Motor Drive System

Abstract

The motor drive system (200) includes a plurality of connection parts connected to a power source, and a plurality of motor drive devices (201a, 201b). Each of the plurality of motor drive devices (201a, 201b) includes a converter unit (2a, 2b), an inverter unit (4a, 4b) that outputs AC power to the motor (100a, 100b) and outputs regenerative energy from the motor (100a, 100b), a regenerative resistance unit (3a, 3b) connected between the converter unit (2a, 2b) and the inverter unit (4a, 4b), and a DC connection terminal unit (61a, 61b) connected to a DC voltage unit. 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 multiple connections is set within a preset allowable range based on the bias condition of the current flowing through each of the motor driving devices (201a, 201b).

Description

[Technical field]

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

[0002] When the motor is decelerated or stopped, regenerative energy generated in the motor is output from the motor to a motor drive device that drives the motor. In order to reduce the voltage rise in the motor drive device caused by the regenerative energy being supplied from the motor to the motor drive device, the motor drive device generally employs 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 a plurality of motor drive devices each having a rectifier circuit, a smoothing capacitor, and an inverter circuit. In each motor drive device, AC power supplied from an AC power source is converted to DC power in the rectifier circuit. This DC power is supplied to the inverter circuit via the smoothing capacitor. The DC voltage section of the motor drive device is connected to the DC voltage section of the other motor drive device via an inverse parallel circuit having a transistor and a diode. The DC voltage section is a section in which the applied voltage is a DC voltage, and is a section from the output terminal of the rectifier circuit to the input terminal of the inverter circuit. Regenerative energy supplied from the motor to the motor drive device is distributed to the other motor drive device via the smoothing capacitor. In the configuration disclosed in Patent Document 1, the current from one of the motor drive devices connected to each other is controlled by the transistor of each motor drive device. According to the technology of Patent Document 1, in the motor drive system, the regenerative energy supplied from the motor to the motor drive device is distributed to the other motor drive devices, thereby making it possible to effectively utilize the regenerative energy. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-248281 Summary of the Invention [Problem to be solved by the invention]

[0005] In the case of the motor drive system disclosed in the above Patent Document 1, in order to enable the distribution of regenerative energy between the motor drive devices, each motor drive device needs a component such as a transistor or a diode, which is a component for controlling the current between the motor drive devices. In the motor drive system disclosed in the above Patent Document 1, components that are not required when the motor drive device is used alone are added to each motor drive device, so the number of components in each motor drive device increases compared to when the motor drive device is used alone. The increase in the number of components makes the configuration of each motor drive device complex and large.

[0006] The present disclosure has been made in consideration of the above, and has an object to provide a motor drive system that is simple and compact in configuration and enables effective utilization of regenerative energy. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, the motor drive system according to the present disclosure includes a plurality of connection parts connected to a power source, and a plurality of motor drive devices each connected to the power source via a connection part and driving a motor by power supply 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 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 a voltage is applied that is a DC voltage. The DC connection terminal units of the plurality of motor drive devices are connected to each other by a cable, a harness, a metal plate, or a connector. The impedance of each of the plurality of connection parts is set within a preset allowable range based on the bias condition of the current flowing through each of the motor drive devices. The bias condition is a condition that enables power supply to a plurality of motors driven by a plurality of motor driving devices. Effect of the Invention

