JP5432097B2 - Inverter-driven rotating electrical machine system - Google Patents

Description

  The present invention relates to an inverter-driven rotating electrical machine system.

  In recent years, variable speed operation of rotating electrical machines using an inverter power source has been actively performed in various fields such as electric power, industry, automobiles, railways, and home appliances from the viewpoint of energy saving. However, in rotating electrical machines, various problems such as bearing electrical corrosion, EMI / EMC (Electro Magnetic Interferency / Electro Magnetic Compatibility), insulation, etc. have occurred with the drive of the inverter, and various countermeasure technologies are currently being studied for these problems. Yes.

  For example, there is Patent Document 1 or the like regarding a bearing electric corrosion countermeasure technology for a rotating electrical machine accompanying inverter driving. In Patent Document 1, a common mode choke or other filter is inserted between the inverter and the rotating electric machine, and the common mode voltage applied to the rotating electric machine is reduced by sharing the common mode voltage with the filter element. This prevents the electric corrosion of bearings of rotating electrical machines that occurs due to the addition of.

Japanese Patent No. 4260110

  However, in the conventional method, there is a problem that the electrolytic corrosion of the bearing cannot be prevented when the common mode choke cannot be laid due to the installation space limitation of the inverter-driven rotating electrical machine system. In addition, since a common mode choke is used, there is a problem that care must be taken not to saturate the core with load current.

  In view of the above problems, an object of the present invention is to provide an inverter-driven rotating electrical machine system that can prevent electrolytic corrosion of a bearing without a common mode choke.

  An object of the present invention is to provide a part of a DC power supply in an inverter-driven rotating electrical machine system including an inverter including an inverter that converts a DC power supply into a multiphase, and an ungrounded multiphase rotating electrical machine connected to the inverter. Is grounded via the first impedance, the neutral point of the stator winding of the multiphase rotating electrical machine is connected to the frame via the second impedance, and the grounding point of the first impedance is connected to the multiphase rotating electrical machine. This is achieved by connecting between frames.

  According to the present invention, even if there is no common mode choke, the common mode voltage can be reduced and the electrolytic corrosion of the bearing can be prevented.

1 is a circuit diagram of an inverter-driven rotating electrical machine system according to a first embodiment of the present invention. The figure which shows the rotary electric machine which connected the neutral point and frame of the stator coil | winding inside the rotary electric machine. The figure which shows the rotary electric machine which connected the neutral point and frame of the stator winding | coil in the rotary electric machine terminal box. The figure which shows the impedance element comprised with a capacitor | condenser. The figure which shows the admittance-frequency characteristic of the impedance element of FIG. The figure which shows the impedance element comprised by the parallel connection of a capacitor | condenser and resistance. The figure which shows the admittance-frequency characteristic of the impedance element of FIG. The figure which shows the impedance element comprised by resistance, a capacitor | condenser, and an inductance. The figure which shows the admittance-frequency characteristic of the impedance element of FIG. The figure which shows the impedance element comprised by the series connection of resistance and a capacitor | condenser. The figure which shows the admittance-frequency characteristic of the impedance element of FIG. The figure explaining the effect | action by the circuit of an inverter drive rotary electric machine system. The figure which shows the frequency characteristic of the shaft voltage Vb added between the inner ring | wheel and outer ring | wheels of a bearing. The figure which shows the effect confirmation experiment circuit of this invention. The figure which shows the effect confirmation result in 150 times impedance. The figure which shows the effect confirmation result in 0.15 time impedance. The figure which shows the effect confirmation result in 0.015 time impedance. The figure which shows the measurement result of an axial voltage when changing the value of impedance Zm. The circuit diagram of the inverter drive rotary electric machine system of the 2nd Example of this invention. The circuit diagram of the inverter drive rotary electric machine system of the 3rd Example of this invention.

