Preliminary charging circuit and motor drive apparatus

Abstract

This preliminary charging circuit preliminarily charges a smoothing capacitor connected to the DC output side of a converter that coverts inputted AC power into DC power and outputs the DC power. The preliminary charging circuit comprises: a switch unit that includes a switching element which electrically connects a three-phase AC power supply with the AC input side of the converter during an on time, and which electrically disconnects the three-phase AC power supply and the AC input side of the converter during an off time; a power supply voltage detection circuit that detects the AC voltage of the three-phase AC power supply; and a control unit that controls on / off of the switching element of the switch unit on the basis of information pertaining to the AC voltage detected by the power supply voltage detection circuit.

Description

Pre-charging circuit and motor drive device

[0001] The present invention relates to a pre-charging circuit and a motor driving device.

[0002] In a motor drive device, AC power input from an AC power supply is converted into DC power by a converter (rectifier circuit) and output to a DC link, and then the DC power in the DC link is converted into AC power by an inverter, and this AC power is supplied as power to drive the motor. The DC link refers to a circuit portion that electrically connects the DC output side of the converter and the DC input side of the inverter, and is sometimes called a "DC link portion," "DC link," "DC link portion," "DC bus," or "DC intermediate circuit."

[0003] The DC link is provided with a smoothing capacitor that has the function of suppressing pulsation in the DC output of the converter and storing DC power. The smoothing capacitor must be charged to a predetermined voltage after the motor drive device is powered on and before the motor starts to drive (i.e., before the inverter starts power conversion). This charging is also called "pre-charging" or "initial charging."

[0004] Because pre-charging begins when no energy is stored in the smoothing capacitor, a large inrush current flows from the AC power supply through the converter to the DC link immediately after the motor drive device is powered on. For this reason, the DC link is generally provided with a pre-charging circuit that pre-charges the smoothing capacitor while suppressing the inrush current that occurs immediately after the motor drive device is powered on. The pre-charging circuit is sometimes called an "initial charging circuit" or an "inrush current suppression circuit."

[0005] Generally, a pre-charging circuit consists of a pre-charging resistor that suppresses inrush current and a switching element connected in parallel with the pre-charging resistor. During pre-charging, the switching element is kept off to suppress the inrush current using the pre-charging resistor, and after pre-charging is completed, the switching element is turned on to bypass the pre-charging resistor.

[0006] For example, there is known an inrush current prevention circuit for a DC power supply circuit including a rectifier circuit supplied with power from an AC power supply via a semiconductor switching element and a smoothing capacitor connected to the output side of the rectifier circuit, the inrush current prevention circuit comprising: power supply voltage detection means for detecting the output voltage of the AC power supply; terminal voltage detection means for detecting the terminal voltage of the smoothing capacitor while the semiconductor switching element is off; and control means for executing switching control at startup of the DC power supply circuit, which turns on the semiconductor switching element each time the absolute value of the voltage detected by the power supply voltage detection means reaches a peak value and then falls to a target level that is a predetermined level higher than the voltage detected by the terminal voltage detection means, and maintains the on state for at least a predetermined time period that is set during the period until the absolute value of the voltage detected by the power supply voltage detection means rises to the target level (see, for example, Patent Document 1).

[0007] For example, there is known a power control device that includes a semiconductor element that performs a switching operation to turn on and off the AC output of an AC power supply, control means that controls the switching of the semiconductor element based on an external input signal, and output current detection means that detects the output current that is turned on and off by the semiconductor element and supplied to a load, and that when the detected value of the output current detection means exceeds a predetermined reference value, the control means controls the semiconductor element in an active region so that the output current falls below the reference value (see, for example, Patent Document 2).

[0008] JP 2007-129875 A JP 09-212245 A

[0009] If an abnormality such as a short circuit occurs in the motor drive device, an overcurrent will flow from the AC input side to the converter, posing a risk of damaging the motor drive device. The problem to be solved by the present disclosure is to protect the motor drive device from an overcurrent that occurs on the AC input side of the converter.

[0010] According to one aspect of the present disclosure, a pre-charging circuit that pre-charges a smoothing capacitor connected to a DC output side of a converter that converts input AC power into DC power and outputs it includes a switch unit having a switching element that electrically connects between a three-phase AC power supply and the AC input side of the converter when turned on and electrically disconnects between the three-phase AC power supply and the AC input side of the converter when turned off, a power supply voltage detection circuit that detects the AC voltage of the three-phase AC power supply, and a control unit that controls the on / off of the switching element of the switch unit based on information related to the AC voltage detected by the power supply voltage detection circuit.

[0011] According to another aspect of the present disclosure, a motor drive device includes a converter, a smoothing capacitor, the pre-charging circuit, and an inverter that converts DC power into AC power for driving the motor and outputs the AC power.

[0012] According to one aspect of the present disclosure, it is possible to protect a motor drive device from an overcurrent occurring on the AC input side of a converter.

[0013] FIG. 1 is a diagram showing a pre-charging circuit and a motor drive device according to a first embodiment of the present disclosure. FIG. 2 is a flowchart showing an operation flow of a pre-charging process by the pre-charging circuit according to the first embodiment of the present disclosure. FIG. 3 is a flowchart showing an operation flow of an overcurrent protection process by a motor drive device having a pre-charging circuit according to the first to third embodiments of the present disclosure. FIG. 4 is a waveform diagram showing a specific example of the operation of a switch unit in the pre-charging process by the pre-charging circuit according to the first embodiment of the present disclosure. FIG. 5 is a diagram showing a pre-charging circuit and a motor drive device according to a second embodiment of the present disclosure. FIG. 6 is a waveform diagram showing a specific example of the operation of a switch unit in the pre-charging process by the pre-charging circuit according to the second embodiment of the present disclosure. FIG. 7 is a diagram showing a pre-charging circuit and a motor drive device according to a third embodiment of the present disclosure. FIG. 8 is a waveform diagram showing a specific example of the operation of a switch unit in the pre-charging process by the pre-charging circuit according to the third embodiment of the present disclosure.

[0014] Hereinafter, a pre-charging circuit and a motor drive device according to an embodiment will be described with reference to the drawings. In the following description, components having the same or similar functions will be designated by the same reference numerals. Duplicate descriptions of those components may be omitted.

[0015] First Embodiment FIG. 1 is a diagram showing a pre-charging circuit and a motor driving device according to a first embodiment of the present disclosure.

[0016] In the first embodiment and the second and third embodiments described below, a case where a motor 6 is controlled by a motor drive device 100 connected to a three-phase AC power supply 5 is illustrated as an example. Examples of the three-phase AC power supply 5 include a three-phase 400V AC power supply, a three-phase 200V AC power supply, and a three-phase 600V AC power supply. Furthermore, in each embodiment, the type of motor 6 is not particularly limited, and may be, for example, an induction motor or a synchronous motor. Furthermore, the number of phases of the motor 6 is not particularly limited in each embodiment, and may be, for example, three-phase or single-phase. Here, as an example, the motor 6 is three-phase. Furthermore, the number of motors 6 is not particularly limited in each embodiment, and may be multiple. Here, as an example, the number of motors 6 is one. Machines in which the motor 6 is installed include, for example, machine tools, robots, forging machines, injection molding machines, industrial machines, and the like.

[0017] 1, a motor drive device 100 according to a first embodiment of the present disclosure includes a pre-charging circuit 1, a converter 2, a smoothing capacitor 3, and an inverter 4. The pre-charging circuit 1 may also be referred to as an "initial charging circuit" or an "inrush current suppression circuit."

[0018] The converter 2 is a rectifier that converts input AC power into DC power and outputs the DC power to a DC link, which is the DC output side of the converter 2. The converter 2 is configured as a three-phase bridge circuit. Examples of the converter 2 include a PWM switching control rectifier, a diode rectifier, and a 120-degree conduction rectifier. In the example shown in FIG. 1 , the converter 2 is configured as a PWM switching control rectifier. For example, when the converter 2 is configured as a PWM switching control rectifier or a 120-degree conduction rectifier, the converter 2 is configured as a bridge circuit of switching elements and diodes connected in antiparallel to the switching elements, and each switching element is controlled to be turned on and off in response to a drive command received from a higher-level control circuit (not shown), thereby performing bidirectional AC / DC power conversion. In this case, examples of the switching elements include FETs, IGBTs, thyristors, GTOs (Gate Turn-Off Thyristors), transistors, etc., but other switching elements may also be used.

[0019] The smoothing capacitor 3 is provided in a DC link between the DC output side of the converter 2 and the DC input side of the inverter 4. The smoothing capacitor 3 is sometimes called a DC link capacitor. The smoothing capacitor 3 has the function of suppressing pulsation in the DC output of the converter 2 and the function of storing DC power used by the inverter 4 to generate AC power. Examples of the smoothing capacitor 3 include an electrolytic capacitor and a film capacitor.

