JP7127290B2 - Surge voltage suppressor, power conversion device and polyphase motor drive device using the same - Google Patents

Description

The present invention relates to a surge voltage suppression device for suppressing a surge voltage applied to a polyphase motor, a power conversion device using the same, and a multiphase motor drive device.

When a multi-phase motor is driven by a multi-phase inverter with three or more phases having switching elements, an excessive surge voltage is applied to the multi-phase motor according to the switching timing of the switching elements, causing damage between lines and ground of the multi-phase motor. In addition, the life of the insulation of the motor windings may be shortened due to partial discharge.
In order to suppress the surge voltage applied to this polyphase motor, a surge voltage suppressing circuit described in Patent Document 1 has been proposed.
In the surge voltage suppression circuit described in Patent Document 1, one end of a series circuit of a resistor and a capacitor is connected to each of a three-phase cable connected between a motor and an inverter that drives the motor, and each series circuit The other ends of the circuits are connected together and connected to the DC voltage neutral point of the inverter.

By the way, in the prior art disclosed in Patent Document 1, a series circuit of a resistor and a capacitor is connected to each of the three-phase cables between the motor and the inverter. For this reason, an excessive current flows through the surge suppression circuit under specific conditions, causing abnormal heating of the resistor, and in the worst case, there is a concern that it may burn out. Also, it is known that the surge voltage applied to the motor increases due to a reflection phenomenon when the length of the cable connecting the inverter and the motor is longer than a certain length. Furthermore, if the resonant frequency of the inductance of the cable and the capacitor of the surge suppression circuit matches or approaches the switching frequency of the inverter, series resonance causes excessive current.

The length of the cable that connects the inverter and the motor varies depending on the factory or plant where the motor drive device is applied, and the switching frequency (carrier frequency) of the inverter is less than ten kHz. , it is very difficult to completely avoid the above-mentioned conditions that cause excessive current.
As a result, there is no choice but to set detailed restrictions (switching frequency and cable length) on the application conditions of the surge suppression circuit. is selected, the surge suppression circuit becomes large.

In order to solve this problem, as described in Patent Document 2, each terminal of the electric wire in the main line between the inverter device and the motor is branched from each terminal and connected to the electric wire of the subordinate line to form a full-bridge rectifier. A lossless surge energy regeneration type surge voltage suppression system has been proposed in which an AC terminal is connected to a subordinate line, a capacitor is connected to a DC terminal of a rectifier, and this DC terminal is connected to a DC terminal of an inverter device.

JP 2008-283755 A JP 2010-136564 A

By the way, in the prior art described in Patent Document 2, when the output voltage of the inverter is an ideal step voltage, the rectifier is connected to the subordinate line branched from the terminal to which the main line from the inverter of the motor is connected. By connecting the AC terminals and setting the characteristic impedance of the main line and the characteristic impedance of the sub-line to be equal, the reflection coefficient from the motor end to the inverter end of the main line can be approximated to zero. Therefore, the propagating wave that has propagated through the main line and reached the end of the motor is propagated to the subordinate line as it is. Therefore, only by generating a voltage equivalent to the propagating wave at the motor terminals, it is possible to suppress the generation of a surge voltage having a voltage value higher than that.

However, if the output voltage of the inverter is not an ideal step voltage but has a rise time before reaching a predetermined amplitude, the reflection coefficient at the AC input terminal of the rectifier becomes "1" and the AC input terminal of the rectifier becomes Among the arriving propagating waves, the waveform component in the rising period is reflected toward the motor terminals, generating a surge voltage at the motor terminals. To prevent this surge voltage, it becomes necessary to connect a capacitor to the AC input terminal of the rectifier. Therefore, the same problem as in the prior art described in Patent Document 1 arises.
Therefore, the present invention has been made by paying attention to the above-described problems of the prior art, and provides a surge voltage generator capable of absorbing the reflection component reflected from the electric motor terminal and propagated through the motor cable on the reactor side. An object of the present invention is to provide a suppression device, a power conversion device and a polyphase motor drive device using the suppression device.

In order to achieve the above object, one aspect of a surge voltage suppressing device according to the present invention includes: a polyphase motor cable connecting between a polyphase motor and a polyphase inverter that drives the polyphase motor; A filter is provided between the inverter and the polyphase reactor interposed on the polyphase inverter side of the motor cable, the polyphase reactor of the polyphase cable, and the polyphase reactor side between the polyphase motor A diode bridge comprising: a diode bridge circuit in which polyphase diode legs are connected in parallel, each of which has an intermediate point connected to a connection point; The DC high potential side and the DC low potential side of the circuit are individually connected to the DC high potential side and the DC low potential side of the polyphase inverter, and the resistance value of the return current suppression resistor is propagated from the polyphase motor side via the motor cable. It is set to a value that prevents specular reflection of the reflected voltage at the output end of the filter , and is set to a value that causes negative reflection that reverses the polarity of the reflected voltage at the output end of the filter .

Further, one aspect of the power converter according to the present invention includes a polyphase inverter that drives a polyphase motor, and the surge voltage suppression device described above.
Further, a polyphase motor drive device according to the present invention includes a polyphase motor, an inverter for driving the polyphase motor, and the surge voltage suppression device described above.

According to one aspect of the present invention, since the impedance of the return current suppression resistor connected to the polyphase diode bridge circuit connected to the reactor side is adjusted so as not to increase the reflected voltage from the polyphase motor, the capacitor is used. Therefore, it is possible to provide a surge voltage suppression device, a power conversion device and a multi-phase motor drive device using the same, which are free from the resonance problem and the restriction due to excessive current when using a capacitor.

