TWI844453B - Electromagnetic interference suppressing method - Google Patents

Abstract

An electromagnetic interference suppressing method is disclosed. The electromagnetic suppressing method is used in a power supply including a first conversion circuit and a second conversion circuit, wherein the first conversion circuit receives an input voltage and outputs a first output voltage, and the second conversion circuit receives the first output voltage and outputs a load current. The electromagnetic interference suppressing method comprises: performing an electromagnetic interference suppression action when the input voltage received by the first conversion circuit is a DC voltage; under the electromagnetic interference suppression action, judging whether the load current is greater than a preset current and is less than a current upper limit, wherein when the load current is greater than the preset current and less than the current upper limit, controlling the first output voltage to be variable, and controlling a peak-to-peak value of the first output voltage not to be zero under different load currents.

Description

Electromagnetic Interference Suppression Methods

This case is related to the field of power supply, and in particular to a method for suppressing electromagnetic interference.

With the rapid development of the information industry, power supplies have played an indispensable role. The input voltage received by the power supply is divided into alternating current and direct current. In addition, the power supply can generally be divided into two levels, namely the first conversion circuit and the second conversion circuit, wherein the second conversion circuit can be, for example, a resonant conversion circuit.

When the first conversion circuit receives AC power, the output voltage of the first conversion circuit has a twice-frequency mains voltage characteristic. The second conversion circuit, which is a resonant conversion circuit, adjusts the output voltage of the first conversion circuit. The switching frequency of the resonant conversion circuit varies by about ±6kHz at rated power. This frequency variation is similar to the characteristic of frequency jitter. Such characteristics can make the frequency of electromagnetic interference generated by the second conversion circuit evenly dispersed in the range of ±6kHz (<150kHz) and the twice-frequency range of about ±12kHz (>150kHz), so that better electromagnetic interference suppression characteristics can be obtained.

However, when the first conversion circuit receives DC power, the output voltage of the first conversion circuit no longer has a double frequency mains voltage. Correspondingly, the switching frequency of the second conversion circuit changes only by a small amplitude of ±0.2kHz. Since this frequency variation is very small, the frequency of the electromagnetic interference generated by the second conversion circuit will be concentrated at N times the current switching frequency (N=1,2,3....). In this way, since there is no frequency jitter characteristic, when the first conversion circuit receives DC power, the electromagnetic interference suppression effect of the power supply is extremely poor.

Therefore, it is necessary to develop an electromagnetic interference suppression method to solve the problems faced by previous technologies.

The purpose of this case is to provide an electromagnetic interference suppression method to solve the problem that the electromagnetic interference suppression effect of the traditional power supply is extremely poor when receiving a DC input voltage.

To achieve the above-mentioned purpose, a preferred embodiment of the present invention is a method for suppressing electromagnetic interference, which is applied to at least one power supply. Each power supply includes a first conversion circuit and a second conversion circuit. The first conversion circuit receives an input voltage and outputs a first output voltage and an output current. The second conversion circuit is controlled by frequency modulation and receives the first output voltage and the output current, and outputs a load current and a second output voltage. The electromagnetic interference suppression method includes: connecting the first conversion circuit of at least one power supply to the first conversion circuit of the power supply. When the received input voltage is a direct current voltage, at least one power supply performs an electromagnetic interference suppression action; and in the electromagnetic interference suppression action, it is determined whether the load current is greater than a preset current and less than a current upper limit, and when the load current is less than the preset current or greater than the current upper limit, the first output voltage is controlled to be fixed, and when the load current is greater than the preset current and less than the current upper limit, the first output voltage is controlled to be variable, and the peak-to-peak value of the first output voltage is controlled to be non-zero under different load currents.

To achieve the above-mentioned purpose, another preferred embodiment of the present invention is an electromagnetic interference suppression method, which is applied to at least one power supply, each power supply comprising a first conversion circuit and a second conversion circuit, the first conversion circuit receiving an input voltage and outputting a first output voltage and an output current, the second conversion circuit being controlled by frequency modulation, receiving the first output voltage and the output current, and outputting a load current and a second output voltage, the electromagnetic interference suppression method The method includes: when the input voltage received by the first conversion circuit of at least one power supply is a DC voltage, at least the power supply performs an electromagnetic interference suppression action; and under the electromagnetic interference suppression action, it is determined whether the load current is greater than a preset current and less than the current upper limit, and when the load current is greater than the preset current and less than the current upper limit, the first output voltage is controlled to change, and the peak-to-peak value of the first output voltage is controlled to be non-zero under different load currents.

