Noise attenuation circuit

Abstract

To provide a noise attenuation circuit capable of attenuating common mode noise in a wide frequency band while avoiding oscillation.SOLUTION: A noise attenuation circuit comprises: an auxiliary coil wound around a core of a common mode coil provided between a power storage device and an inverter; and a conversion circuit 51 that converts a current detected at the auxiliary coil into an attenuation current. The conversion circuit 51 comprises: a low-pass filter 52; and an amplifier circuit 53 provided at a post stage of the low-pass filter 52. The low-pass filter 52 comprises: an amplifier 52a; a capacitor 52b and a resistor 52c connected in series between an inverted input terminal of the amplifier 52a and an output terminal; and a resistor 52d connected in parallel to the capacitor 52b and the resistor 52c. A cut-off frequency of the low-pass filter 52 prescribed by the capacitor 52b and the resistor 52d is lower than a first resonance frequency of a closed circuit including the common mode coil.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a noise attenuation circuit.

Background Art

[0002] A canceller circuit for attenuating common-mode noise generated in a motor or the like is known. For example, Patent Document 1 describes a common-mode noise canceller circuit device including a primary coil provided between a DC high-voltage power supply and a three-phase inverter circuit, a secondary coil electromagnetically coupled to the primary coil, and a noise cancellation circuit. In this device, when a common-mode current flows through the primary coil, a common-mode voltage is generated in the secondary coil, and a common-mode cancellation current having a phase opposite to that of the common-mode current is generated by the noise cancellation circuit based on the common-mode voltage.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the device described in Patent Document 1, in a closed circuit including a noise cancellation circuit, there is a resonance frequency defined by an inductance component such as a primary coil and a capacitance component such as an output capacitor included in the noise cancellation circuit. In order to avoid oscillation at the resonance frequency, a high-pass filter may be provided in the noise cancellation circuit. However, with such a configuration, there is a possibility that noise cannot be sufficiently attenuated in the low-frequency band.

[0005] The present disclosure describes a noise attenuation circuit capable of attenuating common-mode noise in a wide frequency band while avoiding oscillation.

Means for Solving the Problem

[0006] The noise attenuation circuit according to one aspect of the present disclosure is a circuit that is provided between a power storage device and an inverter that converts DC power supplied from the power storage device into AC power, and generates an attenuation current for attenuating the noise current generated in the inverter. This noise attenuation circuit includes an auxiliary coil wound around the core of a common mode coil provided between the power storage device and the inverter, and a conversion circuit that amplifies the current detected by the auxiliary coil and converts it into an attenuation current. The conversion circuit includes a first low-pass filter and an amplification circuit provided at the subsequent stage of the first low-pass filter. The first low-pass filter includes an amplifier having an inverting input terminal, a non-inverting input terminal to which one end of the auxiliary coil is connected, and an output terminal, a capacitor and a first resistor connected in series between the inverting input terminal and the output terminal, and a second resistor connected in parallel with the capacitor and the first resistor. The cut-off frequency of the first low-pass filter defined by the capacitor and the second resistor is lower than the first resonance frequency of the closed circuit including the common mode coil.

[0007] In this noise attenuation circuit, in the conversion circuit, the current detected by the auxiliary coil is amplified and converted into an attenuation current for attenuating the noise current. When the phase of the input and the phase of the output at a predetermined location in a closed circuit including a common mode coil are in the same phase (phase difference is 0°) and the gain of the closed circuit is greater than 0 dB, it is known that oscillation occurs. In the above noise attenuation circuit, a first low-pass filter is provided at one end of the auxiliary coil. In the first low-pass filter, a capacitor and a first resistor are connected in series between the inverting input terminal and the output terminal of the amplifier, and a second resistor is connected in parallel with the capacitor and the first resistor. The cut-off frequency of the first low-pass filter defined by the capacitor and the second resistor is lower than the first resonance frequency of the closed circuit including the common mode coil. Therefore, at frequencies lower than the first resonance frequency, a phase delay occurs due to the first low-pass filter, and at the first resonance frequency, the phase of the output with respect to the phase of the input at a predetermined location in the closed circuit including the common mode coil is delayed. Therefore, oscillation can be avoided at the first resonance frequency without reducing the gain in the low frequency band to 0 dB or less, so that common mode noise can be attenuated even in the low frequency band. As a result, it is possible to attenuate common mode noise in a wide frequency band while avoiding oscillation.

