Motor drive unit

Abstract

This motor drive device that drives a motor using three-phase alternating current as a power source comprises: a rectifier circuit that rectifies the three-phase alternating current; a current detection circuit that detects DC current rectified by the rectifier circuit; and a crosspoint detection circuit that detects the crosspoint between the current detected by the current detection circuit and a prescribed current value, and outputs a control signal indicating whether to drive the motor based on the detection result.

Description

[Technical Field]

[0001] The present disclosure relates to a motor drive device that drives a motor. [Background technology]

[0002] BACKGROUND ART Conventionally, motor driving devices that use three-phase AC as a power source are known (see, for example, Patent Document 1).

[0003] When a three-phase AC power source has a missing phase, the motor drive device may not be able to drive the motor normally if the load on the motor being driven is relatively large.

[0004] For this reason, if there is a possibility that the motor cannot be driven normally due to a missing phase in the three-phase AC that serves as the power source, it is desirable not to drive the motor. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-116186 Summary of the Invention

[0006] Therefore, the present disclosure aims to provide a motor drive device that can output a control signal to prevent a motor from being driven when there is a possibility that the motor cannot be driven normally due to a missing phase in the three-phase AC that serves as the power source.

[0007] A motor drive device according to one aspect of the present disclosure is a motor drive device that drives a motor using three-phase AC as a power source, and includes a rectifier circuit that rectifies the three-phase AC, a current detection circuit that detects the DC current rectified by the rectifier circuit, and a crosspoint detection circuit that detects a crosspoint between the current detected by the current detection circuit and a predetermined current value, and outputs a control signal indicating whether or not to drive the motor based on the detection result.

[0008] This provides a motor drive device that can output a control signal to prevent the motor from being driven when there is a possibility that the motor cannot be driven normally due to a missing phase in the three-phase AC that serves as the power source. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram showing the configuration of a motor drive system according to the first embodiment. [Figure 2A] FIG. 2A is a waveform diagram showing a voltage waveform in a low load state when there is no missing phase in the three-phase AC. [Figure 2B] FIG. 2B is a waveform diagram showing a voltage waveform in a high load state when there is no missing phase in the three-phase AC. [Figure 2C] FIG. 2C is a waveform diagram showing a voltage waveform in a low load state when there is a missing phase in the three-phase AC. [Figure 2D] FIG. 2D is a waveform diagram showing a voltage waveform in a high load state when there is a missing phase in the three-phase AC. [Figure 3A] FIG. 3A is a waveform diagram showing current waveforms and the number of times cross points are detected in a low load state when there is no missing phase in the three-phase AC. [Figure 3B] FIG. 3B is a waveform diagram showing the current waveform and the number of times cross points are detected when there is no missing phase in the three-phase AC and the load is high. [Figure 3C] FIG. 3C is a waveform diagram showing current waveforms and the number of times cross points are detected in a low load state when there is a missing phase in the three-phase AC. [Figure 3D] FIG. 3D is a waveform diagram showing the current waveform and the number of times cross points are detected when there is a missing phase in the three-phase AC and the load is high. [Figure 4] FIG. 4 is a flowchart showing the motor stop processing. [Figure 5]FIG. 5 is a block diagram showing the configuration of a motor drive system according to the second embodiment. [Figure 6] FIG. 6 is a block diagram showing the configuration of a motor drive system according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] A specific example of a motor control device according to one aspect of the present disclosure will be described below with reference to the drawings. Each of the embodiments shown here represents one specific example of the present disclosure. Therefore, the numerical values, shapes, components, arrangement and connection of the components, steps (processes), and order of steps shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, each drawing is a schematic diagram and is not necessarily a precise illustration.

[0011] In addition, the comprehensive or specific aspects of the present disclosure may be realized as a system, a method, an integrated circuit, a computer program, or a recording medium such as a computer-readable CD-ROM (Compact Disc Read Only Memory), or may be realized as any combination of a system, a method, an integrated circuit, a computer program, and a recording medium.

[0012] (Embodiment 1) FIG. 1 is a block diagram showing the configuration of a motor drive system 1 according to the first embodiment.

[0013] As shown in FIG. 1, the motor drive system 1 includes a motor drive device 10, a three-phase AC power supply 20, a motor 30, and a display device 40.

