Motor drive circuit, injection molding machine with the same, and power supply circuit

Abstract

To reduce common mode noise in relatively small-sized configuration in a motor drive circuit which drives a motor using a three-phase AC power source.SOLUTION: A motor drive circuit 10 drives a motor 150 using a three-phase AC power source 20. The motor drive circuit comprises a converter 233, an inverter 231, an AC power line ACL connecting the three-phase AC power source 20 with the converter 233, and a noise compensation circuit 220. The converter 233 converts an input AC voltage from the three-phase AC power source 20 into a DC voltage. The inverter 231 converts the DC voltage into an AC voltage and drives the motor 150. The noise compensation circuit 220 supplies a voltage signal, which is obtained by inverting and amplifying common node noise detected in the AC power line ACL, to the AC power line ACL.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a motor drive circuit, an injection molding machine including the same, and a power supply circuit.

Background Art

[0002] Japanese Patent Application Laid-Open No. 10-94244 (Patent Document 1) discloses a configuration in which an active common mode noise canceller (ACC) is applied to the main circuit of a system for driving an induction motor by a voltage type PWM (Pulse Width Modulation) inverter. In the system of Japanese Patent Application Laid-Open No. 10-94244 (Patent Document 1), it is possible to reduce the common mode voltage generated during the switching of the power semiconductor element in a power conversion device such as an inverter.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventionally, in order to reduce common mode noise generated in a motor drive circuit having a power conversion device such as a converter, a configuration using a noise filter in which capacitors are arranged between each phase of a three-phase AC power line and the ground potential is known. Such a noise filter can reduce common mode noise with a relatively simple configuration.

[0005] On the one hand, when the generated common-mode noise is large, it is necessary to increase the capacitance of the capacitor to be arranged. However, increasing the capacitance of the capacitor of the noise filter has problems that the device size increases and the leakage current due to the noise filter increases. Conversely, if the capacitance of the capacitor is insufficient, the influence of the common-mode noise reaches the power supply equipment, and the leakage breaker of the power supply equipment may operate, or it may cause malfunction of other peripheral devices connected to the same power supply.

[0006] The ACC disclosed in Japanese Patent Application Laid-Open No. 10-94244 (Patent Document 1) detects the common-mode voltage in the power line between the inverter that drives the motor and the motor, and supplies a voltage with a phase opposite to the common-mode voltage to the power line via a common-mode transformer, thereby reducing the common-mode noise.

[0007] However, when applying the ACC of Japanese Patent Application Laid-Open No. 10-94244 (Patent Document 1) to a configuration in which a plurality of motors are connected to the same power circuit, such as an injection molding machine, it is necessary to arrange an ACC for each motor, so the entire device becomes large.

[0008] The present disclosure has been made to solve such problems, and its object is to reduce common-mode noise with a relatively small configuration in a motor drive circuit that drives a motor with a three-phase AC power supply.

Means for Solving the Problems

[0009] The motor drive circuit according to the first aspect of the present disclosure drives a motor by a three-phase AC power supply. The motor drive circuit includes a converter, an inverter, an AC power line connecting the three-phase AC power supply and the converter, and a noise compensation circuit connected to the AC power line. The converter converts the input AC voltage from the three-phase AC power supply into a DC voltage. The inverter converts the DC voltage to generate a three-phase output AC voltage to drive the motor. The noise compensation circuit is configured to reduce the common-mode noise current flowing through the AC power line. The noise compensation circuit includes, for each phase of the AC power line, a first capacitor and a second capacitor, a resistor, and an amplifier. The first capacitor and the resistor are connected in series between the corresponding power line and the ground potential. The amplifier inverts and amplifies the voltage at the connection node between the first capacitor and the resistor. The second capacitor is connected between the output terminal of the amplifier and the corresponding power line.

