Rectifier and motor drive device

Abstract

The present invention provides a rectifier and a motor drive device. The rectifier (1) includes: a main circuit unit (11) that performs power conversion between AC power on the three-phase AC power supply (2) side and DC power on the DC side through the rectification operation of rectifying elements and the on / off operation of switching elements; a power calculation unit (12) that calculates the value of the power flowing between the three-phase AC power supply (2) side and the DC side via the main circuit unit (11); and a control unit (14) that performs control to execute the on / off operation of the switching elements, and the control unit (14) changes the length of the on-period in each cycle of the on / off operation performed on the switching elements according to the value of the power calculated by the power calculation unit (12).

Description

Technical Field

[0001] The present invention relates to a rectifier and a motor drive device having a power regeneration function. Background Art

[0002] In a motor drive device that controls the drive of a motor in a machine tool, a forging press, an injection molding machine, an industrial machine, or various robots, AC power supplied from a three-phase AC power source is converted into DC power by a rectifier and output to a DC (direct current) link, and the DC power in the DC link is converted into AC power by an inverter, and the AC power is supplied as power for driving the motor. The "DC link" refers to a circuit portion that electrically connects the DC output side of the rectifier and the DC input side of the inverter, and is sometimes also referred to as a "DC link section", "DC link", "DC link section", "DC bus", or "DC intermediate circuit".

[0003] As a rectifier in a motor drive device, a 120-degree conduction mode rectifier that can return the regenerative power generated when the motor decelerates to the three-phase AC power source side is widely used. The 120-degree conduction mode rectifier is composed of a three-phase bridge circuit in which power elements having rectifying elements and switching elements are respectively provided on the upper arms and lower arms of each of the three phases. In the 120-degree conduction mode rectifier, the phases of the three-phase AC power source are detected. Whenever the voltage of each phase of the three-phase AC power source alternates, the switching element in the upper arm of the phase in which the voltage of the three-phase AC power source is the maximum in each phase is turned on, and the switching element in the lower arm of the phase in which the voltage of the three-phase AC power source is the minimum is turned on. Thus, DC power is converted into AC power and regenerated in the three-phase AC power source. Here, the "degree" in "120 degrees" refers to a unit representing the phase angle of the three-phase voltage or three-phase current.

[0004] For example, as described in Japanese Patent Laid-Open No. 2017-42016, a motor drive device is known, which is characterized by having: a converter that converts DC power into AC power and regenerates it in the AC power source; a 120-degree conduction regeneration control unit that controls the converter to regenerate power from the converter to the AC power source in a 120-degree conduction mode; a PWM regeneration control unit that controls the converter to regenerate power from the converter to the AC power source in a PWM control mode; an input voltage detection unit that detects the power supply voltage input from the AC power source to the converter; a DC link voltage detection unit that detects the DC link voltage as the output voltage of the converter; and a regeneration mode switching unit that arbitrarily switches between the 120-degree conduction mode and the PWM control mode based on the voltage value of the DC link voltage detection unit during a power regeneration operation.

[0005] For example, as described in Japanese Patent Application Laid-Open No. 2010-22187, a method is known for adjusting the regenerative power of a system-side power converter (10) that performs fundamental-frequency switching operations with a bridge circuit. The bridge circuit is equipped with controllable semiconductor switches (T1, T2, T3, T4, T5, T6). In this method, the fundamental-frequency switching operations of the semiconductor switches (T1 to T6) are performed depending on the desired direction of power flow through the bridge circuit. A control signal (30) for the semiconductor switches (T1 to T6) is derived based on the fundamental-frequency switching operations and the turn-on delay of the power converter (10) that depends on system quantities. The turn-on delay is either pre-assigned each time depending on system quantities or obtained based on characteristics that can be pre-assigned. to obtain the turn-on delay.

[0006] For example, as described in Japanese Patent Application Laid-Open No. 2013-165600, a three-phase converter device is known, comprising: a power conversion unit that reversibly converts AC power from a three-phase AC power supply into DC power; a phase detection unit that detects the voltage phase of the three-phase AC power supply; a current detection unit that detects the three-phase AC current flowing between the three-phase AC power supply and the power conversion unit; and a DC voltage detection unit that detects the DC voltage on the output side of the power conversion unit. The power conversion unit has three arms, and in each of the phases of the three-phase AC power supply, a group of a rectifying element and a switching element connected in anti-parallel with the rectifying element are connected in series. On the other hand, the power conversion unit is equipped with a drive signal output unit. In the regenerative mode where the DC power is regenerated on the three-phase AC power supply side, the drive signal output unit outputs a drive signal for turning on / off the switching elements of each phase arm based on the voltage phase detected by the phase detection unit. The three-phase converter device is characterized in that, in the regenerative mode, whenever the magnitudes of the voltages of each phase alternate, the drive signal output unit determines the phase with the maximum voltage and the phase with the minimum voltage based on the voltage phase of the three-phase AC power supply detected by the phase detection unit, and sets a reference drive signal so that the switching elements of the upper arm connected to the phase with the maximum voltage and the switching elements of the lower arm connected to the phase with the minimum voltage among the three upper arms and the three lower arms are both turned on. The reference drive signal is set with a turn-on operation time, and a DC quantity is calculated based on the three-phase AC current detected by the current detection unit. A turn-off operation time corresponding to the magnitude of the DC quantity is set, and a turn-on correction drive signal is output. The turn-on correction drive signal is used to adjust the turn-on operation time of the reference drive signal to be shortened by the turn-off operation time.

[0007] For example, as described in Japanese Patent Application Laid-Open No. 2011-151918, a motor drive device includes: a rectifier that converts a three-phase AC input power supply into a DC power supply; and an inverter that converts the DC power supply into an AC power supply with a desired frequency, controls the rectifier to perform power regeneration, and the motor drive device further includes: a detection unit that detects an input voltage and an input current supplied from the three-phase AC input power supply; an instantaneous effective power calculation unit that calculates an instantaneous effective power supplied from the rectifier to the inverter based on the input voltage and the input current detected by the detection unit; a DC component calculation unit that calculates a DC component of the effective power supplied from the rectifier to the inverter based on the power value calculated by the instantaneous effective power calculation unit; and a regeneration operation stop determination unit that makes the following determination: comparing the value of the DC component calculated by the DC component calculation unit with a specified threshold, and if the value of the DC component is greater than the threshold, stopping the power regeneration operation of returning the regeneration power supplied from the inverter to the three-phase AC input power supply.

[0008] For example, as described in Japanese Patent Application Laid-Open No. 2004-180427, a power regeneration converter is known, which includes: a phase detection unit that is disposed between a three-phase AC power supply and a control device for performing variable speed control of a three-phase induction motor and detects a voltage phase of the three-phase AC power supply; a regeneration transistor that switches a terminal voltage of a smoothing capacitor to perform a power regeneration operation in the three-phase AC power supply, and the smoothing capacitor accumulates an induced electromotive force generated when the three-phase induction motor decelerates; and a regeneration signal generation unit that generates a conduction cutoff drive signal of the regeneration transistor based on a detection signal of the phase detection unit. The power regeneration converter is characterized in that it further includes a correction unit that monitors a voltage waveform of the three-phase AC power supply and corrects a change time of the conduction cutoff drive signal of the regeneration transistor generated by the regeneration signal generation unit when a deviation is detected with respect to an alternating moment of the phase voltage.

