CN110299833A - It is a kind of inhibit Buck converter common mode Conduction Interference common-mode voltage offset method and circuit - Google Patents

Abstract

The invention discloses a kind of common-mode voltages for inhibiting Buck converter common mode Conduction Interference to offset method and circuit, described to offset method are as follows: by offsetting the common-mode voltage of Buck converter, realizes and inhibits its common mode Conduction Interference；The common-mode voltage for offsetting Buck converter is two windings of addition on input power cord；Described two windings are coupled with output inductor winding.The invention proposes using common-mode voltage to offset method to realize the inhibition for conducting common mode, by offsetting the common-mode voltage of Buck converter, to inhibit its common mode Conduction Interference；It is coupled by the present invention by the way that two windings are added on input power cord with output inductor winding, realizes the common-mode voltage for offsetting Buck converter；The present invention realizes simply, does not need to increase compensating electric capacity, therefore avoid the consistency problem of compensating electric capacity tolerance introducing, so that the present invention has higher practicability.

Description

A common-mode voltage cancellation method for suppressing common-mode conduction interference of Buck converter and its circuit

technical field

The invention belongs to the technical field of Buck converter common-mode conduction interference suppression, and in particular relates to a common-mode voltage cancellation method and circuit for suppressing Buck converter common-mode conduction interference.

Background technique

Since the power device works in a high-frequency switching state, there are nodes with high-frequency potential changes in the power electronic converter. 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 (Common Mode, CM) conduction interference, and enter the power grid through the input power line, affecting the operation 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 protection 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 winding of the common mode inductor flows the input current. Therefore, the volume and weight of the common mode inductor are large, which restricts the improvement of power supply efficiency and power density.

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

See Figure 1, common-mode current cancellation method, where the 25Ω resistor 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 converter common-mode interference model, respectively. The added cancellation branch is composed of the compensation voltage source v _com and the compensation capacitor C _com . When the current _{i com} flowing through the compensation branch is equal to the common mode current in generated by the converter, the equivalent test impedance flowing through the LISN The current is zero, that is, the common mode conduction interference is suppressed. At this time, the compensation voltage and compensation capacitance satisfy:

In Figure 1, the common-mode current generated by the converter is canceled by adding a parallel cancellation branch. However, there is a tolerance in the compensation capacitor, which will affect the effect of common-mode interference cancellation.

See Fig. 2, it is 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, thereby 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 consistency problems caused by capacitor tolerances.

According to Fig. 2, establishing a compensation voltage source v _com equal to the equivalent interference source v _ENS is the key to realizing common-mode interference cancellation. In the 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), and v _Q is the voltage from the switching node to the power ground, that is, the drain-source voltage of the lower transistor. Since v _Q has the same AC component as the voltage v _Lf of the output filter inductor winding, that is

v _Q =v _Lf (3)

According to the condition of common mode interference cancellation v _com =v _ENS in Figure 2, combined with formula (2) and formula (3), it can be obtained

v _com = kv _Lf (4)

It can be seen from formula (4) that the required compensation voltage v _com is related to the ratio k of the corresponding parasitic capacitance in the circuit and the voltage v _Lf at both ends of the inductor. Accordingly, an auxiliary winding with a suitable number of turns can be wound on the inductor in a magnetic coupling manner, and the auxiliary winding provides the required compensation voltage, as shown in FIG. 3 .

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

Contents 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 common-mode conduction interference of Buck converters for the above-mentioned deficiencies in the prior art.

For realizing above-mentioned technical purpose, the technical scheme that the present invention takes is:

A common-mode voltage cancellation method for suppressing Buck converter common-mode conduction interference, the cancellation method is: by canceling the common-mode voltage of Buck converter, realizing suppressing its common-mode conduction disturbance;

The common-mode voltage of the described offset Buck converter is to add two windings on the input power line;

The two windings are coupled to the output filter inductor winding.

Preferably, one of the two windings is connected to the positive pole of the input power supply and the positive pole of the Buck converter circuit input, and the other winding is connected to the negative pole of the input power supply and the negative pole of the Buck converter circuit input.

Preferably, the relationship between the above-mentioned two windings and the terminals of the same name of the output filter inductor winding is: the terminals connected to the positive and negative poles of the input power supply respectively, and the terminals connected to the switch node in the output filter inductor winding are terminals of the same name.

Preferably, 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 output filter inductor winding to the parasitic capacitance in the Buck converter circuit to the safety ground.

