DC fan EMI suppression circuit based on filter capacitor

Abstract

The utility model relates to the technical field of EMI testing, in particular to a direct current fan EMI suppression circuit based on a filter capacitor, which comprises a direct current power supply, a three-phase inverter bridge, a controller and the filter capacitor, the direct current power supply provides stable direct current voltage for the circuit, the three-phase inverter bridge consists of a plurality of high-end switches and low-end switches, and the high-end switches and the low-end switches are connected with the controller. Each phase is of a half-bridge structure formed by a pair of high-end and low-end switches, the controller generates PWM signals according to system requirements, controls the switches to be switched on and switched off alternately and converts direct-current voltage into three-phase alternating-current waveforms, and in order to suppress high-frequency noise generated in the switching process, a filter capacitor is connected in parallel to the middle point of each half-bridge of the circuit, so that high-frequency noise generated in the switching process is suppressed. According to the electromagnetic interference suppression circuit, electromagnetic interference is remarkably reduced in a low-pass filtering mode, conducted interference in the frequency band ranging from 150 kHz to 30 MHz is reduced by 12-14 dB, radiation emission is remarkably reduced, the electromagnetic interference suppression scheme effectively improves the electromagnetic compatibility of the direct-current fan, the circuit design is simplified, and cost is reduced.

Description

Technical Field

[0001] This utility model relates to the field of EMI testing technology, and in particular to an EMI suppression circuit for DC fans based on filter capacitors. Background Technology

[0002] With the continuous development of power electronics technology, DC fans, as an important driving device, are widely used in industries, home appliances, and automobiles. However, since DC fans use electronic switching technology for power conversion, this technology is prone to generating electromagnetic interference (EMI) during high-speed switching, which can affect the performance of the equipment and the normal operation of other electronic devices. Therefore, how to effectively reduce the EMI interference of DC fans and improve their electromagnetic compatibility (EMC) has become an urgent problem to be solved in the current technical field.

[0003] In existing DC fan circuit designs, EMI interference typically originates from the following aspects:

[0004] High-speed switching of switching devices: DC fans use inverter circuits to convert DC power to AC power. The frequent switching operations during the inverter process generate strong high-frequency noise, leading to electromagnetic interference.

[0005] Circuit layout and power management: Improper circuit layout can lead to excessively long current paths, thereby increasing the propagation range of interference signals. Especially in inverter circuits, improper placement of switching devices can further amplify electromagnetic noise.

[0006] Insufficient filtering measures: Although conventional power supply filter capacitors can suppress high-frequency noise, improper selection, parameter settings, and arrangement of capacitors make it difficult to effectively filter out high-frequency noise generated during switching, resulting in electromagnetic interference that cannot be effectively suppressed.

[0007] While some existing technologies attempt to suppress EMI by adding filters, electromagnetic shielding, or improving switching devices, the following problems still exist:

[0008] Limited filtering effect: Existing filtering methods often only solve part of the high-frequency noise problem and fail to achieve comprehensive EMI suppression, especially in the low-frequency to mid-frequency range (such as 150kHz to 30MHz) where the interference level is high.

[0009] Balancing cost and size: Some traditional EMI suppression measures often require additional shielding materials and filtering components, which not only increases costs but may also lead to larger equipment size, affecting the overall design and use of the system.

[0010] Complexity of control strategies: Some designs employ complex control strategies (such as soft start, soft shutdown, etc.) to suppress EMI, but these strategies often require high computational and hardware costs and may affect the system's real-time performance and response speed.

[0011] Therefore, a highly efficient, low-cost, and simple EMI suppression solution is urgently needed to address the electromagnetic interference problem in DC fan circuits. An ideal solution should significantly reduce EMI levels while ensuring circuit performance and guaranteeing system stability and reliability under various operating conditions. Utility Model Content

[0012] The purpose of this invention is to provide an EMI suppression circuit for DC fans based on a filter capacitor, so as to solve the problems mentioned in the background art.

[0013] To solve the above-mentioned technical problems, this utility model provides the following technical solution: an EMI suppression circuit for a DC fan based on filter capacitors, including a DC power supply VM, high-side switches K1, K3, and K5, low-side switches K2, K4, and K6, filter capacitors C1, C2, and C3, and a motor terminal M. The DC power supply (VM) is connected to the high-side switches (K1, K3, and K5); the low-side switches (K2, K4, and K6) are connected to the DC negative terminal or ground; the high-side and low-side switches are paired to form a three-phase half-bridge inverter structure, which is driven by a PWM signal to alternately turn on and off; the filter capacitors (C1, C2, and C3) are connected in parallel between the midpoint of the three-phase half-bridge and ground to filter out high-frequency noise and improve EMI performance.

