Buck-boost converter and common-mode voltage suppression method thereof

Abstract

The invention discloses a buck-boost converter and a common-mode voltage suppression method thereof, and belongs to the technical field of power electronics, the buck-boost converter comprises a buck-boost module and a common-mode voltage suppression module, and the buck-boost module is connected with the common-mode voltage suppression module; the common-mode voltage suppression module comprises a first winding, a second winding, a first capacitor and a second capacitor, a first end of the first winding is connected with a midpoint of a power inductor of the buck-boost module through the second capacitor, and a second end of the first winding is connected with a power ground; the first end of the second winding is connected with the protection ground through the first capacitor, and the second end of the second winding is connected with the power ground. Common-mode voltage suppression can be achieved only through the passive cancellation winding and the compensation capacitor, an additional auxiliary power supply and a calculation circuit are not needed, the system size can be reduced, and the power density can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a buck-boost converter and a common-mode voltage suppression method thereof. Background Art

[0002] The new generation of wide bandgap power devices has increased the switching frequency of the converter. While the performance and power density of the converter have been greatly improved, it has also brought more serious electromagnetic interference, bringing more challenges to electromagnetic noise suppression technology. Buck-boost converters are widely used in distributed power systems, portable power supply systems, new energy power generation systems and other application scenarios with a wide voltage input range because of their small size, simple circuit, and both boost and buck functions. However, the electromagnetic noise problem they generate cannot be ignored. In addition, users' demand for more energy-saving, more portable, and higher-performance power supplies has driven engineers to continuously pursue higher efficiency, smaller size, and better performance power supply design solutions, which has also brought more challenges to the electromagnetic compatibility design of power supplies. In addition, the high frequency of the converter will also bring serious electromagnetic compatibility problems.

[0003] For buck-boost converters, the switch tube generates a lot of heat during operation. To prevent the switch tube from overheating and damage, an external heat sink is usually connected to the ground. The parasitic capacitance between the switch tube and the heat sink becomes a path for conducting electromagnetic interference. In addition, the semiconductor switch tube in the converter will have a short rising edge and falling edge during the opening and closing process, causing the parasitic capacitance in the converter under high-frequency operation to generate induced electrical signals. These electrical signals will cause the original PWM signal to mutate and generate strong electromagnetic interference noise. Electromagnetic interference (EMI) can pollute the external electromagnetic environment through line conduction and space radiation, affecting the stability of the converter and the external power supply system, reducing the performance of electrical equipment, and in severe cases causing great harm to human health.

[0004] There are two main methods for suppressing electromagnetic interference in buck-boost converters. One is to design an EMI filter based on the spectrum of the original noise, and the other is to adjust the control strategy to effectively attenuate the noise in the circuit. The design of the filter is relatively cumbersome, and the filter is usually large, which reduces the power density of the system. The existing method of reducing noise by adjusting the control strategy is complicated and difficult to implement. Summary of the invention

[0005] The present invention aims to provide a buck-boost converter and a common-mode voltage suppression method thereof, which adopts a passive cancellation method, and makes the equivalent common-mode noise source zero by adding a passive cancellation winding and a compensation capacitor, thereby canceling the common-mode voltage. The circuit structure is simple, the operation is easy, and no complicated calculation is required, and the common-mode voltage suppression effect is obvious.

[0006] To achieve the above object, the technical solution of the present invention is: A buck-boost converter comprises a buck-boost module and a common-mode voltage suppression module, wherein the buck-boost module is connected to the common-mode voltage suppression module; the common-mode voltage suppression module comprises a first winding, a second winding, a first capacitor, and a second capacitor, wherein a first end of the first winding is connected to a midpoint of a power inductor of the buck-boost module via the second capacitor, a second end of the first winding is connected to a power ground, a first end of the second winding is connected to a protection ground via the first capacitor, and a second end of the second winding is connected to a power ground.

[0007] Furthermore, the positions of the same-named ends of the first winding and the second winding are opposite.

[0008] Furthermore, the first winding and the second winding are realized by a transformer.

[0009] Furthermore, the first capacitor C com The value of is: , Among them, the capacitor C pA It is the parasitic capacitance from the midpoint of the bridge arm of the buck-boost module to ground.

[0010] Furthermore, the buck-boost module is a four-switch buck-boost module.

