Buck-boost DC / DC converter feedback loop parameter design method

Abstract

The invention provides a buck-boost DC / DC converter feedback loop parameter design method. The method comprises the following steps: establishing a feedback loop model; the feedback loop model is divided into a voltage reference unit feedback link, a photoelectric coupler primary part feedback link, a photoelectric coupler feedback link and a photoelectric coupler secondary part feedback link; constructing a transfer function of a feedback loop model based on the transfer function of the feedback link of the voltage reference unit, the transfer function of the feedback link of the primary part of the photoelectric coupler, the transfer function of the feedback link of the photoelectric coupler and the transfer function of the feedback link of the secondary part of the photoelectric coupler; obtaining expressions of zero pole cutoff frequency, pole frequency and zero point frequency of the feedback loop model based on the transfer function of the feedback loop model; and obtaining the resistance values of a first resistor, a second resistor and a third resistor and the capacitance values of a first capacitor and a second capacitor of the feedback loop model based on the expressions of the zero pole cutoff frequency, the pole frequency and the zero point frequency of the feedback loop model.

Description

Technical Field

[0001] The invention relates to the technical field of switching power supplies, and in particular to a method for designing feedback loop parameters of a buck-boost DC / DC converter. Background Art

[0002] In practical applications, many DC / DC converters use TL431 and optocoupler feedback loops. TL431 can not only provide an accurate voltage reference, but also can be used as a traditional operational amplifier in the feedback loop; while the optocoupler can not only isolate the control signal from the power signal, but also has a function similar to a transconductance operational amplifier.

[0003] At present, the TL431 and optocoupler feedback loop realizes the parameter design of the loop by repeatedly debugging the empirical value. This method needs to be debugged many times, and the design margin cannot be guaranteed. Summary of the invention

[0004] The present invention provides a buck-boost DC / DC converter feedback loop parameter design method, which can solve the technical problems in the prior art that the parameter design of the feedback loop needs to be debugged multiple times and the design margin cannot be guaranteed.

[0005] The present invention provides a method for designing feedback loop parameters of a buck-boost DC / DC converter, the method comprising:

[0006] A feedback loop model of a buck-boost DC / DC converter is established, wherein the feedback loop model includes a photoelectric coupler, a voltage reference unit, a reference resistor, a first resistor, a second resistor, a third resistor, a first capacitor, and a second capacitor; the secondary part input end of the photoelectric coupler is respectively connected to the first end of the second capacitor and the first end of the third resistor and then connected to the control signal compensation end of the controlled object, and the secondary part output end is respectively connected to the second end of the second capacitor and the second end of the third resistor and then connected to the input ground; the primary part input end of the photoelectric coupler is connected to the first end of the second resistor, and the primary part output end is respectively connected to the first end of the first capacitor and the cathode of the voltage reference unit; the reference end of the voltage reference unit is respectively connected to the second end of the first capacitor, the first end of the first resistor, and the first end of the reference resistor, and the anode is connected to the second end of the reference resistor and then connected to the output ground; the second end of the first resistor is connected to the second end of the second resistor and then connected to the output end of the controlled object;

[0007] The feedback loop model is divided into a voltage reference unit feedback link, a photoelectric coupler primary part feedback link, a photoelectric coupler feedback link and a photoelectric coupler secondary part feedback link, wherein the voltage reference unit feedback link includes a voltage reference unit, a reference resistor, a first resistor and a first capacitor, the photoelectric coupler primary part feedback link includes a photoelectric coupler primary part and a second resistor, and the photoelectric coupler secondary part feedback link includes a photoelectric coupler secondary part, a third resistor and a second capacitor;

[0008] A transfer function of a feedback link of a voltage reference unit is constructed based on the output voltage and the cathode voltage of the voltage reference unit;

[0009] A transfer function of the feedback link of the primary part of the photocoupler is constructed based on the primary current of the photocoupler and the cathode voltage of the voltage reference unit;

[0010] Constructing the transfer function of the feedback link of the optocoupler based on the primary current and secondary current of the optocoupler;

[0011] Constructing a transfer function of the feedback link of the secondary part of the photocoupler based on the capacitance value of the second capacitor and the resistance value of the third resistor;

