JP2008306833A - Pwm electric equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide PWM electric equipment which prevents a large voltage from being applied to a line end coil and can increase a rated voltage within a fixed range of insulation margin, when a surge voltage intrudes in the electric equipment. <P>SOLUTION: In the electric equipment to be operated by being connected to a PWM frequency converter 2 via a power supply cable 3, when an interphase capacitance in the terminal part of the electric equipment is Cm, a resonance frequency of each coil 5 constituting the electric equipment is fc, and an inductance of a power supply cable 2 is Lc, the relation satisfies the formula: fc>1/(5√(Lc*Cm)). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a PWM electric device that operates by being connected to a PWM frequency converter via a power supply cable and has improved surge voltage resistance, such as an electric motor or a generator of a rotating machine.

  As is well known, a PWM (pulse width modulation) frequency converter and an electrical device such as a rotating machine such as an AC motor or an AC generator are connected by a power supply cable, and the connected AC motor is driven by frequency-converted electric power or AC. It performs frequency conversion of power from the generator.

  In such a case, for example, in an AC motor driven by a PWM frequency converter that switches at high speed, if there is a mismatch between the characteristic impedance of the feeding cable and the impedance of the AC motor, the PWM frequency converter is caused by this mismatch. The surge voltage is reflected at the connecting portion of the AC motor and a high voltage is generated by superimposition of the reflected surge voltage (see, for example, Non-Patent Document 1). Further, the generated high voltage vibrates with a period of time for which the reflected surge voltage makes two round trips through the power supply cable as a period, and therefore may be described as a resonance phenomenon due to the inductance and capacitance of the power supply cable (for example, Patent Document 1) reference).

  Further, when the generated surge voltage enters the connected AC motor, if the rising waveform of the voltage is steep, a large voltage is concentrated and applied to the line end coil. For example, when the ratio of the maximum voltage applied to the line end coil with respect to the maximum voltage change at the terminal of the AC motor is defined as the sharing ratio, the sharing ratio may exceed 80% (see, for example, Non-Patent Document 1). . The increase in voltage due to such impedance mismatch and the increase in the sharing ratio in the line end coil may damage the line end coil.

Therefore, in conventional AC motors, an insulation circuit that has been reinforced to withstand a high voltage applied to the line end coil due to an assumed surge voltage, or an electric circuit that does not generate a high voltage due to the surge voltage. Or was done. As an electric circuit that prevents the generation of high voltage, there is a method of smoothing the high-speed switching waveform of the PWM frequency converter by inserting a reactor or a filter between the PWM frequency converter and the feeding cable, There is a method of connecting a series circuit of a capacitor and a resistor as an impedance matching unit between the power supply cable and the AC motor (see, for example, Patent Document 1 and Non-Patent Document 2).
Japanese Patent No. 2707814 (page 2) IEEJ Technical Report No. 739, August 1999, Inverter Surge Insulation Investigation Special Committee, “Influence of Inverter Surge on Insulation System”, p. 12-20 IEC, TS 60034-25, TECNICICAL SPECIFICATION, 2004/04, “Rotating electrical machines Part 25”, p. 44-45

  Since conventional PWM electric devices such as AC motors are configured as described above, even in low-voltage electric devices driven at a relatively low voltage, for example, the insulation treatment has been strengthened to withstand high voltages due to surge voltages. In addition, when a reactor or a filter is inserted between the PWM frequency converter and the power supply cable, a reactor of a size corresponding to the rated current or a variety of electric devices having different rated voltages is used. It is necessary to prepare a filter, and the method of connecting a series circuit of a capacitor and a resistor as an impedance matching unit has a problem that heat is generated in the resistor.

  The present invention has been made to solve these problems. The object of the present invention is to prevent a large voltage from being applied to the line-end coil when a surge voltage enters the electrical equipment, and to provide constant insulation. An object of the present invention is to provide an electrical device for PWM capable of increasing the rated voltage within a margin range.