[0011] The present invention also provides a common mode voltage suppression method for a buck-boost converter, comprising: Connecting the first end of the first winding to the midpoint of the power inductor of the buck-boost converter through the second capacitor, and connecting the second end of the first winding to the power ground; connecting the first end of the second winding to the protection ground through the first capacitor, and connecting the second end of the second winding to the power ground; Extract the parasitic capacitance between each part of the buck-boost converter and the protection ground; Establish a common-mode equivalent circuit after adding the first winding and the second winding, and simplify the circuit to obtain the simplest common-mode equivalent circuit; According to the established common-mode equivalent circuit and the simplest common-mode equivalent circuit, the capacitance of the first capacitor is calculated to achieve cancellation of the common-mode voltage.

[0012] Furthermore, the positions of the same-named ends of the first winding and the second winding are opposite.

[0013] Furthermore, the first winding and the second winding are realized by a transformer.

[0014] Furthermore, an impedance analyzer is used to extract the parasitic capacitance between each part of the buck-boost converter and the protection ground.

[0015] Further, according to the established common-mode equivalent circuit and the simplest common-mode equivalent circuit, the capacitance of the first capacitor is calculated, including: According to the common-mode equivalent circuit, the equivalent common-mode noise source V after adding the passive cancellation winding is obtained. ENS The expression is: , In the formula, C com Represents the first capacitor; V Q2 and V Q4 They represent the noise source Q using the substitution theorem. 2 and Q 4 The equivalent noise voltage source is: capacitor C sum Represents the total parasitic capacitance in the simplest common-mode equivalent circuit, and its expression is as follows: , Among them, the capacitor C pC That is, the parasitic capacitance of the input port to ground; capacitance C pE That is, the parasitic capacitance of the negative bus to the ground; capacitance C pD That is, the parasitic capacitance of the output port to ground; capacitance C pA That is, the switch tube Q 1 With the switch tube Q 2 The parasitic capacitance of the bridge arm midpoint to ground; capacitance C pB That is, the switch tube Q 3 With the switch tube Q 4 The parasitic capacitance of the bridge arm midpoint to ground of the bridge arm formed; According to the simplest common-mode equivalent circuit, the common-mode voltage V CM The expression is as follows: ; The equivalent common mode noise source V after adding the passive cancellation winding ENS Substitute the common mode voltage V into the expression CM The expression of common mode voltage V CM =0, the capacitance of the first capacitor is: .

[0016] Beneficial effects: The present invention provides a buck-boost converter and a common-mode voltage suppression method thereof, establishes a common-mode equivalent circuit that takes parasitic capacitance into consideration after adding a passive cancellation winding, and the equivalent circuit is simple to calculate and relatively easy to implement; the passive cancellation winding is used to achieve the effect of introducing a compensation voltage source, and the noise voltage source in the buck-boost converter is canceled, so that the equivalent common-mode noise voltage is zero, and the suppression effect on the common-mode voltage is better; the addition of the cancellation voltage source can be achieved by using a single transformer, and the method is simple and easy to operate; the common-mode voltage suppression can be achieved only by using a passive cancellation winding and a compensation capacitor, and no additional auxiliary power supply and calculation circuit are required, which is beneficial to reducing the system volume and improving the power density.

[0017] In order to make the above features and advantages of the invention more obvious and easy to understand, embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The present invention is a circuit diagram of a buck-boost converter.

[0019] Figure 2 for Figure 1 Schematic diagram of the common-mode equivalent circuit of the buck-boost converter.

[0020] Figure 3 for Figure 1 Schematic diagram of the simplest common-mode equivalent circuit of the buck-boost converter in FIG.

[0021] Figure 4 The present invention is a flowchart of a common-mode voltage suppression method for a buck-boost converter.

[0022] Figure 5 A circuit diagram showing a line impedance stabilization network connected between an input voltage and a buck-boost converter.

[0023] Figure 6 Schematic diagram of the common-mode voltage spectrum of the buck-boost converter before and after passive cancellation. DETAILED DESCRIPTION

[0024] In order to make the purpose and technical solution of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of 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.

[0025] Figure 1 FIG. 1 is a circuit diagram of a buck-boost converter of the present invention. Figure 1As shown, a buck-boost converter 1 of the present invention comprises a buck-boost module 11 and a common-mode voltage suppression module 12 , and the buck-boost module 11 is connected to the common-mode voltage suppression module 12 .

