阅读说明：本技术 频率调制的dc-dc转换器的降emi方法及其装置 (EMI reducing method and device for frequency modulated DC-DC converter ) 是由 廖柱帮 潘鸿标 于 2020-06-01 设计创作，主要内容包括：本公开实施例提出了频率调制的DC-DC转换器的降EMI方法及其装置。根据本公开实施例的方法包括：对所述频率调制的DC-DC转换器的输入电压进行预调节,使得所述频率调制的DC-DC转换器为了输出电压稳定而改变其操作频率实现期望的频率扩展。根据本公开实施例可以在保持频率调制的DC-DC转换器的输出稳定的同时,扩展开关噪声频谱,降低平均EMI噪声水平。(The embodiment of the disclosure provides an EMI reduction method and an EMI reduction device of a frequency-modulated DC-DC converter. The method according to the embodiment of the disclosure comprises the following steps: the input voltage of the frequency modulated DC-DC converter is preconditioned such that the frequency modulated DC-DC converter changes its operating frequency for output voltage stabilization to achieve a desired frequency spread. According to the embodiment of the disclosure, the output of the frequency-modulated DC-DC converter can be kept stable, and meanwhile, the switching noise frequency spectrum is expanded, and the average EMI noise level is reduced.)

1. A method of reducing electromagnetic interference, EMI, for a frequency modulated DC-DC converter, comprising:

the input voltage of the frequency modulated DC-DC converter is preconditioned such that the frequency modulated DC-DC converter changes its operating frequency for output voltage stabilization to achieve a desired frequency spread.

2. The method of claim 1, wherein the desired frequency spread is determined according to a desired average reduction level of electromagnetic interference noise (EMI).

3. The method of claim 1 or 2, wherein the pre-conditioning is performed by a pre-conditioner configured to: generating a varying output voltage as an input voltage of the frequency modulated DC-DC converter from a varying reference voltage.

4. The method of claim 3, wherein the varying portion of the reference voltage is referred to as a reference modulation voltage, which is determined according to the following equation:

V_{ref_modulation}＝f_sw/G_{ref_DCbus}G_{DCbus_f}，

wherein f is_swIs the operating frequency, G, of said frequency modulated DC-DC converter_{DCbus_f}Is a transfer function of the frequency modulated DC-DC converter from an input voltage to an operating frequency, G_{ref_DCbus}Is a transfer function of the pre-conditioner from a reference voltage to an output voltage.

5. The method of claim 1 or 2, wherein the frequency modulated DC-DC converter comprises an isolated type and a non-isolated type.

6. The method of claim 3, wherein the preconditioner comprises a Pulse Width Modulation (PWM) converter.

7. The method of claim 6, wherein the PWM converter comprises a PWM AC-DC converter and a PWM DC-DC converter.

8. A pre-conditioner for a frequency modulated DC-DC converter, comprising:

an input configured to receive an input voltage;

a reference voltage terminal configured to receive a reference voltage, wherein the reference voltage is varied;

a converter configured to convert a received input voltage into an output voltage based on a reference voltage, the output voltage varying with a variation of the reference voltage;

an output configured to provide the output voltage as an input voltage of the frequency modulated DC-DC converter;

wherein a variation in the output voltage of the pre-conditioner causes the frequency modulated DC-DC converter to change its operating frequency for output voltage stabilization to achieve a desired frequency spread.

9. The preconditioner of claim 8, wherein the pattern of variation of the reference voltage is determined in accordance with a desired level of reduction of an average value of electromagnetic interference noise (EMI).

10. The pre-conditioner according to claim 8 or 9, wherein the varying reference voltage is referred to as a reference modulation voltage, which is determined according to the following equation:

V_{ref_modulation}＝f_sw/Gr_{ef_DCbus}G_{DCbus_f}，

wherein f is_swIs the operating frequency, G, of said frequency modulated DC-DC converter_{DCbus_f}Is a transfer function from an input voltage to an operating frequency of said frequency modulated DC-DC converter, G_{ref_DCbus}Is a transfer function of the pre-conditioner from a reference voltage to an output voltage.