[0010] The motor drive circuit according to the second aspect of the present disclosure drives a motor by a three-phase AC power supply. The motor drive circuit includes a converter, an inverter, an AC power line connecting the three-phase AC power supply and the converter, and a noise compensation circuit connected to the AC power line. The converter converts the input AC voltage from the three-phase AC power supply into a DC voltage. The inverter converts the DC voltage to generate a three-phase output AC voltage to drive the motor. The noise compensation circuit is configured to reduce the common-mode noise current flowing through the AC power line. The noise compensation circuit includes an amplifier, and a first capacitor, a second capacitor, and a resistor provided for each phase of the AC power line. The first capacitor and the resistor are connected in series between the corresponding power line and the ground potential in each phase of the AC power line. The amplifier is connected to the connection node between the first capacitor and the resistor in each phase of the AC power line, and inverts and amplifies the input voltage. The second capacitor is connected between the output terminal of the amplifier and the corresponding power line in each phase of the AC power line.

[0011] The power supply circuit according to the third aspect of the present disclosure is used in a motor drive circuit using a three-phase AC power supply. The power supply circuit includes a converter, an AC power line connecting the three-phase AC power supply and the converter, and a noise compensation circuit connected to the AC power line. The converter converts the AC voltage from the three-phase AC power supply into a DC voltage. The noise compensation circuit is configured to reduce the common mode noise current flowing through the AC power line. The noise compensation circuit includes, for each phase of the AC power line, a first capacitor and a second capacitor, a resistor, and an amplifier. The first capacitor and the resistor are connected in series between the corresponding power line and the ground potential. The amplifier inverts and amplifies the voltage at the connection node between the first capacitor and the resistor. The second capacitor is connected between the output terminal of the amplifier and the corresponding power line.

Advantages of the Invention

[0012] In the motor drive circuit according to the present disclosure, a voltage signal obtained by inverting and amplifying the common mode noise detected in the AC power line connecting the three-phase AC power supply and the converter is supplied to the AC power line. Thereby, it is possible to reduce the common mode noise while suppressing an increase in the capacitance of the capacitor of the noise filter.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their description will not be repeated.

[0015] [Embodiment 1] (Configuration of Injection Molding Machine) FIG. 1 is a diagram for explaining the configuration of an injection molding machine 100 equipped with a motor drive circuit according to Embodiment 1. For convenience of explanation, the floor surface on which the injection molding machine 100 is arranged is taken as the XY plane, and the direction perpendicular to the floor surface is taken as the Z-axis direction. The positive direction of the Z-axis may be referred to as the upper surface side or the upper direction, and the negative direction may be referred to as the lower surface side or the lower direction. Note that the injection molding machine 100 in Embodiment 1 is shown as a horizontal injection molding machine, but it is not limited to the horizontal type and may be a vertical injection molding machine. Further, the features of the present disclosure are applicable to other industrial machines such as machine tools, press devices, extrusion molding machines, and / or laser processing machines as long as they have a motor drive circuit having a power converter including switching elements.

[0016] Referring to FIG. 1, the injection molding machine 100 includes a clamping device 110 for clamping a mold, an injection device 120 for melting and injecting an injection material, an operation panel 130, a control device 140, and a servo amplifier 160. In FIG. 1, the clamping device 110 is arranged on the negative X-axis side with respect to the injection device 120.

[0017] The clamping device 110 includes a bed 111, a fixed platen 112, a clamping housing 113, a movable platen 114, tie bars 115, a clamping mechanism 116, molds 117 and 118, and a ball screw 119. The bed 111 is arranged on the floor surface, and devices such as the fixed platen 112, the clamping housing 113, and the movable platen 114 are mounted on its upper surface.

[0018] The stationary platen 112 is fixed to the end of the bed 111 on the side closer to the injection device 120 (i.e., the positive direction of the X-axis). The clamping housing 113 is arranged at the end of the bed 111 in the negative direction of the X-axis. The stationary platen 112 and the clamping housing 113 are connected by a tie bar 115 including a plurality of bars. The clamping housing 113 is movable in the X-axis direction on the bed 111.

[0019] The movable platen 114 is arranged between the stationary platen 112 and the clamping housing 113 on the bed 111. The movable platen 114 is configured to be movable in the X-axis direction. The clamping housing 113 and the movable platen 114 are connected by a clamping mechanism 116. The clamping mechanism 116 has a toggle mechanism. A ball screw 119 is connected to the toggle mechanism, and by driving a servo motor 151 arranged in the clamping housing 113 to rotate the ball screw 119, the movable platen 114 can be relatively moved in the X-axis direction with respect to the clamping housing 113. Note that as the clamping mechanism 116, a direct-acting cylinder driven by hydraulic pressure may be used.