[0008] In some embodiments, the combined impedance of the capacitor and the first resistor may be smaller than the resistance value of the second resistor at frequencies higher than the first resonance frequency. At frequencies lower than the first resonance frequency, a phase delay occurs due to the first low-pass filter, and at the first resonance frequency, the phase is further delayed by 180°. In the above configuration, at frequencies higher than the first resonance frequency, the capacitor and the first resistor become dominant, so the phase delay approaches -180°. Therefore, an attenuation current having a phase opposite to the current flowing through the auxiliary coil can be generated. As a result, it is possible to maintain the attenuation effect while enabling attenuation of common mode noise in a wide frequency band.

[0009] In some embodiments, the conversion circuit may further include a second low-pass filter provided at the subsequent stage of the amplification circuit. The cut-off frequency of the second low-pass filter may be lower than the second resonance frequency defined by the parasitic capacitance and the parasitic inductance between the common-mode coil and the auxiliary coil. It is known that oscillation occurs when the phase of the input and the phase of the output at a predetermined location of the closed circuit including the parasitic capacitance are in the same phase (the phase difference is a multiple of 360°) and the gain of the closed circuit is greater than 0 dB. In the above configuration, since the cut-off frequency of the second low-pass filter is lower than the second resonance frequency, the frequency components above the cut-off frequency are attenuated, and the gain at the second resonance frequency becomes 0 dB or less. Thereby, it becomes possible to avoid oscillation.

Effect of the Invention

[0010] According to the present disclosure, it is possible to attenuate common-mode noise in a wide frequency band while avoiding oscillation.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0012] Hereinafter, a noise attenuation circuit according to an embodiment will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or equivalent elements are denoted by the same reference numerals, and overlapping descriptions are omitted.

[0013] With reference to FIG. 1, the configuration of a power supply device including a noise attenuation circuit according to an embodiment will be described. FIG. 1 is a schematic configuration diagram of a power supply device including a noise attenuation circuit according to an embodiment. The power supply device 1 shown in FIG. 1 is a device that supplies AC power to a motor M. The power supply device 1 includes a power storage device 2, a main circuit 3, an inverter 4, a noise attenuation circuit 5, and a power supply transformer 6. In the power supply device 1, the noise current In generated by the inverter 4 is attenuated by the noise attenuation circuit 5.

[0014] The power storage device 2 supplies DC power to the inverter 4. The power storage device 2 can be used, for example, as a battery for various vehicles such as forklifts, hybrid vehicles, and electric vehicles. The power storage device 2 is composed of, for example, a lithium ion battery, a lead storage battery, a nickel metal hydride battery, or the like.

[0015] The main circuit 3 includes a common mode coil 31, a common mode coil 32, a connection line 33, a connection line 34, a capacitor 35, and a capacitor 36. The common mode coil 31 and the common mode coil 32 are wound around a core formed of a magnetic material and constitute a common mode choke coil.

[0016] In the common mode choke coil, when a common mode current (hereinafter referred to as "common mode current") flows through the common mode coil 31 and the common mode coil 32, magnetic flux is generated by the electromagnetic induction phenomenon in the common mode coil 31 and the common mode coil 32. In this case, the directions of the generated magnetic fluxes are the same, and the magnetic fluxes of each other strengthen each other, and the common mode choke coil functions as an inductor. When a differential mode current flows through the common mode coil 31 and the common mode coil 32, the directions of the generated magnetic fluxes are opposite, so the magnetic fluxes cancel each other out. As a result, the common mode choke coil does not function as an inductor for the differential mode current.

