CN110289752B - A common-mode voltage cancellation method and circuit for suppressing common-mode conducted interference of LLC resonant converters - Google Patents

Abstract

The invention discloses a common mode voltage cancellation method and circuit for suppressing the common mode conduction interference of an LLC resonant converter. The cancellation method is as follows: suppressing the common mode conduction interference of the LLC resonant converter ; The common mode voltage of the LLC resonant converter is canceled by adding two windings on the input power line; the two windings are coupled with the transformer. The invention proposes to use the common mode voltage cancellation method to realize the suppression of the common mode conduction, by canceling the common mode voltage of the LLC resonant converter, thereby suppressing its common mode conduction interference; the invention adds two windings on the input power line , and couple it with the transformer to cancel the common mode voltage of the LLC resonant converter; the present invention is simple to implement and does not need to increase the compensation capacitor, thus avoiding the consistency problem introduced by the compensation capacitor tolerance, so that the present invention has higher practicality.

Description

A common-mode voltage cancellation method for suppressing common-mode conducted interference of LLC resonant converters and circuit

technical field

The invention belongs to the technical field of common mode conduction interference suppression of LLC resonant converters, and particularly relates to a common mode voltage cancellation method and circuit for suppressing common mode conduction interference of LLC resonant converters.

Background technique

Since power devices work in high-frequency switching states, there are nodes with high-frequency potential changes in power electronic converters. The high-frequency changing potential will generate displacement current in the parasitic capacitance between these nodes and the protective ground, which will cause common mode (CM) conduction interference, and enter the power grid through the input power line, affecting the performance of other equipment in the same power grid. normal work.

In order to suppress the common mode conduction interference of the converter, a common mode filter composed of a common mode inductor and a Y capacitor is usually added between the input power supply and the converter. Since the Y capacitor is connected between the input power line and the protective ground, its capacitance is limited by the leakage current and has an upper limit. Thus, in order to achieve the required attenuation requirements, the common mode inductance is often large. In addition, the windings of the common mode inductors carry the input current. Therefore, the volume and weight of the common mode inductor are relatively large, which restricts the improvement of power efficiency and power density.

Commonly used interference suppression methods include common mode current cancellation method and common mode voltage cancellation method.

Referring to Figure 1, the common mode current cancellation method, in which the 25Ω resistance is the equivalent test impedance of common mode interference, and C _sum and v _ENS are the total parasitic capacitance and equivalent interference source in the common mode interference model of the converter, respectively. The added elimination branch is composed of a compensation voltage source v _com and a compensation capacitor C _com . When the current i _com flowing through the compensation branch is equal to the common mode current i _n generated by the converter, the equivalent test impedance of the LISN flows through the current i com. The current is zero, that is, the common mode conduction interference is suppressed. At this time, the compensation voltage and compensation capacitor satisfy:

In Figure 1, the common mode current generated by the converter is offset by the added parallel cancellation branch, but the compensation capacitor has a tolerance, which will affect the effect of common mode interference cancellation.

Referring to Figure 2, for the common mode voltage cancellation method, a compensation voltage source v _com is connected in series in the loop. When v _com = v _ENS , the voltage applied to both ends of the 25Ω equivalent test impedance is zero, thus eliminating the common mode interference . Since this method directly cancels the common mode voltage of the converter, it is called the common mode voltage cancellation method. This method does not require compensation capacitors and avoids the consistency problem caused by capacitance tolerances.

According to Figure 2, establishing a compensation voltage source v _com equal to the equivalent interference source v _ENS is the key to realizing the cancellation of common mode interference. In Buck converter, its equivalent interference source v _ENS can be expressed as the following form, namely:

v _ENS = kv _Q (2)

Among them, k is the ratio of the corresponding parasitic capacitance in the circuit (0<k<1), v _Q is the voltage from the switching node to the power ground, that is, the drain-source voltage of the lower tube. Since v _Q has the same AC component as the voltage v _Lf of the output filter inductor winding, i.e.

v _Q = v _Lf (3)

According to the common-mode interference cancellation condition v _com =v _ENS in Fig. 2, combining equations (2) and (3), we can get

v _com = kv _Lf (4)

It can be known from formula (4) that the required compensation voltage v _com is related to the ratio k of the corresponding parasitic capacitance in the LLC resonant converter circuit and the voltage v _Lf across the inductor. Accordingly, an auxiliary winding with a suitable number of turns can be wound on the inductor by means of magnetic coupling, and the auxiliary winding provides the required compensation voltage, as shown in Figure 3.

According to Figure 3, in order to obtain the required compensation voltage, the compensation voltage kv _Lf should be added to the two input power lines of the converter, so that the common mode voltage from the LISN test terminal to the input side of the converter power supply is kv _Lf .

