Inverter and motor drive device for suppressing common mode current

Abstract

This inverter comprises: an inverter main circuit that is connected to a converter through a DC link, converts DC power into AC power for a load circuit, and outputs the AC power; a DC link capacitor that is provided at a DC output side of the converter in the DC link; a ground capacitor section that is provided between the inverter main circuit and the DC link capacitor in the DC link and comprises a positive-side ground capacitor having one end connected to ground and another end connected to a positive potential line of the DC link, and a negative-side ground capacitor having one end connected to ground and another end connected to a negative potential line of the DC link; a common mode choke part that is provided between the inverter main circuit and the ground capacitor section in the DC link; and a bypass section that connects, to ground, each AC power line connecting the AC output side of the inverter main circuit and the load circuit.

Description

[Technical Field]

[0001] The present invention relates to an inverter and a motor drive device that suppress common-mode current. [Background technology]

[0002] The main source of various noises, including radiated noise generated in motor drive devices that drive motors using inverters, is the common-mode current that flows through the power lines within the motor drive device. Common-mode current is a noise current that flows through tiny stray capacitance that occurs between the power line and ground, and flows in the same direction in both the outbound and return paths of the power line. As the frequency increases, even tiny stray capacitances lower the impedance, making it easier for common-mode current to flow. Various circuits have been proposed to suppress common-mode current.

[0003] For example, there is known a noise filter that suppresses EMI noise generated in a power conversion device, which comprises a common mode transformer consisting of a primary winding inserted in series in a power supply line on the input side of the power conversion device and a secondary winding electromagnetically coupled to the primary winding, a capacitor connected between both terminals of the secondary winding of the common mode transformer, and a grounding capacitor connected between the power supply line connecting the common mode transformer and the power conversion device and earth, and which is characterized in that the resonant frequency of an LC parallel resonant circuit formed by the secondary winding of the common mode transformer and the capacitor is set to the frequency band of common mode noise (see, for example, Patent Document 1).

[0004] For example, a known grid-connected inverter includes: a single-phase or three-phase inverter that pulse-width modulates the output of a DC power supply; a first capacitor group arranged on the input side of the inverter and consisting of a first capacitor connected in series to form a neutral point; a second capacitor group arranged on the output side of the inverter and consisting of a second capacitor connected in series to form a neutral point; a bypass path for common-mode current formed by connecting the neutral point of the first capacitor group with the neutral point of the second capacitor group; one or more common-mode choke coils arranged between the first capacitor group and the second capacitor group and on the input or output side of the inverter to suppress common-mode current generated in the inverter; an output filter consisting of a first reactor and a third capacitor for converting a pulse-width modulated voltage waveform output from the inverter into a sinusoidal single-phase or three-phase AC; and a resonance suppression circuit that suppresses resonance that occurs between the inter-winding capacitance of the common-mode choke coil and the first reactor of the output filter (see, for example, Patent Document 2).

[0005] For example, a known power transmitting device includes an AC line filter that is provided on an AC power line connected to an AC power source and connected to ground; an inverter that converts power supplied from the AC power source through the AC line filter into transmission power; a transmission coil that is electrically connected to the inverter and configured to receive the transmission power from the inverter and transmit it contactlessly to a receiving coil of a power receiving device; and a common mode filter that is provided on a power line between the inverter and the transmission coil, wherein the common mode filter includes a first Y capacitor that is not connected to the ground and is connected to the power line between the AC line filter and the inverter (see, for example, Patent Document 3).

[0006] For example, a power supply circuit that converts at least one of the frequency and voltage of an input AC voltage is known, characterized by having two line bypass capacitors provided between each of two supply lines of the input AC voltage and ground, and two inductance elements connected in series to each of the two line bypass capacitors (see, for example, Patent Document 4). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-136058 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-223667 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-208596 [Patent Document 4] Japanese Patent Application Laid-Open No. 2008-182784 Summary of the Invention [Problem to be solved by the invention]

[0008] Generally, a motor drive device is provided with inverters corresponding to the number of motors. Therefore, when a noise suppression circuit such as a common-mode choke coil or a common-mode transformer is provided on the AC output side of the inverter, multiple expensive and bulky noise suppression circuits must be provided corresponding to the number of motors to be driven in the motor drive device, resulting in increased cost and size of the motor drive device. Furthermore, in motor drive devices that control the drive of motors in machine tools, forging machines, injection molding machines, industrial machinery, and various robots, it is particularly important to suppress high-frequency common-mode currents that affect radiated noise. Therefore, there is a need for a compact, low-cost inverter and motor drive device that can suppress common-mode currents over a wide frequency range. [Means for solving the problem]

[0009] According to one aspect of the present disclosure, an inverter includes: an inverter main circuit section connected via a DC link to a converter that converts AC power from an AC power source into DC power, and that converts the DC power into AC power for a load circuit and outputs the AC power; a DC link capacitor provided on a DC output side of the converter in the DC link; a grounding capacitor section provided on the DC link between the DC link capacitor and the inverter main circuit section, the grounding capacitor having one end connected to ground and one end connected to a positive potential line of the DC link and a negative grounding capacitor having one end connected to ground and one end connected to a negative potential line of the DC link; a common mode choke section provided on the DC link between the grounding capacitor section and the inverter main circuit section, and that suppresses common mode current; and a bypass section that connects each AC power line connecting the AC output side of the inverter main circuit section to the load circuit to ground. The ground is an amplifier ground, which is the ground of a servo amplifier constituting an inverter including an inverter main circuit section, and is different from a power supply ground, which is the ground for the AC power supply, and the bypass section is provided with a common mode capacitor section for suppressing common mode current, and the common mode capacitor section has a configuration in which one end of each of a plurality of capacitors is connected to a corresponding one of the AC power lines and the other end of each is connected to a neutral point, and one end of a grounding capacitor is connected to the neutral point and the other end is connected to the inverter side ground. do.