1 is a circuit diagram showing a first embodiment of the invention; FIG. FIG. 4 is a waveform diagram for explaining the principle of surge voltage generation; FIG. 4 is a waveform diagram when no current-limiting resistor is provided, where (a) shows a diode current waveform, and (b) shows waveforms of an inverter output terminal voltage, a filter output voltage, and a motor receiving terminal voltage. FIG. 4 is a waveform diagram showing diode current with and without a current-limiting resistor; FIG. 4 is a waveform diagram showing line-to-line voltages at power receiving ends of a motor with and without a current-limiting resistor; FIG. 4 is a waveform diagram showing a line-to-line voltage of a motor power receiving end in the case where no current-limiting resistor is provided and in the first embodiment; FIG. 4 is a waveform diagram showing diode currents in the case where no current-limiting resistor is provided and in the first embodiment; FIG. 5 is a waveform diagram showing the presence or absence of a current-limiting resistor and the line-to-line voltage of the filter output terminals of the first embodiment; FIG. 4 is a waveform diagram showing presence/absence of a current-limiting resistor and a line-to-line voltage of a motor power receiving end in the first embodiment; It is a cross-sectional view showing a four-core cable. FIG. 2 is a diagram showing the characteristic impedance of a motor cable, where (a) is a characteristic diagram showing the relationship between the nominal cross-sectional area and the characteristic impedance, and (b) is a characteristic diagram showing the relationship between the allowable current and the characteristic impedance. . It is a circuit diagram which shows the modification of 1st Embodiment. It is a circuit diagram showing another modification of the first embodiment. FIG. 14 is a circuit diagram for explaining how to set the resistance value of the current-limiting resistor in FIG. 13; FIG. 5 is a waveform diagram showing current-limiting resistance loss in the second embodiment of the present invention; FIG. 10 is a waveform diagram showing a line-to-line voltage at power receiving end of the motor according to the second embodiment; FIG. 4 is a waveform diagram for explaining the effect of switching intervals of an inverter on a surge voltage; FIG. 11 is a waveform diagram showing a motor power receiving end line voltage for each resistance value of a current-limiting resistor according to the third embodiment of the present invention; It is a circuit diagram showing a fourth embodiment of the present invention. It is a circuit diagram which shows the modification of 4th Embodiment. It is a circuit diagram which shows the other modification of 4th Embodiment. FIG. 11 is a circuit diagram showing still another modification of the fourth embodiment; FIG. 23 is a diagram showing a leakage current suppression impedance that can be applied to the modification of FIG. 22; It is a circuit diagram which shows 5th Embodiment of this invention.

An embodiment of the present invention will now be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between thickness and planar dimension, the ratio of thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined with reference to the following description. In addition, it is a matter of course that there are portions with different dimensional relationships and ratios between the drawings.
Further, the embodiments shown below are examples of devices and methods for embodying the technical idea of the present invention. It does not specify the layout, etc., to the following. Various modifications can be made to the technical idea of the present invention within the technical scope defined by the claims.

First, a first embodiment of a motor drive device including a surge voltage suppression device representing one aspect of the present invention will be described.
As shown in FIG. 1, a motor drive device 10 includes a three-phase AC power source 11, a power conversion device 13 to which the three-phase AC power output from the three-phase AC power source 11 is input via a transformer 12, and a and a three-phase motor 14 driven by the three-phase power output from the power conversion device 13 .
The power conversion device 13 includes a pulse width modulation (PWM) converter (hereinafter referred to as a PWM converter) 21 that converts three-phase AC power input from the transformer 12 via a three-phase reactor 20 into DC power, and this converter 21 and a three-phase inverter 23 that converts the smoothed DC power into three-phase AC power and supplies it to the three-phase motor 14. there is

Here, in the PWM converter 21, as shown in FIG. 1, an R-phase switching leg CSLr, an S-phase switching leg CSLs, and a T-phase switching leg CSLt are connected in parallel between a high potential side wiring Lp and a low potential side wiring Ln. with a full bridge circuit.
The R-phase switching leg CSLr is connected in series with two switching elements Q11 and Q12 each composed of, for example, an insulated gate bipolar transistor (IGBT). The S-phase switching leg CSLs and the T-phase switching leg CSLt are also connected in series with switching elements Q13, Q14 and Q15, Q16 similar to those of the R-phase switching leg CSLr. Freewheeling diodes D11 to D16 are connected in anti-parallel to the switching elements Q11 to Q16.

An intermediate point between switching elements Q11, Q13 and Q15 and switching elements Q12, Q14 and Q16 of each switching leg CSLr, CSLs and CSLt is connected to the output side of the transformer 12 .
Further, a gate signal, which is a pulse width modulation (PWM) signal, is input from a gate drive circuit (not shown) to the gates of the switching elements Q11 to Q16, thereby converting AC power from the transformer 12 into DC power. Output to the high potential side wiring Lp and the low potential side wiring Ln.

Note that the converter is not limited to the PWM converter 21, and a diode bridge rectifier circuit configured only from diodes D11 to D16 by eliminating the switching elements Q11 to Q16 of the PWM converter 21 can be applied.
In addition, as shown in FIG. 1, the three-phase inverter 23 includes a U-phase switching leg ISLu, a V-phase switching leg ISLv and a W-phase switching leg ISLu between the high potential side wiring Lp and the low potential side wiring Ln to which the smoothing capacitor 22 is connected. It has a full bridge circuit in which the switching legs ISLw are connected in parallel.

The U-phase switching leg ISLu is connected in series with two switching elements Q21 and Q22, each composed of, for example, an insulated gate bipolar transistor (IGBT). The V-phase switching leg ISLv and the W-phase switching leg ISLw are also connected in series with switching elements Q23, Q24 and Q25, Q26 similar to those of the U-phase switching leg ISLu. Freewheeling diodes D21 to D26 are connected in anti-parallel to the switching elements Q21 to Q26, respectively.
In addition, the AC output terminal, which is the connection point between the switching elements Q21, Q23 and Q25 of the switching legs ISLu, ISLv and ISLw and the switching elements Q22, Q24 and Q26, is connected to the three-phase motor 14 via the three-phase motor cable 24. It is connected to the motor terminals tu, tv and tw. Here, the motor cable 24 includes a U-phase cable Lu connected between the AC output terminals of the switching elements Q21 and Q22 and the motor terminal tu, and a U-phase cable Lu connected between the AC output terminals of the switching elements Q23 and Q24 and the motor terminal tv. It is composed of a V-phase cable Lv and a W-phase cable Lw connected between the AC output ends of the switching elements Q25 and Q26 and the motor terminal tw.

Further, a gate signal, which is a pulse width modulation (PWM) signal, is input to the gates of the switching elements Q21 to Q26 of the three-phase inverter 23 from a gate drive circuit (not shown). The three-phase inverter 23 converts the DC power supplied from the high-potential side wiring Lp and the low-potential side wiring Ln to which the smoothing capacitor 22 is connected into AC power, which is supplied to the three-phase motor 14 via the motor cable 24 . do.
A voltage clamp type dV/dt filter 30 is provided on the motor cable 24 between the three-phase inverter 23 and the three-phase motor 14 . This voltage clamp type dV/dt filter 30 includes a three-phase reactor 31 connected to the three-phase inverter 23 side of each phase cable Lu to Lw of the motor cable 24, and a three-phase reactor 31 side of each phase cable Lu to Lw. A connected diode bridge circuit 32 and a current limiting resistor 33 as a return current suppression resistor connected to the AC input side of the diode bridge circuit 32 are provided.

