阅读说明：本技术 交流电动机驱动系统 (AC motor driving system ) 是由 大石将幸 渡部一喜 藤田雄己 一濑博行 于 2020-03-24 设计创作，主要内容包括：具有连接于交流电源(1)并使交流电源侧与负载侧绝缘的电源变压器(2)、交流电动机(4)和将从电源变压器(2)输出的交流电压变换为输出交流电压并输出至交流电动机(4)的电力变换器(3),并且具备一端连接于电源变压器(2)的负载侧且另一端被接地的电容分量(15)。(The power supply device is provided with a power transformer (2) connected to an AC power supply (1) and insulating the AC power supply side from the load side, an AC motor (4), and a power converter (3) converting the AC voltage output from the power transformer (2) into an output AC voltage and outputting the output AC voltage to the AC motor (4), and is also provided with a capacitance component (15) having one end connected to the load side of the power transformer (2) and the other end grounded.)

1. An AC motor drive system, wherein,

comprising: a power transformer connected to an AC power supply and insulating an AC power supply side from a load side; an AC motor; and a power converter that converts the ac voltage output from the power transformer into an output ac voltage and outputs the output ac voltage to the ac motor, wherein the ac motor drive system includes a capacitance component having one end connected to a load side of the power transformer and the other end grounded.

2. The alternating current motor drive system according to claim 1,

the power converter includes a capacitance component having one end connected to a power line connecting the power converter and the ac motor, and the other end grounded.

3. The alternating current motor drive system according to claim 1 or 2,

the ac motor further includes a capacitance component, one end of which is connected to a winding portion of the ac motor, and the other end of which is grounded.

4. The alternating current motor drive system according to claim 1,

the motor is provided with a low impedance element, one end of which is connected to a winding part of the AC motor, and the other end of which is grounded.

5. The alternating-current motor drive system according to any one of claims 1 to 4,

the capacitance component is composed of a substance including an insulator or a semiconductor in a non-conductive state.

Technical Field

The present application relates to an ac motor drive system.

Background

When an ac motor is operated at a variable speed, an input voltage at a commercial frequency is generally received from a three-phase ac power supply such as a power system via a power transformer, and converted into an arbitrary output voltage and output frequency by a power converter.

The composition of the three-phase output voltages of the power converter is not zero, and the output voltages contain common-mode components. This common mode voltage is applied to a stray capacitance of the ac motor to become a neutral point voltage, and a part thereof becomes a shaft voltage applied to the insulating lubricant between the bearings. When the shaft voltage exceeds the insulation breakdown voltage of the bearing, a high-energy discharge current flows through the bearing, causing a problem that electrolytic corrosion occurs in the bearing and the life is reduced.

In order to suppress the occurrence of such bearing galvanic corrosion, a circuit for suppressing a common mode voltage or a common mode current has been proposed as disclosed in non-patent document 1 below. That is, the following is proposed in the conventional art: the method of suppressing the neutral point voltage applied to the ac motor is performed by a method of dividing the common mode current by using a passive element, a method of increasing the impedance of the common mode path and sharing the voltage by the impedance element (hereinafter, these methods are referred to as passive methods), or a method of injecting a voltage having a phase opposite to that of the common mode voltage by using an active element to suppress the neutral point voltage applied to the ac motor (hereinafter, this method is referred to as active methods).

Documents of the prior art

Non-patent document

Non-patent document 1: "methods for suppressing leakage current, surge voltage, and shaft voltage of variable speed AC drive", japan electrical engineering society, journal D, vol 118, phase 9, pp.975-9801998, 9 months ("variable speed AC ドライブ leakage れ current サージ voltage suppression method" "outer velocity vibration suppression method と text text 35468D, 118 wo 9, pp.975-980 in 10 years 9 months)

Disclosure of Invention

Technical problem to be solved by the invention

In the conventional technique disclosed in non-patent document 1, in the passive system, the gain is reduced when compensating for the low-frequency voltage due to the impedance frequency characteristics of the passive element. It is conceivable to design the C value or the L value of the passive element to be large in order to compensate for the decrease in gain, but there is a technical problem that the circuit becomes large.

On the other hand, the active system has the following technical problems: due to the influence of the frequency characteristics of active elements such as operational amplifiers and power semiconductor elements or the frequency characteristics of a control system, a phase delay of an output voltage occurs at the time of compensation in a high frequency region, and a compensation gain is lowered, thereby compensating for characteristic deterioration.

