Motor drive system

Abstract

A motor drive system (200) comprises: a plurality of connection units connected to a power supply; and a plurality of motor drive devices (201a, 201b). The plurality of motor drive devices (201a, 201b) each comprise: a converter unit (2a, 2b); an inverter unit (4a, 4b) that outputs AC power to a motor (100a, 100b) and outputs regenerative energy from the motor (100a, 100b); a regenerative resistor unit (3a, 3b) that is connected between the converter unit (2a, 2b) and the inverter unit (4a, 4b); and a DC connection terminal unit (61a, 61b) that is connected to a DC voltage portion. The plurality of motor drive devices (201a, 201b) are connected to each other via the respective DC connection terminal units (61a, 61b). The impedance of each of the plurality of connection units is set within an allowable range set in advance on the basis of the bias condition of the current flowing through each of the motor drive devices (201a, 201b).

Description

Motor Drive System

[0001] The present disclosure relates to a motor drive system including a plurality of motor drive devices.

[0002] When a motor is decelerated or stopped, regenerative energy generated by the motor is output from the motor to a motor drive device that drives the motor. To reduce the voltage rise within the motor drive device caused by the regenerative energy being supplied from the motor to the motor drive device, motor drives generally employ a method in which the regenerative energy is consumed by a resistive load called a regenerative resistor.

[0003] Patent Document 1 discloses a motor drive system including multiple motor drive devices, each having a rectifier circuit, a smoothing capacitor, and an inverter circuit. Each motor drive device converts AC power supplied from an AC power source into DC power in the rectifier circuit. This DC power is then supplied to the inverter circuit via a smoothing capacitor. The DC voltage section of one motor drive device is connected to the DC voltage section of another motor drive device via an anti-parallel circuit including a transistor and a diode. The DC voltage section is a section in which a DC voltage is applied, extending from the output terminal of the rectifier circuit to the input terminal of the inverter circuit. Regenerative energy supplied from a motor to one motor drive device is distributed to the other motor drive devices via a smoothing capacitor. In the configuration disclosed in Patent Document 1, the current flowing from one of the connected motor drive devices to the other is controlled by a transistor in each motor drive device. According to the technology disclosed in Patent Document 1, the motor drive system distributes regenerative energy supplied from the motor to the other motor drive devices, thereby enabling effective utilization of the regenerative energy.

[0004] Japanese Patent Application Publication No. 10-248281

[0005] In the motor drive system disclosed in Patent Document 1, in order to enable the distribution of regenerative energy between the motor drive devices, each motor drive device requires components such as transistors or diodes to control the current between the motor drive devices. In the motor drive system disclosed in Patent Document 1, components that are not required when the motor drive device is used alone are added to each motor drive device, resulting in an increase in the number of components in each motor drive device compared to when the motor drive device is used alone. This increase in the number of components makes the configuration of each motor drive device more complex and larger.

[0006] The present disclosure has been made in view of the above, and has an object to provide a motor drive system that is simple and compact in configuration and that makes it possible to effectively utilize regenerative energy.

[0007] To solve the above-mentioned problems and achieve the object, the present disclosure provides a motor drive system including a plurality of connection parts connected to a power source and a plurality of motor drive devices each connected to the power source via the connection parts and configured to drive a motor with power supplied from the power source. Each of the plurality of motor drive devices includes a converter unit that outputs DC power, an inverter unit that converts the DC power output by the converter unit to AC power and outputs the AC power to the motor, and that outputs regenerative energy from the motor during regenerative operation of the motor, a regenerative resistor unit connected between the converter unit and the inverter unit, and a DC connection terminal unit connected to a DC voltage unit that applies a DC voltage. The plurality of motor drive devices are connected to each other via their respective DC connection terminal units. The impedance of each of the plurality of connection parts is set within a predetermined tolerance range based on the bias condition of the current flowing through each motor drive device.

[0008] The motor drive system according to the present disclosure has a simple and compact configuration and provides the advantage of being able to effectively utilize regenerative energy.

[0009]

[0010] A motor drive system according to an embodiment will be described in detail below with reference to the drawings.

[0011] First Embodiment Fig. 1 is a diagram showing an example of the configuration of a motor drive system 200 according to a first embodiment. The motor drive system 200 includes a plurality of motor drive devices. Each of the plurality of motor drive devices drives a motor. The motor drive system 200 illustrated in the first embodiment includes two motor drive devices 201a and 201b. The motor drive device 201a drives the motor 100a. The motor drive device 201b drives the motor 100b. The motor drive system 200 is connected to an AC power supply 101, which is a three-phase AC power supply.

[0012] The motor drive system 200 includes cables 111a, 111b, and 113, a relay unit 114, and motor drive devices 201a and 201b. The relay unit 114 is connected to the AC power supply 101 via the cable 113. The motor drive device 201a is connected to the relay unit 114 via the cable 111a. The motor drive device 201b is connected to the relay unit 114 via the cable 111b. Each of the cables 111a and 111b is a connection unit connected to the AC power supply 101 via the cable 113 and the relay unit 114. Each of the motor drive devices 201a and 201b is connected to the AC power supply 101 via a connection unit. Each of the motor drive devices 201a and 201b drives the motors 100a and 100b using power supplied from the AC power supply 101. Note that the connection units are not limited to the cables 111a and 111b, and may be a metal plate or the like. The relay unit 114 may be connected to the AC power supply 101 by a metal plate or the like instead of the cable 113. Note that each of the cables 111a and 111b may be connected directly to the AC power supply 101 without going through the relay unit 114 and the cable 113.

[0013] The motor drive device 201a includes a converter unit 2a, a regenerative resistor unit 3a, an inverter unit 4a, a control unit 5a, and a DC connection unit 6a. The converter unit 2a converts AC power supplied to the motor drive device 201a from an AC power supply 101 into DC power. The converter unit 2a includes an AC input terminal unit 21a, a rectifier 22a, and a smoothing capacitor 23a.

[0014] One end of the cable 111a is connected to the relay unit 114. The other end of the cable 111a is connected to the AC input terminal unit 21a. The AC input terminal unit 21a has three terminals L1, L2, and L3 corresponding to the three phases. The rectifier 22a is composed of elements such as diodes or thyristors. The rectifier 22a converts AC power to DC power and outputs the DC power. The smoothing capacitor 23a smoothes the DC voltage output from the rectifier 22a.

[0015] The regenerative resistance unit 3a is a component that consumes regenerative energy supplied from the motor 100a to the motor drive device 201a. The regenerative resistance unit 3a is connected between the converter unit 2a and the inverter unit 4a. The regenerative resistance unit 3a includes a regenerative resistor 31a and a switch element 32a. The switch element 32a is an element that performs switching, such as a transistor. By turning on the switch element 32a, the regenerative energy is consumed by the regenerative resistor 31a.

[0016] The inverter unit 4a includes an inverter circuit 41a and an output terminal unit 42a. The inverter circuit 41a is configured with a plurality of semiconductor elements. In FIG. 1, the inverter circuit 41a is configured with six semiconductor elements. Note that the number of semiconductor elements that make up the inverter circuit 41a is arbitrary. The inverter circuit 41a controls each of the plurality of semiconductor elements in accordance with a control signal input to the inverter circuit 41a from the control unit 5a.

[0017] The inverter circuit 41a controls each of the semiconductor elements in accordance with the control signal to convert the DC power input from the converter unit 2a to the inverter unit 4a into AC power of a desired frequency. The motor drive device 201a converts the AC power from the AC power supply 101 into AC power of a desired frequency using the converter unit 2a and the inverter unit 4a.

[0018] The output terminal unit 42a outputs AC power to the motor 100a. The output terminal unit 42a includes a U-phase terminal, a V-phase terminal, and a W-phase terminal corresponding to the U-phase, V-phase, and W-phase of the motor 100a, respectively. The U-phase terminal of the output terminal unit 42a is connected to the U-phase terminal of the motor 100a. The V-phase terminal of the output terminal unit 42a is connected to the V-phase terminal of the motor 100a. The W-phase terminal of the output terminal unit 42a is connected to the W-phase terminal of the motor 100a. The U-phase terminal, V-phase terminal, and W-phase terminal of the motor 100a are not shown in the figure.

[0019] The control unit 5a includes a power supply circuit 51a and a control circuit 52a. The power supply circuit 51a generates the power used by the control circuit 52a. Since the DC voltage applied to the converter unit 2a is a high voltage of several hundred volts, the power supply circuit 51a generates a voltage of several volts to several tens of volts used by the control circuit 52a. The control circuit 52a generates a control signal and outputs the control signal to the inverter unit 4a. The control circuit 52a is a processing circuit. The processing circuit, which is the control circuit 52a, may be dedicated hardware or may be a processing circuit equipped with a processor.

