EMI (Electro-Magnetic Interference) improvement circuit on direct-current fan

Abstract

The utility model relates to the technical field of EMI testing, in particular to an EMI improvement circuit on a direct-current fan, which comprises a direct-current power supply VM, high-end switches K1, K3 and K5, low-end switches K2, K4 and K6, a common-mode inductor and a motor M. The high-end switches and the low-end switches form a three-phase inverter bridge, each phase is composed of a pair of high-end switches and low-end switches, conversion from direct current to alternating current is realized, and the common-mode inductor is connected with the motor M. The direct-current power supply VM provides stable direct-current input for the inverter bridge, the positive electrode of the direct-current power supply VM is directly connected to the high-end switch, the low-end switch is connected to the direct-current negative electrode or grounded, and the controller outputs PWM signals and drives the high-end switch and the low-end switch to alternately switch on and off at a high speed, so that the inverter bridge outputs modulated three-phase alternating-current electric signals. The three-phase output end of the inverter bridge is respectively connected to the input end of the common mode inductor, and the output end of the common mode inductor is connected to the input end of the motor M. According to the utility model, the electromagnetic radiation can be significantly reduced, and the motor end can obtain a stable and low-noise three-phase AC power supply.

Description

Technical Field

[0001] This utility model relates to the field of EMI testing technology, and in particular to an EMI improvement circuit for a DC fan. Background Technology

[0002] With the continuous development of power electronics and control technologies, DC fans are increasingly widely used in home appliances, automobiles, industrial ventilation, and other fields. However, since DC fans typically use high-speed PWM (pulse width modulation) inverter circuits to achieve DC-to-AC conversion, this high-speed switching process inevitably generates high-frequency noise and electromagnetic interference (EMI), which in turn affects the normal operation of the system and interferes with surrounding equipment.

[0003] Traditional EMI suppression techniques often employ measures such as filter capacitors, common-mode chokes, and shielding. While filter capacitors can reduce high-frequency noise to some extent, they are prone to parasitic oscillations under high-power and high-frequency switching conditions. Furthermore, their aging and losses can affect long-term system reliability. In addition, excessive filter components increase circuit complexity and cost, placing higher demands on manufacturing and assembly processes.

[0004] In existing technologies, some solutions employ common-mode chokes to improve the EMI performance of DC fans. However, these designs often suffer from insufficient suppression and significant impact on load waveforms. Therefore, designing a circuit that is simple in structure, low in cost, and can effectively suppress high-frequency common-mode noise generated by PWM high-speed switching has become a pressing technical challenge in the current DC fan industry. Utility Model Content

[0005] The purpose of this invention is to provide an EMI improvement circuit for a DC fan to solve the problems mentioned in the background art.

[0006] To solve the above-mentioned technical problems, this utility model provides the following technical solution: an EMI improvement circuit for a DC fan, including a DC power supply VM, high-side switches K1, K3, and K5, low-side switches K2, K4, and K6, a common-mode inductor, and a motor M. The high-side switches K1, K3, and K5 and the low-side switches K2, K4, and K6 form a three-phase inverter bridge. The positive terminal of the DC power supply VM is directly connected to the high-side switches, while the low-side switches are connected to the DC negative terminal or grounded.

[0007] According to the above technical solution, each phase arm of the three-phase inverter bridge consists of a pair of high- and low-end switches, which are used to convert DC voltage into modulated three-phase AC power.

[0008] According to the above technical solution, the output terminals of the three-phase inverter bridge are respectively connected to the input terminals of the common-mode inductor, and the output terminals of the common-mode inductor are then respectively connected to the input terminals of the motor M.

[0009] According to the above technical solution, the common-mode inductor consists of three independent windings, which are connected in series in the U, V, and W phase lines of the three-phase inverter bridge output, respectively, to suppress high-frequency common-mode noise generated by PWM switching.

[0010] According to the above technical solution, the PWM signal drives the high-end switch and the low-end switch to alternately turn on and off.

[0011] According to the above technical solution, the U, V and W phases output by the three-phase inverter bridge are respectively connected to the input terminal of the common-mode inductor, with ports 5, 3 and 1. The output terminal of the common-mode inductor is then connected to the input terminal of the motor M.

[0012] Compared with the prior art, the beneficial effects achieved by this utility model are as follows: This utility model, by setting up a DC power supply VM, a three-phase inverter bridge composed of high-side switches (K1, K3, K5) and low-side switches (K2, K4, K6), a common-mode inductor, and a motor M, provides a stable DC voltage through the DC power supply. Under the action of the PWM signal generated by the controller, the inverter bridge converts the DC power into a modulated three-phase AC power output. The three-phase outputs of the inverter bridge are respectively connected to the input terminals of the common-mode inductor. After the common-mode inductor attenuates the high-frequency noise, its output terminal is then connected to the motor terminal, ensuring that the motor receives a stable and low-noise power supply. This design not only simplifies the circuit structure and avoids the parasitic oscillation and aging problems caused by the filter capacitor, but also significantly reduces the conducted interference and radiated emission levels in the 150kHz to 30MHz frequency band, improving the electromagnetic compatibility and operational stability of the DC fan system. It is suitable for automotive, home appliance, and industrial ventilation fields. Attached Figure Description

[0013] 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:

[0014] Figure 1 This utility model proposes an EMI improvement circuit for a DC fan. Detailed Implementation

[0015] 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.