[0026] In a specific embodiment, the buck-boost module 11 is a four-switch buck-boost module (Four-Switch Buck-Boost, FSBB), which specifically includes switch tubes Q 1 , switch tube Q 2 , switch tube Q 3 , switch tube Q 4 With inductance L f , switch tube Q 1 The first end is connected to the input voltage V in The first end of the switch tube Q 1 The second end is connected to the switch tube Q 2 The first end of the switch tube Q 2 The second end is connected to the input voltage V in The second end of the switch tube Q 1 The second end of the inductor L f The first end of the inductor L f The second end is connected to the switch tube Q 3 The second end of the switch tube Q 4 The first end of the switch tube Q 3 The first end of the switch tube Q 4 The second end is connected to the output voltage V o , switch tube Q 2 The second end is connected to the switch tube Q 4 The second end, input voltage V in The second end of the inductor L is connected to the power ground PG. f For the power inductor.

[0027] Optionally, the buck-boost module 11 may further include a capacitor C in , capacitor C in Connect in parallel to the switch tube Q 1 The first end of the switch tube Q 2 Between the second end and the capacitor C in It acts as input filter.

[0028] Optionally, the buck-boost module 11 may further include a capacitor C o , capacitor C o Connect in parallel to the switch tube Q 3 The first end of the switch tube Q 4 Between the second end and the capacitor C o It plays the role of output filtering.

[0029] Optionally, the buck-boost module 11 is also connected to a load RL , load R L is connected in parallel between the first end of switch Q 3 and the second end of switch Q 4 .

[0030] In a specific embodiment, the buck-boost module 11 adopts a two-mode control strategy. The bridge arm formed by switch Q 1 and switch Q 2 always has a potential static point and a potential moving point at the midpoint potential of the bridge arm formed by switch Q 3 and switch Q 4 .

[0031] Furthermore, the common-mode voltage suppression module 12 includes a first winding N1, a second winding N2, capacitor C com , capacitor C s . The first end of the first winding N1 is connected to the midpoint of inductor L s through capacitor C f . The second end of the first winding N1 is connected to the power ground PG. The first end of the second winding N2 is connected to the protection ground PE through capacitor C com . The second end of the second winding N2 is connected to the power ground PG.

[0032] Among them, capacitor C com is a compensation capacitor; the first winding N1 and the second winding N2 form a passive cancellation winding.

[0033] Furthermore, the positions of the same-name ends of the first winding N1 and the second winding N2 are opposite.

[0034] Furthermore, the turns ratio of the first winding N1 to the second winding N2 is 1:1.

[0035] In a specific embodiment, the first winding N1 and the second winding N2 can be implemented by a transformer. The first winding N1 is the primary winding of the transformer, and the second winding N2 is the secondary winding of the transformer; or the first winding N1 is the secondary winding of the transformer, and the second winding N2 is the primary winding of the transformer.

[0036] Furthermore, there are parasitic capacitances between each part of the buck-boost module 11 and the protection ground PE, including capacitor C pC , that is, the parasitic capacitance between the input port and the ground; capacitor C pE , that is, the parasitic capacitance between the negative bus and the ground; capacitor C pD , that is, the parasitic capacitance between the output port and the ground; capacitor C pA , that is, the parasitic capacitance between the midpoint of the bridge arm formed by switch Q 1 and switch Q 2 , that is, the parasitic capacitance between the midpoint of the left bridge arm of the buck-boost module and the ground; capacitor CpB , that is, the switch tube Q 3 With the switch tube Q 4 The parasitic capacitance between the midpoint of the bridge arm and the ground, that is, the parasitic capacitance between the midpoint of the right bridge arm of the buck-boost module and the ground, provides a flow path for the common-mode current, causing common-mode interference.

[0037] exist Figure 1 In the switch tube Q 1 With the switch tube Q 2 The midpoint of the bridge arm is point A, and the switch tube Q 3 With the switch tube Q 4 The midpoint of the bridge arm is point B, and the switch tube Q 1 The first end is point C, the switch tube Q 3 The first end is point D, the switch tube Q 2 The second end of is point E.

