CN110690843B - motor drive - Google Patents

Abstract

To provide a small and low-cost motor drive device capable of reducing a common-mode surge voltage applied to a motor without providing two surge voltage suppression circuits. The motor drive device (10) includes: a PWM rectifier (21) which converts three-phase AC power into DC power and outputs it; and a PWM inverter (23) which converts the DC power output from the PWM rectifier (21) The three-phase AC power is supplied to the motor (14), and the motor drive device (10) utilizes a common-mode surge voltage suppression device (30) connected between the three-phase AC input side and the DC output side of the PWM rectifier (21). ), to suppress the surge voltage applied to the motor (14).

Description

motor drive

technical field

The invention relates to a motor driving device applied to an inverter-driven motor system. The inverter-driven motor system uses a rectifier to convert alternating current into direct current and supplies it to an inverter. The inverter is used to drive the motor.

Background technique

In a motor drive device driven by an inverter, a large surge voltage may be applied to a motor, and the motor may be damaged or burnt due to insulation breakdown. In particular, when a system configuration is used in combination with a PWM rectifier controlled by a pulse width modulation (hereinafter referred to as PWM) signal and a PWM inverter similarly controlled by a PWM signal, a greater surge voltage.

The surge voltage that causes damage to the motor is classified into normal mode surge voltage and common mode surge voltage, wherein the normal mode surge voltage is the one that causes the insulation breakdown between the wires of the motor winding Normal-mode component, common-mode surge voltage is the common-mode component that causes insulation breakdown between the motor windings and the frame.

The normal mode surge voltage is generated depending on the switching speed and switching pattern of the PWM inverter.

On the other hand, the common-mode surge voltage is the sum of the aforementioned normal-mode surge voltage, the common-mode voltage variation generated by the PWM inverter, and the common-mode voltage variation generated by the PWM rectifier.

That is, when an inverter-driven motor system is constructed including a PWM rectifier, the common-mode surge voltage becomes larger.

Various countermeasures for reducing this surge voltage have been proposed. For example, in the prior art described in Patent Document 1, a surge voltage suppression circuit is connected to a motor wiring between an inverter and a motor as a load. In this surge voltage suppression circuit, reactors are arranged on the output lines of the inverter, and one end is connected to the other end of the capacitor between these reactors and the induction motor and the negative side DC wiring on the input side of the inverter. A diode bridge circuit is connected between the connection point of the capacitor and the induction motor, and the DC output side of the diode bridge circuit is connected to the positive and negative DC wirings of the inverter.

The normal-mode surge voltage generated in the inverter is reduced by the surge voltage suppression circuit. At this time, the common mode surge voltage also exhibits some reduction effect, and the common mode surge voltage also reduces the reduction amount of the normal mode surge voltage.

On the other hand, many countermeasures for reducing both the normal-mode surge voltage and the common-mode surge voltage have also been proposed. For example, in the prior art described in Patent Document 2, a first surge voltage suppression circuit composed of a reactor and a capacitor is connected between the inverter and the motor, and a reactor is connected to the input side of the PWM rectifier. and a second surge voltage suppression circuit composed of capacitors.

The first surge voltage suppression circuit is composed of only reactors and capacitors without the diode bridge circuit described in the prior art described in Patent Document 1.

The second surge voltage suppression circuit is composed of reactors and capacitors, wherein the reactors are respectively connected to the input ends of the PWM rectifiers, one end of the capacitors is connected between these reactors and the AC power supply, and the other ends of the capacitors are connected to each other and then connected to the PWM rectifier. Connect to the negative terminal on the output side of the rectifier.

Therefore, the normal mode surge voltage and the common mode voltage variation caused by the inverter are reduced by the first surge voltage suppression circuit, and the common mode voltage variation caused by the PWM rectifier is reduced by the second surge voltage suppression circuit . As a result, both the normal-mode surge voltage and the common-mode surge voltage can be significantly reduced.

prior art literature

patent documents

Patent Document 1: Japanese Patent Laid-Open No. 2004-320888

Patent Document 2: Japanese Patent Application Laid-Open No. 9-294381

Contents of the invention

The problem to be solved by the invention

However, in order to further reduce the common-mode surge voltage with respect to the conventional technology described in Patent Document 1, a first surge voltage suppression circuit and a second surge voltage suppression circuit are provided as in the conventional technology described in Patent Document 2. The complicated circuit structure is a cause of an increase in the size of the corresponding equipment and an increase in cost. In addition, in the prior art described in Patent Document 2, the first surge voltage suppressing circuit and the second surge voltage suppressing circuit are respectively connected to a pair of DC parts connected between the PWM rectifier and the PWM inverter. The midpoint connection of the capacitor. In these first and second surge voltage suppression circuits, a reactor and a capacitor are connected in series to form an LC series resonance circuit. Since two LC series resonant circuits are connected in series, a multiple resonant system is formed, and excessive voltage/current generation at each other's resonant frequencies cannot be suppressed.