[0020] The inverter 4 is connected to the DC output side of the converter 2 via a smoothing capacitor 3. The inverter 4 converts DC power in the DC link into AC power for driving a motor and outputs the converted AC power to the AC output side of the inverter 4. The inverter 4 is composed of switching elements and a bridge circuit of diodes connected in antiparallel to the switching elements. The inverter 4 is composed of a three-phase bridge circuit when the motor 6 is a three-phase AC motor, and a single-phase bridge circuit when the motor 6 is a single-phase AC motor. In the example shown in FIG. 1 , the motor 6 is a three-phase AC motor, so the inverter 4 is composed of a three-phase bridge circuit. Examples of switching elements include FETs, IGBTs, thyristors, GTOs, and transistors, but other switching elements may also be used. The power conversion operation of the inverter 4 is controlled, for example, by a PWM switching control method. That is, the inverter 4 receives a drive command (PWM switching command) from a higher-level control circuit (not shown) to convert DC power in the DC link into AC power for driving a motor and output the AC power to the motor 6. Furthermore, during motor regeneration, the inverter 4 receives a drive command (PWM switching command) from a higher-level control circuit (not shown) and converts the AC power regenerated by the motor 6 into DC power, which is then output to the DC link.

[0021] The power conversion operation of the inverter 4 is controlled based on drive commands generated by a host control circuit, similar to a typical motor drive device. The host control circuit generates drive commands for controlling the speed, torque, or rotor position of the motor 6 based on the speed of the motor 6 (speed feedback), the current flowing through the windings of the motor 6 (current feedback), a predetermined torque command, and an operation program for the motor 6. Note that the configuration of the host control circuit defined here is merely an example, and the configuration of the host control circuit may also be defined by terms such as a position command generator, a torque command generator, and a switching command generator. Furthermore, for example, if the converter 2 is configured as a PWM switching control rectifier or a 120-degree conduction rectifier, the power conversion operation of the converter 2 is controlled based on the drive commands generated by the host control circuit.

[0022] The pre-charging circuit 1 is provided between a three-phase AC power supply 5 and the AC input side of the converter 2. The pre-charging circuit 1 includes a switch unit 11, a power supply voltage detection circuit 12, a control unit 13, a current detection circuit 14, and a capacitor voltage detection circuit 15.

[0023] The switch unit 11 includes a switching element that electrically connects the three-phase AC power supply 5 and the AC input side of the converter 2 when turned on, and electrically disconnects the three-phase AC power supply 5 and the AC input side of the converter 2 when turned off. In the first embodiment, the switch unit 11 includes an R-phase switching element S R , S-phase switching element S S , and T-phase switching element S T Among the three-phase power lines between the three-phase AC power source 5 and the AC input side of the converter 2, an R-phase power line is provided with an R-phase switching element S R is provided on the S-phase power line, and an S-phase switching element S S is provided on the T-phase power line, and a T-phase switching element S T will be established.

[0024] R-phase switching element S R , S-phase switching element S S , and T-phase switching element S T When turned on, each of the R-phase switching elements S conducts current flowing from the three-phase AC power supply 5 to the AC input side of the converter 2, and when turned off, electrically cuts off the connection between the three-phase AC power supply 5 and the AC input side of the converter 2. R , S-phase switching element S S , and T-phase switching element S T Examples of the R-phase switching element S include an IGBT and a MOSFET. R , S-phase switching element S S , and T-phase switching element S T A diode is connected in antiparallel to each of the

[0025] The power supply voltage detection circuit 12 detects the AC voltage (phase voltage or line voltage) of the three-phase AC power supply 5. Data relating to the value of the AC voltage of the three-phase AC power supply 5 detected by the power supply voltage detection circuit 12 is sent to the control unit 13. The data relating to the value of the AC voltage of the three-phase AC power supply 5 includes information relating to the amplitude and phase of the AC voltage of the three-phase AC power supply 5. The data relating to the AC voltage detected by the power supply voltage detection circuit 12 may be used by a higher-level control circuit to control the power conversion operation of the converter 2.

[0026] The current detection circuit 14 detects the current of each phase flowing from the three-phase AC power supply 5 to the AC input side of the converter 2. Data relating to the value of the current of each phase detected by the current detection circuit 14 is sent to the control unit 13. The data relating to the value of the current of each phase includes information on the amplitude and phase of the current. Note that the data relating to the current of each phase detected by the current detection circuit 14 may be used by a higher-level control circuit to control the power conversion operation of the converter 2.

[0027] The capacitor voltage detection circuit 15 detects the capacitor voltage, which is the voltage applied between the positive and negative terminals of the smoothing capacitor 3. The capacitor voltage detection circuit 15 may detect the terminal voltage of the DC link, which is the DC output side of the converter 2 (the potential difference between the positive potential on the DC output side of the converter 2 and the negative potential on the DC output side of the converter 2), as the capacitor voltage. Data relating to the value of the capacitor voltage detected by the capacitor voltage detection circuit 15 is sent to the control unit 13. The data relating to the value of the capacitor voltage detected by the capacitor voltage detection circuit 15 may be used by a higher-level control circuit to control the power conversion operation of the inverter 4 and the power conversion operation of the converter 2.

[0028] The control unit 13 controls the pre-charging of the smoothing capacitor 3 by controlling the on / off of the switching element in the switch unit 11 based on information related to the AC voltage detected by the power supply voltage detection circuit 12. When the control unit 13 controls the on / off of the switch unit 11 for pre-charging the smoothing capacitor 3, data related to the current values ​​of each phase detected by the current detection circuit 14 and data related to the capacitor voltage value detected by the capacitor voltage detection circuit 15 may be used.

[0029] Furthermore, when the current detected by the current detection circuit 14 is an overcurrent, the control unit 13 controls to turn off all the switching elements of the switch unit 11, thereby electrically disconnecting the three-phase AC power supply 5 from the AC input side of the converter 2. This makes it possible to protect the motor drive device from an overcurrent occurring on the AC input side of the converter. Note that, since a surge voltage may occur when the switch unit 11 cuts off the overcurrent, the R-phase switching element S R , S-phase switching element S S , and T-phase switching element S T A surge absorbing circuit such as a varistor may be connected in parallel to each of the above.

[0030] The control unit 13 controls the on / off of the switching elements in the switch unit 11 for pre-charging as follows: If the converter 2 is configured as a PWM switching control type rectifier or a 120-degree conduction type rectifier, all switching elements in the converter 2 are turned off during the pre-charging period, and the converter 2 simply functions as a diode rectifier.

[0031] First, during the pre-charging period, the control unit 13 controls the R-phase switching element S R , S-phase switching element S S , and T-phase switching element S TThe control unit 13 determines the phase having the second largest phase voltage among the three phase voltages detected by the power supply voltage detection circuit 12 as the conducting phase.

[0032] The control unit 13 then controls the switching elements of the conducting phases to switch from off to on at a timing when the switch-on condition is satisfied. The timing when the switch-on condition is satisfied can be acquired by referring to data relating to the value of the AC voltage of the three-phase AC power supply 5 detected by the power supply voltage detection circuit 12. For example, any of the following timings is set as the timing when the switch-on condition is satisfied. A first example of the timing when the switch-on condition is satisfied is a timing that is earlier by a first predetermined time τ1 than the timing when the magnitude relationship between the phase voltage of the conducting phase and the phase voltage of the minimum magnitude phase is reversed. A second example of the timing when the switch-on condition is satisfied is a timing when the line voltage between the conducting phase and the phase with the minimum magnitude is lower than a predetermined voltage threshold V th The timing when the switch-on condition is satisfied is as follows: AC power flows from the three-phase AC power supply 5 to the AC input side of the converter 2 through the switching element of the conducting phase that is turned on at the timing when the switch-on condition is satisfied. Then, DC power that flows out from the AC output side of the converter 2 through the diode of the converter 2 flows into the smoothing capacitor 3, and the smoothing capacitor 3 is charged.

[0033] Furthermore, after the conducting phase switching elements are turned on, the control unit 13 controls the conducting phase switching elements to switch from on to off at a timing when a switch-off condition is satisfied. The timing when the switch-off condition is satisfied can be obtained by referring to data related to the AC voltage value of the three-phase AC power supply 5 detected by the power supply voltage detection circuit 12. Alternatively, the timing when the switch-off condition is satisfied can be obtained by referring to data related to the current values ​​of each phase detected by the current detection circuit 14. For example, any of the following is set as the timing when the switch-off condition is satisfied. A first example of the timing when the switch-off condition is satisfied is the timing when the current flowing through the conducting phase switching elements becomes approximately zero. The current flowing through the conducting phase switching elements is detected by the current detection circuit 14. A second example of the timing when the switch-off condition is satisfied is the timing when a second predetermined time τ2 has elapsed since the magnitude of the conducting phase phase voltage becomes the smallest among the three phase voltages.

