitance and size of the common-mode capacitor, can be adjusted and selected accordingly based on the actual noise frequency band characteristics. Specific implementation eight:

[0070] like Fig. 9 and Fig.10 As shown in the figure, a three-phase common-mode filter for a brushless motor is tested and verified on a motor product. Fig. 9 This is the RE (Radiated Emission) test result without filtering measures. It can be seen that its radiation intensity exceeds the standard seriously (radiation at multiple frequency points in the range of 90M~240MHz exceeds the standard), with the highest exceeding the standard by nearly 6dB. After loading the filter of the utility model, its noise radiation intensity is significantly reduced, achieving a noise reduction effect of more than 14dB (from exceeding the standard by 5.5dB to having a margin of 8.9dB), ensuring that the overall margin of the product is greater than 6dB (such as Fig.10, the minimum margin is nearly 9dB), and passed the RE test.

[0071] The above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by ordinary technicians in this technical field within the essential scope of the present invention also fall within the protection scope of the present invention.

Claims

1. A three-phase common mode filter for a brushless motor, characterized in that: The invention comprises a three-phase common-mode inductor and a common-mode capacitor, wherein the three-phase common-mode inductor is fixed on a lower partition (5), the three-phase common-mode inductor is fixed on a PCB (6) through the lower partition (5), the common-mode capacitor is arranged inside the PCB (6), the PCB (6) is fixed on a housing bottom (7), an housing top (1) is buckled and arranged on the housing bottom (7), and the three-phase common-mode inductor is fixed inside the housing top (1) through the lower partition (5) and the PCB (6).

2. The three-phase common mode filter of a brushless motor according to claim 1, characterized in that: The three-phase common mode inductor comprises a magnetic ring (2) and an inner partition (3); the magnetic ring (2) is plugged with the inner partition (3), and the inner partition (3) divides the magnetic ring (2) into three spaces.

3. The three-phase common mode filter of a brushless motor according to claim 2, characterized in that: Three coils (4) are evenly wound on the magnetic ring (2).

4. The three-phase common mode filter of a brushless motor according to claim 3, characterized in that: The three coils (4) are respectively and evenly arranged in three spaces separated by the inner partition plate (3).

5. The three-phase common mode filter of a brushless motor according to claim 4, characterized in that: The coil (4) is in the shape of a flat wire structure.

6. The three-phase common mode filter of a brushless motor according to claim 5, characterized in that: The coil (4) is fixed on the PCB board (6) by welding.

7. The three-phase common mode filter of a brushless motor according to claim 1, characterized in that: The PCB board (6) is electrically connected to the bottom (7) of the housing by welding, and a common-mode capacitor is fixed in the PCB board (6) by welding.

8. The three-phase common mode filter of a brushless motor according to claim 1, characterized in that: A capacitor is arranged on the line of the driving signal connected to the bottom (7) of the housing.

9. The three-phase common mode filter of a brushless motor according to claim 1, characterized in that: The bottom (7) of the housing fixes the entire three-phase common mode filter on the PCB of the motor by welding.

10. The three-phase common mode filter of a brushless motor according to claim 1, characterized in that: The bottom (7) of the housing is fixed on a small plate by welding to form a filter device with three inputs and three outputs.

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