Therefore, an object of the present invention is to provide a small and low-cost motor drive device that can reduce the voltage applied to the motor without providing two surge voltage suppression circuits as in the prior art described in the above-mentioned Patent Document 2. common-mode surge voltage.

solutions to problems

In order to achieve the above objects, the motor drive device according to the present invention includes: a PWM rectifier that converts three-phase AC power into DC power and outputs it; and a PWM inverter that converts the DC power output from the PWM rectifier into three-phase DC power. The three-phase AC power is then supplied to the motor, and the motor drive device uses a common-mode surge voltage suppression device connected between the three-phase AC input side and the DC output side of the PWM rectifier to suppress the surge voltage applied to the motor.

The effect of the invention

According to the present invention, it is possible to provide a small and low-cost motor drive device that reduces the common-mode surge voltage applied to the motor.

Description of drawings

FIG. 1 is a circuit diagram showing a first embodiment of a motor drive device according to the present invention.

Fig. 2 is a diagram illustrating the principle of surge voltage generation, (a) is a circuit diagram illustrating the generation of common-mode surge voltage, and (b) is a circuit illustrating the principle of suppression of common-mode surge voltage.

Fig. 3 is a diagram illustrating a state of surge suppression in the first embodiment, (a) showing a case where a common-mode surge voltage suppressor is not used, and (b) showing a case where a common-mode surge voltage suppressor is used.

FIG. 4 is a circuit diagram showing a modified example of the first embodiment.

5 is a circuit diagram showing a second embodiment of the common-mode surge voltage suppression device of the motor drive device according to the present invention.

FIG. 6 is a circuit diagram showing an equivalent circuit of the first embodiment.

7 is a circuit diagram showing a first modified example of the second embodiment of the common-mode surge voltage suppressor.

8 is a circuit diagram showing a second modified example of the second embodiment of the common-mode surge voltage suppressor.

9 is a circuit diagram showing a third modified example of the second embodiment of the common-mode surge voltage suppressor.

10 is a circuit diagram showing the overall configuration of a motor drive device for explaining a fifth embodiment of the common-mode surge voltage suppression device.

11 is a block diagram showing a first modified example of the first to fifth embodiments of the motor drive device according to the present invention.

12 is a block diagram showing a second modified example of the first to fifth embodiments of the motor drive device according to the present invention.

13 is a block diagram showing a third modified sequence of the first to fifth embodiments of the motor drive device according to the present invention.

14 is a block diagram showing a fourth modified example of the first to fifth embodiments of the motor drive device according to the present invention.

Explanation of reference signs

11: Three-phase AC power supply; 12: Power transformer; 13: Power conversion device; 14: Three-phase motor; 21: PWM rectifier; 22: Smoothing capacitor; 23: PWM inverter; 24: Output cable; 25 : Input side cable; 30: Common mode surge voltage suppression device; 31: Input side capacitor; 32: Three-phase AC reactor; 33: Output side capacitor; 40: Normal mode surge voltage suppression device.

Detailed ways

Next, an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar symbols are attached to the same or similar parts.

In addition, the embodiments shown below are examples of devices and methods for realizing the technical idea of the present invention, and the technical idea of the present invention does not specify the material, shape, structure, arrangement, etc. of the structural components as the following materials , shape, structure, configuration, etc. Various modifications can be added to the technical idea of the present invention within the technical scope defined in the claims described in the claims.

Next, a first embodiment of the motor drive device according to the present invention will be described with reference to the drawings.

As shown in FIG. 1 , the motor drive device includes: a three-phase AC power supply 11; a power conversion device 13, which receives three-phase AC power output from the three-phase AC power supply 11 via a power transformer 12; and a three-phase motor 14, which Driven by the three-phase power output from the power conversion device 13 .

The power transformer 12 is set as a Δ-Y connection, the primary side of the power transformer 12 connected to the three-phase AC power supply 11 is set as a Δ connection, and the secondary side of the power transformer 12 connected to the power conversion device 13 is set as Y (star) connection. The neutral point of the Y-connection on the secondary side of the power transformer 12 is grounded.

