JP5740824B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device including a conversion unit that performs power conversion by a switching operation and supplies power to an inductive load.

  2. Description of the Related Art Conventionally, there is provided a power conversion device including an inverter unit configured to convert input DC power into AC power having a predetermined frequency by switching operation of a plurality of switching elements and to supply the AC power to an inductive load. Are known. In such a power conversion device, generally, an electrolytic capacitor having a relatively large capacity for smoothing the AC power of the AC power source rectified by the rectifier circuit is provided on the input side of the inverter unit. .

  On the other hand, as disclosed in Patent Document 1, for example, an electrolytic capacitor having a large capacitance capable of absorbing voltage fluctuation caused by the power supply frequency is used as a carrier frequency among voltage fluctuations generated during switching operation of the switching element of the inverter unit. A configuration is known in which the rectification portion is reduced in size and cost is reduced by changing to a small-capacitance capacitor capable of absorbing only the corresponding fluctuation component.

JP 2002-51589 A

  By the way, as described above, in the power converter configured to supply power to the inductive load by the inverter unit, even if the driving of the inverter unit is stopped, the inductive load having an inductance component therein is changed from the inductive load to the inverter unit. Current may continue to flow. If it does so, an excessive surge voltage may be applied to an inverter part and this inverter part may be destroyed.

  Further, when the surge voltage as described above is generated, a current flows through the capacitor via the return diode of the inverter unit, so that the capacitor is charged. Due to this charging, the inverter unit may be destroyed even when an overvoltage occurs at both ends of the capacitor, that is, the DC link.

  On the other hand, a method of providing a brake circuit having a resistance in the DC link or making a regenerative configuration using a PWM converter or the like is conceivable. However, if a brake circuit is provided, power is consumed by the resistance of the brake circuit, which is not preferable from the viewpoint of the efficiency of the power converter. If a PWM converter or the like is provided, the circuit configuration and control become complicated, leading to an increase in the cost of the entire apparatus.

  On the other hand, in a power conversion device having a small-capacitance capacitor as in the configuration of Patent Document 1, the voltage of the DC link is likely to increase because the capacitance of the capacitor is small. For this reason, the power conversion device having the configuration of Patent Document 1 must be operated at a high speed even if the brake circuit or the PWM converter as described above is provided, and a high-speed controller is required. This leads to complicated control. Further, in the configuration as in Patent Document 1, it is conceivable to provide an overvoltage prevention mechanism in order to prevent an overvoltage at the time of abnormality. However, the overvoltage prevention mechanism operates every time the inverter unit stops, and the overvoltage Since the operation frequency of the prevention mechanism increases, it is necessary to improve the durability of the overvoltage prevention mechanism accordingly, leading to an increase in the cost of the entire apparatus.

  The present invention has been made in view of the above points, and an object of the present invention is to drive a converter in a power converter including a converter such as an inverter that supplies power to an inductive load. It is to realize a configuration that does not damage the component equipment even if the operation is stopped by a low-cost configuration.

  In order to achieve the above object, in the power conversion device (1) according to the present invention, when power supply to the inductive load (3) is stopped, the current flowing through the inductive load (3) becomes a predetermined value or less. Until the switching element (Su, Sv, Sw, Sx, Sy, Sz) of the conversion unit (13) is switched.

  Specifically, the first invention has a plurality of switching elements (Su, Sv, Sw, Sx, Sy, Sz), and inputs electric power to the switching elements (Su, Sv, Sw, Sx, Sy). , Sz) is intended for a power conversion device including a conversion unit (13) configured to be converted into AC power having a predetermined frequency and output to an inductive load (3).

  And when stopping the electric power supply to the said inductive load (3), the electric current determination part (16) which determines whether the electric current which flows into this inductive load (3) is below a predetermined value, and the said electric current determination Switching in which the switching element (Su, Sv, Sw, Sx, Sy, Sz) continues the switching operation until the current flowing through the inductive load (3) is determined to be less than the predetermined value by the section (16) And a control unit (15).

The input power is single-phase AC power, and the switching control unit (15) indicates that the current (iu, iv, iw) of each phase flowing through the inductive load (3) is the phase of the single-phase AC. The switching elements (Su, Sv, Sw, Sx) so that the absolute value sum of the currents (iu, iv, iw) of the respective phases periodically becomes a predetermined minimum target value. , Sy, Sz), and the current determination unit (16) determines that the current (iu, iv, iw) flowing through the inductive load (3) is based on the phase of the single-phase AC. It shall be judged whether it is below the value.

With the above configuration, when the power supply from the converter (13) to the inductive load (3) is stopped, the switching elements (Su, Sv, Sw, Sx, Sy, Sz) in the converter (13) Instead of suddenly stopping the switching operation, the current flowing through the inductive load (3) is reduced to a predetermined value or less, and then the switching operation of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) is stopped. be able to. As a result, the surge voltage generated by stopping the drive of the converter (13) can be kept low, and the components in the power converter (1) can be prevented from being damaged by the surge voltage or overvoltage caused by capacitor charging. I can .