The present application discloses a technique for solving the above-described technical problem, and an object thereof is to provide an ac motor drive system capable of reliably preventing occurrence of a problem such as electrolytic corrosion of a bearing of an ac motor without increasing the size of a compensation circuit for common mode voltage suppression.

Means for solving the problems

The application discloses an AC motor driving system includes: a power transformer connected to an AC power supply and insulating an AC power supply side from a load side; an AC motor; and a power converter that converts the ac voltage output from the power transformer into an output ac voltage and outputs the output ac voltage to the ac motor, wherein the ac motor drive system includes a capacitance component having one end connected to a load side of the power transformer and the other end grounded.

Effects of the invention

According to the ac motor drive system disclosed in the present application, it is possible to reliably prevent occurrence of a problem such as electrolytic corrosion of a bearing of the ac motor without increasing the size of the compensation circuit for common mode voltage suppression.

Drawings

Fig. 1 is a circuit diagram of a three-phase input ac motor drive system according to embodiment 1 of the present application.

Fig. 2 is an equivalent circuit of a common mode path of a three-phase input ac motor drive system as a reference example.

Fig. 3 is an equivalent circuit of a common mode path of a three-phase input ac motor drive system according to embodiment 1 of the present application.

Fig. 4 is a circuit diagram of an ac motor drive system according to embodiment 2 of the present application.

Fig. 5 is an equivalent circuit of a common mode path of an ac motor drive system according to embodiment 2 of the present application.

Fig. 6 is a circuit diagram of an ac motor drive system according to embodiment 3 of the present application.

Fig. 7 is an equivalent circuit of a common mode path of an ac motor drive system according to embodiment 3 of the present application.

Fig. 8 is a circuit diagram of an ac motor drive system according to embodiment 4 of the present application.

Fig. 9 is an equivalent circuit of a common mode path of an ac motor drive system according to embodiment 4 of the present application.

Fig. 10 is a circuit diagram of an ac motor drive system according to embodiment 5 of the present application.

Fig. 11 is an equivalent circuit of a common mode path of an ac motor drive system according to embodiment 5 of the present application.

Reference numerals

1: an alternating current power supply; 2: a power transformer; 3: a power converter; 4: an AC motor; 5: a stray capacitance; 6. 7, 8: a three-phase power line; 9. 10: a ground line; 11. 12: a ground point; 13: a ground line; 14: an arbitrary point of the winding portion; 15: a capacitance component; 16: a capacitor; 17: a capacitor for grounding the winding part; 18: a low impedance element.

Detailed Description

Hereinafter, an ac motor drive system according to the present embodiment will be described with reference to the drawings. In the drawings, elements denoted by the same reference numerals are the same or equivalent elements, and are common to all the embodiments described below.

The form of the constituent elements described throughout the specification is merely an example, and is not limited to the form described in the specification. In particular, the combination of the components is not limited to the combination in each embodiment, and the components described in other embodiments can be applied to other embodiments.

Embodiment 1.

Fig. 1 is a circuit diagram of a three-phase input ac motor drive system according to embodiment 1.

The three-phase input ac motor system according to embodiment 1 includes a power system, an ac power supply 1 such as a self-contained voltage source, a power transformer 2, a power converter 3, a star-connected ac motor 4, a three-phase power line 6, a three-phase power line 7, a three-phase power line 8, a ground line 9, a ground line 10, and a ground line 13 connecting between the ground line 9 and the ground line 10. The power transformer 2 ensures electrical insulation between the ac power source 1, the power converter 3, and the load. The power converter 3 includes a forward conversion circuit including semiconductor elements, an electric storage element for storing dc power, and a reverse conversion circuit including semiconductor elements (both not shown). The three-phase power line 6 is connected between the alternating current power supply 1 and the power transformer 2. The three-phase power line 7 is connected between the power transformer 2 and the power converter 3. The three-phase power line 8 connects between the power converter 3 and the ac motor 4. The ground line 9 is connected between an arbitrary point of the load-side winding portion of the power transformer 2 and the ground point 11. The ground line 10 connects the ac motor 4 and the ground point 12.

Here, in the ac motor system shown in fig. 1, a case in which the Y connection method is used for the ac motor 4 is shown, but the Δ connection method can also be applied to the ac motor system of embodiment 1. Further, 14 is an arbitrary point of the winding portion of the ac motor 4.

In order to ensure electrical insulation from the load, the ac power transmitted from the ac power supply 1 is received by the power transformer 2, and the power converter 3 converts the input voltage of a fixed voltage and a fixed frequency into a variable frequency and variable voltage, so that the ac motor 4 is driven at a variable speed.