[0020] The DC connection unit 6a includes a DC connection terminal unit 61a. The DC connection terminal unit 61a includes a positive terminal P and a negative terminal N. The positive terminal P is connected to a positive portion of the DC voltage unit. The negative terminal N is connected to a negative portion of the DC voltage unit. The DC voltage unit is a portion where a DC voltage is applied, and extends from the output terminal of the rectifier 22a to the input terminal of the inverter unit 4a. In the example shown in FIG. 1 , the positive terminal P and the negative terminal N are connected between the rectifier 22a and the smoothing capacitor 23a.

[0021] The motor drive device 201b includes a converter unit 2b, a regenerative resistor unit 3b, an inverter unit 4b, a control unit 5b, and a DC connection unit 6b. The converter unit 2b converts AC power supplied to the motor drive device 201b from the AC power supply 101 into DC power. The converter unit 2b includes an AC input terminal unit 21b, a rectifier 22b, and a smoothing capacitor 23b. One end of the cable 111b is connected to the relay unit 114. The other end of the cable 111b is connected to the AC input terminal unit 21b. Details of the converter unit 2b are the same as those of the converter unit 2a.

[0022] The regenerative resistance unit 3b is connected between the converter unit 2b and the inverter unit 4b. The regenerative resistance unit 3b includes a regenerative resistor 31b and a switch element 32b. Details of the regenerative resistance unit 3b are the same as those of the regenerative resistance unit 3a. The inverter unit 4b includes an inverter circuit 41b and an output terminal unit 42b. Details of the inverter unit 4b are the same as those of the inverter unit 4a. The control unit 5b includes a power supply circuit 51b and a control circuit 52b. Details of the control unit 5b are the same as those of the control unit 5a. The DC connection unit 6b includes a DC connection terminal unit 61b. Details of the DC connection unit 6b are the same as those of the DC connection unit 6a.

[0023] Motor drive system 200 includes cable 62. DC connection terminal 61a of motor drive device 201a and DC connection terminal 61b of motor drive device 201b are connected to each other via cable 62. DC connection terminal 61a and DC connection terminal 61b may be connected to each other by a harness or a metal plate instead of cable 62. Alternatively, DC connection terminal 61a and DC connection terminal 61b may be connected to each other by mating a connector attached to DC connection terminal 61a with a connector attached to DC connection terminal 61b. In other words, motor drive devices 201a and 201b, which are multiple motor drive devices, are connected to each other via DC connection terminals 61a and 61b.

[0024] The number of motor drive devices included in motor drive system 200 is not limited to two and may be three or more. Each of the multiple motor drive devices included in motor drive system 200 is connected to AC power supply 101 via a connection portion, and drives a motor with power supplied from AC power supply 101. Each of the multiple motor drive devices has a configuration similar to that of motor drive devices 201a, 201b. The DC connection terminals of the motor drive devices included in the multiple motor drive devices are connected to each other by cables 62, harnesses, metal plates, connectors, or the like.

[0025] Next, we will explain the driving states of the motors 100a and 100b, and the paths and magnitudes of currents flowing through the motor drive system 200. Figure 2 is a diagram for explaining a first example of the paths and magnitudes of currents in the motor drive system 200 according to the first embodiment. Figure 2 shows a simplified configuration of the motor drive system 200.

[0026] Here, each of the motors 100a and 100b is assumed to have three states, as described below. The first state is a rotating state in which a rotor (not shown) is rotated by consuming power. The second state is a regenerative state in which regenerative power is generated by slowing down the rotation of the rotor in the rotating state. The third state is a stopped state in which the rotor is stopped.

[0027] In the first example shown in FIG. 2 , motor 100a is rotating and motor 100b is stopped. In the first example, current flows from AC power supply 101 to motor 100a via path 400. Path 400 passes through relay unit 114, cable 111a, converter unit 2a, and inverter unit 4a. Because DC connection terminal 61a and DC connection terminal 61b are connected to each other, in the first example, path 401 also exists, through which current flows from AC power supply 101 to motor 100a via motor drive device 201b. Path 401 passes through relay unit 114, cable 111b, converter unit 2b, DC connection terminal 61b, DC connection terminal 61a, and inverter unit 4a.

[0028] In the first example, the current flowing through path 400 is greater than the current flowing through path 401. In FIG. 2 , the dashed arrow representing path 400 is thicker than the dashed arrow representing path 401, thereby indicating that the current flowing through path 400 is greater than the current flowing through path 401. In this manner, the thickness of the dashed arrows in FIG. 2 is varied to indicate the magnitude relationship of the flowing currents. In FIGS. 3 to 6 , the magnitude relationship of the currents in each path is also indicated in the same manner as in FIG. 2 . Note that the magnitude of the current flowing through path 400 and the magnitude of the current flowing through path 401 vary depending on the variations in the impedance of cables 111a, 111b, and 62, or variations in the components within motor drive system 200. One example of component variations is individual differences between rectifiers 22a and 22b.

[0029] 3 is a diagram illustrating a second example of the paths and magnitudes of currents in motor drive system 200 according to the first embodiment. Fig. 3 shows a simplified configuration of motor drive system 200. In the second example shown in Fig. 3, motor 100a is in a rotating state, and motor 100b is also in a rotating state.

[0030] In the second example, a current flows from the AC power supply 101 to the motor 100a via a path 402. The path 402 is the same as the path 400 shown in FIG. 2 . Because the DC connection terminal 61a and the DC connection terminal 61b are connected, in the second example, a path 403 also exists, through which a current flows from the AC power supply 101 to the motor 100a via the motor drive device 201b. The path 403 is the same as the path 401 shown in FIG. 2 . In the second example, the current flowing through the path 402 is larger than the current flowing through the path 403. Note that the magnitude of the current flowing through the path 402 and the magnitude of the current flowing through the path 403 each vary depending on the variations in the impedance of the cables 111a, 111b, and 62, the variations in the components within the motor drive system 200, and the like.

[0031] In the second example, current flows from the AC power supply 101 to the motor 100b via path 404. Path 404 passes through the relay unit 114, the cable 111b, the converter unit 2b, and the inverter unit 4b. Because the DC connection terminal unit 61a and the DC connection terminal unit 61b are connected to each other, in the second example, there is also a path 405 through which current flows from the AC power supply 101 to the motor 100b via the motor drive device 201a. Path 405 passes through the relay unit 114, the cable 111a, the converter unit 2a, the DC connection terminal unit 61a, the DC connection terminal unit 61b, and the inverter unit 4b. In the second example, the current flowing through path 404 is greater than the current flowing through path 405. The magnitude of the current flowing through path 404 and the magnitude of the current flowing through path 405 each vary depending on the variations in the impedance of cables 111a, 111b, and 62, or variations in the components within motor drive system 200.

[0032] Fig. 4 is a diagram illustrating a third example of the current paths and magnitudes in motor drive system 200 according to the first embodiment. Fig. 4 shows a simplified configuration of motor drive system 200. In the third example shown in Fig. 4, motor 100a is in a rotating state, and motor 100b is in a regenerative state.

[0033] In the third example, current flows from the AC power supply 101 to the motor 100a via a path 406. The path 406 is the same as the path 400 shown in Fig. 2. Because the DC connection terminal 61a and the DC connection terminal 61b are connected to each other, in the third example, there is also a path 407 through which current flows from the AC power supply 101 to the motor 100a via the motor drive device 201b. The path 407 is the same as the path 401 shown in Fig. 2.

[0034] Furthermore, in the third example, regenerative power is generated in motor 100b, and thus there is also a path 408 through which current flows from motor 100b to motor 100a. Path 408 is a path that runs from motor 100b through inverter unit 4b, DC connection terminal unit 61b, DC connection terminal unit 61a, and inverter unit 4a. By consuming the regenerative power generated in motor 100b in motor 100a, motor drive system 200 can effectively utilize the regenerative power.

[0035] In the third example, the current flowing through path 406 is greater than the current flowing through path 407 and greater than the current flowing through path 408. Note that the magnitude of the current flowing through path 406, the magnitude of the current flowing through path 407, and the magnitude of the current flowing through path 408 each vary depending on the variation in the impedance of cable 111a, cable 111b, and cable 62, the variation in the components within motor drive system 200, and the like.