Controlled conversion unit as this in (13), the phase currents (iu, iv, iw) the absolute value sum of periodically becomes the minimum target value, the phase of the single-phase AC phase current ( The timing at which the sum of absolute values of (iu, iv, iw) is minimized can be understood. Therefore, the current determination unit (16) determines whether the current flowing through the inductive load (3) is equal to or less than the predetermined value based on the phase of the single-phase alternating current.

Moreover, 2nd invention is the power converter device of 1st invention, An input is connected to the single phase alternating current power supply (2), A single phase alternating current is full-wave rectified and it supplies to the said conversion part (13) A rectifier (11) is provided, and the input of the converter (13) is connected to a capacitor (12) having a capacity such that the maximum pulsation width of the voltage across the input is at least twice the minimum value. And

  In this configuration, since the capacitance of the capacitor is smaller than that of a general power converter, if the voltage of the capacitor (12) rises due to the stop of driving of the converter (13), the capacitor (12) is also easily damaged. . However, in this configuration, when the converter (13) is stopped, the current that continues to flow through the converter (13) can be reduced, and the surge voltage generated in the power converter (1) is reduced. be able to. Therefore, in the power conversion device (1) having the small-capacitance capacitor (12) as described above, it is possible to prevent the component parts from being damaged by the surge voltage when the conversion unit (13) is stopped.

Moreover, 3rd invention is the power converter device of 1st invention, WHEREIN: The said conversion part (31) is connected to the input AC power supply (2), AC power supplied from the said AC power supply (2) is used. It is assumed that the power is directly converted into a predetermined plurality of phases of AC power.

  With this configuration, in a so-called direct power converter that converts alternating current into alternating current having a predetermined characteristic, the surge voltage can be kept low as in the first invention.

According to a fourth aspect of the present invention, in the power conversion device according to any one of the first to third aspects, the inductive load (3) outputs power to a load that performs only powering operation.

  When power is output from the inductive load (3) to a load that also performs regenerative operation, current flows to the conversion unit (13) side for a relatively long time during regeneration. Therefore, it is difficult to prevent damage to the power converter. However, if the power is output from the inductive load (3) to the load that performs only the power running operation as described above, when the drive of the conversion unit (13) is stopped by applying the configuration of each invention described above, It is possible to prevent a voltage that may damage the components from being applied to the inside of the power converter (1).

According to the power converter (1) of the present invention, when the power supply to the inductive load (3) is stopped, the switching element (until the current flowing through the inductive load (3) becomes a predetermined value or less. In order to continue the switching operation of Su, Sv, Sw, Sx, Sy, Sz), when the converter (13) stops driving, an excessive voltage is applied to the power converter (1) and the components are damaged. Can be prevented. In addition, it is not necessary to provide a brake circuit or the like, and the overvoltage prevention mechanism does not operate when the apparatus is stopped, so that the cost of the entire apparatus can be reduced .

Also, according to the first invention, each phase current (iu, iv, iw) without detecting a said current (iu, iv, iw) be to determine whether it is less than a predetermined value As a result, control in the current determination unit (16) becomes easier.

Furthermore, according to the second invention, in the configuration in which the capacitor (12) provided on the input side of the converter (13) has a small capacity, when the converter (13) is stopped, the components of the power converter are It becomes possible to prevent damage by the surge voltage.

According to the third invention, in the so-called direct power converter, it is possible to prevent the components of the power converter from being damaged by the surge voltage when driving of the converter (13) is stopped.

Further, according to the fourth invention, since the inductive load (3) outputs power to a load that performs only power running operation, the regenerative load (3) regenerates compared to a case where power is output to a load that also performs regenerative operation. The time for the current to flow to the side is short. Therefore, the components of the first to ninth inventions can prevent the component parts from being damaged by the surge voltage.

FIG. 1 is a circuit diagram showing a schematic configuration of a power conversion device according to Related Art 1 of the present invention. FIG. 2 is a diagram illustrating the operation of the control unit when the power supply to the motor is stopped. FIG. 3 is a flowchart showing the operation of the control unit in FIG. FIG. 4 is a diagram illustrating a three-phase current waveform output to a motor from a power conversion device including a conventional capacitor having a capacitance. FIG. 5 is a diagram showing a waveform when a current having a waveform as shown in FIG. 4 is converted into an absolute value. FIG. 6 is a diagram illustrating a three-phase current waveform output to the motor from the power conversion device including a small-capacitance capacitor. FIG. 7 is a diagram showing a waveform when a current having a waveform as shown in FIG. 6 is converted into an absolute value. FIG. 8 is a circuit diagram illustrating a schematic configuration of a power conversion device according to Modification 2 of Related Art 1. FIG. 9 is a circuit diagram showing a schematic configuration of a power conversion device according to Related Art 2 of the present invention. FIG. 10 is a circuit diagram illustrating a schematic configuration of the power conversion apparatus according to the second embodiment .