[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. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a configuration example of a motor drive system according to a first embodiment; [Diagram 2] FIG. 1 is a diagram for explaining a first example of a path and magnitude of a current in the motor drive system according to the first embodiment; [Diagram 3] FIG. 11 is a diagram for explaining a second example of a path and magnitude of a current in the motor drive system according to the first embodiment. [Figure 4] FIG. 11 is a diagram for explaining a third example of a path and magnitude of a current in the motor drive system according to the first embodiment. [Diagram 5] FIG. 11 is a diagram for explaining a fourth example of a path and magnitude of a current in the motor drive system according to the first embodiment. [Figure 6] FIG. 11 is a diagram for explaining a fifth example of a path and magnitude of a current in the motor drive system according to the first embodiment. [Figure 7] FIG. 1 is a diagram for explaining variations in forward voltage in a rectifier provided in the motor drive system according to the first embodiment; [Figure 8] FIG. 1 is a first diagram for explaining a tolerance range of impedance of each cable included in the motor drive system according to the first embodiment; [Figure 9] FIG. 2 is a second diagram for explaining the allowable range of impedance of each cable provided in the motor drive system according to the first embodiment; [Figure 10] FIG. 1 is a first diagram for explaining impedance characteristics of each cable provided in a motor drive system according to a second embodiment; [Figure 11] FIG. 2 is a second diagram for explaining impedance characteristics of each cable provided in the motor drive system according to the second embodiment; [Figure 12] FIG. 11 is a diagram for explaining the allowable range of impedance of each cable provided in the motor drive system according to the second embodiment. [Figure 13] FIG. 13 is a diagram showing a configuration example of a motor drive system according to a third embodiment; [Figure 14] FIG. 11 is a diagram for explaining a first example of a path and magnitude of a current in a motor drive system according to a third embodiment. [Figure 15] FIG. 13 is a diagram for explaining a second example of a path and magnitude of a current in the motor drive system according to the third embodiment. [Figure 16] FIG. 13 is a diagram for explaining a third example of a path and magnitude of a current in the motor drive system according to the third embodiment. [Figure 17] FIG. 11 is a diagram for explaining a fourth example of a path and magnitude of a current in the motor drive system according to the third embodiment. [Figure 18] FIG. 11 is a diagram for explaining a fifth example of a path and magnitude of a current in the motor drive system according to the third embodiment. [Figure 19] FIG. 11 is a diagram for explaining the allowable range of impedance of each cable provided in the motor drive system according to the third embodiment. [Figure 20] FIG. 1 is a first diagram for explaining impedance characteristics of each cable provided in a motor drive system according to a fourth embodiment; [Figure 21] FIG. 2 is a second diagram for explaining impedance characteristics of each cable provided in the motor drive system according to the fourth embodiment; [Figure 22] FIG. 13 is a diagram for explaining the allowable range of impedance of each cable provided in the motor drive system according to the fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0011] Embodiment 1 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 a motor 100a. The motor drive device 201b drives a 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 source 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 source 101, which is a power source, via the cable 113 and the relay unit 114. Each of the motor drive devices 201a and 201b, which are a plurality of motor drive devices, is connected to the AC power source 101 via a connection unit. Each of the motor drive devices 201a and 201b drives the motors 100a and 100b by power supply from the AC power source 101. The connection unit is 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 source 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 source 101 without going through the relay unit 114 and the cable 113.

[0013] The motor driving 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 driving device 201a from an AC power source 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 an element such as a diode or a thyristor. 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 part 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 making the switch element 32a conductive, the regenerative energy is consumed by the regenerative resistor 31a.

[0016] The inverter section 4a includes an inverter circuit 41a and an output terminal section 42a. The inverter circuit 41a is composed of a plurality of semiconductor elements. In FIG. 1, the inverter circuit 41a is composed of six semiconductor elements. Note that the number of semiconductor elements constituting the inverter circuit 41a is arbitrary. The inverter circuit 41a controls each of the plurality of semiconductor elements according to a control signal input from the control section 5a to the inverter circuit 41a.

[0017] The inverter circuit 41a controls each of the semiconductor elements according to a 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 source 101 into AC power of a desired frequency by 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. Note that the U-phase terminal, V-phase terminal, and W-phase terminal of the motor 100a are not shown in the drawings.

[0019] The control unit 5a includes a power supply circuit 51a and a control circuit 52a. The power supply circuit 51a generates 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 that 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 in which a voltage is applied as a DC voltage, and is a portion 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 driving 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 from an AC power source 101 to the motor driving device 201b 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 resistance 31b and a switch element 32b. The 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. The 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. The 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. The details of the DC connection unit 6b are the same as those of the DC connection unit 6a.

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

[0024] The number of motor drive devices provided in motor drive system 200 is not limited to two and may be three or more. Each of the multiple motor drive devices provided 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. DC connection terminal portions 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, a description will be given of the driving states of the motors 100a and 100b, and the path and magnitude of the current flowing through the motor drive system 200. Fig. 2 is a diagram for explaining a first example of the path and magnitude of the current in the motor drive system 200 according to the first embodiment. Fig. 2 shows a simplified configuration of the motor drive system 200.

[0026] Here, each of the motors 100a, 100b is assumed to have three states, which will be 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 decelerating 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, the motor 100a is rotating and the motor 100b is stopped. In the first example, a current flows from the AC power supply 101 to the motor 100a through a path 400. The path 400 passes through the relay unit 114, the cable 111a, the converter unit 2a, and the inverter unit 4a. Since the DC connection terminal unit 61a and the DC connection terminal unit 61b are connected to each other, in the first example, there is also a path 401 through which a current flows from the AC power supply 101 to the motor 100a through the motor drive device 201b. The path 401 passes through the relay unit 114, the cable 111b, the converter unit 2b, the DC connection terminal unit 61b, the DC connection terminal unit 61a, and the inverter unit 4a.

