Power converter, vehicle drive system, noise suppression method

Abstract

This power conversion device comprises: an inverter circuit to the input side of which a positive electrode wire and a negative electrode wire are connected, and which converts an input current flowing through the positive electrode wire and the negative electrode wire into an output current and outputs the output current to a load device; an output power line that is connected between the inverter circuit and the load device, and through which the output current including a noise current flows; a magnetic core through which the output power line penetrates; and a first noise recirculation line and a second noise recirculation line for recirculating the noise current. The first noise recirculation line and the second noise recirculation line are each provided to run parallel to the output power line. One ends of the first noise recirculation line and the second noise recirculation line are each electrically connected to ground on the load device side. The other ends of the first noise recirculation line and the second noise recirculation line are each electrically connected to the negative electrode wire. The first noise recirculation line penetrates through the magnetic core.

Description

Technical Field

[0001] The present invention relates to a power conversion device, a vehicle drive system, and a noise suppression method.

Background Art

[0002] Power conversion devices that apply power semiconductor devices such as IGBTs (Insulated Gate Bipolar Transistors) are widely used not only in general industrial fields but also in various fields such as railways and automobiles because of their good energy-saving performance and controllability. However, the steep changes in current and voltage due to the switching operation of power semiconductor devices include high-frequency noise components, which may cause electromagnetic interference to peripheral devices.

[0003] For example, in a railway system, it is known that electromagnetic radiation noise derived from a power conversion device such as a drive inverter mounted on a vehicle causes an induced fault in a ground signal protection device arranged on a track, and it is necessary to take countermeasures. In recent years, in order to save energy, in a drive inverter of a railway vehicle, the use of a SiC (Silicon Carbide)-MOSFET (Metal Oxide Semiconductor Field Effect Transistor), which has a faster switching speed than an IGBT, as a power semiconductor device has been increasing. However, the higher switching speed associated with the adoption of SiC-MOSFETs is a factor in increasing electromagnetic radiation noise in the high-frequency range, so noise suppression is an issue in drive systems for railway vehicles.

[0004] In a motor-inverter system typified by a drive system for railway vehicles, a common-mode current is generated by the switching operation of a power semiconductor device, and electromagnetic radiation noise is generated by this current. The motor connected to the inverter has a stray capacitance with respect to the grounding system (corresponding to the vehicle body and rails in a railway system), and the common-mode current leaks to the grounding system through this stray capacitance. The electromagnetic radiation noise generated by this leaked common-mode current causes problems such as induced faults.

[0005] Conventional techniques for suppressing noise caused by common-mode current in motor inverter systems are known, for example, in Patent Documents 1 and 2. Patent Document 1 discloses a method for reducing noise by changing the ratio of noise current flowing back to the inverter side and noise current flowing out to the ground side by connecting the ground terminal of an inverter device and the ground terminal of a load device such as a motor with a lead wire. Patent Document 2 discloses a method for suppressing high-frequency noise interference caused by common-mode current by connecting the ground wire on the power supply side and the ground wire on the load side of a power converter via a common-mode current return line, and winding the output power line of the power converter and the common-mode current return line on the same magnetic core. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 5-22985 [Patent Document 2] Japanese Patent Publication No. 2001-86734 [Overview of the project] [Problems that the invention aims to solve]

[0007] While the conventional technologies described in Patent Documents 1 and 2 are effective in reducing noise in the relatively low frequency range (for example, the frequency band below 100 kHz), they may not provide sufficient noise reduction for relatively high-frequency noise (for example, the frequency band above 1 MHz), such as noise generated in inverters employing SiC-MOSFETs.

[0008] The present invention has been made in view of the above-mentioned points, and its main objective is to suppress high-frequency electromagnetic radiation noise caused by common-mode current in a power conversion device and a vehicle drive system using the same. [Means for solving the problem]