11. The preconditioner of claim 8 or 9, wherein the frequency-modulated DC-DC converter comprises an isolated and a non-isolated type.

12. The pre-conditioner of claim 8 or 9, wherein the pre-conditioner comprises a Pulse Width Modulation (PWM) converter.

13. The preconditioner of claim 12, wherein the PWM converter comprises a PWMAC-DC converter, and a PWM DC-DC converter.

14. A switching power supply, comprising:

a pre-conditioner according to any of claims 8 to 13; and

a frequency-modulated DC-DC converter,

wherein the output of the pre-conditioner is connected to the input of the frequency modulated DC-DC converter.

Technical Field

The present disclosure relates to switching power supplies, and more particularly, to a method of reducing an average value of electromagnetic interference (EMI) for a frequency modulated converter and a corresponding apparatus thereof.

Background

The switching power supply is a high-frequency electric energy conversion device, and mainly utilizes power semiconductor devices (such as bipolar transistors, MOS (metal oxide semiconductor) transistors and the like) to periodically turn on and turn off the electronic switching devices through a control circuit, so that the power semiconductor devices perform pulse modulation on input voltage, and the functions of voltage conversion, output voltage regulation and automatic voltage stabilization are realized. For different switching power supply topologies, a width modulation (PWM) method and a frequency modulation (fm) method are two control methods commonly used for the switching power supply.

High conversion efficiency and low electromagnetic interference (EMI) are key requirements for switching power supplies.

For switching power supplies using PWM control, one known mechanism that is effective in reducing the average EMI noise level is direct switching frequency modulation. Direct switching frequency modulation causes switching frequency jitter of the PWM controlled converter, which spreads the spectrum of the switching noise, thereby reducing the average EMI noise level.

Frequency-modulated switching power supplies use switching frequency modulated resonant and quasi-resonant converter topologies, which can minimize the switching losses of the power semiconductor devices. However, direct switching frequency modulation suitable for PWM switching power supplies to reduce EMI noise is not suitable for switching frequency modulated converters. This will increase the requirements on the EMI filter, resulting in a larger filter size and hence more power consumption for the fm switched mode power supply.

Therefore, there is a need for an effective mechanism suitable for use in a frequency-modulated switching power supply that reduces the average EMI noise and thus reduces the size and loss of the EMI filter.

Disclosure of Invention

It is an object of embodiments of the present disclosure to reduce the average EMI noise of a frequency-modulated switching power supply. In particular, embodiments of the present disclosure propose to regulate the input voltage of a frequency modulated converter such that the regulated voltage has a predefined pattern of variation, and then to use the regulated voltage as the input voltage of the frequency modulated converter. As the input voltage varies, the frequency modulated converter will vary its switching frequency according to its feedback control loop to maintain a stable output voltage. Thus, according to embodiments of the present disclosure, a frequency modulated converter will naturally implement frequency modulation while maintaining a stable output voltage, thereby spreading the spectrum of switching noise and reducing the average EMI noise level.

According to a first aspect of the present disclosure, a method of reducing electromagnetic interference, EMI, for a frequency modulated DC-DC converter is provided. The method comprises the following steps: the input voltage of the frequency modulated DC-DC converter is preconditioned such that the frequency modulated DC-DC converter changes its operating frequency for output voltage stabilization to achieve a desired frequency spread. In some embodiments, the preconditioning may be performed by a preconditioner.

According to a second aspect of the present disclosure, there is provided a pre-conditioner for a frequency modulated DC-DC converter, comprising: an input configured to receive an input voltage; a reference voltage terminal configured to receive a reference voltage, wherein the reference voltage is varied; a converter configured to convert a received input voltage into an output voltage based on a reference voltage, the output voltage varying with a variation of the reference voltage; an output configured to provide the output voltage as an input voltage of the frequency modulated DC-DC converter. Wherein a variation in the output voltage of the pre-conditioner causes the frequency modulated DC-DC converter to change its operating frequency for output voltage stabilization to achieve a desired frequency spread.