The electrical equipment for PWM of the present invention is
In an electrical device for PWM that operates by connecting to a PWM frequency converter via a power supply cable,
When the interphase capacitance at the terminal portion of the electrical device is Cm, the resonance frequency of each coil constituting the electrical device is fc, and the inductance of the power supply cable is Lc,
fc> 1 / (5√ (Lc · Cm))
It is characterized by being,
Furthermore, the electrical device is a rotating machine,
Further, the product (Lc · Cm) of the inductance Lc of the feeding cable and the interphase capacitance Cm at the terminal portion of the electric device is larger than 10 ⁻¹⁴ sec ² , and the resonance frequency of each coil constituting the electric device fc is 2 MHz or more,
In addition, in an electrical device for PWM that operates by connecting to a PWM frequency converter via a feeding cable,
When the electrical device is a three-phase electrical device, the interphase capacitance at the terminal portion of the electrical device is Cm, the resonance frequency of each coil constituting the electrical device is fc, and the inductance of the feeding cable is Lc,
fc> 1 / (5√ (Lc (Cm + Ca)))
A capacitor having a capacitance Ca satisfying the condition is connected between the three phases of the electrical device,
In addition, in an electrical device for PWM that operates by connecting to a PWM frequency converter via a feeding cable,
When the electrical device is a three-phase electrical device, the interphase capacitance at the terminal portion of the electrical device is Cm, the resonance frequency of each coil constituting the electrical device is fc, and the inductance of the feeding cable is Lc,
fc> 1 / (5√ (Lc (Cm + (2/3) Cb)))
A capacitor having a capacitance of Cb that satisfies the following condition is connected between each phase of the electrical device and the core of the electrical device,
Further, when the rise time of the interphase voltage surge waveform at the terminal portion of the electrical device is Tr, the resonance frequency of each coil constituting the electrical device is set to a frequency f1 = 1 / (4Tr) corresponding to the rise time Tr. Is set to a frequency 2f1 = 1 / (2Tr) or more.

  In the present invention, in order to prevent a large voltage from being concentrated on the line end coil of the PWM electric device, the inductance of the power feeding cable, the interphase capacitance at the terminal portion of the electric device, the winding start of each coil constituting the electric device, and The relationship of the resonance frequency between the end of winding is applied.

  According to the present invention, when the ratio of the maximum voltage applied between the start and end of winding of the line end coil with respect to the maximum voltage change between phases in the terminal portion of the PWM electrical device is defined as the sharing ratio, Since it is configured to be close to (1 / the number of interphase series coils), when a surge voltage caused by the switching operation of the PWM frequency converter enters the electrical equipment, a large voltage is not applied to the line end coil. It is possible to improve the insulation reliability.

  In addition, the rated voltage can be increased within a certain range of insulation margin, and if the number of interphase series coils is selected appropriately, the relationship between the rated voltage of electrical equipment and insulation reliability is optimized. Thus, it is possible to obtain the effect that the insulation reliability of the electric device can be made highly accurate.

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

  First, a first embodiment will be described with reference to FIGS. FIG. 1 is a diagram showing a system configured by connecting a PWM frequency converter and a PWM electrical device, and FIG. 2 is a diagram illustrating a rise time of an interphase voltage waveform at a terminal portion and voltage sharing of a first coil in the PWM electrical device. FIG. 3 is an equivalent circuit diagram when the number of interphase series coils of the electrical device for PWM is four, and FIG. 4 is a start and end of winding of one coil of the electrical device for PWM. FIG. 5 is a diagram showing the relationship between the resonance frequency between the first coil and the voltage sharing ratio of the first coil, and FIG. 5 shows the rise time of the voltage waveform between the terminals due to the capacitance of the terminal portion of the power supply cable and the PWM electric device. FIG. 6 is a circuit diagram used for investigating the influence. FIG. 6 is a diagram showing the relationship between the cable length of the power feeding cable and the rise time of the voltage waveform between terminals at the terminal portion of the PWM electric device. FIG. Transform the relationship shown The resonance frequency on the vertical axis, shows taking terminal voltage waveform rise time at the terminal portion on the vertical axis.

  As shown in FIG. 1, for example, a PWM electric device 1 configured by a three-phase rotating machine such as a three-phase AC motor or an AC generator and a PWM frequency converter 2 are connected by a power feeding cable 3, and PWM frequency Electric power can be transferred from the converter 2 to the PWM electrical device 1 or from the PWM electrical device 1 to the PWM frequency converter 2.

  In the electrical device for PWM 1, a plurality of coils 5, for example, n coils 5 from the first to the nth, are arranged in series between the phases in a slot (not shown) formed in the core 4. Is embedded as such. In addition, the coils 5 connected in series between the phases are Δ-connected, and the interphase capacitances at the terminal portions Um, Vm, and Wm are Cm. In addition, although connection of each coil 5 is made into delta connection, Y connection may be sufficient.