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

  FIG. 1 shows a circuit diagram of an inverter-driven rotating electrical machine system according to a first embodiment of the present invention. In FIG. 1, the inverter 1 is composed of a forward converter 2 that converts an AC voltage into DC, a smoothing capacitor 3 that smoothes and stores the DC voltage, and an inverse converter 4 that switches the DC voltage into AC. The In the inverter 1 of the first embodiment, the intermediate point of the smoothing capacitor 3 is grounded via the ground impedance 12.

  The output voltage of the inverter 1 is applied to the rotating electrical machine 6 via the three-phase cable 5. A neutral point 7 of the stator winding of the rotating electrical machine 6 is connected to the rotating electrical machine frame 9 via an element 8. The frame 9 of the rotating electrical machine is insulated from the surrounding ground 40, and the frame 9 is connected to the ground terminal 11 of the inverter 1 through the shield 10 of the cable 5.

  A specific structural example of the rotating electrical machine of the first embodiment is shown in FIGS. In the rotating electrical machine of FIG. 2, the three-phase cable 5 is connected to the lead wire of the rotating electrical machine at the terminal box 22 of the rotating electrical machine 6. The stator winding of the rotating electrical machine 6 is connected in a Y shape, and its neutral point connection line 23 is connected to the frame 9 via the element 8. The frame 9 is a connection terminal provided in the terminal box 22 and is connected to the ground terminal 11 on the inverter side via the shield 10 of the three-phase cable 5.

  In the rotating electrical machine of FIG. 3, the three-phase cable 5 is connected to the lead wire of the rotating electrical machine at the terminal box 22 of the rotating electrical machine 6. The stator winding of the rotating electrical machine 6 is connected in a Y shape, and its neutral point connection line 23 is drawn out to the terminal of the terminal box. The terminal of the neutral point connection line 23 and the frame 9 are connected by the element 8 in the terminal box 22. The frame 9 is connected to the shield 10 of the three-phase cable 5 through a connection terminal provided in the terminal box 22, and is connected to the ground terminal 11 on the inverter side.

  An example of the impedance element 8 that can be employed in the first embodiment of FIG. 1 and an example of its admittance (vertical axis) -frequency (horizontal axis) characteristics will be described with reference to FIGS.

  A first example of the impedance element 8 is shown in FIG. The element 8a in FIG. FIG. 5 shows the admittance (vertical axis) -frequency (horizontal axis) characteristics of the element 8a. In the element 8a using the capacitor C, the admittance increases with respect to the frequency. For this reason, compared with the case where the resistor is used for the element 8, the neutral point of the stator winding of the rotating electric machine and the frame are better coupled in the high frequency region, and the element 8 is used in the high frequency inverter than in the case where the resistor is used. There is an advantage that can be downsized. When the resistor R is used for the element 8, the admittance is constant regardless of the frequency (horizontal axis) as shown by the dotted line in FIG.

  A second example of the impedance element 8 is shown in FIG. The element 8b in FIG. 6 is composed of a parallel circuit of a capacitor C and a resistor R. FIG. 7 shows the admittance-frequency characteristics of the element 8b. In the element 8b using the parallel circuit of the capacitor C and the resistor R, the admittance increases with respect to the frequency as in FIG. However, since the resistors are connected in parallel, a certain admittance can be secured even on the low frequency side. For this reason, it is possible to secure the coupling between the neutral point of the stator winding of the rotating electrical machine and the frame in a wide range of low to high frequencies.

  A third example of the impedance element 8 is shown in FIG. The element 8c shown in FIG. 8 includes a series circuit of a resistor R, a capacitor C, and an inductance L. The admittance-frequency characteristic of the element 8c is shown in FIG. The element 8c using the series circuit of the resistor R, the capacitor C, and the inductance L has a resonance frequency f0, and the characteristics change before and after this. On the lower frequency side than the resonance frequency f0, the admittance increases as the frequency increases. However, on the higher frequency side than the resonance frequency of the capacitor C and the inductance L, the admittance decreases as the frequency increases. Therefore, it is possible to prevent the generation of high-frequency common mode current flowing from the neutral point of the stator winding to the frame while securing the coupling between the neutral point of the stator winding of the rotating electrical machine and the frame at low to medium frequencies. Can do.

