Noise filter

Abstract

Provided is a small noise filter capable of sufficiently reducing high-frequency electromagnetic noise even when used in a power converter capable of changing the number of driving phases. A noise filter is provided with: a common mode choke connected to the output side of a multiphase power converter capable of changing the number of driving phases; a variable gain circuit which is connected to the output side of the common mode choke, changes gain according to the number of driving phases of the power converter, and outputs a signal that counteracts the high-frequency noise; and a Y capacitor that outputs a signal from the variable gain circuit to the output side of the common mode choke.

Description

Technical Field

[0001] This invention relates to a noise filter, and more specifically, to a noise filter installed on the output side of a multiphase power converter capable of changing the number of driving phases. Background Technology

[0002] Conventionally, such noise filters have been proposed that include: an X capacitor connected between a pair of power lines; a Y capacitor connected between the pair of power lines and ground potential; a common-mode choke inserted between the pair of power lines; and a magnetic shield that suppresses magnetic interference between the common-mode choke and the X and Y capacitors (for example, see Patent Document 1).

[0003] Patent Document 1: Japanese Patent Application Publication No. 2008-078844 Summary of the Invention However, in power converters such as multiphase boost circuits that can change the number of drive phases to cope with high current, the more drive phases there are, the higher the frequency of the generated electromagnetic noise shifts, and the larger the amplitude of the low-frequency electromagnetic noise becomes. Therefore, when using the noise filter described above, in order to reduce high-frequency electromagnetic noise over a wide bandwidth, it is necessary to increase the size of the common-mode choke that constitutes the filter, which is difficult to install in limited spaces such as when mounted on a vehicle.

[0004] The main objective of the noise filter of the present invention is to provide a small noise filter that can sufficiently reduce high-frequency electromagnetic noise even when used in a power converter that can change the number of drive phases.

[0005] To achieve the above-mentioned main objectives, the noise filter of the present invention adopts the following scheme.

[0006] The noise filter of the present invention is installed on the output side of a multiphase power converter capable of changing the number of driving phases, and is characterized by comprising: A common-mode choke is connected to the output side of the power converter; A variable gain circuit, connected to the output side of the common-mode choke, changes its gain according to the number of driving phases of the power converter and outputs an inverted signal to cancel high-frequency noise; and The Y capacitor outputs the signal from the variable gain circuit to the output side of the common-mode choke.

[0007] The noise filter of the present invention comprises: a common-mode choke connected to the output side of a power converter; a variable gain circuit connected to the output side of the common-mode choke, which changes the gain according to the number of driving phases of the power converter and outputs an inverse signal to cancel 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. Since the variable gain circuit changes the gain according to the number of driving phases of the power converter and outputs an inverse signal to cancel high-frequency noise, it is possible to reduce high-frequency electromagnetic noise over a wide bandwidth without increasing the size of the common-mode choke.

[0008] In the noise filter of the present invention, the variable gain circuit may include: a high-pass filter connected to the output side of the common-mode choke; an inverting amplifier circuit that inverts and amplifies the signal from the high-pass filter and outputs it; and an amplification rate changing circuit that changes the amplification rate of the inverting amplifier circuit by switching a switching element. Thus, the amplification rate of the inverting amplifier circuit can be easily changed by switching the switching element. In this case, the amplification rate changing circuit may include: a first resistor disposed between the output of the high-pass filter and the input of the inverting amplifier circuit; and at least one parallel amplification switch circuit connected in series with a switching element and a second resistor connected in parallel with the first resistor. The parallel amplification switch circuits connected in parallel with the first resistor can allow one, two, or three or more parallel amplification switch circuits to be connected in parallel with the first resistor. Thus, by connecting multiple parallel amplification switch circuits in parallel with the first resistor, the gain can be changed into multiple stages depending on the number of parallel amplification switch 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 the subsequent stage. Attached Figure Description

[0009] Figure 1 This is a schematic structural diagram showing the structure of a noise filter 20 as an embodiment of the present invention.

[0010] Figure 2 This is an explanatory diagram of the variable amplification inverting amplifier circuit 25.

[0011] Figure 3 This is a table showing an example of the relationship between the switching operation of the amplification rate changing circuit 26 and the input resistance Rin of the inverting amplifier circuit 27 and the gain G of the inverting amplifier circuit 27.

[0012] Figure 4 This is an explanatory diagram illustrating an example of the relationship between the number of driving phases of boost circuits 12a to 12f and the frequency and amplitude of electromagnetic noise. Detailed Implementation

[0013] Next, the methods (implementation methods) for carrying out the present invention will be described. Figure 1 This is a schematic structural diagram showing the structure of a noise filter 20 according to one embodiment of the present invention. The noise filter 20 of this embodiment functions as a filter that removes high-frequency electromagnetic noise by being installed on the output side of a multi-phase boost circuit 12a-12f that boosts the voltage of the battery 10. In this embodiment, the boost circuits on which the noise filter 20 is installed are configured as six boost circuits 12a-12f connected in parallel and driven in 2-phase, 4-phase, and 6-phase configurations. Furthermore, each of the boost circuits 12a-12f is configured as a known boost circuit consisting of a reactor L, a transistor Tr as a switching element, and a diode D. A smoothing capacitor 18 is installed between the boost circuits 12a-12f and the noise filter 20.