[0009] The power conversion device according to the present invention comprises: an inverter circuit having positive and negative wiring connected to the input side, which converts the input current flowing through the positive and negative wiring into an output current and outputs it to a load device; an output power line connected between the inverter circuit and the load device through which the output current, including noise current, flows; a magnetic core through which the output power line passes; and a first noise return line and a second noise return line for each of the noise currents to return, respectively. The first noise return line and the second noise return line are laid so as to run parallel to the output power line, respectively. One end of the first noise return line and the second noise return line are electrically connected to the ground on the load device side, respectively. The other end of the first noise return line and the second noise return line are electrically connected to the negative wiring, respectively. The first noise return line passes through the magnetic core. The vehicle drive system according to the present invention comprises a power converter and a motor connected to the power converter via an output power line, wherein the output current output from the power converter is used to generate a driving force in the motor, and the driving force is used to drive the vehicle. The noise suppression method according to the present invention is a method for suppressing noise current included in the output current from a power converter to a load device, wherein the output power line through which the output current flows is passed through a magnetic core, a first noise return line and a second noise return line are laid so as to run parallel to the output power line, the first noise return line is passed through the magnetic core, one end of the first noise return line and the second noise return line are electrically connected to the ground on the load device side, and the other end of the first noise return line and the second noise return line are electrically connected to the negative electrode wiring connected to the input side of the power converter. [Effects of the Invention]

[0010] According to the present invention, in a power conversion device and a vehicle drive system using the same, high-frequency electromagnetic radiation noise caused by common-mode current can be suppressed. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows the circuit configuration of a vehicle drive system according to the first embodiment of the present invention. [Figure 2] This is an explanatory diagram of noise current in a vehicle's drive system. [Figure 3] This is an explanatory diagram illustrating the noise suppression effect of the present invention. [Figure 4] This figure shows the simulation results of the noise suppression effect of the present invention. [Figure 5] This figure shows the circuit configuration of a vehicle drive system according to a second embodiment of the present invention. [Figure 6] This figure shows the circuit configuration of a vehicle drive system according to a third embodiment of the present invention. [Figure 7] This figure shows the circuit configuration of a vehicle drive system according to a fourth embodiment of the present invention. [Figure 8] This figure shows the circuit configuration of a vehicle drive system according to a fifth embodiment of the present invention. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described below with reference to the drawings.

[0013] (First Embodiment) Figure 1 is a diagram showing the circuit configuration of a vehicle drive system according to the first embodiment of the present invention. The vehicle drive system 1 of this embodiment is a system for driving vehicles such as railway vehicles and automobiles, and is configured to include a motor 101 and a power converter 200.

[0014] The motor 101 acts as a load device for the power converter 200 and rotates in accordance with the output current output from the power converter 200. The driving force generated by the rotational drive of this motor 101 can be used to drive the vehicle on which the vehicle drive system 1 is installed.

[0015] The power conversion device 200 includes an inverter circuit 202, a filter reactor 201, a filter capacitor 203, and a magnetic core 206.

[0016] The inverter circuit 202 has a positive electrode wiring 204 and a negative electrode wiring 205 connected to its input side. A DC input current flows through the positive electrode wiring 204 and the negative electrode wiring 205 to the input side of the inverter circuit 202. The inverter circuit 202 has switching elements such as IGBTs or SiC-MOSFETs, and by driving these switching elements to switch, it converts the DC input current into an AC output current.

[0017] The power conversion device 200 and the motor 101 are connected via an output power line 301, and the output current from the power conversion device 200 flows through the output power line 301 and is input to the motor 101. Thereby, AC power is supplied from the power conversion device 200 to the motor 101, and the motor 101 is rotationally driven.

[0018] Note that the output current flowing through the output power line 301 includes a noise current generated by the switching operation of the inverter circuit 202 in the power conversion device 200 or the like. If this noise current leaks to the outside, it may have an adverse effect on other devices. Therefore, in this embodiment, in order to suppress the leakage of the noise current by returning the output current flowing through the output power line 301 to the power conversion device 200, noise reflux lines 302 and 303 are provided between the power conversion device 200 and the motor 101 in addition to the output power line 301.

[0019] The noise return lines 302 and 303 are laid parallel to the output power line 301, respectively. One end of the noise return lines 302 and 303 is electrically connected to the ground (earth potential) 401 on the motor 101 side via the motor 101 housing. Note that the connection points between the noise return lines 302 and 303 and the motor 101 housing do not necessarily have to coincide and may be far apart. The ground 401 corresponds to, for example, the body of the vehicle on which the vehicle drive system 1 is installed, or the rails on which the railway vehicle runs. The other ends of the noise return lines 302 and 303 are electrically connected to the negative electrode wiring 205, respectively. The noise return line 302 and the output power line 301 pass through a common magnetic core 206. On the other hand, the noise return line 303 does not pass through the magnetic core 206.

