Pre-charging circuit and motor drive device

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

[Technical Field]

[0001] This invention relates to a pre-charging circuit and a motor drive device. [Background technology]

[0002] In a motor drive system, the AC power input from the AC power source is converted to DC power by a converter (rectifier circuit) and output to the DC link. Further, an inverter converts the DC power in the DC link back to AC power, and this AC power is supplied as the driving power for the motor. The DC link refers to the circuit section that electrically connects the DC output side of the converter and the DC input side of the inverter, and is sometimes called the "DC link section," "DC link," "DC bus," or "DC intermediate circuit."

[0003] The DC link is equipped with a smoothing capacitor that has the function of suppressing the pulsation component of the converter's DC output and also storing DC power. The smoothing capacitor needs to be charged to a predetermined voltage between the time the motor drive unit is powered on and before the motor starts driving (i.e., before the power conversion operation by the inverter starts). This charging is also called "pre-charging" or "initial charging".

[0004] Since pre-charging begins when no energy is stored in the smoothing capacitor, a large inrush current flows from the AC power supply to the DC link via the converter immediately after the motor drive unit is powered on. For this reason, the DC link is generally equipped with a pre-charging circuit that pre-charges the smoothing capacitor while suppressing the inrush current that occurs immediately after the motor drive unit is powered on. This 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 in the off state to suppress inrush current with the pre-charging resistor, and after pre-charging is complete, the switching element is turned on to bypass the pre-charging resistor.

[0006] For example, an inrush current prevention circuit for a DC power supply circuit is known, comprising a rectifier circuit powered from an AC power supply via a semiconductor switching element and a smoothing capacitor connected to the output side of the rectifier circuit, the circuit comprising: a power supply voltage detection means for detecting the output voltage of the AC power supply; a terminal voltage detection means for detecting the terminal voltage of the smoothing capacitor during the off period of the semiconductor switching element; and a control means for performing switching control at startup of the DC power supply circuit, which turns on the semiconductor switching element at each timing when the absolute value of the voltage detected by the power supply voltage detection means reaches a peak value and then drops 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 a predetermined period set at least until the absolute value of the voltage detected by the power supply voltage detection means rises to the target level, wherein the control means terminates the switching control and maintains the semiconductor switching element in the on state when the voltage detected by the terminal voltage detection means rises to a predetermined specified voltage or higher in response to the execution of the switching control (see, for example, Patent Document 1).

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

[0008] [Patent Document 1] Japanese Patent Publication No. 2007-129875 [Patent Document 2] Japanese Patent Application Publication No. 09-212245 [Overview of the project] [Problems that the invention aims to solve]

[0009] If an abnormality such as a short circuit occurs in the motor drive unit, an overcurrent may flow from the AC input side to the converter, potentially destroying the motor drive unit. The problem that this disclosure aims to solve is to protect the motor drive unit from overcurrent generated on the AC input side of the converter. [Means for solving the problem]

[0010] According to one aspect of the present disclosure, a pre-charging circuit for pre-charging a smoothing capacitor connected to the DC output side of a converter that converts input AC power to DC power and outputs it comprises: a switch section having a switching element that electrically connects a three-phase AC power supply and the AC input side of the converter when ON and electrically disconnects the three-phase AC power supply and the AC input side of the converter when OFF; a power supply voltage detection circuit that detects the AC voltage of the three-phase AC power supply; and a control section that controls the on / off state of the switching element of the switch section based on information regarding the AC voltage detected by the power supply voltage detection circuit. The switch section is provided with a set of a switching element and a diode connected in antiparallel to the switching element, which conducts current flowing from the three-phase AC power supply to the AC input side of the converter when ON and electrically blocks the connection between the three-phase AC power supply and the AC input side of the converter when OFF. This set is provided for each phase of the three-phase power line between the three-phase AC power supply and the AC input side of the converter. The control unit determines the phase with the second largest phase voltage among the three phase voltages detected by the power supply voltage detection circuit as the conducting phase, and reverses the magnitude relationship between the phase voltage of the conducting phase and the phase voltage of the phase with the smallest magnitude. Control is performed to switch the conducting phase switching element from off to on at a timing earlier than a first predetermined time, or when the line voltage between the conducting phase and the phase with the smallest magnitude falls below a predetermined voltage threshold. After the conducting phase switching element is turned on, control is performed to switch the conducting phase switching element from on to off at a timing when the current flowing through the conducting phase switching element becomes approximately zero, or when a second predetermined time has elapsed since the magnitude of the conducting phase voltage became the smallest of the three phase voltages. .

[0011] Furthermore, according to one aspect of this disclosure, the motor drive device comprises a converter, a smoothing capacitor, the above-mentioned pre-charging circuit, and an inverter that converts DC power into AC power for motor driving and outputs it. [Effects of the Invention]

[0012] According to one aspect of this disclosure, the motor drive can be protected from overcurrents generated on the AC input side of the converter. [Brief explanation of the drawing]

[0013] [Figure 1] This figure shows a pre-charging circuit and motor drive device according to the first embodiment of the present disclosure. [Figure 2] This flowchart shows the operation flow of the pre-charging process by the pre-charging circuit according to the first embodiment of this disclosure. [Figure 3] This flowchart shows the operation flow of the overcurrent protection process by a motor drive device having a pre-charging circuit according to the first to third embodiments of this disclosure. [Figure 4] This waveform diagram shows 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 this disclosure. [Figure 5] This figure shows a pre-charging circuit and motor drive device according to a second embodiment of the present disclosure. [Figure 6] This waveform diagram shows 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 this disclosure. [Figure 7] This figure shows a pre-charging circuit and motor drive device according to a third embodiment of the present disclosure. [Figure 8] This waveform diagram shows 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 this disclosure. [Modes for carrying out the invention]

[0014] The pre-charging circuit and motor drive device of the embodiment will be described below with reference to the drawings. In the following description, components having the same or similar functions will be denoted by the same reference numerals. Duplication of these components may be omitted.

[0015] <First Embodiment> Figure 1 shows a preliminary charging circuit and motor drive device according to a first embodiment of the present disclosure.

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

[0017] As shown in Figure 1, the motor drive device 100 according to the first embodiment of this disclosure comprises 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] Converter 2 is a rectifier that converts the input AC power into DC power and outputs this DC power to the DC link, which is the DC output side of Converter 2. Converter 2 is composed of a three-phase bridge circuit. Examples of Converter 2 include PWM switching control rectifiers, diode rectifiers, and 120-degree energizing rectifiers. In the example shown in Figure 1, Converter 2 is composed of a PWM switching control rectifier. For example, when Converter 2 is composed of a PWM switching control rectifier or a 120-degree energizing rectifier, it consists of a bridge circuit of switching elements and diodes connected in antiparallel, and each switching element is controlled on or off in accordance with a drive command received from a higher-level control circuit (not shown) to perform AC-DC power conversion. In this case, examples of switching elements include FETs, IGBTs, thyristors, GTOs (Gate Turn-Off thyristors), and transistors, but other switching elements may also be used.

[0019] The smoothing capacitor 3 is installed in the 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 referred to as a DC link capacitor. The smoothing capacitor 3 has the function of suppressing the pulsation component of the DC output of the converter 2 and the function of storing the DC power used by the inverter 4 to generate AC power. Examples of smoothing capacitors 3 include electrolytic capacitors and film capacitors.