[0020] Molds 117 and 118 are respectively arranged on the movable platen 114 and the stationary platen 112. The mold 117 and the mold 118 are arranged to face each other between the movable platen 114 and the stationary platen 112. By moving the mold 117 in the X-axis direction using the clamping mechanism 116, the mold 117 and the mold 118 can be brought into close contact with each other or the mold 117 can be separated from the mold 118. In the following description, the process of shifting from the state where the molds 117 and 118 are separated to the state where they are in close contact is referred to as "clamping". Also, the process of shifting from the state where the molds 117 and 118 are in close contact to the state where they are separated is referred to as "mold opening".

[0021] In the clamping process, with the molds 117 and 118 in close contact, the interior of the molds is filled with a molten material (resin), cooled, and solidified, enabling the formation of a product with a desired shape. After the product is formed, in the mold-opening process, with the mold 117 separated from the mold 118, by operating a protruding mechanism (not shown) arranged on the movable platen 114, the formed product can be removed from the mold 117. The protruding mechanism is driven by a servo motor 152 arranged on the movable platen 114. Note that the process of removing the product using the protruding mechanism is referred to as the "protrusion" process.

[0022] The injection device 120 includes a base 121, a heating cylinder 122, a drive device 124, a hopper 125, an injection moving device 127, and a temperature sensor 128. The base 121 is arranged on the floor surface on the positive X-axis side of the bed 111, and the drive device 124 is mounted on its upper surface. Servo motors 153 and 154 are arranged in the drive device 124.

[0023] The drive device 124 is provided with a heating cylinder 122 extending in the X-axis direction. The heating cylinder 122 includes a heater (not shown) for heating the interior, a screw 123, and an injection nozzle 126. The screw 123 is driven by a servo motor 153 in the drive device 124 and is configured to be rotatable with the X-axis direction as the rotation axis. Also, the screw 123 is configured to be movable in the X-axis direction by a servo motor 154. The injection nozzle 126 is arranged at the end of the heating cylinder 122 on the side of the clamping device 110 (i.e., the end in the negative X-axis direction). The heating cylinder 122 heats and melts the bead-shaped resin material input from the hopper 125 and kneads it using the screw 123 to generate a molten material. Thus, the process of melting the resin material is referred to as the "plasticization" process.

[0024] The injection moving device 127 is constituted by, for example, a mechanism using a hydraulic cylinder or a mechanism using a ball screw, and connects the driving device 124 and the fixed platen 112 of the mold clamping device 110. When the injection moving device 127 is constituted by a mechanism using a ball screw, the injection moving device 127 is driven by the driving device 124 to move the driving device 124 and the heating cylinder 122 in the X-axis direction. By bringing the injection nozzle 126 into contact with the sprue bush of the mold 118 in the mold clamping device 110 by the injection moving device 127 and injecting the molten material from the injection nozzle 126, the cavity of the molds 117, 118 is filled with the molten material. The servo motor 154 applies pressure to the molten material by moving the screw 123 in the heating cylinder 122 in the negative direction of the X-axis, and maintains the injection of the molten material into the molds 117, 118 and the pressure of the molten material after injection constant.

[0025] Note that the configuration of the injection moving mechanism is not limited to the configuration in which the entire injection device is moved by a ball screw disposed between the fixed platen 112 and the driving device 124 as described above, and other configurations may be used. For example, a configuration in which the device frame and the fixing member at the rear of the heating cylinder are connected using a ball screw to move the heating cylinder itself in the mold direction may be used. Alternatively, a configuration in which the slide base on which the injection device is mounted and the device frame are connected using a ball screw, and the injection device is moved together with the slide base to bring the injection nozzle into contact with the mold may be used.

[0026] Note that the process of injecting the molten material into the molds 117, 118 is referred to as the "injection" process. Further, after the injection process, the process of holding the molten material filled in the molds 117, 118 at a constant pressure and cooling it is referred to as the "pressure holding" process.

[0027] The temperature sensor 128 is disposed near the injection nozzle 126 in the heating cylinder 122. The temperature sensor 128 detects the temperature of the molten material inside the heating cylinder 122 and outputs it to the control device 140. The control device 140 controls the heater based on the detected value of the temperature sensor 128 to adjust the temperature of the molten material to a desired temperature.