The power conversion device 13 includes: a PWM rectifier 21 that is controlled by pulse width modulation (hereinafter referred to as PWM) for converting three-phase AC power input from the power transformer 12 via a three-phase AC reactor 32 into DC power; capacitor 22, which smoothes the DC power output from the PWM rectifier 21; and a PWM inverter 23, which is used to convert the DC power smoothed by the smoothing capacitor 22 into three-phase AC power and supply it to PWM control of the three-phase motor 14 .

Here, as shown in FIG. 1 , the PWM rectifier 21 includes a full bridge in which an R-phase switching arm CSLr, an S-phase switching arm CSLs, and a T-phase switching arm CSLt are connected in parallel between the positive-side wiring Lp and the negative-side wiring Ln. circuit.

In the R-phase switching arm CSLr, two switching elements Q11 and Q12 including, for example, insulated gate bipolar transistors (IGBTs) are connected in series. Also in the S-phase switching arm CSLs and the T-phase switching arm CSLt, switching elements Q13 and Q14 and switching elements Q15 and Q16 similar to those of the R-phase switching arm CSLr are connected in series. In addition, freewheeling diodes D11 to D16 are connected in antiparallel to respective switching elements Q11 to Q16.

In addition, the three-phase AC reactor 32 is composed of three reactors Lcr, Lcs, and Lct. One end of each reactor Lcr, Lcs, and Lct is connected to the output side of the power transformer 12, and the other end of each reactor Lcr, Lcs, and Lct is connected to each switching arm CSLr, CSLs, and CSLt as switching elements Q11, Q13, and Q15 and The middle point of the connection points of the switching elements Q12, Q14 and Q16.

Then, a gate signal formed by a pulse width modulation (PWM) signal is input to the gates of the respective switching elements Q11 to Q16 from a gate drive circuit (not shown), whereby the AC power from the power transformer 12 is converted into DC power. Then output to the positive side wiring Lp and the negative side wiring Ln.

In addition, as shown in FIG. 1 , the PWM inverter 23 includes a U-phase switching arm ISLu, a V-phase switching arm ISLv, and a W-phase switching arm ISLw connected in parallel between the positive-side wiring Lp and the negative-side wiring Ln. In the bridge circuit, a smoothing capacitor 22 is connected between the positive-side wiring Lp and the negative-side wiring Ln.

In the U-phase switching arm ISLu, two switching elements Q21 and Q22 formed of, for example, insulated gate bipolar transistors (IGBTs) are connected in series. Also in the V-phase switching arm ISLv and the W-phase switching arm ISLw, switching elements Q23 and Q24 and switching elements Q25 and Q26 similar to those of the U-phase switching arm ISLu are connected in series. In addition, freewheeling diodes D21 to D26 are connected to respective switching elements Q21 to Q26 in antiparallel.

Connection points between switching elements Q21 , Q23 , and Q25 and switching elements Q22 , Q24 , and Q26 of each switching arm ISLu, ISLv, and ISLw are connected to the three-phase motor 14 via a three-phase output side cable 24 .

Furthermore, a gate signal formed of a pulse width modulation (PWM) signal is input to the gates of the respective switching elements Q21 to Q26 of the PWM inverter 23 from a gate drive circuit (not shown). In this PWM inverter 23, the DC power supplied from the positive pole side wiring Lp and the negative pole side wiring Ln connected to the DC output side of the PWM rectifier 21 is converted into AC power and supplied to the three-phase power supply via the three-phase output side cable 24. phase motor 14.

In this way, in the power conversion device 13 including the PWM rectifier 21 and the PWM inverter 23 , power conversion is performed by switching the switching elements. Therefore, a normal-mode surge voltage depending on the switching speed and switching mode of the PWM inverter is generated.

In addition, in the power conversion device 13 having the above-mentioned configuration, a common-mode surge voltage is generated as described above. The sum of Vcmm_inv and the common mode voltage variation Vcmm_cnv generated by the PWM rectifier 21 .

In addition, in the case of constructing a system combining a PWM rectifier and a PWM inverter, there are far more unfavorable situations of motor damage caused by inverter surge than in the case of using a single PWM inverter. The unfavorable condition of the motor damage caused by the power surge.

From this point of view, the addition of the PWM rectifier 21, that is, the common-mode voltage variation Vcmm_cnv generated by the PWM rectifier 21 is the direct cause of damage to the motor, and if the common-mode voltage variation Vcmm_cnv generated by the PWM rectifier 21 can be appropriately reduced, then Prevents motor damage caused by inverter surge voltage.