1: Power supply

2: First conversion circuit

3: Second conversion circuit

Vin: Input voltage

Vo1: first output voltage

Io: output current

IL: load current

IL_stop: default current

IL_max: current upper limit

Vo2: Second output voltage

4: First controller

5: Second controller

S1~S2: Steps of electromagnetic interference suppression method

Vo1_ref: voltage reference value

△Vo1: Peak to peak value

△fsw: Variation

FIG. 1 is a flow chart of the steps of the electromagnetic interference suppression method of the preferred embodiment of the present invention; FIG. 2 is a schematic diagram of the structure of the power supply to which the electromagnetic interference suppression method shown in FIG. 1 is applied; FIG. 3 is a characteristic curve of the power supply when the electromagnetic interference suppression method shown in FIG. 1 controls the first output voltage to be variable and the peak-to-peak value of the first output voltage is fixed under different loads; FIG. 4 is a characteristic curve of the power supply shown in FIG. 1; The magnetic interference suppression method controls the first output voltage to be variable, and the peak-to-peak value of the first output voltage changes linearly with different load currents. Figure 5 is a connection diagram of the power supply shown in Figure 2 in multiple situations. Figure 6 is a voltage and current timing diagram when multiple first output voltages output by multiple first conversion circuits of multiple power supplies have phase differences.

Figure 7 is a schematic diagram of the voltage and current timing of the power supply when the multiple first output voltages output by the multiple first conversion circuits of the multiple power supplies do not have a phase difference and when the multiple first output voltages output by the multiple first conversion circuits of the multiple power supplies have a phase difference.

Some typical embodiments that embody the features and advantages of this case will be described in detail in the following description. It should be understood that this case can have various variations in different forms, all of which do not deviate from the scope of this case, and the descriptions and drawings therein are essentially for illustrative purposes rather than for limiting this case.

Please refer to Figures 1, 2, 3 and 4, wherein Figure 1 is a step flow chart of the electromagnetic interference suppression method of the preferred embodiment of the present invention, Figure 2 is a structural schematic diagram of the power supply to which the electromagnetic interference suppression method shown in Figure 1 is applied, Figure 3 is a characteristic curve diagram of the power supply when the electromagnetic interference suppression method shown in Figure 1 controls the first output voltage to be variable and the peak-to-peak value of the first output voltage is fixed under different loads, and Figure 4 is a characteristic curve diagram of the electromagnetic interference suppression method shown in Figure 1 when the first output voltage is controlled to be variable and the peak-to-peak value of the first output voltage changes linearly with different load currents. The electromagnetic interference suppression method of this embodiment can be applied to a power supply 1 as shown in FIG. 2, wherein the power supply 1 includes a first conversion circuit 2 and a second conversion circuit 3. The first conversion circuit 2 receives an input voltage Vin and outputs a first output voltage Vo1 and an output current Io. The second conversion circuit 3 is controlled by frequency modulation and receives the first output voltage Vo1 and the output current Io, and outputs a load current IL and a second output voltage Vo2. As can be seen from the above, the first output voltage Vo1 and the output current Io output by the first conversion circuit 2 are the input voltage and the input current received by the second conversion circuit 3.

Please refer to Figure 5, which is a schematic diagram of the connection of the power supply shown in Figure 2 in multiple situations. The electromagnetic interference suppression method mentioned in this case can be applied not only to a single power supply 1 as shown in Figure 2, but also to multiple power supplies 1, wherein the input ends of multiple power supplies 1 are electrically connected in parallel, that is, the input ends of multiple first conversion circuits 2 of multiple power supplies 1 are connected in parallel. In addition, the output ends of multiple power supplies 1 are electrically connected in parallel, that is, the output ends of multiple second conversion circuits 3 of multiple power supplies 1 are connected in parallel.

In some embodiments, the first conversion circuit 2 may be, but is not limited to, a boost circuit or a buck circuit, and the second conversion circuit 3 may be a resonant conversion circuit, such as an LLC resonant conversion circuit or an LCL resonant conversion circuit. In addition, the power supply 1 further includes a first controller 4 and a second controller 5, the first controller 4 is used to control the operation of the first conversion circuit 2, the second controller 5 is used to control the operation of the second conversion circuit 3, and the first controller 4 and the second controller 5 communicate with each other.