[0009] For example, as described in Japanese Patent Application Laid-Open No. 2017-184365, a power conversion device that performs power conversion between an AC power supply and a DC load or a DC power supply is known. The power conversion device is characterized by including: an inverter circuit; a current detection unit that detects an AC current of the AC power supply; a voltage controller that generates a command voltage of the inverter circuit based on an AC current signal detected by the current detection unit; and a correction unit that has a gain with respect to a specific frequency and corrects the command voltage based on the AC current signal, and the correction unit corrects the command voltage after it is output from the voltage controller. SUMMARY OF THE INVENTION

[0010] In a rectifier constituted by a three-phase bridge circuit in which power elements each having a rectifying element and a switching element are respectively provided in the upper arms and lower arms of each of the three phases, during power operation, if the peak value of the input voltage on the three-phase AC power supply side is higher than the DC voltage on the DC side, current flows from the three-phase AC power supply side toward the DC side via the rectifying elements in the rectifier. On the other hand, during regeneration, by controlling the on / off operation of the switching elements in the rectifier, it is possible to make the current flow from the DC side toward the three-phase AC power supply side via the switching elements in the rectifier. In a rectifier in the 120-degree conduction mode, when switching from the regeneration state to the power operation state, a surge current is generated due to the stop of the on / off operation of the switching elements. The magnitude of the surge current depends, for example, on the impedance in the rectifier and the inverter or the capacitance of the capacitor provided in the DC link. When the surge current is generated, there is a problem that components in the rectifier or capacitors provided on the DC side of the rectifier are damaged.

[0011] In addition, in a rectifier in the 120-degree conduction mode, regardless of the magnitude of the regenerative power regenerated from the DC side to the three-phase AC power supply side during regeneration, each switching element always becomes in the on state for an interval of 120 degrees per cycle of the three-phase AC power supply. When the regenerative power is large, the regenerative power is stably regenerated from the DC side to the three-phase AC power supply side. However, when the regenerative power is small, over-regeneration occurs in which the DC voltage on the DC side of the rectifier drops sharply immediately after switching to the regeneration state. When over-regeneration occurs, the regeneration operation is stopped and the power operation state is returned to. As a result, when the DC voltage rises again, so-called "resonance" occurs in which the switching between the regeneration state and the power operation state is frequently repeated to start the regeneration operation again. The frequency of resonance depends, for example, on the impedance in the rectifier and the inverter or the capacitance of the capacitor provided in the DC link. When resonance occurs in which the state frequently changes between the regeneration state and the power operation state, there is a problem that components such as capacitors provided on the DC side of the rectifier abnormally heat up.

[0012] Therefore, a technique is desired to prevent the surge current generated when switching from the regeneration state to the power operation state in a rectifier having a power regeneration function and a motor drive device including the rectifier, and to prevent resonance in which the switching between the regeneration state and the power operation state is frequently repeated when the regenerative power is small.

[0013] According to one aspect of the present disclosure, a rectifier includes: a main circuit unit having a rectifying element and a switching element connected in anti-parallel with the rectifying element, the main circuit unit performing power conversion between AC power on the three-phase AC power supply side and DC power on the DC side through the rectifying operation of the rectifying element and the turn-on and turn-off operations of the switching element; a power calculation unit calculating the value of the power flowing between the three-phase AC power supply side and the DC side via the main circuit unit; and a control unit performing control to execute the turn-on and turn-off operations of the switching element, the control unit changing the length of the on-period in each cycle of the turn-on and turn-off operations performed on the switching element according to the value of the power calculated by the power calculation unit.

[0014] In addition, according to one aspect of the present disclosure, a motor drive device includes: the rectifier; a capacitor provided in a DC link as the DC side of the rectifier; and an inverter connected to the rectifier via the DC link, converting DC power supplied from the DC link into AC power for motor drive and outputting the AC power. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention is more clearly understood by referring to the following drawings.

[0016] Figure 1 FIG. is a diagram showing a rectifier and a motor drive device according to an embodiment of the present disclosure.

[0017] Figure 2A FIG. is a circuit diagram illustrating a main circuit unit in the rectifier and showing a main circuit diagram of a power element according to a first mode in which the rectifying element is constituted by a diode.

[0018] Figure 2B FIG. is a circuit diagram illustrating a main circuit unit in the rectifier and showing a main circuit diagram of a power element according to a second mode in which the rectifying element is constituted by a switching element.

[0019] Figure 3A FIG. is a diagram explaining the operation of a rectifier performing power regeneration based on a 120-degree power supply method and showing a circuit diagram of a rectifier constituted by a three-phase bridge circuit of power elements.

[0020] Figure 3B FIG. is a diagram explaining the operation of a rectifier performing power regeneration based on a 120-degree power supply method and showing the relationship between the waveforms of the three-phase AC power supply voltage during power regeneration and the turn-on and turn-off operations of the switching elements in the power elements.

[0021] Figure 4A FIG. is a diagram explaining the operation of a rectifier according to an embodiment of the present disclosure and illustrating a resonance in which the switching between a regeneration state and a power running state occurring when the regenerated power is small is frequently repeated.

[0022] Figure 4B FIG. Figure 4B is a diagram for explaining the operation of a rectifier according to an embodiment of the present disclosure, and shows a first example related to a change in the length of the on-period of each cycle of a switching element in the rectifier according to an embodiment of the present disclosure.

[0023] Figure 4C FIG. Figure 4C is a diagram for explaining the operation of a rectifier according to an embodiment of the present disclosure, and shows a second example related to a change in the length of the on-period of each cycle of a switching element in the rectifier according to an embodiment of the present disclosure.

[0024] Figure 5A FIG. Figure 5A is a diagram showing the relationship between the waveforms of a three-phase AC power supply voltage in a rectifier 1 according to an embodiment of the present disclosure and the on / off operation of a switching element in a power element, and shows the relationship between the waveforms of the three-phase AC power supply voltage and the on / off operation of the switching element in a region where the regenerative power is large.

[0025] Figure 5B FIG. Figure 5B is a diagram showing the relationship between the waveforms of a three-phase AC power supply voltage in a rectifier 1 according to an embodiment of the present disclosure and the on / off operation of a switching element in a power element, and shows the relationship between the waveforms of the three-phase AC power supply voltage and the on / off operation of the switching element in a region where the regenerative power is small.

[0026] Figure 6 FIG. Figure 6 is a flowchart showing the operation process of a rectifier according to an embodiment of the present disclosure.

[0027] Figure 7 FIG. Figure 7 is a flowchart showing the operation process of a rectifier according to a first modification example of an embodiment of the present disclosure.

[0028] Figure 8 FIG. Figure 8 is a diagram showing a rectifier and a motor drive device according to a second modification example of an embodiment of the present disclosure.

[0029] Figure 9 FIG. Figure 9 is a flowchart showing the operation process of a rectifier according to a second modification example of an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] A rectifier and a motor drive device having a power regeneration function will be described with reference to the following drawings. For ease of understanding, the scales of these drawings are appropriately changed. The embodiments shown in the drawings are an example for implementation and are not limited to the illustrated embodiments.

[0031] Here, as an example, a rectifier provided in a motor drive device will be described. However, each embodiment can also be applied to a case where a rectifier is provided in a machine other than the motor drive device.

[0032] Figure 1 FIG. is a diagram showing a rectifier and a motor drive device according to an embodiment of the present disclosure. Hereinafter, it is assumed that structural elements given the same reference numerals in different drawings have the same functions.

[0033] As an example, a case where a motor 3 is controlled by a motor drive device 100 connected to a three-phase AC power supply 2 is shown. The type of the motor 3 is not particularly limited. For example, it may be an induction motor or a synchronous motor. In addition, the number of phases of the motor 3 is also not limited. In Figure 1 as an example, the motor 3 is assumed to be a three-phase AC motor. The machine provided with the motor 3 includes, for example, a machine tool, a robot, a forging press, an injection molding machine, an industrial machine, a conveying machine, various electrical appliances, etc. When giving an example of the three-phase AC power supply 2, there are a three-phase AC 400V power supply, a three-phase AC 200V power supply, a three-phase AC 600V power supply, etc.