[0014] The motor 30 is driven by a motor driving device 10 .

[0015] The three-phase AC power supply 20 supplies the motor drive device 10 with a three-phase AC current consisting of an L1 phase, an L2 phase, and an L3 phase.

[0016] Display device 40 displays an image based on a control signal (described later) output from motor drive device 10.

[0017] The motor drive device 10 uses three-phase AC power supplied from a three-phase AC power supply 20 as a power source to drive a motor 30 .

[0018] As shown in FIG. 1, the motor driving device 10 includes a rectifier circuit 11, a current detection circuit 12, a cross-point detection circuit 13, an inverter 14, and a smoothing circuit 15.

[0019] The rectifier circuit 11 rectifies the three-phase AC supplied from the three-phase AC power supply 20. Hereinafter, the DC rectified by the rectifier circuit 11 and before being smoothed by the smoothing circuit 15 described next will also be referred to as "unsmoothed DC."

[0020] The smoothing circuit 15 is supplied with the unsmoothed DC rectified by the rectifier circuit 11 and smoothes the supplied unsmoothed DC. Hereinafter, the DC smoothed by the smoothing circuit 15 is also referred to as "smoothed DC."

[0021] The inverter 14 is supplied with the smoothed DC that has been smoothed by the smoothing circuit 15, and drives the motor 30. More specifically, the inverter 14 converts the supplied smoothed DC into three-phase AC, and supplies the converted three-phase AC to the motor 30, thereby driving the motor 30.

[0022] When the load on the motor 30 increases, the three-phase AC power supplied from the inverter 14 to the motor 30 increases, which increases the voltage drop of the smoothed DC supplied to the inverter 14.

[0023] When inverter 14 is converting smoothed DC into three-phase AC, if a control signal (described later) instructing motor 30 not to be driven is input from crosspoint detection circuit 13, inverter 14 stops the conversion into three-phase AC.

[0024] When the inverter 14 stops conversion to three-phase AC, and receives a control signal (described later) from the crosspoint detection circuit 13 to drive the motor 30, the inverter 14 starts conversion to three-phase AC.

[0025] 2A and 2B are waveform diagrams showing voltage waveforms in a low load state when there is no missing phase in the three-phase AC, and in a high load state when there is no missing phase in the three-phase AC.

[0026] 2A is a waveform diagram showing a state in which a relatively small load is applied to the motor 30, such that the voltage of the smoothed DC current drops only to a level equal to or higher than the minimum voltage of the unsmoothed DC current, when there is no missing phase in the three-phase AC input to the rectifier circuit 11 (hereinafter also referred to as a "low load state") . Fig. 2B is a waveform diagram showing a state in which a relatively large load is applied to the motor 30, such that the voltage of the smoothed DC current drops to a level lower than the minimum voltage of the unsmoothed DC current, when there is no missing phase in the three-phase AC input to the rectifier circuit 11 (hereinafter also referred to as a "high load state").

[0027] 2C and 2D are waveform diagrams showing voltage waveforms in a low load state when there is a missing phase in the three-phase AC, and in a high load state when there is a missing phase in the three-phase AC.

[0028] 2A, 2B, 2C, and 2D, the vertical axis represents voltage and the horizontal axis represents time. L1-L2, L2-L3, and L3-L1 represent the voltage difference between the L1 phase and the L2 phase, the voltage difference between the L2 phase and the L3 phase, and the voltage difference between the L3 phase and the L1 phase, respectively. Vrec is the unsmoothed DC voltage rectified by the rectifier circuit 11. Vpn is the smoothed DC voltage smoothed by the smoothing circuit 15.

[0029] Returning to FIG. 1, the description of motor driving device 10 will continue.

[0030] The current detection circuit 12 detects the unsmoothed DC current rectified by the rectifier circuit 11 .

[0031] The crosspoint detection circuit 13 detects a crosspoint between the current detected by the current detection circuit 12 and a predetermined current value (here, the predetermined current value is set to 0 [A]). A crosspoint refers to a state where the current detected by the current detection circuit 12 and the predetermined current value are the same value. Here, the crosspoint detection circuit 13 detects a crosspoint by detecting a change point where the current detected by the current detection circuit 12 changes from a state where the current is equal to or less than the predetermined current value to a state where the current is greater than the predetermined current value.