[0017] The common-mode coils 31 and 32 are provided between the power storage device 2 and the inverter 4. One end of the common-mode coil 31 is connected to the positive terminal of the power storage device 2. The other end of the common-mode coil 31 is connected to the connection line 33. One end of the common-mode coil 32 is connected to the negative terminal of the power storage device 2. The other end of the common-mode coil 32 is connected to the connection line 34.

[0018] The connection line 33 connects the common-mode coil 31 and the inverter 4. Specifically, one end of the connection line 33 is connected to the other end of the common-mode coil 31. The other end of the connection line 33 is connected to the inverter 4.

[0019] The connection line 34 connects the common-mode coil 32 and the inverter 4. Specifically, one end of the connection line 34 is connected to the other end of the common-mode coil 32. The other end of the connection line 34 is connected to the inverter 4.

[0020] The capacitors 35 and 36 are Y capacitors and are provided between the connection line 33 and the connection line 34 and the ground potential (earth). Specifically, one end of the capacitor 35 is connected to the other end of the connection line 33. The other end of the capacitor 35 is connected to the ground potential (earth). One end of the capacitor 36 is connected to the ground potential (earth). The other end of the capacitor 36 is connected to the other end of the connection line 34.

[0021] The inverter 4 converts the DC power as the input power supplied from the power storage device 2 into AC power and outputs it to the motor M. In the present embodiment, the inverter 4 is a three-phase inverter and has a plurality of switching elements (not shown). The switching element is an element that can switch electrical opening and closing. As the switching element, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), an IGBT (Insulated Gate Bipolar Transistor), a bipolar transistor, etc. are used. Note that the inverter 4 includes a drive circuit (not shown), and the power supply voltage is supplied from the power transformer 6 to the drive circuit.

[0022] The noise attenuation circuit 5 is a circuit that generates an attenuation current Ic for attenuating the noise current In (common mode current) generated in the inverter 4. The noise attenuation circuit 5 is provided between the power storage device 2 and the inverter 4. The noise attenuation circuit 5 includes an auxiliary coil 50 and a conversion circuit 51. The noise attenuation circuit 5 detects the noise current In in the auxiliary coil 50 and generates an attenuation current Ic having a phase opposite to that of the noise current In, thereby attenuating the noise current In generated in the inverter 4.

[0023] The auxiliary coil 50 is wound around the cores of the common mode coil 31 and the common mode coil 32 and detects the noise current In. One end of the auxiliary coil 50 is connected to the ground potential (earth). The other end of the auxiliary coil 50 is connected to the conversion circuit 51. The auxiliary coil 50 outputs the detected noise current In to the conversion circuit 51. When the noise current In flows through the auxiliary coil 50, a common mode voltage is generated. Therefore, it can be said that the auxiliary coil 50 outputs the common mode voltage to the conversion circuit 51.

[0024] The conversion circuit 51 is a circuit that amplifies the noise current In (common-mode voltage) detected by the auxiliary coil 50 and converts it into a damping current Ic. The input terminal 51a of the conversion circuit 51 is connected to the other end of the auxiliary coil 50. The output terminal 51b of the conversion circuit 51 is connected to the connection line 34. The conversion circuit 51 generates a current with a phase opposite to that of the noise current In and outputs it as the damping current Ic, thereby attenuating the noise current In generated in the inverter 4. The circuit configuration of the conversion circuit 51 will be described later.

[0025] The power transformer 6 is connected to the power storage device 2. The power transformer 6 converts the power storage voltage of the power storage device 2 into a voltage for supplying the drive circuit of the inverter 4 and the noise attenuation circuit 5, and supplies the converted voltage to the drive circuit of the inverter 4 and the noise attenuation circuit 5.