[0012] Constructing a transfer function of a feedback loop model based on a transfer function of a voltage reference unit feedback link, a transfer function of a primary part feedback link of a photocoupler, a transfer function of a photocoupler feedback link, and a transfer function of a secondary part feedback link of a photocoupler;

[0013] Based on the transfer function of the feedback loop model, the expressions of the zero-pole cutoff frequency, pole frequency and zero frequency of the feedback loop model are obtained; wherein the ratio of the open-loop cutoff frequency of the feedback loop model to the DC gain of the object under test is used as the zero-pole cutoff frequency of the feedback loop model; the output pole frequency of the controlled object is used as the zero frequency of the feedback loop model; and the equivalent series zero frequency of the controlled object is used as the pole frequency of the feedback loop model;

[0014] The resistance values ​​of the first resistor, the second resistor, and the third resistor and the capacitance values ​​of the first capacitor and the second capacitor of the feedback loop model are obtained based on the expressions of the zero-pole cutoff frequency, the pole frequency, and the zero frequency of the feedback loop model.

[0015] Preferably, the transfer function of the voltage reference unit feedback link is constructed by the following formula:

[0016]

[0017] Where H1(s) represents the transfer function of the voltage reference unit feedback link, s represents the transfer factor, V o (s) represents the output voltage, V TL431(s) represents the cathode voltage of the voltage reference unit, R1 represents the resistance value of the first resistor, and C1 represents the capacitance value of the first capacitor.

[0018] Preferably, the transfer function of the feedback link of the primary part of the optocoupler is constructed by the following formula:

[0019]

[0020] in,

[0021] Where H2(s) represents the transfer function of the feedback link of the primary part of the optocoupler, I f (s) represents the primary current of the optocoupler, R2 represents the resistance value of the second resistor, V f (s) represents the primary voltage of the photocoupler.

[0022] Preferably, the transfer function of the photoelectric coupler feedback link is constructed by the following formula:

[0023]

[0024] Where H3(s) represents the transfer function of the optocoupler feedback link, I c (s) represents the secondary current of the photocoupler, and CTR represents the current constant ratio.

[0025] Preferably, the transfer function of the feedback link of the secondary part of the optocoupler is constructed by the following formula:

[0026]

[0027] Wherein, H4(s) represents the transfer function of the feedback link of the secondary part of the optocoupler, C2 represents the capacitance value of the second capacitor, R3 represents the resistance value of the third resistor, and / / represents parallel connection.

[0028] Preferably, the transfer function of the feedback loop model is constructed by the following formula:

[0029]

[0030] Where H(s) represents the transfer function of the feedback loop model.

[0031] Preferably, the expression of the zero-pole cutoff frequency is obtained by the following formula:

[0032]

[0033] The expression for the pole frequency is obtained by the following formula:

[0034]

[0035] The expression for the zero frequency is obtained by the following formula:

[0036]

[0037] In the formula, f p0 represents the zero-pole cutoff frequency, f p represents the pole frequency, f z Indicates the zero frequency.

[0038] Preferably, obtaining the resistance values ​​of the first resistor, the second resistor, and the third resistor and the capacitance values ​​of the first capacitor and the second capacitor of the feedback loop model based on the expressions of the zero-pole cutoff frequency, the pole frequency, and the zero frequency of the feedback loop model includes:

[0039] When setting the voltage division, the resistance value of the first resistor is selected;

[0040] Substitute the output pole frequency of the controlled object into the expression of the zero frequency of the feedback loop model to obtain the capacitance value of the first capacitor;

[0041] When setting the photoelectric coupler to work in static state, the resistance value of the second resistor is selected;

[0042] Substitute the ratio of the open-loop cutoff frequency of the feedback loop model to the DC gain of the object under test into the expression of the zero-pole cutoff frequency of the feedback loop model to obtain the resistance value of the third resistor;

[0043] Substitute the equivalent series zero frequency of the controlled object into the expression of the pole frequency of the feedback loop model to obtain the capacitance value of the second capacitor.

[0044] Preferably, the capacitance value of the first capacitor is obtained by the following formula:

[0045]

[0046] The resistance value of the third resistor is obtained by the following formula:

[0047]

[0048] in,

[0049] The capacitance value of the second capacitor is obtained by the following formula:

[0050]

[0051] In the formula, f P ′ represents the output pole frequency of the controlled object, f cross represents the open-loop cutoff frequency of the feedback loop model, G0 represents the DC gain of the object under test, and f esr Indicates the equivalent series zero frequency of the controlled object.