[0028] In the first example, the current flowing through the path 400 is larger than the current flowing through the path 401. In FIG. 2, the dashed arrow indicating the path 400 is made thicker than the dashed arrow indicating the path 401 to indicate that the current flowing through the path 400 is larger than the current flowing through the path 401. In this manner, the thickness of the dashed arrow is changed in FIG. 2 to indicate the magnitude relationship of the flowing current. In FIG. 3 to FIG. 6, the magnitude relationship of the current in each path is indicated in the same manner as in FIG. 2. Note that the magnitude of the current flowing through the path 400 and the magnitude of the current flowing through the path 401 each vary depending on the variation in the impedance of the cable 111a, the cable 111b, and the cable 62, or the variation of the components in the motor drive system 200. An example of the variation of the components is the individual difference of the rectifiers 22a and 22b.

[0029] Fig. 3 is a diagram for explaining a second example of the path and magnitude of a current 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 in a rotating state.

[0030] In the second example, a current flows from the AC power supply 101 to the motor 100a through a path 402. The path 402 is the same as the path 400 shown in FIG. 2. Since the DC connection terminal unit 61a and the DC connection terminal unit 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 through 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 variation in the impedance of the cable 111a, the cable 111b, and the cable 62, or the variation in the components in the motor drive system 200, etc.

[0031] In the second example, a current flows from the AC power supply 101 to the motor 100b through a path 404. The path 404 passes through the relay unit 114, the cable 111b, the converter unit 2b, and the inverter unit 4b. Since the DC connection terminal unit 61a and the DC connection terminal unit 61b are connected to each other, in the second example, a path 405 also exists through which a current flows from the AC power supply 101 to the motor 100b through the motor drive device 201a. The 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 the path 404 is larger than the current flowing through the 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 variation in impedance between cable 111a, cable 111b, and cable 62, or the variation in components within motor drive system 200, etc.

[0032] Fig. 4 is a diagram for explaining a third example of the path and magnitude of a current 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, a 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. Since the DC connection terminal unit 61a and the DC connection terminal unit 61b are connected to each other, in the third example, there is also a path 407 through which a current flows from the AC power supply 101 to the motor 100a via the motor driving device 201b. The path 407 is the same as the path 401 shown in Fig. 2.

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

[0035] In the third example, the current flowing through path 406 is larger than the current flowing through path 407 and is also larger 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 impedance of cable 111a, cable 111b, and cable 62, the variation in components within motor drive system 200, or the like.

[0036] Fig. 5 is a diagram for explaining a fourth example of the path and magnitude of a current 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 in a regenerative state.

[0037] In the fourth example, regenerative power is generated in the motor 100a, and thus a path 409 exists through which a current flows from the motor 100a to the inverter unit 4a. The current that flows through the path 409 reaches the regenerative resistance unit 3a, and the regenerative power generated in the motor 100a is consumed in 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 that flows through the path 410 reaches the regenerative resistance unit 3b, and the regenerative power generated in the motor 100b is consumed in 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 in motor drive system 200 and the magnitude of the current flowing through the path 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, power exceeding the power required to drive one motor may be transmitted through one motor drive device. For example, power may be biased to one of motor drive devices 201a and 201b due to variations in impedance between 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 for explaining a fifth example of the path and magnitude of a current 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 in a rotating state.

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

[0043] In the fifth example, a case will be described where the impedance of cable 111b is made larger than the impedance of cable 111a. When the impedance of cable 111b is larger than the impedance of cable 111a, as shown in FIG. 6, the current flowing through path 412 is larger than the current flowing through path 413. When the current flowing through path 412 is larger than the current flowing through path 413, power exceeding the power required to drive one motor is propagated to motor driving device 201a. In other words, a bias in power occurs between motor driving device 201a and motor driving device 201b such that the power propagating through motor driving device 201a is larger than the power propagating through motor driving device 201b.

[0044] In order to enable the motor drive system 200 to supply power to the motors 100a, 100b even if such a power imbalance occurs, it becomes necessary to design each of the motor drive devices 201a, 201b so that it can withstand the transmission of power greater than the power required to drive one motor. Specifically, in order to ensure heat resistance or current resistance, measures such as increasing the size of the components of the converter units 2a, 2b or expanding the wiring width on the wiring board are required. Alternatively, it becomes necessary to increase the size of the chassis for heat dissipation. Such measures will result in an increase in the size of the configuration of each of the motor drive devices 201a, 201b.

[0045] The power propagating through the motor driving device 201a is greater than the power propagating through the motor driving device 201b when the impedance of the path from the AC power source 101 to the motor driving device 201a is smaller than the impedance of the path from the AC power source 101 to the motor driving device 201b, and the voltage of the motor driving device 201a is higher than the voltage of the motor driving device 201b. Examples of the case where the impedance of the cable 111a is smaller than the impedance of the cable 111b include a case where the cable 111a is thicker than the cable 111b, a case where the cable 111a is shorter than the cable 111b, or a case where the mutual inductance in the cable 111a is greater than the mutual inductance in the 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 the cable 111a or the cable 111b is also referred to as the line-to-line distance. The length of the cable 111a or the cable 111b is also referred to as the cable length.