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature and is not intended to limit the present invention, its application, or its use.

<< Related art 1 of invention >>
-Overall configuration-
FIG. 1 shows a schematic configuration of a power conversion device (1) according to Related Art 1 of the present invention. The power conversion device (1) includes a converter circuit (11), a capacitor (12), and an inverter circuit (13) (conversion unit). The power conversion device (1) is connected to a single-phase AC power source (2). The electric power is converted into electric power having a predetermined frequency and is supplied to a three-phase AC motor (3) (inductive load, hereinafter also referred to as a motor). The three-phase AC motor (3) is for driving a compressor (load) provided in a refrigerant circuit of an air conditioner, for example. That is, the power conversion device (1) is configured to supply power to an inductive load for driving a load that performs only power running operation.

  The converter circuit (11) is connected to the AC power source (2) and configured to full-wave rectify an AC voltage. The converter circuit (11) is a diode bridge circuit in which a plurality of (four in the present embodiment) diodes (D1 to D4) are connected in a bridge shape, and is connected to the AC power source (2). Yes. That is, the converter circuit (11) is an example of the rectifying unit of the present invention.

  The capacitor (12) is provided between the converter circuit (11) and an inverter circuit (13) described later. This capacitor (12) is constituted by, for example, a film capacitor, and a ripple voltage (carrier) generated when a switching element (Su, Sv, Sw, Sx, Sy, Sz) described later of the inverter circuit (13) performs a switching operation. It is configured to have a capacitance capable of absorbing only the voltage fluctuation corresponding to the frequency. That is, the capacitor (12) is a small-capacitance capacitor that does not have a capacitance that smoothes the voltage rectified by the converter circuit (11) (voltage fluctuation caused by the power supply voltage).

  Thus, the waveform of the voltage across the capacitor (12) pulsates at 2f (Hz) in the case of a single-phase voltage of frequency f (Hz), and 6f in the case of a three-phase voltage of frequency f (Hz). Pulsates at (Hz). In the case of a single-phase voltage having a frequency f (Hz), the capacitor (12) is configured such that the maximum value of the pulsation of the both-end voltage is twice or more the minimum value.

  The inverter circuit (13) is connected in parallel to the capacitor (12) on the output side of the converter circuit (11). The inverter circuit (13) is formed by bridge-connecting a plurality of switching elements (Su, Sv, Sw, Sx, Sy, Sz) (for example, six in the case of a three-phase alternating current). That is, the inverter circuit (13) includes three switching legs in which two switching elements are connected in series with each other. In each switching leg, the upper arm switching elements (Su, Sv, Sw) and the lower arm The midpoints of the switching elements (Sx, Sy, Sz) are connected to the coils (3a, 3b, 3c) of the three-phase AC motor (3), respectively.

  The inverter circuit (13) converts the output voltage of the converter circuit (11) into a three-phase AC voltage having a predetermined frequency by turning on / off the switching elements (Su, Sv, Sw, Sx, Sy, Sz). The three-phase AC motor (3) is configured to be supplied. In this embodiment, a free-wheeling diode (Du, Dv, Dw, Dx, Dy, Dz) is connected in antiparallel to each of the switching elements (Su, Sv, Sw, Sx, Sy, Sz). Has been.

  The power conversion device (1) includes a control unit (14) for driving and controlling the switching elements (Su, Sv, Sw, Sx, Sy, Sz) of the inverter circuit (13). When an operation command for instructing operation or stop is input, the control unit (14) is configured so that the current value detected from the inverter circuit (13) approaches the current value corresponding to the command. A drive signal is output to (Su, Sv, Sw, Sx, Sy, Sz). That is, the control unit (14) performs feedback control on the current flowing through the inverter circuit (13).

  The control unit (14) includes a switching control unit (15) that outputs a drive signal for switching the switching elements (Su, Sv, Sw, Sx, Sy, Sz), and the inverter circuit (13). When the power supply to the motor (3) is stopped, the current flowing through the motor (3) is a predetermined value (a value when the current is converted into an absolute value. This corresponds to a predetermined range X shown in Fig. 2. The same applies hereinafter.) A current determination unit (16) for determining whether or not the range is below.

  The current determination unit (16) is configured such that a current flowing through the motor (3) generates a surge voltage generated when the switching operation of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) is stopped. It is configured to determine whether or not the value is equal to or less than a predetermined value that is smaller than the breakdown voltage of the component. The current determination unit (16) outputs a stop signal instructing the switching control unit (15) to stop the switching operation when the current flowing through the motor (3) is equal to or less than the predetermined value. It is configured as follows. Here, the above components are switching elements (Su, Sv, Sw, Sx, Sy, Sz), diodes (Du, Dv, Dw, Dx, Dy, Dz) and capacitors (12) of the inverter circuit (13). Means the diodes (D1 to D4) of the converter circuit (11).