[0010] According to another aspect of the present disclosure, a motor drive device includes a converter, the inverter, and a motor control unit that controls driving of a motor that is a load circuit. [Effects of the Invention]

[0011] According to one aspect of the present disclosure, it is possible to realize a small-sized, low-cost inverter and motor drive device that can suppress common-mode currents over a wide frequency band. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram illustrating an inverter according to a first embodiment of the present disclosure and a motor drive device including the inverter; [Figure 2] 1 is a circuit diagram illustrating a common mode current flowing through an inverter according to a first embodiment of the present disclosure and a motor connected thereto. [Figure 3] 1 is a circuit diagram showing an equivalent circuit relating to noise of an inverter and a motor connected thereto according to a first embodiment of the present disclosure. [Figure 4] 1 is a diagram showing a case where a plurality of motors are driven by an inverter according to a first embodiment of the present disclosure and a motor drive device including the inverter; [Figure 5] 1 is a diagram illustrating a case where a single-phase AC motor is driven by an inverter according to a first embodiment of the present disclosure and a motor drive device including the inverter. FIG. [Figure 6] FIG. 10 is a diagram illustrating an inverter according to a second embodiment of the present disclosure and a motor drive device including the inverter. [Figure 7] FIG. 10 is a diagram illustrating an inverter according to a third embodiment of the present disclosure and a motor drive device including the inverter. [Figure 8] FIG. 10 is a diagram illustrating an inverter according to a modified example of the third embodiment of the present disclosure and a motor drive device including the inverter. [Figure 9] FIG. 10 is a diagram illustrating an inverter according to a fourth embodiment of the present disclosure and a motor drive device including the inverter. [Figure 10] FIG. 10 is a diagram illustrating an inverter according to a fifth embodiment of the present disclosure and a motor drive device including the inverter. [Figure 11] FIG. 1 is a diagram showing frequency-impedance characteristics of an LC series resonant circuit. DETAILED DESCRIPTION OF THE INVENTION

[0013] An inverter and a motor drive device for suppressing common-mode current will be described below with reference to the drawings. In each drawing, like components are assigned like reference symbols. For ease of understanding, the scale of these drawings has been changed as appropriate. The illustrated embodiments are examples for carrying out the present invention, and the present invention is not limited to these embodiments.

[0014] There are two ways that conducted noise is transmitted: normal mode (also known as "differential mode") and common mode. Normal mode is a propagation mode in which the wiring serves as the noise's outgoing path and the ground serves as the noise's return path. Common mode is a propagation mode in which noise flows in the same direction on the outgoing and return paths through the minute stray capacitance that occurs between each wiring and the ground. As the frequency of the common mode current increases, the impedance decreases even with a minute stray capacitance, making it easier for the common mode current to flow. Conducted noise can become radiated noise, with power lines and signal lines acting as antennas.

[0015] First Embodiment FIG. 1 is a diagram illustrating an inverter according to a first embodiment of the present disclosure and a motor drive device including the inverter.

[0016] In the motor drive device 100, the number of inverter main circuit units 11 that supply motor drive power to the motors 300 corresponds to the number of motors 300. When the motor drive device 100 drives multiple motors 300, multiple inverter main circuit units 11 are provided corresponding to the number of motors 300. One converter 2 is provided for multiple inverters. The type of motor 300 is not particularly limited, and may be, for example, an induction motor or a synchronous motor. Machines in which the motor 300 may be installed include, for example, machine tools, robots, forging machines, injection molding machines, industrial machines, etc.

[0017] The number of phases of the AC power supply 200 and the motor 300 is not particularly limited to each embodiment, and may be, for example, three-phase or single-phase. Examples of the AC power supply 200 include a three-phase 400V AC power supply, a three-phase 200V AC power supply, a three-phase 600V AC power supply, and a single-phase 100V AC power supply. Fig. 1 shows, as an example, a case in which one three-phase AC motor 300 is driven by a motor drive device 100 connected to a three-phase AC power supply 200.

[0018] According to the first embodiment of the present disclosure, the motor driving device 100 includes a converter 2, an inverter 1, and a motor control unit 3.

[0019] Converter 2 converts AC power supplied from AC power source 200 into DC power and outputs this DC power to a DC link, which is the DC output side of converter 2. The DC link refers to a circuit portion that electrically connects the DC output side of converter 2 and the DC input side of inverter main circuit 11, and may also be referred to as a "DC link portion," "DC link," "DC link portion," or "DC intermediate circuit." The DC link is composed of a positive potential line 21P and a negative potential line 21N.

[0020] In the example shown in FIG. 1, the AC power supply 200 is a three-phase AC power supply, so the converter 2 is configured with a three-phase bridge circuit. However, if the AC power supply 200 is a single-phase AC power supply, the converter 2 is configured with a single-phase bridge circuit. Examples of the converter 2 include a diode rectifier, a 120-degree conduction rectifier, and a PWM switching control rectifier. In the example shown in FIG. 1, the converter 2 is configured with a diode rectifier. For example, if the converter 2 is configured with a 120-degree conduction rectifier and a PWM switching control rectifier, it is configured with a bridge circuit of switching elements and diodes connected in reverse parallel to the switching elements, and each switching element is controlled on and off in response to a drive command received from the motor control unit 3 to perform bidirectional AC / DC power conversion. In this case, examples of the switching elements include FETs, IGBTs, thyristors, GTOs (Gate Turn-Off Thyristors), and transistors, but other semiconductor elements may also be used.

[0021] The DC input side of the inverter 1 and the DC output side of the converter 2 are connected via a DC link. The inverter 1 includes an inverter main circuit unit 11, a DC link capacitor 12, a grounding capacitor unit 13, a common mode choke core 14 which is a common mode choke unit, and a common mode capacitor unit 15-1 which is a bypass unit.

[0022] The DC link capacitor 12 is provided on the DC output side of the converter 2 in the DC link. The DC link capacitor 12 is sometimes called a smoothing capacitor. The DC link capacitor 12 has the function of suppressing pulsation in the DC output of the converter 2 and the function of storing DC power used by the inverter main circuit 11 to generate AC power. The DC link capacitor 12 is required to store a large amount of power, and therefore is configured, for example, by an electrolytic capacitor.

