Noise filter

Abstract

This invention provides a compact noise filter that sufficiently reduces high-frequency electromagnetic noise even when used in a power converter with a changeable number of drive phases. [Solution] The power converter comprises a common mode choke coil connected to the output side of a multi-phase power converter with a changeable number of drive phases, a variable gain circuit connected to the output side of the common mode choke coil that changes the gain according to the number of drive phases of the power converter and outputs a signal that inverts and cancels high-frequency noise, and a Y capacitor that outputs the signal from the variable gain circuit to the output side of the common mode choke coil.

Description

Technical Field

[0001] The present disclosure relates to a noise filter, and more particularly to a noise filter attached to the output side of a multi-phase power converter whose drive phase number can be changed.

Background Art

[0002] Conventionally, as this type of noise filter, there has been proposed one including an X capacitor connected between a pair of power lines, Y capacitors respectively connected between a pair of power lines and a ground potential, a common mode choke coil inserted into a pair of power lines, and a magnetic shield for suppressing magnetic interference between the common mode choke coil, the X capacitor, and the Y capacitor (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in a power converter such as a multi-phase boost circuit whose drive phase number can be changed to cope with a large current, the higher the drive phase number, the more the frequency of the generated electromagnetic noise shifts to the high-frequency side and the amplitude of the low-frequency electromagnetic noise increases. Therefore, when using the above-described noise filter, it is necessary to increase the size of the common mode choke coil that constitutes the filter in order to reduce high-frequency electromagnetic noise in a wide range, which makes it difficult to install in a limited space as in the case of mounting on a vehicle.

[0005] The main object of the noise filter of the present disclosure is to provide a small-sized noise filter that can sufficiently reduce high-frequency electromagnetic noise even when used in a power converter whose drive phase number can be changed. [Means for solving the problem]

[0006] The noise filter of this disclosure employs the following means to achieve the primary objective described above.

[0007] The noise filter in this disclosure is A noise filter attached to the output side of a multi-phase power converter with a changeable number of drive phases, A common mode choke coil connected to the output side of the power converter, A gain-variable circuit connected to the output side of the common-mode choke coil, which changes the gain according to the number of drive phases of the power converter and outputs a signal that inverts and cancels high-frequency noise, A Y capacitor outputs the signal from the variable gain circuit to the output side of the common mode choke coil, It is characterized by being equipped with [the following features].

[0008] The noise filter of this disclosure comprises a common-mode choke coil connected to the output side of a power converter, a variable-gain circuit connected to the output side of the common-mode choke coil that changes its gain according to the number of drive phases of the power converter and outputs a signal that inverts and cancels high-frequency noise, and a Y capacitor that outputs the signal from the variable-gain circuit to the output side of the common-mode choke coil. Because the variable-gain circuit changes its gain according to the number of drive phases of the power converter and outputs a signal that inverts and cancels high-frequency noise, it is possible to reduce high-frequency electromagnetic noise over a wide range without increasing the size of the common-mode choke coil.

[0009] In the noise filter of this disclosure, the variable gain circuit may include a high-pass filter connected to the output side of the common-mode choke coil, an inverting amplifier circuit that inverts and amplifies the signal from the high-pass filter and outputs it, and an amplification factor changing circuit that changes the amplification factor of the inverting amplifier circuit by switching a switching element. In this way, the amplification factor of the inverting amplifier circuit can be easily changed by switching the switching element. In this case, the amplification factor changing circuit may include a first resistor provided between the output of the high-pass filter and the input of the inverting amplifier circuit, and at least one parallel amplification switching circuit in which a switching element connected in parallel with the first resistor and a second resistor are connected in series. The parallel amplification switching circuit is connected in parallel with the first resistor, and one, two, or three or more parallel amplification switching circuits may be connected in parallel with the first resistor. If multiple parallel amplification switching circuits are connected in parallel with the first resistor in this way, the gain can be changed in multiple stages according to the number of parallel amplification switching circuits connected in parallel. Furthermore, the variable gain circuit may include a voltage follower connected to the output side of the high-pass filter, which outputs the signal from the high-pass filter as a stable signal to a subsequent stage. [Brief explanation of the drawing]

