CN110690843A - motor drive - Google Patents

Abstract

Provided is 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. A motor drive device (10) includes: a PWM rectifier (21) that converts three-phase AC power into DC power and outputs it; and a PWM inverter (23) that converts the DC power output from the PWM rectifier (21) The three-phase AC power is supplied to a 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 drive device applied to an inverter-driven motor system. The inverter-driven motor system uses a rectifier to convert alternating current into direct current and then supplies it to an inverter, and uses the inverter to drive the motor.

Background technique

In a motor drive device driven by an inverter, a large surge voltage is applied to the motor, which may cause breakage or burnout due to insulation breakdown. In particular, in the case of a system configuration in which a PWM rectifier controlled by a pulse width modulation (hereinafter referred to as PWM) signal is used in combination with a PWM inverter controlled by a PWM signal in the same manner, the motor is applied more surge voltage.

Surge voltages that cause motor breakage are classified into normal mode surge voltages and common mode surge voltages, wherein the normal mode surge voltages cause insulation breakdown between wires of the motor windings The normal mode component, the common mode surge voltage is the common mode component which causes the insulation breakdown between the motor winding 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 above-mentioned normal mode surge voltage, the common mode voltage fluctuation by the PWM inverter, and the common mode voltage fluctuation by the PWM rectifier.

That is, when a PWM rectifier is included to build an inverter-driven motor system, 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 serving as a load. In this surge voltage suppressing circuit, reactors are arranged on the output lines of the inverter, respectively, and one end is connected to the negative-side DC line on the input side of the inverter and the other end of the capacitor between these reactors and the induction motor. For connection, 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 this surge voltage suppression circuit. At this time, the common mode surge voltage also has 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 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 an inverter and a motor, and a reactor is connected to an input side of a PWM rectifier. and a second surge voltage suppression circuit formed by a capacitor.

The first surge voltage suppression circuit is composed of only a reactor and a capacitor 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 terminals 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. The negative terminal of the output side of the rectifier is connected.

Therefore, the first surge voltage suppression circuit reduces the normal mode surge voltage and the common mode voltage fluctuation caused by the inverter, and the second surge voltage suppression circuit reduces the common mode voltage fluctuation caused by the PWM rectifier. . As a result, both the normal mode surge voltage and the common mode surge voltage can be greatly reduced.

prior art literature

Patent Literature

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

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

SUMMARY OF THE INVENTION

Invention to solve problem

However, in order to reduce the common-mode surge voltage with respect to the prior art described in Patent Document 1, a first surge voltage suppressing circuit and a second surge voltage suppressing circuit are provided as in the prior art described in Patent Document 2. The complicated circuit structure is the cause of the increase in size of the equipment and the 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 a pair connected between the DC portion between the PWM rectifier and the PWM inverter. The middle point of the capacitor is connected. In these first surge voltage suppressing circuit and second surge voltage suppressing circuit, a reactor and a capacitor are connected in series to constitute an LC series resonance circuit. Since the two LC series resonance circuits are connected in series, a multiple resonance system is formed, and it is impossible to suppress the generation of excessive voltage/current at the mutual resonance frequencies.

Therefore, an object of the present invention is to provide a small and low-cost motor drive device capable of reducing the amount of surge voltage applied to the motor without providing two surge voltage suppressing circuits as in the prior art described in Patent Document 2 above. Common mode surge voltage.

solution to the problem

In order to achieve the above object, 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 AC power. The phase AC power is supplied to the motor, and the motor drive device suppresses the surge voltage applied to the motor using a common mode surge voltage suppressor connected between the three-phase AC input side and the DC output side of the PWM rectifier.

effect of 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.

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

3 is a diagram illustrating a surge suppression state according to the first embodiment, wherein (a) shows the case where the common mode surge voltage suppressor is not used, and (b) shows the case where the common mode surge voltage suppressor is used.

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

5 is a circuit diagram showing a second embodiment of the common mode surge voltage suppressing 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 modification of the second embodiment of the common mode surge voltage suppressing device.

8 is a circuit diagram showing a second modification of the second embodiment of the common mode surge voltage suppressing device.

9 is a circuit diagram showing a third modification of the second embodiment of the common mode surge voltage suppressing device.

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 suppressing device.

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

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

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

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

Description of reference numerals

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 side 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 description of the drawings below, the same or similar symbols are attached to the same or similar parts.