[0014] The noise filter 20 of the embodiment includes: a common-mode choke 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 21, which changes the gain G according to the number of driving phases of the boost circuits 12a to 12f and outputs an inverted signal to cancel 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, and functions as a variable gain electromagnetic interference (EMI) filter.

[0015] The common-mode choke 21 is a known common-mode choke.

[0016] 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 to connect the junction of the Y capacitor to a reference potential (ground) via a resistor. The voltage follower 24 is composed of an operational amplifier that receives the output from the junction of the Y capacitor in the high-pass filter 23 and functions as an amplifier circuit with a gain of 1.

[0017] like Figure 2An enlarged view of the variable-rate inverting amplifier circuit 25 is shown. The variable-rate inverting amplifier circuit 25 is composed of an amplification rate changing circuit 26 and an inverting amplifier circuit 27. The amplification rate changing circuit 26 is configured to change the input resistance Rin of the inverting amplifier circuit 27, and includes: a resistor R1 connected to the output side of the voltage follower 24 and to the inverting input side of the inverting amplifier circuit 27; a first changing circuit that connects a switch SW1 connected in parallel with the resistor R1 and a resistor R2 in series; and a second changing circuit that connects a switch SW2 connected in parallel with the resistor R1 and the first changing circuit and a resistor R3 in series. The inverting amplifier circuit 27 is a known inverting amplifier circuit having an operational amplifier and a feedback resistor Rf input to the negative terminal of the operational amplifier. The inverting amplifier circuit 27 amplifies the signal by gain G and outputs it to the junction terminal of the Y capacitor 28. The gain G is determined by the input resistance Rin and the feedback resistor Rf, and the input resistance Rin is changed by the switching operation of the amplification rate changing circuit 26.

[0018] Figure 3 This is a table showing an example of the relationship between the switching operation of the amplification rate changing circuit 26 and the input resistance Rin of the inverting amplifier circuit 27 and the gain G of the inverting amplifier circuit 27. As for the input resistance Rin, the combined resistance consisting of resistors R1, R2, and R3, and the combined resistance when R1=R2=R3=R are shown. Furthermore, regarding the gain G, the gain G when R1=R2=R3=R is shown. The input resistance Rin of the inverting amplifier circuit 27 becomes resistance R1 (Rin=R1, Rin=R) when both switches SW1 and SW2 are set to open; it becomes the combined resistance of resistances R1 and R2 (Rin=R1·R2 / (R1+R2), Rin=R / 2) when both switches SW1 and SW2 are set to open; and it becomes the combined resistance of resistances R1, R2, and R3 (Rin=R1·R2·R3 / (R1·R2+R2·R3+R3·R1), Rin=R / 3) when both switches SW1 and SW2 are set to open. If R1=R2=R3=R, then the gain G of the inverting amplifier circuit 27 becomes |G|=Rf / R when both switches SW1 and SW2 are set to open, |G|=2·Rf / R when switch SW1 is set to open and switch SW2 is set to open, and |G|=3·Rf / R when both switches SW1 and SW2 are set to open.

[0019] If the input voltage of the voltage follower 24 is set to Vcm as the noise voltage detected by the high-pass filter 23, and the potential difference across the Y capacitor 28 is set to Vcy, then equation (1) holds. Equation (2) is obtained by solving for Vcm. On the other hand, if the common-mode current is set to icy and the impedance of the Y capacitor 28 is set to Zcy, then equation (3) is obtained. Equation (4) is obtained from equations (2) and (3). From equation (4), it can be seen that the variable gain inverting amplifier circuit 25 is equivalent to setting the impedance of the Y capacitor 28 to 1 / (1+G) times.