[0023] The inverter main circuit unit 11 converts DC power in the DC link into AC power (motor-driving AC power) for driving the motor 300, which is a load circuit, and outputs the converted power. The inverter main circuit unit 11 is composed of switching elements and a bridge circuit of diodes connected in antiparallel to the switching elements. In the example shown in FIG. 1, the motor 300 is a three-phase AC motor, so the inverter main circuit unit 11 is composed of a three-phase bridge circuit. Examples of switching elements include FETs, IGBTs, thyristors, GTOs, and transistors, but other semiconductor elements may also be used. The AC output side of the inverter main circuit unit 11 and the motor 300, which is a load circuit, are electrically connected by three-phase AC power lines: a U-phase power line 22U, a V-phase power line 22V, and a W-phase power line 22W.

[0024] The power conversion operation of the inverter main circuit unit 11 is controlled by, for example, a PWM switching control system. That is, upon receiving a drive command (PWM switching command) from the motor control unit 3, the inverter main circuit unit 11 converts DC power in the DC link into AC power for driving the motor and outputs it to the motor 300, and during motor regeneration, converts AC power regenerated by the motor 300 into DC power and outputs it to the DC link.

[0025] The power conversion operation of inverter main circuit unit 11 is controlled based on drive commands generated by motor control unit 3, similar to a typical motor drive device. Motor control unit 3 generates drive commands for controlling the speed, torque, or rotor position of motor 300 based on the speed of motor 300 (speed feedback), the current flowing through the windings of motor 300 (current feedback), a predetermined torque command, and an operation program for motor 300. Note that the configuration of motor control unit 3 defined here is merely an example, and the configuration of motor control unit 3 may also be defined by including terms such as position command generation unit, torque command generation unit, and switching command generation unit.

[0026] The motor drive device 100 includes an arithmetic processing unit (processor). Examples of arithmetic processing units include an IC, an LSI, a CPU, an MPU, and a DSP. This arithmetic processing unit includes a motor control unit 3. The motor control unit 3 included in the arithmetic processing unit is a functional module implemented by, for example, a computer program executed on the processor. For example, if the motor control unit 3 is implemented in the form of a computer program, the functions of each unit can be realized by operating the arithmetic processing unit in accordance with the computer program. The computer program for executing the processing of the motor control unit 3 may be provided in the form of a computer-readable recording medium, such as a semiconductor memory, a magnetic recording medium, or an optical recording medium. Alternatively, the motor control unit 3 may be realized as a semiconductor integrated circuit into which a computer program for implementing the function is written.

[0027] The ground of the servo amplifier that constitutes the inverter 1 is referred to as an amplifier ground 71. The ground for the AC power supply 200 is referred to as a power supply ground 72. The amplifier ground 71 and the power supply ground 72 are connected by a cable, and the impedance of this cable is referred to as a ground impedance 65.

[0028] The grounding capacitor section 13 is provided between the DC link capacitor 12 and the inverter main circuit section 11 in the DC link. The grounding capacitor section 13 includes a positive-side grounding capacitor 31P and a negative-side grounding capacitor 31N. The positive-side grounding capacitor 31P and the negative-side grounding capacitor 31N are so-called Y capacitors (ground capacitors). That is, one end of the positive-side grounding capacitor 31P is connected to the amplifier ground 71, and the other end of the positive-side grounding capacitor 31P is connected to the positive potential line 21P of the DC link. One end of the negative-side grounding capacitor 31N is connected to the amplifier ground 71, and the other end of the negative-side grounding capacitor 31N is connected to the negative potential line 21N of the DC link. The positive-side grounding capacitor 31P and the negative-side grounding capacitor 31N are required to have good frequency characteristics, and are therefore configured using, for example, a film capacitor or a ceramic capacitor.

[0029] Common mode choke core 14, which is a common mode choke section, is provided in the DC link between ground capacitor section 13 and inverter main circuit section 11. Therefore, in the DC link, DC link capacitor 12, ground capacitor section 13, and common mode choke core 14 are provided in this order from the DC output side of converter 2 toward the DC input side of inverter main circuit section 11.

[0030] Common mode choke core 14 is made of, for example, a ferrite core. Examples of ferrite that can be used to make the ferrite core include Ni-Zn ferrite and Mn-Zn ferrite. For example, it is preferable to use a ferrite that has high impedance even in a frequency band of 30 MHz or higher for common mode choke core 14.

[0031] The common mode choke core 14 has a hollow portion 51 through which the positive potential line 21P and negative potential line 21N of the DC link are inserted. When current flows through the positive potential line 21P and negative potential line 21N inserted through the hollow portion 51 of the common mode choke core 14, the magnetic fluxes generated by the common mode current (i.e., noise current) reinforce each other, so the common mode choke core 14 has a high impedance to the common mode current. On the other hand, the magnetic fluxes generated by the normal mode current cancel each other out, so the common mode choke core 14 has a low impedance to the normal mode current. Furthermore, when current flows through the positive potential line 21P and negative potential line 21N inserted through the hollow portion 51 of the common mode choke core 14, magnetic flux is generated in the common mode choke core 14, and the current energy is converted into magnetic energy. However, as the current changes, the magnetic flux is converted back into current by electromagnetic induction, with some of the magnetic flux being consumed as magnetic loss. Therefore, the common mode choke core 14 can suppress only the common mode current. In a normal coil, most of the impedance is a reactance component, but in the common mode choke core 14 made of a ferrite core, the imaginary part of the complex permeability is large, i.e., the resistance component is very large. Details of complex permeability will be described later.

[0032] The common mode choke core 14 is different from a common mode choke coil. A common mode choke coil has a configuration in which two conductor wires are wound around a single core (e.g., ring-shaped) so that the magnetic field is oriented in the same direction. Winding conductor wires around a core increases inductance, but parasitic capacitance appears between the conductor wires. If a common mode choke coil were used instead of the common mode choke core 14, high-frequency common-mode current would flow from the converter 2 to the inverter main circuit unit 11 through the parasitic capacitance appearing between the conductor wires, thereby weakening the common-mode current suppression effect. Therefore, in the first embodiment of the present disclosure, a common mode choke core 14 having high impedance even in a frequency band above 30 MHz is used instead of a common mode choke coil, so as to be able to suppress high-frequency common-mode current, for example, 30 MHz.