[0038] More specifically, the buck-boost converter of the present application adopts the passive cancellation concept to compensate the common-mode noise voltage, and utilizes the characteristics that the midpoint potential of the power inductor in the buck-boost converter jumps synchronously with the potential of the noise source, and leads the midpoint potential of the power inductor through the passive cancellation winding composed of the first winding N1 and the second winding N2, and connects it to the safe ground through the compensation capacitor. By selecting the appropriate compensation capacitor value, the compensation current The common mode current generated by nodes A and B where the voltage in the circuit changes at high frequency The magnitudes are equal and the directions are opposite, thus suppressing the common-mode conduction interference caused by the nodes with high-frequency voltage jumps in the circuit. is the current flowing through capacitor C com The current, is the current flowing through capacitor C PA The current, is the current flowing through capacitor C PB of current.

[0039] Furthermore, the same-name terminals of the passive cancellation windings are located opposite to each other to provide a common-mode current Compensation current in opposite direction Then, the transformer excitation inductance is appropriately designed. The transformer excitation inductance belongs to the common mode voltage suppression module 12. This module does not process the main power current, so it needs to present a high impedance characteristic for the main power current. Therefore, the value of the transformer excitation inductance should be greater than the inductance L f The value of .

[0040] In a specific embodiment, according to engineering experience, the magnitude of the excitation inductance is taken as 10 times the inductance L f Values ​​work better.

[0041] The following is an introduction to the working principle of a buck-boost converter of the present invention. Figure 1 The parasitic capacitances of the buck-boost converter can be established Figure 2 Common-mode equivalent circuit of buck-boost converter, voltage source With capacitor C com After being connected in series, they are connected in parallel at the common mode voltage V CM The two ends of the capacitor C pC Connected in parallel with the common mode voltage V CM The voltage source V Q2 With capacitor C pA After being connected in series, they are connected in parallel at the common mode voltage V CM The two ends of the capacitor C pE Connected in parallel with the common mode voltage V CM The voltage source V Q4 With capacitor C pB After being connected in series, they are connected in parallel at the common mode voltage V CM The two ends of the capacitor C pD Connected in parallel with the common mode voltage V CM The common mode voltage V CM The second terminal is connected to the protection ground PE. Q2 and voltage source V Q4 They represent the noise source Q using the substitution theorem. 2 and Q 4 The equivalent noise voltage source is represents the compensation voltage source obtained by equivalently treating the second winding N2 using the substitution theorem; the common mode voltage V CM Indicates the common mode voltage collected by the line impedance stabilization network. Figure 3 Common mode voltage V CM Expressed as the voltage across a 25Ω resistor.

[0042] Figure 3 for Figure 1 The simplest common-mode equivalent circuit of the buck-boost converter in the circuit, the common-mode voltage V CM , capacitor C sum , equivalent common mode noise source V ENS Connected in series to form a loop, the common mode voltage V CM and the equivalent common-mode noise source V ENS The midpoint of the series connection is connected to the protective earth PE.

[0043] In a specific embodiment, the switch tube Q 1 , switch tube Q 2 , switch tube Q 3 , switch tube Q 4 The same model, capacitor C pA With capacitor C pB The difference is very small, and the capacitor C can be considered in subsequent analysispA With capacitor C pB equal.

[0044] Depend on Figure 2 The common-mode equivalent circuit in the figure obtains the equivalent common-mode noise source V after adding the passive cancellation winding. ENS The expression is: Where, V Q2 and V Q4 They represent the substitution theorem for the switch tube Q 2 (i.e. noise source) and the switch tube Q 4 (i.e., noise source) is equivalent to the noise voltage source; capacitor C sum Represents the total parasitic capacitance in the simplest common-mode equivalent circuit, and its expression is as follows: .

[0045] As mentioned above, the function of the compensation capacitor is to make the compensation current equal to the common-mode current generated by the high-frequency jump node in the circuit and opposite in direction, thereby suppressing the common-mode conduction interference caused by the high-frequency jump node in the circuit. com The value should be such that the common-mode voltage V CM is zero.

[0046] according to Figure 3 The simplest common-mode equivalent circuit, the common-mode voltage V can be obtained from the impedance voltage divider formula CM The expression is as follows: .

[0047] Let the common mode voltage V CM =0, and the common-mode voltage V CM The expression satisfies the following equation: , After simplification, we get: Then we get the capacitance C com The value of is: .

[0048] In this embodiment, the compensation voltage source The acquisition of is related to the midpoint potential of the power inductor and can be achieved using a transformer without the need for additional auxiliary power supply and operation circuit.

[0049] like Figure 4 As shown, the present invention also provides a common mode voltage suppression method for a buck-boost converter, comprising steps S1 to S4.