In addition, the embodiment shown below is intended to illustrate an apparatus and method for embodying 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 components to the following materials , shape, structure, configuration, etc. Regarding the technical idea of the present invention, various modifications can be added within the technical scope defined by 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 to which three-phase AC power output from the three-phase AC power supply 11 is input via a power transformer 12; and a three-phase motor 14 to which It is driven by the three-phase power output from the power conversion device 13 .

The power transformer 12 is connected to a delta-Y connection, the primary side of the power transformer 12 connected to the three-phase AC power source 11 is connected to a delta connection, and the secondary side of the power transformer 12 connected to the power conversion device 13 is connected to 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 performs pulse width modulation (hereinafter referred to as PWM) control for converting the three-phase AC power input from the power transformer 12 via the three-phase AC reactor 32 into DC power; smoothing A capacitor 22 for smoothing the DC power output from the PWM rectifier 21; and a PWM inverter 23 for converting the DC power smoothed by the smoothing capacitor 22 into three-phase AC power and supplying 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 electrode side wiring Lp and the negative electrode side wiring Ln circuit.

In the R-phase switching arm CSLr, two switching elements Q11 and Q12 composed of, 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 which are the same as the switching elements of the R-phase switching arm CSLr are connected in series. Further, the freewheeling diodes D11 to D16 are connected in antiparallel to the 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 of the reactors Lcr, Lcs, and Lct is connected to the output side of the power transformer 12, and the other end of each of the reactors Lcr, Lcs, and Lct is connected to the switching elements Q11, Q13, and Q15 of the switching arms CSLr, CSLs, and CSLt as switching elements Q11, Q13, and Q15. The middle point of the connection point of the switching elements Q12, Q14 and Q16.

Then, by inputting a gate signal formed by a pulse width modulation (PWM) signal to the gate of each switching element Q11 to Q16 from a gate drive circuit (not shown), the AC power from the power transformer 12 is converted into DC power. It is then output to the positive electrode side wiring Lp and the negative electrode 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 electrode side wiring Lp and the negative electrode side wiring Ln. In the bridge circuit, a smoothing capacitor 22 is connected between the positive electrode side wiring Lp and the negative electrode side wiring Ln.

In the U-phase switching arm ISLu, two switching elements Q21 and Q22 composed 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 which are the same as the switching elements of the U-phase switching arm ISLu are connected in series. In addition, the freewheeling diodes D21 to D26 are respectively connected to the respective switching elements Q21 to Q26 in an antiparallel manner.

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

Then, a gate signal formed by a pulse width modulation (PWM) signal is input to the gate of each of the switching elements Q21 to Q26 of the PWM inverter 23 from a gate drive circuit (not shown). In the PWM inverter 23 , the DC power supplied from the positive-side wiring Lp and the negative-side wiring Ln connected to the DC output side of the PWM rectifier 21 is converted into AC power, and then supplied to the three-phase output side 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 causing the switching elements to perform switching operations. Therefore, a normal mode surge voltage is generated depending on the switching speed and switching mode of the PWM inverter.

Then, in the power conversion device 13 having the above-described configuration, as described above, a common mode surge voltage is generated, and the common mode surge voltage is a normal mode surge voltage and a common mode voltage fluctuation generated by the PWM inverter 23 . The sum of Vcmm_inv and the common mode voltage variation Vcmm_cnv generated by the PWM rectifier 21 .

In addition, when a system combining a PWM rectifier and a PWM inverter is constructed, the damage to the motor caused by the inverter surge is much more than when a single PWM inverter is used. The bad condition of motor damage caused by the surge of the device.

From this point of view, the addition of the PWM rectifier 21, that is, the common mode voltage fluctuation Vcmm_cnv generated by the PWM rectifier 21 is the direct cause of damage to the motor. If the common mode voltage fluctuation Vcmm_cnv generated by the PWM rectifier 21 can be appropriately reduced, it is possible to Prevents motor damage caused by inverter surge voltage.

Therefore, the present invention provides the common-mode surge voltage suppressing device 30 that greatly reduces only the common-mode voltage fluctuation Vcmm_cnv generated by the PWM rectifier 21 .

The common mode surge voltage suppression device 30 includes an input side capacitor 31 provided between the secondary side of the power transformer 12 and the three-phase AC reactor 32 and a zero-sequence component (Japanese: zero-phase component) of the three-phase AC reactor 32 ), and the 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 that are connected in a star shape 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 wiring Ln which are the DC output side of the PWM rectifier 21 .