  A fourth example of the impedance element 8 is shown in FIG. The element 8d in FIG. 10 is composed of a series circuit of a resistor R and a capacitor C. FIG. 11 shows the admittance-frequency characteristics of the element 8d. In the element 8d using the series circuit of the resistor R and the capacitor C, the admittance increases with respect to the frequency on the low frequency side as in FIG. However, the admittance is constant at high frequencies. For this reason, it is possible to prevent the generation of high-frequency noise current flowing from the neutral point of the stator winding to the frame while securing the coupling between the neutral point of the stator winding of the rotating electrical machine and the frame at low to medium frequencies. Can do.

  In the above, examples of various elements have been described. In short, the characteristics shown in FIGS. 5, 6, and 8 show high admittance in the high frequency range, and the neutral point and frame of the stator winding of the rotating electrical machine in a wide range of high frequencies. Can be secured. In the characteristics shown in FIG. 7, the admittance is high in the band around the resonance frequency, and the neutral point of the stator winding of the rotating electrical machine and the frame can be secured in this range.

  Accordingly, the capacity of each element is determined according to the frequency of the inverter-driven rotating electrical machine system, and an element in a frequency band that can secure the coupling between the neutral point of the stator winding of the rotating electrical machine and the frame is obtained. Can do.

  The operation of the inverter-driven rotating electrical machine system according to the first embodiment will be described with reference to FIG. FIG. 12 shows the moment when the positive and negative electrodes of the DC voltage of the inverter are distributed to the three-phase stator windings of the rotating electrical machine by switching the inverter. There are other inverter DC voltage distribution modes. Here, the operation will be described using an example thereof, but the operation and effects of the present invention are not limited to this switching mode.

  In FIG. 12, the inverter distributes the positive pole of the DC voltage to one phase (U phase) of the three-phase stator winding and the negative pole to the other two phases (V phase, W phase) of the three-phase stator winding. Yes. As a result, a DC voltage E is applied to the Y-connected rotating electrical machine winding, a voltage of 2E / 3 is applied to one phase (U phase), and E / 3 is applied to the other two phases (V phase, W phase). The voltage is shared. As a result, when viewed from the intermediate point 30 of the inverter DC circuit, the common mode voltage Vc of the equation (1) is generated between the neutral point 7 of the rotating electrical machine and the intermediate point 30 of the inverter DC circuit.

  Conventionally, a common mode choke is inserted in the DC power source of the inverter and the intermediate portion 128 of the rotating electric machine stator winding so that the common mode voltage Vc is not applied to the rotating electric machine. However, since the size of the inverter-driven rotating electrical machine system to which the common mode choke is attached is increased, an apparatus that does not use the common mode choke may prevent the common mode voltage Vc from being applied to the rotating electrical machine outside the rotating electrical machine. Can not.

  Therefore, in the present invention, the common mode voltage Vm shared in the rotating electrical machine is reduced by the following method, and the shaft voltage Vb generated thereby is reduced to prevent the electrolytic corrosion of the bearing. As will be apparent from the following description, the common mode voltage Vm shared within the rotating electrical machine is the voltage applied between the neutral point 7 and the frame 9 of the rotating electrical machine stator winding, and the shaft voltage Vb is the bearing. This is the voltage generated in the part.

  In the inverter-driven rotating electrical machine system of the present invention, first, the neutral point 7 of the rotating electrical machine stator winding and the frame 9 are connected by an impedance Zm. At this time, the magnitude of the impedance Zm satisfies the magnitude relationship of the equation (2). Specifically, when the impedance between the stator winding and the rotor of the rotating electrical machine is Zwr and the impedance between the rotor and the frame 9 is Zrf, the neutral point 7 and the frame 9 of the rotating electrical machine stator winding Are connected with the impedance Zm of the equation (2).