Therefore, the present invention provides a common-mode surge voltage suppression device 30 that only significantly reduces the common-mode voltage variation Vcmm_cnv generated by the PWM rectifier 21 .

The common-mode surge voltage suppression device 30 includes an input-side capacitor 31 disposed between the secondary side of the power transformer 12 and the three-phase AC reactor 32 and the zero-sequence component (Japanese: zero-phase component) of the three-phase AC reactor 32 ), and an output-side capacitor 33 provided on the output side of the PWM rectifier 21.

The input-side capacitor 31 is composed of three capacitors Ccr, Ccs, and Cct star-connected to the output side of the power transformer 12 . One end of each of these capacitors Ccr, Ccs, and Cct is connected to the secondary side of the power transformer 12, and the other ends are connected to each other.

The output side capacitor 33 includes two capacitors Cs1 and Cs2 connected in series between the positive electrode wiring Lp and the negative electrode wiring Ln that are the DC output side of the PWM rectifier 21 .

Further, the other end of the connected capacitors Ccr, Ccs, and Cct of the input side capacitor 31 is connected to the connection point between the capacitors Cs1 and Cs2 of the output side capacitor 33 .

Next, the operation of the first embodiment described above will be described.

The motor drive device includes a PWM rectifier 21 , a PWM inverter 23 , and a motor 14 , and the neutral point of the secondary side of the power transformer 12 on the system side is grounded. When such a system is constructed, the common mode surge voltage applied to the motor 14 becomes large. This common-mode surge voltage is the common-mode component of the motor surge obtained by adding the common-mode voltage variation Vcom_con generated in the PWM rectifier 21 and the common-mode voltage variation Vcom_inv generated in the PWM inverter 23. The sum of the normal-mode components of the surge voltage generated in

Here, every time the switching element constituting the PWM rectifier 21 switches, a common-mode voltage fluctuation occurs between the DC unit and the ground. Generally, when the switching element performs one switching, a common-mode voltage variation of 1/3 of the DC intermediate voltage occurs. However, depending on the switching pattern of the switching elements of the PWM rectifier 21 , there are conditions where common-mode voltage fluctuations increase, and a larger common-mode surge voltage is applied to the motor 14 .

Furthermore, as shown in FIG. 1 , the secondary side of the power supply transformer 12 on the system side is grounded at a neutral point, and a common-mode voltage fluctuation occurs based on this point. That is, the farther the neutral point ground from the power transformer 12 is, the greater the common-mode voltage variation is applied, that is, the farthest electric motor 14 is applied with the largest common-mode voltage variation.

At this time, as shown in (a) of FIG. 2 , if the input-side capacitor 31 that is star-connected is not connected to the DC output side of the PWM rectifier 21, that is, the DC intermediate portion, then the capacitor 31 connected to the input side of the PWM rectifier 21 The virtual neutral points of the three phases of the star-connected input side capacitor 31 are the most stable relative to the ground in the motor drive device, and the input side of the PWM rectifier 21 is the most stable from the neutral point of the power transformer 12 on the system side. recent.

However, as described above, the PWM rectifier 21 generates a common-mode voltage, so as shown in (a) of FIG. On the other hand, a large common-mode voltage variation Vcom_con that varies stepwise to 1/3 of the DC intermediate voltage occurs.

Therefore, in this embodiment, the common mode surge voltage suppression device 30 which connects the input side and the output side of the PWM rectifier 21 is provided.

With this common mode surge voltage suppressor 30, as shown in (b) of FIG. The virtual neutral point is connected to the DC intermediate part.

With such a configuration, since the output-side capacitor 33 operates to short-circuit the high frequency of the DC intermediate portion, it is possible to significantly suppress the sudden common-mode voltage variation Vcom_con.

However, if the virtual neutral point on the input side and the DC intermediate part are simply short-circuited through the capacitors Cs1 and Cs2 of the output side capacitor 33, the original role of the PWM rectifier 21 cannot be exerted, that is, the input current can be made sinusoidal. Wave.

In order to prevent this, a reactor effective against common mode components (zero sequence components) is required on the input side of the PWM rectifier 21 . In addition, FIG. 1 is a diagram in which the reactor effective for the common mode component is constituted by the zero-sequence component of the three-phase AC reactor 32 of the PWM rectifier 21 , but a common mode reactor may be newly added. In addition, a common mode reactor can also be connected to the DC intermediate part.