The three-phase reactor 31 includes a U-phase reactor 31u inserted in the U-phase cable Lu, a V-phase reactor 31v inserted in the V-phase cable Lv, and a W-phase reactor 31w inserted in the W-phase cable Lw. have
The diode bridge circuit 32 includes three sets of diode legs 32u, 32v and 32w connected in parallel between a high potential side wiring Lp1 and a low potential side wiring Ln1 on the DC output side.
The diode leg 32u has two diodes D31 and D32 connected in series between the high potential side wiring Lp1 and the low potential side wiring Ln1, the cathode of the diode D31 being connected to the high potential side wiring Lp1, and the anode being the cathode of the diode D32. , and the anode of the diode D32 is connected to the low potential side wiring Ln1. Further, an AC input terminal, which is an intermediate point between the diodes D31 and D32, is connected to a connection point P1u between the U-phase reactor 31u of the three-phase reactor 31 and the U-phase cable Lu of the motor cable 24.

Diode legs 32v and 32w also have two diodes D33, D34 and D35, D36 connected in series in the forward direction between high potential side wiring Lp1 and low potential side wiring Ln1, like diode leg 32u. The AC input end, which is the middle point of the diodes D33 and D34, is connected to the connection point P1v between the V-phase reactor 31v of the three-phase reactor 31 and the V-phase cable Lv of the motor cable 24. An intermediate point between the diodes D35 and D36 is connected to a connection point P1w between the W-phase reactor 31w of the three-phase reactor 31 and the W-phase cable Lw of the motor cable 24.

The current limiting resistor 33 is composed of resistors Ru, Rv and Rw individually connected between the AC input terminals of the diode legs 32u, 32v and 32w and the connection points P1u, P1v and P1w. Here, the resistance values of the resistors Ru, Rv and Rw are determined between the connection points P1u, P1v and P1w of the phase cables Lu, Lv and Lw of the motor cable 24 and the power receiving terminals tu, tv and tw of the three-phase motor 14. are set to values equivalent to the characteristic impedances Zu, Zv and Zw of .
The high potential side wiring Lp1 is connected to the high potential side wiring Lp of the power conversion device 13, and the low potential side wiring Ln1 is connected to the low potential side wiring Ln of the power conversion device 13.

Here, the inverter surge voltage suppression principle of the voltage clamp type dV/dt filter 30 will be described.
First, the case where the voltage clamp type dV/dt filter 30 is not provided with the current limiting resistor 33 will be described.
As is well known, the inverter surge voltage is caused by an impedance mismatch at the end of the motor cable 24 on the side of the three-phase motor 14 because the voltage output from the three-phase inverter 23 has a short rising and falling time. This is caused by the conspicuous appearance of the accompanying voltage reflection.

Therefore, it is effective to lengthen the voltage change time in order to reduce the surge voltage. In the voltage clamp type dV/dt filter 30, the inductance Lf of the reactor 31 and the characteristic impedance Zc (Zu, Zv, Zw) of the motor cable 24 act like an LR filter at high frequencies. 2A, the rise time of the voltage at the filter output terminal is lengthened as shown by the solid line in FIG.
Then, the surge voltage applied to the motor power receiving end is the voltage of the motor power receiving end without the filter shown by the dotted line in FIG. can be reduced as

However, if the current-limiting resistor 33 is not provided, the return current continues to flow from the three-phase reactor 31 through the switching elements of the diode bridge circuit 32 and the three-phase inverter 23 and back to the three-phase reactor 31 without attenuation. As shown in FIG. 3(a), the return current flowing through the diode at this time continues to flow after the filter output end voltage reaches the DC intermediate voltage Ed as shown in FIG. 3(b). This return current causes problems such as heating of the diode and increased loss. Therefore, the current limiting resistor 33 is required to suppress the return current.

Therefore, the circuit behavior when the current-limiting resistor 33 is provided will be described with reference to FIGS. Without the current-limiting resistor 33, although there is inductance in the path through which the return current flows, there is no element that actively attenuates the current. Therefore, as shown in FIG. 3(a), the amplitude of the return current is large and the attenuation is very slow.
On the other hand, by providing the current-limiting resistor 33 in the path through which the return current flows, the return current can be reduced. That is, as shown in FIG. 4, the diode current when the current-limiting resistor 33 is not provided has a damped oscillation waveform in which the amplitude is large and the attenuation is slow as shown by the dotted line, whereas the current-limiting resistor 33 is provided. In this case, it can be seen that the return current has a small amplitude and rapidly decreases as indicated by the solid line.

However, by providing the current-limiting resistor 33, the line-to-line surge voltage at the motor power receiving end is reduced, as indicated by the dotted line in FIG. It becomes a large peak voltage, resulting in a large surge voltage.
On the other hand, as in the first embodiment, by making the resistance value of the current-limiting resistor 33 equal to the characteristic impedance Zc of the motor cable 24, the current-limiting resistor 33 is provided as indicated by the solid line in FIG. Surge voltage can be suppressed. That is, by setting the resistance value of the current-limiting resistor 33 to be equal to the characteristic impedance Zc of the motor cable, the peak value of the line-to-line voltage between the motor power receiving terminals can be reduced to the limit indicated by the dotted line in FIG. It can be equivalent to the peak voltage value of the line-to-line voltage at the power receiving end of the motor when no current resistance is provided. In other words, the maximum value of the line-to-line voltage of the motor power receiving end does not change between the case where the current-limiting resistor is provided and the case where the current-limiting resistor is not provided, and both are approximately 1.3 Ed.

Further, as shown in FIG. 7, the diode current is compared with the damped oscillation waveform in the case where the current limiting resistor 33 is not provided as shown by the dotted line, and the current limiting resistor 33 is provided and the resistance value is set as described above. In this case, as indicated by the solid line, the amplitude is small, and the vibration waveform can be quickly damped without becoming an oscillating waveform.
The principle and effects of this embodiment will be described in detail with reference to FIGS. 8 and 9. FIG. FIG. 8 shows the filter output end voltage in the present embodiment shown by the solid line, when the current limiting resistor 33 shown by the dotted line is provided, and when the current limiting resistor 33 shown by the alternate long and short dash line is not provided. When the semiconductor element of the inverter switches at time t1, the voltage rises with a first-order lag waveform with a time constant Lf/Zc determined by the filter reactor Lf and the characteristic impedance Zc of the motor cable. For example, in the verification shown in FIG. 8, the rise time at which the inverter output terminal voltage reaches the inverter DC intermediate voltage Ed is set to 0.1 μs, but by connecting the filter 30, the rise time is delayed to about 2 μs. be able to.