[0052] Preferably, the open-loop cut-off frequency of the feedback loop model is set to 1 / 3 of the switching frequency of the controlled object.

[0053] By applying the technical solution of the present invention, a feedback loop model of a buck-boost DC / DC converter is established, and the feedback loop model is divided into a voltage reference unit feedback link, a photoelectric coupler primary part feedback link, a photoelectric coupler feedback link and a photoelectric coupler secondary part feedback link; the transfer function of each link is obtained respectively, so as to obtain the transfer function of the feedback loop model; finally, parameter design is performed based on the transfer function of the feedback loop model, without the need to debug the parameters multiple times, and the designed parameters have a margin, thereby improving the loop stability of the buck-boost DC / DC converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The included drawings are used to provide a further understanding of the embodiments of the present invention, which constitute a part of the specification, are used to illustrate the embodiments of the present invention, and together with the text description, explain the principles of the present invention. Obviously, the drawings in the following description are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0055] Figure 1 A schematic diagram of a feedback loop of a buck-boost DC / DC converter provided according to an embodiment of the present invention is shown;

[0056] Figure 2 Shows Figure 1 Schematic diagram of the feedback link of the voltage reference unit in the feedback loop;

[0057] Figure 3 Shows Figure 1 Schematic diagram of the feedback link of the primary part of the optocoupler in the feedback loop;

[0058] Figure 4 Shows Figure 1 Schematic diagram of the feedback link of the secondary part of the optocoupler in the feedback loop. DETAILED DESCRIPTION

[0059] It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0061] Unless otherwise specifically stated, the relative arrangement of the parts and steps described in these embodiments, numerical expressions and numerical values ​​do not limit the scope of the present invention. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be regarded as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0062] The present invention provides a method for designing feedback loop parameters of a buck-boost DC / DC converter, the method comprising:

[0063] Establish the feedback loop model of the buck-boost DC / DC converter, such as Figure 1As shown, the feedback loop model includes a photoelectric coupler, a voltage reference unit, a reference resistor, a first resistor, a second resistor, a third resistor, a first capacitor and a second capacitor; the secondary part input end of the photoelectric coupler is respectively connected to the first end of the second capacitor and the first end of the third resistor and then connected to the control signal compensation end of the controlled object, and the secondary part output end is respectively connected to the second end of the second capacitor and the second end of the third resistor and then connected to the input ground; the primary part input end of the photoelectric coupler is connected to the first end of the second resistor, and the primary part output end is respectively connected to the first end of the first capacitor and the cathode of the voltage reference unit; the reference end of the voltage reference unit is respectively connected to the second end of the first capacitor, the first end of the first resistor, and the first end of the reference resistor, and the anode is connected to the second end of the reference resistor and then connected to the output ground; the second end of the first resistor is connected to the second end of the second resistor and then connected to the output end of the controlled object;

[0064] The feedback loop model is divided into the voltage reference unit feedback link, the optocoupler primary part feedback link, the optocoupler feedback link and the optocoupler secondary part feedback link, such as Figure 2-Figure 4 As shown, the voltage reference unit feedback link includes a voltage reference unit, a reference resistor, a first resistor, and a first capacitor, the photoelectric coupler primary part feedback link includes a photoelectric coupler primary part and a second resistor, and the photoelectric coupler secondary part feedback link includes a photoelectric coupler secondary part, a third resistor, and a second capacitor; wherein the reference resistor is a known value;

[0065] A transfer function of a feedback link of a voltage reference unit is constructed based on the output voltage and the cathode voltage of the voltage reference unit;

[0066] A transfer function of the feedback link of the primary part of the photocoupler is constructed based on the primary current of the photocoupler and the cathode voltage of the voltage reference unit;

[0067] Constructing the transfer function of the feedback link of the optocoupler based on the primary current and secondary current of the optocoupler;

[0068] Constructing a transfer function of the feedback link of the secondary part of the photocoupler based on the capacitance value of the second capacitor and the resistance value of the third resistor;

[0069] Constructing a transfer function of a feedback loop model based on a transfer function of a voltage reference unit feedback link, a transfer function of a primary part feedback link of a photocoupler, a transfer function of a photocoupler feedback link, and a transfer function of a secondary part feedback link of a photocoupler;