[0034] A motor drive device 100 according to an embodiment of the present disclosure includes a rectifier 1, a capacitor 4, and an inverter 5.

[0035] The rectifier 1 has a power regeneration function and performs power conversion between the AC power on the three-phase AC power supply 2 side and the DC power on the DC side. Details of the structure and operation of the rectifier 1 will be described later. In addition, an electromagnetic contactor, an AC reactor, etc. may be connected to the three-phase AC power supply 2 side of the rectifier 1, but illustration of these is omitted.

[0036] The capacitor 4 is provided in a DC link that connects the DC output side of the rectifier 1 and the DC input side of the inverter 5. The capacitor 4 has a function of accumulating DC power and a function of suppressing the pulsation amount of the DC output of the rectifier 1, and this DC power is used for the inverter 5 to generate AC power. As an example of the capacitor 4, for example, there are an electrolytic capacitor or a film capacitor, etc.

[0037] The inverter 5 is connected to the rectifier 1 via a DC link, converts the DC power supplied from the DC link into AC power for driving the motor 3, and outputs it. The inverter 5 only needs to have a structure capable of converting DC power into AC current. For example, there is a PWM inverter having switching elements inside. When the motor 3 is a three-phase AC motor, the inverter 5 is configured as a three-phase bridge circuit. When the motor 3 is a single-phase motor, the inverter 5 is composed of a single-phase bridge circuit. When the inverter 5 is configured as a PWM inverter, the inverter 5 is composed of a bridge circuit of rectifying elements and switching elements connected in anti-parallel with the rectifying elements. In this case, as examples of the switching elements, there are FETs, IGBTs, thyristors, GTO thyristors (Gate Turn-OFF thyristors), bipolar transistors, etc., but other semiconductor elements can also be used. The motor 3 controls the speed, torque, or the position of the rotor based on the AC power supplied from the inverter 5. In addition, the inverter 5 can also convert the AC power regenerated in the motor 3 into DC power and return it to the DC link on the DC side by appropriately performing PWM control on the on / off operation of the switching elements.

[0038] Next, the structure of the rectifier 1 will be described.

[0039] The rectifier 1 according to an embodiment of the present disclosure includes a main circuit unit 11, a power calculation unit 12, a state determination unit 13, and a control unit 14. In addition, the rectifier 1 includes an input voltage detection unit 15, a DC voltage detection unit 16, an input current detection unit 21, a DC current detection unit 22, and a phase detection unit 23.

[0040] The main circuit unit 11 performs power conversion between the AC power on the three-phase AC power supply 2 side and the DC power on the DC side through the rectifying action of the rectifying elements and the on / off operation of the switching elements. The main circuit unit 11 has a three-phase bridge circuit in which power elements are respectively provided on the upper arm and the lower arm of each phase, and the power element is composed of a rectifying element and a switching element connected in anti-parallel with the rectifying element. As examples of the switching elements, there are FETs, IGBTs, thyristors, GTO thyristors (Gate Turn-OFF thyristors), bipolar transistors, etc., but other semiconductor elements can also be used.

[0041] In each of the three phases of the main circuit unit 11, the power elements provided on the upper arm and the lower arm are composed of a group of a rectifying element responsible for the rectifying function and a switching element responsible for the power regeneration function. Here, the ways of the power elements are listed below. In Figure 1 the example shown, a diode is used as the rectifying element. However, as an alternative example, a switching element can also be used for the rectifying element.

[0042] Figure 2A It is a circuit diagram illustrating the main circuit section in a rectifier, and shows a main circuit diagram of a power element related to a first mode in which the rectifying element is composed of a diode. Figure 2B It is a circuit diagram illustrating the main circuit section in a rectifier, and shows a main circuit diagram of a power element related to a second mode in which the rectifying element is composed of a switching element.

[0043] In the case of the first mode where, as Figure 2A shown, the diode D is used as the rectifying element, the switching element S is connected in anti-parallel with the diode D so that the conduction direction when the switching element S is turned on is the opposite direction to the conduction direction of the diode D. The power element composed of the group of the switching element S and the diode D is provided in the upper arm and the lower arm respectively in each of the three phases. In the power running state, the AC power on the three-phase AC power supply 2 side is converted into DC power by the rectifying action of the diode D and output to the DC side. In the regeneration state, the DC power on the DC side is converted into AC power by the on / off operation of the switching element S and output to the three-phase AC power supply 2 side.

[0044] In the case of the second mode where, as Figure 2B shown, the switching element S2 is used as the rectifying element, the switching element S1 is connected in anti-parallel with the switching element S2 so that the conduction direction when the switching element S1 is turned on is the opposite direction to the conduction direction when the switching element S2 is turned on. The power element composed of the group of the switching element S1 and the switching element S2 is provided in the upper arm and the lower arm respectively in each of the three phases. The switching element S1 is responsible for the power regeneration function, and the switching element S2 is responsible for the rectifying function. In the power running state, the AC power on the three-phase AC power supply 2 side is converted into DC power by keeping the switching element S2 turned on all the time and output to the DC side. In the regeneration state, the DC power on the DC side is converted into AC power by the on / off operation of the switching element S1 and output to the three-phase AC power supply 2 side. In this way, the switching element S2 as Figure 2B shown has a complete function as a rectifying element, and thus is not used for power regeneration. In the present embodiment and the first and second modification examples described later, when the main circuit section 11 is in the regeneration state and when the main circuit section is in the power running state and the power value P calculated by the power calculation unit is less than the first power threshold P th1 the "switching element" that performs the on / off operation refers to the switching element S1 responsible for the power regeneration function, rather than the switching element S2 responsible for the rectifying function.

[0045] When the description returns to Figure 1When this occurs, the power calculation unit 12 calculates the value P of the power flowing between the three-phase AC power supply 2 side and the DC side via the main circuit unit 11. Here, for example, the direction of the power flowing from the three-phase AC power supply 2 side to the DC side via the main circuit unit 11 is defined as positive, and the direction of the power flowing from the DC side to the three-phase AC power supply 2 side via the main circuit unit 11 is defined as negative. Therefore, the value of the power (power running power) calculated by the power calculation unit 12 in the power running state is positive, and the value of the power (regenerative power) calculated by the power calculation unit 12 in the regenerative state is negative. Here, the following describes the calculation processing method performed by the power calculation unit 12.

[0046] The power calculation unit 12 according to the first method calculates the value P of the power flowing between the three-phase AC power supply 2 side and the DC side via the main circuit unit 11 by multiplying the value of the input voltage input from the three-phase AC power supply 2 side to the main circuit unit 11 by the value of the input current. The value of the input voltage input from the three-phase AC power supply 2 side to the main circuit unit 11 is detected by the input voltage detection unit 15. The value of the input current input from the three-phase AC power supply 2 side to the main circuit unit 11 is detected by the input current detection unit 21. Since both the input voltage and the input current are detected as vectors, the value P of the power calculated by the power calculation unit 12 represents any one of positive, negative, or 0.