A common-mode voltage cancellation circuit for suppressing common-mode conduction interference of a Buck converter, comprising a Buck converter circuit and two windings; the two windings are arranged on the input power line of the Buck converter circuit, and the two windings Coupled with the output filter inductor winding of the Buck converter circuit.

Preferably, one of the two windings is connected to the positive pole of the input power supply and the positive pole of the Buck converter circuit input, and the other winding is connected to the negative pole of the input power supply and the negative pole of the Buck converter circuit input.

Preferably, the relationship between the above-mentioned two windings and the terminals of the same name of the output filter inductor winding is: the terminals connected to the positive and negative poles of the input power supply respectively, and the terminals connected to the switch node in the output filter inductor winding are terminals of the same name.

Preferably, 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 output filter inductor winding to the parasitic capacitance in the Buck converter circuit to the safety ground.

The present invention has the following beneficial effects:

The present invention proposes to use the common-mode voltage cancellation method to realize the suppression of common-mode conduction, by offsetting the common-mode voltage of the Buck converter, thereby suppressing its common-mode conduction interference;

The present invention realizes offsetting the common-mode voltage of the Buck converter by adding two windings on the input power line and coupling them with the output filter inductance winding;

The present invention is simple to implement and does not need to increase the compensation capacitor, thus avoiding the consistency problem caused by the tolerance of the compensation capacitor, thus making the present invention have higher practicability.

Description of drawings

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

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

Fig. 3 is a realization principle diagram of the common-mode voltage cancellation method.

Fig. 4 is an implementation schematic diagram of a common-mode voltage cancellation method for suppressing common-mode conduction interference of a Buck converter according to the present invention.

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

Fig. 6 is the circuit diagram of Buck converter.

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

Fig. 8 is the Thevenin equivalent circuit diagram of the Buck converter.

Detailed ways

Embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings.

A common-mode voltage cancellation method for suppressing Buck converter common-mode conduction interference of the present invention, said cancellation method is: by canceling the common-mode voltage of Buck converter, realizing suppressing its common-mode conduction disturbance;

The common-mode voltage of the described offset Buck converter is to add two windings on the input power line;

The two windings are coupled to the output filter inductor winding.

In an embodiment, one of the two windings is connected to the positive pole of the input power supply and the positive pole of the Buck converter circuit input, and the other winding is connected to the negative pole of the input power supply and the negative pole of the Buck converter circuit input.

In the embodiment, the relationship between the two windings and the terminals with the same names as the output filter inductor winding is shown in Figure 5: the terminals A and C respectively connected to the positive and negative poles of the input power supply, and the terminals connected to the switch node in the output filter inductor winding M is the end of the same name.

In the embodiment, the number of turns N _AB and N _CD of the two windings are equal, and the number of turns of the two windings is determined by the number of turns N _Lf of the output filter inductor winding and the parasitic capacitance in the Buck converter circuit to the safety ground Ratio decides. As shown in Figure 5, the specific expressions of N _AB and N _CD are:

A common-mode voltage cancellation circuit for suppressing common-mode conduction interference of a Buck converter of the present invention comprises a Buck converter circuit and two windings; the two windings are arranged on the input power line of the Buck converter circuit, and the Both windings are coupled to the output filter inductor windings of the Buck converter circuit.

In an embodiment, one of the two windings is connected to the positive pole of the input power supply and the positive pole of the Buck converter circuit input, and the other winding is connected to the negative pole of the input power supply and the negative pole of the Buck converter circuit input.

In the embodiment, the relationship between the two windings and the terminals of the same name of the output filter inductor winding is: the terminals connected to the positive and negative poles of the input power supply respectively, and the terminals connected to the switch node in the output filter inductor winding are the terminals of the same name.

In an embodiment, 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 output filter inductor winding to the parasitic capacitance in the Buck converter circuit to the safety ground.

The working principle of the present invention is as follows: Referring to FIG. 4 , the number of turns N _AB and N _CD of the common-mode inductor winding AB and the common-mode inductor winding CD are both kN _PQ , where N _PQ is the number of turns of the filter inductor winding. If the leakage inductance of the winding is ignored, 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 Buck converter with common-mode voltage cancellation. The number of turns of the common-mode inductor windings AB and CD is kN _Lf , where N _Lf is the number of turns of the filter inductor winding.

The following specifically deduces the expressions of the equivalent interference source v _ENS and the capacitance C _sum of the Buck converter's common-mode conducted interference, and determines the number of turns of the common-mode inductor winding accordingly.