[0032] Furthermore, based on the detection result of the crosspoints, the crosspoint detection circuit 13 outputs a drive signal indicating whether or not to drive the motor 30. More specifically, the crosspoint detection circuit 13 (1) outputs a control signal indicating that the motor 30 should not be driven when the number of crosspoints detected in one cycle of the three-phase AC input to the rectifier circuit 11 is two, and (2) outputs a control signal indicating that the motor 30 should be driven when the number of crosspoints detected in one cycle of the three-phase AC input to the rectifier circuit 11 is zero or six. The reason why the crosspoint detection circuit 13 outputs the drive signal in this manner is that if there is a missing phase in the three-phase AC input to the rectifier circuit 11, the number of crosspoints detected by the crosspoint detection circuit 13 in one cycle of the three-phase AC input to the rectifier circuit 11 will be two, and if there is no missing phase in the three-phase AC input to the rectifier circuit 11, the number of crosspoints detected by the crosspoint detection circuit 13 in one cycle of the three-phase AC input to the rectifier circuit 11 will be zero or six. In other words, if there is a missing phase in the three-phase AC input to the rectifier circuit 11, the crosspoint detection circuit 13 outputs a control signal indicating that the motor 30 should not be driven, and if there is no missing phase in the three-phase AC input to the rectifier circuit 11, the crosspoint detection circuit 13 outputs a control signal indicating that the motor 30 should be driven.

[0033] Below, we will explain with reference to the drawings why, when there is a missing phase in the three-phase AC input to the rectifier circuit 11, the number of crosspoints detected by the crosspoint detection circuit 13 in one cycle of the three-phase AC input to the rectifier circuit 11 will be two, and when there is no missing phase in the three-phase AC input to the rectifier circuit 11, the number of crosspoints detected by the crosspoint detection circuit 13 in one cycle of the three-phase AC input to the rectifier circuit 11 will be zero or six.

[0034] 3A and 3B are waveform diagrams showing current waveforms and the number of cross-point detections in a low-load state when there is no missing phase in the three-phase AC, and in a high-load state when there is no missing phase in the three-phase AC.

[0035] 3C and 3D are waveform diagrams showing current waveforms and the number of crossing points detected under low load conditions when there is a missing phase in the three-phase AC, and the number of crossing points detected under high load conditions when there is a missing phase in the three-phase AC.

[0036] As shown in Fig. 2A, when the load on motor 30 is low and there is no missing phase in the three-phase AC input to rectifier circuit 11, the voltage of the smoothed DC does not drop below the minimum voltage of the unsmoothed DC. Therefore, as shown in Fig. 3A, the current flowing from rectifier circuit 11 to smoothing circuit 15, i.e., the current detected by current detection circuit 12, has a current value of 0 [A] six times during one cycle of the three-phase AC input to rectifier circuit 11. Therefore, as shown in Fig. 3A, crosspoint detection circuit 13 detects crosspoints six times during one cycle of the three-phase AC input to rectifier circuit 11.

[0037] As shown in Fig. 2B, when the load on motor 30 is high and there is no missing phase in the three-phase AC input to rectifier circuit 11, a voltage drop occurs until the voltage of the smoothed DC becomes lower than the minimum voltage of the unsmoothed DC. Therefore, as shown in Fig. 3B, the current flowing from rectifier circuit 11 to smoothing circuit 15, i.e., the current detected by current detection circuit 12, never reaches 0 [A] during one cycle of the three-phase AC input to rectifier circuit 11. Therefore, as shown in Fig. 3B, crosspoint detection circuit 13 detects zero crosspoints during one cycle of the three-phase AC input to rectifier circuit 11.

[0038] In this way, when there is no missing phase in the three-phase AC input to the rectifier circuit 11, the crosspoint detection circuit 13 will always detect zero or six crosspoints in one cycle of the three-phase AC input to the rectifier circuit 11.

[0039] As shown in Figures 2C and 2D, when there is a missing phase in the three-phase AC input to the rectifier circuit 11, the voltage of the smoothed DC drops to 0 [V], both when the load on the motor 30 is low and when the load on the motor 30 is high. Therefore, as shown in Figures 3C and 3D, the current flowing from the rectifier circuit 11 to the smoothing circuit 15, i.e., the current detected by the current detection circuit 12, always becomes 0 [A] twice during one cycle of the three-phase AC input to the rectifier circuit 11. Therefore, as shown in Figures 3C and 3D, the crosspoint detection circuit 13 always detects two crosspoints during one cycle of the three-phase AC input to the rectifier circuit 11.