  The switching control unit (15) switches the switching elements (Su, Sv, Sw, Sx, Sy, Sz) according to a current command generated by a command generation unit (not shown) in the control unit (14). It is configured as follows. The switching control unit (15) is configured to switch the switching elements (Su, Sv, Sw, Sx, Sy, Sz) until a stop signal for stopping the switching operation is output from the current determination unit (16). The switching operation is continued. Further, the switching control unit (15), when a stop operation command is input to the control unit (14), to reduce the current flowing through the motor (3) until the predetermined value or less. The switching elements (Su, Sv, Sw, Sx, Sy, Sz) are configured to continue the switching operation. That is, when the stop operation command is input, the switching control unit (15) reduces the current flowing through the motor (3) until a stop signal is output from the current determination unit (16). The switching operation is continued in the switching elements (Su, Sv, Sw, Sx, Sy, Sz).

-Control unit operation-
Hereinafter, the operation of the control unit (14) will be described with reference to FIGS. In the following description, for simplification of explanation, one phase of the three-phase AC motor (3) will be described.

  As shown in FIG. 2, when a stop operation command is input to the control unit (14), conventionally, the switching operation is also stopped. However, in the present invention, the current flowing through the motor, which is an inductive load, is reduced. The switching operation of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) is continued until it falls within the predetermined range X (below the predetermined value). Specifically, even when an operation stop command signal is input to the control unit (14), the current determination unit (16) determines that the current flowing through the motor is not within the predetermined range (below the predetermined value). The switching controller (15) gradually lowers the modulation degree of the drive signal for the switching elements (Su, Sv, Sw, Sx, Sy, Sz). Thereby, the current supplied from the inverter circuit (13) to the motor gradually decreases. When the current determining unit (16) determines that the current flowing through the motor is within the predetermined range (below a predetermined value), the switching control unit (15) performs the switching element (Su, Sv, Sw, Sx, Sy, Sz) are stopped.

  FIG. 3 shows an operation flow of the control unit (14). When the flow of FIG. 3 starts, first, at step S1, it is determined whether or not the absolute value (current value) of the current flowing through the motor is equal to or less than a predetermined value. If it is determined in step S1 that the absolute value of the current flowing through the motor is equal to or less than a predetermined value (in the case of YES), the process proceeds to step S2, and the switching elements (Su, Sv, Sw, Sx, Sy, The switching operation of Sz) is stopped and this flow is ended (END).

  On the other hand, if it is determined in step S1 that the absolute value of the current flowing through the motor is not less than or equal to the predetermined value (in the case of NO), the process proceeds to step S3 and the current command to be output to the switching control unit (15). To lower the current flowing through the motor. Thereafter, the process returns to step S1, and it is determined again whether or not the absolute value of the current flowing through the motor (3) is equal to or smaller than a predetermined value, and steps S1 and S3 are performed until the absolute value of the current becomes equal to or smaller than the predetermined value. repeat.

  With the configuration as described above, even if a stop operation command is input to the control unit (14), the switching elements (Su, Sv, Sw, Sx) of the inverter circuit (13) until the current flowing through the motor falls within a predetermined range. , Sy, Sz) switching operation does not stop, preventing the current from flowing from the motor side into the inverter circuit (13) due to the switching operation being stopped and damaging the components in the power converter (1) it can. That is, the switching element (Su, Sv, Sw, Sx, Sy, Sz) has a current that flows to the motor below a predetermined value at which the surge voltage generated when the switching operation is stopped becomes a voltage that is less than the breakdown voltage of the component. Thus, the switching operation is continued and the current is gradually reduced. Thereby, even when the switching operation of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) is stopped, an excessive current flows into the power converter (1) from the motor side, and the power converter ( It is possible to prevent the component parts 1) from being damaged.

  Here, whether or not the current flowing through the motor (3) is within a predetermined range is determined within a period determined based on the power supply cycle of the AC power supply (2) (for example, a period of 1/4 or more of the power supply cycle). The maximum value of the current is obtained. For the sake of simplicity, FIG. 2 uses the current waveform in the conventional case where the current hardly pulsates, that is, the capacity of the capacitor is large. However, as in this embodiment, the capacity of the capacitor is Even when the current flowing through the motor (3) is greatly pulsated depending on the power supply frequency of the AC power supply (2), the maximum value of the current may be obtained within the above period. In this case, the current determination unit (16) is configured to be able to detect the maximum value of the current within the period.