[0020] The inverter 4 is connected to the DC output side of the converter 2 via a smoothing capacitor 3, and converts the DC power in the DC link into AC power for motor drive and outputs it to the AC output side of the inverter 4. The inverter 4 consists of a bridge circuit of a switching element and a diode connected in antiparallel to it. The inverter 4 is configured as a three-phase bridge circuit when the motor 6 is a three-phase AC motor, and as a single-phase bridge circuit when the motor 6 is a single-phase AC motor. In the example shown in Figure 1, the motor 6 is a three-phase AC motor, so the inverter 4 is configured as 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 by, for example, 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), converts the DC power in the DC link into AC power for motor drive, and outputs it 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 inverter 4 is controlled based on drive commands created by a higher-level control circuit, similar to a typical motor drive system. The higher-level control circuit generates drive commands to control the speed, torque, or rotor position of motor 6 based on the motor 6's speed (speed feedback), the current flowing through the motor 6's windings (current feedback), a predetermined torque command, and the motor 6's operation program. Note that the configuration of the higher-level control circuit defined here is merely an example, and the configuration of the higher-level control circuit may be defined to include terms such as a position command creation unit, a torque command creation unit, and a switching command creation unit. Furthermore, if converter 2 is configured as a PWM switching control type rectifier or a 120-degree energizing type rectifier, the power conversion operation of converter 2 is controlled based on the drive commands created by the higher-level control circuit.

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

[0023] The switch section 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 it is on, and electrically disconnects them when it is off. In the first embodiment, the switch section 11 includes an R-phase switching element S R , an S-phase switching element S S , and a T-phase switching element S T . Among the three-phase power lines between the three-phase AC power supply 5 and the AC input side of the converter 2, the R-phase power line has the R-phase switching element S R provided thereon, the S-phase power line has the S-phase switching element S S provided thereon, and the T-phase power line has the T-phase switching element S T provided thereon.

[0024] Each of the R-phase switching element S R , the S-phase switching element S S , and the T-phase switching element S T conducts the current flowing from the three-phase AC power supply 5 to the AC input side of the converter 2 when it is on, and electrically disconnects the three-phase AC power supply 5 and the AC input side of the converter 2 when it is off. Examples of the R-phase switching element S R , the S-phase switching element S S , and the T-phase switching element S T include IGBTs, MOSFETs, etc. A diode is connected in anti-parallel to each of the R-phase switching element S R , the S-phase switching element S S , and the T-phase switching element S T .

[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. The data regarding the AC voltage value 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 regarding the AC voltage value of the three-phase AC power supply 5 includes information on the amplitude and phase of the AC voltage of the three-phase AC power supply 5. The AC voltage data detected by the power supply voltage detection circuit 12 may also be used by the 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. The data regarding the current values ​​of each phase detected by the current detection circuit 14 is sent to the control unit 13. The data regarding the current values ​​of each phase includes information such as the amplitude and phase of the current. The data regarding the current of each phase detected by the current detection circuit 14 may also be used by the 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. Alternatively, 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. The data regarding the capacitor voltage value detected by the capacitor voltage detection circuit 15 is sent to the control unit 13. The data regarding the capacitor voltage value detected by the capacitor voltage detection circuit 15 may also be used by the 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 switching elements in the switch unit 11 to turn on and off based on information regarding the AC voltage detected by the power supply voltage detection circuit 12. When the control unit 13 controls the switching unit 11 to turn on and off for the pre-charging of the smoothing capacitor 3, data regarding the current values ​​of each phase detected by the current detection circuit 14 and data regarding the capacitor voltage values ​​detected by the capacitor voltage detection circuit 15 may be used.

[0029] Furthermore, when the current detection circuit 14 detects an overcurrent, the control unit 13 controls all switching elements of the switch unit 11 to turn them off, thereby electrically isolating the connection between the three-phase AC power supply 5 and the AC input side of the converter 2. This protects the motor drive device from overcurrents generated on the AC input side of the converter. Note that when the switch unit 11 shuts off an overcurrent, a surge voltage may be generated, so the R-phase switching element S R S-phase switching element S S , and T-phase switching element S T A surge absorption circuit, such as a varistor, may be connected in parallel to each of these.

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

[0031] First, during the pre-charging period, the control unit 13 controls the R-phase switching element S according to the magnitude of the phase voltage of the AC voltage detected by the power supply voltage detection circuit 12. R S-phase switching element S S , and T-phase switching element S TThe switching element for the phase that should be turned on is determined from among them. The phase of the switching element that should be turned on is called the "conducting phase". The control unit 13 determines the phase with 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 element of the conducting phase to switch from off to on at the timing that satisfies the switch-on condition. The timing that satisfies the switch-on condition can be obtained by referring to data on 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 can be set as the timing that satisfies the switch-on condition. A first example of the timing that satisfies the switch-on condition is a timing that is earlier by a first predetermined time τ1 than the timing at which the relative magnitudes of the phase voltage of the conducting phase and the phase voltage of the phase with the smallest magnitude are reversed. A second example of the timing that satisfies the switch-on condition is when the line voltage between the conducting phase and the phase with the smallest magnitude reaches a predetermined voltage threshold V th The following timing occurs: When the switch-on condition is met, AC power flows from the three-phase AC power supply 5 to the AC input side of converter 2 through the conducting phase switching element that is turned on. Then, DC power that flows out from the AC output side of converter 2 through the diode of converter 2 flows into the smoothing capacitor 3, and the smoothing capacitor 3 is charged.

[0033] Furthermore, after the conducting phase switching element is turned on, the control unit 13 controls the switching element of the conducting phase to switch from on to off at the timing that satisfies the switch-off condition. The timing that satisfies the switch-off condition can be obtained by referring to data on 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 that satisfies the switch-off condition can be obtained by referring to data on the value of the current of each phase detected by the current detection circuit 14. For example, one of the following can be set as the timing that satisfies the switch-off condition. A first example of the timing that satisfies the switch-off condition is the timing when the current flowing through the conducting phase switching element becomes approximately zero. The current flowing through the conducting phase switching element is detected by the current detection circuit 14. A second example of the timing that satisfies the switch-off condition is the timing when a second predetermined time τ2 has elapsed since the magnitude of the phase voltage of the conducting phase became the minimum of the three phase voltages.

[0034] A processing unit (processor) is provided within the motor drive unit 100 or the pre-charging circuit 1. Examples of processing units include ICs, LSIs, CPUs, MPUs, and DSPs. The control unit 13 and the higher-level control circuit (not shown) may be composed of a combination of analog circuits and a processing unit, or they may consist solely of a processing unit, or they may consist solely of analog circuits. For example, if the control unit 13 and the higher-level control circuit are constructed in software program format, the functions of the control unit 13 and the higher-level control circuit can be realized by operating the processing unit according to this software program. Alternatively, the control unit 13 and the higher-level control circuit may be implemented as semiconductor integrated circuits on which software programs realizing the functions of each part are written. Alternatively, the control unit 13 and the higher-level control circuit may be implemented as recording media on which software programs realizing the functions of each part are written. Furthermore, the control unit 13 may be provided within the higher-level control circuit.

[0035] Figure 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 Figure 2 involve the R-phase switching element S R S-phase switching element S S , and T-phase switching element S T This will be executed on all of them.

[0036] Before the motor drive unit 100 is powered on, the R-phase switching element S in the switch unit 11 R S-phase switching element S S , and T-phase switching element S T All of them are turned off. Therefore, the three-phase AC power supply 5 and the AC input side of converter 2 are electrically isolated in all three phase power lines. Also, the smoothing capacitor 3 is not charged. Furthermore, especially if converter 2 is composed of a PWM switching control rectifier or a 120-degree energized rectifier, during the pre-charging period all switching elements in converter 2 are turned off, and converter 2 functions simply as a diode rectifier.