[0034] An arithmetic processing unit (processor) is provided within the motor drive device 100 or the pre-charging circuit 1. Examples of arithmetic processing units include an IC, an LSI, a CPU, an MPU, and a DSP. The control unit 13 and the host control circuit (not shown) may be configured as a combination of an analog circuit and an arithmetic processing unit, or may be configured solely as an arithmetic processing unit, or may be configured solely as an analog circuit. For example, if the control unit 13 and the host control circuit are implemented in the form of a software program, the functions of the control unit 13 and the host control circuit can be realized by operating the arithmetic processing unit in accordance with the software program. Alternatively, the control unit 13 and the host control circuit may be implemented as a semiconductor integrated circuit on which a software program for implementing the functions of each unit is written. Alternatively, the control unit 13 and the host control circuit may be implemented as a recording medium on which a software program for implementing the functions of each unit is written. The control unit 13 may also be provided within the host control circuit.

[0035] 2 is a flowchart showing the operation flow of the pre-charging process by the pre-charging circuit according to the first embodiment of the present disclosure. Steps S101 to S107 in FIG. 2 are performed by the R-phase switching element S R , S-phase switching element S S , and T-phase switching element S T is executed for all of the

[0036] Before the motor drive device 100 is powered on, the R-phase switching element S R , S-phase switching element S S , and T-phase switching element S T are all off. Therefore, the three-phase AC power supply 5 and the AC input side of the converter 2 are electrically disconnected in all three-phase power lines. Furthermore, the smoothing capacitor 3 is not charged. Furthermore, particularly when the converter 2 is configured as a PWM switching control type rectifier or a 120-degree conduction type rectifier, all switching elements in the converter 2 are turned off during the pre-charging period, and the converter 2 simply functions as a diode rectifier.

[0037] When the motor drive device 100 is powered on, the pre-charging circuit 1 starts pre-charging the smoothing capacitor 3, and the process proceeds to step S101.

[0038] In step S101, the control unit 13 determines the phase having the second largest phase voltage among the three phase voltages detected by the power supply voltage detection circuit 12 as the conducting phase.

[0039] In step S102, the control unit 13 determines whether or not a switch-on condition is satisfied. The process of step S102 is repeatedly executed at a cycle shorter than the power supply frequency of the three-phase AC power supply 5.

[0040] If it is determined in step S102 that the switch-on condition is satisfied, in step S103, the control unit 13 performs control to switch the conducting phase switching element from off to on.

[0041] In step S104, the control unit 13 determines whether or not the switch-off condition is satisfied. The process of step S104 is repeatedly executed at a cycle shorter than the power supply frequency of the three-phase AC power supply 5.

[0042] If it is determined in step S104 that the switch-off condition is satisfied, in step S105, the control unit 13 performs control to switch the conducting phase switching element from on to off.

[0043] In step S106, the control unit 13 determines whether or not the pre-charging of the smoothing capacitor 3 has been completed. If the capacitor voltage detected by the capacitor voltage detection circuit 15 has reached a predetermined charging voltage, the control unit 13 determines that the pre-charging of the smoothing capacitor 3 has been completed, and the process proceeds to step S107. If the capacitor voltage detected by the capacitor voltage detection circuit 15 has not reached the predetermined charging voltage, the control unit 13 determines that the pre-charging of the smoothing capacitor 3 has not been completed, and the process returns to step S101. The process of step S106 is repeatedly executed at a cycle shorter than the power supply frequency of the three-phase AC power supply 5.

[0044] When it is determined in step S106 that the preliminary charging of the smoothing capacitor 3 is completed, in step S107, the control unit 13 turns on the R-phase switching element S R , S-phase switching element S S , and T-phase switching element S T After the smoothing capacitor 3 is pre-charged, the R-phase switching element S R , S-phase switching element S S , and T-phase switching element S T is conductive, AC power flows from the three-phase AC power supply 5 to the AC input side of the converter 2, and the converter 2 enters a state in which it can drive the motor 6. The inverter 4 converts the DC power in the DC link into motor-driving AC power and outputs it to the AC output side of the inverter 4. The motor 6 is driven by the motor-driving AC power output from the AC output side of the inverter 4.

[0045] 3 is a flowchart showing the operation flow of overcurrent protection processing by a motor drive device having a pre-charging circuit according to the first to third embodiments of the present disclosure. The flowchart shown in FIG. 3 is also applicable to the second and third embodiments described below.

[0046] 1 and 2 , after the preliminary charging of smoothing capacitor 3 is completed, motor drive device 100 drives motor 6 with motor drive AC power output from the AC output side of inverter 4. While motor 6 is being driven, in step S201, current detection circuit 14 detects the current of each phase flowing from three-phase AC power supply 5 to the AC input side of converter 2.

[0047] In step S202, the control unit 13 determines whether an overcurrent has occurred based on the current detected by the current detection circuit 14. For example, the control unit 13 determines that an overcurrent has occurred when the peak value of the current detected by the current detection circuit 14 exceeds a predetermined threshold value for a predetermined period of time. If an overcurrent has occurred in step S202, the process proceeds to step S203, and if an overcurrent has not been detected, the process returns to step S201. The process of step S202 is repeatedly executed at a predetermined cycle.

[0048] If it is determined in step S202 that an overcurrent has occurred, in step S203, the control unit 13 controls the R-phase switching element S R , S-phase switching element S S , and T-phase switching element S T This completely cuts off the electricity between the three-phase AC power supply 5 and the AC input side of the converter 2, making it possible to protect the motor drive device 100 from an overcurrent.

[0049] The overcurrent protection process by the pre-charging circuit 1 may be performed during the pre-charging process by the pre-charging circuit 1. In this case, for example, the overcurrent protection process by the pre-charging circuit 1 shown in Fig. 3 may be performed before each of steps S101 to S107 in Fig. 2.

[0050] 4 is a waveform diagram showing a specific example of the operation of the switch unit in the pre-charging process by the pre-charging circuit according to the first embodiment of the present disclosure, in which the R-phase voltage of the three-phase AC power supply 5 is indicated by a bold solid line, the S-phase voltage is indicated by a bold dashed line, and the T-phase voltage is indicated by a bold dashed line.

[0051] Here, as an example, the R-phase switching element S R The on / off control for the inverter will be described.

[0052] In the section A1, the R-phase voltage is the largest among the three-phase voltages of the three-phase AC power supply 5, so the R-phase-S-phase line voltage (S-phase reference) V RS and R-phase to T-phase line voltage (T-phase reference) V RT is large. If the R-phase switching element S R When the R-phase switching element S R , the diode D of the R-phase upper arm of the converter 2 RU , smoothing capacitor 3, diode D of the S-phase lower arm of converter 2 SL , and S-phase switching element S S There is a risk that a large current will flow through the path leading to the three-phase AC power supply 5 via the diode connected in antiparallel to the R-phase switching element S. R Keep it off.

[0053] In section A2, the magnitude relationship between the R-phase voltage and the S-phase voltage is reversed, and the R-phase voltage becomes the second largest phase voltage. RS Therefore, in the section A2, the R-phase switching element S R is turned on, the R-phase switching element S R , the diode D of the R-phase upper arm of the converter 2 RU , smoothing capacitor 3, diode D of the S-phase lower arm of converter 2 SL , and S-phase switching element S S On the other hand, in the section A2, no current flows through the path leading to the three-phase AC power supply 5 via the diode connected in antiparallel to the R-phase switching element S RWhen turned on, the R-phase to T-phase line voltage (T-phase reference) V RT A current according to the magnitude of the current flows from the three-phase AC power supply 5 to the R-phase switching element S R , the diode D of the R-phase upper arm of the converter 2 RU , smoothing capacitor 3, diode D of the T-phase lower arm of converter 2 TL , and T-phase switching element S T In section A2, the current flows through a diode connected in antiparallel to the three-phase AC power supply 5. In section A3, the R-phase-T-phase line voltage (T-phase reference) V RT becomes gradually smaller, so that just before the end of section A2, the R-phase switching element S R Therefore, in the first embodiment, the R-phase, which has the second largest phase voltage among the three-phase voltages, is determined to be the conducting phase. Then, the R-phase switching element S, which is the conducting phase, is turned on at a timing that is earlier by a first predetermined time τ1 than the timing at which the magnitude relationship between the R-phase voltage of the conducting phase and the T-phase voltage, which is the smallest phase, is reversed (the timing at which section A2 is switched to section A3). R Alternatively, the line voltage (based on the T phase) V between the R phase, which is the conducting phase, and the T phase, which has the smallest magnitude, is RT is a predetermined voltage threshold V th When the timing becomes as follows, the R-phase switching element S R The shorter the first predetermined time τ1 is, or the shorter the voltage threshold V th The smaller the R-phase to T-phase line voltage (T-phase reference) V RT Therefore, the R-phase switching element S R is turned on, the R-phase switching element S R , the diode D of the R-phase upper arm of the converter 2 RU , smoothing capacitor 3, diode D of the T-phase lower arm of converter 2 TL , and T-phase switching element S T A large current does not flow through the path leading to the three-phase AC power supply 5 via the diode connected in antiparallel to the power supply 5 .