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

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

The motor drive device includes a PWM rectifier 21, a PWM inverter 23, and an electric motor 14, and the secondary side neutral point 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. The common mode surge voltage is the common mode component of the motor surge obtained by adding the common mode voltage fluctuation Vcom_con generated in the PWM rectifier 21 and the common mode voltage fluctuation Vcom_inv generated in the PWM inverter 23 to the PWM inverter 23 . The sum of the normal mode components of the surge voltage generated in .

Here, every time the switching elements constituting the PWM rectifier 21 are switched, a common mode voltage fluctuation occurs between the DC part and the ground. Usually, when the switching element switches once, a common mode voltage fluctuation 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 is a condition that the common mode voltage fluctuation increases, and a larger common mode surge voltage is applied to the motor 14 .

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

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

However, as described above, since the PWM rectifier 21 generates a common-mode voltage, as shown in (a) of FIG. On the other hand, a large common-mode voltage fluctuation Vcom_con that changes in a step-like manner, which is 1/3 of the DC intermediate voltage, occurs.

Therefore, in the present embodiment, the common mode surge voltage suppressing device 30 that connects the input side and the output side of the PWM rectifier 21 is provided.

With this common mode surge voltage suppression device 30 , as shown in FIG. 2( b ), three phases of the input side capacitor 31 provided on the input side of the stable PWM rectifier 21 via the capacitors Cs1 and Cs2 of the output side capacitor 33 The virtual neutral point is connected to the DC intermediate part.

With such a configuration, the output side capacitor 33 operates so as to short-circuit the high frequency of the DC intermediate portion, so that the rapid common mode voltage fluctuation Vcom_con can be greatly suppressed.

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

To prevent this, a reactor effective for 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 zero-sequence component of the three-phase AC reactor 32 of the PWM rectifier 21 constitutes the reactor effective for the common mode component, but a common mode reactor may be newly added. In addition, the common mode reactor may 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 electric motor 14 are combined, the common circuit provided between the input side and the output side of the PWM rectifier 21 can be utilized. The mode surge voltage suppressor 30 greatly suppresses the common mode voltage fluctuation Vcom_con generated by the PWM rectifier 21 , and as a result, a common mode surge voltage suppressor capable of appropriately reducing the common mode surge voltage applied to the motor 14 can be realized.

Furthermore, in order to reduce the common mode surge voltage applied to the motor 14, it is only necessary to provide the common mode surge voltage suppressor 30 between the input side and the output side of the PWM rectifier 21, and the PWM inverter 23 does not need to be provided. 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, since only the common mode surge voltage suppressing device 30 is connected to the intermediate point between the output side capacitors Cs1 and Cs2 of the PWM rectifier 21, it is not connected to the PWM rectifier as described in the prior art of the aforementioned Patent Document 2. The first surge voltage suppression device connected in parallel with the PWM inverter and the second surge voltage suppression circuit connected in parallel with the PWM rectifier are connected between a pair of capacitors on the output side of the LC resonant circuit, so that the LC resonance circuits are not connected in series to form multiple In the case of a resonant system, the common-mode voltage fluctuation that occurs in the PWM rectifier can be reliably suppressed.

In addition, in the above-described first embodiment, the case where the input side capacitor 31 on the input side of the PWM rectifier 21 is star-connected and the output side of the PWM rectifier 21 on the output side of the DC intermediate portion are short-circuited at high frequency. 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. 4 , the connection point between the capacitors Cs1 and Cs2 of the output side capacitor 33 and the connection point of each of the capacitors Ccr to Cct of the input side capacitor 31 may be in the middle. An intermediate capacitor Cm is inserted between the neutral points. Even in this case, the capacitors Cs1 and Cs2 can be eliminated, and the smoothing capacitor 22 of the PWM rectifier and the PWM inverter can be configured by a plurality of capacitor banks connected in series, and the intermediate connection point of the capacitor bank can be used flexibly.

[Second Embodiment]

Next, a second embodiment of the common mode surge voltage suppressor according to the present invention will be described with reference to FIGS. 5 and 6 .

In the second embodiment, generation of excessive voltage/current at the resonant frequency of the LC resonance circuit constituted by the common mode surge voltage suppression filter is prevented.