[0037] When the motor drive unit 100 is powered on, the pre-charging of the smoothing capacitor 3 by the pre-charging circuit 1 begins, and the process enters 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 the switch-on condition is met. The process in step S102 is repeatedly executed at a period 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 met, 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 the switch-off condition is met. The process in step S104 is repeatedly executed at a period 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 met, 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 the pre-charging of the smoothing capacitor 3 is complete. If the capacitor voltage detected by the capacitor voltage detection circuit 15 reaches a predetermined charging voltage, the control unit 13 determines that the pre-charging of the smoothing capacitor 3 is complete and proceeds to step S107. If the capacitor voltage detected by the capacitor voltage detection circuit 15 does not reach a predetermined charging voltage, the control unit 13 determines that the pre-charging of the smoothing capacitor 3 is not complete and returns to step S101. The process in step S106 is repeatedly executed at a cycle shorter than the power supply frequency of the three-phase AC power supply 5.

[0044] If it is determined in step S106 that the pre-charging of the smoothing capacitor 3 is complete, then in step S107 the control unit 13 will turn the R-phase switching element S in the switch unit 11 R S-phase switching element S S , and T-phase switching element S T The control is performed to turn on all of them. After the pre-charge of the smoothing capacitor 3 is complete, the R-phase switching element S R S-phase switching element S S , and T-phase switching element S T Since conductivity is maintained, AC power flows from the three-phase AC power supply 5 to the AC input side of the converter 2, and the motor 6 is ready to be driven. The inverter 4 converts the DC power in the DC link into AC power for motor drive and outputs it to the AC output side of the inverter 4. The motor 6 is driven by the AC power for motor drive output from the AC output side of the inverter 4.

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

[0046] As explained with reference to Figures 1 and 2, after the pre-charging of the smoothing capacitor 3 is complete, the motor drive unit 100 drives the motor 6 with the AC power for motor driving output from the AC output side of the inverter 4. While the motor 6 is being driven, in step S201, 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.

[0047] In step S202, the control unit 13 determines whether or not 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 over a predetermined period of time. If an overcurrent is detected in step S202, the process proceeds to step S203; otherwise, the process returns to step S201. The process in step S202 is repeated at predetermined intervals.

[0048] If it is determined in step S202 that an overcurrent has occurred, in step S203 the control unit 13 will turn the R-phase switching element S in the switch unit 11 R S-phase switching element S S , and T-phase switching element S T This controls all of them to turn them off. As a result, the three-phase AC power supply 5 and the AC input side of the converter 2 are completely electrically isolated, protecting the motor drive unit 100 from overcurrent.

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

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

[0051] Here, as an example, the R-phase switching element S in the switch section 11 R This section describes the on / off control for this.

[0052] In section A1, the R-phase voltage is the largest among the three-phase voltages of the three-phase AC power supply 5, so the line voltage between the R-phase and S-phase (S-phase reference) V RS and the line voltage between the R phase and the T phase (T phase reference) V RT It is large. For example, in section A1, the R-phase switching element S R When turned on, the R-phase switching element S is powered by the three-phase AC power supply 5. R Diode D of the upper arm of the R phase of 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 to the three-phase AC power supply 5 via the diode connected in antiparallel to the R phase switching element S. R Keep it turned off.

[0053] In section A2, the relative magnitudes of the R-phase voltage and S-phase voltage are reversed, and the R-phase voltage becomes the second largest phase voltage. In section A2, the line voltage between the R-phase and S-phase (S-phase reference) V RS Therefore, the R-phase switching element S in section A2 R Even if you turn it on, the three-phase AC power supply 5 will not supply the R-phase switching element S RDiode D of the upper arm of the R phase of 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 diode connected in antiparallel to the three-phase AC power supply 5. On the other hand, in section A2, the R-phase switching element S R When this is turned on, the line voltage between the R phase and the T phase (T phase reference) V RT A current corresponding to the magnitude is supplied from the three-phase AC power supply 5 to the R-phase switching element S R Diode D of the upper arm of the R phase of converter 2 RU , smoothing capacitor 3, diode D of the lower T-phase arm of converter 2 TL , and T-phase switching element S T The current flows through a diode connected in antiparallel to the three-phase AC power supply 5. In section A2, the line voltage between the R phase and the T phase (T phase reference) V RT As it gradually decreases, the R-phase switching element S is located near the end of section A2. R When this is turned on, no large current flows. 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, at a timing that is a first predetermined time τ1 earlier than the timing at which the relative magnitudes of the R phase voltage of the conducting phase and the T phase voltage, which is the phase with the smallest magnitude, are reversed (the timing at which the switch occurs from section A2 to section A3), the R phase switching element S, which is the conducting phase, is turned on. R Switch it from off to on. Alternatively, the line voltage (T phase reference) V between the conducting phase R and the smallest T phase. RT The predetermined voltage threshold V th At the following timing, the R-phase switching element S, which is in the conducting phase, R Switches from off to on. The shorter the first predetermined time τ1, or the voltage threshold V th The smaller the value, the lower the line voltage between the R phase and the T phase (T phase reference) V. RT Therefore, the R-phase switching element S becomes smaller. R Even if you turn it on, the three-phase AC power supply 5 will not supply the R-phase switching element S R Diode D of the upper arm of the R phase of converter 2RU , smoothing capacitor 3, diode D of the lower T-phase arm of converter 2 TL , and T-phase switching element S T No large current flows through the path from the diode connected in antiparallel to the three-phase AC power supply 5.

[0054] In section A3, the R-phase voltage is the smallest among the three-phase voltages of the three-phase AC power supply 5. Therefore, in section A3, the line voltage between the R-phase and S-phase (S-phase reference) V RS Therefore, the R-phase switching element S R Even when it is turned on, the three-phase AC power supply 5 powers the R-phase switching element S R Diode D of the upper arm of the R phase of 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 from the diode connected in antiparallel to the three-phase AC power supply 5. Similarly, the line voltage between the R phase and the T phase (T phase reference) V RT Therefore, the R-phase switching element S R Even when it is turned on, the three-phase AC power supply 5 powers the R-phase switching element S R Diode D of the upper arm of the R phase of converter 2 RU , smoothing capacitor 3, diode D of the lower T-phase arm of converter 2 TL , and T-phase switching element S T No current flows through the diode connected in antiparallel to the three-phase AC power supply 5. In other words, within section A3, the R-phase switching element S R Since no current flows through it, the R-phase switching element S R Even when switching from on to off, no surge voltage is generated, and no switching loss occurs. Therefore, in the first embodiment, the conducting phase R-phase switching element S R At the moment when the current flowing through becomes approximately zero, or when a second predetermined time τ2 has elapsed since the magnitude of the R-phase voltage of the conducting phase became the minimum of the three-phase voltages, the R-phase switching element S RSwitch from on to off.

[0055] 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. If the R-phase switching element S R is maintained in the on state continuously from section A3 to section A4, there is a risk of a large current flowing through the path from the three-phase AC power supply 5 through the R-phase switching element S R , the diode D of the upper arm of the R-phase of the converter 2 RU , the smoothing capacitor 3, the diode D of the lower arm of the S-phase of the converter 2 SL , and the diode connected in anti-parallel to the S-phase switching element S S to the three-phase AC power supply 5. If the R-phase switching element S R is switched from on to off in section A4, a surge voltage will be generated and the switching loss will also increase. Therefore, as described above, at the stage of section A3 before entering section A4, the R-phase switching element S R is switched from on to off. And in section A4, the R-phase switching element S R is maintained in the off state.