  That is, in FIG. 12, between the neutral point 7 of the rotating electrical machine stator winding and the frame 9, there is an equivalent circuit impedance Zwr between the stator winding and the rotor of the rotating electrical machine, and the rotor and frame. Since impedance Zrf between 9 is arranged in series, impedance Zm is newly installed in parallel with this. Further, the value of impedance Zm is selected to be smaller than Zrf + Zwr.

  As a result, in the two paths 122 and 127 from the neutral point 7 of the rotating electrical machine winding of FIG. 12 to the frame 9, the impedance Zm of the newly connected path 122 becomes the dominant impedance.

  In the inverter-driven rotating electrical machine system of the present invention, secondly, the frame 9 is connected to the ground terminal 11 of the inverter. Third, the ground terminal 11 of the inverter is connected to the midpoint 30 of the DC circuit via the ground impedance 12.

  As a result, a closed circuit of the intermediate point 30 of the inverter DC circuit → the neutral point 7 of the rotating electrical machine winding → the impedance Zm → the frame 9 → the inverter ground terminal 11 → the inverter ground impedance 12 → the intermediate point 30 of the inverter DC circuit is completed. By forming this closed circuit, the relationship that the common mode voltage Vc is the sum of the voltage Vm applied to the impedance Zm and the voltage Vi applied to the impedance Zi is established. This means that the common mode voltage Vc is shared by the newly installed impedance Zm and impedance Zi. Therefore, the voltage shared by the impedance Zi is increased (the voltage shared by the impedance Zm is reduced). Thus, the voltage (axial voltage Vb) applied between the neutral point 7 of the rotating electrical machine stator winding and the frame 9 can be reduced.

  Thus, in the present invention, focusing on the impedance balance between the impedance Zm and the impedance Zi, the common mode voltage Vm shared between the neutral point 7 of the stator winding and the frame 9 is reduced inside the rotating electrical machine. It is characterized by that. That is, the neutral point 7 of the rotating electrical machine winding and the frame 9 are connected with the impedance Zm, the frame 9 is connected to the ground terminal 11 of the inverter, and the ground terminal 11 of the inverter is connected to the middle of the DC circuit via the ground impedance 12. By connecting to the point 30 and selecting the impedance Zm appropriately for Zi, the common mode voltage Vm shared between the neutral point 7 of the stator winding and the frame 9 is reduced inside the rotating electrical machine. Take measures against electric corrosion of bearings.

  By the way, in the present invention, for the purpose of preventing electric corrosion of the bearing, the voltage Vb applied to the bearing impedances Cb and Rb of the path 127 must be suppressed to be less than the oil film breakdown voltage Vth of the bearing. Vb can be expressed by using Vm and impedances Zrf and Zwr. Therefore, it is necessary to satisfy the magnitude relation of the expression (3) between these.

  However, since Vm can be expressed by the equation (4) using the common mode voltage Vc and the impedances Zi and Zm, when the equation (4) is substituted into the equation (3), Vb is expressed by the equation (5). Is done.

  Therefore, by setting the impedance Zm connected between the neutral point 7 of the stator winding and the frame 9 inside the rotating electrical machine to be the expression (6), the neutral point 7 of the stator winding and the frame inside the rotating electrical machine. 9 can be reduced, and the voltage Vb applied to the bearing can be made less than the oil film breakdown voltage Vth.

  From the relationship of the above equation (6), in order to make the voltage Vb applied to the bearing less than the oil film breakdown voltage Vth, the impedance Zm connected between the neutral point 7 of the stator winding and the frame 9 inside the rotating electrical machine. It is better to reduce the.

  On the other hand, the common mode current Ic in FIG. 12 can be expressed by the equation (7) using the common mode voltage Vc and the impedances Zi and Zm. This means that the common mode current Ic increases as the impedance Zm connected between the neutral point 7 of the stator winding and the frame 9 is reduced in the rotating electric machine.