When the output voltage of inverter 23 starts to rise from time t1, the voltage propagates through motor cable 24 and eventually reaches the motor. Since the impedance Zm of the motor is larger than the characteristic impedance Zc of the motor cable 24 , specular reflection occurs at the power receiving end of the motor 14 , and the reflected voltage propagates from the motor toward the filter 30 . When this reflected voltage reaches the filter 30 at time t2, the impedance of the filter 30, which depends on the reactor Lf, is larger than the characteristic impedance of the motor cable, so specular reflection also occurs at the filter output end. Such a reflection phenomenon causes the voltage gradient after time t2 to be larger than the voltage gradient from time t1 to time t2.

At time t3, the filter output terminal voltage reaches the DC intermediate voltage Ed of the inverter, and the diode of filter 30 becomes conductive. Then the impedance of the filter 30 changes under the influence of the current limiting resistor 33 .
In the frequency band where the inverter surge voltage becomes a problem, the value of the inductance Lf is set so that the impedance of the filter 30 is dominated by the resistance value Rf of the current limiting resistor 33 over the inductance Lf of the reactor 31 .
The frequency band in which the inverter surge voltage becomes a problem is obtained when the frequency of the oscillation period of the inverter surge voltage (see FIG. 2(b)) and the rising time of the inverter output voltage are Tr (see FIG. 2(a)). , and the frequency of 1/(π·Tr).

Here, in order to make the resistance value Rf of the current limiting resistor 33 dominant over the inductance Lf of the reactor 31, the value of the inductance Lf is set to a value larger than 2/π times the inductance Lc of the motor cable 24. It should be set to (Lf>2Lc/π).
However, increasing the inductance Lf causes problems such as an increase in the size of the filter. Therefore, for the frequency of 1/(.pi..Tr), the value of the inductance Lf is set based on 2.pi..1/(.pi..Tr).Lf>Rf. That is, the value of the inductance Lf is set to a value larger than Tr·Rf/2 (Lf>Tr·Rf/2). As a result, the resistance value Rf of the current-limiting resistor 33 becomes dominant over the inductance Lf of the reactor 31, and can contribute to suppressing the surge voltage.

Since the value of the inductance Lf is set in this way, the voltage reflection at the reactor output end after time t3 is determined by the current limiting resistor 33 of the filter and the characteristic impedance Zc of the motor cable 24. FIG.
In this embodiment, since the resistance value of the current limiting resistor 33 matches the characteristic impedance Zc of the motor cable 24, no reflection occurs at the filter output end after t3.
On the other hand, in the filter 30 provided with a current-limiting resistance, the current-limiting resistance value is determined so as to suppress the return current, and since it does not match the characteristic impedance of the motor cable 24, reflection occurs again. This is the reason why the slope of the filter output terminal voltage after time t3 is larger than that of the present embodiment, as indicated by the dotted line. A filter without the current-limiting resistor 33 has negative reflection because the impedance of the filter is smaller than the characteristic impedance of the motor cable 24, which is about the conduction resistance of the diode.

FIG. 9 shows the voltage at the motor power receiving end in this embodiment, when the current-limiting resistor 33 is provided, and when the current-limiting resistor 33 is not provided. Here, time t1', time t2' and time t3' in FIG. 9 are obtained by adding the time for the voltage to propagate from the filter output end to the motor power receiving end to the time t1, time t2 and time t3 in FIG. be. The voltage at the motor power receiving end becomes a value obtained by multiplying the filter output terminal voltage by the reflection coefficient +1 determined by the characteristic impedance Zc of the cable and the impedance Zm of the motor. , the voltage value of this embodiment becomes maximum. On the other hand, in the filter 30 having the current-limiting resistor 33, the positive reflected voltage continues to propagate as indicated by the one-dot chain line, so the voltage rises even after time t3'. In the filter 30 without the current-limiting resistor 33, a negative reflected voltage begins to propagate as indicated by the dotted line, causing the voltage to drop, and thereafter causing vibration according to the length of the cable and the propagation speed.

Thus, in this embodiment, the reactor 31 of the filter 30 is connected to the AC output end side of the inverter 23, and the diode bridge circuit 32 is connected to the connection points P1u to P1w on the output side of the reactor 31 via the current limiting resistors 33. is doing. Then, by making the resistance value of the current limiting resistor 33 equal to the characteristic impedance Zc of the motor cable 24 between the connection points P1u to P1w and the connection terminals tu to tw of the three-phase motor 14, the current flowing through the diodes of the diode bridge circuit 32 The surge voltage at the motor power receiving end can be effectively suppressed while quickly attenuating the return current.

Next, the setting of the resistance value of the current limiting resistor 33 considering the asymmetry of the motor cable 24 will be described.
The resistance values of the resistors Ru to Rw of the current-limiting resistor 33 may be set individually for each phase according to the type of the motor cable 24 and laying conditions.
For example, the motor cable 24 may use a four-core cable 40 whose cross section is shown in FIG. The four-core cable 40 is formed by bundling a U-phase conductor 40u, a V-phase conductor 40v, a W-phase conductor 40w, and a grounding conductor 40e each coated with an insulation coating and covered with an insulation coating 40c. When such a four-core cable 40 is used, the V-phase is arranged asymmetrically with respect to the U-phase and W-phase. becomes. Reflecting this, the current-limiting resistance value of the V-phase may be set to a value different from that of the U-phase and the W-phase.
When three single-core motor cables are used for U-phase, V-phase, and W-phase, the characteristic impedance is different between adjacent phases and distant phases. This may be reflected in the resistance values of the current limiting resistors Ru, Rv and Rw.

Next, how to determine the characteristic impedance of the motor cable and the resistance value of the current-limiting resistor 33 will be specifically described.
FIG. 11 shows characteristic impedance measurement examples of motor cables including a single-core cable, a 3-core cable, and a 4-core cable. In FIG. 11(a), the horizontal axis is the nominal cross-sectional area of the conductor of the cable, and the vertical axis is the characteristic impedance of the motor cable. In FIG. 11(b), the horizontal axis is the allowable current of the conductor of the cable, and the vertical axis is the characteristic impedance of the motor cable.