[0033] 1 shows an example in which common mode choke core 14 is configured as a ring-shaped ferrite core. Alternatively, common mode choke core 14 may be configured by combining a plurality of plate cores made of ferrite so as to have hollow portion 51.

[0034] The common mode choke section may be any section that has high impedance to the common mode current, which is a high frequency, and therefore a common mode transformer (noise prevention transformer) may be used instead of the common mode choke core 14.

[0035] The detour unit is configured to allow common mode current flowing through U-phase power line 22U, V-phase power line 22V, and W-phase power line 22W, which are AC power lines, to bypass motor 300 and flow to amplifier ground 71 so as not to flow into motor 300. The detour unit has a configuration that connects U-phase power line 22U, V-phase power line 22V, and W-phase power line 22W, which connect the AC output side of inverter main circuit unit 11 to motor 300, which is a load circuit, to amplifier ground 71. In the first embodiment of the present disclosure, a common mode capacitor unit 15-1 is provided as the detour unit.

[0036] Common mode capacitor section 15-1 has a configuration in which one end of each of a plurality of capacitors is connected to a corresponding AC power line and the other end of each is connected to a neutral point, and one end of a grounded capacitor is connected to the neutral point and the other end is connected to ground. In the example shown in Figure 1, motor 300 is a three-phase AC motor, so common mode capacitor section 15-1 has U-phase capacitor 32U, V-phase capacitor 32V, W-phase capacitor 32W, and grounded capacitor 33.

[0037] U-phase capacitor 32U, V-phase capacitor 32V, and W-phase capacitor 32W are Y-connected (star-connected) with U-phase power line 22U, V-phase power line 22V, and W-phase power line 22W. That is, one end of U-phase capacitor 32U is connected to U-phase power line 22U, and the other end of U-phase capacitor 32U is connected to the neutral point. One end of V-phase capacitor 32V is connected to V-phase power line 22V, and the other end of V-phase capacitor 32V is connected to the neutral point. One end of W-phase capacitor 32W is connected to W-phase power line 22W, and the other end of W-phase capacitor 32W is connected to the neutral point. One end of grounding capacitor 33 is connected to the neutral point, and the other end is connected to amplifier ground 71.

[0038] Since U-phase capacitor 32U, V-phase capacitor 32V, W-phase capacitor 32W, and ground capacitor 33 are required to have particularly good frequency characteristics, they are configured with, for example, ceramic capacitors, etc. For example, it is preferable to use ceramic capacitors that have high impedance even in frequency bands of 30 MHz or higher.

[0039] As described above, in the DC link, the DC link capacitor 12, the grounding capacitor section 13, and the common mode choke core 14 are provided in this order from the DC output side of the converter 2 toward the DC input side of the inverter main circuit section 11. In the DC link, the flow of common mode current flowing out from the DC output side of the converter 2 is blocked by the common mode choke core 14, which has high impedance. The blocked common mode current from the DC output side of the converter 2 flows toward the amplifier ground 71 via the grounding capacitor section 13. If the order of the grounding capacitor section 13 and the common mode choke core 14 were reversed (i.e., if the order were DC link capacitor 12, common mode choke core 14, and grounding capacitor section 13), the common mode choke core 14 would no longer be included in the path along which the common mode current flows, and the effect of suppressing the common mode current would be reduced. More specifically, if the arrangement order of the grounding capacitor section 13 and the common mode choke core 14 is reversed, the path through which the common mode current flows will be from the grounding capacitor section 13, to the inverter main circuit section 11, the motor, "propagating through space as radiated noise or displacement current," to the power supply ground 72, the amplifier ground 71, and back to the grounding capacitor section 13 in that order, so that the common mode choke core 14 is no longer included in the path through which the common mode current flows, and the effect of the common mode choke core 14 in suppressing the common mode current will not be realized. Therefore, as shown in Figure 1, it is important that in the DC link, the DC link capacitor 12, the grounding capacitor section 13, and the common mode choke core 14 are arranged in this order from the DC output side of the converter 2 toward the DC input side of the inverter main circuit section 11.

[0040] <Principles of common mode current suppression> Next, the principle of suppressing common mode current in the inverter 1 and the motor drive device 100 according to the first embodiment of the present disclosure will be described.

[0041] 2 is a circuit diagram illustrating a common mode current flowing through an inverter according to the first embodiment of the present disclosure and a motor connected thereto, in which an AC power supply 200 and a converter 2 are omitted.

[0042] The connection relationship between the inverter 1 and the motor 300 shown in Fig. 1 can be expressed by the equivalent circuit shown in Fig. 2. As shown in Fig. 2, the DC link capacitor 12, the positive side grounded capacitor 31P, and the negative side grounded capacitor 31N can be integrated into a capacitor section 18. The DC link capacitor 12 is connected to a DC link voltage V DC is applied. The inverter 1 includes a capacitor unit 18, a common mode choke core 14, and a common mode capacitor unit 15-1. A ground impedance 65 exists between the amplifier ground 71 and the power supply ground 72. The AC power line 22 connecting the inverter 1 and the motor 300 has a common mode impedance 61 of the power line cable and an impedance 62 of the ground cable. In the motor 300, a parasitic capacitance 63 exists between the motor 300 and the ground cable, and a parasitic capacitance 64 exists between the motor 300 and the power supply ground 72.

[0043] In order to reduce the radiation noise in the motor driving device 100, the common mode current I c2 In the first embodiment of the present disclosure, the common mode current I that bypasses the motor 300 is suppressed. c1 However, if the impedance of the parasitic capacitances 63 and 64 of the motor 300 is sufficiently large compared to the impedance of the capacitor unit 18, the common mode current I flows through the common mode capacitor unit 15-1, which is a bypass unit. C1 Therefore, in the first embodiment of the present disclosure, a common mode choke core 14 is further provided to increase the output impedance of the inverter 1. As described above, the common mode choke core 14 has high impedance with respect to the common mode current.