[0028] When the holding pressure process is completed, the mold opening process and the ejection process are executed, and the molded product is taken out.

[0029] The injection molding machine 100 can continuously form products by cyclically repeating the mold clamping process, the injection process, the holding pressure process, the plasticizing process, the mold opening process, and the ejection process.

[0030] Inside the control panel provided on the base 121, a control device 140 and a servo amplifier 160 for driving the servo motors 151 to 154 are stored. The control device 140 includes a CPU (Central Processing Unit) 141 and a memory 142. The control device 140 acquires the detection values of various sensors arranged in the injection molding machine 100 and comprehensively controls the injection molding machine 100. Although not shown in the figure, the servo amplifier 160 includes a plurality of servo amplifiers respectively provided corresponding to the servo motors 151 to 154. In the following description, the servo motors 151 to 154 are also collectively referred to as "servo motor 150".

[0031] The operation panel 130 is a device for an operator to operate the injection molding machine 100, and includes a display device such as a liquid crystal display and an input device such as a keyboard. The operation panel 130 is connected to the control device 140, and can acquire and display the state of the injection molding machine 100, or output a user operation signal from the input device to the control device 140. The operation panel 130 may be a touch panel in which the display device and the input device are integrated. Also, the operation panel 130 may be attached to the bed 111 or the base 121 of the injection molding machine 100, or may be arranged at a position independent of the injection molding machine 100.

[0032] (Configuration of Motor Drive Circuit) FIG. 2 is a block diagram showing an overview of the motor drive circuit 10 in the injection molding machine 100 of FIG. 1. The motor drive circuit 10 generally drives the servo motor 150 using AC power from the utility power supply 20, which is a three-phase AC power supply.

[0033] Referring to FIG. 2, the motor drive circuit 10 includes a filter circuit 210, a noise compensation circuit 220, and a power conversion unit 230. In FIG. 2 and FIGS. 3 to 5 below, servo motors 151 and 152 are described as examples of the servo motor 150.

[0034] The filter circuit 210 is provided on the AC power line ACL that connects the utility power supply 20 and the power conversion unit 230. The filter circuit 210 reduces normal mode noise and common mode noise on the AC power line. The power conversion unit 230 includes a converter and an inverter, as will be described later with reference to FIG. 3. The power conversion unit 230 converts the input AC voltage from the utility power supply 20 into a DC voltage by the converter, and further converts the converted DC voltage into an AC voltage by the inverter to drive the servo motors 151 and 152.

[0035] The noise compensation circuit 220 includes a detection unit 221, an amplification unit 222, and an output unit 223. The detection unit 221 is connected to the AC power line ACL, detects the common mode noise current flowing in each phase of the AC power line ACL, and generates and outputs a voltage (common mode noise voltage) corresponding to the common mode noise current.

[0036] The amplification unit 222 inverts and amplifies the polarity of the common mode noise voltage detected by the detection unit 221 to generate a compensation voltage. The output unit 223 is connected to the AC power line ACL and supplies the compensation voltage generated by the amplification unit 222 to the AC power line ACL. A part or all of the common mode noise generated on the AC power line ACL is canceled out by the compensation voltage supplied by the noise compensation circuit 220.

[0037] FIG. 3 is a diagram for explaining the details of the motor drive circuit 10 in FIG. 2. As described in FIG. 2, the motor drive circuit 10 includes a filter circuit 210, a noise compensation circuit 220, and a power conversion unit 230.

[0038] The filter circuit 210 includes an inductor section Lf including inductors connected to the respective phases of the a-phase, b-phase, and c-phase of the system power supply 20, a capacitor section Cf, and a capacitor section Cy.

[0039] The capacitor section Cf includes three capacitors connected between the respective phases. In other words, the three capacitors included in the capacitor section Cf are delta-connected in the a-phase, b-phase, and c-phase. The capacitor section Cf can reduce the normal mode noise generated in the AC power line ACL.

[0040] The capacitor section Cy includes three capacitors connected between each phase and the ground potential GND. In other words, the three capacitors included in the capacitor section Cy are Y-connected, and the neutral point thereof is connected to the ground potential GND. In each phase, a low-pass filter is constituted by the inductor included in the inductor section Lf and the capacitor included in the capacitor section Cy. The low-pass filter can reduce the common mode noise generated in the AC power line ACL.