[0010] [Figure 1] This diagram shows a schematic configuration of a noise filter 20 as one embodiment of the present disclosure. [Figure 2] This is an enlarged explanatory diagram showing the variable amplification factor inverting amplifier circuit 25. [Figure 3] This is a table showing an example of the relationship between the switch operation of the amplification factor changing circuit 26, the input resistance Rin of the inverting amplifier circuit 27, and the gain G of the inverting amplifier circuit 27. [Figure 4] This is an explanatory diagram illustrating an example of the relationship between the number of drive phases in the boost circuits 12a to 12f and the frequency and amplitude of electromagnetic noise. [Modes for carrying out the invention]

[0011] Next, embodiments for implementing the present disclosure will be described. Figure 1 is a schematic diagram showing the configuration of a noise filter 20 as one embodiment of the present disclosure. The noise filter 20 of the embodiment is attached to the output side of a multi-phase boost circuit 12a to 12f that boosts the voltage of the battery 10 and functions as a filter to remove high-frequency electromagnetic noise. In the embodiment, the boost circuit to which the noise filter 20 is attached consists of six boost circuits 12a to 12f connected in parallel, and is driven as a 2-phase drive, 4-phase drive, or 6-phase drive. The boost circuits 12a to 12f are all well-known boost circuits consisting of a reactor L, a transistor Tr as a switching element, and a diode D. A smoothing capacitor 18 is attached between the boost circuits 12a to 12f and the noise filter 20.

[0012] The noise filter 20 of this embodiment includes a common mode choke coil 21 connected to the output side of the boost circuits 12a to 12f, a variable gain circuit 22 connected to the output side of the common mode choke coil 21, which changes the gain G according to the number of drive phases of the boost circuits 12a to 12f and outputs a signal that inverts and cancels high-frequency noise, and a Y capacitor 28 that outputs the signal from the variable gain circuit 22 to the output side of the common mode choke coil, and functions as a variable gain hybrid EMI (Electro Magnetic Interference) filter.

[0013] The common mode choke coil 21 is configured as a well-known common mode choke coil.

[0014] The variable gain circuit 22 includes a high-pass filter 23, a voltage follower 24, and a variable gain inverting amplifier circuit 25. The high-pass filter 23 is configured as a circuit in which the junction terminal of a Y capacitor is connected to a reference potential (ground) via a resistor. The voltage follower 24 is configured as an operational amplifier that takes the output from the junction terminal of the Y capacitor of the high-pass filter 23 as input and functions as an amplifier circuit with a gain of 1.

[0015] The variable amplification factor inverting amplifier circuit 25 is composed of an amplification factor changing circuit 26 and an inverting amplifier circuit 27, as shown in the enlarged view of the variable amplification factor inverting amplifier circuit 25 in Figure 2. The amplification factor changing circuit 26 is configured as a circuit to change the input resistance Rin of the inverting amplifier circuit 27, and has a first changing circuit in which a resistor R1 connected to the output side of the voltage follower 24 and the inverting input side of the inverting amplifier circuit 27 is connected in series with a switch SW1 connected in parallel with resistor R1 and a resistor R2, and a second changing circuit in which a switch SW2 connected in parallel with resistor R1 and the first changing circuit and a resistor R3 are connected in series. The inverting amplifier circuit 27 is configured as a well-known inverting amplifier circuit comprising an operational amplifier and a feedback resistor Rf input to the negative terminal of the operational amplifier. The inverting amplifier circuit 27 inverts and amplifies the signal with a gain G determined by the input resistance Rin and feedback resistor Rf, which are changed by the switch operation of the amplification factor changing circuit 26, and outputs it to the junction terminal of the Y capacitor 28.