[0056] As described above, the on / off control of the R-phase switching element S in the switch section 11 has been described with reference to FIG. 4. The above description is also applicable to the on / off control of the S-phase switching element S R and the on / off control of the T-phase switching element S S . When the above description is applied to the on / off control of the S-phase switching element S T , replace the R-phase switching element S in the above description S with the S-phase switching element S R , replace the S-phase switching element S in the above description S with the T-phase switching element S S , replace the T-phase switching element S in the above description T with the R-phase switching element S T R R R TWhen applied to on / off control of the R-phase switching element S described above, R T-phase switching element S T Reinterpret the above description as referring to the S-phase switching element S S R-phase switching element S R Reinterpret the above description as referring to the T-phase switching element S T S-phase switching element S S This can be reinterpreted as follows: In other words, during the pre-charging process by the pre-charging circuit 1, the control unit 13 controls the R-phase switching element S in the switch unit 11. R S-phase switching element S S , and T-phase switching element S T Each of these will be controlled to be turned on or off as needed.

[0057] As described above, the motor drive device 100 having the pre-charging circuit 1 according to the first embodiment of this disclosure has both a pre-charging function and a power supply cutoff function in the event of an overcurrent. According to the first embodiment of this disclosure, a pre-charging circuit that can cut off the power supply in the event of an overcurrent on the AC input side of the converter 2 can be realized.

[0058] Conventionally, to protect motor drive units from overcurrent, circuit breakers or fuses were provided on the AC input side of the converter. However, to prevent malfunctions of the circuit breakers or fuses during normal motor operation, it was necessary to select circuit breakers or fuses with a sufficiently large rating to allow for margin. Furthermore, because circuit breakers and fuses are mechanical switches, their switching operation is slow, and in the event of an overcurrent, the power supply may be cut off too late, failing to protect the motor drive unit. In contrast, in the pre-charging circuit according to the first embodiment of this disclosure, a semiconductor switching element is provided 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 ON and electrically disconnects the three-phase AC power supply 5 and the AC input side of the converter 2 when OFF. Therefore, power supply can be cut off quickly in the event of an overcurrent, and the motor drive unit can be protected more reliably. In addition, since there is no need to provide circuit breakers or fuses as in the conventional method, it contributes to miniaturization and cost reduction of the motor drive unit.

[0059] Furthermore, conventional pre-charging circuits were equipped with resistors and switches connected in parallel to the resistors. In contrast, the pre-charging circuit according to the first embodiment of this disclosure does not include charging resistors, thus enabling miniaturization and cost reduction of the motor drive device.

[0060] <Second Embodiment> Figure 5 shows a preliminary charging circuit and motor drive device according to a second embodiment of the present disclosure.

[0061] As shown in Figure 5, the pre-charging circuit 1 according to the second embodiment of the present disclosure includes a switch unit 11 that provides switching elements 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, on two of the three phase power lines between the three-phase AC power supply and the AC input side of the converter. Each switching element is capable of selectively switching between conducting current in a first conducting direction from the three-phase AC power supply 5 to the AC input side of the converter 2 when it is ON, conducting current in a second conducting direction from the AC input side of the converter 2 to the three-phase AC power supply 5 when it is ON, and electrically disconnecting the three-phase AC power supply 5 and the AC input side of the converter 2 when it is 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 Figures 1 to 4.

[0063] In the example shown in Figure 5, as an example, the switch section 11 in the pre-charging circuit 1 is provided with a first R-phase switching element S on the R-phase power line. R1 and the second R-phase switching element S R2 The first S-phase switching element S is provided in the S-phase power line. S1 and the second S-phase switching element S S2 It is equipped with the following.

[0064] Of the three phase power lines between the three-phase AC power supply 5 and the AC input side of the converter 2, the R-phase power line has a first R-phase switching element S. R1 and the second R-phase switching element S R2 A first R-phase switching element S is provided. R1 and the second R-phase switching element S R2 This means that they are connected in antiparallel so that the direction of conduction is reversed when they are ON. First R-phase switching element S R1 When ON, it conducts current in the first conductive direction, from the three-phase AC power supply 5 to the AC input side of the converter 2. Second R-phase switching element S R2When ON, it conducts current in a second conductive direction, from the AC input side of converter 2 to the three-phase AC power supply 5. First R-phase switching element S R1 and the second R-phase switching element S R2 When both are turned off, the three-phase AC power supply 5 and the AC input side of the converter 2 are electrically disconnected in the R-phase power line.

[0065] Of the three phase power lines between the three-phase AC power supply 5 and the AC input side of the converter 2, the S-phase power line has a first S-phase switching element S S1 and the second S-phase switching element S S2 A first S-phase switching element S is provided. S1 and the second S-phase switching element S S2 This means that they are connected in antiparallel so that the direction of conduction is reversed when they are ON. First S-phase switching element S S1 When ON, it conducts current in the first conductive direction from the three-phase AC power supply 5 to the AC input side of the converter 2. Second S-phase switching element S S2 When ON, it conducts current in a second conductive direction, from the AC input side of converter 2 to the three-phase AC power supply 5. First S-phase switching element S S1 and the second S-phase switching element S S2 When both are turned off, the three-phase AC power supply 5 and the AC input side of the converter 2 are electrically disconnected in the S-phase power line.

[0066] The control unit 13 controls the pre-charging of the smoothing capacitor 3 by turning the switching elements in the switch unit 11 on and off based on information about 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 controls all switching elements in the switch unit 11 to turn them off, thereby electrically isolating the connection between the three-phase AC power supply 5 and the AC input side of the converter 2. The flowchart shown in Figure 3 is also applied to the overcurrent protection process of the second embodiment.

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

[0069] The control unit 13 controls the switching element to switch from off to on at the timing that satisfies the switch-on condition. The timing that satisfies the switch-on condition can be obtained by referring to data on 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 can be set as the timing that satisfies the switch-on condition. A first example of the timing that satisfies the switch-on condition is a timing that is earlier by a first predetermined time τ1 than the timing at which the relative magnitudes of the phase voltages of the three phases detected by the power supply voltage detection circuit 12 reverse between the phase with the switching element and the phase without the switching element. In the example shown in Figure 5, this is a timing that is earlier by a first predetermined time τ1 than the timing at which the relative magnitudes of the T-phase voltage and the R-phase or S-phase voltage detected by the power supply voltage detection circuit 12 reverse. A second example of the timing that satisfies the switch-on condition is when the line voltage between the three phases detected by the power supply voltage detection circuit 12 reaches a predetermined voltage threshold V th The timing is as follows: In the example shown in Figure 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 the predetermined voltage threshold V. thThe following timing occurs: When the switch-on condition is met, the control unit 13 controls the switching element of the phase in which the line-to-line voltage relative to the T phase switches from positive to negative, as detected by the power supply voltage detection circuit 12, to switch it from off to on so that current flows in the first conducting direction. Alternatively, when the timing occurs, the control unit 13 controls the switching element of the phase in which the line-to-line voltage relative to the T phase switches from negative to positive, as detected by the power supply voltage detection circuit 12, to switch it from off to on so that current flows in the second conducting direction.