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

[0047] Fig. 7 is a diagram for explaining the variation in the forward voltage in the rectifiers 22a, 22b provided in the motor drive system 200 according to the first embodiment. Fig. 7 shows three curves 414, 415, and 416 that represent the relationship between the forward voltage of the rectifiers 22a, 22b and the current flowing through the rectifiers 22a, 22b. In Fig. 7, the unit of the forward voltage is "V", and the unit of the current is "A".

[0048] Curve 414 represents an example of the relationship between the forward voltage and the current in a case where the forward voltage relative to the current is minimum. Curve 416 represents an example of the relationship between the forward voltage and the current in a case where the forward voltage relative to the current is maximum. Curve 415 represents an example of the relationship between the forward voltage and the current in a case where the forward voltage relative to the current is intermediate between the case shown in curve 414 and the case shown in curve 416. Differences may 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, 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 In order not to take into account the mutual inductance of the cable 111b, the distance between the wires of the cable 111b is infinite. The forward voltages of the rectifiers 22a and 22b may vary depending on the individual differences of the rectifiers 22a and 22b, or the amount of current of the rectifiers 22a and 22b. Here, the forward voltage of the rectifier 22a is smaller than that of the curve 415 shown in FIG. 7, and the forward voltage of the rectifier 22b is larger than that of the curve 415 shown in FIG. 7. As other conditions, the AC power source 101 is a three-phase, 400V, and 50Hz AC power source. The output of each of the motors 100a and 100b is 7kW. The efficiency of each of the motor driving devices 201a and 201b is 86%. The efficiency of the motor driving devices 201a and 201b is the efficiency of converting a DC voltage into an AC voltage to drive the motors 100a and 100b.

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

[0051] In the case where a connection is made via a cable 62, the length of the cable 62 is set to 30 mm, and the cross-sectional area of ​​the cable 62 is set to 3.5 mm. 2 The line distance between the wires of each phase in cable 62 is 10 mm. When there is a connection via cable 62, the current flowing from AC power supply 101 to motor driving device 201a is 47.9 Arms, and the current flowing from AC power supply 101 to motor driving 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 driving device 201a and motor driving device 201b via cable 62, the current flowing from AC power source 101 to motor driving device 201a increases from 24.6 Arms when there is no connection to 47.9 Arms. That is, by connecting motor driving device 201a to motor driving device 201b, the current flowing from AC power source 101 to motor driving device 201a becomes approximately 194% of the current when there is no connection. Also, the loss of rectifier 22a increases from 23.7 W to 45.9 W. That is, by connecting motor driving device 201a to motor driving device 201b, the loss of rectifier 22a becomes approximately 193% of the current when there is no connection.

[0053] On the other hand, by connecting motor driving device 201a and motor driving device 201b via cable 62, the current flowing from AC power source 101 to motor driving device 201b is reduced from 24.6 Arms when there is no connection to 4.2 Arms. That is, by connecting motor driving device 201b to motor driving device 201a, the current flowing from AC power source 101 to motor driving device 201b is approximately 17% of the current flowing when there is no connection. Also, the loss of rectifier 22b is reduced from 42.3 W to 4.2 W. That is, by connecting motor driving device 201b to motor driving device 201a, the loss of rectifier 22b is approximately 10% of the current flowing when there is no connection.

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

[0055] In the motor drive system 200 according to the first embodiment, the impedance of each of the multiple connection parts is set within a preset allowable range based on the bias condition of the current flowing through each of the motor drive devices. Specifically, the impedance of the cable 111a and the impedance of the cable 111b are set within each allowable range. As a result, in the motor drive system 200, even if the DC connection terminal part 61a and the DC connection terminal part 61b are connected by the cable 62, the bias of the current flowing through each of the multiple motor drive devices can be reduced.

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

[0057] Fig. 8 is a first 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. 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 this to be met are that the current flowing from the AC power supply 101 to each of the motor driving 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 changes 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 frequency of 50 Hz of the AC power supply 101.

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

[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 the impedance of each of the cables 111a, 111b when the forward voltage of each of the rectifiers 22a, 22b is unknown and there is variation in the forward voltage of each of the rectifiers 22a, 22b. In reality, since the forward voltage of rectifiers available on the market is unknown, the allowable range is set assuming that there is variation in the forward voltage of each of the rectifiers 22a, 22b.

