Control board card electromagnetic interference suppression method

Abstract

The invention relates to the technical field of electromagnetic interference filtering, in particular to a control board card electromagnetic interference suppression method. According to the method, electromagnetic interference frequency and related parasitic parameters on a control board card are determined by analyzing electromagnetic interference generation and conduction mechanisms around the control board card on the LLC resonant converter, in Pspice simulation software, a sampling circuit is utilized to simulate circuit functions on a key loop, and influence of external electromagnetic interference on the key loop is analyzed, so that the LLC resonant converter is simulated. Based on the analyzed influence of electromagnetic interference on the control board card, the models of various devices on the filter circuit are determined, the designed filter circuit is added into a sampling circuit of the control board card, external electromagnetic interference is suppressed, a decoupling capacitor is added between a power supply of the control board card and the ground plane, internal resonance of the control board card is suppressed, and the control board card is controlled to be in a filtering state. The power density of the switching power supply system is improved, and the reliability of the control signal is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic interference filtering, and in particular to a method for suppressing electromagnetic interference of a control board. Background Art

[0002] In new energy power electronics systems, the LLC resonant converter, a core component, achieves efficient power conversion and electromagnetic interference (EMI) suppression through soft-switching technology and resonant circuits. However, its high performance relies on a high-precision control system. However, complex operating conditions in new energy power electronics systems, such as input voltage fluctuations, load variations, and external electromagnetic interference, often lead to signal distortion, malfunctions, and even failure of control boards. As the core hardware platform for the control algorithm, the secondary-side control board must cope with supply voltage fluctuations and external EMI interference.

[0003] In order to achieve high-efficiency and high-precision energy conversion of the LLC resonant converter under the influence of multiple factors such as load transients, input voltage disturbances and external electromagnetic interference, we propose a control board electromagnetic interference suppression method. Summary of the Invention

[0004] The purpose of the present invention is to solve the complex working conditions such as input voltage fluctuations, load changes and external electromagnetic interference in new energy power electronic systems, which often lead to control board signal distortion, functional abnormalities or even failure. The secondary side control board, as the core hardware platform of the control algorithm, needs to cope with power supply voltage fluctuations and external EMI interference. In order to achieve the LLC resonant converter, it can still maintain high efficiency and high precision energy conversion under the influence of multiple factors such as load transients, input voltage disturbances and external electromagnetic interference.

[0005] To achieve the above object, the present invention provides a method for suppressing electromagnetic interference of a control board, comprising the following steps:

[0006] S1. Analyze the electromagnetic interference generation and conduction mechanism around the control board on the LLC resonant converter, and determine the electromagnetic interference frequency and related parasitic parameters on the control board;

[0007] S2. In the PSpice simulation software, use the sampling circuit to simulate the circuit function of the key loop, design the corresponding filter circuit according to the oscillation frequency of the signal, and analyze the impact of external electromagnetic interference on the key loop;

[0008] S3. Based on the analysis of the impact of electromagnetic interference on the control board, determine the models of various components in the filter circuit, add the designed filter circuit to the sampling circuit of the control board to suppress external electromagnetic interference;

[0009] S4. Add decoupling capacitors between the power supply and ground plane of the control board to suppress the internal resonance of the control board.

[0010] Compared with the prior art, the present invention has the following beneficial effects:

[0011] 1. This control board electromagnetic interference suppression method studies the electromagnetic interference mechanism on the control board, analyzes the frequency and amplitude information of external electromagnetic interference signals, and adds a corresponding filter circuit to the control board to suppress external electromagnetic interference. The cutoff frequency of the filter circuit is set higher than the switching frequency of the switching power supply, thereby improving the power density of the switching power supply system and ensuring the reliability of the control signal.

[0012] 2. Add a decoupling capacitor between the power supply and ground plane of the control board to form a low-impedance path for the return signal to flow into the ground line, suppressing the internal resonance of the control board and allowing the return signal to flow into the expected low-impedance loop, reducing noise interference.

