WO2016031299A1

WO2016031299A1 - Medical device

Info

Publication number: WO2016031299A1
Application number: PCT/JP2015/062175
Authority: WO
Inventors: 船戸　裕樹; 浩和飯嶋; 高橋　昌義
Original assignee: 株式会社日立メディコ
Priority date: 2014-08-29
Filing date: 2015-04-22
Publication date: 2016-03-03
Also published as: JP2016052155A; JP6239468B2

Abstract

　A medical device provided with an AC power supply and a power converter having a switching element connected to the AC power supply, wherein the medical device is characterized in being provided with a series resonance capacitor (201) provided between the device GND and a power supply line connecting the AC power supply and the power converter, a resonance inductor (202) provided so as to be serially connected to the series resonance capacitor between the GND-side terminal of the series resonance capacitor and the device GND, and a high-frequency noise bypass capacitor (203) provided so as to be connected in parallel to the resonance inductor; the resonance frequency of the series resonance capacitor and the resonance inductor being set so as to match the switching frequency of the power converter, and the parallel resonance frequency of the resonance inductor and the high-frequency noise bypass capacitor being set to a value between the switching frequency and the conduction noise restriction start frequency. The present invention makes it possible to reduce leak current while reducing power supply line noise.

Description

Medical equipment

The present invention relates to a medical device.

There is JP 2007-325377 A (Patent Document 1) as background art in this technical field. This publication describes that “a power converter capable of preventing a resonance phenomenon and reducing a common mode voltage of a bus line in a bidirectional converter” is provided.

Japanese Patent Laid-Open No. 2008-245037 (Patent Document 2) states that “improvement of attenuation characteristics for noise components in a band equal to or higher than the self-resonance frequency of the common mode reactor while ensuring a bypass path for high frequency components”. Are listed.

JP 2007-325377 A JP 2008-245037 A

Medical devices need to conform to EMC (Electromagnetic Compatibility) standards in order to ship to the market. One of the EMC standard tests is a conduction noise test, and the device must reduce the noise induced in the power supply line to a regulation value or less. In order to reduce the conduction noise, a method is generally used in which a conduction noise of the power line is caused to flow to the ground by installing a filter between the power line and the ground.

On the other hand, one of the safety standards is the ground leakage current test. According to this standard, the current flowing in the ground wire connecting the equipment and the power source must be less than the regulation value. In order to reduce the ground leakage current, it is important to design so that no current flows from the power line to the ground.

From the above, if a filter is added to meet the EMC test, there is a problem that the ground leakage current increases.

An object of the present invention is to provide a medical device that reduces power line noise to meet EMC conduction noise regulations and reduces leakage current to meet leakage current regulations.

In order to solve the above problems, for example, the configuration described in the claims is adopted. The present application includes a plurality of means for solving the above-mentioned problem. To give an example, a medical device including an AC power source and a power converter having a switching element connected to the AC power source. A series resonance capacitor provided between a power supply line connecting the AC power supply and the power converter, and the device GND, a GND side terminal of the series resonance capacitor, and the device GND A resonance inductor provided so as to be connected in series with the series resonance capacitor, and a high frequency noise bypass capacitor provided so as to be connected in parallel with the resonance inductor. The resonance frequency of the capacitor for resonance and the resonance inductor is set to match the switching frequency of the power converter, and Parallel resonance frequency of the high frequency noise bypass capacitor is characterized in that it is set to a value between the switching frequency and conduction noise restriction start frequency.

According to the present invention, it is possible to provide a medical device that reduces power line noise in order to comply with EMC conduction noise regulations and reduces leakage current in order to conform to leakage current regulations.