[0050] Step S1: connect the first end of the first winding N1 through the capacitor C s Connect the midpoint of the power inductor of the buck-boost converter, connect the second end of the first winding N1 to the power ground, and connect the first end of the second winding N2 through the capacitor C com Connect the protection ground, and connect the second end of the second winding N2 to the power ground.

[0051] In a specific embodiment, the first winding N1 and the second winding N2 can be realized by a transformer, the first winding N1 is the primary winding of the transformer, and the second winding N2 is the secondary winding of the transformer; or the first winding N1 is the secondary winding of the transformer, and the second winding N2 is the primary winding of the transformer.

[0052] Furthermore, the positions of the same-named ends of the first winding N1 and the second winding N2 are opposite.

[0053] Furthermore, the turns ratio of the first winding N1 to the second winding N2 is 1:1.

[0054] Step S2, extracting the parasitic capacitance between each part of the buck-boost converter and the protection ground, including the capacitor C pC , capacitor C pE , capacitor C pD , capacitor C pA With capacitor C pB .

[0055] Among them, the capacitor C pC is the parasitic capacitance of the input port to ground; capacitor C pE is the parasitic capacitance of the negative bus to the ground; capacitance C pD is the parasitic capacitance of the output port to ground; capacitor C pA Q is the switch tube 1 With the switch tube Q 2 The parasitic capacitance of the bridge arm midpoint to ground; capacitance C pB Q is the switch tube 3 With the switch tube Q 4 The parasitic capacitance between the midpoint of the bridge arm and the ground.

[0056] In a specific embodiment, an impedance analyzer is used to extract the parasitic capacitance between various parts of the buck-boost converter and the protection ground.

[0057] Alternatively, if Figure 5 As shown, the line impedance stabilization network 2 (LISN) can be connected to the input voltage V in Between the buck-boost converter 1, it is used to isolate power supply interference and provide a stable test impedance, so as to accurately extract the parasitic capacitance between each part of the buck-boost converter and the protection ground.

[0058] Step S3, establishing a common-mode equivalent circuit after adding the first winding and the second winding, and simplifying the circuit to obtain a simplest common-mode equivalent circuit.

[0059] Further, the step S3 includes using the substitution theorem to derive the noise model, using the current source I Q1 and current source I Q3 Replace the switch tube Q 1 And the switch tube Q 3 , with a voltage source V Q2 and voltage source V Q4 Replace the switch tube Q 2 And the switch tube Q 4 The waveforms of these current sources and voltage sources are exactly the same as the current or voltage borne by their respective switch tubes; The voltage source replaces the second winding N2, and the voltage borne by the second winding N2 is completely consistent. The superposition theorem is used to derive the common mode voltage V of each current source and voltage source. CM The superposition theorem shows that when the current source acts alone, the current source is short-circuited, so only the voltage source reacts to the common-mode voltage V CM influential.

[0060] The common-mode equivalent circuit established in step S3 is as follows: Figure 2 As shown, the simplest common-mode equivalent circuit is as follows Figure 3 shown.

[0061] Step S4, calculating the capacitance C according to the established common mode equivalent circuit and the simplest common mode equivalent circuit com capacitance to achieve common-mode voltage cancellation.

[0062] Furthermore, the step S4 specifically includes the following steps.

[0063] Step S41, according to Figure 2 The common-mode equivalent circuit can be derived using Thevenin's theorem. Figure 3 The simplest common-mode equivalent circuit is Figure 3 The equivalent common-mode noise source V ENS The expression is: Where V Q2 and V Q4 They represent the substitution theorem for the switch tube Q 2 And the switch tube Q 4 The equivalent noise voltage source is: capacitor C sum Represents the total parasitic capacitance in the simplest common-mode equivalent circuit, and its expression is as follows: .

[0064] Step S42, obtaining the common mode voltage V according to the simplest common mode equivalent circuit CM The expression is as follows: .

[0065] Step S43: Set the equivalent common mode noise source V ENS Substitute the common mode voltage V into the expression CM The expression of common mode voltage V CM =0, and the capacitance C com The value of is: .

[0066] Where, let the common mode voltage V CM =0, and the common-mode voltage V CM The expression satisfies the following equation: , After simplification, we get: Then we get the capacitance C com The value of is: .