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

[0063] Since the forward voltages of the rectifiers 22a and 22b are unknown information, it is necessary that the conditions for establishment can be satisfied even if the motor driving device 201a and the motor driving device 201b are interchanged. Therefore, as shown in Fig. 9, the region of the allowable range is a region symmetrical with the straight line 422 as the center. The impedance of each of the cables 111a and 111b can be set with a variation within a preset range centered on the impedance when the relationship represented by the straight line 422 is satisfied.

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

[0065] In the motor driving system 200, the impedances of the cables 111a, 111b may be set to be equal to each other, thereby making it possible to further reduce the bias in the currents flowing through the motor driving devices 201a, 201b.

[0066] According to the first embodiment, the motor drive system 200 can effectively utilize regenerative energy in each of the motor drive devices 201a and 201b by connecting the DC connection terminal unit 61a and the DC connection terminal unit 61b to each other. In the motor drive system 200, the impedance of each of the multiple connection units is set within a preset allowable range based on the establishment condition. This reduces the bias of the current flowing through each of the motor drive devices 201a and 201b, and allows the motor drive system 200 to supply power to the motors 100a and 100b. Even if each of the motor drive devices 201a and 201b is configured to include the converter units 2a and 2b and the inverter units 4a and 4b, the regenerative energy can be distributed between the motor drive devices 201a and 201b without adding any components for controlling the current between the motor drive devices 201a and 201b. Since the number of parts of 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 an effect of being able to effectively utilize regenerative energy with a simple and compact configuration.

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

[0068] Fig. 10 is a first diagram for explaining the impedance characteristics of each of the cables 111a, 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 the cables 111a and 111b is 1 m, and the distance between the cables 111a and 111b is 50 mm. In FIG. 10, a dashed curve 423 represents the impedance of the cable 111a or the cable 111b. The impedance represented by the curve 423 is a composite impedance obtained by combining the resistance component of the cable 111a and the inductance component of the cable 111a. Alternatively, the impedance represented by the curve 423 is a composite impedance obtained by combining the resistance component of the cable 111b and the inductance component of the cable 111b. In FIG. 10, a solid straight line 424 represents the resistance component of the cable 111a or the cable 111b. In FIG. 10, a dotted straight line 425 represents the inductance component of the cable 111a or the cable 111b.

[0070] The resistance component represented by the straight line 424 is constant regardless of the frequency. The inductance component represented by the straight 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, 111b provided in the motor drive system 200 according to the second embodiment. FIG. 11 shows an example of the relationship between the cable length and the 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 areas of the cables 111a, 111b are assumed to be 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 composite 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, the resistance component accounts for approximately 98% of the composite impedance. 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] ÷ Cable cross-sectional area [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 for explaining the allowable range of impedance of each of the cables 111a, 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." Since the impedance of the cables 111a, 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 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. Fig. 12 shows an example of the allowable range of the impedance of each of the cables 111a, 111b in the case where the forward voltage of each of the rectifiers 22a, 22b is unknown and there is variation in the forward voltage of each of the rectifiers 22a, 22b.

[0076] Two curves 429, 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, 111b. In Fig. 12, 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] Since the forward voltages of the rectifiers 22a and 22b are unknown information, it is necessary that the conditions for establishment can be satisfied even if the motor driving device 201a and the motor driving device 201b are interchanged. For this reason, as shown in Fig. 12, the region of the allowable range is set to a region having a symmetric shape with the straight line 431 as the center. The cable lengths of the cables 111a and 111b can be set with a variation within a preset range centered on the cable length when the relationship represented by the straight line 431 is satisfied.

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

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

[0080] In the second embodiment, similarly to the first embodiment, the motor drive system 200 has a simple and compact configuration and provides the effect of being able to effectively utilize regenerative energy.

[0081] Embodiment 3 In the third embodiment, an example in which a plurality of motor drive devices are connected to a DC power supply will be described. In the third embodiment, the same components as those in the first or second embodiment are given the same reference numerals, and the configuration different from the first or second embodiment will be mainly described.

[0082] 13 is a diagram showing an example of a configuration of a motor driving system 300 according to a third embodiment. The motor driving system 300 includes a plurality of motor driving devices. Each of the plurality of motor driving devices drives a motor. The motor driving system 300 illustrated in the third embodiment includes two motor driving devices 301a and 301b. The motor driving device 301a drives the motor 100a. The motor driving 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 the cable 116. The motor drive device 301a is connected to the relay unit 114 via the cable 112a. The motor drive device 301b is connected to the relay unit 114 via the cable 112b. Each of the cables 112a and 112b is a connection unit connected to the DC power supply 115, which is a power supply, via the cable 116 and the relay unit 114. Each of the motor drive devices 301a and 301b, which are a plurality of motor drive devices, is connected to the DC power supply 115 via a connection unit. Each of the motor drive devices 301a and 301b drives the motors 100a and 100b by power supply from the DC power supply 115. The connection parts are not limited to the 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 directly connected to the DC power supply 115 without the relay part 114 and the cable 116.