[0047] The power calculation unit 12 of the second method calculates the value P of the power flowing between the three-phase AC power supply 2 side and the DC side via the main circuit unit 11 by multiplying the value of the voltage on the DC output side of the main circuit unit 11 by the value of the current output from the DC output side of the main circuit unit 11. The value of the voltage on the DC output side of the main circuit unit 11 is detected by the DC voltage detection unit 16. That is, the DC voltage detection unit 16 detects the value of the potential difference between the positive potential appearing at the positive-side terminal on the DC output side of the main circuit unit 11 and the negative potential appearing at the negative-side terminal on the DC output side of the main circuit unit 11 as the value of the voltage on the DC output side of the main circuit unit 11. Alternatively, the DC voltage detection unit 16 may also detect the value of the voltage applied between the positive and negative terminals of the capacitor 4 as the value of the voltage on the DC output side of the main circuit unit 11. The value of the current output from the DC output side of the main circuit unit 11 is detected by the DC current detection unit 22. Here, the direction of the current flowing out from the positive-side terminal on the DC output side of the main circuit unit 11 and flowing into the negative-side terminal is defined as positive. By defining the positive and negative of the DC voltage and the DC current in this way, the value of the power calculated by the power calculation unit 12 represents any one of positive, negative, or 0.

[0048] In addition, the power calculation unit 12 only needs to be implemented by either the first method or the second method. When the power calculation unit 12 is implemented by the second method, for the DC voltage detection unit 16 and the DC current detection unit 22, components provided in the inverter 5 may also be borrowed.

[0049] The state determination unit 13 determines whether the main circuit unit 11 is in a power running state in which the AC power on the three-phase AC power supply 2 side is converted into DC power and output to the DC side, or the main circuit unit 11 is in a regeneration state in which the DC power on the DC side is converted into AC power and output to the three-phase AC power supply 2 side, based on the power value P calculated by the power calculation unit 12. As described above, as an example, the direction of the power flowing from the three-phase AC power supply 2 side to the DC side via the main circuit unit 11 is defined as positive, and the direction of the power flowing from the DC side to the three-phase AC power supply 2 side via the main circuit unit 11 is defined as negative. Therefore, when the power value P calculated by the power calculation unit 12 is positive, the state determination unit 13 determines that the main circuit unit 11 is in the power running state, and when the power value P calculated by the power calculation unit 12 is negative, the state determination unit 13 determines that the main circuit unit 11 is in the regeneration state.

[0050] The control unit 14 controls the turn-on and turn-off operations of the switching elements in the main circuit unit 11 according to the determination result of the state determination unit 13. More specifically, in the case where it is determined by the state determination unit 13 that the main circuit unit 11 is in the regeneration state and in the case where it is determined by the state determination unit 13 that the main circuit unit 11 is in the power running state and the power value P calculated by the power calculation unit 12 is less than the first power threshold P th1 In either of these cases, the control unit 14 performs control to execute the turn-on and turn-off operations of the switching elements in the main circuit unit 11. In addition, in the case where it is determined by the state determination unit 13 that the main circuit unit 11 is in the regeneration state, the control unit 14 determines whether to adopt a 120-degree power supply method in the control of the switching elements of the main circuit unit 11 according to whether the power value P calculated by the power calculation unit 12 is the second power threshold P th2 Hereinafter, the details of the operation of the control unit 14 will be described.

[0051] The phase detection unit 23 detects the phase of the voltage of each phase of the three-phase AC power supply 2. The phase of the voltage detected by the phase detection unit 23 is sent to the control unit 14 and is used for the control of the switching elements in the main circuit unit 11.

[0052] The power calculation unit 12, the state determination unit 13, and the control unit 14 can be constructed, for example, in the form of a software program, or can be constructed as a combination of various electronic circuits and a software program, or can be composed only of various electronic circuits. For example, when constructing them in the form of a software program, by causing an arithmetic processing device such as a DSP or an FPGA to operate according to the software program, the functions of the above-mentioned units can be realized. Additionally or alternatively, the power calculation unit 12, the state determination unit 13, and the control unit 14 can be implemented as a semiconductor integrated circuit in which a software program for realizing the functions of each unit is written. Additionally or alternatively, the power calculation unit 12, the state determination unit 13, and the control unit 14 can be implemented as a recording medium in which a software program for realizing the functions of each unit is written. Further, the power calculation unit 12, the state determination unit 13, and the control unit 14 can be provided, for example, in the numerical control device of a machine tool, or can be provided in a robot controller that controls a robot. Additionally, the input voltage detection unit 15, the DC voltage detection unit 16, the input current detection unit 21, the DC current detection unit 22, and the phase detection unit 23 can be composed of a combination of an analog circuit and a digital circuit, or can be realized by an arithmetic processing device constructed in the form of a software program, or can be composed only of an analog circuit.

[0053] Next, with reference to Figure 3A and Figure 3B the principle of power regeneration based on the 120-degree power supply method will be described.

[0054] Figure 3A is a diagram for explaining the operation of the rectifier for power regeneration based on the 120-degree power supply method, and is a circuit diagram showing a rectifier composed of a three-phase bridge circuit of power elements. Figure 3B is a diagram for explaining the operation of the rectifier for power regeneration based on the 120-degree power supply method, and is a diagram showing the relationship between the waveforms of the three-phase AC power supply voltage during power regeneration and the on / off operation of the switching elements in the power elements.

[0055] As Figure 3A shown, the main circuit section 11 of the rectifier 1 has three legs, namely, the R phase, the S phase, and the T phase. Each phase's leg has an upper arm and a lower arm. The upper arm and the lower arm are respectively provided with power elements composed of rectifying elements and switching elements connected in anti-parallel with the rectifying elements. Here, each arm is referred to as the R-phase upper arm, the R-phase lower arm, the S-phase upper arm, the S-phase lower arm, the T-phase upper arm, and the T-phase lower arm. When the rectifier 1 performs power regeneration according to the 120-degree power supply method, the phase of the three-phase AC power supply is detected, and whenever the voltage of each phase of the three-phase AC power supply alternates, the switching element in the upper arm of the phase with the maximum voltage of the three-phase AC power supply in each phase is turned on, and the switching element in the lower arm of the phase with the minimum voltage of the three-phase AC power supply is turned on.

[0056] As Figure 3B shown, for example, in a 60-degree phase interval where the voltage of the three-phase AC power supply 2 is maximum in the R phase and minimum in the T phase, the switching elements of the upper arm of the R phase and the lower arm of the T phase are turned on respectively, and the switching elements of the other arms are turned off. As a result, a current path from the DC side to the three-phase AC power supply 2 side as shown by the Figure 3A arrow is formed, and thus, the DC power on the DC side is converted into AC power and regenerated by the power supply.

[0057] Further, for example, in a 60-degree phase interval where the voltage of the three-phase AC power supply 2 is maximum in the S phase and minimum in the T phase, the switching elements of the upper arm of the S phase and the lower arm of the T phase are turned on respectively. In a 60-degree phase interval where the voltage of the three-phase AC power supply 2 is maximum in the S phase and minimum in the R phase, the switching elements of the upper arm of the S phase and the lower arm of the R phase are turned on respectively. In a 60-degree phase interval where the voltage of the three-phase AC power supply 2 is maximum in the T phase and minimum in the R phase, the switching elements of the upper arm of the T phase and the lower arm of the R phase are turned on respectively. In a 60-degree phase interval where the voltage of the three-phase AC power supply 2 is maximum in the T phase and minimum in the S phase, the switching elements of the upper arm of the T phase and the lower arm of the S phase are turned on respectively. In a 60-degree phase interval where the voltage of the three-phase AC power supply 2 is maximum in the R phase and minimum in the S phase, the switching elements of the upper arm of the R phase and the lower arm of the S phase are turned on respectively.

[0058] In such power regeneration based on the 120-degree conduction mode, for each of the switching elements, the on state exists in a 120-degree phase interval spanning each cycle of the three-phase AC power supply 2.

[0059] Next, the operation of the rectifier 1 will be described.