[0070] Based on the transfer function of the feedback loop model, the expressions of the zero-pole cutoff frequency, pole frequency and zero frequency of the feedback loop model are obtained; wherein the ratio of the open-loop cutoff frequency of the feedback loop model to the DC gain of the object under test is used as the zero-pole cutoff frequency of the feedback loop model; the output pole frequency of the controlled object is used as the zero frequency of the feedback loop model; and the equivalent series zero frequency of the controlled object is used as the pole frequency of the feedback loop model;

[0071] The resistance values ​​of the first resistor, the second resistor, and the third resistor and the capacitance values ​​of the first capacitor and the second capacitor of the feedback loop model are obtained based on the expressions of the zero-pole cutoff frequency, the pole frequency, and the zero frequency of the feedback loop model.

[0072] The present invention establishes a feedback loop model of a buck-boost DC / DC converter, and divides the feedback loop model into a voltage reference unit feedback link, a photoelectric coupler primary part feedback link, a photoelectric coupler feedback link and a photoelectric coupler secondary part feedback link; then respectively obtains the transfer function of each link, thereby obtaining the transfer function of the feedback loop model; finally, based on the transfer function of the feedback loop model, parameter design is performed, and there is no need to debug the parameters multiple times, and the designed parameters have a margin, thereby improving the loop stability of the buck-boost DC / DC converter.

[0073] According to an embodiment of the present invention, Figure 2 As shown, the transfer function of the voltage reference unit feedback link is constructed by the following formula:

[0074]

[0075] Where H1(s) represents the transfer function of the voltage reference unit feedback link, s represents the transfer factor, V o (s) represents the output voltage, V TL431 (s) represents the cathode voltage of the voltage reference unit, R1 represents the resistance value of the first resistor, and C1 represents the capacitance value of the first capacitor.

[0076] According to an embodiment of the present invention, Figure 3 As shown, the primary voltage V f (s) is approximately a constant voltage source, which is equivalent to a short circuit for small AC signals. Therefore, the transfer function of the feedback link of the primary part of the optocoupler is:

[0077]

[0078] in,

[0079] Where H2(s) represents the transfer function of the feedback link of the primary part of the optocoupler, I f(s) represents the primary current of the optocoupler, R2 represents the resistance value of the second resistor, V f (s) represents the primary voltage of the photocoupler.

[0080] According to an embodiment of the present invention, the transfer function of the feedback link of the optocoupler is constructed by the following formula:

[0081]

[0082] Where H3(s) represents the transfer function of the optocoupler feedback link, I c (s) represents the secondary current of the photocoupler, and CTR represents the current constant ratio.

[0083] According to an embodiment of the present invention, Figure 4 As shown, the transfer function of the feedback link of the secondary side of the optocoupler is constructed by the following formula:

[0084]

[0085] Wherein, H4(s) represents the transfer function of the feedback link of the secondary part of the optocoupler, C2 represents the capacitance value of the second capacitor, R3 represents the resistance value of the third resistor, and / / represents parallel connection.

[0086] According to one embodiment of the present invention, the transfer function of the feedback loop model is constructed by the following formula:

[0087]

[0088] Where H(s) represents the transfer function of the feedback loop model.

[0089] According to an embodiment of the present invention, the expression of the zero-pole cutoff frequency is obtained by the following formula:

[0090]

[0091] The expression for the pole frequency is obtained by the following formula:

[0092]

[0093] The expression for the zero frequency is obtained by the following formula:

[0094]

[0095] In the formula, f p0 represents the zero-pole cutoff frequency, f p represents the pole frequency, f z Indicates the zero frequency.

[0096] According to an embodiment of the present invention, obtaining the resistance values ​​of the first resistor, the second resistor, and the third resistor and the capacitance values ​​of the first capacitor and the second capacitor of the feedback loop model based on the expressions of the zero-pole cutoff frequency, the pole frequency, and the zero frequency of the feedback loop model includes:

[0097] When setting the voltage division, the resistance value of the first resistor is selected;

[0098] Substitute the output pole frequency of the controlled object into the expression of the zero frequency of the feedback loop model to obtain the capacitance value of the first capacitor;

[0099] When setting the photoelectric coupler to work in static state, the resistance value of the second resistor is selected;

[0100] Substitute the ratio of the open-loop cutoff frequency of the feedback loop model to the DC gain of the object under test into the expression of the zero-pole cutoff frequency of the feedback loop model to obtain the resistance value of the third resistor;

[0101] Substitute the equivalent series zero frequency of the controlled object into the expression of the pole frequency of the feedback loop model to obtain the capacitance value of the second capacitor.