  In general, the noise current In generated by leakage of a part of the common mode current increases in proportion to the magnitude of the common mode current. For this reason, there is a lower limit to the impedance Zm connected between the neutral point 7 of the stator winding and the frame 9 inside the rotating electrical machine.

  Thus, in the previous equation (6), the impedance Zm should be small in relation to the oil film breakdown voltage Vth, but the conclusion derived from the equation (7) from the viewpoint of the common mode current is that the impedance Zm There is a lower limit.

  For this reason, the common mode current Ic is further examined. If the allowable limit level (upper limit value) of the common mode current Ic is Ith and the common mode current Ic is expressed using the common mode voltage Vc and the impedances Zi and Zm, it is necessary to satisfy the magnitude relationship of the equation (8). If this is arranged with respect to Zm, equation (9) is obtained.

  In summary, in the present invention, it is necessary to satisfy the relationship of the formula (10) that satisfies the magnitude relationship of the formula (2) and satisfies both the magnitude relationships of the formulas (6) and (9) for the impedance Zm. There is.

  In the present invention, the impedance Zm satisfies the relationship of the expression (10). Here, Zrf and Zwr are values specific to the rotating electrical machine, Ith and Vth are upper limit values and lower limit values determined by the system, Vc. Since this is an assumed value of the system, impedances Zm and Zi that satisfy the magnitude relationship of equation (10) are selected.

  As a result, the impedance Zm satisfying the equation (10) is connected between the neutral point 7 of the stator winding and the frame 9 inside the rotating electric machine, so that a filter such as a common mode choke is used as in the past. Without reducing the common mode voltage Vm shared between the stator winding and the frame inside the rotating electrical machine, the electric corrosion of the bearing can be prevented.

  Here, as an example, the impedance value satisfying the relationship of the equation (10) is selected, but the basic concept of this equation is as follows. In other words, in relation to the impedance of the equivalent circuit from the stator winding of the rotating electrical machine to the frame via the rotor, the voltage Vb applied to the bearing is made less than the oil film breakdown voltage Vth, and the inverter is connected from the midpoint of the DC circuit. In the relationship with the impedance of the circuit that reaches the frame via the ground terminal, an impedance having a value that makes the common mode current not more than the upper limit value is provided between the stator winding of the rotating electrical machine and the frame. Equation (10) expresses this concept as an equation. If the main circuit configuration of the inverter-driven rotating electrical machine system is different, a new equation is generated based on the above idea, or based on actual measured values. The impedance value that satisfies the above relationship can also be obtained.

  Incidentally, the impedance Zwr between the stator winding and the rotor of the rotating electric machine in FIG. 12 is a capacitive load, and the impedance Zrf between the rotor and the frame is a parallel circuit of a resistor and a capacitor (Cb + Crf). . For this reason, the voltage Vb applied to the bearing portion has frequency dependence, and shows a voltage change as shown in FIG.

  In other words, when the horizontal axis represents the frequency and the vertical axis represents the bearing portion voltage, the bearing portion voltage tends to change between when the horizontal axis frequency is equal to or lower than the cut-off frequency fc and above. Is different. In the following cases, the voltage changes in proportion to the frequency, but the voltage of the bearing portion is kept constant in the region above the cutoff frequency. This means that even when a common mode voltage Vm of the same magnitude is shared between the neutral point 7 and the frame 9 of the rotating electrical machine winding, the voltage Vb shared by the bearing portion decreases as the frequency decreases. Means that.

  Therefore, in the present invention, the impedance Zm connected between the neutral point 7 of the stator winding and the frame 9 inside the rotating electric machine is a high-pass filter having a cutoff frequency fc of the formula (11) or a low frequency. By using the bandpass filter having a cutoff frequency of the above equation (11), the shaft voltage can be effectively reduced.