[0036] Fig. 5 is a diagram illustrating a fourth example of the current paths and magnitudes in motor drive system 200 according to the first embodiment. Fig. 5 shows a simplified configuration of motor drive system 200. In the fourth example shown in Fig. 5, motor 100a is in a regenerative state, and motor 100b is also in a regenerative state.

[0037] In the fourth example, regenerative power is generated in the motor 100a, and a path 409 exists through which a current flows from the motor 100a to the inverter unit 4a. The current flowing through the path 409 reaches the regenerative resistance unit 3a, and the regenerative power generated in the motor 100a is consumed by the regenerative resistance unit 3a.

[0038] In the fourth example, regenerative power is generated in the motor 100b, and a path 410 exists through which a current flows from the motor 100b to the inverter unit 4b. The current flowing through the path 410 reaches the regenerative resistance unit 3b, and the regenerative power generated in the motor 100b is consumed by the regenerative resistance unit 3b. Note that the regenerative resistance units 3a and 3b are not shown in FIG. 5.

[0039] 2 to 5, the current path and the magnitude of the current flowing through the path in motor drive system 200 change depending on the state of motors 100a, 100b. In the first example shown in Fig. 2 and the third example shown in Fig. 4, one motor is driven by motor drive system 200. In this case, the power that needs to be output from motor drive system 200 is the power required to drive one motor.

[0040] 3, when two motors are driven by motor drive system 200, there is a possibility that power exceeding the power required to drive one motor may be transmitted through one motor drive device. For example, power may be biased toward one of motor drive devices 201a and 201b due to variations in the impedance of cables 111a, 111b, and 62, or variations in components within motor drive system 200. Such a power bias may cause power exceeding the power required to drive one motor to be transmitted through one of motor drive devices 201a and 201b.

[0041] Fig. 6 is a diagram illustrating a fifth example of the paths and magnitudes of currents in motor drive system 200 according to the first embodiment. Fig. 6 shows a simplified configuration of motor drive system 200. In the fifth example shown in Fig. 6, motor 100a is in a rotating state, and motor 100b is also in a rotating state.

[0042] In the fifth example, a path 411 of a current flowing to the motor 100a is the same as the path 402 shown in Fig. 3. In the fifth example, a path 412 of a current flowing to the motor 100b is the same as the path 405 shown in Fig. 3. In the fifth example, a path 413 of a current flowing to the motor 100b is the same as the path 404 shown in Fig. 3.

[0043] In the fifth example, a hypothetical case will be described in which the impedance of cable 111b is greater than the impedance of cable 111a. When the impedance of cable 111b is greater than the impedance of cable 111a, the current flowing through path 412 is greater than the current flowing through path 413, as shown in FIG. 6 . Because the current flowing through path 412 is greater than the current flowing through path 413, more power than is necessary to drive one motor is transmitted to motor drive device 201a. In other words, a power imbalance occurs between motor drive devices 201a and 201b, such that the power transmitted through motor drive device 201a is greater than the power transmitted through motor drive device 201b.

[0044] To enable the motor drive system 200 to supply power to the motors 100a and 100b even when such a power imbalance occurs, each motor drive device 201a and 201b must be designed to withstand the transmission of power greater than the power required to drive a single motor. Specifically, to ensure heat resistance or current resistance, measures such as increasing the size of the components of the converter units 2a and 2b or widening the wiring width on the wiring board are necessary. Alternatively, a larger chassis for heat dissipation may be required. Such measures will result in an increase in the size of the configuration of each motor drive device 201a and 201b.

[0045] The power propagating through motor drive device 201a is greater than the power propagating through motor drive device 201b when the impedance of the path from AC power supply 101 to motor drive device 201a is smaller than the impedance of the path from AC power supply 101 to motor drive device 201b, and the voltage of motor drive device 201a is higher than the voltage of motor drive device 201b. Examples of when the impedance of cable 111a is smaller than the impedance of cable 111b include when cable 111a is thicker than cable 111b, when cable 111a is shorter than cable 111b, or when the mutual inductance in cable 111a is greater than the mutual inductance in cable 111b. The closer the wires of each phase are to each other, the greater the mutual inductance. In the following description, the distance between the wires of each phase in cable 111a or cable 111b is also referred to as the line-to-line distance. The length of cable 111a or cable 111b is also referred to as the cable length.

[0046] Furthermore, because the forward voltage of rectifier 22a is smaller than the forward voltage of rectifier 22b, the power propagating through motor drive device 201a is greater than the power propagating through motor drive device 201b. The forward voltages of rectifiers 22a and 22b are the voltage drop values ​​of rectifiers 22a and 22b. The losses of rectifiers 22a and 22b are determined by the current and the voltage drop. Furthermore, there may be variations in the forward voltages of rectifiers 22a and 22b due to individual differences.

[0047] 7 is a diagram illustrating the variation in the forward voltages of the rectifiers 22a and 22b included in the motor drive system 200 according to the first embodiment. Three curves 414, 415, and 416 are shown, each representing the relationship between the forward voltages of the rectifiers 22a and 22b and the currents flowing through the rectifiers 22a and 22b. In FIG. 7, the units of the forward voltages are "V" and the units of the currents are "A."

[0048] Curve 414 represents an example of the relationship between forward voltage and current when the forward voltage relative to the current is minimum. Curve 416 represents an example of the relationship between forward voltage and current when the forward voltage relative to the current is maximum. Curve 415 represents an example of the relationship between forward voltage and current when the forward voltage relative to the current is intermediate between the cases shown by curves 414 and 416. Differences can occur in the forward voltages of rectifiers 22a and 22b due to such individual differences.

[0049] Here, a specific calculation result of the current value in the fifth example will be described. Here, the cable length of the cable 111a is 0.1 m, and the cross-sectional area of ​​the cable 111a is 3.5 mm 2 The distance between the wires in the cable 111a is 10 mm. The length of the cable 111b is 1 m, and the cross-sectional area of ​​the cable 111b is 3.5 mm. 2 . Since the mutual inductance of the cable 111b is not taken into consideration, the distance between the wires of the cable 111b is assumed to be infinite. The forward voltages of the rectifiers 22a and 22b may vary depending on the individual differences between the rectifiers 22a and 22b or the amount of current through the rectifiers 22a and 22b. Here, the forward voltage of the rectifier 22a is assumed to be smaller than that of the curve 415 shown in FIG. 7, and the forward voltage of the rectifier 22b is assumed to be larger than that of the curve 415 shown in FIG. 7. Other conditions include the AC power supply 101 being a three-phase, 400V, 50Hz AC power supply. The output of each of the motors 100a and 100b is assumed to be 7kW. The efficiency of each of the motor driving devices 201a and 201b is assumed to be 86%. The efficiency of the motor driving devices 201a and 201b refers to the efficiency of converting DC voltage to AC voltage and driving the motors 100a and 100b.

[0050] If there is no connection via cable 62, the current flowing from AC power supply 101 to motor drive device 201a and the current flowing from AC power supply 101 to motor drive device 201b are equal, at 24.6 Arms. As described above, the forward voltages of rectifiers 22a and 22b are different. The loss in rectifier 22a is 23.7 W, and the loss in rectifier 22b is 42.3 W.

[0051] When there is a connection by the cable 62, the cable length of the cable 62 is 30 mm, and the cross-sectional area of ​​the cable 62 is 3.5 mm. 2 The line-to-line distance, which is the distance between the lines of each phase in cable 62, is 10 mm. When connected via cable 62, the current flowing from AC power supply 101 to motor drive device 201a is 47.9 Arms, and the current flowing from AC power supply 101 to motor drive device 201b is 4.2 Arms. Furthermore, the loss in rectifier 22a is 45.9 W, and the loss in rectifier 22b is 4.2 W.

[0052] In the above example, by connecting motor drive device 201a and motor drive device 201b via cable 62, the current flowing from AC power supply 101 to motor drive device 201a increases from 24.6 Arms when no such connection exists to 47.9 Arms. In other words, by connecting motor drive device 201a to motor drive device 201b, the current flowing from AC power supply 101 to motor drive device 201a becomes approximately 194% of the current when no such connection exists. Furthermore, the loss in rectifier 22a increases from 23.7 W to 45.9 W. In other words, by connecting motor drive device 201a to motor drive device 201b, the loss in rectifier 22a becomes approximately 193% of the current when no such connection exists.