[0060] Figure 4A is a diagram for explaining the operation of the rectifier according to an embodiment of the present disclosure, and illustrates a resonance in which the switching between the regeneration state and the power running state that occurs when the regenerated power is small is frequently repeated. Figure 4B is a diagram for explaining the operation of the rectifier according to an embodiment of the present disclosure, and shows a first example related to the change in the length of the on period of each cycle of the switching elements in the rectifier according to an embodiment of the present disclosure. Figure 4C is a diagram for explaining the operation of the rectifier according to an embodiment of the present disclosure, and shows a second example related to the change in the length of the on period of each cycle of the switching elements in the rectifier according to an embodiment of the present disclosure.

[0061] As Figure 4AAs shown, in a rectifier with a conventional 120-degree power-on method, during the power operation state, the on / off operation of the switching elements in the rectifier stops, and the AC power on the three-phase AC power supply side is converted into DC power by using the rectification operation of the diodes and output to the DC side. In the regeneration state, the switching elements in the rectifier perform on / off operations according to the 120-degree power-on method, converting the DC power on the DC side into AC power and outputting it to the three-phase AC power supply side. That is, in a rectifier with a conventional 120-degree power-on method, during the power operation state, the on / off operation of the switching elements in the rectifier completely stops, and in the regeneration state, the switching elements in the rectifier perform on / off operations according to the 120-degree power-on method. In a rectifier with a conventional 120-degree power-on method, regardless of the magnitude of the regeneration power regenerated from the DC side to the three-phase AC power supply side during regeneration, each switching element always becomes in the on state in an interval spanning 120 degrees per cycle of the three-phase AC power supply. In a region where the regeneration power is small, over-regeneration occurs in which the DC voltage on the DC side of the rectifier drops sharply immediately after switching to the regeneration state. When over-regeneration occurs, the regeneration operation stops and returns to the power operation state. As a result, when the DC voltage rises again, resonance occurs in which the switching between the regeneration state and the power operation state is frequently repeated to start the regeneration operation again. When resonance occurs in which the state frequently changes between the regeneration state and the power operation state, components such as capacitors provided on the DC side of the rectifier overheat abnormally. In addition, in a rectifier with a conventional 120-degree power-on method, when switching from the regeneration state to the power operation state, the on / off operation of the switching elements performed before that completely stops, so inrush current is generated. When inrush current is generated, components inside the rectifier or capacitors provided on the DC side of the rectifier are damaged.

[0062] In contrast, in the rectifier 1 according to an embodiment of the present disclosure, when the state determination unit 13 determines that the main circuit unit 11 is in the power operation state and the value P of the power calculated by the power calculation unit 12 is less than the first power threshold P th1 , the control unit 14 performs control to execute the on / off operation of the switching elements. When the main circuit unit 11 is in the power operation state, the length Φ of the on period in each cycle of the on / off operation performed on the switching elements is set to a value shorter than the length of the on period in each cycle in the 120-degree power-on method (i.e., 120 degrees). In Figure 4B and Figure 4C the example shown, when the main circuit unit 11 is in the power operation state and the value P of the power calculated by the power calculation unit 12 is less than the first power threshold P th1In the case of, the length Φ of the on-period of each cycle is set to a fixed value. As an alternative example, the length Φ of the on-period of each cycle can also be set based on a decreasing function such that the larger the value P of the power calculated by the power calculation unit 12 (since it is in the power running state, P is a positive value), the shorter the length Φ of the on-period of each cycle. In the case of this alternative example, when the value P of the power calculated by the power calculation unit 12 is 0 (zero), the length Φ of the on-period of each cycle is Φ min When the value P of the power calculated by the power calculation unit 12 is consistent with the first power threshold P th1 the length Φ of the on-period of each cycle is 0 (zero). Additionally, as a further alternative example, the length Φ of the on-period of each cycle can be stored in a rewritable storage unit (not shown), and the length Φ of the on-period of each cycle can be rewritten by an external device. In the case of this alternative example, for instance, when the rectifier 1 and the motor drive device 100 are operating, the length Φ of the on-period of each cycle can be changed in real time in an online manner.

[0063] Furthermore, the first power threshold P th1 can be appropriately set according to the application environment of the rectifier 1. When giving an example, it is set to, for example, several hundreds to more than a thousand percentages of the rated output power value (positive value) of the rectifier 1, but it can also be set to other values. Additionally, the first power threshold P th1 can be stored in a rewritable storage unit (not shown) and can be rewritten by an external device. Even after temporarily setting the first power threshold P th1 it is possible to change the first power threshold P th1 to an appropriate value as needed. In the rectifier 1 according to an embodiment of the present disclosure like this, even in a region where the power during power running is small immediately after switching from the regenerative state to the power running state, a current path from the DC side to the three-phase AC power supply 2 side is ensured by causing the switching element to perform on-off operations, and thus, inrush current can be suppressed.

[0064] In addition, in the rectifier 1 according to an embodiment of the present disclosure, when it is determined by the state determination unit 13 that the main circuit unit 11 is in the regenerative state, the control unit 14 performs control to execute the on-off operation of the switching element. When the main circuit unit 11 is in the regenerative state, the length Φ of the on-period of each cycle in the on-off operation performed on the switching element is changed according to the value P of the power calculated by the power calculation unit 12. When described in more detail, it is as follows.

[0065] When the value P of the power calculated by the power calculation unit 12 is greater than the second power threshold P when the main circuit unit 11 is in the regenerative stateth2 In this case, the control unit 14 sets the length Φ of the on-period in each cycle of the on / off operation performed on the switching element to a value shorter than 120 degrees, where 120 degrees is the length of the on-period in each cycle in the 120-degree power supply method. The control unit 14 performs control to execute the on / off operation of the switching element based on this value. In this case, the smaller the absolute value |P| of the power value P calculated by the power calculation unit 12, the shorter the length Φ of the on-period in each cycle of the on / off operation performed on the switching element is set. When the main circuit unit 11 is in the regeneration state, the power value P calculated by the power calculation unit 12 is the second power threshold P th2 In the following cases, the control unit 14 performs control to execute the on / off operation of the switching element by the 120-degree power supply method. In addition, the second power threshold P th2 Only needs to be appropriately set according to the application environment of the rectifier 1. When giving an example, it is set to about several hundreds of percent to more than one thousand percent of the value obtained by giving a negative (-) sign to the rated input power value (positive value) of the rectifier 1, but it can also be set to other values. In addition, regarding the second power threshold P th2 , it can be stored in a rewritable storage unit (not shown) and can be rewritten by an external device. Even after temporarily setting the second power threshold P th2 , it is possible to change the second power threshold P th2 to an appropriate value as needed.

[0066] When the main circuit unit 11 is in the regeneration state and the power value P calculated by the power calculation unit 12 is greater than the second power threshold P th2 , the length Φ of the on-period in each cycle of the on / off operation performed on the switching element is set to shorter than 120 degrees, where 120 degrees is the length of the on-period in each cycle in the 120-degree power supply method. In addition, the smaller the absolute value |P| of the power value P calculated by the power calculation unit 12, the shorter the length Φ of the on-period is set. That is, in this case, the length Φ of the on-period in each cycle of the on / off operation performed on the switching element is represented by a function f(P) that takes the power value P calculated by the power calculation unit 12 as a variable. When the main circuit unit 11 is in the regeneration state and the power value P calculated by the power calculation unit 12 is greater than the second power threshold P th2 , the function f(P) representing the length Φ of the on-period only needs to be a decreasing function.