[0044] FIG. 3 is a circuit diagram showing an equivalent circuit relating to noise of the inverter according to the first embodiment of the present disclosure and the motor connected thereto.

[0045] As shown in FIG. 3, the impedance of the capacitor section 18 is set to Z c , the impedance of the common mode capacitor section 15-1 is Z d , the impedance of the motor 300 is Z m In addition, the common mode current flowing through the motor 300 is I n The DC link voltage applied to the DC link capacitor 12 (not shown in FIG. 3) in the capacitor unit 18 is V DC In the equivalent circuit for noise shown in Figure 3, the common mode current I n can be expressed as in Equation 1.

[0046]

number

[0047] Impedance Z of capacitor section 18 c is the impedance Z of the common mode capacitor section 15-1 d and the impedance Z of the motor 300 m is sufficiently larger than each of (Z c >>Z d , Z m ), Equation 1 can be approximated as Equation 2.

[0048]

number

[0049] From equation 2, the impedance Z of the common mode capacitor part 15-1, which is the bypass part, d The smaller the common mode current I n Furthermore, from the same equation 2, the impedance Z of the capacitor section 18 is cThe larger the common mode current I n Therefore, in the first embodiment of the present disclosure, the impedance Z of the capacitor section 18 is c To increase the common mode current I n A common mode choke core 14 having high impedance to the DC link is provided between the capacitor section 18 and the inverter main circuit section 11.

[0050] Suppose the impedance Z of the motor 300 is m and the impedance Z of the common mode capacitor section 15-1 d Each of these is the impedance Z of the capacitor section 18 c is sufficiently larger than (Z m , Z d >>Z c ), Equation 1 can be approximated as Equation 3.

[0051]

number

[0052] From equation 3, the impedance Z of the motor 300 m and the impedance Z of the common mode capacitor section 15-1 d Each of these is the impedance Z of the capacitor section 18 c is sufficiently larger than (Z m , Z d >>Z c ) is the impedance Z of the motor 300 m Only common mode current I n Therefore, in the first embodiment of the present disclosure, the common mode choke core 14 is provided between the capacitor unit 18 and the inverter main circuit unit 11 in the DC link, and the impedance Z c By increasing the impedance Z of the motor 300, m Regardless of the magnitude of the common mode current I nis made smaller.

[0053] <Driving multiple motors> Generally, motor drive devices often drive multiple motors. Fig. 4 is a diagram showing a case where multiple motors are driven by an inverter according to a first embodiment of the present disclosure and a motor drive device including the inverter. Fig. 4 shows, as an example, a case where three motors 300-1, 300-2, and 300-3 are driven by a motor drive device 100 connected to a three-phase AC power supply 200. The following description can be applied to cases where a number of three-phase AC motors other than three are driven, and can also be applied to cases where multiple single-phase AC motors are driven.

[0054] The AC power supply 200, converter 2, DC link capacitor 12, ground capacitor section 13, common mode choke core 14, inverter main circuit sections 11-1 to 11-3, common mode capacitor section 15-1 which is a bypass section, and motor control section 3 are as described with reference to Figures 1 to 3.

[0055] In the motor drive device 100, the number of inverter main circuit units 11 that supply motor drive power to the motors 300 corresponds to the number of motors 300. An inverter main circuit unit 11-1 is connected to the motor 300-1 via an AC power line. A detour unit 15-1-1 is provided that connects the AC power line connecting the motor 300-1 and the inverter main circuit unit 11-1 to the amplifier ground 71. An inverter main circuit unit 11-2 is connected to the motor 300-2 via an AC power line. A detour unit 15-1-2 is provided that connects the AC power line connecting the motor 300-2 and the inverter main circuit unit 11-2 to the amplifier ground 71. An inverter main circuit unit 11-3 is connected to the motor 300-3 via an AC power line. A detour unit 15-1-3 is provided that connects the AC power line connecting the motor 300-3 and the inverter main circuit unit 11-3 to the amplifier ground 71. The detouring sections 15-1-1, 15-1-2, and 15-1-3 are configured, for example, by the above-mentioned common mode capacitor section, but may also be configured by an LC series resonant circuit, which will be described later.

[0056] The inverter main circuit units 11-1, 11-2, and 11-3 are connected to one converter 2 via a DC link. In the DC link, a DC link capacitor 12, a grounding capacitor unit 13, and a common mode choke core 14 are provided in this order from the DC output side of the converter 2 toward the DC input side of the inverter main circuit unit 11.

[0057] Since there is only one converter 2, the inverter main circuit units 11-1, 11-2, and 11-3 share the DC link. Therefore, regardless of the number of inverter main circuit units (= the number of motors), there is only one DC link capacitor 12, one ground capacitor unit 13, and one common mode choke core 14 provided in the DC link. On the other hand, the number of detour units must be the same as the number of inverter main circuit units (= the number of motors), but the capacitors that make up the detour units are not expensive and do not occupy a large volume. For these reasons, the inverter 1 and motor drive device 100 according to the first embodiment of the present disclosure are small and low-cost.

[0058] <Single-phase AC motor drive> 1 to 4, an example has been described in which a three-phase motor 300 is driven by a motor driving device 100 connected to a three-phase AC power supply 200. The motor driving device 100 can also drive a single-phase AC motor.

[0059] FIG. 5 is a diagram illustrating a case where a single-phase AC motor is driven by the inverter according to the first embodiment of the present disclosure and the motor drive device including the inverter.

[0060] The AC power supply 200, the converter 2, the DC link capacitor 12, the ground capacitor section 13, the common mode choke core 14, and the motor control section 3 are as described with reference to FIGS.

[0061] The single-phase AC motor 300 is connected to a single-phase inverter main circuit unit 11 via an L (live, hot) phase power line 22L and an N (neutral, cold) phase power line 22N, which are AC power lines. The inverter main circuit unit 11 converts DC power in the DC link into single-phase AC power (motor drive AC power) for driving the single-phase motor 300, which is a load circuit, and outputs the converted power. The inverter main circuit unit 11 is composed of a single-phase bridge circuit of switching elements and diodes connected in reverse parallel to the switching elements.