In this way, according to the first embodiment, in the motor drive device in which the PWM rectifier 21, the PWM inverter 23, and the motor 14 are combined, the common circuit provided between the input side and the output side of the PWM rectifier 21 can be used. The common-mode voltage fluctuation Vcom_con generated by the PWM rectifier 21 is significantly suppressed by using the surge voltage suppression device 30 , and as a result, a common-mode surge voltage suppression device capable of appropriately reducing the common-mode surge voltage applied to the motor 14 can be realized.

Furthermore, to reduce the common-mode surge voltage applied to the motor 14, it is only necessary to install the common-mode surge voltage suppression device 30 between the input side and the output side of the PWM rectifier 21, and the PWM inverter 23 is not required. Since the common-mode surge voltage suppressor is provided on the side, the common-mode surge voltage suppressor can be configured with a simple structure.

In addition, only the common-mode surge voltage suppressor 30 is connected to the intermediate point of the output side capacitors Cs1 and Cs2 of the PWM rectifier 21, so it is not connected to the PWM rectifier as described in the prior art of the aforementioned Patent Document 2. The first surge voltage suppressing device connected in parallel with the PWM inverter and the second surge voltage suppressing circuit connected in parallel with the PWM rectifier are connected between a pair of capacitors on the output side of the LC, so it does not occur that the LC resonant circuit is connected in series to form multiple In the case of a resonant system, it is possible to reliably suppress common-mode voltage fluctuations generated in the PWM rectifier.

In addition, in the above-mentioned first embodiment, a case was described in which the input side capacitor 31 connected in star on the input side of the PWM rectifier 21 and the output side of the output side of the PWM rectifier 21 that is high-frequency short-circuited to the DC intermediate portion were described. The connection point of the capacitors Cs1 and Cs2 of the side capacitor 33 is directly connected. However, the present invention is not limited to the above-mentioned configuration, and as shown in FIG. An intermediate capacitor Cm is inserted between the neutral points. In this case, the capacitors Cs1 and Cs2 can also be deleted, and the smoothing capacitor 22 of the PWM rectifier and PWM inverter can be configured by a plurality of capacitor banks connected in series, and the intermediate connection point of the capacitor banks can be used flexibly.

[Second Embodiment]

Next, a second embodiment of the common-mode surge voltage suppression device according to the present invention will be described using FIGS. 5 and 6 .

In this second embodiment, it is intended to prevent excessive voltage/current from being generated at the resonance frequency of the LC resonance circuit constituted by a common-mode surge voltage suppression filter.

That is, in the second embodiment, as shown in FIG. 5 , a damping resistor is connected between the input side capacitor 31 of the common mode surge voltage suppression device 30 and the connection point between the power transformer 12 and the three-phase AC reactor 32 . The attenuation resistor is composed of resistors Rbr, Rbs, and Rbt connected in series to the respective capacitors Ccr, Ccs, and Cct of the input side capacitor 31 .

This damping resistance prevents excessive voltage/current from being generated at the resonance frequency of the LC resonance circuit constituted by the input capacitor 31 , the output capacitor 33 , and the three-phase AC reactor 32 .

That is, if the common mode surge voltage suppression device 30 is represented by an equivalent circuit, it becomes as shown in FIG. 6 .

It can be confirmed that the common-mode surge voltage suppressor 30 is composed of a zero-sequence reactor (Japanese: zero-phase リアクトル) Lr that is a zero-sequence component of the three-phase AC reactor 32, and an input of a three-phase virtual neutral point on the input side. The combined capacitance Cf of the side capacitor 31 and the combined capacitance Cpn of the output side capacitor 33 which performs a high-frequency short-circuit to the DC intermediate part form a closed-loop LC resonant circuit.

The resonant frequency of the LC resonant circuit at However, the excessive voltage/current at the resonant frequency ω0 can be attenuated by using damping resistors Rdr˜Rdt. At this time, in consideration of reducing the generated loss and enhancing the resonance damping effect, it is preferable to set the values of the damping resistors Rdr to Rdt so that the damping coefficient ζ falls within the range of 0.2 to 0.5. Here, if the attenuation coefficient is set to a value less than 0.2, the attenuation effect of excessive voltage/current becomes small, and if the attenuation coefficient is set to a value exceeding 0.5, the attenuation effect of excessive voltage/current will be reduced. becomes larger, but conversely, the loss generated also becomes larger, which is not ideal. In order to exert the effect of reducing excessive voltage/current while suppressing the generated loss, it is more preferable to set the attenuation coefficient to about 0.3.