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 suppressor 30 and the connection point between the power transformer 12 and the three-phase AC reactor 32 . The damping resistance is composed of resistors Rbr, Rbs, and Rbt connected in series with the 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 composed of the input-side capacitor 31 , the output-side capacitor 33 , and the three-phase AC reactor 32 .

That is, when the common mode surge voltage suppressing 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 suppressing device 30 is composed of a zero-sequence reactor (Japanese: zero-phase riaktor) Lr, which is a zero-sequence component of the three-phase AC reactor 32, and an input that forms 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 that short-circuits the DC intermediate portion at high frequency are configured to form a closed-loop LC resonance circuit.

下产生过大的电压/电流，但是能够利用衰减电阻Rdr～Rdt来使该谐振频率ω0下的过大的电压/电流衰减。此时，如果考虑减少产生的损耗和提高谐振衰减效果，则优选的是，以使衰减系数ζ处于0.2～0.5的范围的方式来设定衰减电阻Rdr～Rdt的值。在此，如果将衰减系数设定为小于0.2的值，则过大的电压/电流的衰减效果变小，如果将衰减系数设定为超过0.5的值，则过大的电压/电流的衰减效果变大，但是反之产生的损耗也变大，均不理想。为了在抑制产生的损耗的同时发挥过大电压/电流的减少效果，更优选的是将衰减系数设定为0.3左右。The LC resonant circuit at the resonant frequency

Excessive voltage/current at the resonance frequency ω0 can be attenuated by the damping resistors Rdr to 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 resistances Rdr to Rdt so that the damping coefficient ζ is in 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 an excessively large voltage/current becomes small, and if the attenuation coefficient is set to a value exceeding 0.5, the attenuation effect of an excessively large voltage/current becomes small. becomes larger, but conversely the resulting loss also becomes larger, which is not ideal. It is more preferable to set the attenuation coefficient to about 0.3 in order to exert the effect of reducing the excessive voltage/current while suppressing the generated loss.

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

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

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

5 and FIGS. 7 to 9 are diagrams in which the zero-sequence reactor Lr is constituted by the zero-sequence components of the three-phase AC reactor 32 of the PWM rectifier 21, but a common mode may be newly added similarly to the first embodiment. reactor.

In addition, in the above-mentioned first and second embodiments, the case where the PWM rectifier 21 is provided has been described, but the present invention is not limited to this, and 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 the third embodiment, the resonant frequency of the common mode surge voltage suppressing device 30 and the switching frequency of the PWM rectifier do not match.

That is, in the third embodiment, as shown in FIG. 1 , the motor drive device includes a power transformer 12 , a PWM rectifier 21 , a smoothing capacitor 22 , a PWM inverter 23 , and a motor 14 , and an input to the PWM rectifier 21 is provided. The common mode surge voltage suppressor 30 connected to the output side is used to suppress the common mode voltage fluctuation Vcom_con generated in the PWM rectifier 21 by the common mode surge voltage suppressor 30 .

In such a common mode surge voltage suppressor 30 , as described in the aforementioned second embodiment, a series LC resonance circuit is constituted by the three-phase AC reactor 32 , the input side capacitor 31 and the output side capacitor 33 . Therefore, at the resonance frequency ω0 of the series LC resonance circuit, a resonance state occurs in which excessive voltage/current is generated. This resonance state can be suppressed by the damping resistance of the aforementioned second embodiment, but when the LC resonance frequency coincides with the switching frequency of the PWM rectifier 21, a more excessive voltage/current is generated.

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

That is, in the case of 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 the 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 so that the LC series resonance frequency ω0 of the common mode surge voltage suppressor 30 is less than 8 kHz. Cpn can be.

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, the LC series resonance frequency ω0 of the common mode surge voltage suppressor 30 may be set to be less than 5 kHz.

In addition, a surge voltage suppression filter having a structure similar to that of the present embodiment is proposed to be provided on the output side of the PWM inverter 23, but 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 whose switching frequency can be changed 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, it is necessary to set the LC resonance frequency to be smaller than 1 kHz, and it is necessary to use a surge suppression filter for common mode suppression. Increase in size, or implement additional measures such as setting restrictions on the switching frequency of the PWM inverter 23 .

However, when the common mode surge voltage suppressing device 30 connecting the input side and the output side of the PWM rectifier 21 is provided as in the present embodiment, the switching frequency of the PWM rectifier 21 is higher than the switching frequency of the PWM inverter 23, Therefore, the LC series resonant frequency ω0 of the common mode surge voltage suppressing device 30 can be set as high as five times or more, and it is not necessary to increase the size of the common mode surge voltage suppressing device 30 or to set the switching frequency of the PWM rectifier 21 . subject to additional measures such as restrictions.