  Further, in FIG. 2, the current waveform for one phase of the three-phase AC motor (3) is shown for simplification, but the current waveform for three phases as shown in FIGS. It can also be determined whether or not the current flowing through the motor (3) is equal to or less than a predetermined value as follows. As shown in FIG. 4, in the case of a sinusoidal three-phase alternating current (in the case of a general power converter having a relatively large capacity of the capacitor), it is converted into the absolute value of the current as shown in FIG. Obtain the maximum value of the current or calculate the sum of squares of the currents of the three phases.

  More specifically, when the maximum value of the current is directly obtained according to FIG. 5, the absolute value of the current fluctuates between the peak value Imax and √3 / 2 Imax, as shown by the thick line in FIG. Detect current within the fluctuation range. In addition, even if it is within this fluctuation range, even if it is not possible to obtain an accurate current peak value, a value substantially close to the peak value can be obtained. In this case, the current determination unit (16) may be configured to be able to detect a current for a predetermined period corresponding to the power cycle, or simply configured to detect a current flowing through the motor (3). May be.

  On the other hand, when calculating the sum of squares of the three-phase currents to obtain the maximum value, the sum of squares of the three-phase currents iu, iv, iw iu ^ 2 + iv ^ 2 + iw ^ 2 = 3 / 2Imax ^ 2 is used. The peak value Imax of the current can be calculated. That is, by using this sum of squares, the peak value of the current can be accurately obtained. In this way, in the method for obtaining the peak value of the current using the sum of squares, the peak value Imax may be obtained and compared with the predetermined value, or the peak value Imax ^ 2 may be compared with the square of the predetermined value. May be. In this case, the current determination unit (16) is configured to calculate the sum of squares of the three-phase current and to determine whether the current flowing through the motor (3) is within the predetermined range based on the calculation result. ing.

  Similarly, even when the capacitance of the capacitor is small as in the present embodiment and the three-phase current flowing through the motor (3) pulsates greatly according to the power supply frequency of the AC power supply (2) as shown in FIG. 7 is converted into the absolute value of the current as shown in FIG. 7 to obtain the maximum value of the current in a period of 1/4 or more of the power cycle, or the maximum value is calculated by calculating the sum of squares of the three-phase current in the period. Ask for. Further, a method of obtaining the maximum value of the current by dividing the square sum iu ^ 2 + iv ^ 2 + iw ^ 2 of the three-phase current by sin ^ 2 (2πft) is also conceivable. Here, f means a power supply frequency. When the three-phase current flowing through the motor (3) pulsates greatly as shown in FIG. 6, the envelope of the current (absolute value) of each phase is the absolute value of Im × sin (2πft) as shown in FIG. (Where Im is a predetermined constant), and each phase current varies with the amplitude of the envelope in accordance with the power cycle. Therefore, by dividing the square sum of the three-phase currents by sin ^ 2 (2πft), the maximum value (constant value) of the current can be obtained regardless of the power supply cycle. In the case of this method, when sin ^ 2 (2πft) is a value close to 0, the calculation result diverges, so that the maximum current value is not detected by this method.

  As described above, when the maximum value is obtained by dividing the sum of squares of the three-phase currents by sin ^ 2 (2πft), the current determination unit (16) calculates the sum of squares of the three-phase currents as sin ^ 2 (2πft). The current flowing through the motor (3) is determined to be within the predetermined range based on the result. That is, the current determination unit (16) calculates the sum of squares of the current flowing through the motor (3), and then changes the voltage fluctuation of the power supply voltage based on the calculation result and the fluctuation component of the power supply voltage of the AC power supply. It may be configured to calculate a constant value that does not fluctuate depending on whether or not the current flowing through the motor (3) is within the predetermined range using the constant value.

-Effect of the embodiment-
From the above, when stopping the switching operation of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) of the inverter circuit (13), the current flowing through the motor (3) is reduced when the drive of the inverter circuit (13) is stopped. In order to continue the switching operation of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) until the generated surge voltage is below a predetermined value smaller than the withstand voltage of the components in the power converter (1), When the drive of the inverter circuit (13) is stopped, it is possible to prevent an excessive current from flowing from the motor (3) that is an inductive load to the inverter circuit (13). Therefore, when the drive of the inverter circuit (13) is stopped, the above-described configuration can prevent an excessive surge voltage from being applied to the power conversion device (1), whereby the components in the power conversion device (1) can be prevented. Can be prevented from being damaged.

  Therefore, with the configuration as described above, there is no need to provide a brake circuit or the like in the power conversion device, and an overvoltage is not generated when the device is stopped, thus preventing the overvoltage prevention mechanism from operating when the conversion unit is stopped. it can. Thereby, cost reduction can be aimed at as the whole apparatus.

  In addition, the modulation degree of the drive signal for the switching elements (Su, Sv, Sw, Sx, Sy, Sz) in the inverter circuit (13) should be reduced so that the current flowing through the motor (3) gradually decreases. Thus, the current flowing through the motor (3) can be more reliably reduced to the predetermined value or less.