[0040] The motor stopping process performed by the motor drive system 1 having the above configuration will now be described.

[0041] The motor stop process is a process for stopping the driving of the motor 30 when a phase loss occurs in the three-phase AC supplied from the three-phase AC power supply 20 while the motor drive device 10 is driving the motor 30.

[0042] The motor stop process is started, for example, when the motor drive device 10 starts driving the motor 30.

[0043] FIG. 4 is a flowchart showing the motor stop processing.

[0044] When the motor stop process is started, the cross point detection circuit 13 checks whether the number of cross points detected in one cycle of the three-phase AC input to the rectifier circuit 11 is two or not (step S10).

[0045] In the process of step S10, if the number of times the cross point has been detected is not two (No in step S10), the cross point detection circuit 13 returns to the process of step S10 and repeats the process of step S10.

[0046] In the process of step S10, if the number of times the cross point is detected is two (Yes in step S10), the cross point detection circuit 13 outputs a control signal to the effect that the motor 30 is not driven (step S20).

[0047] When the control signal to not drive the motor 30 is output, the inverter 14 stops converting the smoothed DC into a three-phase AC to be supplied to the motor 30 (step S30).

[0048] When the conversion to three-phase AC to be supplied to the motor 30 is stopped, the motor 30 stops (step S40).

[0049] Furthermore, when a control signal indicating that the motor 30 is not to be driven is output, the display device 40 displays a message indicating that the motor 30 is to be stopped because there is a missing phase in the three-phase AC input to the rectifier circuit 11 (step S50).

[0050] When the process of step S50 is completed, the motor drive system 1 ends its motor stop process.

[0051] <Consideration> As described above, motor drive device 10 outputs a control signal not to drive motor 30 when there is a missing phase in the three-phase AC input to rectifier circuit 11. In this way, motor drive device 10 configured as described above can output a control signal not to drive motor 30 when there is a possibility that motor 30 cannot be driven normally due to a missing phase in the three-phase AC that serves as the power source.

[0052] (Embodiment 2) A motor drive device according to a second embodiment, which is configured by partially modifying motor drive device 10 according to the first embodiment, will be described below.

[0053] In the following, for the motor drive device according to embodiment 2, components that are similar to those of motor drive device 10 will be assigned the same symbols as those that have already been explained, and detailed explanations will be omitted. The explanation will focus on the differences from motor drive device 10.

[0054] FIG. 5 is a block diagram showing the configuration of a motor drive system 1A according to the second embodiment.

[0055] 5, motor drive system 1A is configured by replacing motor drive device 10 of motor drive system 1 according to embodiment 1 with motor drive device 10A. Motor drive device 10A is configured by replacing crosspoint detection circuit 13 of motor drive device 10 with crosspoint detection circuit 13A.

[0056] The crosspoint detection circuit 13 according to the first embodiment is configured such that the predetermined current value is set to 0 [A]. In contrast, the crosspoint detection circuit 13A is configured such that the predetermined current value is set to a positive value X [A]. Here, the positive predetermined current value X [A] is the maximum value of the current flowing from the rectifier circuit 11 to the smoothing circuit 15 when the load on the motor 30 is such that the motor 30 can be driven normally even if there is an open phase in the three-phase AC input to the rectifier circuit 11. As a result, the crosspoint detection circuit 13A configured as described above detects zero crosspoints in one cycle of the three-phase AC input to the rectifier circuit 11 when there is a load on the motor 30 that allows the motor 30 to be driven normally, even if there is an open phase in the three-phase AC input to the rectifier circuit 11.

[0057] On the other hand, according to the crosspoint detection circuit 13A having the above configuration, when there is an open phase in the three-phase AC input to the rectifier circuit 11 and a load equal to or greater than the load at which the motor 30 can be normally driven is applied to the motor 30, the number of crosspoints detected in one cycle of the three-phase AC input to the rectifier circuit 11 will be two, similar to the crosspoint detection circuit 13 according to embodiment 1. Furthermore, according to the crosspoint detection circuit 13A having the above configuration, when there is no open phase in the three-phase AC input to the rectifier circuit 11, the number of crosspoints detected in one cycle of the three-phase AC input to the rectifier circuit 11 will be zero or six, similar to the crosspoint detection circuit 13 according to embodiment 1.