Referring to FIG. 11, as an example, how to determine the resistance value of the current-limiting resistor 33 of the filter 30 used when driving a three-phase motor with a three-phase inverter having a power capacity of 7.5 kW/voltage of 400 V/rated current of 23 A. are described below.
The allowable current of the motor cable 24 is determined for each nominal cross-sectional area. In addition, in order to take into consideration that the allowable amount of heat generation may be reduced depending on the installation conditions, and to keep the voltage drop that occurs in the cable below the allowable range, it is necessary to add 1 to the allowable current specified for each nominal cross-sectional area. Cables may also be selected based on values multiplied by the following coefficients. In the above example, in order to pass a rated current of 23 A, if the cross-sectional area of the applicable conductor is determined from the allowable current determined for each nominal cross-sectional area, the nominal cross-sectional area is 2 mm ² or more. Considering this, the nominal cross-sectional area must be 5.5 mm ² or more.

Here, referring to FIG. 11(a), the characteristic impedance of a 5.5 mm ² cable is 99 Ω for a single-core cable, 61 Ω for a 4-core cable, and 41 Ω for a 3-core cable, and the value varies depending on the cable type. . If the cable to be used is determined, the resistance value of the current limiting resistor 33 may be set to the above value according to the cable. If the cable to be used is unknown, the minimum value of 41Ω or more and the intermediate value of 70Ω or less among the three cables may be set. Alternatively, for example, if the rated current value is relatively small and it is estimated that a multi-core cable will be used, the minimum value of 41 Ω or more and a value between the 4-core cable and the 3-core cable It may be set to a value of 50Ω or less.

In principle, the characteristic impedance of the cable is determined by the radius of the conductor, the distance between the conductors of each UVW phase, the material of the insulator, etc., and does not depend on the length of the cable. Therefore, even if the characteristic impedance of the motor cable 24 is not actually measured, the characteristic impedance can be estimated based on cables having the same current capacity and type. Alternatively, the resistance value of the current-limiting resistor 33 may be set by estimating the characteristic impedance from the allowable current value of the filter and FIG. 11(b). For example, the relationship between the allowable current value I [A] of the cable and the characteristic impedance Zc [Ω] can be expressed by the following approximate expression.

Single-core cable: Zc = 283 x I ^-0.295 [Ω] Formula (1)
3-core cable: Zc=93×I- ^0.266 [Ω] Formula (2)
4-core cable: Zc = 142 x I ^-0.256 [Ω] Formula (3)
With reference to the above formulas (1) to (3), in the case of the filter 30 with an allowable current of 50 A, when using a single-core cable as the motor cable 24, the resistance value of the current limiting resistor 33 is calculated from the above formula (1). Set to 89 Ω (283×50 ^−0.295 ). Similarly, when a three-core cable is used as the motor cable 24, the resistance value of the current limiting resistor 33 can be set by substituting the allowable current I into the above equation (2). Furthermore, when a four-core cable is used as the motor cable 24, the resistance value of the current-limiting resistor 33 can be set by substituting the allowable current I into the above (3).

In the above-described first embodiment, the case where the current limiting resistor 33 is connected to the AC input terminal side of the diode bridge circuit 32 has been described. Current limiting resistors R2u, R2v and R2w are connected in series with the cathode sides of the diodes D31, D33 and D35 of the circuit 32, and current limiting resistors R2x, R2y and R2z are connected in series with the anode sides of the diodes D32, D34 and D36. You may do so. In this case, the resistance values of the current limiting resistors R2u to R2w and R2x to R2z are set to the same values as the current limiting resistors Ru to Rw of the first embodiment. Also in the configuration of FIG. 12, the current limiting resistors R2u to R2w and R2x to R2z are connected to the return current path, so that the same effects as those of the first embodiment can be obtained.

13, current-limiting resistors R3p and R3n are connected to high-potential-side wiring Lp1 and low-potential-side wiring Ln1, which are the DC output side of diode bridge circuit 32, respectively. You may make it In this case, the resistance values of the current limiting resistors R3p and R3n should be set to 3/4 of the resistance of the current limiting resistors Ru to Rw in the first embodiment.
The resistance values of the current limiting resistors R3p and R3n in this case are determined as follows.
14(a) corresponding to FIGS. , (b) and (c), a method of setting the resistance value according to the connection position of the current-limiting resistor 33 will be described.

Under such a condition that the switching elements are conducting, the current in the motor cable 24 and the diode bridge circuit 32 flows along the path indicated by the dotted line in FIG. Regarding this current path, the characteristic impedance on the motor cable side and the resistance component on the diode bridge side are obtained as shown in (1) to (4) below from the point where the reactor, the motor cable, and the diode bridge are connected.

(1) The characteristic impedance value on the motor cable 24 side is common in FIGS. 14(a) to 14(c) and is 3/2Zc.
That is, the characteristic impedance value of the motor cable 24 can be regarded as a series circuit of the impedance Zc of the U-phase path and the parallel connection impedance Zc/2 of the V-phase and W-phase. Therefore, it can be expressed as Zc+Zc/2=3/2Zc.

(2) As shown in FIG. 14(a), the current-limiting resistance value when the current-limiting resistance 33 is connected to the AC input terminal side of the diode bridge circuit 32 is
Ru+(Rv·Rw)/(Rv+Rw),
(3/2) R1 if Ru=Rv=Rw=R1
It can be regarded as a series circuit of the current-limiting resistance Ru of the U-phase path and the parallel connection impedance (RvRw)/(Rv+Rw) of the V-phase and W-phase. If the current-limiting resistance values of all three phases are the same value R1 (Ru=Rv=Rw=R1), it can be expressed as (3/2)R1.

(3) As shown in FIG. 14(b), the current-limiting resistance value when the current-limiting resistance 33 is connected in the diode bridge circuit 32 is
R2u+(R2yR2z)/(R2y+R2z),
(3/2)R2 if R2u=R2y=R2z=R2
It can be regarded as a series circuit of the current-limiting resistance R2u of the U-phase path and the parallel connection impedance (R2yR2z)/(R2y+R2z) of the V-phase and W-phase. A value R2 (R2u=R2y=R2z=R2) where the current-limiting resistance values of all three phases are equal can be represented by (3/2)R2.

(4) As shown in FIG. 14(c), the current-limiting resistance value when a current-limiting resistance is connected to the DC output side of the diode bridge circuit 32 is
R3p+R3n
2R3 if R3p=R3n=R3
It can be regarded as a series circuit of the current limiting resistor R3p of the U-phase path (=DC positive side path) and the current limiting resistor R3n of the V-phase and W-phase paths (=DC negative side path). In the case of a value R3 (R3p=R3n=R3) where the current limiting resistance values on the positive side and the negative side are equal, it can be represented by 2R3.