[0041] The power conversion unit 230 includes inverters 231, 232, a converter 233, and a capacitor Cdc. The inverters 231, 232 correspond to the servo amplifier 160 in FIG. 1. Note that the power supply circuit 250 is constituted by the filter circuit 210, the noise compensation circuit 220, and the converter 233.

[0042] Converter 233 is a PWM rectifier of three-phase full-bridge type that includes six semiconductor switching elements. Converter 233 converts an AC voltage (input AC voltage) from the AC power line ACL into a DC voltage and supplies it to the DC power lines PL1 and NL1. Converter 233 includes three arms (first arm, second arm, third arm) connected in parallel between the DC power lines PL1 and NL1. Each arm includes two semiconductor switching elements connected in series between the power lines PL1 and NL1.

[0043] The power line of phase a is connected to the connection node of the switching element of the first arm. The power line of phase b is connected to the connection node of the switching element of the second arm. The power line of phase c is connected to the connection node of the switching element of the third arm.

[0044] The switching elements included in converter 233 are controlled by a control device (not shown). Thus, the input AC voltage supplied from the AC power line ACL is converted into a DC voltage and supplied to the power lines PL1 and NL1.

[0045] One end of the capacitor Cdc is connected to the power line PL1, and the other end is connected to the power line NL1. Capacitor Cdc smoothes the DC voltage converted in converter 233.

[0046] Each of the inverters 231 and 232 is a three-phase full-bridge type inverter connected in parallel to the power lines PL1 and NL1. Also, the inverters 231 and 232 are respectively connected to the servo motors 151 and 152. Each of the inverters 231 and 232 is controlled by a control device (not shown), converts the DC voltage from the power lines PL1 and NL1 into an AC voltage, and supplies the converted AC voltage to the corresponding servo motors 151 and 152.

[0047] The noise compensation circuit 220 includes capacitors C1 to C7, resistors R1 to R6, amplifiers AP1 to AP3, and DC voltage sources PS1 and PS2. The detection unit 221 includes capacitors C1 to C3 and resistors R1 to R3. The amplification unit 222 includes amplifiers AP1 to AP3. The output unit 223 includes capacitors C4 to C6.

[0048] In the detection unit 221, one end of the capacitor C1 is connected to the a-phase of the AC power line ACL. The other end of the capacitor C1 is connected to one end of the resistor R1. The other end of the resistor R1 is connected to the ground potential GND via the capacitor C7.

[0049] One end of the capacitor C2 is connected to the b-phase of the AC power line ACL. The other end of the capacitor C2 is connected to one end of the resistor R2. The other end of the resistor R2 is connected to the ground potential GND via the capacitor C7.

[0050] One end of the capacitor C3 is connected to the c-phase of the AC power line ACL. The other end of the capacitor C3 is connected to one end of the resistor R3. The other end of the resistor R3 is connected to the ground potential GND via the capacitor C7.

[0051] In other words, the series-connected capacitor C1 and resistor R1, capacitor C2 and resistor R2, and capacitor C3 and resistor R3 are Y-connected, and their neutral point is connected to the ground potential GND via the capacitor C7.

[0052] The amplifiers AP1 to AP3 are inverting amplifiers, which invert the polarity of the signal input to the inverting input terminal and amplify it with a predetermined gain and output it from the output terminal. The amplifiers AP1 to AP3 are supplied with a driving power source from the series-connected DC voltage sources PS1 and PS2. The connection node between the DC voltage source PS1 and the DC voltage source PS2 is connected to the capacitor C7.

[0053] The inverting input terminal of amplifier AP1 is connected to the connection node of capacitor C1 and resistor R1 via resistor R4. The non-inverting input terminal of amplifier AP1 is connected to capacitor C7. The output terminal of amplifier AP1 is connected to the a-phase of the AC power line ACL via capacitor C4 of the output section 223.

[0054] The inverting input terminal of amplifier AP2 is connected to the connection node of capacitor C2 and resistor R2 via resistor R5. The non-inverting input terminal of amplifier AP2 is connected to capacitor C7. The output terminal of amplifier AP2 is connected to the b-phase of the AC power line ACL via capacitor C5 of the output section 223.