[0020] Next, the noise current in the vehicle drive system 1 will be described below with reference to Figure 2. Figure 2 is an explanatory diagram of the noise current in the vehicle drive system 1. Note that the magnetic core 206 and noise return lines 302 and 303 are not shown in Figure 2.

[0021] In the vehicle drive system 1, a common-mode current is generated as the aforementioned noise current. The motor 101 has a stray capacitance with respect to the ground 401, and a portion of the common-mode current (leakage noise current, or inoise) leaks from the motor 101 to the ground 401 through this stray capacitance. The electromagnetic radiation noise generated by this leakage noise current, or inoise, causes problems such as inductive interference.

[0022] In the vehicle drive system 1 of this embodiment, a magnetic core 206 and noise return lines 302 and 303 are provided, as shown in Figure 1. This is intended to suppress the leakage of common-mode current.

[0023] Common-mode current generally contains a mixture of low-frequency components (mainly on the kHz order) and high-frequency components (mainly on the MHz order). Magnetic coupling (mutual inductance) occurs in the magnetic core 206 between the output current flowing through the output power line 301 and the current flowing through the noise return line 302, thus reducing the impedance of the path returning from the output power line 301 to the noise return line 302. In other words, the magnetic core 206 has the effect of increasing the noise current passing through the noise return line 302. However, this effect of the magnetic core 206 is effective for low-frequency components but less effective for high-frequency components. This is because the leakage inductance of the magnetic core 206 increases in the high-frequency range, which increases the impedance of the current path passing through the noise return line 302.

[0024] Therefore, in the vehicle drive system 1 of this embodiment, in addition to the noise return line 302, a noise return line 303 that does not penetrate the magnetic core 206 is introduced to provide a current path for passing high-frequency components of noise current. Since the noise return line 303 does not penetrate the magnetic core 206, unlike the noise return line 302, there is no impedance increase due to the leakage inductance of the magnetic core 206. As a result, it is possible to return high-frequency noise current through the noise return line 303.

[0025] Figure 3 is a schematic diagram illustrating the noise suppression effect of the present invention. In the vehicle drive system 1 of this embodiment, by adopting the configuration shown in Figure 1, a current path as shown in Figure 3 is formed for the common-mode current. That is, the low-frequency component of the common-mode current flowing through the output power line 301 returns to the inverter circuit 202 through the noise return line 302 and the negative electrode wiring 205. Also, the high-frequency component of the common-mode current flowing through the output power line 301 returns to the inverter circuit 202 through the noise return line 303 and the negative electrode wiring 205. As a result, it is possible to suppress leakage noise current (Inoise) leaking from the motor 101 to the ground 401.

[0026] Furthermore, it is preferable that the connection point between the noise return lines 302 and 303 and the negative terminal wiring 205 be located outside the inverter circuit 202, beyond the filter capacitor 203. The reason for this is as follows: When the switching element in the inverter circuit 202 is driven, a rectangular wave-shaped current is generated between the filter capacitor 203 and the inverter circuit 202. This may cause high-frequency voltage oscillations in the wiring between the filter capacitor 203 and the inverter circuit 202. Therefore, if the noise return lines 302 and 303 are connected between the filter capacitor 203 and the inverter circuit 202, there is a risk that the noise current caused by these high-frequency voltage oscillations may leak to the outside through the noise return lines 302 and 303. To avoid this, it is preferable to connect the noise return lines 302 and 303 to the negative terminal wiring 205, avoiding the connection point between the inverter circuit 202 and the filter capacitor 203.

[0027] Figure 4 shows the simulation results obtained by verifying the noise suppression effect of the present invention through circuit simulation. In Figure 4, the dotted line graph represents the simulation result of leakage noise current (Inoise) when only the noise return line 302 is provided, without the magnetic core 206 and noise return line 303. The dashed line graph represents the simulation result of leakage noise current (Inoise) when the magnetic core 206 and noise return line 302 are provided, without the noise return line 303. Furthermore, the solid line graph represents the simulation result of leakage noise current (Inoise) when the magnetic core 206 and noise return lines 302 and 303 are provided.