[0067] For example, such as Figure 4BAs shown, set the length Φ of the on-period for each cycle in the on-off operation performed on the switching element according to a linear decreasing function f(P) as follows: When the value P of the power calculated by the power calculation unit 12 is P th2 (negative value), the length Φ is 120 degrees. When the value P of the power calculated by the power calculation unit 12 is 0 (zero), the length Φ is Φ min (where 0 < Φ min < 120 degrees). As an alternative example, the function f(P) representing the length Φ of the on-period for each cycle can be a higher-order decreasing function or a function such as a hyperbola instead of the Figure 4B shown linear decreasing function. However, this function preferably shows a monotonic decrease in the interval where the value P of the power calculated by the power calculation unit 12 is P th2 (negative value) to 0 (zero).

[0068] Alternatively, for example, as Figure 4C shown, the length Φ of the on-period for each cycle in the on-off operation performed on the switching element can also be set according to a step function f(P) that sets the length Φ of the on-period to a shorter value in stages as the absolute value |P| of the value P of the power calculated by the power calculation unit 12 becomes smaller. In this case, a plurality of power thresholds are set on the regenerative state side, and based on the comparison result between the value P of the power calculated by the power calculation unit 12 and the values of the respective power thresholds, the length Φ of the on-period for each cycle is determined. In the Figure 4C shown example, as an example, three power thresholds P th2a 、P th2b and P th2c are set, and the length Φ of the on-period is set to a step function f(P) such that when the value P of the power calculated by the power calculation unit 12 is P th2c (negative value), Φ is 120 degrees, and when the value P of the power calculated by the power calculation unit 12 is P th2a to 0 (zero), Φ is Φ min (where 0 < Φ min < 120 degrees).

[0069] Alternatively, for example, the length Φ of the on-period for each cycle in the on-off operation performed on the switching element can also be set according to a function f(P) obtained by setting a hysteresis when the regenerative power is increasing and decreasing.

[0070] Figure 5AFIG. 0 is a diagram showing the relationship between the waveforms of the three-phase AC power supply voltage in the rectifier 1 according to one embodiment of the present disclosure and the on / off operations of the switching elements in the power element, and shows the relationship between the waveforms of the three-phase AC power supply voltage and the on / off operations of the switching elements in a region where the regenerative power is large. Figure 5B FIG. 2 is a diagram showing the relationship between the waveforms of the three-phase AC power supply voltage in the rectifier 1 according to one embodiment of the present disclosure and the on / off operations of the switching elements in the power element, and shows the relationship between the waveforms of the three-phase AC power supply voltage and the on / off operations of the switching elements in a region where the regenerative power is small. As Figure 5A shown, in the rectifier 1 according to one embodiment of the present disclosure, when the power value P calculated by the power calculation unit 12 is the second power threshold P th2 In the region where the regenerative power is large and the following conditions are satisfied, the control unit 14 performs control to execute the on / off operations of the switching elements by a 120-degree conduction method. Further, as Figure 5B shown, in the rectifier 1 according to one embodiment of the present disclosure, when the power value P calculated by the power calculation unit 12 is greater than the second power threshold P th2 In the region where the regenerative power is small, the control unit 14 controls the execution of the on / off operations of the switching elements with an on-time Φ = f(P) shorter than 120 degrees, where the 120 degrees is the length of the on-time in each cycle in the 120-degree conduction method. Figure 5B The portion indicated by the slant line in FIG. 12 is a period during which all the switching elements provided in the upper arms and the lower arms of each of the three phases are not turned on in one cycle of the voltage of the three-phase AC power supply 2. As Figure 5B shown, in the region where the regenerative power is small, it is necessary to provide a period during which all the switching elements provided in the upper arms and the lower arms of each of the three phases are not turned on in one cycle of the voltage of the three-phase AC power supply 2. During this non-conduction period, the transfer of power from the DC side to the three-phase AC power supply 2 side is cut off. Therefore, it is possible to prevent the resonance in which the switching between the regenerative state and the power running state that occurs in the case of small regenerative power is repeatedly performed frequently. Further, when the power value P calculated by the power calculation unit 12 is 0 (zero), the on-time length Φmin is made the same as the on-time length Φ set in the case where it is determined that the main circuit unit 11 is in the power running state and the power value P calculated by the power calculation unit 12 is less than the first power threshold Pth1, whereby it is possible to more reliably suppress the surge current that can be generated when switching from the regenerative state to the power running state.

[0071] Figure 6 FIG. 18 is a flowchart showing the operation flow of the rectifier according to one embodiment of the present disclosure.

[0072] In step S101, the power calculation unit 12 calculates the value P of the power flowing between the three-phase AC power supply 2 side and the DC side via the main circuit unit 11.

[0073] In step S102, based on the power value P calculated by the power calculation unit 12, the state determination unit 13 determines whether the main circuit unit 11 is in the power operation state of converting the AC power on the three-phase AC power supply 2 side into DC power and outputting it to the DC side, or whether the main circuit unit 11 is in the regeneration state of converting the DC power on the DC side into AC power and outputting it to the three-phase AC power supply 2 side. If it is determined that the main circuit unit 11 is in the power operation state, the process proceeds to step S103; if it is determined that the main circuit unit 11 is in the regeneration state, the process proceeds to step S104.

[0074] In step S103, the control unit 14 determines whether the power value P calculated by the power calculation unit 12 is less than the first power threshold P th1 . If it is determined that the power value P calculated by the power calculation unit 12 is less than the first power threshold P th1 , the process proceeds to step S107; if it is determined that the power value P calculated by the power calculation unit 12 is greater than or equal to the first power threshold P th1 , the process proceeds to step S108.

[0075] In step S107, the control unit 14 controls to perform the on / off operation of the switching element. Here, the length Φ of the on period in each cycle of the on / off operation performed on the switching element is set to Φ min , and this Φ min is a value shorter than the length of the on period in each cycle of the 120-degree power supply method (i.e., 120 degrees). Thus, even in the region where the power operation power is small immediately after the conversion from the regeneration state to the power operation state, no inrush current will be generated.

[0076] In step S108, the control unit 14 controls to stop performing the on / off operation of the switching element. Thus, the AC power on the three-phase AC power supply 2 side is converted into DC power and output to the DC side only through the rectification action of the rectifying element.

[0077] If it is determined in step S102 that the main circuit unit 11 is in the regeneration state, in step S104, the control unit 14 determines whether the power value P calculated by the power calculation unit 12 is less than or equal to the second power threshold P th2 . If it is determined that the power value P calculated by the power calculation unit 12 is less than or equal to the second power threshold P th2 , the process proceeds to step S105; if it is determined that the power value P calculated by the power calculation unit 12 is greater than the second power threshold P th2In such a case, proceed to step S106.

[0078] In step S105, the control unit 14 performs control to execute the on / off operation of the switching element by the 120-degree power supply method. As a result, the DC power on the DC side is converted into AC power and output to the three-phase AC power supply 2 side.

[0079] In step S106, the control unit 14 sets the length Φ of the on period in each cycle of the on / off operation performed on the switching element to a value shorter than 120 degrees, where 120 degrees is the length of the on period in each cycle in the 120-degree power supply method, and the control unit 14 performs control to execute the on / off operation of the switching element according to this value. In this case, the smaller the absolute value |P| of the power value P calculated by the power calculation unit 12, the shorter the length Φ of the on period in each cycle of the on / off operation performed on the switching element is set. As a result, even when the regenerative power is small, resonance in which the switching between the regenerative state and the power running state is frequently repeated does not occur, and the DC power on the DC side is converted into AC power and output to the three-phase AC power supply 2 side.

[0080] When performing steps S105 to S108, the power calculation process in S101 and the determination processes in steps S102 to S104 are executed at a prescribed cycle. Among them, for convenience, it is described as returning to S101 after processing in steps S105 to S108. Figure 6 In [it], for convenience, it is described as returning to S101 after processing in steps S105 to S108.

[0081] Next, several modified examples of the method for determining whether to adopt the 120-degree power supply method for controlling the switching element of the main circuit unit 11 when the main circuit unit 11 is in the regenerative state are listed below.