In some embodiments, the frequency modulated DC-DC converter may be of an isolated type. In other embodiments, the frequency modulated DC-DC converter may be non-isolated.

In some embodiments, the desired frequency spread may be determined based on a desired average reduction level of electromagnetic interference noise EMI.

In some embodiments, the pre-conditioner may be configured to: generating a varying output voltage as an input voltage of the frequency modulated DC-DC converter from a varying reference voltage.

The varying portion of the reference voltage is referred to as the reference modulation voltage. It can be determined, for example, according to the following equation:

V_{ref_modulation}＝f_sw/G_{ref_DCbus}G_{DCbus_f} (1)，

wherein f is_swIs the operating frequency, G, of said frequency modulated DC-DC converter_{DCbus_f}Is a transfer function from an input voltage to an operating frequency of said frequency modulated DC-DC converter, G_{ref_DCbus}Is a transfer function of the pre-conditioner from a reference voltage to an output voltage.

Optionally, the pre-conditioner may comprise a PWM converter.

The PWM converter may comprise a PWM AC-DC converter, and/or may comprise a PWM DC-DC converter.

Optionally, the pre-conditioner may comprise a boost converter.

Optionally, the pre-conditioner may comprise a buck converter.

According to a third aspect of the present disclosure, there is provided a switching power supply including: a pre-conditioner according to the second aspect of the present disclosure; and a frequency modulated DC-DC converter. Wherein the output of the pre-conditioner is connected to the input of the frequency modulated DC-DC converter.

According to an embodiment of the present disclosure, a scheme for reducing average EMI noise for a frequency modulated converter is provided. A frequency-modulated switching power supply according to an embodiment of the present disclosure may naturally cause a tuning of the switching frequency by pre-tuning the input voltage of the frequency-modulated converter, spreading the switching noise spectrum, reducing the average EMI noise level, and thus reducing the size requirements for the required EMI filter.

Drawings

The above and other features of the present disclosure will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:

fig. 1 schematically shows an example of a frequency modulated DC-DC converter.

Fig. 2 schematically illustrates a flow chart of a method of reducing average electromagnetic interference, EMI, for a frequency modulated DC-DC converter according to an embodiment of the present disclosure.

Fig. 3 schematically illustrates an example of a pre-conditioner and a frequency modulated DC-DC converter for which it is used, according to an embodiment of the disclosure.

Fig. 4 schematically shows an example of a structure under test (UUT) comprising a cascaded boost converter and a frequency modulated LLC converter.

Fig. 5 schematically illustrates an example of a structure under test (UUT) obtained by applying DC bus modulation of an embodiment of the disclosure to the structure of fig. 4.

FIG. 6 is a graph illustrating EMI test results of the structure under test of FIG. 4.

Fig. 7 shows an example of a reference modulation voltage.

FIG. 8 is a graph illustrating EMI test results of the structure under test of FIG. 5.

In the drawings, like reference characters designate the same or similar elements.

Detailed Description

The embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the present disclosure should not be limited to the specific embodiments described below. In addition, for the sake of brevity, detailed descriptions of well-known technologies not directly related to the present disclosure are omitted to prevent confusion of understanding of the present disclosure.

Fig. 1 shows an example of a frequency modulated DC-DC converter.

As shown, the DC-DC converter converts one kind of direct current (input voltage) into another kind of direct current (output voltage), thereby realizing voltage conversion. As is known in the art, the frequency-modulated DC-DC converter shown in fig. 1 may be any converter topology used in a frequency-modulated switching power supply, and during normal operation, the pulse width of the driving signal is kept constant, and the relationship between the output voltage and the input voltage is adjusted by the difference in the frequency of occurrence of pulses.