In the present embodiment, the characteristic impedance value and the current-limiting resistance value obtained as described above should satisfy the magnitude relationship (characteristic impedance value≧resistance value) as described in the embodiment.
Comparing (1) and (2), the impedance on the motor cable side is (3/2) Zc, while the impedance on the diode bridge side is (3/2) R1. Both constants related to resistance are 3/2. Therefore, the current-limiting resistance value of each phase in the arrangement of the current-limiting resistors 33 shown in FIG. It will be.

Next, comparing (1) and (3), the impedance on the motor cable side is (3/2)Zc, whereas the impedance on the diode bridge side is (3/2)R2. Both flow resistance constants are 3/2. Therefore, the current-limiting resistance value of each phase in the arrangement of the current-limiting resistors 33 shown in FIG. . That is, the current-limiting resistance value in the placement of the current-limiting resistor 33 in FIG. 14(b) should be set to the same value as the placement of the current-limiting resistor 33 in FIG. 14(a).

Comparing (1) and (4), the impedance on the motor cable side is (3/2)Zc, whereas the impedance on the diode bridge side is 2R2. It is 3/4 (3/2/2) of the constant related to flow resistance. Therefore, the current-limiting resistance values of the positive side and the negative side of the DC part in the arrangement of the current-limiting resistor 33 in FIG. A value of /4 should be set. That is, the current-limiting resistance value in the placement of the current-limiting resistor 33 in FIG. 14(c) should be set to 3/4 of the placement of the current-limiting resistor 33 in FIG. 14(a).

In the first embodiment, FIG. 7 shows the diode current when a diode having ideal reverse recovery characteristics is applied. The current flows in the direction opposite to the junction direction of . By the way, the switching element of the inverter 23 repeats ON/OFF operation according to the PWM operation, so that the voltage at the output terminal of the inverter 23 outputs a rectangular wave voltage having a PWM pulse width. However, if the reverse recovery time of the diode is longer than this pulse width, the current continues to flow through the diode, which may cause problems such as heat generation and, in some cases, damage. Therefore, it is necessary to use a diode with appropriate reverse recovery characteristics. Specifically, it is preferable to use a high-speed diode whose reverse recovery time is shorter than the PWM pulse width.

Further, in the first embodiment, the resistance value of the current limiting resistor 33 is set to a value equivalent to the specific impedance of the motor cable 24 to maintain the effect of suppressing the surge voltage at the motor power receiving end while suppressing the surge voltage generated by the negative filter. Reduces loss peaks. However, the present invention is not limited to the above configuration, and the resistance value of the current limiting resistor 33 may be set to a value less than the specific impedance of the motor cable 24 .
In this case, the circuit configuration is similar to that of FIG. 1, but by setting the resistance value of the current-limiting resistor 33 to a value less than the specific impedance of the motor cable 24, the peak value of loss is reduced. there is
That is, in the first embodiment, since the current-limiting resistance value is matched with the characteristic impedance of the cable, the instantaneous peak value of the loss caused by the current-limiting resistance 33 becomes a large value. On the other hand, in this embodiment, the peak value of loss can be reduced by setting the current-limiting resistance to a value less than the characteristic impedance of the cable.

FIG. 15 shows the loss generated in the current limiting resistor 33 when one switching element of the inverter operates once for the first embodiment and the second embodiment. In FIG. 15, the vertical axis represents power consumption [W] and the horizontal axis represents time [μs]. In the first embodiment, as indicated by the dotted line, the power consumption increases to a large peak value after the switching element starts operating, and then gradually decreases. On the other hand, in the second embodiment, the peak value of the power consumption after the switching element starts operating is suppressed as shown by the solid line, and then it decreases and attenuates with a small amplitude.
Therefore, it can be confirmed from FIG. 15 that the peak loss value is reduced in the second embodiment.

Also, FIG. 16 shows the surge voltage at the motor power receiving end for the first embodiment and the second embodiment. In FIG. 16, the peak value of the surge voltage is the same between the first embodiment shown by the dotted line and the second embodiment shown by the solid line, and it can be seen that a high surge reduction effect can be obtained while reducing the loss peak.
The surge reduction principle of the second embodiment is the same as that of the filter without the current limiting resistor 33 described in the first embodiment. Since they are added, the negative reflected voltage becomes smaller. Therefore, the voltage oscillation of the motor power receiving end voltage is smaller than that of the filter without the current-limiting resistor 33 . Thus, if the resistance value of the current-limiting resistor 33 is set to a value less than the characteristic impedance of the motor cable 24, the impedance of the filter 30 after diode conduction becomes smaller than the characteristic impedance of the cable, resulting in positive reflection. do not have.
Therefore, the maximum value of the motor power receiving end voltage when the switching element of the inverter switches once can be reduced to the same value as in the first embodiment, regardless of the current-limiting resistance value. Therefore, the value of the current-limiting resistor 33 can be set to an appropriate value in consideration of the peak value of loss, the allowable current of the diode, and the like.

Next, a third embodiment of the present invention will be described with reference to FIGS. 17 and 18. FIG.
This third embodiment is intended to solve the problem of excessive surge voltage occurring during continuous switching in the second embodiment.
That is, in the third embodiment, unlike the second embodiment, the resistance value Rf of the current-limiting resistor 33 is set as follows, instead of the fact that the resistance value of the current-limiting resistor 33 is small.
Zc/2≤current-limiting resistance value Rf≤Zc

A third embodiment according to the present invention will now be described. In this embodiment, by setting the current-limiting resistance to a value less than half the characteristic impedance of the cable, the switching elements of the inverter can switch continuously within a short period of time. It reduces the surge voltage peak value at the motor power receiving end that occurs in the case.
First, with reference to FIG. 17, the behavior when the switching elements of the inverter continuously switch within a short period of time will be described. In FIG. 17, the inverter output end voltage is shown in FIG. 17(a) and the motor power receiving end voltage is shown in FIG. 17(b) when the inverter is continuously switched. FIG. 17(c) shows the case where the switching interval is longer than the surge voltage attenuation time, and FIG. 17(d) shows the case where the switching interval is much shorter than the surge voltage attenuation time. As can be seen from FIG. 17, when the switching interval is shorter than the surge voltage decay time, the surge voltage generated by the first switching is superimposed on the surge voltage generated by the second switching, resulting in a large voltage at the motor power receiving end. Surge voltage occurs.