[0058] Therefore, when there is no missing phase in the three-phase AC input to the rectifier circuit 11, and when there is a missing phase in the three-phase AC input to the rectifier circuit 11 and the load on the motor 30 is sufficient to drive the motor 30 normally, the crosspoint detection circuit 13A outputs a control signal indicating that the motor 30 should be driven, and when there is a missing phase in the three-phase AC input to the rectifier circuit 11 and the load on the motor 30 is sufficient to drive the motor 30 normally or more, the crosspoint detection circuit 13A outputs a control signal indicating that the motor 30 should not be driven.

[0059] <Consideration> The motor drive device 10A configured as described above outputs a control signal to drive the motor 30 when there is no missing phase in the three-phase AC input to the rectifier circuit 11, and also when there is a missing phase in the three-phase AC input to the rectifier circuit 11, as long as the load on the motor 30 is small enough to enable the motor 30 to be driven normally. On the other hand, when there is a missing phase in the three-phase AC input to the rectifier circuit 11 and the load on the motor 30 is equal to or greater than the load that enables the motor 30 to be driven normally, the motor drive device 10A outputs a control signal to not drive the motor 30. In this way, the motor drive device 10A configured as described above can output a control signal to not drive the motor 30 when there is a possibility that the motor 30 cannot be driven normally due to a missing phase in the three-phase AC that serves as the power source.

[0060] (Embodiment 3) A motor drive device according to a third embodiment, which is configured by partially modifying motor drive device 10 according to the first embodiment, will be described below.

[0061] In the following, for the motor drive device according to embodiment 3, components that are similar to those of motor drive device 10 will be assigned the same symbols as those that have already been explained, and detailed explanations will be omitted. The explanation will focus on the differences from motor drive device 10.

[0062] FIG. 6 is a block diagram showing the configuration of a motor drive system 1B according to the third embodiment.

[0063] As shown in Fig. 6, motor drive system 1B is configured by replacing motor drive device 10 according to embodiment 1 with motor drive device 10B. Also, as shown in Fig. 6, motor drive device 10B is configured by adding voltage detection circuit 16 and power calculation circuit 17 to motor drive device 10, and replacing crosspoint detection circuit 13 with crosspoint detection circuit 13B.

[0064] The voltage detection circuit 16 detects the DC voltage smoothed by the smoothing circuit 15 .

[0065] The power calculation circuit 17 calculates the power required to drive the motor 30 based on the current detected by the current detection circuit 12 and the voltage detected by the voltage detection circuit 16 .

[0066] When the calculated power is smaller than a predetermined power value, the power calculation circuit 17 outputs a first signal indicating that the calculated power is smaller than the predetermined power value. Here, the predetermined power value is the maximum power required to drive the motor 30 when the load on the motor 30 is such that the motor 30 can be driven normally even if there is a missing phase in the three-phase AC input to the rectifier circuit 11.

[0067] Similar to the crosspoint detection circuit 13 according to the first embodiment, the crosspoint detection circuit 13B detects a crosspoint between the current detected by the current detection circuit 12 and a predetermined current value (here, the predetermined current value is set to 0 [A]).

[0068] Based on the detection result of the crosspoints, the crosspoint detection circuit 13B outputs a drive signal indicating whether to drive the motor 30. More specifically, (1) when the number of crosspoints detected in one cycle of the three-phase AC input to the rectifier circuit 11 is two and the first signal is not output from the power calculation circuit 17, the crosspoint detection circuit 13B outputs a control signal indicating that the motor 30 is not to be driven, and (2) when the number of crosspoints detected in one cycle of the three-phase AC input to the rectifier circuit 11 is zero or six and when the number of crosspoints detected in one cycle of the three-phase AC input to the rectifier circuit 11 is two and the first signal is output from the power calculation circuit 17, the crosspoint detection circuit 13B outputs a control signal indicating that the motor 30 is to be driven. In other words, when there is a missing phase in the three-phase AC input to the rectifier circuit 11 and the load on the motor 30 is equal to or greater than the load that allows the motor 30 to be driven normally, the crosspoint detection circuit 13B outputs a control signal indicating that the motor 30 should not be driven, and when there is no missing phase in the three-phase AC input to the rectifier circuit 11 and when there is a missing phase in the three-phase AC input to the rectifier circuit 11 and the load on the motor 30 is equal to or greater than the load that allows the motor 30 to be driven normally, the crosspoint detection circuit 13B outputs a control signal indicating that the motor 30 should be driven.