[0055] The inverting input terminal of amplifier AP3 is connected to the connection node of capacitor C3 and resistor R3 via resistor R6. The non-inverting input terminal of amplifier AP3 is connected to capacitor C7. The output terminal of amplifier AP3 is connected to the c-phase of the AC power line ACL via capacitor C6 of the output section 223.

[0056] In a motor drive circuit having a power conversion section including a switching element, switching noise inevitably occurs when the switching element switches. This noise returns from the neutral point of the servo motor to the power line via the ground potential (earth or housing), thereby generating common-mode noise. Since this common-mode noise also occurs in the system power supply that supplies power to the motor drive circuit, it may affect other devices connected to the same power system and cause malfunction of the other devices. Therefore, it is important to reduce the common-mode noise in the motor drive circuit.

[0057] In order to reduce common-mode noise, a configuration in which a filter circuit 210 is provided between a three-phase AC power supply 20 and a power conversion unit 230, as in the motor drive circuit 10X of the comparative example in FIG. 4, has been conventionally known. The filter circuit 210 includes a capacitor section Cy that is Y-connected to each phase, and the neutral point thereof is connected to the ground potential GND. The capacitor section Cy removes or reduces the common-mode noise generated on the AC power line ACL.

[0058] Here, in a motor drive circuit that drives a large-capacity motor, the generated common-mode noise also tends to be large. Therefore, in a motor drive circuit for high-power applications, when removing common-mode noise only with the capacitor section Cy of the filter circuit 210, it is necessary to increase the capacitance of the capacitor used for the capacitor section Cy.

[0059] On the other hand, in the capacitor section Cy, since the noise component of the common-mode noise is absorbed by the capacitor and flows to the ground potential GND, the removed noise component is substantially equivalent to the leakage current. Therefore, if the capacitance of the capacitor section Cy is increased to remove common-mode noise, the leakage current will increase instead. Then, the leakage breaker provided in the device (for example, an injection molding machine) on which the motor drive circuit is mounted or the power supply device that supplies power to the injection molding machine may operate, and the device may stop during operation.

[0060] In the motor drive circuit 10 of Embodiment 1, as described above, a noise compensation circuit 220 is provided. In the detection unit 221, capacitors C1 to C3 are Y-connected via resistors R1 to R3, respectively. In the case of three-phase AC, when no common-mode noise is generated, the potential at the neutral point is basically zero. However, when common-mode noise is generated, the potential of the neutral point fluctuates from zero. That is, a voltage (common-mode voltage) corresponding to the common-mode noise is generated at the connection node between the capacitor and the resistor of each phase in the detection unit 221.

[0061] The common mode voltages detected by the detection unit 221 for the corresponding phases are respectively input to the inverting input terminals of the amplifiers AP1 to AP3. As a result, voltages having polarities opposite to the input common mode voltages are output from the output terminals of the amplifiers AP1 to AP3. Then, the output voltages from the amplifiers AP1 to AP3 are input as compensation voltages to the corresponding phases of the AC power line ACL through the capacitors C4 to C6 of the output unit 223, respectively. Therefore, part or all of the common mode noise generated in each phase of the AC power line ACL is canceled by the compensation voltage supplied from the noise compensation circuit 220.

[0062] Therefore, in the motor drive circuit 10 of the first embodiment, common mode noise can be reduced without increasing the capacitance of the capacitor unit Cy in the filter circuit 210.

[0063] Also, in the noise compensation circuit 220 of the motor drive circuit 10, detection and compensation of common mode noise are performed on the AC power line ACL on the primary side of the power conversion unit 230. Therefore, even when a plurality of servo motors are driven as shown in FIG. 3, the influence of common mode noise can be reduced by one compensation circuit for the entire motor drive circuit, so that the device can be miniaturized. Further, since the noise compensation circuit 220 does not use a common mode transformer, a compensation circuit can be realized with a relatively small circuit.

[0064] Each of the "capacitors C1 to C3" in the first embodiment corresponds to the "first capacitor" in the present disclosure. Each of the "capacitors C4 to C6" in the first embodiment corresponds to the "second capacitor" in the present disclosure. The "capacitor unit Cy" in the first embodiment corresponds to the "third capacitor" in the present disclosure.