  Further, the maximum value of the current can be accurately obtained by obtaining the maximum value from the sum of squares of the three-phase currents flowing through the motor (3). In particular, when the current flowing through the motor (3) pulsates greatly due to the small capacity of the capacitor, the maximum current value can be obtained more accurately by setting the calculation period according to the power cycle. . Moreover, by dividing the sum of squares of the three-phase currents by sin ^ 2 (2πft), the maximum value of the current can be obtained without being affected by the pulsation of the current, and the maximum value can be easily calculated. can do.

<< Modification 1 of Related Technology 1 >>
The related technology 1 may be configured as follows.

  In the above embodiment, the single-phase AC power source (2) is used as the AC power source. However, the present invention is not limited to this, and a three-phase AC power source may be used. As a matter of course, in this case, it is necessary to form a converter circuit with six diodes.

  In addition, the current determination unit (16) determines whether the current flowing through the motor (3) is equal to or less than the predetermined value based on a detected value from the three-phase AC at a certain moment (hereinafter referred to as an instantaneous current value). You may make it determine. Examples of the instantaneous current value include the sum of squares of the phase current at a certain moment and the maximum absolute value of the phase current.

In the related technology 1, the capacitor (12) of the power converter (1) cannot absorb the voltage fluctuation of the AC power supply (2), but the switching element (Su, Sv, Sw, Sx, Sy, Sz) The component corresponding to the carrier frequency among the voltage fluctuations generated at the time of the switching operation is assumed to have an absorbable capacitance, but this is not restrictive, and a general electrolytic capacitor may be used. In this case, since the current flowing through the motor (3) does not pulsate (see FIG. 4), when obtaining the maximum value of the current, it is converted to the absolute value of the current as shown in FIG. What is necessary is just to obtain | require the maximum value of a current, or to calculate the sum of the squares of a three-phase current and to obtain the maximum value.

<< Modification 2 of Related Technology 1 >>
FIG. 8 is a circuit diagram illustrating a schematic configuration of the power conversion device (20) according to the second modification of the related technique 1. In this example, a converter circuit (21) is provided instead of the converter circuit (11) and a clamp circuit (22) is provided instead of the capacitor (12) in the power conversion device (1) of the related art 1. . The clamp circuit (22) is a circuit that accumulates an induced current flowing from the motor (3) (inductive load) to the converter circuit (11) via the inverter circuit (13) and holds it at a constant voltage.

The converter circuit (21) is connected to a three-phase AC power source as an AC power source (2), and rectifies and outputs the three-phase AC power. That is, the converter circuit (21) is an example of the rectifying unit of the present invention. The converter circuit (21) of the present modification includes six transistors (Q1, Q2,..., Q6) and six diodes (D5, D6,..., D10). Six transistors (Q1, Q2,..., Q6) are bridge-connected. Of these transistors, the transistors (Q1, Q2, Q3) have the emitters connected to the anodes of the diodes (D5, D6, D7), respectively. The cathodes of the diodes (D5, D6, D7) are connected to the positive DC link (L1). On the other hand, in the transistors (Q4, Q4, Q6), the cathodes of the diodes (D8, D9, D10) are connected to the collectors, respectively. The diodes (D8, D9, D10) have anodes connected to the negative DC link (L2), respectively. Even with this configuration, the current from the inverter circuit (13) cannot be regenerated in the AC power supply (2), as in the converter circuit (11) of Related Art 1.

Also in this modified example, as in the related art 1, until the current determining unit (16) determines that the current flowing through the inductive load (3) is equal to or less than the predetermined value, the switching elements (Su, Sv, Sw, Sx, By continuing the switching operation of Sy, Sz), it is possible to prevent an excessive current from flowing from the motor (3), which is an inductive load, to the inverter circuit (13) when the drive of the inverter circuit (13) is stopped. Therefore, even in this modification, when the drive of the inverter circuit (13) is stopped, it is possible to prevent an excessive surge voltage from being applied to the components in the power converter (20). It is possible to prevent the component parts from being damaged.

Embodiment 1 of the Invention
In Embodiment 1 of the present invention, an example will be described in which it is possible to determine whether or not the current flowing through the motor (3) is equal to or less than the predetermined value by simpler control than the related technique 1. The power conversion device according to the first embodiment is obtained by changing the configuration of the control unit (14) of the related technology 1. Specifically, also in this embodiment, the control unit (14) includes a switching control unit (15) and a current determination unit (16), and the configuration of the switching control unit (15) is the same as that of the related technique 1. Although it is a structure, the structure of the electric current determination part (16) has a structure different from the thing of related technology 1.