[0102] According to an embodiment of the present invention, the capacitance value of the first capacitor is obtained by the following formula:

[0103]

[0104] The resistance value of the third resistor is obtained by the following formula:

[0105]

[0106] in,

[0107] The capacitance value of the second capacitor is obtained by the following formula:

[0108]

[0109] In the formula, f P ′ represents the output pole frequency of the controlled object, f cross represents the open-loop cutoff frequency of the feedback loop model, G0 represents the DC gain of the object under test, and f esr Indicates the equivalent series zero frequency of the controlled object.

[0110] According to an embodiment of the present invention, the open-loop cutoff frequency of the feedback loop model is set to 1 / 3 of the switching frequency of the controlled object. In addition, it is necessary to ensure that the open-loop cutoff frequency is significantly lower than the zero frequency f of the right half plane of the controlled object. RHP .

[0111] According to an embodiment of the present invention, the voltage reference unit adopts TL431, and the photoelectric coupler adopts ACPL-217.

[0112] In summary, the present invention provides a method for designing feedback loop parameters of a buck-boost DC / DC converter, establishes a feedback loop model of the buck-boost DC / DC converter, and divides the feedback loop model into a voltage reference unit feedback link, a photoelectric coupler primary part feedback link, a photoelectric coupler feedback link, and a photoelectric coupler secondary part feedback link; then obtains the transfer function of each link respectively, thereby obtaining the transfer function of the feedback loop model; finally, based on the transfer function of the feedback loop model, parameter design is performed, without the need to debug the parameters multiple times, and the designed parameters have a margin, thereby improving the loop stability of the buck-boost DC / DC converter.

[0113] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0114] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0115] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for designing feedback loop parameters of a buck-boost DC / DC converter, characterized in that: The method comprises: A feedback loop model of a buck-boost DC / DC converter is established, wherein the feedback loop model includes a photoelectric coupler, a voltage reference unit, a reference resistor, a first resistor, a second resistor, a third resistor, a first capacitor, and a second capacitor; the secondary part input end of the photoelectric coupler is respectively connected to the first end of the second capacitor and the first end of the third resistor and then connected to the control signal compensation end of the controlled object, and the secondary part output end is respectively connected to the second end of the second capacitor and the second end of the third resistor and then connected to the input ground; the primary part input end of the photoelectric coupler is connected to the first end of the second resistor, and the primary part output end is respectively connected to the first end of the first capacitor and the cathode of the voltage reference unit; the reference end of the voltage reference unit is respectively connected to the second end of the first capacitor, the first end of the first resistor, and the first end of the reference resistor, and the anode is connected to the second end of the reference resistor and then connected to the output ground; the second end of the first resistor is connected to the second end of the second resistor and then connected to the output end of the controlled object; The feedback loop model is divided into a voltage reference unit feedback link, a photoelectric coupler primary part feedback link, a photoelectric coupler feedback link and a photoelectric coupler secondary part feedback link, wherein the voltage reference unit feedback link includes a voltage reference unit, a reference resistor, a first resistor and a first capacitor, the photoelectric coupler primary part feedback link includes a photoelectric coupler primary part and a second resistor, and the photoelectric coupler secondary part feedback link includes a photoelectric coupler secondary part, a third resistor and a second capacitor; A transfer function of a feedback link of a voltage reference unit is constructed based on the output voltage and the cathode voltage of the voltage reference unit; A transfer function of the feedback link of the primary part of the photocoupler is constructed based on the primary current of the photocoupler and the cathode voltage of the voltage reference unit; Constructing the transfer function of the feedback link of the optocoupler based on the primary current and secondary current of the optocoupler; Constructing a transfer function of the feedback link of the secondary part of the photocoupler based on the capacitance value of the second capacitor and the resistance value of the third resistor; Constructing a transfer function of a feedback loop model based on a transfer function of a voltage reference unit feedback link, a transfer function of a primary part feedback link of a photocoupler, a transfer function of a photocoupler feedback link, and a transfer function of a secondary part feedback link of a photocoupler; Based on the transfer function of the feedback loop model, the expressions of the zero-pole cutoff frequency, pole frequency and zero frequency of the feedback loop model are obtained; wherein the ratio of the open-loop cutoff frequency of the feedback loop model to the DC gain of the object under test is used as the zero-pole cutoff frequency of the feedback loop model; the output pole frequency of the controlled object is used as the zero frequency of the feedback loop model; and the equivalent series zero frequency of the controlled object is used as the pole frequency of the feedback loop model; The resistance values ​​of the first resistor, the second resistor, and the third resistor and the capacitance values ​​of the first capacitor and the second capacitor of the feedback loop model are obtained based on the expressions of the zero-pole cutoff frequency, the pole frequency, and the zero frequency of the feedback loop model.