Figure 6 shows the circuit diagram of the Buck converter, where C _D1 is the parasitic capacitance from the switching node M to the protection ground; C _S1 , C _S2 and C _S3 are the positive pole of the output voltage, the power ground, and the drain of the switching tube Q to the ground, respectively. The parasitic capacitance of the protective ground. The common-mode interference model of the Buck converter is derived by applying the substitution theorem. In the Buck converter, the potential of the switch node M is high-frequency jump, and its common-mode interference is mainly caused by _CD1 . For this reason, first replace the freewheeling diode D _f with an AC voltage source whose waveform is consistent with the voltage waveform at both ends. Since dv _o /dt<<dv _Df /dt, the output capacitor can be considered as a short circuit. In order to avoid a pure voltage source loop in the circuit, the switching tube Q and the filter inductance L _f are respectively replaced by an alternating current source consistent with the current waveform flowing through them. Finally, considering the 25Ω equivalent test impedance of common-mode interference on the LISN side, the common-mode interference model of the Buck converter can be obtained, as shown in Figure 7.

Use the superposition theorem to simplify the network at the right end of the 25Ω resistor in the model: only consider the effect of the current source, and short-circuit the voltage source v _Df , then the current source i _Q and i _Lf are short-circuited, which has no effect on common-mode interference; only consider the voltage The role of the source, open the current source i _Q and i _Lf , and then perform Thevenin equivalent of this sub-circuit, the obtained circuit is shown in Figure 8. in

C _sum ＝C _D1 +C _S1 +C _S2 (5b)

It can be seen from Figure 6 that since v _Df is the same as the AC component of the filter inductor voltage v _Lf , the expression of the equivalent interference source can be written as k _buck v _Lf . Therefore, as shown in FIG. 4 , the common-mode inductor windings AB and CD are coupled with the output filter inductor winding, and the number of turns of the windings is k _buck N _Lf .

The above are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions under the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those of ordinary skill 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 Buck converter common-mode conduction disturbance, is characterized in that: described cancellation method is: by canceling the common-mode voltage of Buck converter, realizes suppressing its common-mode conduction disturbance; The common-mode voltage of the described offset Buck converter is to add two windings on the input power line; The two windings are coupled to the output filter inductor winding. 2. A common-mode voltage cancellation method for suppressing common-mode conducted interference of a Buck converter according to claim 1, wherein one of the two windings is connected to the positive pole of the input power supply and the Buck converter circuit The positive pole of the input, and the other winding connects the negative pole of the input power supply to the negative pole of the Buck converter circuit input. 3. A kind of common-mode voltage cancellation method for suppressing Buck converter common-mode conducted interference according to claim 1, characterized in that: the relationship between the two windings and the same-named end of the output filter inductor winding is: and the input power supply The terminals connected to the positive and negative poles respectively, and the terminal connected to the switch node in the output filter inductor winding are terminals with the same name. 4. A kind of common-mode voltage cancellation method for suppressing common-mode conducted interference of Buck converter according to claim 1, characterized in that: the turns of the two windings are equal, and the turns of the two windings are filtered by the output The number of turns of the inductor winding is determined by the ratio of the parasitic capacitance to the safety ground in the Buck converter circuit. 5. A common-mode voltage cancellation circuit for suppressing Buck converter common-mode conduction disturbance, is characterized in that: comprise Buck converter circuit and two windings; Described two windings are located on the input power supply line of Buck converter circuit , the two windings are coupled with the output filter inductor winding of the Buck converter circuit. 6. A common-mode voltage cancellation circuit for suppressing common-mode conducted interference of a Buck converter according to claim 5, wherein one of the two windings is connected to the positive pole of the input power supply and the Buck converter circuit The positive pole of the input, and the other winding connects the negative pole of the input power supply to the negative pole of the Buck converter circuit input. 7. A kind of common-mode voltage cancellation circuit for suppressing common-mode conducted interference of Buck converter according to claim 5, characterized in that: the relationship between the two windings and the same-named end of the output filter inductor winding is: and the input power supply The terminals connected to the positive and negative poles respectively, and the terminal connected to the switch node in the output filter inductor winding are terminals with the same name. 8. A common-mode voltage cancellation circuit for suppressing common-mode conducted interference of a Buck converter 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 filtered by the output The number of turns of the inductor winding is determined by the ratio of the parasitic capacitance to the safety ground in the Buck converter circuit.