[0016] FIG. 3 is a list showing an example of the relationship between the switch operation of the amplification factor change circuit 26, the input resistance Rin of the inverting amplifier circuit 27, and the gain G of the inverting amplifier circuit 27. As the input resistance Rin, the combined resistance by the resistors R1, R2, R3 and the combined resistance when R1 = R2 = R3 = R are shown. Also, for the gain G, the one when R1 = R2 = R3 = R is shown. The input resistance Rin of the inverting amplifier circuit 27 becomes the resistance R1 (Rin = R1, Rin = R) by turning off both of the switches SW1 and SW2, and becomes the combined resistance of the resistance R1 and the resistance R2 (Rin = R1·R2 / (R1+R2), Rin = R / 2) by turning on the switch SW1 and turning off the switch SW2, and becomes the combined resistance of the resistance R1, the resistance R2, and the resistance R3 (Rin = R1·R2·R3 / (R1·R2+R2·R3+R3·R1), Rin = R / 3) by turning on both of the switches SW1 and SW2. The gain G of the inverting amplifier circuit 27 becomes |G| = Rf / R when both of the switches SW1 and SW2 are turned off, |G| = 2·Rf / R when the switch SW1 is turned on and the switch SW2 is turned off, and |G| = 3·Rf / R when both of the switches SW1 and SW2 are turned on, provided that R1 = R2 = R3 = R.

[0017] Assuming that the input voltage of the voltage follower 24 is Vcm as the noise voltage detected by the high-pass filter 23 and the potential difference across both ends of the Y capacitor 28 is Vcy, the following equation (1) holds. Solving this for Vcm gives equation (2). On the other hand, assuming that the common-mode current is icy and the impedance of the Y capacitor 28 is Zcy, equation (3) is obtained. Equation (4) is obtained from equation (2) and equation (3). As can be seen from equation (4), the variable-gain inverting amplifier circuit 25 is equivalent to reducing the impedance of the Y capacitor 28 by a factor of 1 / (1 + G).

[0018] Vcm = -G·Vcm + Vcy (1) Vcm = Vcy / (1 + G) (2) Vcy = Zcy·icy (3) Vcm = Zcy·icy / (1 + G) (4)

[0019] In this embodiment, when the boost circuits 12a to 12f are driven in two phases, switches SW1 and SW2 are both turned off and the gain G is set to |G|=Rf / R. When the boost circuits 12a to 12f are driven in four phases, switch SW1 is turned on and switch SW2 is turned off and the gain G is set to |G|=2·Rf / R, or when both switches SW1 and SW2 are turned off, the gain is set to |G|=Rf / R. When the boost circuits 12a to 12f are driven in six phases, switches SW1 and SW2 are both turned on and the gain G is set to |G|=3·Rf / R. Figure 4 shows an example of the relationship between the number of driven phases of the boost circuits 12a to 12f and the frequency and amplitude of electromagnetic noise. When the number of driven phases of the boost circuits 12a to 12f is increased, the electromagnetic noise shifts to the higher frequency side, and the amplitude increases at the same frequency (for example, 150kHz). Therefore, in the noise filter 20 of this embodiment, the amplification factor of the inverting amplifier circuit 27 is increased so that high-frequency electromagnetic noise can be effectively removed even when the number of drive phases of the boost circuits 12a to 12f is increased. That is, when the number of drive phases of the boost circuits 12a to 12f is small (for example, when two phases are driven), the amplitude of low-frequency electromagnetic noise is smaller than when the number of drive phases is large, so the gain G of the inverting amplifier circuit 27 is not increased too much so that electromagnetic noise can be reduced over a wide frequency band up to high frequencies. When the number of drive phases of the boost circuits 12a to 12f is large (for example, when six phases are driven), the amplitude of low-frequency electromagnetic noise is large, so the gain G of the inverting amplifier circuit 27 is increased so that the main purpose is to remove low-frequency electromagnetic noise with large amplitude.