[0028] From the simulation results in Figure 4, it can be confirmed that in the vehicle drive system 1 of this embodiment, by providing the noise return line 303, the leakage noise current (Inoise) leaking to the ground 401 is smaller compared to when only the noise return line 302 is used or when the noise return line 302 and the magnetic core 206 are used together.

[0029] (Second embodiment) A second embodiment of the present invention is described below. In the first embodiment described above, an example was described in which the noise return lines 302 and 303 are directly connected to the negative terminal wiring 205. In this embodiment, an example is described in which the noise return lines 302 and 303 are connected to the negative terminal wiring 205 via resistors.

[0030] Figure 5 shows the circuit configuration of a vehicle drive system according to a second embodiment of the present invention. In the vehicle drive system 1A of this embodiment, the power converter 200A further includes resistors 304 and 305 provided between the noise return lines 302 and 303 and the negative electrode wiring 205, in addition to the configuration of the power converter 200 described in the first embodiment. That is, in the power converter 200A of this embodiment, the noise return lines 302 and 303 are connected to the negative electrode wiring 205 via resistors 304 and 305, respectively.

[0031] The input current to the inverter circuit 202 normally flows from the positive terminal wiring 204 through the filter reactor 201 into the inverter circuit 202 and out through the negative terminal wiring 205 to the grounding system. However, in the configuration of the power converter 200 shown in Figure 1, as described in the first embodiment, in addition to these current paths, a current path may be formed that connects to the grounding system through noise return lines 302 and 303. As a result, the input current to the inverter circuit 202 may flow out to the grounding system through this current path, potentially causing a large current to flow. To avoid this, it is necessary to increase the impedance of the noise return path through the noise return lines 302 and 303 to a certain extent.

[0032] In this embodiment, as shown in Figure 5, in the power converter 200A, noise return lines 302 and 303 are connected to the negative terminal wiring 205 via resistors 304 and 305, respectively. This increases the impedance of the noise return path through the noise return lines 302 and 303 compared to the first embodiment, preventing large currents from flowing out to the grounding system through the noise return lines 302 and 303. It is desirable that the resistance values ​​of resistors 304 and 305 be, for example, around a few ohms.

[0033] (Third embodiment) A third embodiment of the present invention is described below. In this embodiment, an example is described in which the noise return lines 302 and 303 are connected to the negative terminal wiring 205 via capacitors.

[0034] Figure 6 shows the circuit configuration of a vehicle drive system according to a third embodiment of the present invention. In the vehicle drive system 1B of this embodiment, the power converter 200B further includes capacitors 306 and 307 provided between the noise return lines 302 and 303 and the negative electrode wiring 205, in addition to the configuration of the power converter 200 described in the first embodiment. That is, in the power converter 200B of this embodiment, the noise return lines 302 and 303 are connected to the negative electrode wiring 205 via capacitors 306 and 307, respectively.

[0035] As described in the second embodiment, in order to prevent a large current from flowing out to the grounding system through the noise return lines 302 and 303 from the input current of the inverter circuit 202, the impedance of the noise return path by the noise return lines 302 and 303 needs to be increased to a certain extent. Therefore, in this embodiment, as shown in Figure 6, in the power converter 200B, the noise return lines 302 and 303 are connected to the negative terminal wiring 205 via capacitors 306 and 307, respectively. As a result, compared to the first embodiment, the impedance of the noise return path by the noise return lines 302 and 303 is increased, preventing a large current from flowing out to the grounding system through the noise return lines 302 and 303.

[0036] Capacitors 306 and 307 have high impedance in the low-frequency range. Therefore, the connection method of the noise return lines 302 and 303 as in this embodiment is an effective method for preventing the inflow of low-frequency input current from the inverter circuit 202. On the other hand, capacitors 306 and 307 have low impedance in the high-frequency range. Therefore, they do not interfere with high-frequency leakage noise current (Inoise) caused by the noise return lines 302 and 303. Thus, it is possible to effectively recover leakage noise current (Inoise) while preventing the inflow of input current from the inverter circuit 202.

[0037] (Fourth embodiment) A fourth embodiment of the present invention is described below. In this embodiment, an example is described in which the noise return lines 302 and 303 are connected to the negative terminal wiring 205 via a series-connected capacitor and resistor.