[0026] In the power supply device 1, when DC power is supplied from the power storage device 2 to the inverter 4, a noise current In is generated by the switching operation of the inverter 4. At this time, the noise current In flows through the common-mode coil 31 and the common-mode coil 32, and the auxiliary coil 50 detects the noise current In flowing through the common-mode coil 31 and the common-mode coil 32. Then, the conversion circuit 51 generates a damping current Ic with a phase opposite to that of the noise current In from the noise current In detected by the auxiliary coil 50 and supplies it to the inverter 4 (connection line 34). Thereby, the noise current In is attenuated.

[0027] Here, in the power supply device 1, a closed circuit C1 and a closed circuit C2 are formed. The closed circuit C1 includes one of the common mode coils 31 and 32 and one of the capacitors 35 and 36. Specifically, for example, the closed circuit C1 is a circuit that sequentially circulates through a capacitor (for example, a Y capacitor) connected to the ground in the power storage device 2, the common mode coil 31, the connection line 33, the capacitor 35, and the ground. The closed circuit C2 includes the parasitic capacitance generated between the common mode coils 31 and 32 and the auxiliary coil 50. Specifically, for example, the closed circuit C2 is a circuit that sequentially circulates through the connection line 34, the parasitic capacitance generated between the common mode coil 32 and the auxiliary coil 50, the auxiliary coil 50, and the conversion circuit 51.

[0028] In the closed circuit C1, there exists a resonance frequency fr1 (first resonance frequency). The resonance frequency fr1 is defined by the inductance component and capacitance component included in the closed circuit C1. The resonance frequency fr1 is defined, for example, by the inductance of the common mode coil 31 and the capacitance value of the capacitor 35. In the closed circuit C2, there exists a resonance frequency fr2 (second resonance frequency). The resonance frequency fr2 is a frequency higher than the resonance frequency fr1 and is defined by the inductance component and capacitance component included in the closed circuit C2. The resonance frequency fr2 is defined, for example, by the parasitic capacitance between the common mode coil 32 and the auxiliary coil 50 and the parasitic inductance included in the closed circuit C2.

[0029] Next, with reference to FIG. 2, the circuit configuration of the conversion circuit 51 will be described. FIG. 2 is a diagram showing the circuit configuration of the conversion circuit shown in FIG. 1. As shown in FIG. 2, the conversion circuit 51 includes a low-pass filter 52 (first low-pass filter), an amplifier circuit 53, a low-pass filter 54 (second low-pass filter), and an output capacitor 55.

[0030] The low-pass filter 52 is a circuit for delaying the phase of the noise current In (common mode voltage) detected by the auxiliary coil 50. The low-pass filter 52 includes an amplifier 52a, a capacitor 52b, a resistor 52c (first resistor), and a resistor 52d (second resistor).

[0031] The non-inverting input terminal of the amplifier 52a is connected to the input terminal 51a (the other end of the auxiliary coil 50). The capacitor 52b and the resistor 52c are connected in series between the inverting input terminal and the output terminal of the amplifier 52a. Specifically, one end of the capacitor 52b is connected to the inverting input terminal of the amplifier 52a, the other end of the capacitor 52b is connected to one end of the resistor 52c, and the other end of the resistor 52c is connected to the output terminal of the amplifier 52a. The resistor 52d is connected in parallel with the capacitor 52b and the resistor 52c. Specifically, one end of the resistor 52d is connected to the inverting input terminal of the amplifier 52a, and the other end of the resistor 52d is connected to the output terminal of the amplifier 52a.

[0032] The cut-off frequency fc1 of the low-pass filter 52 is defined by the capacitance value of the capacitor 52b and the resistance value of the resistor 52d. The capacitance value of the capacitor 52b and the resistance value of the resistor 52d are set so that the cut-off frequency fc1 is lower than the resonance frequency fr1 of the closed circuit C1. The resistance value of the resistor 52c is smaller than the resistance value of the resistor 52d. More specifically, the capacitance value of the capacitor 52b, the resistance value of the resistor 52c, and the resistance value of the resistor 52d are set so that the combined impedance of the capacitor 52b and the resistor 52c is smaller than the resistance value of the resistor 52d at frequencies higher than the resonance frequency fr1. As an example, the capacitance value of the capacitor 52b is set to 1500 pF, the resistance value of the resistor 52c is set to 1 kΩ, and the resistance value of the resistor 52d is set to 10 kΩ.