Therefore, in the motor drive device in which the PWM rectifier 21, the PWM inverter 23, and the motor 14 are combined, a common mode surge voltage suppressing device that can appropriately reduce the common mode surge applied to the motor 14 can be realized. In addition, it is possible to prevent the generation of excessive voltage/current due to the coincidence of the LC resonance frequency of the common mode surge voltage suppression device 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 the 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 suppressing 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 shape, and in the case of performing a two-phase modulation operation, it also generates an odd-numbered order (3, 9, 15...) times three times the power supply frequency. spectrum of lower harmonics. When this low-order harmonic spectrum overlaps with the LC resonant frequency of the common mode surge voltage suppression device, excessive voltage/current is 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 suppressor 30 to a frequency of the third-order harmonic component exceeding the minimum power supply frequency, Practically speaking, it is set to be equal to or higher than the 21st harmonic component of the 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, the PWM rectifier 21, the PWM inverter 23, and the motor can be The common mode surge voltage applied to the motor 14 is appropriately reduced in the system configuration in which the 14 is combined.

In addition, it is possible to realize a common mode surge voltage suppressing device that can prevent the LC series resonance frequency of the common mode surge voltage suppressing device 30 from agreeing with the third harmonic component of the power supply frequency due to 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 suppressing device 30 are determined by narrowing the target to the above-mentioned low-order harmonic components, particularly the third-order harmonic components. Specifically, the smaller the inductance L is, the smaller the structure of the common mode surge voltage suppressing device 30 is. However, when the inductance L is reduced, the current flowing back in the common mode surge voltage suppressing device 30 increases, so output currents such as the current flowing through the switching elements of the PWM inverter 23, the current flowing through the three-phase AC reactor, etc. Increase.

When the inductance L is increased in order to reduce the output current, the size of the common mode surge voltage suppressing device 30 is increased. Therefore, as a general goal, if the reactor of the common mode surge voltage suppressing device 30 is determined so that the output current is equal to or less than 1/8 of the rated current of the PWM rectifier 21, the common mode surge voltage can not be suppressed. The size of the device 30 reduces the output current.

[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 the fifth embodiment, the LC series resonant frequency of the common mode surge voltage suppressing device and the resonant frequency of the entire system of the motor drive device are set to be different from each other.

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

When the length of the output-side cable 24 between the PWM inverter 23 and the motor 14 is 200 m in the 10 kW motor drive device, the resonant frequency of the entire system is 20 kHz to 40 kHz, which is higher than the aforementioned PWM rectifier 21 . The switching frequency is high and will not be a big problem under current conditions.

However, the resonant frequency of the entire system may become lower due to the cable length, shielded wires, influence of other filters, and the like. In addition, with the spread of next-generation power semiconductors such as SiC and GaN, the switching frequency of the PWM rectifier 21 is expected to increase to about 100 kHz, which is a resonant frequency that does not want to match the resonant frequency of the common mode surge voltage suppressor 30. The condition that the resonant frequency of the entire system and the resonant frequency of the common mode surge voltage suppressing device 30 are equal is increasing.

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

In addition, in the above-described first to fifth embodiments, the following conditions were described: for one PWM rectifier 21 , each of the PWM inverter 23 and the electric motor 14 is one. However, the present invention is not limited to this, and even when a plurality of motors 14 are driven by one PWM inverter 23 as shown in FIG. In the configuration of the plurality of PWM inverters 23 and the motors 14 (common converter method), the common mode surge voltage suppressing device 30 may be connected to the input side and the output side of the PWM rectifier 21 .

In particular, in the case of the shared converter method, even if more than ten inverters 23 and motors 14 are connected to one PWM rectifier 21 , it is only necessary to add one common mode surge voltage suppressor 30 to the PWM rectifier 21 . Yes, since the protection effect for all the motors 14 can be obtained by using one common mode surge voltage suppressor 30, the total cost and installation volume can be reduced by reducing the number of applications of the common mode surge voltage suppressor 30. bring big effect.