  The elements applicable to the present invention shown in FIGS. 4, 6, 8, and 10 described above all have the characteristics of a high-pass filter or a band-pass filter. From these viewpoints, these elements are also applicable. It can be explained that it is desirable to use for the impedance Zm connected between the neutral point 7 of the stator winding and the frame 9 inside the rotary electric machine.

  As described above, the main structure of the first embodiment and the action of preventing electric corrosion of the bearing have been described. By the way, in the first embodiment, as described with reference to FIG. 1, the frame 9 of the rotating electrical machine is insulated from the surrounding ground 40 and connected to the ground terminal 11 of the inverter 1 through the shield 10 of the cable 5. By doing in this way, among the common mode current Ic shown in FIG. 12, the noise current In leaking to other than the closed circuit of the inverter and the rotating electrical machine can be suppressed.

  For this reason, compared with the case where the frame 9 is not connected to the ground terminal 11 of the inverter 1 via the shield 10 of the cable 5, the noise current In can be reduced even for the same common mode current Ic. The allowable value Ith of the limited common mode current Ic can be set high. That is, as shown in the equation (8), the lower limit of Zm can be made smaller, and in some cases, the neutral point of the rotating electrical machine winding and the frame can be connected with a small resistance or directly.

  The results of verifying the effects of the first embodiment will be described with reference to FIGS. First, FIG. 14 shows a test circuit diagram for effect verification. By connecting a Y-connected capacitor 157 to the three-phase cable connecting the inverter 1 and the rotating electrical machine 6 and observing the voltage appearing at the neutral point 158, the common mode voltage Vm applied to the rotating electrical machine 6 from the outside is increased. The thickness was measured in a pseudo manner. It should be noted that the pseudo means that the common mode voltage Vm should be measured with reference to the midpoint 30 of the DC voltage of the inverter 1, but this time, the ground is used as a reference due to the measurement limitation of the single ground probe of the digital oscilloscope. The voltage is used as a substitute because it is measured. On the other hand, a capacitor 153 was connected between the stator winding neutral point 7 of the rotating electrical machine 6 and the frame 9. The voltage applied between the stator winding neutral point 7 and the frame 9 was measured, and the sharing of the common mode voltage inside the rotating electrical machine was evaluated.

  Using the upper limit of Zm on the right side of equation (2) as a reference (that is, 1 time), the measurement result when the impedance Zm is increased 150 times is shown in FIG. 15, and the measurement result when the impedance Zm is increased 0.15 times. FIG. 16 shows the measurement results when the magnification is 0.015, respectively. In any figure, the pseudo common mode voltage (1601, 1701, 1801) applied to the rotating electrical machine from the outside in order from the upper stage, the common mode voltage (1602, 1702,. 1802), shaft voltages (1603, 1703, 1803) generated between the rotor shaft and the frame, and currents (1604, 1704, 1804) flowing through the bearings.

  The results of FIGS. 15, 16, and 17 are evaluated from various viewpoints. First, the magnitude of the pseudo common mode voltage (1601, 1701, 1801) applied to the rotating electrical machine from the outside does not change greatly regardless of the magnitude of the impedance Zm. Whether it is 150 times (1601) or 0.015 times (1801), the values are within the range of ± 100 (v) and have the same fluctuation range. This indicates that since the common mode choke is not used in the present invention, the voltage applied to the rotating electrical machine from the outside does not greatly decrease.

  However, when looking at the inside of the rotating electrical machine, the common mode voltage (1602, 1702, 1802) shared between the stator winding neutral point 7 and the frame 9 is greatly reduced when the impedance Zm is less than the reference value. To drop. At 150 times (1602), variation within a range close to ± 100 (v) is shown, but the fluctuation range of 0.15 times (1702) is clearly small, and at 0.015 times (1802), the value is small. Hardly fluctuates.