[0053] On the other hand, by connecting motor drive device 201a and motor drive device 201b via cable 62, the current flowing from AC power supply 101 to motor drive device 201b is reduced to 4.2 Arms from 24.6 Arms when no connection is made. In other words, by connecting motor drive device 201b to motor drive device 201a, the current flowing from AC power supply 101 to motor drive device 201b is reduced to approximately 17% of the current when no connection is made. Furthermore, the loss in rectifier 22b is reduced from 42.3 W to 4.2 W. In other words, by connecting motor drive device 201b to motor drive device 201a, the loss in rectifier 22b is reduced to approximately 10% of the current when no connection is made.

[0054] In this way, in the fifth example, the connection between DC connection terminal portion 61a and DC connection terminal portion 61b by cable 62 may change the way current flows in each of motor drive devices 201a, 201b compared to when there is no connection by cable 62. The change in the way current flows affects the heat generation of components in each of motor drive devices 201a, 201b.

[0055] In motor drive system 200 according to the first embodiment, the impedance of each of the multiple connections is set within a predetermined tolerance range based on the bias condition of the current flowing through each motor drive device. Specifically, the impedance of cable 111a and the impedance of cable 111b are set within each other's tolerance range. As a result, in motor drive system 200, even if DC connection terminal 61a and DC connection terminal 61b are connected by cable 62, it is possible to reduce the bias of the current flowing through each of the multiple motor drive devices.

[0056] The condition for the imbalance of the current flowing through each motor drive device can also be said to be a condition that enables the supply of power to motors 100a, 100b by motor drive system 200. In the following description, the condition for the imbalance of the current flowing through each motor drive device is also referred to as the condition that is met.

[0057] Fig. 8 is a first diagram for explaining the allowable range of impedance of each of the cables 111a and 111b provided in the motor drive system 200 according to the first embodiment. Fig. 8 shows an example of the relationship between the impedance of the cable 111a and the impedance of the cable 111b. The vertical axis of the graph shown in Fig. 8 represents the impedance of the cable 111a. The horizontal axis of the graph shown in Fig. 8 represents the impedance of the cable 111b.

[0058] Here, the conditions for fulfillment are that the current flowing from the AC power supply 101 to each of the motor drive devices 201a, 201b is 45 Arms or less, and the loss of each of the rectifiers 22a, 22b is 45 W or less. The impedance of each of the cables 111a, 111b includes a resistance component and an inductance component. The inductance component varies depending on the frequency. Here, the impedance of each of the cables 111a, 111b is the impedance when the frequency is 300 Hz. 300 Hz is the fundamental frequency of the current when rectifying a three-phase AC power supply, and is six times the 50 Hz frequency of the AC power supply 101.

[0059] FIG. 8 shows an example of the allowable impedance range of each cable 111a, 111b when the forward voltage of one of the rectifiers 22a, 22b is known and the forward voltage of the other rectifier is assumed to vary. Two curves 417, 418 connecting some of the plots shown in FIG. 8 represent the boundaries of the allowable range. In FIG. 8, the hatched area between curves 417 and 418 represents the allowable impedance range of each cable 111a, 111b. Note that a dashed straight line 419 in FIG. 8 represents the relationship between the impedance of cable 111a and the impedance of cable 111b when the impedances of cable 111a and cable 111b are equal. The allowable range includes the impedances of each cable 111a, 111b when the impedances of cable 111a and cable 111b are equal.

[0060] Fig. 9 is a second diagram for explaining the allowable range of the impedance of each of the cables 111a and 111b provided in the motor drive system 200 according to the first embodiment. Fig. 9 shows an example of the relationship between the impedance of the cable 111a and the impedance of the cable 111b. The vertical axis of the graph shown in Fig. 9 represents the impedance of the cable 111a. The horizontal axis of the graph shown in Fig. 9 represents the impedance of the cable 111b.

[0061] 9 shows an example of the allowable range of impedance of each of the cables 111 a and 111 b when the forward voltage of each of the rectifiers 22 a and 22 b is unknown and there is assumed to be variation in the forward voltage of each of the rectifiers 22 a and 22 b. In reality, since the forward voltages of rectifiers available on the market are unknown, the allowable range is set assuming that there is variation in the forward voltage of each of the rectifiers 22 a and 22 b.

[0062] The circular plots in FIG. 9 are the same as those shown in FIG. 8 . The square plots in FIG. 9 are newly added plots that are not present in FIG. 8 . Two curves 420 and 421 connecting some of the plots shown in FIG. 9 each represent the boundaries of the allowable range. In FIG. 9 , the hatched area between the curves 420 and 421 represents the allowable range of the impedance of each of the cables 111 a and 111 b. Note that the dashed line 422 in FIG. 9 represents the relationship between the impedance of the cable 111 a and the impedance of the cable 111 b when the impedances of the cables 111 a and 111 b are equal to each other.

[0063] Because the forward voltages of rectifiers 22a and 22b are unknown, it is necessary that the conditions be satisfied even if motor drive device 201a and motor drive device 201b are swapped. Therefore, as shown in Figure 9, the allowable range is a region symmetrical about line 422. The impedance of each cable 111a and 111b can be set with a variation within a preset range, centered on the impedance when the relationship represented by line 422 is satisfied.

[0064] In the motor drive system 200, the impedance of each cable 111a, 111b is set within an allowable range, thereby reducing the imbalance in the current flowing through each motor drive device 201a, 201b, and enabling the motor drive system 200 to supply power to the motors 100a, 100b.

[0065] In the motor drive system 200, the impedances of the cables 111a and 111b may be set equal to each other, thereby further reducing the imbalance in the currents flowing through the motor drive devices 201a and 201b.

[0066] According to the first embodiment, motor drive system 200 can effectively utilize regenerative energy in each of motor drive devices 201a and 201b by interconnecting DC connection terminal 61a and DC connection terminal 61b. In motor drive system 200, the impedance of each of the multiple connections is set within a predetermined allowable range based on a condition for establishment. This reduces the imbalance in the current flowing through each of motor drive devices 201a and 201b, enabling motor drive system 200 to supply power to motors 100a and 100b. Even if each of motor drive devices 201a and 201b is configured to include converter units 2a and 2b and inverter units 4a and 4b, regenerative energy can be distributed between motor drive devices 201a and 201b without adding components for controlling the current between motor drive devices 201a and 201b. Because the number of parts in each of motor drive devices 201a, 201b does not need to be increased compared to when each of motor drive devices 201a, 201b is used alone, the configuration of each of motor drive devices 201a, 201b can be simplified and made compact. As a result, motor drive system 200 has the effect of being able to effectively utilize regenerative energy with a simple and compact configuration.

[0067] Embodiment 2 In embodiment 2, an example will be described in which the length of each of a plurality of connection parts in motor drive system 200 shown in Fig. 1 is set within a preset tolerance range based on the bias condition of the current flowing through each motor drive device. In embodiment 2, the cable length of cable 111a and the cable length of cable 111b are set within a preset tolerance range.

[0068] Fig. 10 is a first diagram for explaining the impedance characteristics of the cables 111a and 111b provided in the motor drive system 200 according to the second embodiment. The vertical axis of the graph shown in Fig. 10 represents the impedance of the cable 111a or the cable 111b. The horizontal axis of the graph shown in Fig. 10 represents the frequency. In Fig. 10, the unit of impedance is "mΩ" and the unit of frequency is "Hz."

[0069] Here, the cross-sectional area of ​​the cables 111a and 111b is set to 2 mm 2 Assume that the cable length of cables 111a and 111b is 1 m, and the distance between cables 111a and 111b is 50 mm. In FIG. 10 , dashed curve 423 represents the impedance of cable 111a or cable 111b. The impedance represented by curve 423 is a composite impedance that combines the resistance component of cable 111a and the inductance component of cable 111a. Alternatively, the impedance represented by curve 423 is a composite impedance that combines the resistance component of cable 111b and the inductance component of cable 111b. In FIG. 10 , solid line 424 represents the resistance component of cable 111a or cable 111b. In FIG. 10 , dotted line 425 represents the inductance component of cable 111a or cable 111b.

[0070] The resistance component represented by the line 424 is constant regardless of the frequency. The inductance component represented by the line 425 increases exponentially as the frequency increases. Therefore, the increase in the synthetic impedance represented by the curve 423 gradually increases as the frequency increases.