  Also in this embodiment, the load of the inverter circuit (13) is a three-phase AC motor (3) (inductive load), and the motor (3) according to the power frequency of the AC power source (2) as shown in FIG. The switching control unit (15) controls the inverter circuit (13) so that the three-phase current flowing in the) pulsates (that is, the torque of the motor (3) fluctuates). Specifically, the switching control unit (15) determines that the current (iu, iv, iw) (hereinafter also referred to as motor current) flowing through the motor (3) is the output of the single-phase AC power source (2) (single-phase Each of the inverter circuits (13) is pulsated at a frequency corresponding to the frequency of (AC) and the sum of the absolute values of the currents (iu, iv, iw) of each phase periodically becomes a predetermined minimum target value. The switching operation of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) is controlled. In the example of FIG. 6, the current (iu, iv, iw) of each phase is minimum (generally zero) in the vicinity of the phase of the single-phase alternating current 0 °, 180 °,... (So-called zero-cross timing where the voltage is switched). (Refer to the timings of T1, T2, and T3 in FIG. 6). That is, in the inverter circuit (13), the minimum target value is substantially zero, and the sum of absolute values of the phase currents (iu, iv, iw) periodically becomes the minimum value.

On the other hand, the current determination unit (16) of the present embodiment determines whether the motor current (iu, iv, iw) is equal to or less than the predetermined value based on the phase of the single-phase alternating current. . As described above, the absolute value sum of the motor currents (iu, iv, iw) periodically takes the minimum value (see FIG. 6). That is, the timing at which the sum of the absolute values of the phase currents (iu, iv, iw) becomes smaller than a certain value (timing at which the value becomes the minimum value in this example) can be known from the phase of the single-phase AC. Therefore, the current determination unit (16) of the present embodiment outputs the stop signal based on the phase of the single-phase alternating current. Specifically, the current determination unit (16) outputs the stop signal to the switching control unit (15) at the zero cross timing. Note that the detection of the zero cross can be realized by easier control than the detection of the current value as in the related art 1 described above.

-Operation of the control unit (14) of the first embodiment-
Also in the present embodiment, when a stop operation command is input to the control unit (14), the current determination unit (if the current flowing through the motor (3) is not within a predetermined range (predetermined value or less)) While being determined by 16), the switching control unit (15) outputs a drive signal to the switching elements (Su, Sv, Sw, Sx, Sy, Sz). Thereby, even after the operation command of stop is input, the pulsated motor current (iu, iv, iw) flows in the inverter circuit (13) as shown in FIG. On the other hand, after receiving the stop operation command, the current determination unit (16) outputs the stop signal at the single-phase AC zero-cross timing. When the stop signal is output in this way, the switching control unit (15) stops the switching operation of each switching element (Su, Sv, Sw, Sx, Sy, Sz) of the inverter circuit (13). At the timing when the switching operation of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) stops, the motor current (iu, iv, iw) is controlled to the minimum, so power from the motor (3) side Excessive current does not flow into the converter (1). Therefore, also in this embodiment, it is possible to prevent the components of the power conversion device (1) from being damaged.

-Effect in Embodiment 1-
As described above, in the present embodiment, since it is possible to determine whether the motor current is equal to or less than a predetermined value without detecting the current as in Related Art 1, the control unit (14) (specifically, current Control in the determination unit (16)) becomes easier.

  Note that the phase at which the current determination unit (16) outputs the stop signal is not necessarily a zero-cross phase in the single-phase AC, and the magnitude of the motor current does not damage each component. Any phase may be used as long as it is apparent that the size is controlled. For example, it may be slightly behind the zero cross phase position.

<< Related art 2 of invention >>
FIG. 9 is a circuit diagram showing a schematic configuration of a power conversion device (30) according to Related Art 2 of the present invention. This power converter (30) receives three-phase alternating current as input and converts the input three-phase alternating current (three-phase input alternating current) into three-phase alternating current (three-phase output alternating current) having a predetermined voltage and frequency. To the motor (3). Specifically, a matrix converter unit (31) and a control unit (14) are provided. This matrix converter part (31) is an example of the conversion part of this invention.

  Specifically, as shown in FIG. 9, the matrix converter unit (31) includes nine bidirectional switches (32). In FIG. 9, in order to identify each bidirectional switch (32), a branch number is attached after the code (32-1, 2,..., 9). As shown in FIG. 9, in this matrix converter section (31), three bidirectional switches (32) are connected for each phase (R, S, T) of the three-phase input AC. In addition, one of these three bidirectional switches (32) is connected to the three-phase input AC phase (U), one to the phase (V), and the other one to the phase (W). For example, three bidirectional switches (32-1,2,3) are connected to the R phase of the three-phase AC power source (2), and these three bidirectional switches (32-1,2,3) Among them, the bidirectional switch (32-1) is the three-phase output AC phase (U), the bidirectional switch (32-2) is the phase (V), and the bidirectional switch (32-3) is the phase (W). Each is connected.

  In said matrix converter part (31), it is possible to regenerate the electric current from a motor (3) (inductive load) to the alternating current power supply (2) side by switching operation. This power converter (30) also does not have a large-capacity capacitor, and regeneration is not performed when the matrix converter section (31) is stopped. When the section (31) is stopped, surge voltage is generated and overvoltage is likely to occur.