In the prior art, in order to obtain a stable output voltage, it is generally necessary to provide a stable input voltage. However, fluctuations in the input voltage are often unavoidable. To obtain a stable output, the DC-DC converter typically includes a feedback control loop. When the output voltage fluctuates, the frequency-modulated DC-DC converter can change the frequency of the pulse through the adjustment of the feedback control loop, thereby realizing the control and adjustment of the circuit to stabilize the output voltage.

The EMI noise reduction problem of frequency modulated DC-DC converters is considered below.

As mentioned before, direct switching frequency modulation is not suitable for frequency modulated converters, since a change in the switching frequency affects the relationship between the output voltage and the input voltage, causing the output voltage to jitter, which is undesirable.

Instead of conventionally providing a stable input voltage for output voltage stabilization, the present disclosure proposes to pre-adjust the input voltage of the frequency modulated converter such that the adjusted voltage has a predefined pattern of variations, the adjusted voltage having the predefined variations being taken as the input voltage of the frequency modulated converter. As the input voltage varies, the frequency modulated converter will vary its switching frequency according to its feedback control loop to maintain a stable output voltage. Thus, according to the embodiments of the present disclosure, the switching frequency is naturally modulated by purposefully changing the input voltage using the feedback control function inherent to the frequency-modulated DC-DC converter, the spectrum of the switching noise is expanded, and the average EMI noise level is reduced.

Fig. 2 illustrates a flow chart of a method 200 of reducing average electromagnetic interference EMI for a frequency modulated DC-DC converter according to an embodiment of the present disclosure.

As shown, in step S210, an input voltage is acquired. The input voltage may be either direct current or alternating current.

In step S220, the acquired input voltage is pre-adjusted to have a predefined variation. The predefined variation may be determined based on an expected average reduction level of electromagnetic interference noise EMI, circuit design, and/or experimentation.

In the case where the input voltage is an alternating current, it is necessary to convert the alternating current into a direct current. This AC-DC conversion may be implemented using any known or future developed AC-DC converter and will not be described herein. The main idea of the disclosed embodiment is that the obtained direct current (which may be the direct current obtained directly in step S210 or the direct current obtained by AC-DC converting the alternating current in step S210) is modulated to have a predefined variation.

In step S230, the regulated voltage is provided as an input voltage of the frequency modulated DC-DC converter. The input voltage of the frequency modulated DC-DC converter has a predefined variation which will cause the frequency modulated DC-DC converter to change its operating frequency for the output voltage to be stable, thereby achieving the desired frequency spread.

With the method 200, the spectrum of the switching noise of a frequency modulated DC-DC converter can be naturally spread, reducing the average EMI noise level.

Fig. 3 illustrates a pre-conditioner 300 and a frequency modulated DC-DC converter 400 for use therewith, in accordance with an embodiment of the present disclosure.

The frequency modulated DC-DC converter 400 may be one specific example of the converter shown in fig. 1.

The pre-conditioner 300 is configured to generate a varying output voltage as an input voltage of the frequency modulated DC-DC converter from a varying reference voltage. The preconditioner 300 may implement the method 200 shown in fig. 2.

The pre-conditioner 300 may be implemented as a voltage converter including an input terminal, a reference voltage terminal, and an output terminal.

The input of pre-conditioner 300 may be configured to receive an input voltage.

The reference voltage terminal of pre-conditioner 300 may be configured to receive a reference voltage, wherein the reference voltage includes a varying portion.

Preconditioner 300 operates to convert the received input voltage to an output voltage, also referred to in fig. 3 as a DC bus (DC bus) voltage, based on a reference voltage. The DC bus voltage varies with a variation of the reference voltage.

The output of the pre-conditioner 300 may be configured to provide the DC bus voltage as the input voltage of the frequency modulated DC-DC converter.

The input voltage received at the input of pre-conditioner 300 may be either ac or dc. Depending on the type of input voltage, the pre-conditioner 300 will select different converters accordingly. If the input voltage is AC, then pre-conditioner 300 may select an AC-DC converter. If the input voltage is direct current, pre-conditioner 300 may select a DC-DC converter. Generally, pre-conditioner 300 may select a PWM converter.