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

[0071] Figure 6 is a waveform diagram showing a specific example of the operation of the switch section in the pre-charging process by the pre-charging circuit according to the second embodiment of the present disclosure. In Figure 6, the R-phase voltage of the three-phase AC power supply 5 is shown by a bold solid line, the S-phase voltage is shown by a bold dashed line, and the T-phase voltage is shown 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 SR2 A first S-phase switching element S is provided in the S-phase power line. S1 and the second S-phase switching element S S2 When a first R-phase switching element S is provided, R1 and the second R-phase switching element S R2 This section describes the on / off control for this.

[0073] In section A1, the R-phase voltage is the largest among the three-phase voltages of the three-phase AC power supply 5, so the line voltage between the R-phase and T-phase (T-phase reference) is V, with the T-phase directly connected to the power supply as the reference. RT It is large. For example, in section A1, the first R-phase switching element S R1 When turned on, the first R-phase switching element S is powered by the three-phase AC power supply 5. R1 Diode D of the upper arm of the R phase of converter 2 RU , smoothing capacitor 3, diode D of the lower T-phase arm of converter 2 TL , and there is a risk that a large current will flow through the path to the three-phase AC power supply 5 via the T-phase power line. Therefore, in section A1, the first R-phase switching element S R1 The state of being turned off is maintained. Also, in section A1, as will be described later, the second R-phase switching element S continues from section A4. R2 It's turned on.

[0074] In section A2, the relative magnitudes of the R-phase voltage and the S-phase voltage are reversed, and the R-phase voltage becomes the second largest phase voltage.

[0075] For example, in section A2, the second R-phase switching element S R2 If left on, the first S-phase switching element S will receive power from the three-phase AC power supply 5. S1 Diode D of the upper S-phase arm of converter 2 SU , smoothing capacitor 3, diode D of the lower R phase arm of converter 2 RL , and the second R-phase switching element S R2 Current flows through the path leading to the three-phase AC power supply 5. Therefore, in the second embodiment, the second R-phase switching element S, which was turned on, R2At the moment when the current flowing through becomes approximately zero, or when the line voltage between the R phase and the T phase (T phase reference) V RT At the timing when the switching from negative to positive occurs (the timing when the R phase switches from section A4 to section A1), a second predetermined time τ2 has elapsed, and the second R phase switching element S R2 This controls the switching between on and off.

[0076] On the other hand, in section A2, the line voltage between the R phase and the T phase (T phase reference) V RT It gradually decreases. For example, in section A2, the first R-phase switching element S R1 When this is turned on, the first R-phase switching element S is powered by the three-phase AC power supply 5. R1 Diode D of the upper arm of the R phase of converter 2 RU , smoothing capacitor 3, diode D of the lower T-phase arm of converter 2 TL Current flows through the T-phase power line and the path leading to the three-phase AC power supply 5. Near the end of section A2, the first R-phase switching element S R1 If this is turned on, no large current will flow. Therefore, in the second embodiment, at a timing earlier by a first predetermined time τ1 than the timing at which the relative magnitudes of the T-phase voltage and the R-phase or S-phase voltage detected by the power supply voltage detection circuit 12 reverse (the timing at which the R-phase switches from section A2 to section A3), or the line voltage between the R-phase and the T-phase with the smallest magnitude (T-phase reference) V RT The predetermined voltage threshold V th At the following point, the line voltage between the R phase and the T phase (T phase reference) V RT A first R-phase switching element S that switches from positive to negative R1 The control switches from off to on to allow current to flow in the first direction of conduction.

[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 first R-phase switching element S is supplied from the three-phase AC power supply 5. R1 Diode D of the upper arm of the R phase of converter 2 RU, smoothing capacitor 3, diode D of the lower T-phase arm of converter 2 TL The current flowing through the path to the three-phase AC power supply 5 via the T-phase power line was, in section A3, the line voltage between the R-phase and T-phase (T-phase reference) V RT The result is negative, and furthermore, the second R-phase switching element S R2 Since it is off, the current stops flowing. Therefore, in the second embodiment, the first R-phase switching element S was turned on. R1 At the moment when the current flowing through becomes approximately zero, or at the moment when a second predetermined time τ2 has elapsed since the timing of the switching from positive to negative and from negative to positive of the line voltage (the timing of the switch from section A2 to section A3 for the R phase), the line voltage between the R phase and the T phase (T phase reference) V RT A first R-phase switching element S that switches from positive to negative R1 This controls the switching between on and off.

[0078] In section A4, the relative magnitudes of the R-phase voltage and the S-phase voltage are reversed, and the R-phase voltage becomes the second largest phase voltage.

[0079] For example, in section A4, the first R-phase switching element S R1 and the second S-phase switching element S S2 When this is turned on, the first R-phase switching element S is powered by the three-phase AC power supply 5. R1 Diode D of the upper arm of the R phase of converter 2 RU , smoothing capacitor 3, diode D of the S-phase lower arm of converter 2 SL There is a risk that a large current will flow through the path to the three-phase AC power supply 5 via the S-phase power line. Therefore, the first R-phase switching element S R1 and the second S-phase switching element S S2 We will keep it off.

[0080] On the other hand, the line voltage between the R phase and the T phase (T phase reference) V RT The absolute value of gradually decreases. In section A4, the second R-phase switching element S R2When this is turned on, the three-phase AC power supply 5 is connected to the T-phase power line, and diode D on the upper T-phase arm of converter 2. TU , smoothing capacitor 3, diode D of the lower R phase arm of converter 2 RL , second R-phase switching element S R2 Current flows through the path leading to the three-phase AC power supply 5. Near the end of section A4, the second R-phase switching element S R2 If this is turned on, no large current will flow. Therefore, in the second embodiment, at a timing earlier by a first predetermined time τ1 than the timing at which the relative magnitudes of the T-phase voltage and the R-phase or S-phase voltage detected by the power supply voltage detection circuit 12 reverse (the timing at which the R-phase switches from section A3 to section A4), or the line voltage between the R-phase and the T-phase with the smallest magnitude (T-phase reference) V RT The absolute value of is a predetermined voltage threshold V th At the following point, the line voltage between the R phase and the T phase (T phase reference) V RT A second R-phase switching element S that switches from negative to positive. R2 The control switches from off to on to allow current to flow in the second direction of conduction.

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

[0082] Referring to Figure 6, the first R-phase switching element S in the switch section 11 R1 and the second R-phase switching element S R2 The on / off control for the first S-phase switching element S was explained. The above explanation refers to the first S-phase switching element S S1 and the second S-phase switching element S S2 It can also be applied to on / off control of the first R-phase switching element S in the switch unit 11 during the pre-charging process by the pre-charging circuit 1. R1 , 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 will be controlled to be turned on or off as needed.

[0083] Furthermore, in Figure 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 is provided in the S-phase power line. S1 and the second S-phase switching element S S2 An example of where such an element is provided was described. The above description describes a first S-phase switching element S on the S-phase power line. S1 and the second S-phase switching element S S2 A first T-phase switching element S is provided in the T-phase power line. T1 and the second T-phase switching element S T2 This also applies to examples where a first R-phase switching element S is provided in the R-phase power line. R1 and the second R-phase switching element S R2 A first T-phase switching element S is provided in the T-phase power line. T1 and the second T-phase switching element S T2 This can also be applied to cases where such a feature is provided.

[0084] The second embodiment of this disclosure has the advantage of achieving the effects of the first embodiment, in addition to being able to reduce the number of diodes that were provided in the pre-charging circuit in the first embodiment. Furthermore, the second embodiment of this disclosure has the advantage of reducing the time required to complete pre-charging because the conduction frequency is increased compared to the first embodiment.

[0085] <Third Embodiment> Figure 7 shows a preliminary charging circuit and motor drive device according to a third embodiment of the present disclosure.