[0054] In the section A3, the R-phase voltage is the smallest among the three-phase voltages of the three-phase AC power supply 5. Therefore, in the section A3, the R-phase-S-phase line voltage (S-phase reference) V RS Therefore, the R-phase switching element S R Even when the R-phase switching element S is turned on, the R-phase switching element S R , the diode D of the R-phase upper arm of the converter 2 RU , smoothing capacitor 3, diode D of the S-phase lower arm of converter 2 SL , and S-phase switching element S S No current flows through the path leading to the three-phase AC power supply 5 via the diode connected in antiparallel to the R-phase and T-phase line voltages (based on the T-phase) V RT Therefore, the R-phase switching element S R Even when the R-phase switching element S is turned on, the R-phase switching element S R , the diode D of the R-phase upper arm of the converter 2 RU , smoothing capacitor 3, diode D of the T-phase lower arm of converter 2 TL , and T-phase switching element S T No current flows through the path leading to the three-phase AC power supply 5 via the diode connected in antiparallel to the R-phase switching element S. R Since no current flows through the R-phase switching element S R Therefore, in the first embodiment, even if the R-phase switching element S is switched from ON to OFF, no surge voltage is generated and no switching loss occurs. R When the current flowing through the R-phase switching element S becomes substantially zero, or when a second predetermined time τ2 has elapsed since the magnitude of the R-phase voltage of the conducting phase becomes the smallest of the three phase voltages, the R-phase switching element S R Switch from on to off.

[0055] In the section A4, the magnitude relationship between the R-phase voltage and the S-phase voltage is reversed, and the R-phase voltage becomes the second largest phase voltage. R When the ON state is maintained, the R-phase switching element S R, the diode D of the R-phase upper arm of the converter 2 RU , smoothing capacitor 3, diode D of the S-phase lower arm of converter 2 SL , and S-phase switching element S S There is a risk that a large current will flow through the path leading to the three-phase AC power supply 5 via the diode connected in antiparallel to the R-phase switching element S R When the R-phase switching element S is switched from ON to OFF, a surge voltage occurs and the switching loss increases. R In section A4, the R-phase switching element S R Keep it off.

[0056] As described above, referring to FIG. 4, the R-phase switching element S R The above description has been made on the ON / OFF control of the S-phase switching element S S and T-phase switching element S T The above explanation can also be applied to the on / off control of the S-phase switching element S S When applied to the on / off control of the R-phase switching element S R S-phase switching element S S and the S-phase switching element S S T-phase switching element S T and the T-phase switching element S T R-phase switching element S R In addition, the above description can be read as follows: T When applied to the on / off control of the R-phase switching element S R T-phase switching element S T and the S-phase switching element S S R-phase switching element S R and the T-phase switching element S T S-phase switching element S SThat is, during the pre-charging process by the pre-charging circuit 1, the control unit 13 switches the R-phase switching element S R , S-phase switching element S S , and T-phase switching element S T Each of these is appropriately controlled to be turned on and off.

[0057] As described above, the motor drive device 100 having the pre-charging circuit 1 according to the first embodiment of the present disclosure has both a pre-charging function and a power-off function when an overcurrent occurs. According to the first embodiment of the present disclosure, it is possible to realize a pre-charging circuit that can cut off the power supply when an overcurrent occurs on the AC input side of the converter 2.

[0058] Conventionally, a breaker or fuse has been provided on the AC input side of a converter to protect the motor drive device from overcurrent. However, to prevent malfunction of the breaker or fuse during normal motor operation, it was necessary to select a breaker or fuse with a large rating with a margin of error. Furthermore, because breakers and fuses are mechanical switches, their opening and closing operations are slow, which can delay power cutoff when an overcurrent occurs, making it impossible to protect the motor drive device. In contrast, the pre-charging circuit according to the first embodiment of the present disclosure includes a semiconductor switching element as a switch unit 11 that electrically connects the three-phase AC power supply 5 and the AC input side of the converter 2 when turned on and electrically disconnects the power supply 5 and the AC input side of the converter 2 when turned off. This allows for rapid power cutoff when an overcurrent occurs, thereby more reliably protecting the motor drive device. Furthermore, since there is no need for a breaker or fuse as in the past, this contributes to the miniaturization and cost reduction of the motor drive device.

[0059] Furthermore, while conventional pre-charging circuits are provided with a resistor and a switch connected in parallel to the resistor, the pre-charging circuit according to the first embodiment of the present disclosure does not include a charging resistor, which allows for a smaller and less expensive motor drive device.

[0060] Second Embodiment FIG. 5 is a diagram showing a pre-charging circuit and a motor driving device according to a second embodiment of the present disclosure.

[0061] 5 , a pre-charging circuit 1 according to a second embodiment of the present disclosure includes, as a switch unit 11, switching elements that are provided in two phases of a three-phase power line between a three-phase AC power source and the AC input side of the converter and can be turned on and off in both directions, from the three-phase AC power source 5 to the AC input side of the converter 2 and from the AC input side of the converter 2 to the three-phase AC power source 5. Each switching element is selectively switched between conducting a current flowing in a first conduction direction from the three-phase AC power source 5 to the AC input side of the converter 2 when on, conducting a current flowing in a second conduction direction from the AC input side of the converter 2 to the three-phase AC power source 5 when on, and electrically blocking electrical connection between the three-phase AC power source 5 and the AC input side of the converter 2 when off.

[0062] The converter 2, smoothing capacitor 3, inverter 4, three-phase AC power supply 5, motor 6, power supply voltage detection circuit 12, current detection circuit 14, and capacitor voltage detection circuit 15 are as described with reference to FIGS.

[0063] In the example shown in FIG. 5, the switch unit 11 in the pre-charging circuit 1 is, for example, a first R-phase switching element S R1 and the second R-phase switching element S R2 and a first S-phase switching element S provided on the S-phase power line. S1 and the second S-phase switching element S S2 It is equipped with:

[0064] Of the three-phase power lines between the three-phase AC power source 5 and the AC input side of the converter 2, the R-phase power line is provided with a first R-phase switching element S R1 and the second R-phase switching element S R2 The first R-phase switching element S R1 and the second R-phase switching element S R2 The first R-phase switching element S is connected in anti-parallel so that the conduction directions of the first R-phase switching element S are opposite to each other when they are turned on. R1When turned on, the second R-phase switching element S conducts a current flowing in a first conduction direction from the three-phase AC power supply 5 to the AC input side of the converter 2. R2 When turned on, the first R-phase switching element S conducts a current flowing in a second conduction direction from the AC input side of the converter 2 to the three-phase AC power supply 5. R1 and the second R-phase switching element S R2 When both of these are turned off, the R-phase power line is electrically disconnected between the three-phase AC power supply 5 and the AC input side of the converter 2 .

[0065] Of the three-phase power lines between the three-phase AC power source 5 and the AC input side of the converter 2, the S-phase power line is provided with a first S-phase switching element S S1 and the second S-phase switching element S S2 The first S-phase switching element S S1 and the second S-phase switching element S S2 The first S-phase switching element S is connected in anti-parallel so that the conduction direction when turned on is opposite to the first S-phase switching element S. S1 When turned on, the second S-phase switching element S conducts a current flowing in a first conduction direction from the three-phase AC power supply 5 to the AC input side of the converter 2. S2 When turned on, the first S-phase switching element S conducts a current flowing in a second conduction direction from the AC input side of the converter 2 to the three-phase AC power supply 5. S1 and the second S-phase switching element S S2 When both of these are turned off, the S-phase power line is electrically disconnected between the three-phase AC power supply 5 and the AC input side of the converter 2 .

[0066] The control unit 13 controls the pre-charging of the smoothing capacitor 3 by controlling the on / off of the switching element in the switch unit 11 based on information related to the AC voltage detected by the power supply voltage detection circuit 12 .

[0067] Furthermore, when the current detected by the current detection circuit 14 is an overcurrent, the control unit 13 performs control to turn off all switching elements in the switch unit 11, thereby electrically disconnecting the three-phase AC power supply 5 from the AC input side of the converter 2. The flowchart shown in Fig. 3 is also applied to the overcurrent protection process of the second embodiment.

[0068] The control unit 13 controls the on / off of the switch unit 11 for pre-charging as follows: If the converter 2 is configured as a PWM switching control type rectifier or a 120-degree conduction type rectifier, all switching elements in the converter 2 are turned off during the pre-charging period, and the converter 2 simply functions as a diode rectifier.