[0013] As a further improvement of this technical solution, the specific steps of S1 determining the electromagnetic interference frequency and related parasitic parameters on the control board are as follows:

[0014] S1.1.1. Interference source location: Determine the main interference sources and their frequency characteristics through spectrum analysis and simulation;

[0015] S1.1.2. Conduction path mapping: Use a near-field probe to scan the control board, locate the interference coupling position, and analyze the conduction path in combination with the parasitic parameter model;

[0016] S1.1.3. Parameter extraction and verification: Extract parasitic parameters through actual measurement and simulation tools, build interference propagation model, compare actual measurement and simulation results, and correct model parameters.

[0017] The beneficial effect of adopting the above further improvements is to reduce interference generation starting from the selection of power devices and the design of resonant parameters. By optimizing parasitic inductance / capacitance, the interference conduction efficiency is reduced, and the malfunction of the control chip (such as MCU) due to EMI is avoided, thus ensuring the stable operation of the LLC converter in a wide temperature and complex electromagnetic environment.

[0018] As a further improvement of the technical solution, S2 uses a sampling circuit to simulate the circuit function on the key loop, wherein the sampling circuit includes a differential operational amplifier AD8138, a capacitor C1, a capacitor C2 and a capacitor C3;

[0019] The positive input of the differential op amp AD8138 is connected to one end of the resistor R5 and one end of the resistor R2 in parallel. The other end of the resistor R5 is connected to the input VIN. The negative input of the differential op amp AD8138 is connected to one end of the resistor R6 and one end of the resistor R1 in parallel. The VCOM pin of the differential op amp AD8138 is connected to one end of the resistor R7 and one end of the capacitor C3 in parallel. The other end of the capacitor C3 is connected to the other end of the resistor R7 and is grounded.

[0020] The positive output of the differential op amp AD8138 is connected to the other end of the resistor R1 and in parallel to one end of the resistor R3. The negative output of the differential op amp AD8138 is connected to the other end of the resistor R2 and in parallel to one end of the resistor R4. The other end of the resistor R4 is connected to one end of the capacitor C2. The other end of the capacitor C2 is connected to one end of the capacitor C1 and to ground. The other end of the capacitor C1 is connected to the other end of the resistor R3.

[0021] The beneficial effect of adopting the above-mentioned further improvements is that the sampling circuit converts the dynamic characteristics of key circuits (such as power conversion circuits and signal links) into quantifiable electrical signals through real-time acquisition of physical quantities such as current, voltage, and temperature. The circuit transfer function is fitted by sampling data to ensure the consistency of the dynamic response of the simulation model and the actual system. High-speed sampling (sampling rate ≥ 10 times the highest signal frequency, following the Nyquist criterion) is used to record transient processes such as switching actions and load mutations to avoid missing key details in the simulation.

[0022] As a further improvement of this technical solution, the specific steps of determining the models of various components in the filter circuit in S3 are as follows:

[0023] S3.1.1. Determine the filter circuit topology and cutoff frequency: Select an LC low-pass filter circuit to suppress high-frequency interference, and use the LC low-pass filter formula to calculate the cutoff frequency;

[0024] S3.1.2. Determine the types and values ​​of capacitors and inductors;

[0025] S3.1.3. Locate the interference source in the sampling circuit and connect it to the filtering circuit.

[0026] As a further improvement of the present technical solution, the S3.1.1 adopts an LC low-pass filter circuit, wherein the LC low-pass filter circuit includes an inductor L1 and an inductor L2, a capacitor C4 and a capacitor C5;

[0027] One end of the inductor L1 is connected to one end of the resistor R8, the other end of the resistor R8 is connected to the oscilloscope V9, the other end of the inductor L1 is connected to one end of the capacitor C4 and to one end of the inductor L2, the other end of the capacitor C4 is grounded, the other end of the inductor L2 is connected to one end of the capacitor C5 and to the input VIN, and the other end of the capacitor C5 is grounded.

[0028] As a further improvement of the present technical solution, S3.1.1 uses the formula of LC low-pass filtering to calculate the cutoff frequency, wherein the formula of LC low-pass filtering is:

[0029]

[0030] Among them, f c is the cut-off frequency, L is the inductance, C is the capacitance, and π is the circular constant.