Further, the inductance of the power supply cable 3 that connects each terminal portion Um, Vm, Wm of the PWM electrical device 1 and each corresponding terminal portion Ui, Vi, Wi of the PWM frequency converter 2 is Lc. . The core 4 of the PWM electrical device 1 is grounded by connecting the ground terminal Gm to the ground terminal Gi of the PWM frequency converter 2 via the power feeding cable 3. If the resonance frequency of one of the coils 5 arranged between the phases of the PWM electrical device 1 is fc, the relationship between the resonance frequency fc, the interphase capacitance Cm, and the inductance Lc of the feeding cable 3 is expressed as follows. ,
fc> 1 / (5√ (Lc · Cm))
It has become.

  By doing in this way, even when a surge voltage enters the PWM electrical device 1 such as an AC motor, a high voltage is not applied to the first coil 5 which is the line end of the coil 5 connected in series between the phases, The reliability of insulation can be increased, and the rated voltage of the PWM electric apparatus 1 such as an AC motor can be increased within a certain range of insulation margin.

  The above embodiment having such a configuration will be further described with reference to FIGS.

  In FIG. 2, the horizontal axis represents the rise time of the interphase voltage waveform of the terminal portion in the PWM electrical apparatus 1, and the vertical axis represents the start and winding of the first coil 5 of the line end coil with respect to the change in the maximum voltage at the terminal portion. It is the 1st coil share ratio (voltage share ratio of the 1st coil) which is the ratio of the maximum voltage applied during the end. For example, in the PWM electrical apparatus 1 with the number of interphase series coils n = 4, if the four coils 5 share the voltage equally, the first coil sharing ratio is 25% and the number of interphase series coils is n = 8. In this case, if the eight coils 5 share the voltage equally, the first coil sharing ratio is 12.5%.

Further, FIG. 2 shows each coil 5 when the number of interphase series coils of the PWM electrical device 1 is n = 4 and when the number of interphase series coils is n = 8, and when each coil 5 is independent. When the resonance frequency between the winding start and the winding end is 370 kHz, it is a combination of 2 × 2 cases when the frequency is 3.7 MHz.
(A) The number of series coils between phases is n = 4, the resonance frequency of each coil is 370 kHz,
(B) The number of series coils between phases is n = 4, the resonance frequency of each coil is 3.7 MHz,
(C) The number of series coils between phases is n = 8, the resonance frequency of each coil is 370 kHz,
(D) The number of series coils between phases is n = 8, and the resonance frequency of each coil is 3.7 MHz.
Four curves are drawn by using (a) to (d) as parameters.

Further, for the four curves in FIG. 2, in the Δ-connected PWM electrical device 1 exemplifying an equivalent circuit in FIG. 3, the case where the number of interphase series coils is n = 4 and n = 8 is 1 Using the transient circuit calculation program EMTP (Electro-Magnetic Transient program) with the above (a) to (d) as parameters, applying voltage to the phases and grounding the remaining two phases, the PWM frequency converter from the pulse power supply A pulse power supply voltage simulating the generated voltage of 2 was applied, and the inductance L1 per coil was changed to determine the sharing ratio of the first coil 5 with respect to the rise time Tr. When the inductance L1 per coil in the equivalent circuit or the capacitance C1 to ground per coil changes, the resonance frequency f1 of each coil 5 becomes
f1 = 1 / (2π√ (L1 · C1))
Change according to

  Note that the resonance period shown in FIG. 2 is a period corresponding to the resonance frequency f1, and was obtained by resonance period = 1 / f1. Further, the resonance rise shown in FIG. 2 is obtained by the rise time Tr corresponding to the resonance frequency f1 and the resonance rise = 1 / (4f1).

  FIG. 4 also shows that the inductance L1 per coil is changed in three cases in which the rise time Tr of the interphase voltage waveform between the terminal portions is Tr = 0.1 μsec, Tr = 0.25 μsec, and Tr = 1 μsec. It is the graph which calculated by changing the resonant frequency f1 of each coil 5, and drew the horizontal axis as the resonant frequency f1 between the winding start of each coil 5, and the winding end as a share ratio.

  2 and 4 obtained in this way, if the rise time Tr of the interphase voltage waveform between the terminal portions is short, there is no difference in the sharing ratio depending on the number n of interphase series coils, and the rise time of the interphase voltage waveform between the terminal portions. When Tr is long, it becomes clear that the sharing ratio decreases when the number n of interphase series coils is increased.