  As a result, when the magnitude of the impedance Zm is less than the reference value, the shaft voltage (1603, 1703, 1803) also decreases, and the bearing oil film breakdown voltage level (1605, 1705, 1805) indicated by the dotted line decreases. To do. The shaft voltage at 150 times exceeds the breakdown voltage level (1605) of the bearing oil film at various places, but the shaft voltage at 0.015 times has a margin within the breakdown voltage level (1805) of the bearing oil film. It is settled.

  Along with this, when the magnitude of the impedance Zm is 150 times the reference value, a pulsed spark current 1606 accompanying the grease oil film breakdown of the bearing was observed in the current (1604) flowing through the bearing. In the currents (1704, 1804) flowing through the bearing when the magnitude of Zm was less than the reference value, the pulsed bearing current accompanying the oil film breakage did not occur. From the above, it was confirmed that the present invention can prevent electrolytic corrosion of the bearing.

  FIG. 18 shows the magnitude of the axial voltage when the magnitude of the impedance Zm is changed with the upper limit value of Zm on the right side of the equation (2) as a reference (that is, 1 time). In this figure, the horizontal axis represents the upper limit value of Zm on the right side of Equation (2). In FIGS. 15, 16, and 17, the magnitude of impedance Zm is 150 times (FIG. 16) and 0.15 times ( 17) and 0.015 times (FIG. 18). The vertical axis is the axial voltage.

  First, in this figure, it can be seen that the axial voltage has a characteristic of increasing to the right with respect to Zm, and becomes larger as Zm increases. When Zm is larger than 1 time, the shaft voltage 1901 is higher than the oil film breakdown voltage level 1900. However, if Zm is made less than 1 time, the shaft voltage decreases and becomes lower than the breakdown voltage level 1900 of the oil film. When Zm is decreased, the shaft voltage 1901 is further lowered as originally 1902. However, in this experiment, noise was superimposed on the shaft voltage measurement result as indicated by 1803 in FIG. 17, so in FIG. 18, the decrease in shaft voltage stopped at the noise level 1903 and did not decrease to 1.0 Vp or less. It is considered a thing. As a result, it was shown that the common mode voltage can be reduced and the electrolytic corrosion of the bearing can be prevented without the common mode choke according to the present invention.

  A circuit diagram of the inverter-driven rotating electrical machine system according to the second embodiment of the present invention is shown in FIG. In the second embodiment, the inverter 1 includes a forward converter 2 that converts AC voltage to DC, a smoothing capacitor 3 that smoothes and stores the DC voltage, and an inverse converter 4 that switches DC voltage and converts it to AC. Composed. In the inverter 1 of the second embodiment, the low voltage side 143 of the smoothing capacitor 3 is grounded via the ground impedance 12. The output voltage of the inverter 1 is applied to the rotating electrical machine 6 via the three-phase cable 5. A neutral point 7 of the stator winding of the rotating electrical machine 6 is connected to the rotating electrical machine frame 9 via an impedance element 8. The frame 9 of the rotating electrical machine is insulated from the surrounding ground 40, and the frame 9 is twisted with the cable 5 or at least through the ground wire 140 disposed in the same wire sheath, piping, and duct. Connected to the ground terminal 11.

  In the second embodiment, unlike the first embodiment, the negative electrode side 143 is grounded via the ground impedance 12 instead of the intermediate portion of the DC voltage. As described above, depending on the design of the inverter, not the intermediate portion of the DC voltage but the negative electrode side or the positive electrode side is grounded. However, the effect of the present invention does not depend on where the grounding point of the inverter DC voltage portion is taken.

  Further, in the second embodiment, unlike the first embodiment, the inverter is connected via the ground wire 140 in which the frame 9 of the rotating electrical machine is associated with the cable 5, or at least disposed in the same wire sheath, piping, and duct. Is connected to the ground terminal 11. When the shielded cable is not used, the ground wire adjacent to the main power cable is used in this way, so that the current flows in proportion to the common mode current Ic, and the noise current In that causes peripheral devices to malfunction can be reduced. Leakage can be suppressed.