[0086] As shown in Figure 7, the pre-charging circuit 1 according to the third embodiment of the present disclosure includes a switch unit 11 that provides a switching element in the three-phase power line between the three-phase AC power supply and the AC input side of the converter, which can be switched 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 capable of selectively switching between conducting current in a first conducting direction from the three-phase AC power supply 5 to the AC input side of the converter 2 when it is on, conducting current in a second conducting direction from the AC input side of the converter 2 to the three-phase AC power supply 5 when it is on, and electrically disconnecting the three-phase AC power supply 5 and the AC input side of the converter 2 when it is 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 Figures 1 to 4.

[0088] A first R-phase switching element S is provided in 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 A first R-phase switching element S is provided. R1 and the second R-phase switching element S R2 This means that they are connected in antiparallel so that the direction of conduction is reversed when they are ON. First R-phase switching element S R1 When ON, it conducts current in the first conductive direction, from the three-phase AC power supply 5 to the AC input side of the converter 2. Second R-phase switching element S R2 When ON, it conducts current in a second conductive direction, from the AC input side of converter 2 to the three-phase AC power supply 5. First R-phase switching element S R1 and the second R-phase switching element S R2 When both are turned off, the three-phase AC power supply 5 and the AC input side of the converter 2 are electrically disconnected in the R-phase power line.

[0089] A first S-phase switching element S is provided in the S-phase power line between the three-phase AC power supply 5 and the AC input side of the converter 2. S1 and the second S-phase switching element S S2 A first S-phase switching element S is provided. S1 and the second S-phase switching element S S2 This means that they are connected in antiparallel so that the direction of conduction is reversed when they are ON. First S-phase switching element S S1 When ON, it conducts current in the first conductive direction from the three-phase AC power supply 5 to the AC input side of the converter 2. Second S-phase switching element S S2 When ON, it conducts current in a second conductive direction, from the AC input side of converter 2 to the three-phase AC power supply 5. First S-phase switching element S S1 and the second S-phase switching element S S2 When both are turned off, the three-phase AC power supply 5 and the AC input side of the converter 2 are electrically disconnected in the S-phase power line.

[0090] A first T-phase switching element S is provided in the T-phase power line between the three-phase AC power supply 5 and the AC input side of the converter 2. T1 and the second T-phase switching element S T2 A first T-phase switching element S is provided. T1 and the second T-phase switching element S T2 This means that they are connected in antiparallel so that the direction of conduction is reversed when they are ON. First T-phase switching element S T1 When ON, it conducts current in the first conductive direction, from the three-phase AC power supply 5 to the AC input side of the converter 2. Second T-phase switching element S T2 When ON, it allows current to flow in a second conductive direction, from the AC input side of converter 2 to the three-phase AC power supply 5. First T-phase switching element S T1 and the second T-phase switching element S T2 When both are turned off, the three-phase AC power supply 5 and the AC input side of the converter 2 are electrically disconnected in the T-phase power line.

[0091] The control unit 13 controls the pre-charging of the smoothing capacitor 3 by turning the switch unit 11 on and off based on information regarding 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 controls all switching elements in the switch unit 11 to turn them off, thereby electrically isolating the connection between the three-phase AC power supply 5 and the AC input side of the converter 2. The flowchart shown in Figure 3 is also applied to the overcurrent protection process of the third embodiment.

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

[0094] The control unit 13 controls the switching element to switch from off to on at the timing that satisfies the switch-on condition. The timing that satisfies the switch-on condition can be obtained by referring to data on 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 can be set as the timing that satisfies the switch-on condition. A first example of the timing that satisfies the switch-on condition is a timing that is earlier by a first predetermined time τ1 than the timing at which the relative magnitudes of the three-phase voltages detected by the power supply voltage detection circuit 12 reverse. A second example of the timing that satisfies the switch-on condition is when the line voltage between the three phases detected by the power supply voltage detection circuit 12 reaches a predetermined voltage threshold V thThe following timing occurs: When the switch-on condition is met, the control unit 13 controls the switching element of the phase in which the line voltage between the three phases detected by the power supply voltage detection circuit 12 switches from off to on so that current flows in the first conducting direction. When the same timing occurs, the control unit 13 controls the switching element of the phase in which the line voltage between the three phases detected by the power supply voltage detection circuit 12 switches from off to on so that current flows in the second conducting direction.

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

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

[0097] Here, as an example, the first R-phase switching element S R1 , second S-phase switching element S S2and the second T-phase switching element S T2 This section describes the on / off control for this.

[0098] In section A1, the R-phase voltage is the largest among the three-phase voltages of the three-phase AC power supply 5. The line-to-line voltage between the R-phase and S-phase (S-phase reference) V RS The voltage gradually decreases, but the line voltage between the R phase and the T phase (T phase reference) V RT It gradually increases. Near the end of section A1, the first R-phase switching element S R1 and the second S-phase switching element S S2 If this is turned on, no large current will flow. Therefore, in the third embodiment, at a timing earlier by a first predetermined time τ1 than the timing at which the relative magnitudes of the three phase voltages detected by the power supply voltage detection circuit 12 reverse (the timing at which the R phase and S phase switch from section A1 to section A2), or the line voltage between the R phase and the S phase (S phase reference) V RS The predetermined voltage threshold V th At the following point, the line voltage between the R phase and the S phase (S phase reference) V RS A first R-phase switching element S that switches from positive to negative R1 The control switches from off to on to allow current to flow in the first conducting direction, and the line voltage between the S phase and R phase (R phase reference) V SR A second S-phase switching element S that switches from negative to positive. S2 Control is performed to switch from off to on so that the current flowing in the second conducting direction is conducted. This allows the three-phase AC power supply 5 to supply power to the first R-phase switching element S R1 Diode D of the upper arm of the R phase of 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 Current flows through this path to the three-phase AC power supply 5.

[0099] In section A2, the relative magnitudes of the R-phase voltage and S-phase voltage are reversed, and the R-phase voltage becomes the second largest phase voltage, resulting in a line voltage (S-phase reference) V between the R-phase and S-phase. RSThis becomes negative. Therefore, in the third embodiment, the first R-phase switching element S that was turned on R1 and the second S-phase switching element S S1 At the moment when the current flowing through becomes approximately zero, or when the line voltage between the R phase and S phase (S phase reference) V RS At the moment when the switch from positive to negative occurs (the moment when the switch occurs from section A1 to section A2), the second predetermined time τ2 has elapsed, and the line voltage between the R phase and the S phase (S phase reference) V RS A first R-phase switching element S that switches from positive to negative R1 and the line voltage between the S phase and the R phase (S phase reference) V SR A second S-phase switching element S that switches from negative to positive. S1 This controls the switching between on and off.

[0100] Furthermore, in section A2, the S-phase voltage is the largest among the three-phase voltages of the three-phase AC power supply 5. Line-to-line voltage between R-phase and S-phase (S-phase reference) V RS The voltage gradually increases, but the line voltage between the R phase and the T phase (T phase reference) V RT It gradually decreases. Near the end of section A2, the first R-phase switching element S R1 and the second T-phase switching element S T2 If this is turned on, no large current will flow. Therefore, in the third embodiment, at a timing earlier by a first predetermined time τ1 than the timing at which the relative magnitudes of the three-phase voltages detected by the power supply voltage detection circuit 12 reverse (the timing at which the R phase and T phase switch from section A2 to section A3), or the line voltage between the R phase and the T phase (T phase reference) V RT The predetermined voltage threshold V th At the following point, the line voltage between the R phase and the T phase (T phase reference) V RT A first R-phase switching element S that switches from positive to negative R1 The control switches from off to on to allow current to flow in the first conducting direction, and the line voltage between the T phase and R phase (R phase reference) V TR A second T-phase switching element S that switches from negative to positive. T2Control is performed to switch from off to on so that the current flowing in the second conducting direction is conducted. This allows the three-phase AC power supply 5 to supply power to the first R-phase switching element S R1 Diode D of the upper arm of the R phase of converter 2 RU , smoothing capacitor 3, diode D of the lower T-phase arm of converter 2 TL , and the second T-phase switching element S T1 Current flows through this path to the three-phase AC power supply 5.