According to this second embodiment, in addition to the effects of the above-mentioned first embodiment, it is also possible to prevent the inductance of the three-phase AC reactor 32 constituting the common mode surge voltage suppression device 30 and the input-side capacitor 31 and the output-side capacitor Excessive voltage/current is generated at the resonant frequency of the LC resonant circuit formed by the electrostatic capacitance of 33. Therefore, it is possible to provide a common mode surge voltage suppression device that prevents excessive voltage/current from being generated due to LC resonance.

At this time, by setting the values of the damping resistors Rdr to Rdt so that the damping coefficients are about 0.3, the effect of reducing excessive voltage/current can be exhibited while suppressing loss caused by the damping resistors Rdr to Rdt.

Note that the damping resistor is not limited to being connected in series with the input capacitor 31 , and may be connected as a single resistor Rd to the connection line between the input capacitor 31 and the output capacitor 33 as shown in FIG. 7 . Alternatively, as shown in FIG. 8 , resistors Rs1 and Rs2 may be connected in series between capacitors Cs1 and Cs2 of the output side capacitor 33 . In addition, as shown in FIG. 9 , the resistors Rdr to Rdt may be connected in parallel to the reactors Lcr to Lcrt of the three-phase AC reactor 32 . In short, as long as the excessive voltage/current caused by the LC resonance of the common-mode surge voltage suppressor 30 can be reduced, the damping resistor can be inserted at any position in the common-mode surge voltage suppressor 30 .

5 and 7 to 9 are diagrams in which the zero-sequence reactor Lr is constituted by the zero-sequence component of the three-phase AC reactor 32 of the PWM rectifier 21, but it is also possible to newly add a common mode like the first embodiment. reactor.

In addition, in the above-mentioned first embodiment and second embodiment, the case where the PWM rectifier 21 is provided has been described, but it is not limited to this, and it can also be applied to a diode rectifier in which three sets of diode arms are connected in parallel. The diode arm is formed by connecting two diodes in series.

[Third Embodiment]

Next, a third embodiment of the motor drive device according to the present invention will be described with reference to the aforementioned FIG. 1 .

In this third embodiment, the resonant frequency of the common-mode surge voltage suppressor 30 and the switching frequency of the PWM rectifier do not coincide.

That is, in the third embodiment, as shown in FIG. The common-mode surge voltage suppressor 30 connected to the output side suppresses the common-mode voltage variation Vcom_con generated in the PWM rectifier 21 by the common-mode surge voltage suppressor 30 .

In such a common mode surge voltage suppression device 30 , a series LC resonant circuit is constituted by the three-phase AC reactor 32 , the input capacitor 31 and the output capacitor 33 as described in the second embodiment. Therefore, at the resonance frequency ω0 of the series LC resonance circuit, an excessive voltage/current is generated in a resonance state. This resonant state can be suppressed by the attenuation resistor of the aforementioned second embodiment, but when the LC resonant frequency coincides with the switching frequency of the PWM rectifier 21 , a further excessive voltage/current will be generated.

Therefore, in the third embodiment, by setting the series resonance frequency ω0 of the common mode surge voltage suppressor 30 lower than the switching frequency of the PWM rectifier 21 , generation of excessive voltage/current is prevented.

That is, for the PWM rectifier 21, for example, in the case of 10 kW or less, the switching frequency is generally about 8 kHz to 10 kHz even if it is a model whose switching frequency can be changed.

Therefore, the capacitance Cf of the input side capacitor 31, the inductance Lr of the three-phase AC reactor 32, and the capacitance of the output side capacitor 33 are set such that the LC series resonance frequency ω0 of the common mode surge voltage suppressor 30 is less than 8 kHz. Cpn will do.

Here, in the case of the PWM rectifier 21 exceeding 100 kW, the switching frequency of the PWM rectifier 21 may be 5 kHz or less. In this case, it is sufficient to set the LC series resonance frequency ω0 of the common-mode surge voltage suppressor 30 to be less than 5 kHz.

In addition, although it has been proposed to provide a surge voltage suppressing filter having a structure similar to that of the present embodiment on the output side of the PWM inverter 23 , in this case, a three-phase AC reactor is not required in principle, and the structure is different. In addition, there are many PWM inverters 23 capable of changing the switching frequency to 1 kHz or less.