[0082] In the above-described embodiment, whether to adopt the 120-degree power supply method for controlling the switching element of the main circuit unit 11 when the main circuit unit 11 is in the regenerative state is determined based on the comparison between the power value P calculated by the power calculation unit 12 and the second power threshold P th2 In the first modified example, the control unit 14 determines whether to adopt the 120-degree power supply method for controlling the switching element of the main circuit unit 11 when the main circuit unit 11 is in the regenerative state based on the peak value of the input voltage input from the three-phase AC power supply 2 side to the main circuit unit 11 and the DC voltage value on the DC side of the main circuit unit 11 instead of the comparison between the power value P calculated by the power calculation unit 12 and the second power threshold P th2 In the first modified example, the control unit 14 determines whether to adopt the 120-degree power supply method for controlling the switching element of the main circuit unit 11 when the main circuit unit 11 is in the regenerative state based on the peak value of the input voltage input from the three-phase AC power supply 2 side to the main circuit unit 11 and the DC voltage value on the DC side of the main circuit unit 11 instead of the comparison between the power value P calculated by the power calculation unit 12 and the second power threshold P

[0083] Figure 7 is a flowchart showing the operation flow in the rectifier according to the first modified example of one embodiment of the present disclosure.

[0084] Figure 7 Each process of steps S101 to S103 and S105 to S108 shown is the same as Figure 6 each process of steps S101 to S103 and S105 to S108 shown. However, when it is determined in step S102 that the main circuit unit 11 is in the regenerative state, the process proceeds to step S109.

[0085] In step S109, the control unit 14 determines whether the difference between the DC voltage value on the DC side of the main circuit unit 11 and the crest value of the input voltage is greater than the voltage threshold V th . The DC voltage value on the DC side of the main circuit unit 11 is detected by the DC voltage detection unit 16, and the crest value of the input voltage input from the three-phase AC power supply 2 to the main circuit unit 11 is detected by the input voltage detection unit 15. In addition, in Figure 1 , the arrows from the input voltage detection unit 15 and the DC voltage detection unit 16 to the control unit 14 are not shown in the figure. The voltage threshold V th can be appropriately set according to the application environment of the rectifier 1. When giving an example, it is set to about several tens to several hundreds of percentages of the rated output voltage value of the rectifier 1, but it can also be set to other values. In addition, regarding the voltage threshold V th , it can be stored in a rewritable storage unit (not shown) and can be rewritten by an external device. Even after temporarily setting the voltage threshold V th , it is possible to change the voltage threshold V th to an appropriate value as needed. In step S109, when it is determined that the difference between the DC voltage value on the DC side of the main circuit unit 11 and the crest value of the input voltage is greater than the voltage threshold V th , the process proceeds to step S105. When it is determined that the difference between the DC voltage value on the DC side of the main circuit unit 11 and the crest value of the input voltage is equal to or less than the voltage threshold V th , the process proceeds to step S106.

[0086] In step S105, the control unit 14 performs control to execute the on / off operation of the switching element by the 120-degree conduction method. Thereby, the DC power on the DC side is converted into AC power and output to the three-phase AC power supply 2 side.

[0087] In step S106, the control unit 14 sets the length Φ of the on-period in each cycle of the on-off operation performed on the switching element to a value shorter than 120 degrees, where 120 degrees is the length of the on-period in each cycle in the 120-degree power supply method. The control unit 14 controls to perform the on-off operation of the switching element according to this value. In this case, the smaller the absolute value |P| of the power value P calculated by the power calculation unit 12, the shorter the value set for the length Φ of the on-period in each cycle of the on-off operation performed on the switching element.

[0088] In the second modification of the rectifier 1 according to an embodiment of the present disclosure, the control unit 14 is based on the number of times of switching between the regenerative state and the power running state within a specified time from when the state determination unit 13 determines the regenerative state and the number of times threshold C th for comparison instead of comparing the power value P calculated by the power calculation unit 12 with the second power threshold P th2 to determine whether to adopt the 120-degree power supply method for controlling the switching element of the main circuit unit 11.

[0089] Figure 8 is a diagram showing a rectifier and a motor drive device according to a second modification of an embodiment of the present disclosure.

[0090] As Figure 8 shown, the rectifier 1 according to the second modification of an embodiment of the present disclosure further includes a switching number determination unit 17 in the Figure 1 rectifier 1 shown.

[0091] The switching number determination unit 17 determines whether the switching between the regenerative state and the power running state has occurred more than the number of times threshold C within a specified time from when the state determination unit 13 determines the regenerative state based on the determination result determined by the state determination unit 13 th or more. The determination result determined by the switching number determination unit 17 is notified to the control unit 14. The above-mentioned "specified time" can be appropriately set according to the application environment of the rectifier 1. When giving an example, it is set to about several seconds, but it can also be set to other values. In addition, the number of times threshold C th and the above-mentioned "specified time" can be stored in a rewritable storage unit (not shown) and can be rewritten by an external device. Even after temporarily setting the number of times threshold C th and the above-mentioned "specified time", the number of times threshold C th and the above-mentioned "specified time" can be changed to appropriate values according to needs.

[0092] When it is determined by the switching number determination unit 17 that the switching between the regenerative state and the power running state has occurred more than the number of times threshold C within the specified time thIn the above case, the control unit 14 sets the length of the on-period in each cycle of the on-off operation performed on the switching element to a value shorter than the length of the on-period in each cycle in the 120-degree power supply mode, and the control unit 14 controls to perform the on-off operation of the switching element according to this value. In this case, the smaller the absolute value |P| of the power value P calculated by the power calculation unit 12, the shorter the value that can be set for the length Φ of the on-period in each cycle of the on-off operation performed on the switching element.

[0093] The control unit 14 does not determine by the switching number determination unit 17 that the switching between the regeneration state and the power running state has occurred the number of times threshold C within a specified time th In the above case, the control unit 14 controls to perform the on-off operation of the switching element by the 120-degree power supply mode. In addition, the number of times threshold C th Only needs to be appropriately set according to the application environment of the rectifier 1. When giving an example, it is set to about several times, but it can also be set to other values. Setting the value of the number of times threshold C th to a smaller value can more effectively suppress the abnormal heating of the capacitor caused by the resonance in which the switching between the regeneration state and the power running state is repeatedly performed frequently.

[0094] In the second modification example, regarding the circuit structure elements other than the switching number determination unit 17 and the control unit 14, they are the same as the Figure 1 circuit structure elements shown, so the same reference numerals are given to the same circuit structure elements to omit the detailed description of the circuit structure elements.

[0095] The switching number determination unit 17 can be constructed, for example, in the form of a software program, or can be constructed by a combination of various electronic circuits and software programs, or can be composed only of various electronic circuits. For example, when constructing them in the form of a software program, by making an arithmetic processing device such as a DSP or an FPGA operate according to the software program, the functions of the above-mentioned respective units can be realized. Additionally, or the switching number determination unit 17 can be realized as a semiconductor integrated circuit in which a software program for realizing the functions of the respective units is written. Additionally, or the switching number determination unit 17 can be realized as a recording medium in which a software program for realizing the functions of the respective units is written. Further, the switching number determination unit 17 can be provided, for example, in the numerical control device of a machine tool or in the robot controller for controlling a robot.

[0096] Figure 9 is a flowchart showing the operation flow in the rectifier according to the second modification example of an embodiment of the present disclosure.

[0097] Figure 9The processes of steps S101 to S103 and S105 to S108 shown are the same as Figure 6 the processes of steps S101 to S103 and S105 to S108 shown. Among them, when it is determined in step S102 that the main circuit section 11 is in the regenerative state, the process proceeds to step S110.