[0038] Figure 7 shows the circuit configuration of a vehicle drive system according to a fourth embodiment of the present invention. In the vehicle drive system 1C of this embodiment, the power converter 200C further includes resistors 304, 305 and capacitors 306, 307 provided between the noise return lines 302, 303 and the negative electrode wiring 205, in addition to the configuration of the power converter 200 described in the first embodiment. Resistor 304 is connected in series with capacitor 306, and resistor 305 is connected in series with capacitor 307. That is, in the power converter 200C of this embodiment, the noise return lines 302, 303 are connected to the negative electrode wiring 205 via the series-connected resistors 304, 305 and capacitors 306, 307, respectively.

[0039] As described in the third embodiment, connecting the noise return lines 302 and 303 to the negative terminal wiring 205 via capacitors 306 and 307 is an effective method for preventing the inflow of low-frequency input current from the inverter circuit 202. However, in the circuit configuration shown in Figure 6 described in the third embodiment, resonance may occur between the inductances of capacitors 306 and 307 and the noise return lines 302 and 303, potentially generating unintended resonant currents. Therefore, in this embodiment, as shown in Figure 7, in the power converter 200C, in addition to capacitors 306 and 307, the noise return lines 302 and 303 are connected to the negative terminal wiring 205 via resistors 304 and 305, respectively. This prevents resonance from occurring in the noise return lines 302 and 303.

[0040] (Fifth embodiment) A fifth embodiment of the present invention is described below. In this embodiment, an example is described in which multiple noise return lines that do not penetrate the magnetic core 206 are provided.

[0041] Figure 8 shows the circuit configuration of a vehicle drive system according to a fifth embodiment of the present invention. In the vehicle drive system 1D of this embodiment, the power converter 200D further includes a noise return line 310 in addition to the configurations of the power converter 200 described in the first embodiment. The noise return line 310, like the noise return line 303, is connected between the housing of the motor 101 and the negative electrode wiring 205 without passing through the magnetic core 206. That is, the power converter 200D of this embodiment has two noise return lines 303 and 310, which are laid parallel to the output power line 301, with one end electrically connected to the ground 401 on the motor 101 side and the other end electrically connected to the negative electrode wiring 205. This lowers the impedance of the noise return path, increases the noise return effect, and further reduces leakage noise current (Inoise).

[0042] In the circuit configuration shown in Figure 8, an example is shown in which a noise return wire 310 is added that is connected between the housing of the motor 101 and the negative electrode wiring 205 without passing through the magnetic core 206, similar to the noise return wire 303. However, a noise return wire may also be added that passes through the magnetic core 206 and is connected between the housing of the motor 101 and the negative electrode wiring 205, similar to the noise return wire 302. Furthermore, two or more of each of these noise return wires may be added. In other words, the vehicle drive system 1D of this embodiment can have multiple noise return wires, at least one of the following: noise return wires that pass through the magnetic core 206 and are connected between the housing of the motor 101 and the negative electrode wiring 205, and noise return wires that do not pass through the magnetic core 206 and are connected between the housing of the motor 101 and the negative electrode wiring 205.

[0043] According to the embodiments of the present invention described above, the following effects and advantages are achieved.

[0044] (1) The power converters 200 to 200D include an inverter circuit 202 that has positive terminal wiring 204 and negative terminal wiring 205 connected to the input side, converts the input current flowing through the positive terminal wiring 204 and negative terminal wiring 205 into an output current and outputs it to a load device, which is a motor 101, an output power line 301 connected between the inverter circuit 202 and the motor 101 through which the output current including noise current flows, a magnetic core 206 through which the output power line 301 passes, and noise return lines 302 and 303 for returning the noise current, respectively. The noise return lines 302 and 303 are laid parallel to the output power line 301, respectively, one end of the noise return line 302 and 303 is electrically connected to the ground 401 on the motor 101 side, respectively, and the other end of the noise return line 302 and 303 is electrically connected to the negative terminal wiring 205, respectively. The noise return line 302 penetrates the magnetic core 206. In this manner, high-frequency electromagnetic radiation noise due to common-mode current can be suppressed in the power converters 200-200D and the vehicle drive systems 1-1D using them.