[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 first R-phase switching element S is supplied from the three-phase AC power supply 5. R1 Diode D of the upper arm of the R phase of converter 2 RU , smoothing capacitor 3, diode D of the lower T-phase arm of converter 2 TL The current flowing through the path to the three-phase AC power supply 5 via the T-phase power line was, in section A3, the line voltage between the R-phase and T-phase (T-phase reference) V RT Since it becomes negative, the flow stops. Therefore, in the third embodiment, the first R-phase switching element S that was turned on R1 and the second T-phase switching element S T2 At the moment when the current flowing through becomes approximately zero, or when the line voltage between the R phase and the T phase (T phase reference) V RT Switching from positive to negative and the line voltage between the T phase and R phase (R phase reference) V TR At the timing when the switch from negative to positive occurs (the timing when the R phase and T phase switch from section A2 to section A3), a second predetermined time τ2 has elapsed, and the line voltage between the R phase and T phase (T phase reference) V RT A first R-phase switching element S that switches from positive to negative R1 and the line voltage between the T phase and the R phase (R phase reference) V TR A second T-phase switching element S that switches from negative to positive. T2 This controls the switching between on and off.

[0102] In section A4, the relative magnitudes of the R-phase voltage and S-phase voltage are reversed, but the line voltage between the R-phase and S-phase (S-phase reference) V RS As it gradually increases, the first R-phase switching element S R1 and the second S-phase switching element S S2 Keep it off.

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

[0104] Referring to Figure 8, the first R-phase switching element S in the switch section 11 R1 , second S-phase switching element S S2 and the second T-phase switching element S T2 The on / off control for the first S-phase switching element S was explained. The above explanation refers to the first S-phase switching element S S1 , second T-phase switching element S T2 and the second R-phase switching element S R2 On / off control for the first T-phase switching element S T1 , second R-phase switching element S R2 and the second S-phase switching element S S2 It can also be applied to on / off control of the first R-phase switching element S in the switch unit 11 during the pre-charging process by the pre-charging circuit 1. R1 , 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 will be controlled to be turned on or off as needed.

[0105] The third embodiment of this disclosure has the advantage of achieving the effects of the first and second embodiments, in addition to not limiting the phase of the switching element to be turned on to the phase having the second phase voltage among the three phase voltages. Furthermore, the third embodiment of this disclosure has the advantage of reducing the time required to complete pre-charging because the conduction frequency is increased compared to the first and second embodiments.

[0106] <Matters applicable 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 this disclosure, the voltage of the smoothing capacitor 3 gradually increases. Therefore, the first predetermined time τ1 or voltage threshold V used when switching the switching element in the switch unit 11 from off to on is gradually increased. th If the pre-charging by the pre-charging circuit 1 continues while the voltage remains constant, the difference between the voltage of the smoothing capacitor 3 and the line-to-line voltage of the three-phase AC power supply 5 will gradually decrease. As the difference between the voltage of the smoothing capacitor 3 and the line-to-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 will gradually decrease, and the charging function of the pre-charging circuit 1 to the smoothing capacitor 3 will gradually decline.

[0108] Therefore, in the first to third embodiments of this disclosure, during the pre-charging period by the pre-charging circuit 1, a first predetermined time τ1 or voltage threshold V is used when the control unit 13 switches the switching element in the switch unit 11 from off to on. th The first predetermined time τ1 or voltage threshold V th This information is stored, for example, in a rewritable memory unit (not shown) within the auxiliary charging circuit 1. The memory unit may consist of an electrically erasable and recordable non-volatile memory such as EEPROM (registered trademark), or a high-speed read / write random access memory such as DRAM or SRAM.

[0109] The following applies to the first predetermined time τ1 or voltage threshold V thHere are some methods for making changes.

[0110] In the first modification method, a first predetermined time τ1 or voltage threshold V is used when the control unit 13 switches the switching element in the switch unit 11 from off to on, in accordance with the voltage of the smoothing capacitor 3 detected by the capacitor voltage detection circuit 15. th The first predetermined time τ1 is made longer, or the voltage threshold V is changed. That is, the higher the voltage of the smoothing capacitor 3 detected by the capacitor voltage detection circuit 15, the longer the voltage threshold V is made. th This increases the voltage across the smoothing capacitor 3. As a result, the on-time of the switching element in the switch unit 11 increases as the voltage across the smoothing capacitor 3 increases. This suppresses the gradual decrease in power flowing from the three-phase AC power supply 5 to the smoothing capacitor 3 via the converter 2, and maintains the charging function of the pre-charging circuit 1 for the smoothing capacitor 3.

[0111] In the second modification method, a first predetermined time τ1 or voltage threshold V is used by the control unit 13 to switch the switching element in the switch unit 11 from off to on, depending on the elapsed time since the start of pre-charging of the smoothing capacitor 3 by the pre-charging circuit 1. th The following is changed: In other words, the longer the elapsed time from the start of pre-charging of the smoothing capacitor 3, the longer the first predetermined time τ1 becomes, or the voltage threshold V th This increases the time 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 becomes. This suppresses the gradual decrease in power flowing from the three-phase AC power supply 5 to the smoothing capacitor 3 via the converter 2, and maintains the charging function of the pre-charging circuit 1 for the smoothing capacitor 3.

[0112] In the third modification method, a first predetermined time τ1 or voltage threshold V is used when the control unit 13 switches the switching elements in the switch unit 11 from off to on, according to 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. thThe first predetermined time τ1 or voltage threshold V is changed. th If pre-charging by the pre-charging circuit 1 continues while the voltage remains constant, the difference between the voltage of the smoothing capacitor 3 and the line-to-line voltage of the three-phase AC power supply 5 gradually decreases. The peak values ​​of the currents of each phase flowing from the three-phase AC power supply 5 to the converter decrease. Therefore, in the third modification method, the current detection circuit 14 detects the peak values ​​of the currents of each phase flowing from the three-phase AC power supply 5 to the converter, and the first predetermined time τ1 is gradually lengthened or the voltage threshold V is adjusted so that the detected peak values ​​of the currents are maintained. th Gradually increase the size.

[0113] In the fourth modification method, the first predetermined time τ1 or voltage threshold V used when the control unit 13 switches the switching element in the switch unit 11 from off to on is used. th This is changed at a predetermined rate of increase. That is, the first predetermined time τ1 is lengthened at a constant rate of increase, or the voltage threshold V th Increase it at a constant rate of increase.