Issues, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

It is a figure which shows the power supply device structure of the medical device concerning one Example of this invention. It is a figure which shows the structure of the filter concerning one Example of this invention. It is a figure which shows the definition of the terminal for calculating the filter characteristic concerning one Example of this invention. It is a figure which shows the result of having calculated the filter characteristic concerning one Example of this invention. It is a figure which shows the structure of this invention which suppresses the noise by the antiresonance concerning one Example of this invention. It is a figure which shows the structure which forms a resonance circuit for every phase of the power wire concerning one Example of this invention. It is a figure which shows the structure using the inductive coupling concerning one Example of this invention. It is a figure which shows the form of mounting concerning one Example of this invention. It is a figure which shows the structure which changes the value of the filter element concerning one Example of this invention dynamically.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a configuration of a power supply device of a medical device according to an embodiment of the present invention. Here, a CT (Computed Tomography) apparatus is taken as an example. The medical device is connected to a three-phase AC power supply 101, and the three-phase AC power supply line is connected to a converter 103 that is a power converter for generating a DC voltage from the AC power supply through a filter 102 for blocking noise. It is connected. In this embodiment, the power converter refers to a converter only or a configuration including a converter unit.

In the case of a CT apparatus, the DC voltage generated by the converter 103 is supplied to the inverter 105 via the high voltage wiring laid on the slip ring 104. The high voltage generated by the inverter 105 is supplied to the X-ray tube and used to generate X-rays.

The converter 103 and the inverter 105 obtain a desired voltage and current waveform by performing a switching operation using a switching element for high voltage such as IGBT. The inverter and the converter are generally mounted on a metal frame or casing, and the frame or casing is grounded on the power supply side via the ground wire 106.

Therefore, the frame and the casing are electrically connected to the power supply ground (ground), and become the device GND (ground) 107. The three-phase power supply is 50 Hz / 60 Hz, and the voltage varies depending on the device specifications such as 100 V to 400 V and the use of the power supply. The switching frequency of the converter 103 and the inverter 105 is about several kHz to several tens of kHz.

Next, noise generation and filtering will be described. The switching operation of the converter 103 generates harmonic noise of the switching frequency. The generated noise propagates to the power supply side via the power supply line.

The noise filter is provided to suppress the conduction noise generated in the device. The types of filters can be broadly classified into active filters and passive filters. However, active filters have a relatively complicated circuit configuration, so that they are expensive and difficult to apply to power lines such as power lines. On the other hand, the passive filter has a relatively simple configuration, is low in cost, and can be easily applied to a power line. Therefore, in this embodiment, a passive filter is mounted. Inductance and capacitance are used as elements constituting the passive filter.

¡Inductance has the effect of increasing the high frequency impedance and suppressing noise propagation by inserting it in series with the power line. As a method for realizing the inductance, for example, there are methods such as forming a power supply line in a coil shape and using a magnetic material such as ferrite.

Further, the capacitance has an effect of bypassing only the high-frequency current to the GND by being inserted between the power supply line and the device GND. For this reason, a wire and an element with a small current value and a small current capacity can be used, and the size and cost can be suppressed.
Here, EMC regulation and ground leakage current regulation will be described. Among the EMC regulations, the conduction noise test regulates the amount of conduction noise that propagates to the power supply. For example, the frequency range of conduction noise regulation for medical devices is 150 kHz to 30 MHz. Here, the frequency that is the starting point (lower end value) in the frequency range subject to conduction noise regulation is defined as the conduction noise regulation start frequency.

On the other hand, in the ground leakage current regulation, an ammeter is used to regulate the current value flowing through the ground wire connecting the device and the power source ground. As an example, according to IEC-60601, there is a condition that the ground leakage current of a medical device must be 5 mA or less. Here, a primary filter of CR (C = 0.015 μF, R = 10 kΩ) is used for the measurement. The ammeter used for measurement is defined as having a bandwidth of 1 MHz.

As described above, in medical equipment, it is necessary to comply with both EMC regulations and ground leakage current regulations. In this embodiment, a noise filter is provided in consideration of this.

The configuration of the noise filter of this embodiment will be described with reference to FIG. In addition, this noise filter shall be mounted between the converter 103 which is a three-phase alternating current power supply 101 and a power converter.

A series resonance capacitor (Cy) 201 is mounted between each phase of the power supply line of the three-phase AC power supply 101 and the device GND 107, and a resonance inductor (Lp) 202 is connected between the terminal connecting the three phases and the device GND 107. Provide. Further, a high frequency noise bypass capacitor (Cp) 203 connected in parallel with the inductor 202 is provided.