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a common-mode voltage cancellation method and circuit for suppressing the common-mode conduction interference of LLC resonant converters in view of the above-mentioned deficiencies of the prior art.

In order to realize the above-mentioned technical purpose, the technical scheme adopted in the present invention is:

A common mode voltage cancellation method for suppressing the common mode conduction interference of an LLC resonant converter, the cancellation method is: suppressing the common mode conduction interference of the LLC resonant converter by canceling the common mode voltage;

The common mode voltage of the LLC resonant converter is cancelled by adding two windings on the input power line;

The two windings are coupled to the transformer.

Preferably, the above two windings are respectively connected to the positive pole of the input power supply and the positive pole of the LLC resonant converter circuit input, and the negative pole of the input power supply and the negative pole of the LLC resonant converter circuit input, respectively.

Preferably, the relationship between the two windings with the same name and the primary winding of the transformer is: the terminals connected to the positive and negative electrodes of the input power supply respectively, and the terminals connected to the power ground in the primary winding of the transformer are the same terminals.

Preferably, the number of turns of the two windings is equal, and the number of turns of the two windings is determined by the ratio of the number of turns of the primary winding of the transformer to the parasitic capacitance to the safety ground in the LLC resonant converter circuit.

A common-mode voltage cancellation circuit for suppressing common-mode conduction interference of an LLC resonant converter, comprising an LLC resonant converter circuit and two windings; the two windings are arranged on an input power line of the LLC resonant converter circuit, and the two windings are The windings are coupled to the transformer of the LLC resonant converter circuit.

Preferably, the above two windings are respectively connected to the positive pole of the input power supply and the positive pole of the LLC resonant converter circuit input, and the negative pole of the input power supply and the negative pole of the LLC resonant converter circuit input, respectively.

Preferably, the relationship between the two windings with the same name and the primary winding of the transformer is: the terminals connected to the positive and negative electrodes of the input power supply respectively, and the terminals connected to the power ground in the primary winding of the transformer are the same terminals.

Preferably, the number of turns of the two windings is equal, and the number of turns of the two windings is determined by the ratio of the number of turns of the primary winding of the transformer to the parasitic capacitance to the safety ground in the LLC resonant converter circuit.

The present invention has the following beneficial effects:

The invention proposes to use the common-mode voltage cancellation method to realize the suppression of the common-mode conduction, and suppress the common-mode conduction interference of the LLC resonant converter by canceling the common-mode voltage;

By adding two windings on the input power line and coupling them with the transformer, the invention realizes the cancellation of the common mode voltage of the LLC resonant converter;

The present invention is simple to implement and does not need to increase the compensation capacitor, thus avoiding the consistency problem introduced by the tolerance of the compensation capacitor, thereby making the present invention more practical.

Description of drawings

FIG. 1 is a schematic diagram of the circuit structure of the common mode current cancellation method.

FIG. 2 is a schematic diagram of a circuit structure of a common mode voltage cancellation method.

Figure 3 is a schematic diagram of the implementation of the common mode voltage cancellation method.

FIG. 4 is a schematic diagram of the realization of a common mode voltage cancellation method for suppressing the common mode conduction interference of the LLC resonant converter of the present invention.

FIG. 5 is a schematic circuit diagram of a common-mode voltage cancellation circuit for suppressing the common-mode conducted interference of the LLC resonant converter according to the present invention.

FIG. 6 is a circuit diagram of an LLC resonant converter.

Fig. 7 is the circuit diagram of the common mode interference model of LLC resonant converter.

FIG. 8 is a Thevenin equivalent circuit diagram of the LLC resonant converter.

FIG. 9 is a schematic diagram of a transformer physical model used to calculate the structural parameters of the transformer windings.

FIG. 10 is a schematic diagram of the equivalent model of the transformer used to calculate the structural parameters of the transformer windings.

Detailed ways

The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

The present invention provides a common mode voltage cancellation method for suppressing the common mode conduction interference of the LLC resonant converter. The cancellation method includes: suppressing the common mode conduction interference of the LLC resonant converter by canceling the common mode voltage;

The common mode voltage of the LLC resonant converter is cancelled by adding two windings on the input power line;

The two windings are coupled to the transformer.

In the embodiment, the above two windings are respectively connected to the positive pole of the input power supply and the positive pole of the LLC resonant converter circuit input, and the negative pole of the input power supply and the negative pole of the LLC resonant converter circuit input.

In the embodiment, the relationship between the same name terminals of the above-mentioned two windings and the primary winding of the transformer is shown in Figure 5: the terminals A and C, which are respectively connected to the positive and negative poles of the input power supply, are the same name terminals with the terminal a in the primary winding of the transformer. .