[0114] While embodiments of this disclosure have been described in detail, this disclosure is not limited to the individual embodiments described above. These embodiments can be added, replaced, modified, partially deleted, etc., in any way that does not depart from the spirit of the invention or the intent of the invention derived from the claims and their equivalents. For example, the order of operations and processes in the embodiments described above are shown as examples only and are not limited thereto. The same applies when numerical values ​​or mathematical formulas are used in the description of the embodiments described above. [Explanation of Symbols]

[0115] 1. Backup charging circuit 2 Converters 3. Smoothing Capacitor 4 Inverters 5 Three-phase AC power supply 6 motors 11 Switch section 12 Power supply voltage detection circuit 13 Control Unit 14 Current detection circuit 15 Capacitor voltage detection circuit 100 Motor drive unit D RL Diode on the lower arm of the R phase D SL Diode on the lower arm of the S phase D TL Diode on the lower arm of the T phase D RU Diode on the upper arm of the R phase D SU Diode on the upper arm of the S phase D TU Diode on the upper arm of the T phase S 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 the DC output side of a converter that converts input AC power into DC power and outputs it, A switch unit having a switching element that electrically connects the three-phase AC power supply and the AC input side of the converter when it is ON, and electrically disconnects the three-phase AC power supply and the AC input side of the converter when it is OFF, A power supply voltage detection circuit for detecting the AC voltage of the three-phase AC power supply, A control unit that controls the on / off state of the switching element of the switch unit based on information regarding the AC voltage detected by the power supply voltage detection circuit, Equipped with, The switch unit is provided with a set of a switching element and a diode connected in antiparallel to the switching element, which conducts current from the three-phase AC power supply to the AC input side of the converter when ON and electrically disconnects the connection between the three-phase AC power supply and the AC input side of the converter when OFF, on each phase of the three-phase power line between the three-phase AC power supply and the AC input side of the converter. The control unit, The power supply voltage detection circuit determines that the phase with the second largest phase voltage among the three phase voltages is the conducting phase, and controls are performed to switch the switching element of the conducting phase from off to on at a timing earlier by a first predetermined time than the timing at which the relative magnitudes of the phase voltage of the conducting phase and the phase voltage of the smallest phase reverse, or at the timing when the line voltage between the conducting phase and the smallest phase falls below a predetermined voltage threshold. A backup charging circuit that, after the conducting phase switching element is turned on, controls the conducting phase switching element to switch from on to off when the current flowing through the conducting phase switching element becomes approximately zero, or when a second predetermined time has elapsed since the magnitude of the conducting phase voltage became the minimum of the three phase voltages.

2. A pre-charging circuit for pre-charging a smoothing capacitor connected to the DC output side of a converter that converts input AC power into DC power and outputs it, A switch unit having a switching element that electrically connects the three-phase AC power supply and the AC input side of the converter when it is ON, and electrically disconnects the three-phase AC power supply and the AC input side of the converter when it is OFF, A power supply voltage detection circuit for detecting the AC voltage of the three-phase AC power supply, A control unit that controls the on / off state of the switching element of the switch unit based on information regarding the AC voltage detected by the power supply voltage detection circuit, Equipped with, The switch unit is equipped with a switching element on two of the three phase power lines between the three phase AC power supply and the AC input side of the converter, which is capable of selectively switching between conducting current in a first conducting direction from the three phase AC power supply to the AC input side of the converter when it is ON, conducting current in a second conducting direction from the AC input side of the converter to the three phase AC power supply when it is ON, and electrically disconnecting the three phase AC power supply and the AC input side of the converter when it is OFF. The control unit, At a timing earlier than the timing at which the relative magnitudes of the phase voltages of the three phases, including the phase voltages of the phase equipped with the switching element and the phase without the switching element, reverse, or at the timing at which the line voltages between the three phases, as detected by the power supply voltage detection circuit, fall below a predetermined voltage threshold, the switching element of the phase in which the line voltage between the phase equipped with the switching element and the phase without the switching element, as detected by the power supply voltage detection circuit, switches from off to on so that it conducts in the first direction of conduction, and the switching element of the phase in which the line voltage switches from negative to positive, switches from off to on so that it conducts in the second direction of conduction. A backup charging circuit that, after the switching element is turned on, controls the switching element to turn off when the current flowing through the switched-on switching element becomes approximately zero, or when a second predetermined time has elapsed since the line voltage switched from positive to negative and from negative to positive.

3. A pre-charging circuit for pre-charging a smoothing capacitor connected to the DC output side of a converter that converts input AC power into DC power and outputs it, A switch unit having a switching element that electrically connects the three-phase AC power supply and the AC input side of the converter when it is ON, and electrically disconnects the three-phase AC power supply and the AC input side of the converter when it is OFF, A power supply voltage detection circuit for detecting the AC voltage of the three-phase AC power supply, A control unit that controls the on / off state of the switching element of the switch unit based on information regarding the AC voltage detected by the power supply voltage detection circuit, Equipped with, The switch unit is provided with a switching element in the three-phase power line between the three-phase AC power supply and the AC input side of the converter, which is capable of selectively switching between conducting current in a first conducting direction from the three-phase AC power supply to the AC input side of the converter when it is ON, conducting current in a second conducting direction from the AC input side of the converter to the three-phase AC power supply when it is ON, and electrically disconnecting the three-phase AC power supply and the AC input side of the converter when it is OFF. The control unit, At a timing earlier than the timing at which the relative magnitudes of the three phase voltages detected by the power supply voltage detection circuit reverse, or at the timing at which the line voltage between the three phases detected by the power supply voltage detection circuit falls below a predetermined voltage threshold, control is performed to switch the switching element of the phase in which the line voltage between the three phases detected by the power supply voltage detection circuit switches from off to on so that current flows in the first conducting direction, and control is performed to switch the switching element of the phase in which the line voltage between the three phases detected by the power supply voltage detection circuit switches from negative to positive so that current flows in the second conducting direction. A backup charging circuit that, after the switching element is turned on, controls the switching element to turn off when the current flowing through the switched-on switching element becomes approximately zero, or when a second predetermined time has elapsed since the line voltage switched from positive to negative and from negative to positive.

4. The system includes a current detection circuit that detects the current of each phase flowing from the three-phase AC power supply to the AC input side of the converter. The pre-charging circuit according to any one of claims 1 to 3, wherein when the current detected by the current detection circuit is an overcurrent, the control unit controls the switching element of the switch unit to turn it off, thereby electrically isolating the connection between the three-phase AC power supply and the AC input side of the converter.

5. The pre-charging circuit according to claim 1 or 3, wherein the first predetermined time or the voltage threshold used by the control unit to switch the switching element from off to on is changed according to the voltage of the smoothing capacitor.

6. The pre-charging circuit according to claim 5, wherein the voltage of the smoothing capacitor increases, the first predetermined time used by the control unit to switch the switching element from off to on is increased, or the voltage threshold is increased.

7. The pre-charging circuit according to claim 1 or 3, wherein the first predetermined time or the voltage threshold used by the control unit to switch the switching element from off to on is changed according to the elapsed time since the start of pre-charging of the smoothing capacitor.

8. The pre-charging circuit according to claim 7, wherein the longer the elapsed time since 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.

9. The pre-charging circuit according to claim 1 or 3, wherein the first predetermined time or the voltage threshold used by the control unit to switch the switching element from off to on is changed according to the peak value of the current of each phase flowing from the three-phase AC power supply to the AC input side of the converter during the pre-charging period of the smoothing capacitor.

10. The pre-charging circuit according to claim 1 or 3, wherein the first predetermined time used by the control unit to switch the switching element from off to on is gradually increased at a constant rate, or the voltage threshold is gradually increased at a constant rate.

11. The aforementioned converter, The smoothing capacitor and, A pre-charging circuit according to any one of claims 1 to 3, An inverter that converts the aforementioned DC power into AC power for motor drive and outputs it, A motor drive device equipped with the following features.

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