[0014] According to the above technical solution, the capacitance values ​​of the filter capacitors (C1, C2, C3) are between 1μF and 4.7μF to provide the best EMI suppression effect.

[0015] According to the above technical solution, the high-end and low-end switches work alternately to output a modulated AC waveform, and the high-frequency interference generated during the switching process is reduced by the filter capacitor.

[0016] According to the above technical solution, each phase consists of a pair of switches forming a half-bridge, namely, K1 and K2, K3 and K4, K5 and K6, forming a three-phase inverter bridge structure.

[0017] According to the above technical solution, C1 corresponds to the first half-bridge, C2 corresponds to the second half-bridge, and C3 corresponds to the third half-bridge.

[0018] According to the above technical solution, the filtered three-phase output is converged at the motor end M.

[0019] Compared with the prior art, this utility model aims to effectively reduce the electromagnetic interference generated by the DC fan during operation by optimizing circuit design and filtering measures, thereby improving the electromagnetic compatibility (EMC) of the system and ensuring the high performance and reliability of the DC fan in practical applications.

[0020] The electromagnetic interference suppression circuit includes a DC power supply, a three-phase inverter bridge, a controller, and filter capacitors. The DC power supply provides a stable DC voltage to the circuit. The three-phase inverter bridge consists of multiple high-side and low-side switches. Each phase consists of a pair of high-side and low-side switches forming a half-bridge structure. The controller generates PWM signals according to system requirements, controlling the switches to alternately turn on and off, converting the DC voltage into a three-phase AC waveform. To suppress the high-frequency noise generated during the switching process, filter capacitors are connected in parallel at the midpoint of each half-bridge, significantly reducing electromagnetic interference through low-pass filtering.

[0021] The beneficial effects of this utility model are mainly reflected in the following aspects:

[0022] Significantly reduced electromagnetic interference (EMI): Through optimized layout of filter capacitors, high-frequency noise generated during circuit operation is effectively reduced, ensuring the electromagnetic compatibility of the system.

[0023] Improved system reliability: The optimized electromagnetic interference suppression design improves the stability and long-term operational reliability of the DC fan system and reduces the impact of electromagnetic interference on other equipment.

[0024] Cost reduction and simplified design: Compared with traditional electromagnetic interference suppression methods, the solution of this utility model does not require the addition of complex electromagnetic shielding or additional filtering components, which simplifies the design and reduces manufacturing costs.

[0025] Compliant with international standards: The electromagnetic interference suppression scheme of this utility model complies with the relevant standards of CISPR 25 and CISPR 22 Class B, can meet the stringent EMI test requirements, and is suitable for a variety of application scenarios.

[0026] Therefore, this invention not only improves the electromagnetic compatibility of DC fans, but also has good practicality, applicable to various industrial, home appliance and automotive fields, and has broad application prospects. Attached Figure Description

[0027] The accompanying drawings are provided to further illustrate the present invention and form part of the specification. They are used together with the embodiments of the present invention to explain the present invention, but do not constitute a limitation thereof. In the drawings:

[0028] Figure 1 This invention proposes an EMI suppression circuit for DC fans based on a filter capacitor. Detailed Implementation

[0029] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0030] Example:

[0031] Reference Figure 1 An EMI suppression circuit for a DC fan based on filter capacitors includes a DC power supply VM, high-side switches K1, K3, and K5, low-side switches K2, K4, and K6, filter capacitors C1, C2, and C3, and a motor terminal M. VM serves as a positive voltage input, directly supplying the high-side switches K1, K3, and K5; while the low-side switches K2, K4, and K6 are respectively connected to the DC negative terminal or ground. Each phase consists of a pair of switches forming a half-bridge, i.e., K1 and K2, K3 and K4, and K5 and K6, forming a three-phase inverter bridge structure. The PWM signals output by the controller (not shown in the figure) are respectively... The drive circuits sent to the high-side and low-side switches cause them to alternately turn on and off at high speed, thereby converting the DC power supply VM into a modulated AC waveform. The output of each half-bridge, i.e. the midpoint between the high-side and low-side switches, is connected to ground in parallel through a filter capacitor (C1 corresponds to the first half-bridge, C2 corresponds to the second half-bridge, and C3 corresponds to the third half-bridge). These filter capacitors are used to filter out the high-frequency noise generated during the PWM switching process, forming a low-pass filter effect and improving EMI performance. The three-phase output after filtering is converged to the motor terminal M, providing the motor with an AC voltage that meets the drive requirements.