[0084] The motor driving 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 from a DC power supply 115 to the motor driving device 301a. 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. Since DC power is supplied to the motor driving device 301a, the converter unit 2a does not need to be provided 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 portion 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 configured with six semiconductor elements. Note that the number of semiconductor elements that configure 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 side portion of the DC voltage unit. The negative terminal N is connected to a negative side portion of the DC voltage unit. The DC voltage unit is a portion in which the voltage is a DC voltage, and is a portion 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] The motor driving device 301b 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 receives DC power supplied from a DC power supply 115 to the motor driving device 301b. The converter unit 2b outputs the DC power. The converter unit 2b includes an AC input terminal unit 21b, a rectifier 22b, a smoothing capacitor 23b, and a 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 similar to those of the converter unit 2a. Since DC power is supplied to the motor driving device 301b, the converter unit 2b does not need to be provided 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 resistance 31b and a switch element 32b. The 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. The 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. The 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. The 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 portion 61a of motor drive device 301a and DC connection terminal portion 61b of motor drive device 301b are connected to each other via cable 62. DC connection terminal portion 61a and DC connection terminal portion 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 terminal portions 61a and 61b.

[0092] The number of motor drive devices provided in motor drive system 300 is not limited to two and may be three or more. Each of the multiple motor drive devices provided 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. DC connection terminal portions 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, a description will be given of the driving states of the motors 100a and 100b, and the path and magnitude of the current flowing through the motor drive system 300. Fig. 14 is a diagram for explaining a first example of the path and magnitude of the current 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, it is assumed that the motor 100a is rotating and the motor 100b is stopped. In the first example, a current flows from the DC power supply 115 to the motor 100a through a path 500. The path 500 is a path that passes through the relay unit 114, the cable 112a, the converter unit 2a, and the inverter unit 4a. Since the DC connection terminal unit 61a and the DC connection terminal unit 61b are connected, in the first example, there is also a path 501 through which a current flows from the DC power supply 115 to the motor 100a through the motor drive device 301b. The path 501 is a path that passes through the relay unit 114, the cable 112b, the converter unit 2b, the DC connection terminal unit 61b, the DC connection terminal unit 61a, and the inverter unit 4a.

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

[0096] Fig. 15 is a diagram for explaining a second example of the path and magnitude of a current in motor drive system 300 according to the third embodiment. Fig. 15 shows a simplified configuration of motor drive system 300. In the second example shown in Fig. 15, motor 100a is in a rotating state, and motor 100b is in a rotating state.

[0097] In the second example, a current flows from the DC power supply 115 to the motor 100a through a path 502. The path 502 is the same as the path 500 shown in FIG. 14. Since the DC connection terminal unit 61a and the DC connection terminal unit 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 through 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 larger 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 variation in the impedance of the cable 112a, the cable 112b, and the cable 62, or the variation in the components in the motor drive system 300, etc.

[0098] In the second example, a 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. Since the DC connection terminal unit 61a and the DC connection terminal unit 61b are connected, in the second example, a path 505 also exists through which a 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 larger 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 variation in impedance of cables 112a, 112b, and 62, or the variation in components within motor drive system 300, etc.

[0099] Fig. 16 is a diagram for explaining a third example of the path and magnitude of a current 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, a current flows from the DC power supply 115 to the motor 100a via a path 506. The path 506 is the same as the path 500 shown in Fig. 14. Since the DC connection terminal unit 61a and the DC connection terminal unit 61b are connected, in the third example, there is also a path 507 through which a current flows from the DC power supply 115 to the motor 100a via the motor driving device 301b. The path 507 is the same as the path 501 shown in Fig. 14.

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

[0102] In the third example, the current flowing through path 506 is larger than the current flowing through path 507 and is also larger 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 impedance of cable 112a, cable 112b, and cable 62, the variation in components within motor drive system 300, or the like.

[0103] Fig. 17 is a diagram for explaining a fourth example of the path and magnitude of a current 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 in a regenerative state.

[0104] In the fourth example, regenerative power is generated in the motor 100a, and thus a path 509 exists through which a current flows from the motor 100a to the inverter unit 4a. The current that flows through the path 509 reaches the regenerative resistance unit 3a, and the regenerative power generated in the motor 100a is consumed in 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 that flows through the path 510 reaches the regenerative resistance unit 3b, and the regenerative power generated in the motor 100b is consumed in the regenerative resistance unit 3b. Note that the regenerative resistance units 3a and 3b are not shown in FIG. 17.