The pre-conditioner 300 may be implemented using an existing voltage converter. The difference is that the reference voltage terminal of the voltage converter in the prior art is usually connected to a constant reference voltage, whereas the reference voltage of the voltage converter when used as a preconditioner in the present application will use a reference voltage with predefined variations instead of a constant voltage. For the sake of simplicity, this varying part of the reference voltage is also referred to as reference modulation voltage in the following. By controlling the variation of the reference voltage, the output voltage (DC bus voltage) of the pre-conditioner 300 can be controlled to vary according to a desired pattern.

The pre-conditioner 300 is connected in cascade with a frequency modulated DC-DC converter 400. The frequency modulated DC-DC converter 400 may be isolated or non-isolated. The present disclosure is not limited in this respect. The DC bus voltage fed to the frequency modulated DC-DC converter 400 is controlled to vary according to the desired pattern so that the frequency modulated DC-DC converter 400 will respond by varying its switching frequency to stabilize the output voltage and achieve the purpose of spreading.

In order to achieve the goal of reducing the average EMI noise of a frequency modulated DC-DC converter, the operating frequency of the converter (i.e. the switching frequency f) should be considered_sw) And its variation pattern to achieve effective average noise reduction. For example, typical conducted EMI specifications require that devices meet both quasi-peak and mean limits. Common standards such as FCC15, EN55022 and Cispr 22 specify mean limits that are 13dBuV below the quasi-peak limit for class a and 10dBuV below that required for class B. In practical cases, the average EMI noise level may be similar to the quasi-peak level, depending on the operating conditions and converter topology. Furthermore, the operating frequency spread range of the converter should be larger than the bandwidth of the band pass filter of the EMI measurement device according to the EMI standard in order to obtain an average noise reduction of the fundamental frequency component. For conducted EMI standards such as FCC15 and EN55022, the bandwidth of the bandpass filter is 9 kHz. This determines the switching frequency f_swThe spread spectrum range and the variation pattern of (c).

As previously mentioned, as the input voltage varies, the frequency modulated converter will vary its switching frequency according to its feedback control loop to maintain a stable output voltage. Operating frequency f of the frequency modulated DC-DC converter 400_swAnd an input voltage V_{DC_bus}The relationship between is determined by the topology of the converter 400 and can be expressed as follows：

f_sw＝V_{DC_bus}G_{DCbus_f} (1)

Wherein f is_swIs the operating frequency, V, of the frequency modulated DC-DC converter 400_{DC_bus}Is the input voltage, G, of the frequency modulated DC-DC converter 400_{DCbus_f}Is the transfer function from the input voltage to the operating frequency of the frequency modulated DC-DC converter 400.

F is determined at a mean reduction level according to the desired electromagnetic interference noise EMI_swAfter the desired extension range and variation pattern, V can be easily obtained as follows according to equation (1)_{DC_bus}Variation pattern of (2):

V_{DC_bus}＝f_sw/G_{DCbus_f} (2)。

DC-DC converter 400, G for a given frequency modulation_{DCbus_f}Is determined, the input voltage V may then be determined according to the desired mean reduction level of the electromagnetic interference noise EMI_DC-busDesired range and style of variation.

Is aware of V_DC-busThe desired range and pattern of variation of the reference voltage may be determined. Assume that the transfer function of pre-conditioner 300 from the reference voltage to the output voltage is G_{ref_DCbus}Then, then

V_DC-bus＝V_{ref_modulation}G_{ref_DCbus} (3)，

Wherein V_{ref_modulation}Is the reference modulation voltage, V, of the pre-conditioner 300_DC-busIs the output voltage, G, of the pre-conditioner 300_{ref_DCbus}Is the transfer function of the pre-conditioner 300 from the reference voltage to the output voltage.