Moreover, it is shown that the reference of the rise time of the voltage waveform between the terminal portions is the resonance frequency f1 of each coil 5. Therefore, in order to prevent a high voltage from being applied to the first coil 5 at the line end when a surge voltage enters the PWM electrical device 1 such as an AC motor,
(1) Increasing the rise time Tr of the voltage waveform between the terminals.
(2) The resonance frequency f1 of each coil 5 is increased.
(3) Increase the number n of interphase coils.
It can be seen that a device satisfying these three conditions may be used.

  Incidentally, the interphase capacitance Cm contained in the PWM electrical device 1 itself connected to the tip of the power supply cable 3 has a short rise time of the voltage generated by the PWM frequency converter 2 (a general PWM frequency converter). 2 is approximately 0.1 μsec or less), the surge voltage waveform of the terminal portion of the PWM electrical device 1 is a gentle waveform. This is because the rise time Tr of the voltage waveform between the terminal portions becomes a part of the resonance waveform of the inductance Lc of the power feeding cable 3 and the interphase capacitance Cm in the terminal portion of the PWM electric device 1. Note that most of the interphase electrostatic capacitance Cm at the terminal portion of the PWM electric device 1 is determined by a capacitor formed by the conductor of the coil 5, the ground insulating material, and the conductor of the core 4 in an AC motor, for example.

Further, FIG. 5 shows that the electrostatic capacitance Cm of the terminal portion of the power supply cable 3 and the PWM electric device 1 is between terminals with respect to a waveform having a short rise time Tr of the voltage generated by the PWM frequency converter 2 (for example, 1 μsec or less). It is an equivalent circuit for calculating the influence of the voltage waveform on the rise time Tr. In the following examination results, the pulse power supply voltage simulating the voltage generated by the PWM frequency converter 2 is implemented as an ideal step voltage (rise time = 0 μsec). Further, as shown in Table 1, the characteristic impedance Z of the feeding cable 3 and the propagation speed v of the feeding cable 3 are set as shown in Table 1, and the cable length of the feeding cable 3 is arbitrarily changed.

  FIG. 6 is a result of calculating the influence of the cable length of the power feeding cable 3 on the rise time Tr of the applied voltage at the terminal portion of the PWM electrical device 1, and the horizontal axis represents the cable length (m) of the power feeding cable 3. The vertical axis represents the rise time Tr (sec). Further, FIG. 7 shows a result when the horizontal axis of FIG. 6 is converted into a resonance frequency fr (where fr = 1 / (2π√ (Lc · Cm))).

  From FIG. 7, when the relationship between the resonance frequency fr (Hz) of the interphase capacitance Cm between the power supply cable 3 and the PWM electrical device 1 and the rise time Tr (sec) is read, Tr = (0 .4 / fr). Further, from FIG. 6, for example, the rise time Tr when using the power supply cable 3 (Z = 50Ω, v = 200 m / sec) under the condition 2 is minimum when Cm = 10 nF even when the cable length is as short as 1 m. It becomes about 100 nsec.

This transforms the above equation,
Tr = 2.5√ (Lc · Cm) (Equation (1)) The rise time Tr becomes the minimum rise time of the surge voltage that can be applied to the PWM electrical device 1. That is, no matter how short the rise time of the voltage generated by the PWM frequency converter 2 is, the rise time Tr of the interphase voltage waveform at the terminal portion becomes longer than the expression (1).

For this reason, in order to prevent a high voltage from being applied to the first coil 5 at the line end when a surge voltage enters the PWM electrical device 1 such as an AC motor,
(1) Increasing the rise time Tr of the voltage waveform between the terminals.
(2) The resonance frequency fr of each coil 5 is increased.
(3) Increase the number n of interphase coils.
It is sufficient to satisfy the following three conditions. Among these conditions, the minimum value of the condition (1) is determined by the equation (1) from the inductance Lc of the power supply cable 3 and the interphase capacitance Cm at the terminal portion of the PWM electric device 1. When this minimum value is combined with the conditions (2) and (3) shown in FIGS. 2 and 4, when a surge voltage enters the PWM electric device 1 such as an AC motor, a high voltage is applied to the line. A device design guideline for preventing the end first coil 5 from being applied can be derived.