2. The method according to claim 1, characterized in that The transfer function of the voltage reference unit feedback link is constructed by the following formula: Where H1(s) represents the transfer function of the voltage reference unit feedback link, s represents the transfer factor, V o (s) represents the output voltage, V TL431 (s) represents the cathode voltage of the voltage reference unit, R1 represents the resistance value of the first resistor, and C1 represents the capacitance value of the first capacitor.

3. The method according to claim 1, characterized in that The transfer function of the feedback link of the primary part of the optocoupler is constructed by the following formula: in, Where H2(s) represents the transfer function of the feedback link of the primary part of the optocoupler, I f (s) represents the primary current of the optocoupler, R2 represents the resistance value of the second resistor, V f (s) represents the primary voltage of the photocoupler.

4. The method according to claim 1, characterized in that: The transfer function of the optocoupler feedback link is constructed by the following formula: Where H3(s) represents the transfer function of the optocoupler feedback link, I c (s) represents the secondary current of the photocoupler, and CTR represents the current constant ratio.

5. The method according to claim 1, characterized in that The transfer function of the feedback link of the secondary side of the optocoupler is constructed by the following formula: Wherein, H4(s) represents the transfer function of the feedback link of the secondary part of the optocoupler, C2 represents the capacitance value of the second capacitor, R3 represents the resistance value of the third resistor, and / / represents parallel connection.

6. The method according to claim 1, characterized in that The transfer function of the feedback loop model is constructed as follows: Where H(s) represents the transfer function of the feedback loop model.

7. The method according to claim 1, characterized in that The expression for the zero-pole cutoff frequency is obtained by the following formula: The expression for the pole frequency is obtained by the following formula: The expression for the zero frequency is obtained by the following formula: In the formula, f p0 represents the zero-pole cutoff frequency, f p represents the pole frequency, f z Indicates the zero frequency.

8. The method according to claim 1, characterized in that Obtaining the resistance values ​​of the first resistor, the second resistor, and the third resistor and the capacitance values ​​of the first capacitor and the second capacitor of the feedback loop model based on the expressions of the zero-pole cutoff frequency, the pole frequency, and the zero-point frequency of the feedback loop model includes: When setting the voltage division, the resistance value of the first resistor is selected; Substitute the output pole frequency of the controlled object into the expression of the zero frequency of the feedback loop model to obtain the capacitance value of the first capacitor; When setting the photoelectric coupler to work in static state, the resistance value of the second resistor is selected; Substitute the ratio of the open-loop cutoff frequency of the feedback loop model to the DC gain of the object under test into the expression of the zero-pole cutoff frequency of the feedback loop model to obtain the resistance value of the third resistor; The equivalent series zero frequency of the controlled object is substituted into the expression of the pole frequency of the feedback loop model to obtain the capacitance value of the second capacitor.

9. The method according to claim 1, characterized in that: The capacitance value of the first capacitor is obtained by the following formula: The resistance value of the third resistor is obtained by the following formula: in, The capacitance value of the second capacitor is obtained by the following formula: In the formula, f P ′ represents the output pole frequency of the controlled object, f cross represents the open-loop cutoff frequency of the feedback loop model, G0 represents the DC gain of the object under test, and f esr Indicates the equivalent series zero frequency of the controlled object.

10. The method according to claim 1, characterized in that The open-loop cutoff frequency of the feedback loop model is set to 1 / 3 of the switching frequency of the controlled object.

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