In addition, as described above, the insulation breakdown of the motor due to the surge voltage occurs not only due to the common mode component, but also sometimes occurs due to the normal mode surge component. Only for a motor to which a more severe surge voltage is applied by combining these two components, connect the normal mode surge between the AC output side of the PWM inverter and the motor 14 as shown in FIGS. 13 and 14 . The voltage suppressing device 40 can thereby 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-connected connection between the three-phase reactor and the motor 14 are used. composed of capacitors.

FIG. 13 shows a case where a plurality of motors 14 are driven by one PWM inverter 23 as in FIG. 11 described above, and the normal mode surge voltage suppressing device 40 is provided between the PWM inverter 23 and the lower side between the motors 14 .

14 shows a case where a plurality of sets of PWM inverters 23 and motors 14 are driven by one PWM rectifier 21 as in FIG. 12 described above, and the normal mode surge voltage suppressing device 40 is provided on the lower side. Between the PWM inverter 23 and the motor 14 .

Claims (11)

1. A motor drive device comprising: a PWM rectifier which converts three-phase AC power into DC power and outputs it; and a PWM inverter which converts the DC power output from the PWM rectifier into three-phase AC power and supplies it to the electric motor, the electric motor drive device is characterized in that, The surge voltage applied to the motor is suppressed by a common mode surge voltage suppressing device connected between the three-phase AC input side and the DC output side of the PWM rectifier. 2. The motor drive device according to claim 1, characterized in that, The common mode surge voltage suppression device includes: an input side capacitor, which is formed by star-connecting the capacitor connected to the three-phase AC input side of the PWM rectifier; an output side capacitor that makes a high frequency connection to the DC output side of the PWM rectifier by means of a capacitor; and The inductance component is connected between the connection point between the input side capacitor and the three-phase AC and the connection point between the output side capacitor and the DC output side of the PWM rectifier, and is effective for the common mode component, Wherein, the three-phase virtual neutral point formed by the input side capacitor is connected with the neutral point of the output side capacitor. 3. The motor drive device according to claim 2, characterized in that, A damping resistor is inserted into a path formed by the input side capacitor, the PWM rectifier, the output side capacitor, and the inductance component of the common mode surge voltage suppressing device. 4. The motor drive device according to claim 3, characterized in that: The attenuation coefficient formed by the LC resonance of the common mode component of the attenuation resistor and the common mode surge voltage suppressor is set to be in the range of 0.2 to 0.5. 5. The motor drive device according to any one of claims 1 to 4, wherein The LC resonance frequency of the common mode component of the common mode surge voltage suppressing device is set lower than the switching frequency of the PWM rectifier. 6. The motor drive device according to any one of claims 1 to 5, wherein The LC resonance frequency of the common mode component of the common mode surge voltage suppressing device is set to be higher than the third harmonic frequency of the three-phase AC power supply. 7. A motor drive device comprising: a PWM rectifier which converts three-phase AC power into DC power and outputs it; and a PWM inverter which converts the DC power output from the PWM rectifier into three-phase AC power and supplies it to the electric motor, the electric motor drive device is characterized in that, The surge voltage applied to the motor is suppressed by using the common mode surge voltage suppressing device connected between the three-phase AC input side and the DC output side of the PWM rectifier, 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 of the loop formed via the three-phase AC system rectifier-the PWM inverter-the motor-ground frequency. 8. The motor drive device according to any one of claims 1 to 6, wherein The configuration is such that at least one of the PWM inverters and at least two or more of the motors are provided for one of the PWM rectifiers, and the common mode surge voltage suppression device is connected to the one of the PWM rectifiers. . 9. The motor drive device according to any one of claims 1 to 6, wherein A plurality of the PWM inverters and a plurality of the motors are connected to one PWM rectifier, and the common mode surge voltage suppressing device is connected to the one PWM rectifier. 10. The motor drive device according to claim 7 or 8, characterized in that: A normal mode surge voltage suppressor is connected between the one PWM inverter and the motor. 11. A motor drive device comprising: a PWM rectifier which converts three-phase AC power into DC power and outputs it; and a PWM inverter which converts the DC power output from the PWM rectifier into three-phase AC power and supplies it to the electric motor, the electric motor drive device is characterized in that, The surge voltage applied to the motor is suppressed by using the common mode surge voltage suppressing device connected between the three-phase AC input side and the DC output side of the PWM rectifier, The LC resonance frequency of the common mode component of the common mode surge voltage suppressing device is set to be higher than the LC resonance of the loop formed via the three-phase AC system rectifier-the PWM inverter-the motor-ground frequency.

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