  However, also in this embodiment, the control unit (14) allows each bidirectional switch (14) until the current determining unit (16) determines that the current flowing through the motor (3) (inductive load) is equal to or less than the predetermined value. Continue the switching operation of 32-1,2,3). Thereby, when the drive of the matrix converter part (31) is stopped, it is possible to prevent an excessive current from flowing from the motor (3) to the matrix converter part (31). Therefore, even in this embodiment, it is possible to prevent an excessive surge voltage from being applied to the components in the power converter (30) when the matrix converter (31) is stopped. It is possible to prevent the component parts from being damaged.

<< Embodiment 2 >>
FIG. 10 is a circuit diagram illustrating a schematic configuration of the power conversion apparatus according to the second embodiment. The matrix converter unit (31) of this example is configured to take a single-phase alternating current as an input and convert the input single-phase alternating current into a three-phase output alternating current having a predetermined voltage and frequency.

Specifically, the matrix converter section (31) of the present embodiment includes six bidirectional switches (32-1, 2,..., 6) as shown in FIG. In this matrix converter section (31), three bidirectional switches (32) are connected for each single-phase input AC phase (A, B). Three bidirectional switches (32) connected to the respective phases (A, B) are respectively connected to three-phase output AC phases (U, V, W). For example, the phase A of the single-phase AC power supply (2) is connected to three bidirectional switches (32-1, 2, 3), and among these three bidirectional switches (32-1, 2, 3) The bidirectional switch (32-1) is the three-phase output AC phase (U), the bidirectional switch (32-2) is the phase (V), and the bidirectional switch (32-3) is the phase (W). It is connected.

Also in the present embodiment , the control unit (14) allows each bidirectional switch (14) until the current determining unit (16) determines that the current flowing to the motor (3) (inductive load) is equal to or less than the predetermined value. Continue the switching operation of 32-1,2, ..., 6). Therefore, also in this embodiment , it is possible to obtain the same effect as that of the power conversion device (30) of the related technique 2 .

Then , by applying the control method described in the first embodiment to the matrix converter unit (31) of the present embodiment , the motor current (iu, iv, iw) is set to the predetermined value based on the phase of the single-phase AC. You may make it determine whether it is the following.

  As described above, the present invention is useful for a power conversion device including a conversion unit that performs power conversion by a switching operation and supplies power to an inductive load.

1 Power converter 2 AC power supply 3 Three-phase AC motor (inductive load)
11 Converter circuit 12 Capacitor (component)
13 Inverter circuit (conversion unit)
14 Control Unit 15 Switching Control Unit 16 Current Determination Unit 31 Matrix Converter Unit (Conversion Unit)
Su, Sv, Sw, Sx, Sy, Sz Switching elements (components)
Du, Dv, Dw, Dx, Dy, Dz Freewheeling diode (component)
D1-D4 diode (component)

Claims (4)

It has a plurality of switching elements (Su, Sv, Sw, Sx, Sy, Sz), and the input power is changed to a predetermined frequency by the switching operation of the switching elements (Su, Sv, Sw, Sx, Sy, Sz). A power conversion device including a conversion unit (13) configured to convert to AC power and output to an inductive load (3),
A current determination unit (16) for determining whether or not a current flowing through the inductive load (3) is equal to or less than a predetermined value when stopping power supply to the inductive load (3);
The switching element (Su, Sv, Sw, Sx, Sy, Sz) is switched until the current determination unit (16) determines that the current flowing through the inductive load (3) is equal to or less than the predetermined value. A switching control unit (15) to be continued;
With
The input power is single-phase AC power,
In the switching control unit (15), the current (iu, iv, iw) of each phase flowing through the inductive load (3) pulsates according to the phase of the single-phase alternating current, and the current (iu, iv, iw) to control the switching operation of each of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) so that the sum of absolute values periodically becomes a predetermined minimum target value.
The current determination unit (16) determines whether the current (iu, iv, iw) flowing through the inductive load (3) is equal to or less than the predetermined value based on the phase of the single-phase alternating current. A power converter. In the power converter device of Claim 1 ,
The input is connected to a single-phase AC power supply (2), and includes a rectifying unit (11) for full-wave rectifying the single-phase AC and supplying the converted unit (13)
A power converter, wherein a capacitor (12) having a capacity in which the maximum value of the pulsation width of the voltage across the input is twice or more the minimum value is connected to the input of the converter (13). The power converter according 請 Motomeko 1,
The converter (31) is connected to an AC power source (2) at an input, and directly converts AC power supplied from the AC power source (2) into AC power of a predetermined plurality of phases. Power converter. The power converter according to any one of claims 1 to 3 ,
The said inductive load (3) outputs motive power with respect to the load which performs only a power running operation, The power converter device characterized by the above-mentioned.

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