[0032] The circuit's operation begins with a stable supply of DC power to VM, with the positive terminal directly connected to the high-side switches K1, K3, and K5, while the low-side switches K2, K4, and K6 are connected to the DC negative terminal or ground, respectively. The controller generates precise PWM signals according to system requirements, and through the drive circuit, controls the alternating on and off of the high-side and low-side switches, converting the DC voltage into a modulated AC waveform. The three half-bridges (each composed of a pair of high-side and low-side switches) work together to form a three-phase AC current at the motor terminal M. This inverter method not only achieves energy conversion but also ensures the stability and accuracy of the output waveform.

[0033] During high-speed switching, high-frequency noise and electromagnetic interference are inevitably generated. Therefore, filter capacitors C1, C2, and C3 are connected in parallel at the midpoint of each half-bridge. The capacitance values ​​of these capacitors range from 1μF to 4.7μF. These capacitors form a low-pass filter, which quickly filters out the high-frequency interference generated by the PWM switching, making the output AC waveform smoother. The filtered signal is then transmitted to the motor terminal M through the interface, ensuring that the motor receives a high-quality drive voltage.

[0034] Furthermore, simulation and experimental tests demonstrate that this scheme effectively reduces EMI interference levels, meeting stringent EMI testing standards. Simultaneously, the combined design of the inverter bridge and filter capacitors simplifies manufacturing and assembly processes, improving the overall reliability and stability of the system. This proves that the circuit not only achieves efficient DC-to-AC conversion but also significantly suppresses noise through meticulous filter design, ensuring the excellent performance of the DC fan in practical applications.

[0035] EMI Improvement Simulation Analysis:

[0036] 1. Spectrum Analysis

[0037] The spectral characteristics of the inverter output waveform were analyzed using FFT (Fast Fourier Transform). The changes in EMI levels before and after the test are as follows:

[0038]

[0039] 2. Time-domain waveform comparison

[0040] Unoptimized circuit: The voltage oscillation amplitude reaches 15V during switching, and there are obvious high-frequency glitches.

[0041] Optimized circuit: Oscillation amplitude reduced to 3V, glitches significantly reduced.

[0042] 3. Conducted Interference Test

[0043] Conducted noise of DC power lines was tested according to CISPR25 standard:

[0044] Frequency range Limit (dBμV) Before optimization (dBμV) Optimized (dBμV) 150kHz-500kHz 60 57.8 43.1 500kHz-1MHz 54 50.2 39.5 1MHz-10MHz 48 45.7 35.8

[0045] 4. Radiated emission test

[0046] According to CISPR 22 Class B standard, the radiated emission was measured at a test distance of 3 meters:

[0047]

[0048] Simulation and Experimental Conclusions

[0049] Through simulation and experimental testing, this solution reduces conducted interference by 12-14 dB in the 150 kHz to 30 MHz range, far exceeding industry standards. Simultaneously, radiated emissions are also significantly reduced, with optimized emissions all below the CISPR 22 Class B limit by approximately 10 dB. This solution, through filtering design, significantly suppresses electromagnetic noise, ensuring high performance and high reliability of the DC fan in practical applications.

[0050] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0051] Finally, it should be noted that the above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model. Although the utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. An EMI suppression circuit for a DC fan based on filter capacitors, comprising a DC power supply VM, high-side switches K1, K3, and K5, low-side switches K2, K4, and K6, filter capacitors C1, C2, and C3, and a motor terminal M, characterized in that: The DC power supply VM is connected to the high-side switches K1, K3, and K5; The low-end switches K2, K4, and K6 are connected to the DC negative terminal or grounded. The high-end and low-end switches are paired to form a three-phase half-bridge inverter structure, which is driven by a PWM signal to alternately turn on and off; The filter capacitors C1, C2, and C3 are connected in parallel between the midpoint of the three-phase half-bridge and ground to filter out high-frequency noise.

2. The EMI suppression circuit for a DC fan based on a filter capacitor according to claim 1, characterized in that: The capacitance values ​​of the filter capacitors C1, C2, and C3 are between 1μF and 4.7μF to provide optimal EMI suppression.

3. The EMI suppression circuit for a DC fan based on a filter capacitor according to claim 1, characterized in that: The high-end and low-end switches work alternately to output a modulated AC waveform, and the high-frequency interference generated during the switching process is reduced by the filter capacitor.

4. The EMI suppression circuit for a DC fan based on a filter capacitor according to claim 1, characterized in that: Each phase consists of a pair of switches forming a half-bridge, namely K1 and K2, K3 and K4, and K5 and K6, forming a three-phase inverter bridge structure.

5. The EMI suppression circuit for a DC fan based on a filter capacitor according to claim 4, characterized in that: C1 corresponds to the first half-bridge, C2 corresponds to the second half-bridge, and C3 corresponds to the third half-bridge.

6. The EMI suppression circuit for a DC fan based on a filter capacitor according to claim 1, characterized in that: The filtered three-phase output is converged at the motor terminal M.

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