[0069] The control unit 13 controls the switching elements to switch from off to on at a timing when a switch-on condition is satisfied. The timing when the switch-on condition is satisfied can be acquired by referring to data relating to the value of the AC voltage of the three-phase AC power supply 5 detected by the power supply voltage detection circuit 12. For example, one of the following timings is set as the timing when the switch-on condition is satisfied. A first example of the timing when the switch-on condition is satisfied is a timing that is earlier by a first predetermined time τ1 than a timing when the magnitude relationship between the phases with switching elements and the phases without switching elements among the three phase voltages detected by the power supply voltage detection circuit 12 is reversed. In the example shown in FIG. 5 , the timing is a timing that is earlier by a first predetermined time τ1 than a timing when the magnitude relationship between the T-phase voltage and the R-phase or S-phase voltage detected by the power supply voltage detection circuit 12 is reversed. A second example of the timing when the switch-on condition is satisfied is a timing when the line voltages between the three phases detected by the power supply voltage detection circuit 12 exceed a predetermined voltage threshold V th In the example shown in FIG. 5, the absolute value of the line voltage between the R phase and the T phase or the absolute value of the line voltage between the S phase and the T phase detected by the power supply voltage detection circuit 12 is equal to or lower than a predetermined voltage threshold V thWhen the timing at which the switch-on condition is satisfied arrives, the control unit 13 performs control to switch from off to on the switching elements of the phases where the line voltage with respect to the T phase reference, detected by the power supply voltage detection circuit 12, has switched from positive to negative so as to conduct current flowing in a first conduction direction. Alternatively, when this timing arrives, the control unit 13 performs control to switch from off to on the switching elements of the phases where the line voltage with respect to the T phase reference, detected by the power supply voltage detection circuit 12, has switched from negative to positive so as to conduct current flowing in a second conduction direction.

[0070] Furthermore, after a switching element (i.e., a switching element that is the target of the above-described control of switching from off to on) is turned on, the control unit 13 controls the switching element to switch from on to off at a timing when a switch-off condition is satisfied. The timing when the switch-off condition is satisfied can be obtained by referring to data related to the value of the AC voltage of the three-phase AC power supply 5 detected by the power supply voltage detection circuit 12. Alternatively, the timing when the switch-off condition is satisfied can be obtained by referring to data related to the value of the current of each phase detected by the current detection circuit 14. For example, any of the following is set as the timing when the switch-off condition is satisfied. A first example of the timing when the switch-off condition is satisfied is the timing when the current flowing through the switched-on switching element becomes approximately zero. A second example of the timing when the switch-off condition is satisfied is the timing when a second predetermined time τ2 has elapsed since the line voltage was switched from positive to negative and from negative to positive.

[0071] 6 is a waveform diagram showing a specific example of the operation of the switch unit in the pre-charging process by the pre-charging circuit according to the second embodiment of the present disclosure, in which the R-phase voltage of the three-phase AC power supply 5 is indicated by a bold solid line, the S-phase voltage is indicated by a bold dashed line, and the T-phase voltage is indicated by a bold dashed line.

[0072] Here, as an example, a first R-phase switching element S is connected to the R-phase power line. R1 and the second R-phase switching element S R2 a first S-phase switching element SS1 and the second S-phase switching element S S2 When the first R-phase switching element S R1 and the second R-phase switching element S R2 The on / off control for the inverter will be described.

[0073] In the section A1, the R-phase voltage is the largest among the three-phase voltages of the three-phase AC power supply 5, so the R-phase-T-phase line voltage (T-phase reference) V RT is large. Suppose that the first R-phase switching element S R1 When the first R-phase switching element S is turned on, the three-phase AC power supply 5 supplies power to the first R-phase switching element S. R1 , the diode D of the R-phase upper arm of the converter 2 RU , smoothing capacitor 3, diode D of the T-phase lower arm of converter 2 TL , and the T-phase power line to the three-phase AC power supply 5. Therefore, in the section A1, the first R-phase switching element S R1 In addition, in the section A1, the second R-phase switching element S continues to be turned off from the section A4 as will be described later. R2 is turned on.

[0074] In section A2, the magnitude relationship between the R-phase voltage and the S-phase voltage is reversed, and the R-phase voltage becomes the second largest phase voltage.

[0075] Suppose that the second R-phase switching element S R2 is kept on, the first S-phase switching element S S1 , the diode D of the upper arm of the S-phase of the converter 2 SU , smoothing capacitor 3, diode D of the R-phase lower arm of converter 2 RL , and the second R-phase switching element S R2 Therefore, in the second embodiment, the second R-phase switching element S R2 When the current flowing through the RTWhen the second predetermined time τ2 has elapsed since the timing of the change from negative to positive (the timing of the change from section A4 to section A1 for the R phase), the second R-phase switching element S R2 The control unit 100 controls the switching from on to off.

[0076] On the other hand, in section A2, the R-phase-T-phase line voltage (T-phase reference) V RT becomes gradually smaller. Suppose that the first R-phase switching element S R1 When the first R-phase switching element S is turned on, the three-phase AC power supply 5 supplies the first R-phase switching element S R1 , the diode D of the R-phase upper arm of the converter 2 RU , smoothing capacitor 3, diode D of the T-phase lower arm of converter 2 TL , and the T-phase power line to the three-phase AC power supply 5. Just before the end of section A2, the first R-phase switching element S R1 Therefore, in the second embodiment, a voltage V between the R phase and the T phase with the smallest magnitude (T phase reference) is detected at a timing earlier than the timing at which the magnitude relationship between the T phase voltage and the R phase or S phase voltage detected by the power supply voltage detection circuit 12 is reversed (the timing at which the R phase switches from section A2 to section A3). RT is a predetermined voltage threshold V th When the timing becomes as follows, the R-phase to T-phase line voltage (T-phase reference) V RT The first R-phase switching element S R1 The control circuit 100 controls the switching from OFF to ON so as to conduct a current flowing in the first conduction direction.

[0077] In section A3, the R-phase voltage is the smallest among the three-phase voltages of the three-phase AC power supply 5. In section A2 before entering section A3, the R-phase voltage is supplied from the three-phase AC power supply 5 to the first R-phase switching element S R1 , the diode D of the R-phase upper arm of the converter 2 RU , smoothing capacitor 3, diode D of the T-phase lower arm of converter 2 TL, and the current flowing through the path leading to the three-phase AC power supply 5 via the T-phase power line is reduced to the R-phase-T-phase line voltage (T-phase reference) V RT becomes negative, and the second R-phase switching element S R2 Therefore, in the second embodiment, the first R-phase switching element S R1 When the current flowing between the R-phase and T-phase terminals becomes substantially zero, or when a second predetermined time τ2 has elapsed since the time when the line voltage is switched from positive to negative and vice versa (the time when the R-phase terminal switches from section A2 to section A3), the R-phase-T-phase line voltage (T-phase reference) V RT The first R-phase switching element S R1 The control unit 100 controls the switching from on to off.

[0078] In section A4, the magnitude relationship between the R-phase voltage and the S-phase voltage is reversed, and the R-phase voltage becomes the second largest phase voltage.

[0079] Suppose that the first R-phase switching element S R1 and the second S-phase switching element S S2 When the first R-phase switching element S is turned on, the three-phase AC power supply 5 supplies the first R-phase switching element S R1 , the diode D of the R-phase upper arm of the converter 2 RU , smoothing capacitor 3, diode D of the S-phase lower arm of converter 2 SL , and the S-phase power line to the three-phase AC power supply 5. Therefore, R1 and the second S-phase switching element S S2 About to stay off.

[0080] On the other hand, the line voltage between the R phase and the T phase (based on the T phase) V RT The absolute value of the second R-phase switching element S R2 When the power supply is turned on, the three-phase AC power supply 5 is connected to the T-phase power line, and the diode D TU , smoothing capacitor 3, diode D of the R-phase lower arm of converter 2 RL, the second R-phase switching element S R2 The current flows through the path leading to the three-phase AC power supply 5 via the second R-phase switching element S R2 Therefore, in the second embodiment, the voltage V between the R phase and the T phase with the smallest magnitude (T phase reference) is detected at a timing earlier than the timing at which the magnitude relationship between the T phase voltage and the R phase or S phase voltage detected by the power supply voltage detection circuit 12 is reversed (the timing at which the R phase switches from section A3 to section A4). RT The absolute value of V is a predetermined voltage threshold value V th When the timing becomes as follows, the R-phase to T-phase line voltage (T-phase reference) V RT The second R-phase switching element S R2 The control circuit 100 controls the switching from OFF to ON so as to conduct a current flowing in the second conduction direction.

[0081] Section A4 is followed by section A1, where the above-described on / off control is executed again.

[0082] As described above, the first R-phase switching element S in the switch unit 11 is R1 and the second R-phase switching element S R2 The above description has been made on the on / off control of the first S-phase switching element S S1 and the second S-phase switching element S S2 During the pre-charging process by the pre-charging circuit 1, the control unit 13 controls the first R-phase switching element S R1 , the second R-phase switching element S R2 , the first S-phase switching element S S1 and the second S-phase switching element S S2 Each of these is appropriately controlled to be turned on and off.