[0106] As shown in Figures 14 to 17, the current path in motor drive system 300 and the magnitude of the current flowing through the path change depending on the state of motors 100a, 100b. In the first example shown in Figure 14 and the third example shown in Figure 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, power exceeding the power required to drive one motor may be transmitted through one motor drive device. For example, power may be biased to one of motor drive devices 301a and 301b due to variations in impedance between 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 for explaining a fifth example of the path and magnitude of a current in motor drive system 300 according to the third embodiment. Fig. 18 shows a simplified configuration of motor drive system 300. In the fifth example shown in Fig. 18, motor 100a is in a rotating state, and motor 100b is in a rotating state.

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

[0110] In the fifth example, a case will be described where the impedance of cable 112b is made larger than the impedance of cable 112a. When the impedance of cable 112b is larger than the impedance of cable 112a, as shown in FIG. 18, the current flowing through path 512 is larger than the current flowing through path 513. When the current flowing through path 512 is larger than the current flowing through path 513, power exceeding the power required to drive one motor is propagated to motor driving device 301a. That is, a power imbalance occurs between motor driving device 301a and motor driving device 301b such that the power propagating through motor driving device 301a is larger than the power propagating through motor driving device 301b.

[0111] In order to enable the motor drive system 300 to supply power to the motors 100a, 100b even if such a power imbalance occurs, it becomes necessary to design each of the motor drive devices 301a, 301b so that it can withstand the transmission of power greater than the power required to drive one motor. Specifically, in order to ensure heat resistance or current resistance, measures such as increasing the size of the components of the converter units 2a, 2b or expanding the wiring width on the wiring board are required. Alternatively, it becomes necessary to increase the size of the chassis for heat dissipation. Such measures will result in an increase in the size of the configuration of each of the motor drive devices 301a, 301b.

[0112] The power propagating through motor driving device 301a is greater than the power propagating through motor driving device 301b when the impedance of the path from DC power supply 115 to motor driving device 301a is smaller than the impedance of the path from DC power supply 115 to motor driving device 301b, and the voltage of motor driving device 301a is higher than the voltage of motor driving device 301b. Examples of the impedance of cable 112a being 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 pole of DC power supply 115 and the line corresponding to the negative pole of DC power supply 115, the greater the mutual inductance. In the following description, the distance between the line corresponding to the positive electrode and the line corresponding to the negative electrode in the cable 112a or the cable 112b is also referred to as the line distance, and 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, 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 distance in cable 112b is 1 m. Other conditions include a DC voltage of DC power supply 115 of 400 V. The output of each of motors 100a, 100b is 7 kW. The efficiency of each of motor driving devices 301a, 301b is 86%. The efficiency of motor driving devices 301a, 301b refers to the efficiency of converting DC voltage into AC voltage to drive motors 100a, 100b.

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

[0115] In the case where a connection is made via a cable 62, the length of the cable 62 is set to 30 mm, and the cross-sectional area of ​​the cable 62 is set to 3.5 mm. 2 The line distance between the line corresponding to the positive electrode and the line corresponding to the negative electrode in cable 62 is 10 mm. When there is a connection via cable 62, the current flowing from DC power supply 115 to motor driving device 301a is 36.8 Arms, and the current flowing from DC power supply 115 to motor driving device 301b is 4.2 Arms.

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

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

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

[0119] In the motor drive system 300 according to the third embodiment, the impedance of each of the multiple connection parts is set within a preset allowable range based on the bias condition 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 allowable range. As a result, in the motor drive system 300, even if the DC connection terminal part 61a and the DC connection terminal part 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, 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 is that the current flowing from the DC power supply 115 to each of the motor driving 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 changes 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 when the frequency is 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 show the boundary of the allowable range. In FIG. 19, the hatched area between the curves 514 and 515 shows the allowable range of the impedance of each of the cables 112a and 112b. In FIG. 19, a dashed straight line 516 shows 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 region of the tolerance is a region symmetrical about the line 516. The impedance of each of the cables 112a, 112b can be set with a variation within a preset range, centered on the impedance when the relationship represented by the line 516 is satisfied.

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

[0125] In the motor driving system 300, the impedances of the cables 112a, 112b may be set to be equal to each other, thereby making it possible to further reduce the bias of the currents flowing through the motor driving devices 301a, 301b.

[0126] According to the third embodiment, the motor drive system 300 can effectively utilize regenerative energy in each of the motor drive devices 301a and 301b by connecting the DC connection terminal unit 61a and the DC connection terminal unit 61b to each other. In the motor drive system 300, the impedance of each of the multiple connection units is set within a preset allowable range based on the establishment condition. This reduces the bias of the current flowing through each of the motor drive devices 301a and 301b, and enables the motor drive system 300 to supply power to the motors 100a and 100b. Even if each of the motor drive devices 301a and 301b is configured to include the converter units 2a and 2b and the inverter units 4a and 4b, the regenerative energy can be distributed between the motor drive devices 301a and 301b without adding any components for controlling the current between the motor drive devices 301a and 301b. Since the number of parts of 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 an effect of being able to effectively utilize regenerative energy with a simple and compact configuration.