In the third embodiment, the surge voltage generated in this way is reduced, and the resistance value of the current limiting resistor 33 is set to a value in the range from half to less than the characteristic impedance of the motor cable 24 . FIG. 18 shows the motor power receiving end voltage when the resistance value of the current limiting resistor 33 is changed. Here, the solid line indicates the case where the resistance value of the current-limiting resistor 33 is set to the characteristic impedance Zc/2 of the motor cable 24, and the dotted line indicates the case where the resistance value of the current-limiting resistor 33 in the first embodiment is set to the characteristic impedance of the motor cable 24. The dashed line shows the case where the resistance value of the current limiting resistor 33 is set to the characteristic impedance Zc/4 of the motor cable 24, and the thin line shows the case where the current limiting resistor 33 is not provided. .

It can be seen that a surge voltage oscillation occurs due to the reflection at the end of the cable, and the minimum voltage value at time t4' becomes smaller as the resistance value of the current-limiting resistor 33 becomes smaller. Then, when the minimum voltage value becomes lower than the DC intermediate voltage Ed of the inverter 23, due to the superimposition of the above-described surge voltage, a high-level surge voltage that does not occur when the switching element switches only once is generated. Therefore, in the third embodiment, the local minimum value of the surge voltage is equal to or higher than the DC intermediate voltage Ed of the inverter 23, and in order to prevent the generation of a high level surge voltage accompanying continuous switching as described above, the current limiting resistor is set within the above range of Zc/2≤current-limiting resistance Rf≤Zc. As can be seen from FIG. 18, the surge voltage oscillation is small when the current-limiting resistance value is set to half the characteristic impedance of the cable, and its minimum value never falls below the DC intermediate voltage Ed of the inverter 23.

Next, a fourth embodiment of the invention will be described with reference to FIG.
In the fourth embodiment, the zero-phase surge voltage component can be reduced.
That is, in the fourth embodiment, as shown in FIG. 19, the diode leg 34 for ground is added between the high potential side wiring Lp1 and the low potential side wiring Ln1 of the diode bridge circuit 32 . The ground diode leg 34 connects diodes D41 and D42 in series between the high-potential wiring Lp1 and the low-potential wiring Ln1, and connects the intermediate point of the diodes D41 and D42 to the ground. In addition to suppressing the line-to-line surge voltage described in the first to third embodiments, the ground surge voltage is also reduced.

That is, in addition to the line-to-phase voltage of the reactor 31, the voltage to ground can also be clamped to the DC intermediate voltage Ed by the diode bridge circuit 32 described above. As a result, the voltage to ground at the motor power receiving end, that is, the surge voltage of the zero-phase component can also be reduced.
Here, the surge voltage of the zero-phase component is a surge voltage generated between the frame potential of the three-phase motor 14 and the motor windings, and causes damage to the ground. In general, the surge voltage of the zero-phase component varies greatly depending on factors such as the switching operation of the three-phase inverter and PWM inverter, how the ground is taken, and the number of inverters and motors that are operated in parallel. is also difficult to deal with.

However, in the fourth embodiment, the diode bridge circuit 32 includes the diode leg 34 for ground, and the intermediate point between the diodes D41 and D42 of the diode leg 34 for ground is connected to the ground, thereby suppressing the surge voltage of the zero-phase component. can be clamped to the DC intermediate voltage Ed, and a large suppression effect can be obtained for the surge voltage of the zero-phase component.
In addition, the effect of suppressing the surge voltage of the zero-phase component can be easily achieved by simply connecting the diode leg 34 for grounding, which is grounded at the intermediate point, in parallel with the three-phase diode legs 32u to 32w that constitute the rectifying bridge circuit in the diode bridge circuit 32. can get to Furthermore, the effect of suppressing the surge voltage of the zero-phase component is not affected by the switching operation of the three-phase inverter or the PWM inverter, how the inverter is grounded, or the number of inverters and motors that are operated in parallel.

In addition, as shown in FIGS. 20 and 21, the ground diode leg 34 can also be applied to FIGS. 11 and 12, which are modifications of the first embodiment.
In addition, in the fourth embodiment, the case where the intermediate point of the ground diode leg 34 is directly grounded has been described, but the present invention is not limited to this. A leakage current suppression impedance Ze for suppressing leakage current may be connected between the point and the ground. Specifically, the leakage current suppressing impedance Ze is represented by a leakage current suppressing resistor Re shown in FIG. Any one of the series circuits of the shown leakage current suppression resistor Re and the grounding capacitor Ce for suppressing the low-frequency current component may be selected.

Next, a fifth embodiment of the present invention will be described with reference to FIG.
In this fifth embodiment, a snubber capacitor is connected to the DC output terminal side of the diode bridge circuit 32 .
That is, in the fifth embodiment, as shown in FIG. 24, in the configuration of the first embodiment described above, between the high potential side wiring Lp1 and the low potential side wiring Ln1, which are the DC output terminals of the diode bridge circuit 32, A snubber capacitor Cs is connected. By arranging the snubber capacitor Cs in the immediate vicinity of the diode bridge circuit 32, it is possible to prevent overvoltage breakdown of the diodes. Also, the snubber capacitor Cs is 0. It is composed of a small capacitance of several μF or less, and has a smaller capacitance than the capacitor used in the surge voltage suppression circuit described in Patent Document 1 and the like. Therefore, since the unwanted resonance frequency of the present invention is much higher than the switching frequency, an excessive current due to series resonance does not occur.

The snubber capacitor Cs can be connected to the DC output terminal side of the diode bridge circuit 32 also in the second to fourth embodiments.
In addition, in the first to fifth embodiments, the connection position of the current-limiting resistor 33 is provided on the AC input end side, the DC output end side of the diode bridge circuit 32, and in the diode bridge circuit 32. It is not limited to this, and a plurality of resistors can be divided and arranged in the return current path. The point is that a current-limiting resistor should be connected to the current path of the return current.

Further, in the first to fifth embodiments described above, the surge suppression device is connected between the three-phase inverter and the motor cable, but the surge suppression device may be arranged inside the inverter. In short, the surge suppression device may be connected between the output terminals of the switching elements forming the inverter and the motor cable, and may be arranged inside or outside the main body of the inverter device or the power conversion device.
Further, in the first to fifth embodiments described above, the three-phase inverter 23 constituting the power conversion device 13 drives the three-phase motor 14. However, a multi-phase motor with four or more phases is driven by the multi-phase inverter. The present invention can also be applied when In this case, the diode bridge circuit 32 may be connected in parallel with the number of diode legs corresponding to the number of phases of the multiphase motor.

Further, in the first to fifth embodiments, the case where one power conversion device 13 drives one three-phase motor 14 has been described, but one power conversion device 13 drives a plurality of three-phase motors 14. The present invention can also be applied to cases. Furthermore, the present invention can also be applied to a case where a plurality of sets of three-phase inverters and three-phase motors are connected to one converter that constitutes the power conversion device 13 .