Here, the series resonance capacitor, the resonance inductor, and the high frequency noise bypass capacitor may be mounted on a substrate included in the power converter, or may be mounted on a substrate dedicated to a noise filter. The power converter substrate or the noise filter dedicated substrate is provided with a power supply connection terminal and a GND connection terminal. In the case where the power converter is mounted on a substrate, it is not necessary to provide a filter substrate in particular, so that the cost can be reduced. On the other hand, when mounted on a noise filter dedicated substrate, the presence or absence of the filter can be easily changed by attaching and detaching the noise filter dedicated substrate according to the situation.

In this configuration, the series resonance frequency of the capacitor 201 and the inductor 202 is adjusted to the switching frequency of the converter 103, for example, 10 kHz. Thereby, the impedance between the power supply line and the ground becomes small at the switching frequency of the converter 103, the switching current can be bypassed to the device GND 107, and the leakage noise to the outside of the device can be reduced.

In addition, by using an LC series resonance circuit including the inductor 202 and the capacitor 201, the impedance between the power supply line and the device GND 107 can be kept high at a frequency lower than the series resonance frequency set as described above. That is, the switching current of the converter 103 can be bypassed to the device GND 107, and the amount of power source frequency (50 Hz / 60 Hz) current flowing to the device GND 107 can be reduced.

Further, the capacitor 203 is set so that the parallel resonance frequency of the inductor 202 and the capacitor 203 is equal to or higher than the switching frequency of the converter 103 (that is, the series resonance frequency of the inductor 202 and the capacitor 201) and less than 150 kHz, which is the EMC conduction noise regulation start frequency. By selecting this value, this filter has a capacitive impedance characteristic in a band equal to or higher than the parallel resonance frequency of the inductor 202 and the capacitor 203, and the ground impedance of the power supply line can be lowered at 150 kHz or higher.

Hereinafter, the effect of the noise filter of this embodiment will be described in detail. First, FIG. 3 shows definitions of terminals for calculating the filter characteristics of this embodiment. The characteristic obtained by the terminal definition in FIG. 3A is herein referred to as a normal mode characteristic. The characteristic obtained in FIG. 3B is a common mode characteristic.

The normal mode characteristic is a component in which current is input from one or two phases of the three-phase power supply line and is also output from one or two phases, and does not leak to the GND line. The common mode characteristic is a component that is input from the three-phase power supply line and leaks to the GND line. That is, the definition of the input / output terminal in FIG. 3A is a normal mode characteristic, and FIG. 3B represents a common mode characteristic.

First, considering the current path flowing from the three-phase AC power source 101 in FIG. 1 toward the noise filter 102, this is because the three-phase AC power source 101 generates an AC voltage with reference to the midpoint. The current flowing through the inverter 105 is the return path for the V and W phases. Therefore, it is important that the characteristic of the noise filter 102 at this time is such that the normal mode characteristic of the definition (a) does not disturb the power supply current.

On the other hand, when considering a noise current path from a noise source flowing in the direction of the noise filter 102 from the converter 103 in FIG. 1, this is a noise component (normal mode component) flowing between the phases as a conduction noise component generated by switching of the inverter 105. ) And a current component having the same phase among the currents of each phase, that is, an in-phase component (common mode component), the characteristic of the noise filter 102 at this time is the common mode characteristic of the filter of FIG. It is important to have the characteristic of reducing the in-phase component of noise.

Fig. 4 shows the results of calculating the filter characteristics of this example. Here, the inductor (Lp) 202 = 3 mH, the capacitor (Cy) 201 = 25 nF, and the capacitor (Cp) 203 = 5 nF. The switching frequency of converter 103 is assumed to be 10 kHz, and the series resonance frequency of inductor 202 and capacitor 201 is 10 kHz.

For the normal mode characteristics of definition (a), as shown in (A), high impedance is realized at low frequencies (50 Hz / 60 Hz), while for common mode characteristics of definition (b) At 10 kHz, the impedance is low due to series resonance. Further, as shown in (C), by selecting the capacitor 203 so that the parallel resonance frequency of the inductor 202 and the capacitor 203 is 10 kHz or more and less than 150 kHz, the impedance is reduced to 150 kHz or more with respect to the common mode characteristic of the definition (b). realizable.