Further, as a feature of embodiment 1, a capacitance component 15 is provided between the load side of the power transformer 2 and the grounding point 11. The capacitance component 15 in this case is composed of one or more insulators (e.g., capacitors) or semiconductors in a non-conductive state (e.g., diodes or semiconductor switching elements in an off state).

Fig. 2 is an equivalent circuit of a common mode path of a general ac motor drive system as a reference example in a case where the capacitance component 15, which is a characteristic of embodiment 1, is not provided. In this equivalent circuit, a power converter 3 as a generation source of a common mode voltage and a stray capacitor 5 inevitably generated in an ac motor 4 are connected in series.

On the other hand, fig. 3 is an equivalent circuit of a common mode path of the ac motor drive system in the case where the capacitance component 15, which is a characteristic of embodiment 1, is provided. In this equivalent circuit, in addition to the power converter 3 as a generation source of the common mode voltage and the stray capacitance 5 of the ac motor 4, a capacitance component 15 is provided between the power transformer 2 and the grounding point 11, and the stray capacitance 5 and the capacitance component 15 are connected in series with each other via the grounding line 13.

At this time, if Vc is a common mode voltage that is a composite of three-phase output voltages of power converter 3 and Vn is a neutral point voltage of ac motor 4 applied to stray capacitance 5 of ac motor 4, common mode voltage Vc is applied to stray capacitance 5 of ac motor 4 in its entirety in the equivalent circuit of the reference example shown in fig. 2. Namely, Vn ═ Vc.

In contrast, in the equivalent circuit of embodiment 1 shown in fig. 3, the common mode voltage Vc is divided by the stray capacitance 5 and the capacitance component 15 of the ac motor 4. That is, when the capacitance value of the stray capacitance 5 of the ac motor 4 is C0 and the capacitance value of the capacitance component 15 is C1, the neutral point voltage Vn applied to the stray capacitance 5 is C1/(C0+ C1) times the common mode voltage Vc based on the voltage division formula. That is to say that the first and second electrodes,

Vn＝Vc·C1/(C0+C1) (1)

as can be seen from equation (1) above, the neutral point voltage Vn decreases as the capacitance value C1 of capacitance component 15 decreases. In other words, the neutral point voltage Vn is reduced by a small circuit. In addition, since the voltage division formula has no frequency dependence, the compensation gain is not reduced in the low frequency compensation unlike other passive methods. In addition, since no active element is used, even a high-frequency component is not affected by the frequency characteristics of the control system. Therefore, there is no limitation on the compensation effect when the neutral point voltage Vn is reduced.

A method of inserting the capacitive component 15 is shown here.

As the capacitance component 15, for example, the power transformer 2 may be in a non-grounded state, or a capacitor, one or more insulators, or a semiconductor in a non-conductive state may be inserted into the ground line 9. The insulator may be in any state of gas, liquid, or solid. Further, the ground line 9 may be absent in practice as long as the capacitance is electrically exhibited between any point of the load-side winding portion of the power transformer 2 and the ground point 11. Note that, an arbitrary point of the load-side winding portion of the power transformer 2 is preferably a neutral point if it is Y-connected and is preferably a V-phase connection portion if it is Δ -connected, but the present invention is not limited thereto.

As described above, in embodiment 1, the common mode voltage Vc is divided by connecting the capacitance component 15 in series to the stray capacitance 5 of the ac motor 4 in the common mode path. In this case, the smaller the capacitance value C1 of capacitance component 15 is designed to be, the more the neutral point voltage Vn applied to stray capacitance 5 of ac motor 4 can be reduced. Further, since the share voltage ratio of the capacitance is determined only by the capacitance ratio, there is no frequency dependency. Accordingly, it is possible to prevent occurrence of a problem such as electrolytic corrosion of the bearing of the ac motor 4 by adding only a small circuit.

The configuration of embodiment 1 is not limited to the above configuration, and the basic principle of the present application is to connect the capacitance component 15 in series in the common mode path, and as a method for this, the capacitance component 15 is added between the load-side winding of the power transformer 2 and the grounding point 11. Thus, the connection mode of the three-phase power transformer 2 is not limited, and may be a Δ -Y connection, a Y- Δ connection, a Δ - Δ connection, a Y-Y connection, or a multiple connection mode.

Embodiment 2.

Fig. 4 is a circuit diagram of an ac motor drive system according to embodiment 2 of the present application.