DESCRIPTION OF SYMBOLS 10... Motor drive device, 11... Three-phase AC power supply, 12... Transformer, 13... Power converter, 14... Three-phase motor, 20... Three-phase reactor, 21... Pulse width modulation (PWM) converter, 22... Smoothing capacitor, 23...Three-phase inverter, 24...Motor cable, Lu...U-phase cable, Lv...V-phase cable, Lw...W-phase cable, tu-tw...Power receiving terminal, 31...Three-phase reactor, 31u...U-phase reactor, 31v... V-phase reactor 31w W-phase reactor 32 Diode bridge circuit 32u U-phase diode leg 32v V-phase diode leg 32w W-phase diode leg 33 Current-limiting resistor 34 Ground diode leg Ru~Rw, R2u~R2w, R2x~R2z, R3p, R3n...current limiting resistor, Ze...leakage current suppression impedance, Cs is a snubber capacitor

Claims (13)

A polyphase motor cable connecting between a polyphase motor and a polyphase inverter that drives the polyphase motor, and a filter provided between the polyphase inverter,
The filter is
a polyphase reactor inserted on the side of the polyphase inverter of the motor cable;
a diode bridge circuit in which polyphase diode legs are connected in parallel, each of which has an intermediate point connected to a connection point between the motor cable and the polyphase reactor;
Return current suppression resistors individually interposed in current paths passing through the polyphase diode legs;
with
the DC high potential side and the DC low potential side of the diode bridge circuit are individually connected to the DC high potential side and the DC low potential side of the multiphase inverter;
The resistance value of the return current suppression resistor is set to a value that prevents specular reflection at the output end of the filter of the reflected voltage propagating from the polyphase motor side via the motor cable , and the polarity of the reflected voltage is set to A surge voltage suppressor set to a value such that a negative reflection, which is reflected back, occurs at the output of said filter . A polyphase motor cable connecting between a polyphase motor and a polyphase inverter that drives the polyphase motor, and a filter provided between the polyphase inverter,
The filter is
a polyphase reactor inserted on the side of the polyphase inverter of the motor cable;
a diode bridge circuit in which polyphase diode legs are connected in parallel, each of which has an intermediate point connected to a connection point between the motor cable and the polyphase reactor;
Return current suppression resistors individually interposed in current paths passing through the polyphase diode legs;
with
the DC high potential side and the DC low potential side of the diode bridge circuit are individually connected to the DC high potential side and the DC low potential side of the multiphase inverter;
The resistance value of the return current suppression resistor is set to a value that prevents specular reflection at the output end of the filter of the reflected voltage propagating from the polyphase motor side via the motor cable, and is equal to or less than the characteristic impedance of the motor cable. and a surge voltage suppressing device, wherein the minimum value of the line-to-line voltage of the power receiving end of the polyphase motor is set to a value equal to or higher than the DC voltage of the polyphase inverter. A polyphase motor cable connecting between a polyphase motor and a polyphase inverter that drives the polyphase motor, and a filter provided between the polyphase inverter,
The filter is
a polyphase reactor inserted on the side of the polyphase inverter of the motor cable;
a diode bridge circuit in which polyphase diode legs are connected in parallel, each of which has an intermediate point connected to a connection point between the motor cable and the polyphase reactor;
Return current suppression resistors individually interposed in current paths passing through the polyphase diode legs;
with
the DC high potential side and the DC low potential side of the diode bridge circuit are individually connected to the DC high potential side and the DC low potential side of the multiphase inverter;
the resistance value of the return current suppression resistor is set to a value that prevents specular reflection at the output end of the filter of the reflected voltage propagating from the polyphase motor side via the motor cable;
The surge voltage suppression device, wherein the inductance value of the polyphase reactor is set to a value larger than 2/π times the inductance of the motor cable. A polyphase motor cable connecting between a polyphase motor and a polyphase inverter that drives the polyphase motor, and a filter provided between the polyphase inverter,
The filter is
a polyphase reactor inserted on the side of the polyphase inverter of the motor cable;
a diode bridge circuit in which polyphase diode legs are connected in parallel, each of which has an intermediate point connected to a connection point between the motor cable and the polyphase reactor;
Return current suppression resistors individually interposed in current paths passing through the polyphase diode legs;
with
the DC high potential side and the DC low potential side of the diode bridge circuit are individually connected to the DC high potential side and the DC low potential side of the multiphase inverter;
the resistance value of the return current suppression resistor is set to a value that prevents specular reflection at the output end of the filter of the reflected voltage propagating from the polyphase motor side via the motor cable;
Surge voltage suppression wherein the inductance value of the polyphase reactor is set to a value greater than a value obtained by dividing the multiplication value of the resistance value of the return current suppression resistor and the rise time of the output voltage of the polyphase inverter by 2. Device. 5. A surge voltage suppression device according to claim 1 , wherein the inductance value of said polyphase reactor is set to a value larger than 2/[pi] times the inductance of said motor cable. 4. The inductance value of the polyphase reactor is set to a value larger than a value obtained by dividing the multiplication value of the resistance value of the return current suppression resistor and the rise time of the output voltage of the polyphase inverter by 2 . A surge voltage suppressor according to any one of claims 1 to 3. The surge voltage suppression device according to any one of claims 1 to 6 , wherein the return current suppression resistor is connected between a midpoint of each polyphase diode leg of the diode bridge circuit and the connection point. The return current suppression resistor is connected between the high potential side of the diode bridge circuit and the high potential side of the multiphase inverter, and the low potential side of the diode bridge circuit and the low potential side of the multiphase inverter, respectively. The surge voltage suppression device according to any one of claims 1 to 6 . 9. The surge according to any one of claims 1 to 8 , wherein the diode bridge circuit has a diode leg for ground connected in parallel with the multiphase diode leg, and a middle point of the diode leg for ground is connected to ground. Voltage suppressor. 10. A surge voltage suppressor according to claim 9 , wherein a leakage current suppressing impedance is connected between the intermediate point of said ground diode leg and ground. 11. The surge voltage suppression device according to claim 10 , wherein said leakage current suppression impedance is composed of at least one of a resistor and a capacitor. a multiphase inverter that drives a multiphase motor;
A surge voltage suppressor according to any one of claims 1 to 11 ;
A power conversion device with a polyphase motor;
a multiphase inverter that drives the multiphase motor;
A surge voltage suppressor according to any one of claims 1 to 11 ;
A polyphase motor drive with

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