For example, looking at a graph in which the rise time Tr of the phase voltage waveform at the terminal portion of the PWM electrical device 1 in FIG. 4 is Tr = 250 nsec, the resonance frequency f1 between the start and end of winding per coil is 300 kHz or less. The ratio is 60%, but if the resonance frequency f1 is designed to be 2 MHz, the sharing ratio is suppressed to 40%. That is, the inductance Lc of the feeding cable 3 and the interphase capacitance Cm of the PWM electrical device 1 are set so that the minimum rise time Tr is about 250 nsec, and the resonance frequency f1 of each coil 5 is 2 MHz. If the number of slots of the electrical device for PWM 1 is determined, the sharing ratio of the first coil 5 becomes 40% or less. Since this minimum rise time Tr is determined by the equation (1), the product (Lc · Cm) of the inductance Lc of the power feeding cable 3 and the interphase capacitance Cm of the PWM electrical device 1 at which the minimum rise time Tr is 250 nsec or more is It may be 10 ⁻¹⁴ sec ² or more.

In addition, when a surge voltage enters the PWM electrical device 1, the suppression effect for preventing a high voltage from being applied to the first coil 5 at the line end is that the resonance frequency of each coil 5 is the PWM electrical device 1. A frequency f = 1 (= 1 / (2Tr)) or more of the frequency f1 (= 1 / (4Tr)) corresponding to the voltage waveform rise time Tr of the terminal portion can be obtained sufficiently practically. Using this and the expression (1), the resonance frequency of each coil 5 constituting the PWM electrical device 1 is expressed as a general expression as fc.
fc> 1 / (5√ (Lc · Cm))
Therefore, if this equation is satisfied, the suppression effect can be obtained.

  In the present embodiment, the three-phase device has been described. However, a multi-phase device such as a six-phase device may be used, and the connection of each coil 5 is a Δ connection, but a Y connection may be used. The feeding cable 3 may also be any of a 3-core, 4-core, etc. multi-core cable and a single-core cable.

  Next, a second embodiment will be described with reference to FIG. FIG. 8 is a diagram showing a system configured by connecting a PWM frequency converter and an electric device for PWM. In addition, the same code | symbol is attached | subjected to the same part as 1st Embodiment, description is abbreviate | omitted, and the structure of this embodiment different from 1st Embodiment is demonstrated.

This embodiment is the first embodiment,
fc> 1 / (5√ (Lc · Cm))
As shown in FIG. 8, a capacitor 6 having a capacitance of Ca is connected between the three terminal portions Um, Vm, and Wm of the PWM electrical device 1 as shown in FIG. Has been.

By connecting the capacitor 6 between the phases in this way, the capacitance Ca enters in parallel with the interphase capacitance Cm of the PWM electrical device 1, and Cm in the above equation (1) is expressed as (Cm + Ca). You just have to replace it,
Tr = 2.5√ (Lc · (Cm + Ca))
It becomes. As a result, the same effect as that of the first embodiment can be obtained.

That is, when the inductance Lc of the power feeding cable 3, the capacitance Cm between the terminals of the PWM electric device 1, and the resonance frequency of each coil 5 constituting the PWM electric device 1 is fc,
fc> 1 / (5√ (Lc · (Cm + Ca)))
The same suppression effect can be obtained if the capacitor 6 having the capacitance Ca that satisfies the above condition is connected between the three-phase phases at the terminal portion of the PWM electric device 1.

  Next, a third embodiment will be described with reference to FIG. FIG. 9 is a diagram showing a system configured by connecting a PWM frequency converter and an electrical device for PWM. In addition, the same code | symbol is attached | subjected to the same part as 1st Embodiment, description is abbreviate | omitted, and the structure of this embodiment different from 1st Embodiment is demonstrated.

This embodiment is the same as the second embodiment, but is the first embodiment.
fc> 1 / (5√ (Lc · Cm))
In the case where the above relationship cannot be satisfied, as shown in FIG. 9, the three terminal portions Um, Vm, Wm of the PWM electrical device 1 and the three relative grounds, for example, between the grounded core 4, Capacitors 7 each having a capacitance Cb are connected.

By connecting the capacitor 7 between each phase and the ground in this way, the capacitance (2/3) Cb is placed in parallel with the phase-to-phase capacitance Cm of the PWM electric device 1, and the above (1) It is sufficient to replace Cm in the equation with (Cm + (2/3) Cb),
Tr = 2.5√ (Lc · (Cm + (2/3) Cb))
It becomes. As a result, the same effect as that of the first embodiment can be obtained.

That is, when the inductance Lc of the power feeding cable 3, the capacitance Cm between the terminals of the PWM electric device 1, and the resonance frequency of each coil 5 constituting the PWM electric device 1 is fc,
fc> 1 / (5√ (Lc · (Cm + (2/3) Cb)))
The same suppression effect can be obtained by connecting the capacitor 7 having the capacitance Cb that satisfies the above conditions between the terminal portions Um, Vm, Wm of the PWM electrical device 1 and the three relative grounds.