In addition to the configuration in which the capacitance component 15 is provided between the power transformer 2 and the grounding point 11 shown in embodiment 1, this embodiment 2 further includes a capacitor 16 connected in a Y-shape as a capacitance component connecting the three-phase power line 8, which connects the power converter 3 and the ac motor 4, to the grounding line 13.

Fig. 5 is an equivalent circuit of the common mode path in embodiment 2. Specifically, the power converter 3, a circuit in which the capacitor 16 and the stray capacitance 5 of the ac motor 4 are connected in parallel with each other, and the capacitance component 15 are sequentially connected in series are configured.

On the common mode path, since the stray capacitance 5 of the alternating-current motor 4 and the capacitor 16 are connected in parallel with each other, the combined capacitance increases. That is, when the capacitance value of the capacitor 16 is C2, the capacitance value obtained by combining the stray capacitance 5 is C0+ C2. Therefore, the neutral point voltage Vn of the ac motor 4 applied to the stray capacitance 5 of the ac motor 4 becomes C1/(C0+ C1+ C2) times the common mode voltage Vc based on the voltage division formula. That is to say that the first and second electrodes,

Vn＝Vc·C1/(C0+C1+C2) (2)

as is clear from comparison of the above equations (1) and (2), embodiment 2 has a function of improving the effect of reducing the neutral point voltage Vn as compared with embodiment 1. Further, as shown in embodiment 1, if the capacitance value C1 of the capacitance component 15 is designed to be small, the ratio of C1 to C0+ C2 can be easily improved by the small capacitor 16, and thus the circuit can be prevented from being large-sized. In addition, in the case where the capacitor 16 is inserted, although the leakage current increases due to the decrease in the impedance of the common mode path, the increase amount of the leakage current is limited if the capacitance value C1 of the capacitance component 15 is designed to be small.

As described above, in embodiment 2, the capacitor 16 connecting the three-phase power line 8 and the ground line 13 is connected in parallel to the stray capacitance 5 of the ac motor 4 to adjust the capacitance-voltage ratio, thereby reducing the neutral point voltage Vn applied to the stray capacitance 5.

Further, if a configuration is adopted in which a capacitance component is added to a circuit connecting the three-phase power line 8 and the ground line 13, the capacitor 16 shown in embodiment 2 is not limited to the capacitor 16 wired in the Y-shape shown in fig. 4. For example, the voltage division ratio can be adjusted similarly even in a circuit in which a current-limiting resistor is connected in series or a circuit in which a capacitor is connected to the neutral point of the Y-connected capacitor 16.

Embodiment 3.

Fig. 6 is a circuit diagram of an ac motor drive system according to embodiment 3 of the present application.

In embodiment 3, in addition to the configuration in which the capacitance component 15 is provided between the power transformer 2 and the grounding point 11 shown in embodiment 1, a winding portion grounding capacitor 17 is provided as a capacitance component connected in parallel to the stray capacitance 5 of the ac motor 4 between an arbitrary point 14 of the winding portion of the ac motor 4 and the grounding point 12 on the ac motor side.

Fig. 7 is an equivalent circuit of the common mode path in embodiment 4. Specifically, the power converter 3, a circuit in which the stray capacitance 5 of the ac motor 4 and the winding portion grounding capacitor 17 are connected in parallel, and the capacitance component 15 are sequentially connected in series.

When the capacitance value of the winding-unit grounding capacitor 17 is C3, the stray capacitance 5 and the winding-unit grounding capacitor 17 are connected in parallel with each other on the common-mode path, and therefore the capacitance value obtained by combining the stray capacitance 5 is C0+ C3. Therefore, the neutral point voltage Vn of the ac motor 4 applied to the stray capacitance 5 becomes C1/(C0+ C1+ C3) times of the common mode voltage Vc based on the voltage division formula. That is to say that the first and second electrodes,

Vn＝Vc·C1/(C0+C1+C3) (3)

as is clear from comparison of the above equations (1) and (3), embodiment 3 has a function of improving the effect of reducing the neutral point voltage Vn as compared with embodiment 1. Further, if the capacitance value C1 of the capacitance component 15 is designed to be small, the ratio of C1 to C0+ C3 in the voltage dividing formula can be easily improved by the small winding grounding capacitor 17. Further, the winding portion grounding capacitor 17 is connected to lower the impedance of the common mode path, and thus the leakage current increases, but the increase amount of the leakage current is limited because the capacitance component 15 is designed to be small.

As described above, in embodiment 3, the winding grounding capacitor 17 is connected in parallel to the stray capacitance 5 of the ac motor 4, and the neutral point voltage Vn applied to the stray capacitance 5 of the ac motor 4 can be reduced.