[0045] (2) As a method for suppressing noise current included in the output current from the power converters 200~200D to the motor 101, which is a load device, the output power line 301 through which the output current flows is passed through the magnetic core 206, and noise return lines 302 and 303 are laid parallel to the output power line 301, respectively. In addition, the noise return line 302 is passed through the magnetic core 206, one end of the noise return line 302 and the noise return line 303 are electrically connected to the ground 401 on the motor 101 side, respectively, and the other ends of the noise return line 302 and the noise return line 303 are electrically connected to the negative electrode wiring 205 connected to the input side of the power converters 200~200D, respectively. In this way, high-frequency electromagnetic radiation noise due to common-mode current can be suppressed in the power converters 200~200D and the vehicle drive systems 1~1D using them.

[0046] It should be noted that the present invention is not limited to the embodiments or modifications described above, and can be implemented using any components without departing from the spirit of the invention. Furthermore, each embodiment or modification may be adopted individually, or multiple embodiments may be adopted in any combination. In other words, the present invention can achieve the effects described above by arbitrarily combining the features of each embodiment.

[0047] The embodiments and modifications described above are merely examples, and the present invention is not limited to these, as long as the features of the invention are not impaired. Furthermore, although various embodiments and modifications have been described above, the present invention is not limited to these. Other embodiments conceivable within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention. [Explanation of Symbols]

[0048] 1, 1A, 1B, 1C, 1D: Vehicle drive systems 101: Motor 200, 200A, 200B, 200C, 200D: Power converter 201: Filter Reactor 202: Inverter Circuit 203: Filter Capacitor 204: Positive Wiring 205: Negative Wiring 206: Magnetic core 301: Output power line 302,303: Noise return line 304, 305: Resistors 306, 307: Capacitors 310: Noise return line 401: Grand

Claims

1. An inverter circuit is provided, in which a positive terminal wire and a negative terminal wire are connected to the input side, and the input current flowing through the positive terminal wire and the negative terminal wire is converted into an output current and output to a load device. An output power line connected between the inverter circuit and the load device, through which the output current including noise current flows, A magnetic core through which the output power line passes, The system includes a first noise return line and a second noise return line for returning the noise currents, respectively. The first noise return line and the second noise return line are laid so as to run parallel to the output power line, respectively. One end of the first noise return line and the second noise return line are electrically connected to the ground on the load device side, The other ends of the first noise return wire and the second noise return wire are electrically connected to the negative electrode wiring, respectively. The first noise return line is a power conversion device that penetrates the magnetic core.

2. A power conversion device according to claim 1, The other ends of the first noise return line and the second noise return line are electrically connected to the negative electrode wiring via resistors, respectively, in this power conversion device.

3. A power conversion device according to claim 1 or 2, The other ends of the first noise return line and the second noise return line are electrically connected to the negative electrode wiring via capacitors, respectively, in this power conversion device.

4. A power conversion device according to claim 1 or 2, The other ends of the first noise return line and the second noise return line are electrically connected to the negative terminal wiring via a series-connected capacitor and resistor in a power conversion device.

5. A power conversion device according to either claim 1 or 2, A power conversion device having multiple of at least one of the first noise return lines and the second noise return lines.

6. A power conversion device according to either claim 1 or 2, The power converter and the motor connected via the output power line are comprising: A vehicle drive system that generates a driving force in the motor using the output current output from the power converter, and drives the vehicle using the driving force.

7. A method for suppressing noise current included in the output current from a power converter to a load device, The output power line through which the output current flows is passed through the magnetic core. A first noise return line and a second noise return line are laid so as to run parallel to the output power line, and the first noise return line is passed through the magnetic core. One end of the first noise return line and the second noise return line are electrically connected to the ground on the load device side, A noise suppression method comprising electrically connecting the other ends of the first noise return line and the second noise return line to the negative terminal wiring connected to the input side of the power converter.

8. A noise suppression method according to claim 7, A noise suppression method comprising electrically connecting the other ends of the first noise return line and the second noise return line to the negative electrode wiring via a resistor.

9. A noise suppression method according to claim 7 or 8, A noise suppression method comprising electrically connecting the other ends of the first noise return line and the second noise return line to the negative electrode wiring via a capacitor.

10. A noise suppression method according to claim 7 or 8, A noise suppression method comprising electrically connecting the other ends of the first noise return line and the second noise return line to the negative terminal wiring via a series-connected capacitor and resistor.

11. A noise suppression method according to claim 7 or 8, A noise suppression method comprising providing multiple of at least one of the first noise return lines and the second noise return lines.

Images