[0062] The common mode capacitor section 15-1, which is a bypass section, has a configuration in which the L-phase power line 22L and the N-phase power line 22N, which are AC power lines connecting the AC output side of the inverter main circuit section 11 and the single-phase motor 300, are connected to the amplifier ground 71.

[0063] Common mode capacitor section 15-1 has a configuration in which one end of each of a plurality of capacitors is connected to a corresponding AC power line and the other end of each is connected to a neutral point, and one end of a grounded capacitor is connected to the neutral point and the other end is connected to ground. In the example shown in Figure 5, motor 300 is a single-phase AC motor, so common mode capacitor section 15-1 has L-phase capacitor 32L, N-phase capacitor 32N, and grounded capacitor 33.

[0064] One end of L-phase capacitor 32L is connected to L-phase power line 22L, and the other end of L-phase capacitor 32L is connected to the neutral point. One end of N-phase capacitor 32N is connected to N-phase power line 22N, and the other end of N-phase capacitor 32N is connected to the neutral point. One end of grounding capacitor 33 is connected to the neutral point, and the other end is connected to amplifier ground 71. L-phase capacitor 32L, N-phase capacitor 32N, and grounding capacitor 33 are required to have particularly good frequency characteristics, so they are made of, for example, ceramic capacitors. It is preferable to use ceramic capacitors that have high impedance even in frequency bands of 30 MHz or higher, for example.

[0065] <Second embodiment> FIG. 6 is a diagram illustrating an inverter according to a second embodiment of the present disclosure and a motor drive device including the inverter.

[0066] The second embodiment of the present invention further includes a common mode choke core 16 on the motor 300 side in the inverter 1 and motor drive device 100 according to the first embodiment. Fig. 6 shows, as an example, a case in which one three-phase AC motor 300 is driven by a motor drive device 100 connected to a three-phase AC power supply 200. The following description can also be applied to cases in which a single-phase AC motor or multiple motors are driven.

[0067] The AC power supply 200, converter 2, DC link capacitor 12, ground capacitor section 13, common mode choke core 14, inverter main circuit section 11, common mode capacitor section 15-1, and motor control section 3 are as described with reference to Figures 1 to 5.

[0068] The further common mode choke core 16 has a hollow portion 52 through which the AC power lines, U-phase power line 22U, V-phase power line 22V, and W-phase power line 22W, are inserted, and is provided between the common mode capacitor portion 15-1, which is a bypass portion, and the motor 300.

[0069] The further common mode choke core 16 is made of, for example, a ferrite core. Examples of ferrite that can be used to make the ferrite core include Ni-Zn ferrite and Mn-Zn ferrite. For example, it is preferable to use a ferrite that has high impedance even in a frequency band of 30 MHz or higher for the further common mode choke core 16.

[0070] When current flows through the U-phase power line 22U, V-phase power line 22V, and W-phase power line 22W inserted through the hollow portion 52 of the further common mode choke core 16, the magnetic fluxes generated by the common mode current reinforce each other, resulting in a high impedance for the further common mode choke core 16 to the common mode current. The magnetic fluxes generated by the normal mode current cancel each other out, resulting in a low impedance for the further common mode choke core 16 to the normal mode current. Furthermore, when current flows through the U-phase power line 22U, V-phase power line 22V, and W-phase power line 22W inserted through the hollow portion 52 of the further common mode choke core 16, magnetic flux is generated in the further common mode choke core 16, converting the current energy into magnetic energy. However, as the current changes, the magnetic flux is converted back into current by electromagnetic induction, with some of the magnetic flux being consumed as magnetic loss. Therefore, the further common mode choke core 16 can suppress only the common mode current. In addition, most of the impedance of a normal coil is a reactance component, but the common mode choke core 16 made of a ferrite core has a large imaginary part of the complex permeability, that is, a very large resistance component.

[0071] 6 shows, as an example, a case where the additional common mode choke core 16 is configured as a ring-shaped ferrite core. Alternatively, the additional common mode choke core 16 may be configured by combining a plurality of plate cores made of ferrite so as to have a hollow portion 52. Furthermore, instead of the additional common mode choke core 16, a common mode transformer (noise prevention transformer) may be provided between the common mode capacitor unit 15-1 and the motor 300.

[0072] Suppose the impedance Z of the common mode capacitor section 15-1 is d is the impedance Z of motor 300 m is sufficiently larger than (Z d >>Z m ), Equation 1 can be approximated as Equation 4.

[0073]

number

[0074] From equation 4, the impedance Z of the common mode capacitor section 15-1 is d is the impedance Z of motor 300 m is sufficiently larger than (Z d >>Z m ) is the impedance Z of the capacitor section 18 c Only common mode current I n The impedance Z of the common mode capacitor section 15-1 is d is the common mode current I n Therefore, in the second embodiment of the present disclosure, a common mode choke core 16 is further provided between the common mode capacitor section 15-1 and the motor 300 to reduce the impedance Z m By making the common mode current I n This makes it possible to suppress the problem more reliably.

[0075] <Third embodiment> FIG. 7 is a diagram illustrating an inverter according to a third embodiment of the present disclosure and a motor drive device including the inverter.

[0076] The third embodiment of the present invention further includes a normal mode choke core 17 that suppresses normal mode in the inverter 1 and motor drive device 100 according to the first embodiment. Fig. 7 shows, as an example, a case in which one three-phase AC motor 300 is driven by a motor drive device 100 connected to a three-phase AC power supply 200. The following description can also be applied to cases in which a single-phase AC motor or multiple motors are driven.

[0077] The AC power supply 200, converter 2, DC link capacitor 12, ground capacitor section 13, common mode choke core 14, inverter main circuit section 11, common mode capacitor section 15-1, and motor control section 3 are as described with reference to Figures 1 to 5.

[0078] The normal mode choke core 17 has a hollow portion 53 through which either the positive potential line 21P or the negative potential line 21N of the DC link is inserted, and is provided between the ground capacitor unit 13 and the inverter main circuit unit 11 in the DC link.