The electromagnetic interference suppression method of this embodiment includes the following steps. Step S1, when the input voltage Vin received by the first conversion circuit 2 of the power supply 1 is a DC voltage, at least one power supply 1 performs an electromagnetic interference suppression action. Since the second conversion circuit 3 of the power supply 1 has a good electromagnetic interference suppression effect when the input voltage Vin is an AC voltage, the electromagnetic interference suppression action of the electromagnetic interference suppression method of this case will be performed when the input voltage Vin is a DC voltage.

In step S2, under the electromagnetic interference suppression action, it is determined whether the load current IL is greater than the preset current IL_stop and less than the current upper limit IL_max. When the determination result is that the load current IL is less than the preset current IL_stop or greater than the current upper limit IL_max, the first output voltage Vo1 is controlled to be fixed, that is, the peak-to-peak value △Vo1 of the first output voltage Vo1 is zero (that is, the first output voltage Vo1 is equal to the voltage reference value Vo1_ref). When the load current IL is greater than the preset current IL_stop and less than the current upper limit IL_max, the first output voltage Vo1 is controlled to be variable, and the peak-to-peak value of the first output voltage Vo1 is controlled to be non-zero under different load currents IL. In some embodiments, in step S2, when the load current IL is greater than the preset current IL_stop and less than the current upper limit IL_max, the peak-to-peak value △Vo1 of the first output voltage Vo1 can be controlled to be fixed under different load currents IL, or the peak-to-peak value △Vo1 of the first output voltage Vo1 can be controlled to change linearly with different load currents IL. It is worth mentioning that the peak-to-peak value △Vo1 of the first output voltage Vo1 referred to in this case is zero, which means zero under ideal conditions. However, in actual application, because the first conversion circuit 2 is a switching power conversion circuit, the first output voltage Vo1 will have a small ripple even when it is controlled at a fixed output value. This small ripple is ignored here.

The following will further explain the principle and step S2 of the electromagnetic interference suppression method of this case. When the input voltage Vin is a DC voltage, this case adjusts the input voltage received by the second conversion circuit 3 by controlling the first output voltage Vo1 of the first conversion circuit 2 to change. When the load (i.e., the load current IL) increases, this case increases the control of the first output voltage Vo1, and when the load decreases, this case reduces the control of the first output voltage Vo1. Further explanation, the first output voltage Vo1 of the first conversion circuit 2 is connected to the input of the second conversion circuit 3. Since the second conversion circuit 3 is controlled by frequency modulation, and the input voltage received by the second conversion circuit 3 (i.e., the first output voltage Vo1) is affected by the change, in order to adjust the second output voltage Vo2 to a constant value, the second conversion circuit 3 will change its switching frequency fsw accordingly. If the variation of the first output voltage Vo1 is large, the variation of the switching frequency fsw is also large. On the contrary, if the variation of the first output voltage Vo1 is small, the variation of the switching frequency fsw is also small.

In addition, in the electromagnetic interference characteristics of any conversion circuit (including resonant conversion circuits), it can be observed that when the load increases, the N-order harmonic energy generated by the conversion circuit also increases. Conversely, when the load decreases, the N-order harmonic energy generated by the conversion circuit decreases.

This physical property is known from the limits of electromagnetic interference specifications. When the load increases, the harmonic energy generated will be closer to the maximum limit value; conversely, when the load decreases, the harmonic energy generated will be far away from the maximum limit value. In this way, the first output voltage Vo1 output by the first conversion circuit 2 and the electromagnetic interference characteristics of the second conversion circuit 3 are used in this case to adjust the first output voltage Vo1 output by the first conversion circuit 2 according to different load conditions. When the load increases, the harmonic energy generated will also increase. In order to meet the regulatory limits, the variation of the first output voltage Vo1 output by the first conversion circuit 2 will also increase. Conversely, when the load decreases, the generated harmonic energy will also decrease, so the variation of the first output voltage Vo1 output by the first conversion circuit 2 can be reduced or kept unchanged.