  Next, a fourth embodiment will be described with reference to FIG. 1 and the same parts as those in the first embodiment will be denoted by the same reference numerals.

  This embodiment corresponds to the rise time Tr without checking the values of the inductance Lc of the power supply cable 3 and the capacitance Cm between the terminal portions of the PWM electric device 1 when the rise time Tr is known. If the resonance frequency of each coil 5 constituting the PWM electric device 1 is set to a frequency (= 1 / (2Tr)) that is twice the frequency f1 (= 1 / (4Tr)) or more, the same effect can be obtained. It is done.

It is a figure which shows the system comprised by connecting the PWM frequency converter which is the 1st Embodiment of this invention, and the electrical equipment for PWM. It is a figure which shows the relationship between the rise time of the phase voltage waveform of the terminal part in the electrical equipment for PWM which is the 1st Embodiment of this invention, and the voltage sharing ratio of a 1st coil. FIG. 3 is an equivalent circuit diagram when the number of interphase series coils of the PWM electrical apparatus according to the first embodiment of the present invention is four and Δ-connected. It is a figure which shows the relationship between the resonant frequency between the winding start of one coil of the electrical equipment for PWM which is the 1st Embodiment of this invention, and the end of winding, and the voltage sharing ratio of a 1st coil. It is the circuit diagram used in order to investigate the influence which the electric power feeding cable concerning the 1st Embodiment of this invention and the electrostatic capacitance of the terminal part of the electrical equipment for PWM have on the rise time of the voltage waveform between terminals. It is a figure which shows the relationship between the cable length of the electric power feeding cable concerning the 1st Embodiment of this invention, and the voltage waveform rise time between terminals in the terminal part of the electrical equipment for PWM. 7 is a diagram obtained by converting the relationship shown in FIG. 6 and taking the resonance frequency on the vertical axis and the rise time of the voltage waveform between terminals at the terminal portion on the vertical axis. FIG. It is a figure which shows the system comprised by connecting the PWM frequency converter which is the 2nd Embodiment of this invention, and the electrical equipment for PWM. It is a figure which shows the system comprised by connecting the PWM frequency converter which is the 3rd Embodiment of this invention, and the electrical equipment for PWM.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electric equipment for PWM 2 ... PWM frequency converter 3 ... Power feeding cable 4 ... Core 5 ... Coil 6, 7 ... Capacitor

Claims (6)

In an electrical device for PWM that operates by connecting to a PWM frequency converter via a power supply cable,
When the interphase capacitance at the terminal portion of the electrical device is Cm, the resonance frequency of each coil constituting the electrical device is fc, and the inductance of the power supply cable is Lc,
fc> 1 / (5√ (Lc · Cm))
An electrical device for PWM.   2. The PWM electrical device according to claim 1, wherein the electrical device is a rotating machine. The product (Lc · Cm) of the inductance Lc of the power supply cable and the interphase capacitance Cm at the terminal portion of the electric device is larger than 10 ⁻¹⁴ sec ² , and the resonance frequency fc of each coil constituting the electric device is 2. The electrical device for PWM according to claim 1, wherein the electrical frequency is 2 MHz or more. In an electrical device for PWM that operates by connecting to a PWM frequency converter via a power supply cable,
When the electrical device is a three-phase electrical device, the interphase capacitance at the terminal portion of the electrical device is Cm, the resonance frequency of each coil constituting the electrical device is fc, and the inductance of the feeding cable is Lc,
fc> 1 / (5√ (Lc (Cm + Ca)))
A PWM electric device, wherein a capacitor having a capacitance of Ca satisfying the condition is connected between three phases of the electric device. In an electrical device for PWM that operates by connecting to a PWM frequency converter via a power supply cable,
When the electrical device is a three-phase electrical device, the interphase capacitance at the terminal portion of the electrical device is Cm, the resonance frequency of each coil constituting the electrical device is fc, and the inductance of the feeding cable is Lc,
fc> 1 / (5√ (Lc (Cm + (2/3) Cb)))
A PWM electric device, wherein a capacitor having a capacitance of Cb that satisfies the above condition is connected between each phase of the electric device and the core of the electric device.   When the rise time of the interphase voltage surge waveform at the terminal portion of the electric device is Tr, the resonance frequency of each coil constituting the electric device is set to 2 of the frequency f1 = 1 / (4Tr) corresponding to the rise time Tr. 6. The PWM electric device according to claim 1, wherein the double frequency is set to 2f1 = 1 / (2Tr) or more.

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