Embodiment 4.

Fig. 8 is a circuit diagram of an ac motor drive system according to embodiment 4 of the present application.

In embodiment 4, in addition to the configuration in which the capacitance component 15 is provided between the power transformer 2 and the grounding point 11 shown in embodiment 1, a low impedance element 18 connected in parallel to the stray capacitance 5 of the ac motor 4 is provided between an arbitrary point 14 of the winding portion of the ac motor 4 and the grounding point 12 on the ac motor side. The low impedance element 18 in this case may have a lower impedance than the stray capacitance 5, and for example, a conductive wire may be used.

Fig. 9 is an equivalent circuit of the common mode path in embodiment 4. Specifically, the power converter 3 and the capacitance component 15 are connected in series in this order. Therefore, the neutral point voltage Vn applied to the stray capacitance 5 of the alternating-current motor 4 is zero in principle.

In addition, when the low impedance element 18 is connected, although the leakage current increases due to the decrease in the impedance of the common mode path, the increase amount of the leakage current is limited because the capacitance value C1 of the capacitance component 15 is designed to be small.

As described above, in embodiment 4, low impedance element 18 is connected in parallel to stray capacitance 5 of ac motor 4, and neutral point voltage Vn applied to stray capacitance 5 can be reduced.

Embodiment 5.

Fig. 10 is a circuit diagram of an ac motor drive system according to embodiment 5 of the present application.

In embodiment 5, the structures of embodiments 1 to 3 are combined to form a three-phase input ac motor drive system. That is, in embodiment 5, a capacitance component 15 is provided between the load side of the power transformer 2 and the grounding point 11, a capacitor 16 connected in a Y-shape is connected between the three-phase power line 8 connecting the power converter 3 and the ac motor 4 and the grounding line 13, and a winding portion grounding capacitor 17 is connected in parallel with the stray capacitance 5 of the ac motor 4 between an arbitrary point 14 of the winding portion of the ac motor 4 and the grounding point 12 on the ac motor side.

Fig. 11 is an equivalent circuit of the common mode path in embodiment 5. Specifically, the power converter 3, a circuit in which the stray capacitance 5 of the ac motor 4, the capacitor 16, and the winding portion grounding capacitor 17 are connected in parallel with each other, and the capacitance component 15 are connected in series in this order.

In the common mode path, the stray capacitance 5, the capacitor 16, and the winding-part grounding capacitor 17 are connected in parallel with each other, and therefore the resultant capacitance value is C0+ C1+ C2+ C3. Therefore, the neutral point voltage Vn of the ac motor 4 applied to the stray capacitance 5 becomes C1/(C0+ C1+ C2+ C3) times the common mode voltage Vc based on the voltage division formula. That is to say that the first and second electrodes,

Vn＝Vc·C1/(C0+C1+C2+C3) (4)

as is clear from comparison of the above equations (1) to (4), embodiment 5 has a function of further improving the effect of reducing the neutral point voltage Vn because the combined capacitance is increased as compared with the cases of embodiments 1, 2, and 3.

As described above, in embodiment 5, by combining the structures of embodiments 1 to 3, the neutral point voltage Vn applied to the stray capacitance 5 of the ac motor 4 can be further reduced.

In each of embodiments 1 to 5, the power converter 3 is not limited to the above-described configuration, and may be a cycloconverter (cycloconverter) or a matrix converter (matrix converter) that performs ac-ac direct conversion without an electric storage device in principle.

The ac motor 4 is an induction motor or a synchronous motor, and the connection method thereof is not limited to the Y connection, but may be a Δ connection. Further, an operational amplifier for suppressing conduction noise or radiation noise, or an active-type or passive-type noise filter including a semiconductor element may be connected to the three-phase power lines 6, 7, and 8 to form an ac motor drive system.

The configuration of the present application is not limited to the three-phase input ac motor drive system shown in fig. 1, but is also applicable to a single-phase input ac motor drive system. Therefore, the single-phase ac power supply 1, the single-phase power supply transformer 2, and the single-phase power lines 6 and 7 may be used.

Various exemplary embodiments and examples are described in the present application, but the various features, aspects, and functions described in 1 or more embodiments are not limited to the application in a specific embodiment, and can be applied to the embodiments alone or in various combinations.

Therefore, numerous modifications not illustrated are assumed within the technical scope disclosed in the present application. For example, the case where at least 1 component is modified, added, or omitted is included, and the case where at least 1 component is extracted and combined with the components of other embodiments is also included.