[0067] Furthermore, simulation circuits of the buck-boost converter before and after passive cancellation were built in Saber. Figure 6 The figure shows the common-mode voltage spectrum of the buck-boost converter before and after passive cancellation. It can be seen that compared with the buck-boost converter without passive cancellation, after adopting the passive cancellation-based method, the common-mode voltage of the system is reduced by more than 50dBμV in the 150kHz-30MHz frequency band, verifying that the buck-boost converter and its common-mode voltage suppression method in the present application can effectively suppress the common-mode conducted interference of the buck-boost converter.

[0068] Although the present invention has been disclosed as above by way of embodiments, it is not intended to limit the present invention. Any person having ordinary knowledge in the technical field may make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the scope of the attached patent application.

Claims

1. A buck-boost converter, characterized in that: It includes a buck-boost module and a common-mode voltage suppression module, the buck-boost module is connected to the common-mode voltage suppression module; the common-mode voltage suppression module includes a first winding, a second winding, a first capacitor, and a second capacitor, the first end of the first winding is connected to the midpoint of the power inductor of the buck-boost module through the second capacitor, the second end of the first winding is connected to the power ground, the first end of the second winding is connected to the protection ground through the first capacitor, and the second end of the second winding is connected to the power ground.

2. A buck-boost converter as claimed in claim 1, characterized in that: The first winding and the second winding have the same-name ends at opposite positions.

3. A buck-boost converter as claimed in claim 2, characterized in that: The first winding and the second winding are realized by a transformer.

4. A buck-boost converter as claimed in claim 1, characterized in that: The first capacitor C com The value of is: ， Among them, the capacitor C pA It is the parasitic capacitance from the midpoint of the bridge arm of the buck-boost module to ground.

5. A buck-boost converter as claimed in claim 1, characterized in that: The buck-boost module is a four-switch buck-boost module.

6. A common mode voltage suppression method for a buck-boost converter, characterized in that: include, Connecting the first end of the first winding to the midpoint of the power inductor of the buck-boost converter through the second capacitor, and connecting the second end of the first winding to the power ground; connecting the first end of the second winding to the protection ground through the first capacitor, and connecting the second end of the second winding to the power ground; Extract the parasitic capacitance between each part of the buck-boost converter and the protection ground; Establish a common-mode equivalent circuit after adding the first winding and the second winding, and simplify the circuit to obtain the simplest common-mode equivalent circuit; According to the established common-mode equivalent circuit and the simplest common-mode equivalent circuit, the capacitance of the first capacitor is calculated to achieve cancellation of the common-mode voltage.

7. A common mode voltage suppression method for a buck-boost converter as claimed in claim 6, characterized in that: The first winding and the second winding have the same-name ends at opposite positions.

8. A common mode voltage suppression method for a buck-boost converter as claimed in claim 7, characterized in that: The first winding and the second winding are realized by a transformer.

9. A common mode voltage suppression method for a buck-boost converter as claimed in claim 6, characterized in that: An impedance analyzer is used to extract the parasitic capacitance between the various parts of the buck-boost converter and the protective ground.

10. A common mode voltage suppression method for a buck-boost converter as claimed in claim 6, characterized in that: According to the established common-mode equivalent circuit and the simplest common-mode equivalent circuit, the capacitance of the first capacitor is calculated, including: According to the common-mode equivalent circuit, the equivalent common-mode noise source V after adding the passive cancellation winding is obtained. ENS The expression is: In the formula, C com Represents the first capacitor; V Q2 and V Q4 They represent the noise voltage sources obtained by equivalently treating the switch tubes Q2 and Q4 using the substitution theorem; the capacitor C sum Represents the total parasitic capacitance in the simplest common-mode equivalent circuit, and its expression is as follows: ， Among them, the capacitor C pC That is, the parasitic capacitance of the input port to ground; capacitance C pE That is, the parasitic capacitance of the negative bus to the ground; capacitance C pD That is, the parasitic capacitance of the output port to ground; capacitance C pA That is, the parasitic capacitance between the midpoint of the bridge arm formed by the switch tube Q1 and the switch tube Q2 and the ground; the capacitance C pB That is, the parasitic capacitance between the midpoint of the bridge arm formed by the switch tube Q3 and the switch tube Q4 and the ground; According to the simplest common-mode equivalent circuit, the common-mode voltage V CM The expression is as follows: ； The equivalent common mode noise source V after adding the passive cancellation winding ENS Substitute the common mode voltage V into the expression CM The expression of common mode voltage V CM =0, the capacitance of the first capacitor is: 。

Images