[0031] The beneficial effect of adopting the above further improvements is to accurately match the filtering requirements, avoid parameter redundancy (such as excessive inductance value increasing costs) or insufficient filtering caused by "empirical design", reversely infer the fault source through formulas (such as cutoff frequency offset to determine component parameter drift), and shorten the debugging time.

[0032] As a further improvement of the present technical solution, when determining the type and value of the capacitor and inductor in S3.1.2, the cutoff frequency of the LC low-pass filter circuit is higher than the rate of the driving signal, and the minimum value is 500KHz.

[0033] As a further improvement of this technical solution, when S3.1.2 determines the type and value of the capacitor and inductor, if the filter circuit is used to suppress interference frequencies of 10 MHz and above in another bridge arm drive circuit, the parallel capacitance in the filter circuit is limited to 0.5 nF.

[0034] The beneficial effect of adopting the above-mentioned further improvement is that it can effectively filter out power supply ripple, high-frequency noise generated by the on-off of switching devices (such as MHz-level spike interference), high-frequency interference coupled by electromagnetic radiation, etc. The parasitic capacitance (Cp) of the inductor and the equivalent series inductance (ESL) of the capacitor will cause the actual cut-off frequency to deviate from the theoretical value, especially in the high frequency band (such as greater than 1MHz), where the parasitic effect is more obvious.

[0035] As a further improvement of this technical solution, the specific steps of adding a decoupling capacitor between the power supply and the ground plane of the control board in S4 are as follows:

[0036] S4.1.1. Close to the resonance source: Place the decoupling capacitor just above or just below the resonance area between the power supply and the ground plane.

[0037] S4.1.2, Multi-layer board layering strategy: The decoupling capacitors between the top power plane and the inner ground plane are directly connected to the power pins through vias. The decoupling capacitors between the inner power and ground planes must have vias that pass vertically through the planes to avoid the introduction of additional inductance by horizontal routing.

[0038] As a further improvement of the present technical solution, when adding the decoupling capacitor in S4, the influence of parasitic resistance and parasitic inductance is taken into consideration to form a low-impedance path flowing into the ground line.

[0039] The beneficial effect of adopting the above further improvement is that the decoupling capacitor forms a parallel network with the power plane, which exhibits a low impedance characteristic below its self-resonant frequency (for example, the self-resonant frequency of a 100nF ceramic capacitor is about 10MHz), which is equivalent to providing a "low-resistance path" for high-frequency current, so that the power supply impedance remains low over a wide frequency band;

[0040] By controlling the ESR and ESL of the decoupling capacitors and reducing the parasitic inductance of the loop through PCB layout, the goal is to create a "low impedance, low resonance, and low radiation" current path within a wide bandwidth. This design not only improves power integrity (suppresses ripple and ground bounce) but also reduces EMI noise at the source, ensuring stable operation of the control board in high-speed, high-noise environments.

[0041] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of the overall process of the present invention;

[0043] Figure 2 Schematic diagram of the process of S1 of the present invention;

[0044] Figure 3 Schematic diagram of the process of S3 of the present invention;

[0045] Figure 4 Schematic diagram of the process of S4 of the present invention;

[0046] Figure 5 is a sampling circuit diagram of the present invention;

[0047] Figure 6 LC low-pass filter circuit diagram of the present invention;

[0048] Figure 7 This is a schematic diagram of normal input and output waveforms of the control circuit on the driver board of the present invention;

[0049] Figure 8 A schematic diagram of an input signal of a sampling circuit subjected to external interference according to the present invention;

[0050] Figure 9 A comparison diagram of interference and filtering of an input signal according to the present invention;

[0051] Figure 10This is a comparison diagram of the effects of the first-stage filtering and the second-stage filtering of the input signal of the present invention. DETAILED DESCRIPTION

[0052] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0053] At present, complex working conditions such as input voltage fluctuations, load changes and external electromagnetic interference in new energy power electronic systems often lead to signal distortion, functional abnormalities and even failure of control boards. The secondary-side control board, as the core hardware platform of the control algorithm, needs to cope with power supply voltage fluctuations and external EMI interference. In order to achieve the LLC resonant converter, it can still maintain high efficiency and high-precision energy conversion under the influence of multiple factors such as load transients, input voltage disturbances and external electromagnetic interference.