[0020] In the noise filter 20 of the embodiment described above, the gain G of the gain variable inverting amplifier circuit 25 is changed according to the driving phase number of the boost circuits 12a to 12f. That is, when the driving phase number of the boost circuits 12a to 12f is small, the gain G of the inverting amplifier circuit 27 is set small to reduce electromagnetic noise in a wide frequency band up to high frequencies. When the driving phase number of the boost circuits 12a to 12f is large, the gain G of the inverting amplifier circuit 27 is increased to effectively remove low-frequency electromagnetic noise with a large amplitude. As a result, even if the driving phase number of the boost circuits 12a to 12f is changed, high-frequency electromagnetic noise can be sufficiently reduced without increasing the size of the core of the common mode choke coil 21, and a small-sized filter can be obtained.

[0021] In the embodiment, the noise filter 20 is attached to remove high-frequency electromagnetic noise on the output side of the boost circuits 12a to 12f with variable driving phase numbers. However, the noise filter 20 may be attached to remove high-frequency electromagnetic noise on the output side of a power converter that converts power by switching control of a switching element such as a DC / DC converter or an inverter.

[0022] The correspondence between the main elements of the embodiment and the main elements of the invention described in the column of means for solving the problems will be described. In the embodiment, the boost circuits 12a to 12f correspond to the "multi-phase power converter", and the noise filter 20 corresponds to the "noise filter". Also, the common mode choke coil 21 corresponds to the "common mode choke coil", the gain variable circuit 22 corresponds to the "gain variable circuit", and the Y capacitor 28 corresponds to the "Y capacitor".

[0023] Furthermore, the correspondence between the main elements of the embodiment and the main elements of the invention described in the section on means for solving the problem is merely an example to specifically explain the form in which the embodiment implements the invention described in the section on means for solving the problem, and does not limit the elements of the invention described in the section on means for solving the problem. In other words, the interpretation of the invention described in the section on means for solving the problem should be based on the description in that section, and the embodiment is merely one specific example of the invention described in the section on means for solving the problem.

[0024] Although the present disclosure has been described above using embodiments, the present disclosure is not limited in any way to these embodiments, and can of course be implemented in various forms without departing from the gist of the present disclosure. [Industrial applicability]

[0025] This disclosure can be used in industries such as the manufacturing of noise filters. [Explanation of Symbols]

[0026] 10 Battery, 12A~12F boost circuit, 18 Smoothing capacitor, 20 Noise filter, 21 Common mode choke coil, 22 Variable gain circuit, 23 High-pass filter, 24 Voltage follower, 25 Variable gain inverting amplifier circuit, 26 Amplification factor change circuit, 27 Inverting amplifier circuit, 28 Y capacitor, D diode, L reactor, Tr transistor, R1, R2, R3 resistors, Rf feedback resistor, SW1, SW2 switches.

Claims

1. A noise filter attached to the output side of a multi-phase power converter with a changeable number of drive phases, A common mode choke coil connected to the output side of the power converter, A gain-variable circuit connected to the output side of the common-mode choke coil, which changes the gain according to the number of drive phases of the power converter and outputs a signal that inverts and cancels high-frequency noise, A Y capacitor outputs the signal from the variable gain circuit to the output side of the common mode choke coil, A noise filter characterized by having the following features.

2. A noise filter according to claim 1, The variable gain circuit comprises a high-pass filter connected to the output side of the common-mode choke coil, and an inverting amplifier circuit that inverts and amplifies the signal from the high-pass filter and outputs it. The system includes an amplification factor changing circuit that changes the amplification factor of the inverting amplifier circuit by switching a switching element, Noise filter.

3. A noise filter according to claim 2, The amplification factor changing circuit comprises a first resistor provided between the output of the high-pass filter and the input of the inverting amplifier circuit, and at least one parallel amplification switching circuit in which a switching element connected in parallel with the first resistor and a second resistor are connected in series. Noise filter.

4. A noise filter according to claim 2 or 3, The variable gain circuit includes a voltage follower connected to the output side of the high-pass filter, which outputs the signal from the high-pass filter as a stable signal to a subsequent stage. Noise filter.

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