  A circuit diagram of the inverter-driven rotating electrical machine system of the third embodiment is shown in FIG. In the third embodiment, the inverter 201 includes a smoothing capacitor 3 that stores a DC voltage, and an inverse converter 4 that switches the DC voltage to convert it into an AC. In the inverter 201 of the third embodiment, the intermediate point of the smoothing capacitor 3 is grounded via the ground impedance 12.

  The output voltage of the inverter 201 is applied to the rotating electrical machine 6 through the three-phase cable 5. A neutral point 7 of the stator winding of the rotating electrical machine 6 is connected to the rotating electrical machine frame 9 via an impedance element 8. The frame of the rotating electrical machine is connected to the ground terminal 11 of the inverter via the ground plate 210.

  In the third embodiment, unlike the first and second embodiments, the frame 9 of the rotating electrical machine is not connected to the ground terminal of the inverter via the cable, but is connected via the earth plate 210. Since the inductance of the ground plate is extremely small, by adopting such a structure, leakage of noise current In that flows in proportion to the common mode current Ic and malfunctions the surrounding equipment to the surroundings can be suppressed.

  In the present invention, since a filter such as a common mode choke is not used between the inverter and the rotating electrical machine, the inverter-driven rotating electrical machine system can be miniaturized and can be used in a wide range of fields.

1: Inverter 2: Forward converter 3: Smoothing capacitor 3
4: Inverter 5: Three-phase cable 6: Rotating electric machine 7: Neutral point 8 of stator winding 8: Element 9: Rotating electric machine frame 10: Shield 11: Inverter ground terminal 12: Ground impedance 22: Rotating electric machine Terminal box 23: Neutral point connecting line C of rotating electric machine C: Capacitor R: Resistance L: Inductance 128: Intermediate part 122 of rotating electric machine stator winding, 127: Path from the neutral point of rotating electric machine winding to frame

Claims (5)

In an inverter-driven rotating electrical machine system including an inverter including an inverter that converts a DC power source into a multiphase, and an ungrounded multiphase rotating electrical machine connected to the inverter,
A part of the DC power source is grounded via a first impedance, a neutral point of the stator winding of the multiphase rotating electrical machine and a frame are connected via a second impedance, and the first impedance And connecting between the grounding point and the frame of the multiphase rotating electrical machine ,
The common-mode voltage peak of the inverter is Vc, and the first impedance is Zi (
Ω), the allowable value of the common mode current is Ith (A), the stator winding of the rotating electrical machine and the rotor
Impedance between the rotor and the frame is Zrf (Ω)
), When the breakdown voltage of the bearing oil film is Vth (V), the second impedance Zm is Z
smaller than the sum of wr and Zrf, and

An inverter-driven rotating electrical machine system characterized in that the value satisfies the above . In the inverter-driven rotating electrical machine system according to item 1,
The inverter-driven rotating electrical machine system, wherein the second impedance is selected to a value that causes a voltage applied to the bearing of the multiphase rotating electrical machine to be less than an oil film breakdown voltage of the bearing. In the inverter-driven rotating electrical machine system according to item 1,
The inverter-driven rotating electrical machine system, wherein the second impedance is selected to be a value that makes a current flowing through the first impedance equal to or less than an upper limit value thereof. In the inverter-driven rotating electrical machine system according to item 1,
The second impedance is selected so that the voltage applied to the bearing of the multiphase rotating electrical machine is less than the oil film breakdown voltage of the bearing, and the current flowing through the first impedance is less than or equal to the upper limit value thereof. An inverter-driven rotating electrical machine system characterized by that. In the inverter-driven rotating electrical machine system according to item 1,
The parallel resistance between the inner ring and the outer ring of the bearing of the rotating electric machine is Rb, and the parallel capacitance is (Cb + Crf).
) As the second impedance Zm, the cut-off frequency fc (Hz) is

An inverter-driven rotating electrical machine system using a high-pass filter or a band-pass filter.

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