[0065] [Second Embodiment] In the second embodiment, a motor drive circuit having a noise compensation circuit with a different configuration of an amplification unit will be described.

[0066] FIG. 5 is a diagram for explaining the motor drive circuit 10A of Embodiment 2. In the motor drive circuit 10A, the noise compensation circuit 220 in FIG. 3 is replaced with a noise compensation circuit 220A. More specifically, in the noise compensation circuit 220A, the amplification unit 222 in the noise compensation circuit 220 is replaced with an amplification unit 222A. Note that the power supply circuit 250A is constituted by the filter circuit 210, the noise compensation circuit 220A, and the converter 233. In FIG. 5, other configurations are the same as those in FIG. 3, and descriptions of elements overlapping with FIG. 3 are not repeated.

[0067] Referring to FIG. 5, in the amplification unit 222 in the noise compensation circuit 220, three amplifiers AP1 to AP3 corresponding to each phase were provided, but in the amplification unit 222A, only one amplifier AP is provided. A synthesized (added) signal of signals that have passed through resistors R4 to R6 is input to the inverting input terminal of the amplifier AP. Further, the output terminal of the amplifier AP is branched into three, and is supplied to the a-phase of the AC power line ACL via the capacitor C4, to the b-phase of the AC power line ACL via the capacitor C5, and to the c-phase of the AC power line ACL via the capacitor C6.

[0068] Common-mode noise generally appears as noise having the same voltage level for each phase. Therefore, even in a configuration in which three phases are collectively compensated as in the noise compensation circuit 220A, it is possible to reduce noise. In this case, since the number of amplifiers can be reduced as compared with Embodiment 1, the noise compensation circuit can be miniaturized.

[0069] On the other hand, when a difference occurs in the common-mode noise generated in each phase due to different cable lengths in each phase or different partial circuit configurations, by providing an amplifier for each phase and performing compensation as in Embodiment 1, noise can be appropriately reduced.

[0070] [Aspect] Those skilled in the art will understand that the above-described plurality of exemplary embodiments are specific examples of the following aspects.

[0071] (Item 1) The motor drive circuit according to one aspect drives a motor by a three-phase AC power supply. The motor drive circuit includes a converter, an inverter, an AC power line connecting the three-phase AC power supply and the converter, and a noise compensation circuit connected to the AC power line. The converter converts the input AC voltage from the three-phase AC power supply into a DC voltage. The inverter converts the DC voltage to generate a three-phase output AC voltage to drive the motor. The noise compensation circuit is configured to reduce the common-mode noise current flowing through the AC power line. The noise compensation circuit includes a first capacitor and a second capacitor, a resistor, and an amplifier for each phase of the AC power line. The first capacitor and the resistor are connected in series between the corresponding power line and the ground potential. The amplifier inverts and amplifies the voltage at the connection node between the first capacitor and the resistor. The second capacitor is connected between the output terminal of the amplifier and the corresponding power line.

[0072] (Item 2) The motor drive circuit according to Item 1 further includes a filter circuit including a third capacitor connected between each phase of the AC power line and the ground potential.

[0073] (Item 3) The motor drive circuit according to one aspect drives a motor with a three-phase AC power supply. The motor drive circuit includes a converter, an inverter, an AC power line connecting the three-phase AC power supply and the converter, and a noise compensation circuit connected to the AC power line. The converter converts the input AC voltage from the three-phase AC power supply into a DC voltage. The inverter converts the DC voltage to generate a three-phase output AC voltage to drive the motor. The noise compensation circuit is configured to reduce the common-mode noise current flowing through the AC power line. The noise compensation circuit includes an amplifier, a first capacitor, a second capacitor, and a resistor provided for each phase of the AC power line. The first capacitor and the resistor are connected in series between the corresponding power line and the ground potential in each phase of the AC power line. The amplifier is connected to the connection node between the first capacitor and the resistor in each phase of the AC power line, and inverts and amplifies the input voltage. The second capacitor is connected between the output terminal of the amplifier and the corresponding power line in each phase of the AC power line.

[0074] (Item 4) The injection molding machine according to one aspect includes the motor drive circuit according to any one of Items 1 to 3.