Therefore, when the first output voltage Vo1 is controlled to be variable in step S2, and the peak-to-peak value △Vo1 of the first output voltage Vo1 is fixed under different load currents IL, as shown in FIG. 3, the power supply 1 has three operating ranges, namely, the first operating range to the third operating range. The first operating range corresponds to the load current IL being less than the preset current IL_stop, wherein the preset current IL_stop may be equal to the minimum value of the load current IL when the harmonic energy generated by the power supply 1 meets the regulatory limits, and in the first operating range, the first output voltage Vo1 output by the first conversion circuit 2 is controlled to be fixed. The second operation range corresponds to the load current IL being greater than the preset current IL_stop but less than the current upper limit IL_max. In the second operation range, the first output voltage Vo1 output by the first conversion circuit 2 is controlled to be variable, and the peak-to-peak value △Vo1 of the first output voltage Vo1 is fixed under different load currents IL. In addition, corresponding to the peak-to-peak value △Vo1 being fixed under different load currents IL, the variation △fsw of the switching frequency fsw of the second conversion circuit 3 is also fixed under different load currents IL. The third operation range corresponds to the load current IL being greater than the current upper limit IL_max, wherein the current upper limit IL_max may be but is not limited to the maximum rated output current of the power supply 1, and in the third operation range, the first output voltage Vo1 output by the first conversion circuit 2 is controlled to be fixed.

In addition, when the first output voltage Vo1 is controlled to be variable in step S2, and the peak-to-peak value △Vo1 of the first output voltage Vo1 changes linearly with different load currents IL, as shown in FIG. 4, the power supply 1 has three operating ranges, namely, the first operating range to the third operating range, wherein the execution conditions of the first operating range and the third operating range and the control method of the power supply 1 shown in FIG. 4 are similar to the execution conditions of the first operating range and the third operating range and the control method of the power supply 1 shown in FIG. 3, and are not further described here. In Figure 4, the second operation range corresponds to the load current IL being greater than the preset current IL_stop but less than the current upper limit IL_max. In the second operation range, the first output voltage Vo1 output by the first conversion circuit 2 is controlled to be variable, and the peak-to-peak value △Vo1 of the first output voltage Vo1 changes linearly with different load currents IL. In addition, corresponding to the linear change of the peak-to-peak value △Vo1 with different load currents IL, the change △fsw of the switching frequency fsw of the second conversion circuit 3 also changes linearly with different load currents IL. In addition, in some embodiments, the peak-to-peak value △Vo1 of the first output voltage Vo1 is equal to the subtraction of the load current IL and the preset current IL_stop multiplied by a fixed value.

As can be seen from the above content, the electromagnetic interference suppression method of the present case allows the power supply 1 to perform electromagnetic interference suppression when the input voltage Vin received by the first conversion circuit 2 of the power supply 1 is a DC voltage, so that when the load current IL is greater than the preset current IL_stop and less than the current upper limit IL_max, the first output voltage Vo1 is controlled to be variable, and the peak-to-peak value △Vo1 of the first output voltage Vo1 is controlled to be non-zero under different load currents IL. For example, the first output The peak-to-peak value △Vo1 of the voltage Vo1 is fixed under different load currents IL, or the peak-to-peak value △Vo1 of the first output voltage Vo1 changes linearly with different load currents IL, thereby suppressing electromagnetic interference. On the contrary, when the load current IL is less than the preset current IL_stop or greater than the current upper limit IL_max and there is no electromagnetic interference suppression requirement, the first output voltage Vo1 is controlled to be fixed. In this way, the electromagnetic interference suppression effect of the power supply 1 can be improved.

In some embodiments, the second controller 5 detects the magnitude of the load current IL and notifies the first controller 4 of the detection result, so that the first controller 4 controls the first output voltage Vo1 of the first conversion circuit 2 according to the voltage reference value Vo1_ref (as shown in FIG. 3 or FIG. 4) in the detection result.

Please refer to FIG. 6 , which is a schematic diagram of the voltage and current timing of the power supply when there is a phase difference between the two first output voltages output by the two first conversion circuits of the two power supplies. In some embodiments, when the electromagnetic interference suppression method of the present invention is applied to a plurality of power supplies 1 as shown in FIG. 5, a phase difference can be created in the variation of a plurality of first output voltages Vo1 output by a plurality of first conversion circuits 2 of the plurality of power supplies 1, for example, through mutual communication between an external controller (not shown) or controllers inside the plurality of power supplies 1, so that the current ripples of a plurality of output currents Io output by the plurality of first conversion circuits 2 also have a phase difference and cancel each other out. In this way, the problem of excessive ripples in the output current Io added when the plurality of power supplies 1 are connected in parallel can be avoided. In addition, the phase difference of the plurality of first output voltages Vo1 output by the plurality of first conversion circuits 2 of the plurality of power supplies 1 is 360°/N, where N is the number of power supplies 1. As shown in FIG6 , when the electromagnetic interference suppression method of the present case is applied to two power supplies 1, the two first output voltages Vo1 output by the two first conversion circuits 2 of the two power supplies 1 (the first output voltage output by one of the first conversion circuits 2 is marked as a, and the first output voltage output by the other first conversion circuit 2 is marked as b in FIG6 ) are (360°/2)=180°. The phase difference makes the two output currents Io output by the two first conversion circuits 2 (in Figure 6, the output current Io output by one of the first conversion circuits 2 is marked as a1, and the output current Io output by the other first conversion circuit 2 is marked as b1) also have a phase difference of 180°, so the current ripples of the two output currents Io will cancel each other (such as the sum of Io (a1+b1) in Figure 6).