[0079] Because the common-mode capacitor unit 15-1 is provided as a bypass unit, a normal-mode current flows during switching operation in the inverter main circuit unit 11. For example, when the W-phase upper-arm switching element and the V-phase lower-arm switching element are turned on, a normal-mode current path is formed that flows from the positive potential line 21P through the W-phase upper-arm switching element, the W-phase power line 22W, the W-phase capacitor 32W, the V-phase capacitor 32V, the V-phase power line 22V, and the V-phase lower-arm switching element to the negative potential line 21N. Similar normal-mode current paths are formed in other switching patterns. The normal-mode current causes the switching elements to heat up, resulting in energy loss in the switching elements. Therefore, in the third embodiment of the present invention, a normal-mode choke core 17 is provided in the DC link between the ground capacitor unit 13 and the inverter main circuit unit 11 to suppress the normal-mode current. In the example shown in FIG. 7 , the positive potential line 21P is inserted through the hollow portion 53 as an example, but the negative potential line 21N may also be inserted through the hollow portion 53.

[0080] The imaginary part of the complex permeability μ of the common mode choke core 14 is preferably set to a value larger than the imaginary part of the complex permeability of the normal mode choke core 17. The complex permeability μ is expressed by Equation 5.

[0081]

number

[0082] The inductance L is proportional to μ. Therefore, the impedance of the coil can be expressed as Equation 6.

[0083]

number

[0084] From Equation 6, it can be seen that the imaginary part of the complex permeability corresponds to the real part of the inductance and represents the resistance component.

[0085] Common mode choke core 14 is provided for the purpose of consuming the energy of the common mode current. Therefore, it is preferable to consume energy using a resistance component rather than suppressing current peaks using an inductance component. Therefore, it is desirable to use a ferrite core for common mode choke core 14, which has a large imaginary part of its complex permeability (i.e., a large resistance component) in the high frequency band.

[0086] On the other hand, normal mode choke core 17 is provided for the purpose of suppressing the peak of the normal mode current. Therefore, it is preferable that normal mode choke core 17 is a pure inductance component rather than a resistance component that consumes the energy of the normal mode current. Therefore, it is desirable to use a ferrite core for normal mode choke core 17, which has a small imaginary part of the complex permeability (i.e., a small resistance component) in the high frequency band.

[0087] Unlike common mode current, normal mode current is less likely to be a source of radiation noise, but it does cause loss in switching elements. According to the third embodiment of the present disclosure, common mode current and normal mode current can be suppressed, thereby achieving the effects of suppressing noise and reducing switching loss.

[0088] The normal mode choke core 17 may be provided anywhere in the DC link between the ground capacitor section 13 and the AC input side of the inverter main circuit section 11. Fig. 8 is a diagram showing an inverter according to a modified example of the third embodiment of the present disclosure and a motor drive device including the inverter. In Fig. 7, the normal mode choke core 17 is provided between the common mode choke core 14 and the inverter main circuit section 11, but in Fig. 8, the normal mode choke core 17 is provided between the ground capacitor section 13 and the common mode choke core 14.

[0089] <Fourth embodiment> FIG. 9 is a diagram illustrating an inverter according to a fourth embodiment of the present disclosure and a motor drive device including the inverter.

[0090] The fourth embodiment of the present invention is a combination of the second and third embodiments. Fig. 9 shows, as an example, a case in which one three-phase AC motor 300 is driven by a motor drive device 100 connected to a three-phase AC power supply 200. The following description can also be applied to cases in which a single-phase AC motor or multiple motors are driven.

[0091] The AC power supply 200, converter 2, DC link capacitor 12, ground capacitor section 13, common mode choke core 14, inverter main circuit section 11, common mode capacitor section 15-1, and motor control section 3 are as described with reference to Figures 1 to 5.

[0092] The further common mode choke core 16 has a hollow portion 52 through which the U-phase power line 22U, V-phase power line 22V, and W-phase power line 22W, which are AC power lines, are inserted, and is provided between the common mode capacitor unit 15-1, which is a bypass unit, and the motor 300. Details of the further common mode choke core 16 have been described with reference to FIG. 6.

[0093] The normal mode choke core 17 has a hollow portion 53 through which either the positive potential line 21P or the negative potential line 21N of the DC link is inserted, and is provided in the DC link between the grounding capacitor unit 13 and the inverter main circuit unit 11. Details of the normal mode choke core 17 have been described with reference to FIGS. 7 and 8.

[0094] <Fifth embodiment> FIG. 10 is a diagram illustrating an inverter according to a fifth embodiment of the present disclosure and a motor drive device including the inverter.

[0095] In the fifth embodiment of the present invention, an LC series resonant circuit 15-2 is provided instead of the common mode capacitor section, which is the bypass section, in the inverter 1 and motor drive device 100 according to the first embodiment. Fig. 10 shows, as an example, a case in which one three-phase AC motor 300 is driven by a motor drive device 100 connected to a three-phase AC power supply 200. The following description can also be applied to cases in which a single-phase AC motor or multiple motors are driven.

[0096] The AC power supply 200, converter 2, DC link capacitor 12, ground capacitor section 13, common mode choke core 14, inverter main circuit section 11, common mode capacitor section 15-1, and motor control section 3 are as described with reference to Figures 1 to 5.

[0097] The LC series resonant circuit 15-2, which is the bypass section, has a configuration in which the U-phase power line 22U, the V-phase power line 22V, and the W-phase power line 22W, which are AC power lines connecting the AC output side of the inverter main circuit section 11 and the motor 300, which is the load circuit, are connected to the amplifier ground 71.

[0098] LC series resonant circuit 15-2 includes a plurality of sets each consisting of a capacitor and a coil connected in series. One end of each set is connected to a corresponding AC power line and the other end is connected to a neutral point. One end of a grounded capacitor is connected to the neutral point and the other end is connected to ground. In the example shown in FIG. 10, motor 300 is a three-phase AC motor. LC series resonant circuit 15-2 includes a first set consisting of a U-phase capacitor 34U and a U-phase coil 41U connected in series, a second set consisting of a V-phase capacitor 34V and a V-phase coil 41V connected in series, a third set consisting of a W-phase capacitor 34W and a W-phase coil 41W connected in series, and a grounded capacitor 33. U-phase capacitor 34U, V-phase capacitor 34V, and W-phase capacitor 34W are required to have good frequency characteristics and are therefore implemented using, for example, film capacitors or ceramic capacitors. U-phase coil 41U, V-phase coil 41V, and W-phase coil 41W are configured by general coils. Note that U-phase coil 41U, V-phase coil 41V, and W-phase coil 41W may be substituted by the parasitic impedances of U-phase capacitor 34U, V-phase capacitor 34V, and W-phase capacitor 34W.