From the above, according to the configuration shown in the present embodiment, it is possible to provide a medical device that reduces the leakage current to meet the leakage current regulation while reducing the power line noise to meet the EMC conduction noise regulation. it can.

FIG. 5 shows a configuration of a noise filter for suppressing noise due to anti-resonance in the second embodiment. That is, a method for controlling the quality factor, that is, the Q value, representing the sharpness of resonance by the inductor 202 (Lp) and the capacitor 203 (Cp) in the resonance type filter of the present embodiment is provided.

As described above, it is important that the parallel resonance frequency of the inductor Lp and the capacitor Cp is not less than the switching frequency of the converter and less than the EMC conduction noise regulation start frequency (150 kHz), but the converter noise is not bypassed near the parallel resonance frequency, The amount of propagation to the power supply side increases.

If it is less than 150 kHz, noise suppression is unnecessary from the viewpoint of EMC regulations, but depending on the noise interference in the device and the installation environment of the device, an increase in ground impedance due to parallel resonance can be a problem. In that case, as shown in FIG. 5A and FIG. 5B, the resistor 501 (R) is inserted in parallel with the inductor 202 or connected in series. The Q value of the parallel resonance can be lowered, thereby reducing the ground impedance.

The resistance value is set so that the ground impedance in parallel resonance is less than the desired value. Thereby, the impedance of the parallel resonant frequency of the inductor Lp and the capacitor Cp can be lowered, and the conduction noise can be reduced.

Fig. 6 shows the configuration of a noise filter that forms a resonance circuit for each phase of the power line. As a result, the impedance between the phases also has resonance characteristics. In the first and second embodiments, the phases of the power supply lines are connected by the capacitors 201 (Cy), and this has the effect of suppressing normal mode noise generated between the phases. If it occurs, it can be a path to propagate to other phases.

Since these noise sources differ depending on the device configuration and mounting state, it is desirable to adopt a configuration suitable for the model. However, if there is ground noise independent of any phase, the power line for each phase as shown in FIG. By providing a filter in which an inductor and a capacitor are connected in parallel, impedance between phases can be increased, and noise propagation between phases can be suppressed.

Also in this configuration, the series resonance frequency of the capacitor Cy and the inductor Lp is set to the switching frequency of a noise source such as a converter, the parallel resonance frequency of the capacitor Cp and the inductor Lp is set higher than the switching frequency of the noise source, and the EMC regulation frequency. By making it lower than 150 kHz, it is possible to reduce the leakage current in order to meet the leakage current regulation while reducing the power line noise to meet the EMC conduction noise regulation.

Fig. 7 shows the configuration of a noise filter using inductive coupling with a magnetic material such as a ferrite core. In this configuration, the inductor 202 (Lp) connected to each of the power supply three-phase lines is inductively coupled using a magnetic material so that the magnetic fields generated by the currents of the respective phases are coupled in phase with each other, thereby causing the inductors 202 of the respective phases. Inductance is generated only in the in-phase (common mode) component of the current flowing through the.

As a result, resonance by the capacitor 201 (Cy) and the inductor 202 can be generated only for the common mode component, and no inductance is generated for components other than the common mode component (normal mode component). Functions as a capacitor.

This configuration is effective when the noise component to be bypassed to GND due to resonance can be identified as the common mode. In this configuration, it is not necessary to add an inductor element to each phase, and an inductor can be formed by using a magnetic material such as ferrite in three phases at a time, so that the number of parts can be reduced.

According to the configuration shown in the present embodiment, it is possible to provide a medical device that reduces power line noise in order to meet EMC conduction noise regulations and reduces leakage current to meet leakage current regulations.

FIG. 8 illustrates a specific method for realizing the inductor Lp. FIG. 8A shows an example using a coil component. There are no restrictions on the method of mounting the inductor or capacitor, but the substrate and components can be shared between different devices by separately providing a substrate on which the resonant circuit is mounted as shown in FIG.