Please refer to Figure 7, which is a schematic diagram of the voltage and current timing of the power supply when there is no phase difference between the multiple first output voltages output by the multiple first conversion circuits of the multiple power supplies and when there is a phase difference between the multiple first output voltages output by the multiple first conversion circuits of the multiple power supplies. In Figure 7, two power supplies 1 connected in parallel are used as an example for illustrative explanation, wherein A1 is the waveform of the output current Io output by the first conversion circuit 2 of the first power supply 1, A2 is the waveform of the output current Io output by the first conversion circuit 2 of the second power supply 1, A3 is the waveform of the first output voltage Vo1 output by the first conversion circuit 2 of the first power supply 1, and A4 is the waveform of the first output voltage Vo1 output by the first conversion circuit 2 of the second power supply 1. A5 is the waveform of an output voltage Vo1, A5 is the waveform of the sum of the output current Io output by the first conversion circuit 2 of the first power supply 1 and the output current Io output by the first conversion circuit 2 of the second power supply 1, and T is the judgment point for not allowing the multiple first output voltages output by the multiple first conversion circuits of the multiple power supplies to have a phase difference and allowing the multiple first output voltages output by the multiple first conversion circuits of the multiple power supplies to have a phase difference. As shown in Figure 7, after point T, since the two first output voltages Vo1 output by the two first conversion circuits 2 of the two power supplies 1 have a 180° phase difference, the current ripples of the two output currents Io output by the two first conversion circuits 2 can cancel each other.

Of course, in other embodiments, step S2 of the aforementioned electromagnetic interference suppression method can be changed to: in the electromagnetic interference suppression action, determine whether the load current IL is greater than the preset current IL_stop and less than the current upper limit IL_max, and when the determination result is that the load current IL is greater than the preset current IL_stop and less than the current upper limit IL_max, control the first output voltage Vo1 to be variable, and control the peak-to-peak value of the first output voltage Vo1 to be non-zero under different load currents IL, for example, control the peak-to-peak value △Vo1 of the first output voltage Vo1 to be fixed under different load currents IL, or control the peak-to-peak value △Vo1 of the first output voltage Vo1 to change linearly with different load currents IL.

In summary, this case provides an electromagnetic interference suppression method. When the input voltage received by the first conversion circuit of the power supply is a DC voltage, the electromagnetic interference suppression method allows the power supply to perform electromagnetic interference suppression action, so that when the load current is greater than a preset current and less than the current upper limit, the first output voltage is controlled to be variable, and the peak-to-peak value of the first output voltage is controlled to be non-zero under different load currents. On the contrary, when the load current is less than the preset current or greater than the current upper limit and there is no electromagnetic interference suppression requirement, the first output voltage is controlled to be fixed. In this way, the electromagnetic interference suppression effect of the power supply can be improved.

S1~S2: Steps of electromagnetic interference suppression method

Claims (18)

An electromagnetic interference suppression method is applied to at least one power supply, each of which includes a first conversion circuit and a second conversion circuit. The first conversion circuit receives an input voltage and outputs a first output voltage and an output current. The second conversion circuit is controlled by frequency modulation and receives the first output voltage and the output current, and outputs a load current and a second output voltage. The electromagnetic interference suppression method includes: when the input voltage received by the first conversion circuit of the at least one power supply is a constant voltage, When the load current voltage is greater than the preset current, the at least one power supply performs an electromagnetic interference suppression action; and in the electromagnetic interference suppression action, it is determined whether the load current is greater than a preset current and less than a current upper limit, and when the determination result is that the load current is less than the preset current or greater than the current upper limit, the first output voltage is controlled to be fixed, and when the load current is greater than the preset current and less than the current upper limit, the first output voltage is controlled to be variable, and the peak-to-peak value of the first output voltage is controlled to be non-zero under different load currents. The electromagnetic interference suppression method as described in claim 1, wherein when the load current is greater than the preset current and less than the current upper limit, the peak-to-peak value of the first output voltage is controlled to be constant under different load currents. The electromagnetic interference suppression method as described in claim 1, wherein when the load current is greater than the preset current and less than the current upper limit, the peak-to-peak value of the first output voltage is controlled to change linearly under different load currents. The electromagnetic interference suppression method as described in claim 1, wherein the power supply further includes a first controller and a second controller, the first controller is used to control the operation of the first conversion circuit, the second controller is used to control the operation of the second conversion circuit, and the first controller and the second controller communicate with each other. As described in claim 4, the electromagnetic interference suppression method, wherein the second controller detects the magnitude of the load current and notifies the first controller of a detection result, so that the first controller controls the first output voltage of the first conversion circuit according to the detection result. The electromagnetic interference suppression method as described in claim 1, wherein when the first output voltage is controlled to be variable and the peak-to-peak value of the first output voltage changes linearly with different loads, the peak-to-peak value of the first output voltage is equal to the subtraction of the load current and the preset current multiplied by a fixed value. The electromagnetic interference suppression method as described in claim 1, wherein the first conversion circuit is a boost circuit or a buck circuit, and the second conversion circuit is a resonant conversion circuit. The electromagnetic interference suppression method as described in claim 1, wherein the at least one power supply comprises a plurality of the power supplies, the input ends of the plurality of the power supplies are connected in parallel, the output ends of the plurality of the power supplies are connected in parallel, and the plurality of the first output voltages output by the plurality of the first conversion circuits of the plurality of the power supplies have a phase difference. The electromagnetic interference suppression method as described in claim 8, wherein the phase difference of the plurality of first output voltages output by the plurality of first conversion circuits of the plurality of power supplies is 360°/N, wherein N is the number of the power supplies. An electromagnetic interference suppression method is applied to at least one power supply. Each of the power supplies includes a first conversion circuit and a second conversion circuit. The first conversion circuit receives an input voltage and outputs a first output voltage and an output current. The second conversion circuit is controlled by frequency modulation and receives the first output voltage and the output current, and outputs a load current and a second output voltage. The electromagnetic interference suppression method includes: When the input voltage received by the first conversion circuit of the power supply is a DC voltage, the at least one power supply performs an electromagnetic interference suppression action; and in the electromagnetic interference suppression action, it is determined whether the load current is greater than a preset current and less than a current upper limit. When the load current is greater than the preset current and less than the current upper limit, the first output voltage is controlled to change, and the peak-to-peak value of the first output voltage is controlled to be non-zero under different load currents. The electromagnetic interference suppression method as described in claim 10, wherein when the load current is greater than the preset current and less than the current upper limit, the peak-to-peak value of the first output voltage is controlled to be constant under different load currents. The electromagnetic interference suppression method as described in claim 10, wherein when the load current is greater than the preset current and less than the current upper limit, the peak-to-peak value of the first output voltage is controlled to change linearly under different load currents. As described in claim 10, the electromagnetic interference suppression method, wherein the power supply further includes a first controller and a second controller, the first controller is used to control the operation of the first conversion circuit, the second controller is used to control the operation of the second conversion circuit, and the first controller and the second controller communicate with each other. As described in claim 13, the electromagnetic interference suppression method, wherein the second controller detects the magnitude of the load current and notifies the first controller of a detection result, so that the first controller controls the first output voltage of the first conversion circuit according to the detection result. The electromagnetic interference suppression method as described in claim 10, wherein when the first output voltage is controlled to be variable and the peak-to-peak value of the first output voltage changes linearly with different loads, the peak-to-peak value of the first output voltage is equal to the subtraction of the load current and the preset current multiplied by a fixed value. The electromagnetic interference suppression method as described in claim 10, wherein the first conversion circuit is a boost circuit or a buck circuit, and the second conversion circuit is a resonant conversion circuit. The electromagnetic interference suppression method as described in claim 10, wherein the at least one power supply comprises a plurality of the power supplies, the input ends of the plurality of the power supplies are connected in parallel, the output ends of the plurality of the power supplies are connected in parallel, and the plurality of the first output voltages output by the plurality of the first conversion circuits of the plurality of the power supplies have a phase difference. As described in claim 17, the electromagnetic interference suppression method, wherein the phase difference of the plurality of first output voltages output by the plurality of first conversion circuits of the plurality of power supplies is 360°/N, wherein N is the number of the power supplies.