[0033] Since the low-pass filter 52 is provided for the purpose of delaying the phase of the noise current In (common-mode voltage), the gain of the low-pass filter 52 is set to about 2 times, for example. The low-pass filter 52 outputs the processed signal to the amplifier circuit 53.

[0034] The amplifier circuit 53 is a circuit that amplifies the signal output from the low-pass filter 52. The amplifier circuit 53 is provided at the subsequent stage of the low-pass filter 52. In the present embodiment, the amplifier circuit 53 is a non-inverting amplifier circuit. The amplifier circuit 53 includes an amplifier 53a, a resistor 53b, and a resistor 53c. The non-inverting input terminal of the amplifier 53a is connected to the output terminal of the amplifier 52a. The inverting input terminal of the amplifier 53a is connected to the ground potential via the resistor 53b and is also connected to the output terminal of the amplifier 53a via the resistor 53c. The gain of the amplifier circuit 53 is determined by the resistance value of the resistor 53b and the resistance value of the resistor 53c. The amplifier circuit 53 outputs the amplified signal to the low-pass filter 54.

[0035] The low-pass filter 54 is a circuit for attenuating the high-frequency components of the signal output from the amplifier circuit 53. The low-pass filter 54 is provided at the subsequent stage of the amplifier circuit 53. The low-pass filter 54 is composed of, for example, a capacitor and a resistor. The low-pass filter 54 attenuates the frequency components of fc2 or higher and passes the frequency components lower than the cut-off frequency fc2. The cut-off frequency fc2 of the low-pass filter 54 is set to a frequency lower than the resonance frequency fr2. The cut-off frequency fc2 is set to a frequency at which the gain Gv of the closed-loop C2 becomes 0 dB or less when the phase difference Δθ between the input and output at a predetermined location of the closed-loop C2 is -360°.

[0036] When the phase of the output is ahead of the phase of the input, the phase difference Δθ is a positive value. When the phase of the output lags behind the phase of the input, the phase difference Δθ is a negative value. The low-pass filter 54 outputs the processed signal to the output capacitor 55.

[0037] The output capacitor 55 converts the signal output from the low-pass filter 54 into a damping current Ic. The output capacitor 55 is provided between the low-pass filter 54 and the output terminal 51b (connection line 34). Specifically, one end of the output capacitor 55 is connected to the output terminal of the low-pass filter 54, and the other end of the output capacitor 55 is connected to the output terminal 51b.

[0038] Next, while further referring to FIG. 3, the operation and effect of the noise attenuation circuit 5 will be described. FIG. 3 is a Bode diagram showing the gain characteristic and phase characteristic of the noise attenuation circuit shown in FIG. 1. The horizontal axis of FIG. 3 indicates the frequency (unit: Hz). The left vertical axis of FIG. 3 indicates the gain Gv (unit: dB), and the right vertical axis indicates the phase difference Δθ (unit: °).

[0039] When the phase difference Δθ is an integer multiple of 0° or 360° and the gain Gv is greater than 0 dB, it is known that oscillation occurs. In the noise attenuation circuit 5, a low-pass filter 52 is provided at the other end of the auxiliary coil 50. In the low-pass filter 52, a capacitor 52b and a resistor 52c are connected in series between the inverting input terminal and the output terminal of the amplifier 52a, and a resistor 52d is connected in parallel with the capacitor 52b and the resistor 52c.

[0040] As shown in FIG. 3, the cut-off frequency fc1 of the low-pass filter 52 is set to a frequency lower than the resonance frequency fr1 of the closed circuit C1. For this reason, at a frequency lower than the resonance frequency fr1, a phase delay due to the low-pass filter 52 occurs, so that the phase difference Δθ becomes smaller than 0° at the resonance frequency fr1. Therefore, oscillation can be avoided without reducing the gain Gv in the low-frequency band to 0 dB or less, so that common-mode noise can be attenuated also in the low-frequency band. As a result, it is possible to attenuate common-mode noise in a wide frequency band while avoiding oscillation.