FIG. 8B shows an example of a mounting method for realizing the inductor Lp using a magnetic material such as ferrite. By adopting a system that realizes inductance by winding a wire around a toroidal magnetic body, there is an advantage that the value of the inductor Lp can be easily changed, and the resonance frequency can be easily adjusted after assembly of the device.

FIG. 8C shows an example in which the inductor Lp is realized by substrate wiring. By using a spiral inductor using wiring, the cost can be reduced along with the number of parts. Further, the number of components can be further reduced by designing the spiral inductor with the capacitance between wires and realizing the capacitor Cp with the capacitance between wires instead of as a component.

FIG. 9 shows a configuration of an embodiment in which the value of the filter element is dynamically changed. The main point of this embodiment is to match the switching frequency of the noise source (converter or the like) with the resonance circuit of the filter, but the switching frequency of the noise source may change depending on the state and operation of the apparatus.

In such a case, a signal indicating the switching frequency is transmitted from the control block that outputs a signal of the switching frequency to the resonance filter circuit via the signal line, and the filter is configured such that the inductor Lp, the capacitor Cy, and the resonance frequency match the switching frequency. By changing the value of Cp, the noise current can be bypassed to GND in accordance with the switching frequency that changes.

∙ It may be configured to use parts such as variable capacitors and varicaps, or to switch the series / parallel of multiple capacitors. The variable inductor may be configured to switch the connection of a plurality of components or to use an equivalent inductor using a transistor or the like.

In addition, this invention is not limited to the above-mentioned Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

101 Power supply 102 Filter 103 Converter 104 Slip ring 105 Inverter 106 Ground wire 107 Device GND
201 Capacitor 202 Inductor 203 Capacitor 501 Resistance 701 Inductive coupling 801 Coil 802 Capacitor 803 Substrate 804 Magnetic body 805 Substrate wiring

Claims

AC power supply,
A medical device comprising a power converter having a switching element connected to the AC power source,
A series resonance capacitor provided between a power supply line connecting the AC power supply and the power converter, and the device GND;
A resonance inductor provided so as to be connected in series with the series resonance capacitor between the GND side terminal of the series resonance capacitor and the device GND;
A high-frequency noise bypass capacitor provided so as to be connected in parallel with the resonance inductor,
The resonance frequency of the series resonance capacitor and the resonance inductor is set to match the switching frequency of the power converter,
The medical device is characterized in that a parallel resonance frequency of the resonance inductor and the high frequency noise bypass capacitor is set to a value between the switching frequency and a conduction noise regulation start frequency.
The medical device according to claim 1,
A medical device comprising a resistor or a loss component connected in series with the resonance inductor.
The medical device according to claim 1,
A medical device comprising a resistor or a loss component connected in series with the high-frequency noise bypass capacitor.
The medical device according to claim 1,
The AC power source is a three-phase AC power source,
The resonant inductor and the series resonant capacitor are provided in series between the wiring of each phase of the three-phase AC power supply and the device GND, and the high frequency is connected to each of the resonant inductors. A medical device comprising a noise bypass capacitor connected in parallel.
The medical device according to claim 1,
The medical device, wherein the resonance inductor is made of a magnetic material.
The medical device according to claim 1,
The resonance inductor, the series resonance capacitor, and the high frequency noise bypass capacitor are mounted on a power converter board of the power converter, and the power converter board includes a power connection terminal and a GND connection terminal. A medical device characterized by that.
The medical device according to claim 1,
The resonance inductor, the series resonance capacitor, and the high-frequency noise bypass capacitor are mounted on a noise filter dedicated board, and the noise filter dedicated board includes a power connection terminal and a GND connection terminal. Medical device.
The medical device according to claim 6 or 7,
The medical device according to claim 1, wherein the resonance inductor is an inductor formed of spiral wiring.
The medical device according to claim 1,
The resonance inductor, the series resonance capacitor, or the high frequency noise bypass capacitor is configured by a variable element or a plurality of elements whose values can be changed by an external signal or a manual switch, and control for controlling the switching frequency of the power converter With blocks,
The medical device, wherein the control block and the variable element or a plurality of elements are connected.