[0127] Embodiment 4 In the fourth embodiment, an example will be described in which the length of each of a plurality of connection parts is set within a preset allowable range based on bias conditions of current flowing through each motor drive device in 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 allowable range.

[0128] Fig. 20 is a first diagram for explaining the impedance characteristics of each of the cables 112a, 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 the cables 112a and 112b is 1 m, and the distance between the cables 112a and 112b is 50 mm. In FIG. 20, a dashed curve 517 represents the impedance of the cable 112a or the cable 112b. The impedance represented by the curve 517 is a composite impedance obtained by combining the resistance component of the cable 112a and the inductance component of the cable 112a. Alternatively, the impedance represented by the curve 517 is a composite impedance obtained by combining the resistance component of the cable 112b and the inductance component of the cable 112b. In FIG. 20, a solid straight line 518 represents the resistance component of the cable 112a or the cable 112b. In FIG. 20, a dotted straight line 519 represents the inductance component of the cable 112a or the 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, 112b provided in the motor drive system 300 according to the fourth embodiment. FIG. 21 shows an example of the relationship between the cable length and the 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, 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 composite impedance is dominated by the resistance components of the cables 112a and 112b. In the example shown in FIG. 21, the impedances of the cables 112a and 112b can be considered to be equivalent to the resistance components 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 for explaining the allowable range of impedance of each of the cables 112a, 112b provided 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". Since the impedance of the cables 112a, 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 driving devices 301a, 301b is 30 Arms or less. Fig. 22 shows an example of the allowable range of the impedance of each of the cables 112a, 112b.

[0136] Two curves 523, 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, 112b. In Fig. 22, dashed straight line 525 represents the relationship between the impedance of cable 112a and the impedance of cable 112b when the lengths of cable 112a and cable 112b are equal to each other.

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

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

[0139] In the motor driving system 300, the cables 112a, 112b may have the same cable length, which can further reduce the bias in the current flowing through the motor driving devices 301a, 301b.

[0140] In the fourth embodiment, similarly to the third embodiment, the motor drive system 300 has a simple and compact configuration and provides the effect of being able to 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 be appropriately combined. A part of the configuration of each embodiment can be omitted or modified without departing from the gist of the present disclosure. [Explanation of symbols]

[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 plurality of connections connected to a power source; a plurality of motor drive devices each connected to the power source via the connection portion and configured to drive a motor by power supply from the power source; Each of the plurality of motor driving devices A converter unit that outputs DC power; an inverter unit that converts the DC power output by the converter unit into AC power, outputs the AC power to the motor, and outputs regenerative energy from the motor during a regenerative operation of the motor; a regenerative resistor connected between the converter and the inverter; A DC connection terminal portion connected to a DC voltage portion to which a voltage is applied is a DC voltage; the DC connection terminal portions of the plurality of motor drive devices are connected to each other by a cable, a harness, a metal plate, or a connector; the impedance of each of the plurality of connection parts is set within a preset allowable range based on a bias condition of a current flowing through each of the motor drive devices; The bias condition is a condition for establishing power supply to the plurality of motors driven by the plurality of motor drive devices. A motor drive system comprising:

2. No components are used to control the current between the multiple motor drivers.

2. The motor drive system according to claim 1 .

3. The impedance of each of the plurality of connections is set so that regenerative energy is distributed to the plurality of motor driving devices without controlling current between the plurality of motor driving devices.

2. The motor drive system according to claim 1 .

4. The impedance of each of the plurality of connection parts is set within a tolerance range that is set around the impedance of each of the connection parts when the impedances of the connection parts are equal to each other.

2. The motor drive system according to claim 1 .

5. The impedances of the multiple connection parts are equal to each other.

2. The motor drive system according to claim 1 .

6. The length of each of the plurality of connection parts is set within a preset tolerance range based on the bias condition of the current flowing through each of the motor drive devices.

2. The motor drive system according to claim 1 .

7. The length of each of the plurality of connection parts is set within a tolerance 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.

2. The motor drive system according to claim 1 .

8. The lengths of the plurality of connecting portions are equal to each other.

2. The motor drive system according to claim 1 .

9. The plurality of connection parts are connected to an AC power source which is the power source.

9. The motor drive system according to claim 1, wherein the motor drive system comprises:

10. The plurality of connection parts are connected to a DC power source which is the power source.

9. The motor drive system according to claim 1, wherein the motor drive system comprises:

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