[0020] Vcm = -G·Vcm + Vcy (1) Vcm = Vcy / (1 + G) (2) Vcy=Zcy·icy (3) Vcm=Zcy·icy / (1+G) (4) In the implementation, when the boost circuits 12a to 12f are configured for 2-phase drive, both switches SW1 and SW2 are set to open and the gain G is set to |G| = Rf / R. When the boost circuits 12a to 12f are configured for 4-phase drive, switch SW1 is set to close and switch SW2 is set to open and the gain G is set to |G| = 2·Rf / R. When both switches SW1 and SW2 are set to open and the gain G is set to Rf / R, when the boost circuits 12a to 12f are configured for 6-phase drive, both switches SW1 and SW2 are set to close and the gain G is set to |G| = 3·Rf / R. Figure 4 An example is shown illustrating the relationship between the number of driving phases of the boost circuits 12a to 12f and the frequency and amplitude of electromagnetic noise. Increasing the number of driving phases of the boost circuits 12a to 12f causes the electromagnetic noise to shift towards higher frequencies, resulting in a larger amplitude at the same frequency (e.g., 150 kHz). Therefore, in the noise filter 20 of this embodiment, by increasing the amplification of the inverting amplifier circuit 27, high-frequency electromagnetic noise can be effectively removed even when the number of driving phases of the boost circuits 12a to 12f is increased. That is, when the number of driving phases of the boost circuits 12a to 12f is small (e.g., when driving with 2 phases), the amplitude of low-frequency electromagnetic noise is small compared to when the number of driving phases is large. Therefore, by ensuring that the gain G of the inverting amplifier circuit 27 is not too large, electromagnetic noise can be reduced in a wide bandwidth up to the high frequency. When the number of driving phases of the boost circuits 12a to 12f is large (e.g., when driving with 6 phases), the amplitude of low-frequency electromagnetic noise becomes large. Therefore, the main purpose is to increase the gain G of the inverting amplifier circuit 27 to remove low-frequency electromagnetic noise with large amplitude.

[0021] In the noise filter 20 of the above-described embodiment, the gain G of the variable gain inverting amplifier circuit 25 is changed according to the number of driving phases of the boost circuits 12a to 12f. That is, when the number of driving phases of the boost circuits 12a to 12f is small, the gain G of the inverting amplifier circuit 27 is set to a small value to reduce electromagnetic noise over a wide bandwidth up to high frequencies. When the number of driving phases 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 large amplitude. Therefore, even if the number of driving phases of the boost circuits 12a to 12f is changed, the volume of the magnetic core of the common-mode choke 21 can be increased to sufficiently reduce high-frequency electromagnetic noise, and a small filter can be made.

[0022] In one embodiment, a noise filter 20 is installed to remove high-frequency electromagnetic noise from the output side of the boost circuits 12a to 12f with variable number of driving phases. However, the noise filter 20 may also be installed to remove high-frequency electromagnetic noise from the output side of a power converter that converts power through the switching control of switching elements such as DC / DC converters or inverters.

[0023] The correspondence between the main elements of the implementation method and the main elements of the invention described in the solution to the problem section will be explained. In the implementation method, the boost circuits 12a to 12f correspond to a "multiphase power converter", and the noise filter 20 corresponds to a "noise filter". Furthermore, the common-mode choke 21 corresponds to a "common-mode choke", the variable gain circuit 22 corresponds to a "variable gain circuit", and the Y capacitor 28 corresponds to a "Y capacitor".

[0024] Furthermore, the correspondence between the main elements of the implementation method and the main elements of the invention described in the "Solution to the Problem" column is merely an example of how the implementation method is used to carry out the invention described in the "Solution to the Problem" column, and therefore does not limit the elements of the invention described in the "Means to the Problem" column. That is, the interpretation of the invention described in the "Solution to the Problem" column should be based on the description in that column, and the implementation method is simply a specific example of the invention described in the "Solution to the Problem" column.

[0025] The present invention has been described above using embodiments, but the present invention is not limited to such embodiments. It can of course be implemented in various ways without departing from the spirit of the present invention.

[0026] Industrial availability This invention can be used in industries such as the manufacturing of noise filters.

[0027] Symbol Explanation 10 - Battery; 12a-12f - Boost circuit; 18 - Smoothing capacitor; 20 - Noise filter; 21 - Common-mode choke; 22 - Variable gain circuit; 23 - High-pass filter; 24 - Voltage follower; 25 - Variable gain inverting amplifier circuit; 26 - Gain rate changing 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 mounted on an output side of a multiphase power converter capable of changing the number of phases of driving, characterized by, have: A common-mode choke is connected to the output side of the power converter; A variable gain circuit, which is connected to the output side of the common-mode choke, changes the gain according to the number of driving phases of the power converter and outputs an inverted signal to cancel high-frequency noise; and The Y capacitor outputs the signal from the variable gain circuit to the output side of the common-mode choke.

2. The noise filter according to claim 1, characterized in that, The variable gain circuit includes: a high-pass filter connected to the output side of the common-mode choke; an inverting amplifier circuit that inverts and amplifies the signal from the high-pass filter and outputs it; and an amplification rate changing circuit that changes the amplification rate of the inverting amplifier circuit by switching a switching element.

3. The noise filter according to claim 2, characterized in that, The amplification rate changing circuit includes: a first resistor disposed between the output of the high-pass filter and the input of the inverting amplifier circuit; and at least one parallel amplification switch circuit, which is connected in series with a switching element and a second resistor connected in parallel with the first resistor.

4. The noise filter according to claim 2 or 3, characterized in that, 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 the subsequent stage.

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