[0069] <Consideration> In addition to the case where there is no missing phase in the three-phase AC input to rectifier circuit 11, motor drive device 10B configured as described above suppresses output of a control signal indicating that motor 30 will not be driven and instead outputs a control signal indicating that motor 30 will be driven, even when there is a missing phase in the three-phase AC input to rectifier circuit 11, if the load on motor 30 is small enough to allow motor 30 to be driven normally. On the other hand, motor drive device 10B outputs a control signal indicating that motor 30 will not be driven when there is a missing phase in the three-phase AC input to rectifier circuit 11 and the load on motor 30 is equal to or greater than the load that allows motor 30 to be driven normally. In this way, motor drive device 10B configured as described above can output a control signal indicating that motor 30 will not be driven when there is a possibility that motor 30 cannot be driven normally due to a missing phase in the three-phase AC that serves as the power source.

[0070] (supplement) The motor drive device according to one aspect of the present disclosure has been described above based on Embodiments 1 to 3. However, the present disclosure is not limited to these embodiments. As long as they do not deviate from the spirit of the present disclosure, various modifications that would occur to a person skilled in the art to these embodiments, or configurations constructed by combining components of different embodiments, may also be included within the scope of one or more aspects of the present disclosure.

[0071] (1) In the first to third embodiments, the crosspoint detection circuit 13, the crosspoint detection circuit 13A, and the crosspoint detection circuit 13B may count the number of crosspoints detected in one cycle of the three-phase AC input to the rectifier circuit 11 for each cycle, or may count the average value over multiple cycles.

[0072] (2) In the second embodiment, the predetermined current value X [A] set in the crosspoint detection circuit 13A is the maximum value of the current flowing from the rectifier circuit 11 to the smoothing circuit 15 when the load on the motor 30 is such that the motor 30 can be driven normally even if there is a missing phase in the three-phase AC input to the rectifier circuit 11. In contrast, in another configuration, the predetermined current value X may be a positive value smaller than the maximum value. Even in this configuration, when there is a missing phase in the three-phase AC input to the rectifier circuit 11, the load on the motor 30 is such that the motor 30 can be driven normally when the crosspoint detection circuit 13A outputs a control signal indicating that the motor 30 is to be driven.

[0073] (3) In the third embodiment, the predetermined power value set in the power calculation circuit 17 is the maximum power value for driving the motor 30 when the load on the motor 30 is such that the motor 30 can be driven normally even if there is a phase loss in the three-phase AC input to the rectifier circuit 11. In contrast, in another configuration, the predetermined power value may be a value smaller than the maximum power value. Even in this configuration, when there is a phase loss in the three-phase AC input to the rectifier circuit 11, the load on the motor 30 is such that the motor 30 can be driven normally when the crosspoint detection circuit 13B outputs a control signal indicating that the motor 30 is to be driven.

[0074] (4) In the third embodiment, the voltage detection circuit 16 is configured to detect the smoothed DC voltage smoothed by the smoothing circuit 15. However, as an alternative configuration, the voltage detection circuit 16 may be configured to detect the unsmoothed DC voltage before being smoothed by the smoothing circuit 15.

[0075] (5) An example of a motor drive device according to one aspect of the present disclosure is further described below.

[0076] (a) A motor drive device according to one aspect of the present disclosure is a motor drive device that drives a motor using three-phase AC as a power source, and includes: a rectifier circuit that rectifies the three-phase AC; a current detection circuit that detects the DC current rectified by the rectifier circuit; and a crosspoint detection circuit that detects a crosspoint between the current detected by the current detection circuit and a predetermined current value, and outputs a control signal indicating whether or not to drive the motor based on the detection result.