其中n为变压器匝比，C₀为变压器原副边绕组的结构电容，λ_a和λ_c的具体表达式与变压器的绕组结构有关。In the embodiment, the number of turns N _AB and N _CD of the above two windings are equal, and the number of turns of the two windings is determined by the number of turns N _ab of the primary winding of the transformer and the parasitic capacitance to the safety ground in the LLC resonant converter circuit. ratio decision. As shown in Figure 5, the specific expressions of N _AB and N _CD are:

Among them, n is the turns ratio of the transformer, C ₀ is the structural capacitance of the primary and secondary windings of the transformer, and the specific expressions of λ _a and λ _c are related to the winding structure of the transformer.

A common-mode voltage cancellation circuit for suppressing common-mode conduction interference of an LLC resonant converter, comprising an LLC resonant converter circuit and two windings; the two windings are arranged on an input power line of the LLC resonant converter circuit, and the two windings are The windings are coupled to the transformer of the LLC resonant converter circuit.

In the embodiment, the above two windings are respectively connected to the positive pole of the input power supply and the positive pole of the LLC resonant converter circuit input, and the negative pole of the input power supply and the negative pole of the LLC resonant converter circuit input.

In the embodiment, the relationship between the two windings with the same name and the primary winding of the transformer is: the end connected with the positive and negative poles of the LLC resonant converter respectively, and the end connected with the power ground in the primary winding of the transformer is the same name.

In the embodiment, the number of turns of the above two windings is equal, and the number of turns of the two windings is determined by the ratio of the number of turns of the primary winding of the transformer to the parasitic capacitance to the safety ground in the LLC resonant converter circuit.

The working principle of the present invention is as follows: Referring to FIG. 4 , the common mode inductor winding AB and the common mode inductor winding CD have the number of turns N _AB and N _CD both k _{LLC Nab} , where _Nab is the number of turns of the filter inductor winding. Ignoring the winding leakage inductance, there is v _BD =V _in +v _AB -v _CD =V _in , so adding a common mode inductance winding will not affect the normal operation of the converter. In addition, in order to reduce the copper loss of the common mode inductor winding, the input filter capacitor C _in of the converter should be placed between the converter and the common mode inductor winding, so that the current flowing through the common mode inductor winding is DC.

According to the above analysis, Figure 5 shows the circuit diagram of the LLC resonant converter using common mode voltage cancellation. The turns of the common mode inductor windings AB and CD are both k _{LLC Nab} , where _Nab is the number of turns of the primary winding .

The expression of the equivalent interference source v _ENS of the common mode conduction interference of the LLC resonant converter is specifically deduced below, and the number of turns of the common mode inductor winding is determined accordingly.

Figure ₆ shows the circuit diagram of the LLC resonant converter, where C _S1 and C _D1 are the parasitic capacitances from the drains of the switching transistors Q1 and _Q2 to the protective ground through the heat sink, respectively. The following applies the substitution theorem to derive the common mode interference model of the LLC resonant converter. First, _Q2 is replaced by an AC voltage source _vQ2 of the same waveform as its drain-source voltage, and the series branch of _Lr and _Cr is replaced by an AC voltage source _vres of the same waveform. In the conducted interference frequency band from 150kHz to 30MHz, the equivalent impedance of common mode interference of LISN is 25Ω resistance. The voltage of the output capacitor C _o is basically DC, so C _o is regarded as a short circuit. Ignoring the leakage inductance of the transformer, the transformer is replaced by a controlled voltage/current source, and for the convenience of analyzing the model, the distributed capacitance of the transformer is equivalent to two capacitors C _ae and C _be . To avoid a pure voltage source loop in the circuit, Q ₁ , _DR1 and _DR2 are replaced by current sources with the same current waveforms as their respective current sources. In this way, the common mode interference equivalent circuit of the half-bridge LLC resonant converter is obtained, as shown in FIG. 7 .

Refer to Figure 8, apply the superposition theorem, first only consider the case of the current source, short-circuit the voltage source v _Q2 and v _res , at this time the current sources i _Q1 , i _DR1 and i _DR2 are all short-circuited, so the current source does not affect the common mode Conducted interference. Then, open the current sources i _Q1 , i _DR1 and i _DR2 , and only consider the case where the voltage source acts. Simplifying this circuit, the expression of its equivalent interference source can be obtained as:

When the switching frequency is close to the resonant frequency, the impedance of the series branch of the resonant inductor and the resonant capacitor is much smaller than the impedance of the magnetizing inductor, so the voltage v _res on the series resonant branch can be ignored compared with v _Q2 , and v _Q2 is approximately equal to v _ab . At this time, equation (4) can be expressed as

v _{ENS_LLC} = k _LLC v _ab (5)

where:

The expressions of the two capacitors C _ae and C _be are:

C _ae =[λ _a +n(1-2λ _c )]C ₀ (7a)

C _be =[1-λ _a -n(1-2λ _c )]C ₀ (7b)

Among them, λ _a and λ _c are the winding structure parameters of the transformer, which are determined by the transformer winding structure. C ₀ is the structural capacitance of the primary and secondary windings of the transformer, which can be measured experimentally: short-circuit the terminals of the primary and secondary windings of the transformer respectively, and then measure the capacitance between the two short-circuit points with an LCR meter.