[0016] Example 1:

[0017] Reference Figure 1 An EMI improvement circuit for a DC fan includes a DC power supply VM, high-side switches K1, K3, and K5, low-side switches K2, K4, and K6, a common-mode inductor, and a motor M. The DC power supply VM provides a stable DC voltage. Its positive terminal is directly connected to the high-side switches K1, K3, and K5 of the three-phase inverter bridge, while its negative terminal is grounded or connected to the low-side switches K2, K4, and K6, providing basic power supply conditions for the circuit. A controller (not shown in the figure) generates PWM signals according to load requirements and controls the high-side and low-side switches through a drive circuit, causing K1-K6 to alternately turn on and off at high speed. Each phase consists of a pair of high-side and low-side switches forming a half-bridge (K1 and K2, K3 and K4, K5 and K6), resulting in a three-phase output of U, V, and W. The PWM switching converts the DC voltage into a modulated AC waveform, forming the inverter bridge output.

[0018] The three-phase AC output generated by the inverter bridge is obtained at the midpoint of each half of the bridge, where:

[0019] The U-phase output is connected to the input terminal 5 of the first winding of the common-mode inductor.

[0020] The V-phase output is connected to the input terminal 3 of the second winding of the common-mode inductor.

[0021] The W-phase output is connected to the input terminal 1 of the third winding of the common-mode inductor.

[0022] The common-mode inductor consists of three windings connected in series in the U, V, and W phase lines, respectively, and its output terminals are marked as ports 6, 4, and 2.

[0023] The high-frequency common-mode noise generated during high-speed PWM switching can be effectively attenuated by the common-mode inductor due to its high impedance at high frequencies. This reduces conducted interference in the 150kHz to 30MHz frequency band and improves the EMC performance of the system. The output of the common-mode inductor is connected to the motor input M to ensure that the motor receives a stable and filtered three-phase AC power supply to drive the DC fan to operate efficiently.

[0024] Example 2:

[0025] (1) Conducted interference test:

[0026] Conducted interference tests were performed on the DC fan drive circuit according to the CISPR 25 standard in the frequency band from 150kHz to 30MHz. The test results are shown in the table below:

[0027]

[0028] The data shows that after optimization with common-mode inductors, conducted interference across the entire frequency band was reduced by approximately 12-14 dB, significantly improving the electromagnetic compatibility of the system.

[0029] (2) Radiated emission test:

[0030] According to CISPR 22 Class B standard, the radiated emissions of the circuit were measured under test conditions at a distance of 3 meters. The test data are as follows:

[0031]

[0032]

[0033] Experimental results show that the optimized circuit achieved significant radiation reduction in all test frequency bands, with radiated emissions all below the standard limit by approximately 9-11 dB.

[0034] (3) Time-domain waveform test

[0035] The voltage waveforms generated during the PWM switching process were acquired and compared using an oscilloscope. The test results are as follows:

[0036]

[0037] Data shows that after processing with a common-mode inductor, high-frequency noise and spikes are significantly reduced, the waveform is smoother, and the THD value is significantly improved.

[0038] In the above experiment:

[0039] Conducted interference: By using a common-mode inductor, conducted interference in the 150kHz to 30MHz frequency band was reduced by 12-14dB.

[0040] Radiated emissions: Radiation levels have decreased significantly, with all frequency bands falling below international standard limits by approximately 9-11 dB. Time-domain waveform: Voltage oscillation amplitude has decreased from 15V to 3V, and THD has decreased from 8.5% to 2.1%, ensuring that the motor receives a stable, low-noise drive signal.

[0041] These experimental data fully verify the effectiveness of this patented circuit in improving EMI through common-mode inductors. It not only reduces electromagnetic interference but also simplifies circuit design and improves system reliability and stability, making it suitable for various DC fan drive applications.

[0042] 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.

[0043] 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 improvement circuit for a DC fan, comprising a DC power supply VM, high-side switches K1, K3, and K5, low-side switches K2, K4, and K6, a common-mode inductor, and a motor M, characterized in that: The high-end switches K1, K3, and K5, together with the low-end switches K2, K4, and K6, form a three-phase inverter bridge. The positive terminal of the DC power supply VM is directly connected to the high-side switch, while the low-side switch is connected to the DC negative terminal or grounded.

2. The EMI improvement circuit for a DC fan according to claim 1, characterized in that: Each phase arm of the three-phase inverter bridge consists of a pair of high- and low-end switches, used to convert DC voltage into modulated three-phase AC power.

3. The EMI improvement circuit for a DC fan according to claim 1, characterized in that: The output terminals of the three-phase inverter bridge are connected to the input terminals of the common-mode inductor, and the output terminals of the common-mode inductor are then connected to the motor M.

4. The EMI improvement circuit for a DC fan according to claim 3, characterized in that: The common-mode inductor consists of three independent windings, which are connected in series in the U, V, and W phase lines of the three-phase inverter bridge output, respectively, to suppress high-frequency common-mode noise generated by PWM switching.

5. The EMI improvement circuit for a DC fan according to claim 4, characterized in that: The PWM signal drives the high-side switch and the low-side switch to alternately turn on and off, respectively.

6. The EMI improvement circuit for a DC fan according to claim 3, characterized in that: The U, V, and W phases output from the three-phase inverter bridge are respectively connected to the input terminals of the common-mode inductor, with ports 5, 3, and 1. The output terminals of the common-mode inductor are then respectively connected to the input terminals of the motor M.

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