[0054] Therefore, the present invention proposes to analyze the electromagnetic interference generation and conduction mechanism around the control board on the LLC resonant converter, determine the electromagnetic interference frequency and related parasitic parameters on the control board, simulate the circuit function on the key loop using a sampling circuit in the Pspice simulation software, design a corresponding filter circuit according to the oscillation frequency of the signal, and analyze the impact of external electromagnetic interference on the key loop. Based on the analyzed impact of the electromagnetic interference on the control board, determine the models of various components on the filter circuit, add the designed filter circuit to the sampling circuit of the control board to suppress the external electromagnetic interference, and add a decoupling capacitor between the power supply and the ground plane of the control board to suppress the internal resonance of the control board.

[0055] The details are as follows:

[0056] See also Figure 1 As shown, the present invention provides a method for suppressing electromagnetic interference of a control board, comprising the following steps:

[0057] S1. Analyze the electromagnetic interference generation and conduction mechanism around the control board on the LLC resonant converter, and determine the electromagnetic interference frequency and related parasitic parameters on the control board;

[0058] S2. In the PSpice simulation software, use the sampling circuit to simulate the circuit function of the key loop, design the corresponding filter circuit according to the oscillation frequency of the signal, and analyze the impact of external electromagnetic interference on the key loop;

[0059] S3. Based on the analysis of the impact of electromagnetic interference on the control board, determine the models of various components in the filter circuit, add the designed filter circuit to the sampling circuit of the control board to suppress external electromagnetic interference;

[0060] S4. Add decoupling capacitors between the power supply and ground plane of the control board to suppress the internal resonance of the control board.

[0061] First, analyze the type of electromagnetic interference on the switching power supply control board, study the mechanism of electromagnetic interference on the control board, and determine the frequency characteristics of the interference noise to design the filter circuit. To improve the noise interference suppression ratio, depending on the interference situation, you can add multiple stages of filtering circuits to avoid using a single stage with large capacitors.

[0062] like Figure 2 As shown, the specific steps of S1 determining the electromagnetic interference frequency and related parasitic parameters on the control board are as follows:

[0063] S1.1.1. Interference source location: Determine the main interference sources and their frequency characteristics through spectrum analysis and simulation;

[0064] S1.1.2. Conduction path mapping: Use a near-field probe to scan the control board, locate the interference coupling position, and analyze the conduction path in combination with the parasitic parameter model;

[0065] S1.1.3. Parameter extraction and verification: Extract parasitic parameters through actual measurement and simulation tools, build interference propagation model, compare actual measurement and simulation results, and correct model parameters.

[0066] The power MOSFET or IGBT in the LLC resonant converter generates a steep current / voltage change rate at the switching instant (nanosecond rising / falling edge). According to Maxwell's electromagnetic theory, this high-frequency changing electrical signal excites the electromagnetic field, forming differential mode (DM) and common mode (CM) electromagnetic interference.

[0067] Power port conduction: Interference passes through the DC / DC converter input power terminal and enters the control board through the linear stabilizing impedance network (if not suppressed), appearing as power ripple superimposed on high-frequency noise;

[0068] Signal port conduction: driving signals, sampling signals, etc. receive interference through PCB traces. For example, the sampling circuit is affected by EMI in the power loop, resulting in signal distortion.

[0069] According to the interference frequency and parasitic parameters, the filtering circuit (such as LC filtering with a cutoff frequency fc = 2MHz) and decoupling scheme (such as decoupling capacitors with self-resonant frequency matching) are designed, and the suppression effect is verified through simulation.

[0070] like Figure 5As shown, S2 uses a sampling circuit to simulate the circuit function on the key loop, wherein the sampling circuit includes a differential operational amplifier AD8138, a capacitor C1, a capacitor C2 and a capacitor C3;

[0071] The positive input of the differential op amp AD8138 is connected to one end of the resistor R5 and one end of the resistor R2 in parallel. The other end of the resistor R5 is connected to the input VIN. The negative input of the differential op amp AD8138 is connected to one end of the resistor R6 and one end of the resistor R1 in parallel. The VCOM pin of the differential op amp AD8138 is connected to one end of the resistor R7 and one end of the capacitor C3 in parallel. The other end of the capacitor C3 is connected to the other end of the resistor R7 and grounded.