[0098] In step S110, the switching - times determination section 17 determines whether the number of times of switching between the regenerative state and the power - running state within a specified time from when it is determined by the state determination section 13 to be in the regenerative state reaches the number - of - times threshold C th The above. In step S110, if it is not determined that the number of times of switching between the regenerative state and the power - running state within the specified time reaches the number - of - times threshold C th The above, the process proceeds to step S105. If it is determined that the number of times of switching between the regenerative state and the power - running state within the specified time reaches the number - of - times threshold C th The above, the process proceeds to step S106.

[0099] In step S105, the control section 14 performs control to execute the on - off operation of the switching element in a 120 - degree power - on mode. Thus, the DC power on the DC side is converted into AC power and output to the three - phase AC power supply 2 side.

[0100] In step S106, the control section 14 sets the length Φ of the on - period in each cycle of the on - off operation performed on the switching element to a value shorter than 120 degrees, where 120 degrees is the length of the on - period in each cycle of the 120 - degree power - on mode, and the control section 14 performs control to execute the on - off operation of the switching element according to this value. In this case, the smaller the absolute value |P| of the power value P calculated by the power calculation section 12, the shorter the length Φ of the on - period in each cycle of the on - off operation performed on the switching element is set.

[0101] As described above, in the first modification example and the second modification example, when it is determined in step S103 that the power value P calculated by the power calculation section 12 is less than the first power threshold P th1 In this case, in step S107, control is performed to execute the on - off operation of the switching element. Therefore, even in the region where the power during power running is small immediately after switching from the regenerative state to the power - running state, inrush current does not occur. In addition, based on the determination results of step S109 in the first modification example and step S110 in the second modification example, the on - off operation of the switching element is controlled to prevent resonance in which the switching between the regenerative state and the power - running state is repeatedly performed frequently. Therefore, the capacitor does not heat up abnormally.

[0102] According to one aspect of the present disclosure, in a rectifier having a power regeneration function and a motor drive device including the rectifier, it is possible to prevent a surge current generated when switching from a regeneration state to a power running state, and it is possible to prevent a resonance in which switching between the regeneration state and the power running state occurs frequently in the case where the regenerative power is small.

Claims

1. A rectifier, comprising: A main circuit section that performs power conversion between AC power on the three-phase AC power supply side and DC power on the DC side through the rectification operation of rectifying elements and the on / off operation of switching elements; A power calculation section that calculates the value of the power flowing between the three-phase AC power supply side and the DC side via the main circuit section; A control section that performs control to execute the on / off operation of the switching elements; And A state determination section that determines whether the main circuit section is in a power operation state in which AC power on the three-phase AC power supply side is converted into DC power and output to the DC side or a regeneration state in which DC power on the DC side is converted into AC power and output to the three-phase AC power supply side, based on the value of the power calculated by the power calculation section, The control section controls the on / off operation of the switching elements according to the determination result of the state determination section to change the length of the on-period in each cycle of the on / off operation performed on the switching elements, When it is determined by the state determination section that it is in the power operation state and the value of the power calculated by the power calculation section is less than a first power threshold, the control section changes the length of the on-period in each cycle of the on / off operation performed on the switching elements according to the value of the power calculated by the power calculation section.

2. The rectifier according to claim 1, wherein When it is determined by the state determination section that it is in the regeneration state, the control section changes the length of the on-period in each cycle of the on / off operation performed on the switching elements according to the value of the power calculated by the power calculation section.

3. The rectifier according to claim 1, wherein When it is determined by the state determination section that it is in the power operation state and the value of the power calculated by the power calculation section is equal to or greater than the first power threshold, the control section performs control to stop the on / off operation of the switching elements.

4. The rectifier according to any one of claims 1 to 3, wherein The main circuit section has a three-phase bridge circuit in which power elements are respectively provided on the upper arm and the lower arm of each phase, and the power elements are composed of the rectifying elements and the switching elements connected in anti-parallel with the rectifying elements.

5. The rectifier according to claim 4, wherein When it is determined by the state determination section that it is in the regeneration state and the value of the power calculated by the power calculation section is equal to or less than a second power threshold, the control section performs control to execute the on / off operation of the switching elements in a 120-degree conduction mode, in which, whenever the voltage of each phase alternates, the switching element in the upper arm of the phase with the maximum voltage of the three-phase AC power supply in each phase is turned on, and the switching element in the lower arm of the phase with the minimum voltage of the three-phase AC power supply is turned on. When it is determined by the state determination unit that it is in the regeneration state and the value of the power calculated by the power calculation unit is greater than the second power threshold, the control unit sets the length of the on-period in each cycle of the on / off operation performed on the switching element to a value shorter than the length of the on-period in each cycle in the 120-degree power supply method.

6. The rectifier according to claim 5, wherein When it is determined by the state determination unit that it is in the regeneration state and the value of the power calculated by the power calculation unit is greater than the second power threshold, the smaller the absolute value of the power value calculated by the power calculation unit, the shorter the control unit sets the length of the on-period in each cycle of the on / off operation performed on the switching element.

7. A rectifier comprising: A main circuit unit that performs power conversion between the AC power on the three-phase AC power supply side and the DC power on the DC side through the rectification action of rectifying elements and the on / off operation of switching elements; A power calculation unit that calculates the value of the power flowing between the three-phase AC power supply side and the DC side via the main circuit unit; A control unit that performs control to execute the on / off operation of the switching element; A state determination unit that determines whether the main circuit unit is in the power operation state of converting the AC power on the three-phase AC power supply side into DC power and outputting it to the DC side or the regeneration state of converting the DC power on the DC side into AC power and outputting it to the three-phase AC power supply side based on the value of the power calculated by the power calculation unit; An input voltage detection unit that detects the crest value of the input voltage input from the three-phase AC power supply side to the main circuit unit; And A DC voltage detection unit that detects the DC voltage value on the DC side of the main circuit unit, The control unit controls the on / off operation of the switching element according to the determination result of the state determination unit to change the length of the on-period in each cycle of the on / off operation performed on the switching element, The main circuit unit has a three-phase bridge circuit obtained by respectively disposing power elements on the upper arm and the lower arm of each phase, and the power element is composed of the rectifying element and the switching element connected in anti-parallel with the rectifying element, When it is determined by the state determination unit that it is in the regeneration state and the difference between the DC voltage value and the crest value of the input voltage is greater than the voltage threshold, the control unit performs control to execute the on / off operation of the switching element by the 120-degree power supply method. In the 120-degree power supply method, whenever the voltage of each phase alternates, the switching element in the upper arm of the phase with the maximum voltage of the three-phase AC power supply in each phase is turned on, and the switching element in the lower arm of the phase with the minimum voltage of the three-phase AC power supply is turned on. When it is determined by the state determination unit that it is in the regeneration state and the difference between the DC voltage value and the peak value of the input voltage is equal to or less than the voltage threshold, the control unit sets the length of the on-period in each cycle of the on-off operation performed on the switching element to a value shorter than the length of the on-period in each cycle in the 120-degree power supply method.

8. The rectifier according to claim 7, wherein when it is determined by the state determination unit that it is in the regeneration state and the difference between the DC voltage value and the peak value of the input voltage is equal to or less than the voltage threshold, the smaller the absolute value of the power value calculated by the power calculation unit, the shorter the control unit sets the length of the on-period in each cycle of the on-off operation performed on the switching element.

9. A motor drive device, comprising: the rectifier according to any one of claims 1 to 8; a capacitor provided in a DC link on the DC side of the rectifier; and an inverter connected to the rectifier via the DC link, which converts DC power supplied from the DC link into AC power for motor drive and outputs it.

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