[0077] With the motor drive device configured as described above, by setting the predetermined current value to an appropriate value, it is possible to make the frequency of crosspoint detection different between cases where there is a possibility that the motor cannot be driven normally due to a missing phase in the three-phase AC power source and cases where there is no possibility that the motor cannot be driven normally. Therefore, with the motor drive device configured as described above, when there is a possibility that the motor cannot be driven normally due to a missing phase in the three-phase AC power source, it is possible to output a control signal to not drive the motor.

[0078] (b) Furthermore, the cross point detection circuit may output the control signal indicating that the motor is not to be driven when the number of cross points detected in one cycle of the three-phase AC is two.

[0079] This makes it possible to output a control signal indicating that the motor will not be driven when there is a missing phase in the three-phase AC.

[0080] (c) Furthermore, the predetermined current value may be zero, and the cross point detection circuit may further output the control signal indicating that the motor is to be driven when the number of cross points detected in one cycle of the three-phase AC is 0 or 6.

[0081] This makes it possible to output a control signal indicating that the motor should be driven when there is no missing phase in the three-phase AC.

[0082] (d) Furthermore, the predetermined current value may be a positive value, and the cross point detection circuit may further output the control signal indicating that the motor is to be driven when the number of cross points detected in one cycle of the three-phase AC is 0.

[0083] This allows the predetermined current value to be set to an appropriate value, so that even if there is a missing phase in the three-phase AC, a control signal indicating that the motor should be driven can be output when the load on the motor is small enough that the motor can be driven normally.

[0084] (e) Furthermore, the present invention may further include a power calculation circuit that calculates the power required to drive the motor, and the crosspoint detector may suppress output of the control signal indicating that the motor will not be driven if the power calculated by the power calculation circuit is smaller than a predetermined power value.

[0085] This allows the output of a control signal indicating that the motor will not be driven to be suppressed when the load on the motor is small enough to allow the motor to be driven normally, even if there is a missing phase in the three-phase AC, by setting the specified power value to an appropriate value.

[0086] (f) Furthermore, the power supply may further include a smoothing circuit that smooths the direct current rectified by the rectifier circuit, and an inverter that receives the direct current smoothed by the smoothing circuit and drives the motor, and the current detection circuit may detect the current value using the direct current rectified by the rectifier circuit before it is smoothed by the smoothing circuit.

[0087] This allows the DC current supplied to the inverter to be smoothed. [Industrial Applicability]

[0088] The present disclosure is widely applicable to motor driving devices that drive motors. [Explanation of symbols]

[0089] 1, 1A, 1B Motor Drive System 10, 10A, 10B Motor Drive 11 Rectifier circuit 12 Current detection circuit 13, 13A, 13B Crosspoint detection circuit 14 Inverter 15 Smoothing circuit 16 Voltage detection circuit 17 Power calculation circuit 20 Three-phase AC power supply 30 motor 40 Display device

Claims

1. A motor drive device that drives a motor using three-phase AC as a power source, a rectifier circuit that rectifies the three-phase AC; a current detection circuit that detects the direct current rectified by the rectifier circuit; a cross-point detection circuit that detects a cross-point between the current detected by the current detection circuit and a predetermined current value, and outputs a control signal indicating whether or not to drive the motor based on the detection result, the cross point detection circuit outputs the control signal indicating that the motor is not to be driven when the number of cross points detected in one cycle of the three-phase AC is two. Motor drive device.

2. The predetermined current value is zero, the cross-point detection circuit further outputs the control signal indicating that the motor is to be driven when the number of cross-points detected in one cycle of the three-phase AC is 0 or 6. The motor drive device according to claim 1 .

3. The predetermined current value is a positive value, the cross point detection circuit further outputs the control signal indicating that the motor is to be driven when the number of cross points detected in one cycle of the three-phase AC is 0. The motor drive device according to claim 1 .

4. Further, a power calculation circuit is provided for calculating the power required to drive the motor, the cross-point detection circuit suppresses output of the control signal indicating that the motor is not to be driven when the power calculated by the power calculation circuit is smaller than a predetermined power value. The motor drive device according to claim 1 .

5. Further, a smoothing circuit that smoothes the direct current rectified by the rectifier circuit; an inverter that receives the direct current smoothed by the smoothing circuit and drives the motor, the current detection circuit detects the current value using the direct current rectified by the rectifier circuit before being smoothed by the smoothing circuit. The motor drive device according to any one of claims 1 to 4.

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