Combining the formulas (1) and (3) to obtain

f_sw＝V_{ref_modulation}G_{ref_DCbus}G_{DCbus_f} (4)

V_{ref_modulation}＝f_sw/(G_{ref_DCbus}G_{DCbus_f}) (5)。

By equation (5), can be based on f_swIs desiredSpread spectrum range and variation pattern to determine the reference modulation voltage V of pre-conditioner 300_{ref_modulation}The variation pattern of (2).

It should be understood that the disclosed embodiments are not limited to f_sw，V_{ref_modulation}And a method of determining the modulation range or the variation pattern. Indeed, they may be determined based on desired levels of EMI noise reduction, circuit design, and/or even experimentation.

The embodiment shown in fig. 3 controls the DC bus voltage fed to the frequency modulated DC-DC converter 400 to vary according to the desired pattern by pre-adjusting the input voltage so that the frequency modulated DC-DC converter 400 will respond by changing its switching frequency, expanding the switching noise spectrum, reducing the average EMI noise level, and thus reducing the size requirements for the required EMI filter.

The effect of reducing the average EMI noise of the embodiments of the present disclosure is described below by way of a practical example.

Fig. 4 shows a structure under test (UUT) comprising a cascaded boost converter and a frequency modulated LLC converter, wherein the DC bus modulation of the embodiments of the present disclosure is not applied, i.e. the reference voltage used by the boost converter is a constant voltage. This configuration is common in many applications, including server power supplies, where the boost converter can accept both ac and dc inputs.

Figure 6 shows an EMI plot of UUT output required by EN55022A at 240VDC input and 1500W for the structure under test of figure 4. The quasi-peak, quasi-peak minus-8 dB, mean and mean-8 dB limits are shown on the graph, along with the measured quasi-peak trace and the measured mean trace, respectively. The measurement result meets the EN55022A limit, but the average noise level does not meet the requirement of 8dB margin around 163kHz and 272kHz according to the product specification of the UUT.

In contrast, applying the DC bus modulation of the embodiments of the present disclosure to the structure under test of fig. 4 results in the structure under test of fig. 5. The arrangement of fig. 5 can be seen as a specific example of the arrangement of fig. 3, where the pre-conditioner 300 is a digitally controlled boost converter and the frequency modulated DC-DC converter 400 is a frequency modulated LLC converter. In the test, the DC bus voltage was modulated using a sinusoidal voltage of 10V peak-to-peak as shown in fig. 7 as a reference modulation voltage. The modulation signal is generated by a digital controller that computationally modulates a reference voltage for DC bus voltage modulation. The results of testing the UUT of fig. 5 under the same other input and output conditions as fig. 6 are shown in fig. 8. As shown in fig. 8, where the EMI noise spectrum spreading is observed, the average noise level is much lower and meets the average-8 dB requirement without modifying the EMI filter.

According to the examples shown in fig. 4 to 8, it can be seen that the average EMI noise of the frequency modulated DC-DC converter can be effectively reduced by applying the DC bus modulation proposed by the embodiments of the present disclosure.

It should be understood that fig. 3 illustrates not only an example of a preconditioner according to the present disclosure. In combination with the pre-conditioner and the DC-DC converter cascaded therewith shown in fig. 3, a new type of switching power supply is also formed, which has a reduced average EMI noise.

It should be noted that in the above description, the technical solutions of the present application are shown by way of example only, but the present application is not meant to be limited to the above steps and unit structures. Steps and cell structures may be adjusted and chosen as desired, where possible. Accordingly, certain steps and elements are not essential elements for implementing the general inventive concept of the present application. Therefore, the technical features necessary for the present application are only limited by the minimum requirements capable of realizing the general inventive concept of the present application, and are not limited by the above specific examples.

Further, the reference modulation signal in the present disclosure may be implemented using, but not limited to, a micro control unit MCU, a digital signal processor, a chip, and/or discrete components.

The present application has thus been described with reference to the preferred embodiments. It should be understood that various other changes, substitutions, and additions may be made by those skilled in the art without departing from the spirit and scope of the present application. Accordingly, the scope of the present application is not limited to the particular embodiments described above, but is instead defined by the following claims.