[0071] FIG. 11 is a second diagram for explaining the impedance characteristics of the cables 111a and 111b provided in the motor drive system 200 according to the second embodiment. FIG. 11 shows an example of the relationship between cable length and impedance when the frequency is 300 Hz. The vertical axis of the graph shown in FIG. 11 represents the impedance of the cable 111a or the cable 111b. The horizontal axis of the graph shown in FIG. 11 represents the cable length. In FIG. 11, the unit of impedance is "mΩ" and the unit of cable length is "m". Here, the cross-sectional area of ​​the cables 111a and 111b is set to 2 mm 2 The distance between the cables 111a and 111b is 50 mm.

[0072] In Fig. 11, dashed line 426 represents the impedance of cable 111a or cable 111b, i.e., the combined impedance of cable 111a or cable 111b. In Fig. 11, dashed line 427 represents the resistance component of cable 111a or cable 111b. In Fig. 11, dotted line 428 represents the inductance component of cable 111a or cable 111b.

[0073] As shown in FIG. 11, when the frequency is 300 Hz, the resistance component of the cables 111a and 111b is dominant in the composite impedance. In the example shown in FIG. 11, approximately 98% of the composite impedance is the resistance component. In the example shown in FIG. 11, the impedance of the cables 111a and 111b can be considered to be equivalent to the resistance component of the cables 111a and 111b. The resistance component of the cable is calculated by "resistivity of the cable material [Ω·m] × cable length [m] ÷ cross-sectional area of ​​the cable [m 2 Therefore, it can be said that the impedance of the cables 111a and 111b is proportional to the cable length.

[0074] Fig. 12 is a diagram illustrating the allowable range of impedance of each of the cables 111a and 111b provided in the motor drive system 200 according to the second embodiment. The vertical axis of the graph shown in Fig. 12 represents the cable length of the cable 111a. The horizontal axis of the graph shown in Fig. 12 represents the cable length of the cable 111b. In Fig. 12, the unit of cable length is "m." Because the impedance of the cables 111a and 111b is proportional to the cable length, the graph shown in Fig. 12 is the same as the graph shown in Fig. 9 except that the vertical axis and the horizontal axis each represent the cable length.

[0075] Here, the conditions for fulfillment are that the current flowing from AC power supply 101 to each of motor drive devices 201a, 201b is 45 Arms or less and the loss in each of rectifiers 22a, 22b is 45 W or less. Fig. 12 shows an example of the allowable range of impedance of each of cables 111a, 111b when the forward voltage of each of rectifiers 22a, 22b is unknown and there is variation in the forward voltage of each of rectifiers 22a, 22b.

[0076] Two curves 429 and 430 connecting some of the plots shown in Fig. 12 each represent the boundary of the allowable range. In Fig. 12, the hatched area between curves 429 and 430 represents the allowable range of the impedance of each of cables 111a and 111b. Note that in Fig. 12, a dashed straight line 431 represents the relationship between the impedance of cable 111a and the impedance of cable 111b when the lengths of cable 111a and cable 111b are equal to each other.

[0077] Because the forward voltages of rectifiers 22a and 22b are unknown, it is necessary that the conditions be satisfied even if motor drive device 201a and motor drive device 201b are swapped. For this reason, as shown in Figure 12, the allowable range is set to a region symmetrical about line 431. The cable lengths of cables 111a and 111b can be set with a variation within a preset range, centered on the cable length when the relationship represented by line 431 is satisfied.

[0078] In the motor drive system 200, the cable length of each cable 111a, 111b is set within an allowable range, thereby reducing the imbalance in the current flowing through each motor drive device 201a, 201b, and enabling the motor drive system 200 to supply power to the motors 100a, 100b.

[0079] In the motor drive system 200, the cables 111a and 111b may have the same cable length, which further reduces the imbalance in the current flowing through the motor drive devices 201a and 201b.

[0080] In the second embodiment, as in the first embodiment, the motor drive system 200 has a simple and compact configuration and can effectively utilize regenerative energy.

[0081] Embodiment 3 In embodiment 3, an example will be described in which a plurality of motor drive devices are connected to a DC power supply. In embodiment 3, the same components as those in embodiment 1 or 2 above will be assigned the same reference numerals, and the description will mainly focus on the configuration that differs from embodiment 1 or 2.

[0082] 13 is a diagram showing an example of the configuration of a motor drive system 300 according to a third embodiment. The motor drive system 300 includes a plurality of motor drive devices. Each of the plurality of motor drive devices drives a motor. The motor drive system 300 illustrated in the third embodiment includes two motor drive devices 301a and 301b. The motor drive device 301a drives the motor 100a. The motor drive device 301b drives the motor 100b.

[0083] The motor drive system 300 includes cables 112a, 112b, and 116, a relay unit 114, a DC power supply 115, and motor drive devices 301a and 301b. The relay unit 114 is connected to the DC power supply 115 via cable 116. The motor drive device 301a is connected to the relay unit 114 via cable 112a. The motor drive device 301b is connected to the relay unit 114 via cable 112b. Each of the cables 112a and 112b is a connection unit connected to the DC power supply 115, which is a power source, via the cable 116 and the relay unit 114. Each of the motor drive devices 301a and 301b, which are multiple motor drive devices, is connected to the DC power supply 115 via a connection unit. The motor drive devices 301a and 301b each drive the motors 100a and 100b using power supplied from the DC power supply 115. The connecting parts are not limited to cables 112a and 112b, and may be metal plates, etc. The relay part 114 may be connected to the DC power supply 115 by a metal plate, etc., instead of the cable 116. The cables 112a and 112b may be connected directly to the DC power supply 115 without going through the relay part 114 and the cable 116.

[0084] The motor drive device 301a includes a converter unit 2a, a regenerative resistor unit 3a, an inverter unit 4a, a control unit 5a, and a DC connection unit 6a. The converter unit 2a receives DC power supplied to the motor drive device 301a from a DC power supply 115. The converter unit 2a outputs the DC power. The converter unit 2a includes an AC input terminal unit 21a, a rectifier 22a, a smoothing capacitor 23a, and a DC input terminal unit 24a.

[0085] One end of the cable 112a is connected to the relay unit 114. The other end of the cable 112a is connected to the DC input terminal unit 24a. The DC input terminal unit 24a has a positive terminal and a negative terminal corresponding to the positive terminal and negative terminal of the DC power supply 115. The DC input terminal unit 24a outputs DC power. Because DC power is supplied to the motor drive device 301a, the converter unit 2a does not need to be equipped with the AC input terminal unit 21a and the rectifier 22a. The smoothing capacitor 23a smoothes the DC voltage output from the DC input terminal unit 24a.

[0086] The regenerative resistance unit 3a is a part that consumes regenerative energy supplied from the motor 100a to the motor drive device 301a. The regenerative resistance unit 3a includes a regenerative resistance 31a and a switch element 32a. The inverter unit 4a includes an inverter circuit 41a and an output terminal unit 42a. In FIG. 13, the inverter circuit 41a is composed of six semiconductor elements. Note that the number of semiconductor elements that make up the inverter circuit 41a is arbitrary. The control unit 5a includes a power supply circuit 51a and a control circuit 52a.

[0087] The DC connection unit 6a includes a DC connection terminal unit 61a. The DC connection terminal unit 61a includes a positive terminal P and a negative terminal N. The positive terminal P is connected to a positive portion of the DC voltage unit. The negative terminal N is connected to a negative portion of the DC voltage unit. The DC voltage unit is a portion where the voltage is DC voltage, and extends from the output terminal of the DC input terminal unit 24a to the input terminal of the inverter unit 4a. In the example shown in FIG. 13 , the positive terminal P and the negative terminal N are connected between the DC input terminal unit 24a and the smoothing capacitor 23a.

[0088] Motor drive device 301b includes converter unit 2b, regenerative resistor unit 3b, inverter unit 4b, control unit 5b, and DC connection unit 6b. Converter unit 2b receives DC power supplied to motor drive device 301b from DC power supply 115. Converter unit 2b outputs the DC power. Converter unit 2b includes AC input terminal unit 21b, rectifier 22b, smoothing capacitor 23b, and DC input terminal unit 24b.

[0089] One end of the cable 112b is connected to the relay unit 114. The other end of the cable 112b is connected to the AC input terminal unit 21b. Details of the converter unit 2b are the same as those of the converter unit 2a. Because DC power is supplied to the motor drive device 301b, the converter unit 2b does not need to be equipped with the AC input terminal unit 21b and the rectifier 22b.