[0083] 6, the first R-phase switching element S is connected to the R-phase power line. R1 and the second R-phase switching element S R2 a first S-phase switching element S S1and the second S-phase switching element S S2 The above description has been given of an example in which the first S-phase switching element S is provided on the S-phase power line. S1 and the second S-phase switching element S S2 is provided, and a first T-phase switching element S is provided on the T-phase power line. T1 and the second T-phase switching element S T2 Similarly, the above description can be applied to an example in which a first R-phase switching element S is provided on the R-phase power line. R1 and the second R-phase switching element S R2 is provided, and a first T-phase switching element S is provided on the T-phase power line. T1 and the second T-phase switching element S T2 This is also applicable to an example in which

[0084] In addition to providing the effects of the first embodiment, the second embodiment of the present disclosure has the advantage of being able to eliminate the diodes provided in the pre-charging circuit of the first embodiment. Furthermore, the second embodiment of the present disclosure has the advantage of being able to shorten the time required to complete pre-charging because the frequency of conduction is increased compared to the first embodiment.

[0085] Third Embodiment FIG. 7 is a diagram showing a pre-charging circuit and a motor driving device according to a third embodiment of the present disclosure.

[0086] 7 , a pre-charging circuit 1 according to a third embodiment of the present disclosure includes, as a switch unit 11, switching elements that are provided in a three-phase power line between the three-phase AC power supply and the AC input side of the converter and can be turned on and off in both directions, from the three-phase AC power supply 5 to the AC input side of the converter 2 and from the AC input side of the converter 2 to the three-phase AC power supply 5. Each switching element is selectively switched between conducting a current flowing in a first conduction direction from the three-phase AC power supply 5 to the AC input side of the converter 2 when on, conducting a current flowing in a second conduction direction from the AC input side of the converter 2 to the three-phase AC power supply 5 when on, and electrically blocking electrical connection between the three-phase AC power supply 5 and the AC input side of the converter 2 when off.

[0087] The converter 2, smoothing capacitor 3, inverter 4, three-phase AC power supply 5, motor 6, power supply voltage detection circuit 12, current detection circuit 14, and capacitor voltage detection circuit 15 are as described with reference to FIGS.

[0088] A first R-phase switching element S is connected to the R-phase power line between the three-phase AC power supply 5 and the AC input side of the converter 2. R1 and the second R-phase switching element S R2 The first R-phase switching element S R1 and the second R-phase switching element S R2 The first R-phase switching element S is connected in anti-parallel so that the conduction directions of the first R-phase switching element S are opposite to each other when they are turned on. R1 When turned on, the second R-phase switching element S conducts a current flowing in a first conduction direction from the three-phase AC power supply 5 to the AC input side of the converter 2. R2 When turned on, the first R-phase switching element S conducts a current flowing in a second conduction direction from the AC input side of the converter 2 to the three-phase AC power supply 5. R1 and the second R-phase switching element S R2 When both of these are turned off, the R-phase power line is electrically disconnected between the three-phase AC power supply 5 and the AC input side of the converter 2 .

[0089] A first S-phase switching element S is connected to the S-phase power line between the three-phase AC power source 5 and the AC input side of the converter 2. S1 and the second S-phase switching element S S2 The first S-phase switching element S S1 and the second S-phase switching element S S2 The first S-phase switching element S is connected in anti-parallel so that the conduction direction when turned on is opposite to the first S-phase switching element S. S1 When turned on, the second S-phase switching element S conducts a current flowing in a first conduction direction from the three-phase AC power supply 5 to the AC input side of the converter 2. S2 When turned on, the first S-phase switching element S conducts a current flowing in a second conduction direction from the AC input side of the converter 2 to the three-phase AC power supply 5. S1 and the second S-phase switching element S S2When both of these are turned off, the S-phase power line is electrically disconnected between the three-phase AC power supply 5 and the AC input side of the converter 2 .

[0090] A first T-phase switching element S is connected to the T-phase power line between the three-phase AC power source 5 and the AC input side of the converter 2. T1 and the second T-phase switching element S T2 The first T-phase switching element S T1 and the second T-phase switching element S T2 The first T-phase switching element S is connected in anti-parallel so that the conduction directions of the first T-phase switching element S are opposite to each other when they are turned on. T1 When turned on, the second T-phase switching element S conducts a current flowing in a first conduction direction from the three-phase AC power supply 5 to the AC input side of the converter 2. T2 When turned on, the first T-phase switching element S conducts a current flowing in a second conduction direction from the AC input side of the converter 2 to the three-phase AC power supply 5. T1 and the second T-phase switching element S T2 When both of these are turned off, the T-phase power line is electrically disconnected between the three-phase AC power supply 5 and the AC input side of the converter 2 .

[0091] The control unit 13 controls the pre-charging of the smoothing capacitor 3 by controlling the on / off of the switch unit 11 based on information relating to the AC voltage detected by the power supply voltage detection circuit 12 .

[0092] Furthermore, when the current detected by the current detection circuit 14 is an overcurrent, the control unit 13 performs control to turn off all switching elements in the switch unit 11, thereby electrically disconnecting the three-phase AC power supply 5 from the AC input side of the converter 2. The flowchart shown in Fig. 3 is also applied to the overcurrent protection process of the third embodiment.

[0093] The control unit 13 controls the on / off of the switch unit 11 for pre-charging as follows: If the converter 2 is configured as a PWM switching control type rectifier or a 120-degree conduction type rectifier, all switching elements in the converter 2 are turned off during the pre-charging period, and the converter 2 simply functions as a diode rectifier.

[0094] The control unit 13 controls the switching elements to switch from off to on at a timing when a switch-on condition is satisfied. The timing when the switch-on condition is satisfied can be acquired by referring to data relating to the value of the AC voltage of the three-phase AC power supply 5 detected by the power supply voltage detection circuit 12. For example, any of the following timings is set as the timing when the switch-on condition is satisfied. A first example of the timing when the switch-on condition is satisfied is a timing that is earlier by a first predetermined time τ1 than the timing when the magnitude relationship of the phase voltages of the three phases detected by the power supply voltage detection circuit 12 is reversed. A second example of the timing when the switch-on condition is satisfied is a timing when the line voltage between the three phases detected by the power supply voltage detection circuit 12 becomes lower than a predetermined voltage threshold V th When the timing at which the switch-on condition is satisfied arrives, the control unit 13 performs control to switch from off to on the switching elements of the phases where the line voltages among the three phases detected by the power supply voltage detection circuit 12 have switched from positive to negative so as to conduct current flowing in a first conduction direction. When this timing arrives, the control unit 13 performs control to switch from off to on the switching elements of the phases where the line voltages among the three phases detected by the power supply voltage detection circuit 12 have switched from negative to positive so as to conduct current flowing in a second conduction direction.

[0095] Furthermore, after a switching element (i.e., a switching element that is the target of the above-described control of switching from off to on) is turned on, the control unit 13 controls the switching element to switch from on to off at a timing when a switch-off condition is satisfied. The timing when the switch-off condition is satisfied can be obtained by referring to data related to the value of the AC voltage of the three-phase AC power supply 5 detected by the power supply voltage detection circuit 12. Alternatively, the timing when the switch-off condition is satisfied can be obtained by referring to data related to the value of the current of each phase detected by the current detection circuit 14. For example, any of the following is set as the timing when the switch-off condition is satisfied. A first example of the timing when the switch-off condition is satisfied is the timing when the current flowing through the switched-on switching element becomes approximately zero. A second example of the timing when the switch-off condition is satisfied is the timing when a second predetermined time τ2 has elapsed since the line voltage was switched from positive to negative and from negative to positive.

[0096] 8 is a waveform diagram showing a specific example of the operation of the switch unit in the pre-charging process by the pre-charging circuit according to the third embodiment of the present disclosure, in which the R-phase voltage of the three-phase AC power supply 5 is indicated by a bold solid line, the S-phase voltage is indicated by a bold dashed line, and the T-phase voltage is indicated by a bold dashed line.

[0097] Here, as an example, the first R-phase switching element S R1 , second S-phase switching element S S2 and the second T-phase switching element S T2 The on / off control for the inverter will be described.