Substituting equation (7) into equation (6), we get:

According to equation (8), the turns of the common mode inductor windings AB and CD are both k _{LLC Nab} .

Calculation of transformer winding structure parameters λ _a and λ _c :

Referring to the transformer winding structure shown in Fig. 9 and Fig. 10 as an example, calculate the winding structure parameters λ _a and λ _c . For transformers with other winding structures, the calculation ideas are similar.

Denote the parasitic capacitance between the primary winding Pri1 and the secondary winding Sec1-1 as C ₁ , and the parasitic capacitance between Pri2 and Sec2-2 as C ₂ . The same insulating material of the same thickness is used, so C ₁ and C ₂ are approximately equal.

The displacement currents flowing through Pri1 to Sec1-1 and Pri2 to Sec2-2 are:

Among them, the expression _of λ1 is

Among them, r ₁ is the inner diameter of the primary winding, r ₂ is the outer diameter, and _NP is the number of turns of the primary winding.

Since Pri1 to Sec1-1 and Pri2 to Sec2-2 use the same insulating material with the same thickness, so C ₁ =C ₂ =0.5C ₀ , then the sum of the displacement currents flowing through the two layers of windings is

The general expression for the total displacement current flowing through the distributed capacitance of the primary and secondary windings of the transformer is:

Combining formulas (11) and (12), it can be seen that the winding structure parameters λ _a and λ _c of the transformer are both 0.5.

The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments, and all technical solutions that belong to the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those skilled in the art, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims (8)

1. a common mode voltage cancellation method for suppressing the common mode conduction interference of LLC resonant converter, it is characterized in that: described cancellation method is: by cancelling the common mode voltage of LLC resonance converter, realize suppressing its common mode conduction interference ; The common mode voltage of the LLC resonant converter is cancelled by adding two windings on the input power line; the two windings are coupled to the transformer; Each winding is connected in series with one end of the positive and negative poles of the power supply and one end of the resonant converter circuit. 2. A common mode voltage cancellation method for suppressing common mode conduction interference of LLC resonant converters according to claim 1, characterized in that: the two windings are respectively connected to the positive pole of the input power supply and the LLC resonant converter circuit The positive pole of the input, and the negative pole of the input power supply and the negative pole of the LLC resonant converter circuit input. 3. a kind of common mode voltage cancellation method for suppressing the common mode conduction interference of LLC resonant converter according to claim 1, it is characterized in that: described two windings and the relationship of the same name terminal of transformer primary winding are: with input The terminals connected to the positive and negative poles of the power supply respectively, and the terminal connected to the power ground in the primary winding of the transformer are synonymous terminals. 4. A common mode voltage cancellation method for suppressing common mode conduction interference of LLC resonant converter according to claim 1, wherein the number of turns of the two windings is equal, and the number of turns of the two windings is determined by the transformer The ratio of the number of turns of the primary winding to the parasitic capacitance to safety ground in the LLC resonant converter circuit is determined. 5. A common mode voltage cancellation circuit for suppressing common mode conduction interference of LLC resonant converter, it is characterized in that: comprise LLC resonant converter circuit and two windings; Described two windings are arranged in the input of LLC resonant converter circuit a power line, the two windings are coupled to the transformer of the LLC resonant converter circuit; Each winding is connected in series with one end of the positive and negative poles of the power supply and one end of the resonant converter circuit. 6. The common-mode voltage cancellation circuit for suppressing common-mode conducted interference of LLC resonant converters according to claim 5, wherein the two windings are respectively connected to the positive pole of the input power supply and the LLC resonant converter circuit The positive pole of the input, and the negative pole of the input power supply and the negative pole of the LLC resonant converter circuit input. 7. The common mode voltage cancellation circuit for suppressing the common mode conduction interference of LLC resonant converter according to claim 5, is characterized in that: the relationship between the two windings with the same name of the primary winding of the transformer is: with the input The terminals connected to the positive and negative poles of the power supply respectively, and the terminal connected to the power ground in the primary winding of the transformer are synonymous terminals. 8. The common-mode voltage cancellation circuit for suppressing common-mode conducted interference of LLC resonant converters according to claim 5, wherein the number of turns of the two windings is equal, and the number of turns of the two windings is determined by the transformer The ratio of the number of turns of the primary winding to the parasitic capacitance to safety ground in the LLC resonant converter circuit is determined.

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