Therefore, in the case of a common-mode surge voltage suppression filter connected to the output side of the PWM inverter 23, the LC resonance frequency needs to be set lower than 1 kHz, and the surge suppression filter for common-mode suppression needs to be Additional measures such as increasing the size or setting restrictions on the switching frequency setting of the PWM inverter 23 are implemented.

However, when the common mode surge voltage suppression device 30 connecting the input side and the output side of the PWM rectifier 21 is provided as in this embodiment, the switching frequency of the PWM rectifier 21 is higher than the switching frequency of the PWM inverter 23, Therefore, the LC series resonance frequency ω0 of the common mode surge voltage suppressor 30 can be set to be higher than 5 times, and it is not necessary to increase the size of the common mode surge voltage suppressor 30 or to set the switching frequency of the PWM rectifier 21. Additional measures such as restrictions will be imposed.

Therefore, in the motor drive device in which the PWM rectifier 21, the PWM inverter 23, and the motor 14 are combined, it is possible to realize a common-mode surge voltage suppression device that can appropriately reduce the common-mode surge voltage applied to the motor 14. In addition, it is possible to prevent excessive voltage/current due to the coincidence of the LC resonant frequency of the common-mode surge voltage suppressor 30 with the switching frequency of the PWM rectifier 21 .

[Fourth embodiment]

Next, a fourth embodiment of the motor drive device according to the present invention will be described with reference to the aforementioned FIG. 1 .

In this fourth embodiment, it is assumed that the lower limit value of the LC series resonance frequency of the common mode surge voltage suppressor is set.

That is, in the fourth embodiment, the setting of the lower limit value of the LC resonance frequency ω0 of the common mode surge voltage suppression device 30 shown in FIG. 1 will be described.

The PWM rectifier 21 is a power electronic device for making the three-phase input current into a sine wave. In the case of two-phase modulation operation, an odd-numbered order (3 times, 9 times, 15 times...) of three times the power supply frequency is also generated. The spectrum of the lower harmonics. When the low-order harmonic spectrum overlaps with the LC resonance frequency of the common-mode surge voltage suppression device, excessive voltage/current will be generated.

The higher the frequency of the low-order harmonic spectrum, the smaller the amplitude. Therefore, it is preferable to set the LC series resonance frequency of the common-mode surge voltage suppression device 30 to the frequency of the third-order harmonic component exceeding the minimum power supply frequency, In practical terms, it is set to be equal to or higher than the 21st harmonic component that is a component equal to or higher than 1 kHz for both 50 Hz and 60 Hz.

By setting the lower limit value of the LC series resonance frequency of the common mode surge voltage suppressor 30 to a value exceeding the 21st harmonic component of the power supply frequency in this way, it is possible to combine the PWM rectifier 21 with the PWM inverter 23 and the motor. 14 to properly reduce the common mode surge voltage applied to the motor 14 in the system structure combined.

In addition, it is possible to realize a common mode surge voltage suppressing device capable of preventing the LC series resonance frequency of the common mode surge voltage suppressing device 30 from matching the third harmonic component of the power supply frequency generated by the operation of the PWM rectifier 21 , resulting in excessive voltage/current.

In addition, if only the LC series resonance frequency of the common-mode surge voltage suppressor 30 is set, the values of the inductance L of the three-phase AC reactor 32 and the capacitance C of the input-side capacitor 31 and the output-side capacitor 33 are not unique. determined.

Therefore, the values of the inductance L and the capacitance C of the common mode surge voltage suppression device 30 are determined by narrowing down the target to the above-mentioned low-order harmonic components, especially the third-order harmonic components. Specifically, the smaller the inductance L is, the smaller the structure of the common mode surge voltage suppression device 30 is. However, when the inductance L is reduced, the current flowing back in the common mode surge voltage suppressor 30 increases, so the output current such as the current flowing through the switching element of the PWM inverter 23, the current flowing through the three-phase AC reactor, etc. Increase.

When the inductance L is increased to reduce the output current, the size of the common mode surge voltage suppressor 30 will increase. Therefore, as an approximate target, when the reactor of the common mode surge voltage suppression device 30 is determined so that the output current is 1/8 or less of the rated current of the PWM rectifier 21, the common mode surge voltage can not be suppressed. The device 30 reduces the output current to a large size.

[Fifth Embodiment]

Next, a fifth embodiment of the motor drive device according to the present invention will be described with reference to FIG. 10 .

In this fifth embodiment, the LC series resonance frequency of the common-mode surge voltage suppression device is not made to coincide with the resonance frequency of the entire system of the motor drive device.