[0075] (Item 5) The power supply circuit according to one aspect is used in a motor drive circuit using a three-phase AC power supply. The power supply circuit includes a converter, an AC power line connecting the three-phase AC power supply and the converter, and a noise compensation circuit connected to the AC power line. The converter converts the AC voltage from the three-phase AC power supply into a DC voltage. The noise compensation circuit is configured to reduce the common-mode noise current flowing through the AC power line. The noise compensation circuit includes, for each phase of the AC power line, a first capacitor, a second capacitor, a resistor, and an amplifier. The first capacitor and the resistor are connected in series between the corresponding power line and the ground potential. The amplifier inverts and amplifies the voltage at the connection node between the first capacitor and the resistor. The second capacitor is connected between the output terminal of the amplifier and the corresponding power line.

[0076] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is shown not by the description of the above embodiments but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Explanation of Signs

[0077] 10, 10A, 10X motor drive circuits, 20 system power supply, 100 injection molding machine, 110 clamping device, 111 bed, 112 fixed platen, 113 clamping housing, 114 movable platen, 115 tie bar, 116 clamping mechanism, 117, 118 molds, 120 injection device, 121 base, 122 heating cylinder, 123 screw, 124 drive device, 125 hopper, 126 injection nozzle, 127 injection moving device, 128 temperature sensor, 130 operation panel, 140 control device, 142 memory, 150, 151 - 154 servo motors, 160 servo amplifier, 210 filter circuit, 220, 220A noise compensation circuits, 221 detection unit, 222, 222A amplification units, 223 output unit, 230 power conversion unit, 231, 232 inverters, 233 converter, 250, 250A power supply circuits, ACL alternating current power line, AP, AP1 - AP3 amplifiers, C1 - C7, Cdc capacitors, Cf, Cy capacitor units, GND ground potential, Lf inductor unit, PL1, NL1 power lines, PS1, PS2 DC voltage sources, R1 - R6 resistors.

Claims

1. A motor drive circuit for driving a motor by a three-phase AC power supply, comprising: a converter that converts an input AC voltage from the three-phase AC power supply into a DC voltage; an inverter that converts the DC voltage to generate a three-phase output AC voltage and drives the motor; an AC power line connecting the three-phase AC power supply and the converter; a noise compensation circuit connected to the AC power line and configured to reduce a common-mode noise current flowing through the AC power line; the noise compensation circuit includes, for each phase of the AC power line, a first capacitor and a resistor connected in series between the corresponding power line and the ground potential; an amplifier that inverts and amplifies the voltage of a connection node between the first capacitor and the resistor; a second capacitor connected between an output terminal of the amplifier and the corresponding power line, the motor drive circuit.

2. The motor drive circuit according to claim 1, further comprising a filter circuit including a third capacitor connected between each phase of the AC power line and the ground potential.

3. A motor drive circuit for driving a motor by a three-phase AC power supply, comprising: a converter that converts an input AC voltage from the three-phase AC power supply into a DC voltage; an inverter that converts the DC voltage to generate a three-phase output AC voltage and drives the motor; an AC power line connecting the three-phase AC power supply and the converter; a noise compensation circuit connected to the AC power line and configured to reduce a common-mode noise current flowing through the AC power line; the noise compensation circuit includes a first capacitor and a resistor provided for each phase of the AC power line and connected in series between the corresponding power line and the ground potential; an amplifier connected to a connection node between the first capacitor and the resistor in each phase, inverting and amplifying an input voltage; a second capacitor provided for each phase of the AC power line and connected between an output terminal of the amplifier and the corresponding power line, the motor drive circuit.

4. An injection molding machine comprising the motor drive circuit according to any one of claims 1 to 3.

5. A power supply circuit for a motor drive circuit using a three-phase AC power supply, comprising: a converter that converts an AC voltage from the three-phase AC power supply into a DC voltage; an AC power line connecting the three-phase AC power supply and the converter; A noise compensation circuit connected to the AC power line and configured to reduce the common mode noise current flowing through the AC power line, For each phase of the AC power line, the noise compensation circuit A first capacitor and a resistor connected in series between the corresponding power line and the ground potential, An amplifier that inverts and amplifies the voltage at the connection node between the first capacitor and the resistor, A power supply circuit including a second capacitor connected between the output terminal of the amplifier and the corresponding power line.

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