[0098] In the section A1, the R-phase voltage is the largest among the three-phase voltages of the three-phase AC power supply 5. The R-phase-S-phase line voltage (based on the S-phase) V RS gradually decreases, but the R-phase-T-phase line voltage (T-phase reference) V RT The first R-phase switching element S R1 and the second S-phase switching element S S2Therefore, in the third embodiment, a large current does not flow at a timing that is earlier by a first predetermined time τ1 than the timing at which the magnitude relationship of the phase voltages of the three phases detected by the power supply voltage detection circuit 12 is reversed (the timing at which the R phase and the S phase switch from section A1 to section A2), or at a timing that is earlier by a first predetermined time τ1 than the timing at which the line voltage (S phase reference) V between the R phase and the S phase is reversed. RS is a predetermined voltage threshold V th When the timing becomes as follows, the R-phase to S-phase line voltage (S-phase reference) V RS The first R-phase switching element S R1 , and performs control to switch from OFF to ON so as to conduct a current flowing in the first conduction direction, and the line voltage between the S phase and the R phase (based on the R phase) V SR The second S-phase switching element S S2 , the first R-phase switching element S R1 , the diode D of the R-phase upper arm of the converter 2 RU , smoothing capacitor 3, diode D of the S-phase lower arm of converter 2 SL , and the second S-phase switching element S S1 A current flows through the path leading to the three-phase AC power supply 5 via the above.

[0099] In section A2, the magnitude relationship between the R-phase voltage and the S-phase voltage is reversed, and the R-phase voltage becomes the second largest phase voltage. RS Therefore, in the third embodiment, the first R-phase switching element S R1 and the second S-phase switching element S S1 When the current flowing through the RS When a second predetermined time τ2 has elapsed since the timing when the voltage V1 changes from positive to negative (the timing when the voltage V2 changes from section A1 to section A2), the R-phase-S-phase line voltage (S-phase reference) V RS The first R-phase switching element S R1 and the S-phase-R-phase line voltage (S-phase reference) VSR The second S-phase switching element S S1 The control unit 100 controls the switching from on to off.

[0100] In addition, in section A2, the S-phase voltage is the largest among the three-phase voltages of the three-phase AC power supply 5. The R-phase-S-phase line voltage (based on the S-phase) V RS gradually increases, but the R-phase-T-phase line voltage (T-phase reference) V RT The first R-phase switching element S R1 and the second T-phase switching element S T2 Therefore, in the third embodiment, a large current does not flow at a timing that is earlier by a first predetermined time τ1 than the timing at which the magnitude relationship of the phase voltages of the three phases detected by the power supply voltage detection circuit 12 is reversed (the timing at which the R phase and the T phase switch from section A2 to section A3), or at a timing that is earlier by a first predetermined time τ1 than the timing at which the line voltage (T phase reference) V between the R phase and the T phase is reversed. RT is a predetermined voltage threshold V th When the timing becomes as follows, the R-phase to T-phase line voltage (T-phase reference) V RT The first R-phase switching element S R1 , and performs control to switch from OFF to ON so as to conduct a current flowing in the first conduction direction, and the line voltage between the T phase and the R phase (based on the R phase) V TR The second T-phase switching element S T2 , the first R-phase switching element S R1 , the diode D of the R-phase upper arm of the converter 2 RU , smoothing capacitor 3, diode D of the T-phase lower arm of converter 2 TL , and the second T-phase switching element S T1 A current flows through the path leading to the three-phase AC power supply 5 via the above.

[0101] In section A3, the R-phase voltage is the smallest among the three-phase voltages of the three-phase AC power supply 5. In section A2 before entering section A3, the R-phase voltage is supplied from the three-phase AC power supply 5 to the first R-phase switching element S R1, the diode D of the R-phase upper arm of the converter 2 RU , smoothing capacitor 3, diode D of the T-phase lower arm of converter 2 TL , and the current flowing through the path leading to the three-phase AC power supply 5 via the T-phase power line is reduced to the R-phase-T-phase line voltage (T-phase reference) V RT Therefore, in the third embodiment, the first R-phase switching element S R1 and the second T-phase switching element S T2 When the current flowing through the RT Switching from positive to negative and the line voltage between the T phase and the R phase (based on the R phase) V TR When a second predetermined time τ2 has elapsed since the timing of the switch from negative to positive (the timing of the switch from section A2 to section A3 for the R phase and the T phase), the R-phase-T phase line voltage (T phase reference) V RT The first R-phase switching element S R1 and T-phase-R-phase line voltage (R-phase reference) V TR The second T-phase switching element S T2 The control unit 100 controls the switching from on to off.

[0102] In section A4, the magnitude relationship between the R-phase voltage and the S-phase voltage is reversed, but the R-phase-S-phase line voltage (S-phase reference) V RS Since gradually increases, the first R-phase switching element S R1 and the second S-phase switching element S S2 About keeping it off.

[0103] Section A4 is followed by section A1, where the above-described on / off control is executed again.

[0104] As described above, the first R-phase switching element S in the switch unit 11 is R1 , second S-phase switching element S S2 and the second T-phase switching element S T2 The above description has been made on the on / off control of the first S-phase switching element S S1, second T-phase switching element S T2 and the second R-phase switching element S R2 and the first T-phase switching element S T1 , the second R-phase switching element S R2 and the second S-phase switching element S S2 During the pre-charging process by the pre-charging circuit 1, the control unit 13 controls the first R-phase switching element S R1 , the second R-phase switching element S R2 , the first S-phase switching element S S1 and the second S-phase switching element S S2 , the first T-phase switching element T S1 and the second T-phase switching element S T2 Each of these is appropriately controlled to be turned on and off.

[0105] In addition to the effects of the first and second embodiments, the third embodiment of the present disclosure has the advantage that the phase of the switching element to be turned on does not need to be limited to the phase having the second highest phase voltage among the three-phase voltages. Furthermore, the third embodiment of the present disclosure has the advantage that the conduction frequency is increased compared to the first and second embodiments, thereby shortening the time required to complete pre-charging.

[0106] <Matters commonly applied to the first to third embodiments>

[0107] As the smoothing capacitor 3 is charged by the pre-charging circuit 1 according to the first to third embodiments of the present disclosure, the voltage of the smoothing capacitor 3 gradually increases. Therefore, the first predetermined time τ or the voltage threshold V used when switching the switching element in the switch unit 11 from off to on is th If pre-charging by the pre-charging circuit 1 continues while maintaining a constant value, the difference between the voltage of the smoothing capacitor 3 and the line voltage of the three-phase AC power supply 5 gradually decreases. When the difference between the voltage of the smoothing capacitor 3 and the line voltage of the three-phase AC power supply 5 gradually decreases, the power flowing from the three-phase AC power supply 5 to the smoothing capacitor 3 via the converter 2 gradually decreases, and the charging function of the pre-charging circuit 1 for the smoothing capacitor 3 gradually decreases.

[0108] Therefore, in the first to third embodiments of the present disclosure, during the pre-charging period by the pre-charging circuit 1, the first predetermined time τ or the voltage threshold V used when the control unit 13 switches the switching element in the switch unit 11 from off to on is set to 0. th The first predetermined time τ or the voltage threshold V th are stored in, for example, a rewritable storage unit (not shown) in the pre-charging circuit 1. The storage unit may be configured with, for example, an electrically erasable and recordable non-volatile memory such as an EEPROM (registered trademark), or a random access memory that can be read and written at high speed such as a DRAM or an SRAM.

[0109] Hereinafter, the first predetermined time τ or the voltage threshold V th Here are some ways to change it:

[0110] In the first change method, the first predetermined time τ or the voltage threshold V used when the control unit 13 switches the switching element in the switch unit 11 from off to on is changed according to the voltage of the smoothing capacitor 3 detected by the capacitor voltage detection circuit 15. th That is, the larger the voltage of the smoothing capacitor 3 detected by the capacitor voltage detection circuit 15, the longer the first predetermined time τ1 is set, or the voltage threshold V th As a result, the higher the voltage of the smoothing capacitor 3, the longer the ON time of the switching element in the switch unit 11, so that the gradual decrease in the power flowing from the three-phase AC power supply 5 to the smoothing capacitor 3 via the converter 2 is suppressed, and the charging function of the pre-charging circuit 1 for the smoothing capacitor 3 can be maintained.

[0111] In the second change method, the first predetermined time τ or the voltage threshold V used when the control unit 13 switches the switching element in the switch unit 11 from off to on is changed depending on the elapsed time from the start of pre-charging of the smoothing capacitor 3 by the pre-charging circuit 1. th That is, the longer the time that has elapsed since the start of preliminary charging of the smoothing capacitor 3, the longer the first predetermined time τ1 is set, or the voltage threshold Vth As a result, the longer the time that has elapsed since the start of pre-charging of the smoothing capacitor 3, the longer the on time of the switching element in the switch unit 11, so that the decrease in the power flowing from the three-phase AC power supply 5 to the smoothing capacitor 3 via the converter 2 is gradually suppressed, and the charging function of the pre-charging circuit 1 for the smoothing capacitor 3 can be maintained.