[0072] The positive output of the differential op amp AD8138 is connected to the other end of the resistor R1 and in parallel to one end of the resistor R3. The negative output of the differential op amp AD8138 is connected to the other end of the resistor R2 and in parallel to one end of the resistor R4. The other end of the resistor R4 is connected to one end of the capacitor C2. The other end of the capacitor C2 is connected to one end of the capacitor C1 and to ground. The other end of the capacitor C1 is connected to the other end of the resistor R3.

[0073] In this circuit, VIN is the input signal, which is connected to the inverting input terminal (-IN) of the op amp through resistor R6 (499Ω). At the same time, the other VIN is connected to the non-inverting input terminal (+IN) of the op amp through the voltage divider circuit of resistors R5 (523Ω) and R7 (1kΩ) and then through capacitor C3 (100nF).

[0074] According to the "virtual short" and "virtual open" characteristics of the differential op amp AD8138, the voltages at the inverting and non-inverting terminals are approximately equal (virtual short), and the current flowing into the op amp input terminal is approximately zero (virtual open). The gain of the op amp is determined by the external resistor network R1, R3, R4, and R6.

[0075] Capacitors C1 and C2 are used to filter out high-frequency noise in the output signal, stabilize the output signal, match the characteristics of the output load, and prevent signal reflection. Resistors R3 and R4 are used to limit the output current, protect the op amp, and adjust the amplitude of the output signal.

[0076] like Figure 3 As shown, the specific steps of S3 determining the models of various components in the filter circuit are as follows:

[0077] S3.1.1. Determine the filter circuit topology and cutoff frequency: Select an LC low-pass filter circuit to suppress high-frequency interference, and use the LC low-pass filter formula to calculate the cutoff frequency;

[0078] S3.1.2. Determine the types and values ​​of capacitors and inductors;

[0079] S3.1.3. Locate the interference source in the sampling circuit and connect it to the filtering circuit.

[0080] To prevent large capacitors from slowing signal edges, the parallel capacitor value is limited to less than 1nF (e.g., 1nF for the drive circuit and 0.5nF for high-frequency interference suppression). Ceramic capacitors (such as COG / NP0) are used for high-frequency scenarios. They have low parasitic inductance (<1nH) and low ESR (<50mΩ), making them suitable for frequency bands above 10MHz. The capacitance accuracy should be ±5% (e.g., a 1nF ±5% ceramic capacitor in a 0805 package) to ensure stable filtering characteristics.

[0081] In the high frequency band (>10MHz), use air-core inductors or thin-film inductors (such as wound thin-film inductors) to avoid high-frequency losses in the ferrite core (the magnetic permeability of the core decreases at high frequencies, and the inductance value decays). The parasitic capacitance must be less than 10pF to ensure that the inductor self-resonant frequency is higher than 3 times the cutoff frequency.

[0082] like Figure 6 As shown, S3.1.1 adopts an LC low-pass filter circuit, wherein the LC low-pass filter circuit includes inductors L1 and L2, capacitors C4 and C5;

[0083] One end of the inductor L1 is connected to one end of the resistor R8, the other end of the resistor R8 is connected to the oscilloscope V9, the other end of the inductor L1 is connected to one end of the capacitor C4 and to one end of the inductor L2, the other end of the capacitor C4 is grounded, the other end of the inductor L2 is connected to one end of the capacitor C5 and to the input VIN, and the other end of the capacitor C5 is grounded.

[0084] In this circuit, resistor R8 limits the current and consumes a certain amount of power, converting some electrical energy into heat. When the input signal V9 contains components of different frequencies, the inductive reactance of the inductor and the capacitive reactance of the capacitor vary with the frequency. At low frequencies, the inductive reactance of the inductor is small, which has little effect on blocking low-frequency signals. The capacitive reactance of the capacitor is large, making it difficult for low-frequency signals to be bypassed to ground through the capacitor. Therefore, low-frequency signals can be transmitted relatively smoothly through inductors L1 and L2 to the output terminal VIN.

[0085] First, it passes through resistor R8 and then reaches inductor L1. At L1, the low-frequency signal continues to transmit forward, while part of the high-frequency signal is blocked due to the high inductance of L1. The signal then reaches capacitor C4. At this time, the remaining high-frequency signal is bypassed to ground through C4, further attenuating.

[0086] After passing through capacitor C4, the signal passes through inductor L2, which again blocks the remaining high-frequency signal. Finally, the signal reaches capacitor C5, which bypasses a small amount of high-frequency signal to ground, allowing the output terminal VIN to obtain a relatively pure low-frequency signal.

[0087] To better determine the cutoff frequency range, when determining the type and value of capacitors and inductors in S3.1.2, the cutoff frequency of the LC low-pass filter circuit should be higher than the rate of the drive signal, and the minimum value should be 500 kHz;

[0088] The filter circuit's cutoff frequency must be higher than the drive signal rate, i.e., 500 kHz. Because the drive signal waveform is completely distorted by external lightning interference, a cutoff frequency must be assumed when designing the filter circuit. First, set the filter circuit's cutoff frequency fc > 500 kHz, suppressing frequencies above 1 MHz. Also, limit the parallel capacitance added to the drive circuit to 1 nF. Based on the LC low-pass filter formula (assuming fc = 2 MHz), the required inductor value is as follows. In actual simulation circuits, a 6.8 μH inductor can be used.

[0089] In order to better calculate the cutoff frequency, S3.1.1 uses the formula of LC low-pass filtering to calculate the cutoff frequency, where the formula of LC low-pass filtering is:

[0090]

[0091] Among them, f c is the cut-off frequency, L is the inductance, C is the capacitance, and π is the circular constant.

[0092] To better cope with interference frequencies of 10 MHz and above, when determining the types and values ​​of capacitors and inductors in S3.1.2, if the filter circuit is used to suppress interference frequencies of 10 MHz and above in another bridge arm drive circuit, limit the parallel capacitance in the filter circuit to 0.5 nF;

[0093] When external interference enters the device through parasitic capacitance, only the high-frequency components of the external interference signal enter through the parasitic capacitance due to its impedance characteristics. Therefore, the drive circuit also needs to suppress these high-frequency components. The drive circuit on the other bridge arm suppresses interference frequencies of 10MHz and above, limiting the parallel capacitance in the filter circuit to 0.5nF, resulting in an inductance value of 0.47μH.

[0094] like Figure 4 As shown in the figure, the specific steps for S4 to add a decoupling capacitor between the power supply and ground plane of the control board are as follows:

[0095] S4.1.1. Close to the resonance source: Place the decoupling capacitor just above or just below the resonance area between the power supply and the ground plane.

[0096] S4.1.2, Multi-layer board layering strategy: The decoupling capacitors between the top power plane and the inner ground plane are directly connected to the power pins through vias. The decoupling capacitors between the inner power and ground planes must have vias that pass vertically through the planes to avoid the introduction of additional inductance by horizontal routing.

[0097] The root cause of PCB resonance is the formation of a resonant cavity between the power supply and ground planes at high frequencies. This increases the impedance between the planes, causing the return signal to flow into an unintended low-impedance loop, leading to severe noise interference. The most effective way to improve PCB resonance is to add a decoupling capacitor between the power supply and ground planes at the resonant location. The decoupling capacitor's self-resonant frequency is close to the PCB's resonant frequency, creating a low-impedance path for the return signal to the ground line. Due to the influence of materials and packaging, actual capacitors are not ideal and will have parasitic resistance and inductance.

[0098] In order to better add decoupling capacitors, when adding decoupling capacitors to S4, the influence of parasitic resistance and parasitic inductance is considered to form a low-impedance path flowing into the ground line;

[0099] The self-resonant frequency of a decoupling capacitor is determined by its equivalent series inductance (ESL) and capacitance (C). If the ESL is too large, the self-resonant frequency will be lower than the PCB resonant frequency, causing the capacitor to exhibit inductive impedance (high impedance) at the resonant frequency and be unable to effectively bypass the resonant current.

[0100] ESR can damp the energy oscillation of the resonant circuit and reduce the resonant peak impedance. If the ESR is too small (such as the ideal capacitor ESR = 0), the resonant peak will increase significantly. If the ESR is too large, the DC voltage drop and power consumption will increase.

[0101] The capacitor pin length should be ≤1mm, or a surface-mount package (no pins) should be used, and the capacitor should be directly connected to the power / ground plane through vias to reduce additional parasitic inductance (such as via inductance ≤0.5nH). 2-4 vias (0.3mm diameter) should be connected in parallel at the ground end of the capacitor to reduce the equivalent inductance to 1 / 2-1 / 4 of that of a single via, ensuring that the ground impedance is ≤0.1Ω at high frequencies.

[0102] like Figure 7 As shown in the figure, the normal input and output waveform diagram of the control circuit on the driver board is shown. It can be seen from the figure that the input and output waveforms are not much different, and can accurately express the input waveform.

[0103] like Figure 8 As shown in FIG, a schematic diagram of the input signal on the sampling circuit being interfered with after being subjected to external interference. As can be seen from the figure, when subjected to external electromagnetic interference, the output waveform is greatly different from the input waveform, which affects the expression of the input waveform.

[0104] like Figure 9As shown in the figure, the interference and filtering comparison of the input signal, after adding the filtering circuit, the peak of the input signal waveform is significantly reduced, and the oscillation amplitude of the level is also alleviated.

[0105] like Figure 10 As shown in the figure, the comparison between the first-level filtering and the second-level filtering effects of the input signal is shown. The filter circuit has an attenuation effect on the oscillation amplitude. On the basis of the original first-level filtering circuit, another level is added to form a second-level filtering circuit. After adding the second-level filtering, the input signal is much smoother as a whole. However, there are still voltage spikes at low levels, which need to be suppressed, but the overall signal quality has been significantly improved.

[0106] In summary, the working principle of this solution is as follows:

[0107] This control board electromagnetic interference suppression method studies the electromagnetic interference mechanism on the control board, analyzes the frequency and amplitude information of the external electromagnetic interference signal, and adds a corresponding filter circuit to the control board to suppress the external electromagnetic interference of the board. The cutoff frequency of the filter circuit is set to be higher than the switching frequency of the switching power supply, thereby improving the power density of the switching power supply system and ensuring the reliability of the control signal.

[0108] Adding a decoupling capacitor between the power supply and ground plane of the control board forms a low-impedance path for the return signal to flow into the ground line, suppressing the internal resonance of the control board and allowing the return signal to flow into the expected low-impedance loop, thereby reducing noise interference.

[0109] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely preferred examples of the present invention and are not intended to limit the present invention. Various changes and improvements may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and improvements fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for suppressing electromagnetic interference of a control board, characterized in that: The following steps are involved: S1. Analyze the electromagnetic interference generation and conduction mechanism around the control board on the LLC resonant converter, and determine the electromagnetic interference frequency and related parasitic parameters on the control board; S2. In the PSpice simulation software, use the sampling circuit to simulate the circuit function of the key loop, design the corresponding filter circuit according to the oscillation frequency of the signal, and analyze the impact of external electromagnetic interference on the key loop; S3. Based on the analysis of the impact of electromagnetic interference on the control board, determine the model of the device on the filter circuit, add the designed filter circuit to the sampling circuit of the control board to suppress external electromagnetic interference; S4. Add decoupling capacitors between the power supply and ground plane of the control board to suppress the internal resonance of the control board.

2. The control board electromagnetic interference suppression method according to claim 1, characterized in that: The specific steps of S1 determining the electromagnetic interference frequency and related parasitic parameters on the control board are as follows: S1.1.

1. Interference source location: Determine the main interference sources and their frequency characteristics through spectrum analysis and simulation; S1.1.

2. Conduction path mapping: Use a near-field probe to scan the control board, locate the interference coupling position, and analyze the conduction path in combination with the parasitic parameter model; S1.1.

3. Parameter extraction and verification: Extract parasitic parameters through actual measurement and simulation tools, build interference propagation model, compare actual measurement and simulation results, and correct model parameters.

3. The control board electromagnetic interference suppression method according to claim 1, characterized in that: S2 simulates the circuit function on the key loop using a sampling circuit, wherein the sampling circuit includes a differential operational amplifier AD8138, a capacitor C1, a capacitor C2, and a capacitor C3; The positive input of the differential op amp AD8138 is connected to one end of the resistor R5 and one end of the resistor R2 in parallel. The other end of the resistor R5 is connected to the input VIN. The negative input of the differential op amp AD8138 is connected to one end of the resistor R6 and one end of the resistor R1 in parallel. The VCOM pin of the differential op amp AD8138 is connected to one end of the resistor R7 and one end of the capacitor C3 in parallel. The other end of the capacitor C3 is connected to the other end of the resistor R7 and is grounded. The positive output of the differential op amp AD8138 is connected to the other end of the resistor R1 and in parallel to one end of the resistor R3. The negative output of the differential op amp AD8138 is connected to the other end of the resistor R2 and in parallel to one end of the resistor R4. The other end of the resistor R4 is connected to one end of the capacitor C2. The other end of the capacitor C2 is connected to one end of the capacitor C1 and to ground. The other end of the capacitor C1 is connected to the other end of the resistor R3.

4. The control board electromagnetic interference suppression method according to claim 3, characterized in that: The specific steps of S3 determining the type of components in the filter circuit are as follows: S3.1.

1. Determine the filter circuit topology and cutoff frequency: Select an LC low-pass filter circuit to suppress high-frequency interference, and use the LC low-pass filter formula to calculate the cutoff frequency; S3.1.

2. Determine the types and values ​​of capacitors and inductors; S3.1.

3. Locate the interference source in the sampling circuit and connect it to the filtering circuit.

5. The control board electromagnetic interference suppression method according to claim 4, characterized in that: Said S3.1.1 adopts an LC low-pass filter circuit, wherein the LC low-pass filter circuit includes an inductor L1 and an inductor L2, a capacitor C4 and a capacitor C5; One end of the inductor L1 is connected to one end of the resistor R8, the other end of the resistor R8 is connected to the oscilloscope V9, the other end of the inductor L1 is connected to one end of the capacitor C4 and to one end of the inductor L2, the other end of the capacitor C4 is grounded, the other end of the inductor L2 is connected to one end of the capacitor C5 and to the input VIN, and the other end of the capacitor C5 is grounded.

6. The control board electromagnetic interference suppression method according to claim 4, characterized in that: S3.1.1 calculates the cutoff frequency using the formula for LC low-pass filtering, where the formula for LC low-pass filtering is: Among them, f c is the cut-off frequency, L is the inductance, C is the capacitance, and π is the circular constant.

7. The control board electromagnetic interference suppression method according to claim 1, characterized in that: When determining the type and value of the capacitor and inductor in S3.1.2, the cutoff frequency of the LC low-pass filter circuit is higher than the rate of the driving signal, and the minimum value is 500KHz.

8. The control board electromagnetic interference suppression method according to claim 1, characterized in that: When determining the type and value of the capacitor and inductor in S3.1.2, if the filter circuit is used to suppress interference frequencies of 10 MHz and above in another bridge arm drive circuit, the parallel capacitance in the filter circuit is limited to 0.5 nF.

9. The control board electromagnetic interference suppression method according to claim 1, characterized in that: The specific steps for adding decoupling capacitors between the power supply and ground plane of the control board in S4 are as follows: S4.1.

1. Close to the resonance source: Place the decoupling capacitor just above or just below the resonance area between the power supply and the ground plane. S4.1.2, Multi-layer board layering strategy: The decoupling capacitors between the top power plane and the inner ground plane are directly connected to the power pins through vias. The decoupling capacitors between the inner power and ground planes must have vias that pass vertically through the planes to avoid the introduction of additional inductance by horizontal routing.

10. The control board electromagnetic interference suppression method according to claim 9, characterized in that: When adding the decoupling capacitor S4, the influence of parasitic resistance and parasitic inductance is considered to form a low-impedance path flowing into the ground line.

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