[0099] The first, second, and third sets are Y-connected (star-connected) with respect to the AC power lines, namely, U-phase power line 22U, V-phase power line 22V, and W-phase power line 22W. That is, one end of the first set is connected to U-phase power line 22U, and the other end of the first set is connected to the neutral point. One end of the second set is connected to V-phase power line 22V, and the other end of the second set is connected to the neutral point. One end of the third set is connected to W-phase power line 22W, and the other end of the third set is connected to the neutral point. One end of grounding capacitor 33 is connected to the neutral point, and the other end is connected to amplifier ground 71.

[0100] 11 is a diagram showing the frequency-impedance characteristics of an LC series resonant circuit. In the LC series resonant circuit 15-2, in frequency band B higher than the resonant frequency f0, the impedance increases with increasing frequency. Therefore, the LC series resonant circuit 15-2 can suppress normal mode currents having frequencies in frequency band B higher than the resonant frequency f0. Furthermore, in frequency band A lower than the resonant frequency f0, the properties of a capacitor are more pronounced. Therefore, the fifth embodiment of the present invention is particularly effective in applications where common mode currents having frequencies in frequency band A lower than the resonant frequency f0 can be suppressed.

[0101] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the claims. [Explanation of symbols]

[0102] 1 inverter 2 Converter 3 Motor control unit 11, 11-1, 11-2, 11-3 Inverter main circuit section 12 DC link capacitor 13 Grounding capacitor section 14 Common mode choke core 15-1 Common mode capacitor section 15-1-1, 15-1-2, 15-1-3 Detour section 15-2 LC series resonant circuit 16 More common mode choke cores 17 Normal mode choke core 18 Capacitor section 21P positive potential line 21N negative potential line 22 AC power line 22L L phase power line 22N N phase power line 22U U phase power line 22V V phase power line 22W W phase power line 31P Positive ground capacitor 31N Negative ground capacitor 32L L-phase capacitor 32N N-phase capacitor 32U U-phase capacitor 32V V-phase capacitor 32W W-phase capacitor 33 Grounding capacitor 34U U phase capacitor 34V V-phase capacitor 34W W-phase capacitor 41U U-phase coil 41V V-phase coil 41W W-phase coil 51, 52, 53 Hollow part 61 Common mode impedance of power line cables 62 Impedance of ground cable 63 Parasitic capacitance between the motor and the ground cable 64 Parasitic capacitance between motor and power ground 65 Ground impedance between amplifier ground and power supply ground 71 Amplifier Ground 72 Power Ground 100 Motor drive device 200 AC power supply 300, 300-1, 300-2, 300-3 motors

Claims

1. an inverter main circuit unit connected via a DC link to a converter that converts AC power from an AC power source into DC power, and that converts the DC power into AC power for a load circuit and outputs the AC power; a DC link capacitor provided on a DC output side of the converter in the DC link; a grounded capacitor section that includes a positive-side grounded capacitor having one end connected to the ground and the other end connected to the positive potential line of the DC link, and a negative-side grounded capacitor having one end connected to the ground and the other end connected to the negative potential line of the DC link, and that is provided in the DC link between the DC link capacitor and the inverter main circuit section; a common mode choke unit provided in the DC link between the ground capacitor unit and the inverter main circuit unit, the common mode choke unit suppressing a common mode current; a bypass section that connects each AC power line that connects the AC output side of the inverter main circuit section and the load circuit to the ground; Equipped with the ground is an amplifier ground, which is a ground of a servo amplifier constituting an inverter including the inverter main circuit section, and is different from a power supply ground, which is a ground for the AC power supply; the bypass unit includes a common mode capacitor unit that suppresses a common mode current, the common mode capacitor section has a configuration in which one end of each of a plurality of capacitors is connected to a corresponding one of the AC power lines and the other end of each is connected to a neutral point, and one end of a grounding capacitor is connected to the neutral point and the other end is connected to the ground.

2. The inverter according to claim 1 , wherein the common mode choke section comprises a common mode choke core having a hollow portion through which the positive potential line and the negative potential line are inserted.

3. Further provided with a common mode choke core to suppress common mode current, 3. The inverter according to claim 1, wherein the further common mode choke core has a hollow portion through which the AC power line is inserted, and is provided between the bypass portion and the load circuit.

4. For one converter, a plurality of inverter main circuit sections and the same number of bypass sections as the inverter main circuit sections are provided, the plurality of inverter main circuit units share one DC link; each of the bypass sections connects each of the AC power lines connecting the AC output sides of the plurality of inverter main circuit sections and the load circuit to the ground; The inverter according to claim 1 or 2.

5. Further provided with a normal mode choke core for suppressing normal mode current, 3. The inverter according to claim 1, wherein the normal mode choke core has a hollow portion through which the positive potential line or the negative potential line is inserted, and is provided in the DC link between the ground capacitor unit and the inverter main circuit unit.

6. 6. The inverter according to claim 5, wherein the imaginary part of the complex permeability of said common mode choke section is larger than the imaginary part of the complex permeability of said normal mode choke core.

7. the bypass unit includes an LC series resonant circuit, 3. The inverter according to claim 1, wherein the LC series resonant circuit includes a plurality of sets each consisting of a capacitor and a coil connected in series to each other, one end of each of the sets being connected to a corresponding one of the AC power lines and the other end being connected to a neutral point, and one end of a grounding capacitor being connected to the neutral point and the other end being connected to the ground.

8. the converter; The inverter according to claim 1 or 2; a motor control unit that controls the driving of a motor that is the load circuit; A motor drive device comprising:

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