[0112] In the third modification method, the first predetermined time τ or the voltage threshold V used when the control unit 13 switches the switching element in the switch unit 11 from off to on is changed depending on the peak value of the current of each phase flowing from the three-phase AC power supply 5 to the converter during the pre-charging period of the smoothing capacitor 3 by the pre-charging circuit 1. th The first predetermined time τ or the voltage threshold V th If pre-charging by the pre-charging circuit 1 continues while maintaining a constant value, the difference between the voltage of the smoothing capacitor 3 and the line voltage of the three-phase AC power supply 5 gradually decreases. The peak value of the current of each phase flowing from the three-phase AC power supply 5 to the converter decreases. Therefore, in the third modification method, the current detection circuit 14 detects the peak value of the current of each phase flowing from the three-phase AC power supply 5 to the converter, and gradually lengthens the first predetermined time τ1 or adjusts the voltage threshold V so that the peak value of the detected current is maintained. th Gradually increase the size.

[0113] In the fourth change method, the first predetermined time τ or the voltage threshold V used when the control unit 13 switches the switching element in the switch unit 11 from off to on is changed. th is changed at a predetermined constant rate of increase. That is, the first predetermined time τ is lengthened at a constant rate of increase, or the voltage threshold V th Increase at a constant rate.

[0114] Although the embodiments of the present disclosure have been described in detail, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible in these embodiments without departing from the gist of the invention or the spirit of the present invention derived from the content of the claims and their equivalents. For example, in the above-described embodiments, the order of each operation and the order of each process are shown as examples and are not limited to these. The same applies when numerical values ​​or mathematical expressions are used in the description of the above-described embodiments.

[0115] REFERENCE SIGNS LIST 1 Pre-charging circuit 2 Converter 3 Smoothing capacitor 4 Inverter 5 Three-phase AC power supply 6 Motor 11 Switch unit 12 Power supply voltage detection circuit 13 Control unit 14 Current detection circuit 15 Capacitor voltage detection circuit 100 Motor drive device D RL Diode D of the lower arm of the R phase SL Diode D of the lower arm of the S phase TL Diode D of the lower arm of the T phase RU R-phase upper arm diode D SU S-phase upper arm diode D TU Diode S of the upper arm of the T phase R R-phase switching element S S S-phase switching element S T T-phase switching element S R1 First R-phase switching element S R2 Second R-phase switching element S S1 First S-phase switching element S S2 Second S-phase switching element S T1 First T-phase switching element S T2 Second T-phase switching element

Claims

1. A pre-charging circuit for pre-charging a smoothing capacitor connected to a DC output side of a converter that converts input AC power into DC power and outputs the DC power, a switch unit having a switching element that electrically connects a three-phase AC power supply and an AC input side of the converter when the switching element is turned on and electrically disconnects the three-phase AC power supply and the AC input side of the converter when the switching element is turned off; a power supply voltage detection circuit for detecting an AC voltage of the three-phase AC power supply; a control unit that controls on / off of the switching element of the switch unit based on information about the AC voltage detected by the power supply voltage detection circuit; A pre-charging circuit comprising:

2. a current detection circuit for detecting a current of each phase flowing from the three-phase AC power supply to an AC input side of the converter; 2. The pre-charging circuit according to claim 1, wherein when the current detected by the current detection circuit is an overcurrent, the control unit controls to turn off the switching element of the switch unit, thereby electrically disconnecting the three-phase AC power supply and the AC input side of the converter.

3. 2. The pre-charging circuit according to claim 1, wherein the switch unit includes a pair of a switching element, which when turned on conducts a current flowing from the three-phase AC power supply to the AC input side of the converter and when turned off electrically disconnects the three-phase AC power supply and the AC input side of the converter, and a diode connected in anti-parallel to the switching element, for each phase of a three-phase power line between the three-phase AC power supply and the AC input side of the converter.

4. The control unit is a phase having a second largest phase voltage among the three phase voltages detected by the power supply voltage detection circuit is determined as a conducting phase, and a control is performed to switch a switching element of the conducting phase from off to on at a timing that is a first predetermined time earlier than a timing at which the magnitude relationship between the phase voltage of the conducting phase and the phase voltage of the minimum magnitude is reversed, or at a timing at which the line voltage between the conducting phase and the phase of the minimum magnitude becomes equal to or lower than a predetermined voltage threshold value; 4. The pre-charging circuit according to claim 3, wherein after the switching element of the conducting phase is turned on, control is performed to switch the switching element of the conducting phase from on to off at a timing when a current flowing through the switching element of the conducting phase becomes substantially zero, or at a timing when a second predetermined time has elapsed since a magnitude of a phase voltage of the conducting phase becomes a minimum among three phase voltages.

5. 3. The pre-charging circuit according to claim 1, wherein the switch unit includes switching elements in two phases of a three-phase power line between the three-phase AC power source and the AC input side of the converter, the switching elements being capable of selectively switching between conducting a current flowing in a first conduction direction from the three-phase AC power source to the AC input side of the converter when the switching elements are on, conducting a current flowing in a second conduction direction from the AC input side of the converter to the three-phase AC power source when the switching elements are on, and electrically blocking electrical connection between the three-phase AC power source and the AC input side of the converter when the switching elements are off.

6. The control unit is at a timing that is a first predetermined time earlier than a timing at which the magnitude relationship between the phase having the switching element and the phase not having the switching element is reversed among the three-phase phase voltages detected by the power supply voltage detection circuit, or at a timing at which the line voltage between the three phases detected by the power supply voltage detection circuit becomes equal to or lower than a predetermined voltage threshold, control is performed to switch from off to on for switching elements of a phase in which the line voltage between the phase having the switching element and the phase not having the switching element detected by the power supply voltage detection circuit switches from positive to negative so as to conduct in the first conduction direction, and control is performed to switch from off to on for switching elements of a phase in which the line voltage switches from negative to positive so as to conduct in the second conduction direction; 6. The pre-charging circuit according to claim 5, wherein after the switching element is turned on, control is performed to switch the switching element from on to off at a timing when a current flowing through the switched-on switching element becomes substantially zero, or at a timing when a second predetermined time has elapsed after the line voltage is switched from positive to negative and from negative to positive.

7. 2. The pre-charging circuit according to claim 1, wherein the switch unit includes a switching element in a three-phase power line between the three-phase AC power source and the AC input side of the converter, the switching element being capable of selectively switching between conducting a current flowing in a first conduction direction from the three-phase AC power source to the AC input side of the converter when the switching element is on, conducting a current flowing in a second conduction direction from the AC input side of the converter to the three-phase AC power source when the switching element is on, and electrically blocking electrical connection between the three-phase AC power source and the AC input side of the converter when the switching element is off.

8. The control unit is at a timing a first predetermined time earlier than a timing at which the magnitude relationship of the phase voltages of the three phases detected by the power supply voltage detection circuit is reversed, or at a timing at which the line voltage between the three phases detected by the power supply voltage detection circuit becomes equal to or lower than a predetermined voltage threshold, a control is performed to switch from off to on for a switching element of a phase where the line voltage between the three phases detected by the power supply voltage detection circuit switches from positive to negative so as to conduct a current flowing in the first conduction direction, and a control is performed to switch from off to on for a switching element of a phase where the line voltage between the three phases detected by the power supply voltage detection circuit switches from negative to positive so as to conduct a current flowing in the second conduction direction; 8. The pre-charging circuit according to claim 7, wherein after the switching element is turned on, control is performed to switch the switching element from on to off at a timing when a current flowing through the switched-on switching element becomes substantially zero, or at a timing when a second predetermined time has elapsed since the line voltage was switched from positive to negative and from negative to positive.

9. 9. The pre-charging circuit according to claim 4, wherein the first predetermined time or the voltage threshold used when the control unit switches the switching element from off to on is changed according to the voltage of the smoothing capacitor.

10. 10. The pre-charging circuit according to claim 9, wherein the higher the voltage of the smoothing capacitor, the longer the first predetermined time used by the control unit to switch the switching element from off to on, or the larger the voltage threshold is.

11. 9. The pre-charging circuit according to claim 4, wherein the first predetermined time or the voltage threshold used when the control unit switches the switching element from off to on is changed depending on the elapsed time from the start of pre-charging of the smoothing capacitor.

12. 12. The pre-charging circuit according to claim 11, wherein the longer the elapsed time from the start of pre-charging of the smoothing capacitor, the longer the first predetermined time used by the control unit to switch the switching element from off to on, or the larger the voltage threshold value.

13. 9. The pre-charging circuit according to claim 4 or 8, wherein the first predetermined time or the voltage threshold used when switching the switching element from off to on by the control unit is changed according to a peak value of a current of each phase flowing from the three-phase AC power supply to the AC input side of the converter during a pre-charging period of the smoothing capacitor.

14. 9. The pre-charging circuit according to claim 4 or 8, wherein the first predetermined time used when the control unit switches the switching element from off to on is gradually lengthened at a constant rate of increase, or the voltage threshold is gradually increased at a constant rate of increase.

15. The converter; The smoothing capacitor; A pre-charging circuit according to claim 1; an inverter that converts the DC power into AC power for driving a motor and outputs the AC power; A motor drive device comprising: