Electromagnetic interference suppression method

Abstract

The invention relates to an electromagnetic interference suppression method, which is applied to a power supply comprising a first conversion circuit and a second conversion circuit, 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 method comprises the following steps: executing an electromagnetic interference suppression action when an input voltage received by a first conversion circuit is a direct-current voltage; and under the action of electromagnetic interference suppression, judging 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, controlling the first output voltage to change, and controlling the peak-to-peak value of the first output voltage to be not zero under different load currents.

Description

Technical Field

[0001] The present invention relates to the field of power supply, and more particularly to a method for suppressing electromagnetic interference. Background Art

[0002] 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.

[0003] When the first conversion circuit receives AC power, the output voltage of the first conversion circuit has a twice-frequency mains voltage characteristic. In order to adjust the output voltage of the first conversion circuit, the second conversion circuit, which is a resonant conversion circuit, has a switching frequency of about ±6kHz at rated power. This frequency variation is similar to the characteristics of frequency Gitter. Such characteristics can make the frequency of the 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.

[0004] 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.

[0005] Therefore, it is necessary to develop an electromagnetic interference suppression method to solve the problems faced by the prior art. Summary of the invention

[0006] 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.

[0007] To achieve the above-mentioned purpose, a preferred embodiment of the present case is an electromagnetic interference suppression method, 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: when the input voltage received by the first conversion circuit of at least one power supply is a DC voltage, at least one 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 whether it is less than an upper current limit, and when the judgment result is that the load current is less than the preset current or greater than the upper current 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 upper current 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.

[0008] To achieve the above-mentioned purpose, another preferred embodiment of the present case is an electromagnetic interference suppression method, 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: 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 whether it is less than an upper current limit, when the load current is greater than the preset current and less than the upper current 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 A flowchart of the steps of the electromagnetic interference suppression method of the preferred embodiment of the present invention;

[0010] Figure 2 for Figure 1 A schematic diagram of the structure of a power supply device to which the electromagnetic interference suppression method is applied;

[0011] Figure 3 for Figure 1 The electromagnetic interference suppression method shown is a characteristic curve diagram of the power supply when the first output voltage is controlled to be variable and the peak-to-peak value of the first output voltage is fixed under different loads;

[0012] Figure 4 for Figure 1The electromagnetic interference suppression method shown in the figure controls the first output voltage to change, and the peak-to-peak value of the first output voltage changes linearly with different load currents;

[0013] Figure 5 for Figure 2 A schematic diagram showing the connection of the power supply in multiple situations;

[0014] Figure 6 A schematic diagram of the timing of voltage and current when a plurality of first output voltages output by a plurality of first conversion circuits of a plurality of power supplies have a phase difference;

[0015] Figure 7 The diagram is a voltage and current timing diagram of the power supply when a plurality of first output voltages outputted by a plurality of first conversion circuits of a plurality of power supplies have no phase difference and a plurality of first output voltages outputted by a plurality of first conversion circuits of a plurality of power supplies have a phase difference.

[0016] Description of Figure Numbers

[0017] 1: Power supply

[0018] 2: First conversion circuit

[0019] 3: Second conversion circuit

[0020] Vin: Input voltage

[0021] Vo1: first output voltage

[0022] Io: output current

[0023] IL: Load current

[0024] IL_stop: preset current

[0025] IL_max: current upper limit

[0026] Vo2: Second output voltage

[0027] 4: First Controller

[0028] 5: Second controller

[0029] S1~S2: Steps of electromagnetic interference suppression method

[0030] Vo1_ref: voltage reference value

[0031] △Vo1: Peak to peak value

[0032] △fsw: Change DETAILED DESCRIPTION

[0033] Some typical embodiments that embody the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various variations in different embodiments without departing from the scope of the present invention, and the descriptions and drawings therein are essentially for illustrative purposes rather than for limiting the present invention.

[0034] See also Figure 1 , Figure 2 , Figure 3 and Figure 4 ,in Figure 1 This is a flow chart of the steps of the electromagnetic interference suppression method of the preferred embodiment of the present invention. Figure 2 for Figure 1 The schematic diagram of the structure of the power supply device to which the electromagnetic interference suppression method is applied is shown. Figure 3 for Figure 1 The electromagnetic interference suppression method shown in the figure is a characteristic curve diagram of the power supply when the first output voltage is controlled to be variable and the peak-to-peak value of the first output voltage is fixed under different loads. Figure 4 for Figure 1 The electromagnetic interference suppression method shown in the figure is a characteristic curve diagram in which the first output voltage is controlled to change, 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 Figure 2 In the power supply 1 shown, 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, 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.

[0035] See also Figure 5 , which is Figure 2 The connection diagram of the number of power supplies shown in the figure is in multiple situations. The electromagnetic interference suppression method mentioned in this case can be applied not only to Figure 2 The single power supply 1 shown can also be applied to multiple power supplies 1, wherein the input ends of the multiple power supplies 1 are electrically connected in parallel, that is, the input ends of the multiple first conversion circuits 2 of the multiple power supplies 1 are connected in parallel. In addition, the output ends of the multiple power supplies 1 are electrically connected in parallel, that is, the output ends of the multiple second conversion circuits 3 of the multiple power supplies 1 are connected in parallel.

[0036] 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.

[0037] 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.

[0038] Step S2, 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 judgment result is that the load current IL is less than the preset current IL_stop or greater than the current upper limit IL_max, control the first output voltage Vo1 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), and when 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. 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 that it is zero under ideal conditions. However, in actual applications, since the first conversion circuit 2 is a switching power conversion circuit, the first output voltage Vo1 will have tiny ripples even when it is controlled at a fixed output value. This tiny ripple is ignored here.

[0039] The following will further explain the principle and step S2 of the electromagnetic interference suppression method of the present case. When the input voltage Vin is a DC voltage, the present 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, the present case increases the control of the first output voltage Vo1, and when the load decreases, the present 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 change of the first output voltage Vo1 is large, the change of the switching frequency fsw is also large. On the contrary, if the change of the first output voltage Vo1 is small, the change of the switching frequency fsw is also small.

[0040] Furthermore, in the electromagnetic interference characteristics of any conversion circuit (including resonant conversion circuits), it can be observed that when the load increases, the Nth order harmonic energy generated by the conversion circuit also increases. Conversely, when the load decreases, the Nth order harmonic energy generated by the conversion circuit decreases.

[0041] This physical characteristic is known from the restrictions of the electromagnetic interference specification. 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 farther away from the maximum limit value. Therefore, this case uses the electromagnetic interference characteristics of the first output voltage Vo1 output by the first conversion circuit 2 and the second conversion circuit 3 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 restrictions, the variation of the first output voltage Vo1 output by the first conversion circuit 2 will also increase. Conversely, when the load decreases, the harmonic energy generated will also decrease, so the variation can be reduced or kept unchanged by the first output voltage Vo1 output by the first conversion circuit 2.

[0042] 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, then Figure 3As shown, the power supply 1 has three operating intervals, namely, the first operating interval to the third operating interval. The first operating interval 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 complies with the regulatory limits, and in the first operating interval, the first output voltage Vo1 output by the first conversion circuit 2 is controlled to be fixed. The second operating interval corresponds to the load current IL being greater than the preset current IL_stop but less than the current upper limit IL_max, and in the second operating interval, 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 change △fsw of the switching frequency fsw of the second conversion circuit 3 is also fixed under different load currents IL. The third operating interval 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 operating interval, the first output voltage Vo1 output by the first conversion circuit 2 is controlled to be fixed.

[0043] 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, then Figure 4 As shown, the power supply 1 has three operating ranges, namely, the first operating range to the third operating range, wherein Figure 4 The execution conditions of the first and third operating ranges and the control method of the power supply 1 are similar to those of Figure 3 The execution conditions of the first and third operating ranges and the control method of the power supply 1 are not described in detail here. Figure 4 In the second operation interval, the load current IL is greater than the preset current IL_stop but less than the current upper limit IL_max. In the second operation interval, the first output voltage Vo1 output by the first conversion circuit 2 is controlled to change, 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.

[0044] As can be seen from the above content, the electromagnetic interference suppression method of the present case allows the power supply 1 to perform an electromagnetic interference suppression action 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 peak-to-peak value △Vo1 of the first output 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 performing electromagnetic interference suppression. Conversely, 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.

[0045] 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 can adjust the voltage reference value Vo1_ref ( Figure 3 or Figure 4 As shown) controls the first output voltage Vo1 of the first conversion circuit 2.

[0046] See also Figure 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 case is applied as follows Figure 5 In the multiple power supplies 1 shown, the multiple first output voltages Vo1 output by the multiple first conversion circuits 2 of the multiple power supplies 1 can have a phase difference in the variation, for example, through communication between an external controller (not shown) or internal controllers of the multiple power supplies 1, so that the current ripples of the multiple output currents Io output by the multiple first conversion circuits 2 also have a phase difference and cancel each other out. In this way, the problem of excessive ripples of the added output current Io when the multiple power supplies 1 are connected in parallel can be avoided. In addition, the phase difference of the multiple first output voltages Vo1 output by the multiple first conversion circuits 2 of the multiple power supplies 1 is 360° / N, where N is the number of power supplies 1. As shown in FIG. Figure 6 As shown, when the electromagnetic interference suppression method of the present invention is applied to two power supplies 1, the two first output voltages Vo1 (at Figure 6The first output voltage output by one of the first conversion circuits 2 is labeled as a, and the first output voltage output by the other first conversion circuit 2 is labeled as b) has a phase difference of (360° / 2)=180°, so that the two output currents Io output by the two first conversion circuits 2 (at Figure 6 The output current Io output by one of the first conversion circuits 2 is labeled as a1, and the output current Io output by the other first conversion circuit 2 is labeled as b1) also has a phase difference of 180°, so the current ripples of the two output currents Io will cancel each other (such as Figure 6 The sum of Io in (a1+b1).

[0047] See also Figure 7 , which 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. Figure 7 In the figure, 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, 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 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. By Figure 7 As shown, 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.

[0048] Of course, in other embodiments, step S2 of the aforementioned electromagnetic interference suppression method can be changed to: under 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 judgment 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.

[0049] In summary, the present invention 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 an electromagnetic interference suppression action, so that when the load current is greater than a preset current and less than an upper current 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. Conversely, when the load current is less than the preset current or greater than the upper current 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.

Claims

1. An electromagnetic interference suppression method is applied to at least one power supply, each of which comprises 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 an output current, and 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, wherein the electromagnetic interference suppression method comprises: When the input voltage received by the first conversion circuit of the at least one power supply is a DC voltage, the at least one 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 an upper current limit, and when the judgment result is that the load current is less than the preset current or greater than the upper current 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 upper current 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. 2 . The electromagnetic interference suppression method according to 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. 3 . The electromagnetic interference suppression method according to 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.

4. The electromagnetic interference suppression method according to claim 1, wherein the power supply further comprises 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.

5. The electromagnetic interference suppression method according to claim 4, wherein the second controller detects the magnitude of the load current and notifies the first controller of the detection result, so that the first controller controls the first output voltage of the first conversion circuit according to the detection result.

6. The electromagnetic interference suppression method according to 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. 7 . The electromagnetic interference suppression method according to 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.

8. The electromagnetic interference suppression method according to 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 a phase difference exists between the plurality of the first output voltages output by the plurality of the first conversion circuits of the plurality of the power supplies.

9. The electromagnetic interference suppression method according to claim 8, wherein a phase difference between 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.

10. An electromagnetic interference suppression method, applied to at least one power supply, each of the power supplies 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 comprising: When the input voltage received by the first conversion circuit of the at least one power supply is a DC voltage, the at least one 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 an upper current limit. When the load current is greater than the preset current and less than the upper current limit, the first output voltage is controlled to vary, and the peak-to-peak value of the first output voltage is controlled to be non-zero under different load currents. 11 . The electromagnetic interference suppression method according to 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. 12 . The electromagnetic interference suppression method according to 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. 13 . The electromagnetic interference suppression method according to claim 10 , wherein when a judgment result shows 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.

14. The electromagnetic interference suppression method according to claim 10, wherein the power supply further comprises 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. 15 . The electromagnetic interference suppression method according to claim 14 , wherein the second controller detects the magnitude of the load current and notifies the first controller of the detection result, so that the first controller controls the first output voltage of the first conversion circuit according to the detection result.

16. The electromagnetic interference suppression method according to 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. 17 . The electromagnetic interference suppression method according to 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.

18. The electromagnetic interference suppression method according to 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 a phase difference exists between the plurality of the first output voltages output by the plurality of the first conversion circuits of the plurality of the power supplies. 19 . The electromagnetic interference suppression method according to claim 18 , wherein a phase difference between the first output voltages output by the first conversion circuits of the power supplies is 360° / N, where N is the number of the power supplies.

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