[0090] The regenerative resistance unit 3b is connected between the converter unit 2b and the inverter unit 4b. The regenerative resistance unit 3b includes a regenerative resistor 31b and a switch element 32b. Details of the regenerative resistance unit 3b are the same as those of the regenerative resistance unit 3a. The inverter unit 4b includes an inverter circuit 41b and an output terminal unit 42b. Details of the inverter unit 4b are the same as those of the inverter unit 4a. The control unit 5b includes a power supply circuit 51b and a control circuit 52b. Details of the control unit 5b are the same as those of the control unit 5a. The DC connection unit 6b includes a DC connection terminal unit 61b. Details of the DC connection unit 6b are the same as those of the DC connection unit 6a.

[0091] Motor drive system 300 includes cable 62. DC connection terminal 61a of motor drive device 301a and DC connection terminal 61b of motor drive device 301b are connected to each other via cable 62. DC connection terminal 61a and DC connection terminal 61b may be connected to each other by a harness, a metal plate, a connector, or the like, instead of cable 62. In other words, motor drive devices 301a and 301b, which are multiple motor drive devices, are connected to each other via DC connection terminals 61a and 61b.

[0092] The number of motor drive devices included in motor drive system 300 is not limited to two and may be three or more. Each of the multiple motor drive devices included in motor drive system 300 is connected to DC power supply 115 via a connection portion, and drives a motor with power supplied from DC power supply 115. Each of the multiple motor drive devices has a configuration similar to that of motor drive devices 301a, 301b. The DC connection terminals of the motor drive devices included in the multiple motor drive devices are connected to each other by cables 62, harnesses, metal plates, connectors, or the like.

[0093] Next, we will explain the driving states of the motors 100a and 100b, and the paths and magnitudes of currents flowing through the motor drive system 300. Fig. 14 is a diagram for explaining a first example of the paths and magnitudes of currents in the motor drive system 300 according to the third embodiment. Fig. 14 shows a simplified configuration of the motor drive system 300.

[0094] In the first example shown in FIG. 14 , motor 100a is rotating and motor 100b is stopped. In the first example, current flows from DC power supply 115 to motor 100a via path 500. Path 500 passes through relay unit 114, cable 112a, converter unit 2a, and inverter unit 4a. Because DC connection terminal 61a and DC connection terminal 61b are connected, in the first example, path 501 also exists, through which current flows from DC power supply 115 to motor 100a via motor drive device 301b. Path 501 passes through relay unit 114, cable 112b, converter unit 2b, DC connection terminal 61b, DC connection terminal 61a, and inverter unit 4a.

[0095] In the first example, the current flowing through path 500 is greater than the current flowing through path 501. In FIG. 14 , the dashed arrow representing path 500 is made thicker than the dashed arrow representing path 501, thereby indicating that the current flowing through path 500 is greater than the current flowing through path 501. In this manner, in FIG. 14 , the magnitude relationship of the flowing currents is indicated by changing the thickness of the dashed arrows. In FIGS. 15 to 18 , the magnitude relationship of the currents for each path is indicated in the same manner as in FIG. 14 . Note that the magnitude of the current flowing through path 500 and the magnitude of the current flowing through path 501 each vary depending on the variations in the impedance of cable 112 a, cable 112 b, and cable 62, variations in the components within motor drive system 300, and the like.

[0096] Fig. 15 is a diagram illustrating a second example of the paths and magnitudes of currents in the motor drive system 300 according to the third embodiment. Fig. 15 shows a simplified configuration of the motor drive system 300. In the second example shown in Fig. 15, the motor 100a is in a rotating state, and the motor 100b is also in a rotating state.

[0097] In the second example, a current flows from the DC power supply 115 to the motor 100a via a path 502. The path 502 is the same as the path 500 shown in FIG. 14 . Because the DC connection terminal 61a and the DC connection terminal 61b are connected, in the second example, a path 503 also exists through which a current flows from the DC power supply 115 to the motor 100a via the motor drive device 301b. The path 503 is the same as the path 501 shown in FIG. 14 . In the second example, the current flowing through the path 502 is greater than the current flowing through the path 503. Note that the magnitude of the current flowing through the path 502 and the magnitude of the current flowing through the path 503 each vary depending on the variations in the impedance of the cables 112a, 112b, and 62, the variations in the components within the motor drive system 300, and the like.

[0098] In the second example, current flows from the DC power supply 115 to the motor 100b via a path 504. The path 504 passes through the relay unit 114, the cable 112b, the converter unit 2b, and the inverter unit 4b. Because the DC connection terminal unit 61a and the DC connection terminal unit 61b are connected, in the second example, a path 505 also exists in which current flows from the DC power supply 115 to the motor 100b via the motor drive device 301a. The path 505 passes through the relay unit 114, the cable 112a, the converter unit 2a, the DC connection terminal unit 61a, the DC connection terminal unit 61b, and the inverter unit 4b. In the second example, the current flowing through the path 504 is greater than the current flowing through the path 505. The magnitude of the current flowing through path 504 and the magnitude of the current flowing through path 505 each vary depending on the variations in the impedance of cables 112a, 112b, and 62, or variations in the components within motor drive system 300.

[0099] Fig. 16 is a diagram illustrating a third example of the current paths and magnitudes in motor drive system 300 according to the third embodiment. Fig. 16 shows a simplified configuration of motor drive system 300. In the third example shown in Fig. 16, motor 100a is in a rotating state, and motor 100b is in a regenerative state.

[0100] In the third example, current flows from DC power supply 115 to motor 100a via path 506. Path 506 is the same as path 500 shown in Fig. 14 . Because DC connection terminal 61a and DC connection terminal 61b are connected, in the third example, there is also path 507 through which current flows from DC power supply 115 to motor 100a via motor drive device 301b. Path 507 is the same as path 501 shown in Fig. 14 .

[0101] Furthermore, in the third example, regenerative power is generated in motor 100b, and thus there is also a path 508 through which current flows from motor 100b to motor 100a. Path 508 is a path that runs from motor 100b through inverter unit 4b, DC connection terminal unit 61b, DC connection terminal unit 61a, and inverter unit 4a. By consuming the regenerative power generated in motor 100b in motor 100a, motor drive system 300 can effectively utilize the regenerative power.

[0102] In the third example, the current flowing through path 506 is greater than the current flowing through path 507 and greater than the current flowing through path 508. Note that the magnitude of the current flowing through path 506, the magnitude of the current flowing through path 507, and the magnitude of the current flowing through path 508 each vary depending on the variation in the impedance of cable 112a, cable 112b, and cable 62, the variation in components within motor drive system 300, and the like.

[0103] Fig. 17 is a diagram illustrating a fourth example of the current paths and magnitudes in motor drive system 300 according to the third embodiment. Fig. 17 shows a simplified configuration of motor drive system 300. In the fourth example shown in Fig. 17, motor 100a is in a regenerative state, and motor 100b is also in a regenerative state.

[0104] In the fourth example, regenerative power is generated in the motor 100a, and a path 509 exists through which a current flows from the motor 100a to the inverter unit 4a. The current flowing through the path 509 reaches the regenerative resistance unit 3a, and the regenerative power generated in the motor 100a is consumed by the regenerative resistance unit 3a.

[0105] In the fourth example, regenerative power is generated in the motor 100b, and a path 510 exists through which a current flows from the motor 100b to the inverter unit 4b. The current flowing through the path 510 reaches the regenerative resistance unit 3b, and the regenerative power generated in the motor 100b is consumed by the regenerative resistance unit 3b. Note that the regenerative resistance units 3a and 3b are not shown in FIG. 17 .

[0106] 14 to 17, the current path and the magnitude of the current flowing through the path in motor drive system 300 change depending on the state of motors 100a, 100b. In the first example shown in Fig. 14 and the third example shown in Fig. 16, one motor is driven by motor drive system 300. In this case, the power that needs to be output from motor drive system 300 is the power required to drive one motor.

[0107] 15 , when two motors are driven by motor drive system 300, there is a possibility that power exceeding the power required to drive one motor may be transmitted through one motor drive device. For example, power may be biased toward one of motor drive devices 301a and 301b due to variations in the impedance of cables 112a, 112b, and 62, or variations in components within motor drive system 300. Such a power bias may cause power exceeding the power required to drive one motor to be transmitted through one of motor drive devices 301a and 301b.

[0108] Fig. 18 is a diagram illustrating a fifth example of the current paths and magnitudes in the motor drive system 300 according to the third embodiment. Fig. 18 shows a simplified configuration of the motor drive system 300. In the fifth example shown in Fig. 18, the motor 100a is in a rotating state, and the motor 100b is also in a rotating state.

[0109] In the fifth example, a path 511 of a current flowing to the motor 100a is the same as the path 502 shown in Fig. 15. In the fifth example, a path 512 of a current flowing to the motor 100b is the same as the path 505 shown in Fig. 15. In the fifth example, a path 513 of a current flowing to the motor 100b is the same as the path 504 shown in Fig. 15.

[0110] In the fifth example, a hypothetical case will be described in which the impedance of cable 112b is greater than the impedance of cable 112a. When the impedance of cable 112b is greater than the impedance of cable 112a, the current flowing through path 512 is greater than the current flowing through path 513, as shown in FIG. 18 . Because the current flowing through path 512 is greater than the current flowing through path 513, more power than is necessary to drive one motor is transmitted to motor drive device 301a. In other words, a power imbalance occurs between motor drive devices 301a and 301b, such that the power transmitted through motor drive device 301a is greater than the power transmitted through motor drive device 301b.

[0111] To enable the motor drive system 300 to supply power to the motors 100a and 100b even when such a power imbalance occurs, each motor drive device 301a and 301b must be designed to withstand the transmission of power greater than the power required to drive a single motor. Specifically, to ensure heat resistance or current resistance, measures such as increasing the size of the components of the converter units 2a and 2b or widening the wiring width on the wiring board are necessary. Alternatively, a larger chassis for heat dissipation may be required. Such measures will result in an increase in the size of the configuration of each motor drive device 301a and 301b.

[0112] The power propagating through motor drive device 301a is greater than the power propagating through motor drive device 301b when the impedance of the path from DC power supply 115 to motor drive device 301a is smaller than the impedance of the path from DC power supply 115 to motor drive device 301b and the voltage of motor drive device 301a is higher than the voltage of motor drive device 301b. Examples of when the impedance of cable 112a is smaller than the impedance of cable 112b include when cable 112a is thicker than cable 112b, when cable 112a is shorter than cable 112b, or when the mutual inductance in cable 112a is greater than the mutual inductance in cable 112b. The greater the distance between the line corresponding to the positive electrode of DC power supply 115 and the line corresponding to the negative electrode of DC power supply 115, the greater the mutual inductance. In the following description, the distance between the wire corresponding to the positive electrode and the wire corresponding to the negative electrode in the cable 112a or the cable 112b is also referred to as the “wire distance.” The length of the cable 112a or the cable 112b is also referred to as the “cable length.”

[0113] Here, a specific calculation result of the current value in the fifth example will be described. Here, the cable length of the cable 112a is 0.1 m, and the cross-sectional area of ​​the cable 112a is 3.5 mm 2 The distance between the wires in the cable 112a is 10 mm. The length of the cable 112b is 1 m, and the cross-sectional area of ​​the cable 112b is 3.5 mm. 2 , and the line-to-line distance in cable 112b is 1 m. Other conditions include a DC voltage of 400 V from DC power supply 115. The output of each of motors 100a and 100b is 7 kW. The efficiency of each of motor driving devices 301a and 301b is 86%. The efficiency of motor driving devices 301a and 301b refers to the efficiency of converting DC voltage to AC voltage and driving motors 100a and 100b.

[0114] If there is no connection via cable 62, the current flowing from DC power supply 115 to motor drive device 301a and the current flowing from DC power supply 115 to motor drive device 301b are equal to each other, 20.5 Arms.

[0115] When there is a connection by the cable 62, the cable length of the cable 62 is 30 mm, and the cross-sectional area of ​​the cable 62 is 3.5 mm. 2 The distance between the wires corresponding to the positive and negative electrodes in cable 62 is 10 mm. When connected via cable 62, the current flowing from DC power supply 115 to motor drive device 301a is 36.8 Arms, and the current flowing from DC power supply 115 to motor drive device 301b is 4.2 Arms.

[0116] In the above example, the current flowing from DC power supply 115 to motor drive device 301a increases to 36.8 Arms from 20.5 Arms when there is no connection due to the connection between motor drive device 301a and motor drive device 301b via cable 62. In other words, the current flowing from DC power supply 115 to motor drive device 301a becomes approximately 179% of the current when there is no connection due to the connection between motor drive device 301a and motor drive device 301b.

[0117] On the other hand, the connection between motor drive device 301a and motor drive device 301b via cable 62 reduces the current flowing from DC power supply 115 to motor drive device 301b from 20.5 Arms when there is no connection to 4.2 Arms. In other words, by connecting motor drive device 301b to motor drive device 301a, the current flowing from DC power supply 115 to motor drive device 301b becomes approximately 20% of the current when there is no connection.

[0118] In this way, in the fifth example, the connection between DC connection terminal portion 61a and DC connection terminal portion 61b by cable 62 may change the way current flows in each of motor drive devices 301a, 301b compared to when there is no connection by cable 62. The change in the way current flows affects the heat generation of components in each of motor drive devices 301a, 301b.

[0119] In the motor drive system 300 according to the third embodiment, the impedance of each of the multiple connections is set within a predetermined tolerance range based on the bias conditions of the current flowing through each of the motor drive devices. Specifically, the impedance of the cable 112a and the impedance of the cable 112b are set within each of their respective tolerance ranges. As a result, in the motor drive system 300, even if the DC connection terminal 61a and the DC connection terminal 61b are connected by the cable 62, the bias of the current flowing through each of the multiple motor drive devices can be reduced.

[0120] Fig. 19 is a diagram for explaining the allowable range of the impedance of each of the cables 112a and 112b provided in the motor drive system 300 according to the third embodiment. Fig. 19 shows an example of the relationship between the impedance of the cable 112a and the impedance of the cable 112b. The vertical axis of the graph shown in Fig. 19 represents the impedance of the cable 112a. The horizontal axis of the graph shown in Fig. 19 represents the impedance of the cable 112b.

[0121] Here, the condition for this to be met is that the current flowing from the DC power supply 115 to each of the motor drive devices 301a, 301b is 30 Arms or less. The impedance of each of the cables 112a, 112b includes a resistance component and an inductance component. The inductance component varies depending on the frequency. Here, since the power supply is the DC power supply 115, the impedance of each of the cables 112a, 112b is the impedance at a frequency of 1 Hz.

[0122] FIG. 19 shows an example of the allowable range of the impedance of each of the cables 112a and 112b. Two curves 514 and 515 connecting some of the plots shown in FIG. 19 each represent the boundary of the allowable range. In FIG. 19, the hatched area between the curves 514 and 515 represents the allowable range of the impedance of each of the cables 112a and 112b. Note that in FIG. 19, a dashed straight line 516 represents the relationship between the impedance of the cable 112a and the impedance of the cable 112b when the impedance of the cable 112a and the impedance of the cable 112b are equal to each other. The allowable range includes the impedance of each of the cables 112a and 112b when the impedance of the cable 112a and the impedance of the cable 112b are equal to each other.

[0123] 19, the tolerance range is a region symmetrical about the line 516. The impedance of each of the cables 112a and 112b can be set to vary within a preset range, with the impedance corresponding to the relationship represented by the line 516 at the center.

[0124] In the motor drive system 300, the impedance of each cable 112a, 112b is set within an allowable range, thereby reducing the imbalance in the current flowing through each motor drive device 301a, 301b, and enabling the motor drive system 300 to supply power to the motors 100a, 100b.

[0125] In the motor drive system 300, the impedances of the cables 112a and 112b may be set equal to each other, thereby further reducing the imbalance in the currents flowing through the motor drive devices 301a and 301b.

[0126] According to the third embodiment, motor drive system 300 can effectively utilize regenerative energy in each of motor drive devices 301a, 301b by connecting DC connection terminal 61a and DC connection terminal 61b to each other. In motor drive system 300, the impedance of each of the multiple connections is set within a predetermined allowable range based on a condition for establishment. This reduces the imbalance in the current flowing through each of motor drive devices 301a, 301b, allowing motor drive system 300 to successfully supply power to motors 100a, 100b. Even if each of motor drive devices 301a, 301b is configured to include converter units 2a, 2b and inverter units 4a, 4b, regenerative energy can be distributed between motor drive devices 301a, 301b without adding components for controlling the current between motor drive devices 301a, 301b. Because the number of parts in each of motor drive devices 301a, 301b does not need to be increased compared to when each of motor drive devices 301a, 301b is used alone, the configuration of each of motor drive devices 301a, 301b can be simplified and made compact. As a result, motor drive system 300 has the advantage of being able to effectively utilize regenerative energy with a simple and compact configuration.

[0127] Fourth Embodiment In a fourth embodiment, an example will be described in which the length of each of a plurality of connection parts is set within a preset tolerance range based on the bias condition of the current flowing through each motor drive device in a motor drive system 300 shown in Fig. 13. In the fourth embodiment, the cable length of cable 112a and the cable length of cable 112b are set within a preset tolerance range.

[0128] Fig. 20 is a first diagram for explaining the impedance characteristics of each of the cables 112a and 112b provided in the motor drive system 300 according to the fourth embodiment. The vertical axis of the graph shown in Fig. 20 represents the impedance of the cable 112a or the cable 112b. The horizontal axis of the graph shown in Fig. 20 represents the frequency. In Fig. 20, the unit of impedance is "mΩ" and the unit of frequency is "Hz."

[0129] Here, the cross-sectional area of ​​the cables 112a and 112b is set to 2 mm 2 Assume that the cable length of cables 112a and 112b is 1 m, and the distance between cables 112a and 112b is 50 mm. In FIG. 20 , dashed curve 517 represents the impedance of cable 112a or cable 112b. The impedance represented by curve 517 is a composite impedance that combines the resistance component of cable 112a and the inductance component of cable 112a. Alternatively, the impedance represented by curve 517 is a composite impedance that combines the resistance component of cable 112b and the inductance component of cable 112b. In FIG. 20 , solid line 518 represents the resistance component of cable 112a or cable 112b. In FIG. 20 , dotted line 519 represents the inductance component of cable 112a or cable 112b.

[0130] The resistance component represented by the straight line 518 is constant regardless of the frequency. The inductance component represented by the straight line 519 increases exponentially as the frequency increases. Therefore, the increase in the synthetic impedance represented by the curve 517 gradually increases as the frequency increases.

[0131] FIG. 21 is a second diagram for explaining the impedance characteristics of the cables 112a and 112b provided in the motor drive system 300 according to the fourth embodiment. FIG. 21 shows an example of the relationship between cable length and impedance when the frequency is 1 Hz. The vertical axis of the graph shown in FIG. 21 represents the impedance of the cable 112a or the cable 112b. The horizontal axis of the graph shown in FIG. 21 represents the cable length. In FIG. 21, the unit of impedance is "mΩ" and the unit of cable length is "m". Here, the cross-sectional area of ​​the cables 112a and 112b is set to 2 mm 2 The distance between the cables 112a and 112b is 50 mm.

[0132] In Fig. 21, dashed line 520 represents the impedance of cable 112a or cable 112b, i.e., the composite impedance of cable 112a or cable 112b. In Fig. 21, solid line 521 represents the resistance component of cable 112a or cable 112b. In Fig. 21, dotted line 522 represents the inductance component of cable 112a or cable 112b.

[0133] As shown in FIG. 20, when the frequency is 1 Hz, the resistance component of the cables 112a and 112b is dominant in the composite impedance. In the example shown in FIG. 21, the impedance of the cables 112a and 112b can be considered to be equivalent to the resistance component of the cables 112a and 112b. The resistance component of the cable is calculated by "resistivity of the cable material [Ω·m] × cable length [m] ÷ cross-sectional area of ​​the cable [m 2 Therefore, it can be said that the impedance of the cables 112a and 112b is proportional to the cable length.

[0134] Fig. 22 is a diagram illustrating the allowable range of impedance of each of the cables 112a and 112b included in the motor drive system 300 according to the fourth embodiment. The vertical axis of the graph shown in Fig. 22 represents the cable length of the cable 112a. The horizontal axis of the graph shown in Fig. 22 represents the cable length of the cable 112b. In Fig. 22, the unit of cable length is "m." Because the impedance of the cables 112a and 112b is proportional to the cable length, the graph shown in Fig. 22 is the same as the graph shown in Fig. 19 except that the vertical axis and the horizontal axis each represent the cable length.

[0135] Here, the condition to be met is that the current flowing from the DC power supply 115 to each of the motor drive devices 301a and 301b is 30 Arms or less. Fig. 22 shows an example of the allowable range of the impedance of each of the cables 112a and 112b.

[0136] Two curves 523 and 524 connecting some of the plots shown in Fig. 22 each represent the boundary of the allowable range. In Fig. 22, the hatched area between curves 523 and 524 represents the allowable range of the impedance of each of cables 112a and 112b. In Fig. 22, dashed line 525 represents the relationship between the impedance of cable 112a and the impedance of cable 112b when the lengths of cables 112a and 112b are equal.

[0137] 22, in order to ensure that the conditions for establishment are met even if motor drive device 301a and motor drive device 301b are swapped, the allowable range is set to a region symmetrical about line 525. The cable lengths of cables 112a and 112b can be set with a variation within a preset range, centered on the cable length when the relationship represented by line 525 is met.

[0138] In the motor drive system 300, the cable length of each cable 112a, 112b is set within the allowable range, thereby reducing the imbalance in the current flowing through each motor drive device 301a, 301b, and enabling the motor drive system 200 to supply power to the motors 100a, 100b.

[0139] In the motor drive system 300, the cables 112a and 112b may have the same cable length, which further reduces the imbalance in the current flowing through the motor drive devices 301a and 301b.

[0140] In the fourth embodiment, as in the third embodiment, the motor drive system 300 has a simple and compact configuration and can effectively utilize regenerative energy.

[0141] The configurations shown in the above embodiments are examples of the contents of the present disclosure. The configurations of each embodiment can be combined with other known technologies. The configurations of each embodiment can also be combined as appropriate. Part of the configuration of each embodiment can be omitted or modified without departing from the gist of the present disclosure.

[0142] 2a, 2b converter section, 3a, 3b regenerative resistor section, 4a, 4b inverter section, 5a, 5b control section, 6a, 6b DC connection section, 21a, 21b AC input terminal section, 22a, 22b rectifier, 23a, 23b smoothing capacitor, 24a, 24b DC input terminal section, 31a, 31b regenerative resistor, 32a, 32b switch element, 41a, 41b inverter circuit, 42a, 42b output terminal section, 51a, 51b power supply circuit, 52a, 52b control circuit, 61a, 61b DC connection terminal section, 62, 111a, 111b, 112a, 112b, 113, 116 cable, 100a, 100b motor, 101 AC power supply, 114 relay section, 115 DC power supply, 200, 300 Motor drive system, 201a, 201b, 301a, 301b Motor drive device, 400, 401, 402, 403, 404, 405, 406, 407, 408, 409, 410, 411, 412, 413, 500, 501, 502, 503, 504, 505, 506, 507, 508, 509, 510, 511, 512, 513 Path, 414, 415, 416, 417, 418, 420, 421, 423, 429, 430, 514, 515, 517, 523, 524 Curve, 419, 422, 424, 425, 426, 427, 428, 431, 516, 518, 519, 520, 521, 522, 525 Straight line, L1, L2, L3 terminal, N negative terminal, P positive terminal.

Claims

1. A motor drive system comprising: a plurality of connection parts connected to a power source; and a plurality of motor drive devices, each connected to the power source via the connection parts and driving a motor with power supplied from the power source, wherein each of the plurality of motor drive devices comprises: a converter unit that outputs DC power; an inverter unit that converts the DC power output by the converter unit into AC power and outputs the AC power to the motor, and outputs regenerative energy from the motor during regenerative operation of the motor; a regenerative resistance unit connected between the converter unit and the inverter unit; and a DC connection terminal unit that is connected to a DC voltage unit to which an applied voltage is a DC voltage, wherein the plurality of motor drive devices are connected to each other via each of the DC connection terminal units, and the impedance of each of the plurality of connection parts is set within a preset tolerance range based on bias conditions of current flowing through each of the motor drive devices.

2. The motor drive system according to claim 1, characterized in that the impedance of each of the multiple connection parts is set within an allowable range that is set around the impedance of each connection part when the impedances of each connection part are equal to each other.

3. The motor drive system according to claim 1, characterized in that the impedances of the multiple connection parts are equal to each other.

4. The motor drive system according to claim 1, characterized in that the length of each of the multiple connection parts is set within a preset tolerance range based on the bias conditions of the current flowing through each of the motor drive devices.

5. The motor drive system described in claim 1, characterized in that the length of each of the multiple connection parts is set within an allowable range that is set around the length of each of the connection parts when the lengths of the connection parts are equal to each other.

6. The motor drive system according to claim 1, wherein the lengths of the multiple connection parts are equal to each other.

7. The motor drive system according to any one of claims 1 to 6, characterized in that the multiple connection parts are connected to an AC power source which is the power source.

8. The motor drive system according to any one of claims 1 to 6, characterized in that the multiple connection parts are connected to a DC power supply which is the power supply.

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