[0041] As the frequency increases, the impedance of the capacitor 52b decreases. At a frequency higher than the resonance frequency fr1, the combined impedance of the capacitor 52b and the resistor 52c becomes smaller than the resistance value of the resistor 52d. With this configuration, at frequencies higher than the resonance frequency fr1, it becomes difficult for current to flow through the resistor 52d, and current flows through the capacitor 52b and the resistor 52c. That is, in the low-pass filter 52, the capacitor 52b and the resistor 52c become dominant. As a result, the phase delay due to the low-pass filter 52 approaches 0°. At the resonance frequency fr1, a phase delay of 180° occurs, so the phase difference Δθ at frequencies higher than the resonance frequency fr1 approaches -180°. Therefore, it is possible to generate a damping current Ic that is in the opposite phase to the common-mode current flowing through the auxiliary coil 50. As a result, it is possible to attenuate common-mode noise in a wide frequency band while maintaining the attenuation effect.

[0042] As shown in FIG. 3, the cut-off frequency fc2 of the low-pass filter 54 is set to a frequency lower than the resonance frequency fr2. For this reason, frequency components of fc2 or higher are attenuated, and the gain Gv at the resonance frequency fr2 becomes 0 dB or less. As a result, since the gain Gv when the phase difference Δθ is -360°×n (n is an integer of 1 or more) becomes 0 dB or less, oscillation can be avoided.

[0043] As described above in detail for one embodiment of the present disclosure, the noise attenuation circuit according to the present disclosure is not limited to the above embodiment.

[0044] In the above embodiment, the power supply voltage is supplied to the noise attenuation circuit 5 from the power storage device 2 via the power transformer 6, but the power supply voltage may be supplied from a power source different from the power storage device 2.

Description of Reference Numerals

[0045] 1... Power supply device, 2... Energy storage device, 4... Inverter, 5... Noise attenuation circuit, 31... Common mode coil, 32... Common mode coil, 50... Auxiliary coil, 51... Conversion circuit, 52... Low-pass filter (first low-pass filter), 52a... Amplifier, 52b... Capacitor, 52c... Resistor (first resistor), 52d... Resistor (second resistor), 53... Amplification circuit, 54... Low-pass filter (second low-pass filter), C1... Closed circuit, C2... Closed circuit, M... Motor.

Claims

1. A noise attenuation circuit provided between a power storage device and an inverter that converts DC power supplied from the power storage device into AC power, and generates an attenuation current for attenuating noise current generated in the inverter, an auxiliary coil wound around a core of a common mode coil provided between the power storage device and the inverter, and a conversion circuit that amplifies a current detected by the auxiliary coil and converts it into the attenuation current, wherein the conversion circuit comprises a first low-pass filter, and an amplification circuit provided at a subsequent stage of the first low-pass filter, wherein the first low-pass filter comprises an amplifier having an inverting input terminal, a non-inverting input terminal to which one end of the auxiliary coil is connected, and an output terminal, a capacitor and a first resistor connected in series between the inverting input terminal and the output terminal, and a second resistor connected in parallel with the capacitor and the first resistor, wherein a cut-off frequency of the first low-pass filter defined by the capacitor and the second resistor is lower than a first resonance frequency of a closed circuit including the common mode coil. The noise attenuation circuit

2. The noise attenuation circuit according to claim 1, wherein a combined impedance of the capacitor and the first resistor is smaller than a resistance value of the second resistor at a frequency higher than the first resonance frequency.

3. The conversion circuit further comprises a second low-pass filter provided at a subsequent stage of the amplification circuit, wherein a cut-off frequency of the second low-pass filter is lower than a second resonance frequency defined by a parasitic capacitance and a parasitic inductance between the common mode coil and the auxiliary coil. The noise attenuation circuit according to claim 1 or claim 2

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