That is, as shown in FIG. 10 , the resonance frequency of the entire system of the motor drive device is determined by the secondary side via the power transformer 12-input side cable 25-PWM rectifier 21-PWM inverter 23-output side cable 24-motor 14-The loop formed by the ground wire 26 is determined.

In a 10kW motor drive device, when the length of the output side cable 24 between the PWM inverter 23 and the motor 14 is set to 200m, the overall resonance frequency of the system is 20kHz to 40kHz, which is higher than that of the aforementioned PWM rectifier 21. The switching frequency is high, which is not a big problem in the current situation.

However, the overall resonance frequency of the system may be lower due to cable length, shielded wires, other filters, etc. In addition, with the popularization of next-generation power semiconductors such as SiC and GaN, it is expected that the switching frequency of the PWM rectifier 21 will increase to about 100 kHz. The conditions under which the resonance frequency of the entire system matches the resonance frequency of the common-mode surge voltage suppressor 30 are increasing.

By setting the resonance frequency of the common mode surge voltage suppression device 30 higher than the resonance frequency, it is possible to prevent the flow of a further excessive voltage/current.

In addition, in the said 1st - 5th embodiment, the following conditions were demonstrated that the PWM inverter 23 and the electric motor 14 are one set with respect to one PWM rectifier 21 . However, the present invention is not limited thereto, even if a plurality of motors 14 are driven by one PWM inverter 23 as shown in FIG. In the configuration of a plurality of PWM inverters 23 -motors 14 (common converter system), it is only necessary to connect the common mode surge voltage suppressor 30 to the input side and the output side of the PWM rectifier 21 .

In particular, in the case of a shared converter system, even if more than ten inverters 23 and motors 14 are connected to one PWM rectifier 21, only one common-mode surge voltage suppressor 30 should be added to the PWM rectifier 21. Yes, one common-mode surge voltage suppression device 30 can be used to obtain the protection effect for all motors 14, so by reducing the number of applications of the common-mode surge voltage suppression device 30, the total cost can be reduced and the installation volume can be reduced. Bring big effect.

In addition, as described above, the insulation breakdown of the motor due to the surge voltage may occur not only due to the common mode component but also due to the normal mode surge component. Only for motors to which more severe surge voltages are applied due to the combination of these two components, connect the normal mode surge voltage between the AC output side of the PWM inverter and the motor 14 as shown in Fig. 13 and Fig. 14 . The voltage suppression device 40 can thus constitute a more reliable motor drive device.

Here, as the normal mode surge voltage suppressing device 40, for example, a three-phase reactor connected between the PWM inverter 23 and the motor 14 and a star connection connected between the three-phase reactor and the motor 14 are used. of capacitors.

In FIG. 13 , a case where a plurality of motors 14 are driven by one PWM inverter 23 in the same manner as in FIG. Between the motor 14.

In FIG. 14, a case where a set of a plurality of PWM inverters 23 and motors 14 is driven by one PWM rectifier 21 in the same manner as in FIG. between the PWM inverter 23 and the motor 14 .

Claims (3)

1. A motor driving device is provided with: a PWM rectifier that converts three-phase ac power into dc power and outputs the dc power; and a PWM inverter for converting the DC power outputted from the PWM rectifier into three-phase AC power and supplying the three-phase AC power to the motor, wherein the motor driving device is characterized in that,

using a common mode surge voltage suppression device connected between a three-phase ac input side and a dc output side of the PWM rectifier to suppress a surge voltage applied to the motor,

the LC resonance frequency of the common mode component of the common mode surge voltage suppression device is set to be higher than the LC resonance frequency of a loop formed via a three-phase ac system rectifier-the PWM inverter-the motor-ground.

2. The motor drive apparatus according to claim 1, wherein,

the common mode surge voltage suppression device includes:

an input-side capacitor formed by star-wiring a capacitor connected to a three-phase ac input side of the PWM rectifier;

an output-side capacitor connected to a direct-current output side of the PWM rectifier at a high frequency via a capacitor; and

an inductance component which is connected between a connection point of the input side capacitor and the three-phase alternating current and a connection point of the output side capacitor and the direct current output side of the PWM rectifier and is effective for a common mode component,

wherein a three-phase virtual neutral point formed by the input-side capacitor is connected to a neutral point of the output-side capacitor.

3. The motor drive apparatus according to claim 1 or 2, wherein,

a normal mode surge voltage suppression device is connected between 1 PWM inverter and the motor.