JP2016111729A - Inverter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inverter device which eliminates the need for putting restrictions on an operational condition even in the case that no smoothing capacitor is provided or the capacity of a smoothing capacitor is set to a small value.SOLUTION: In an inverter device 14, a series circuit comprising a forward direction diode 9 and a capacitor 10 is connected between direct current power supply lines between a rectifier circuit 3 for rectifying an alternating voltage 1 and an inverter circuit. Furthermore, discharge means 11 configured to be able to discharge the electric charge of the capacitor to a positive side direct current power supply line 4, is connected in parallel to the diode. Control means performs a control so as to discharge the capacitor through the discharge means.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to an inverter device.

  In the inverter device, a commercial three-phase AC voltage is rectified by a rectifier circuit composed of a diode bridge, and a DC power source smoothed by a smoothing capacitor (main circuit capacitor) is supplied to the inverter circuit. The current flowing through the rectifier circuit has two modes determined by the capacity of the smoothing capacitor and the load current amount. The first mode is a continuous current mode in which the rectifier diode is continuously conducted during a phase of 120 degrees, and the second mode is a current discontinuous mode in which the conduction of the rectifier diode is discontinuous.

  In the continuous current mode, the smoothing capacitor has no effect of smoothing the DC power supply voltage, and only acts to absorb regenerative energy. In the current discontinuous mode, since the smoothing capacitor smoothes the DC power supply voltage, the power supply input current has a distorted waveform with two peaks (see FIG. 12). If there is no smoothing capacitor, the current continuous mode is set.

  The distorted power supply input current waveform contains a harmonic component, which adversely affects devices connected to the same power supply system. Since the current continuous mode can significantly reduce the power source current harmonics compared to the discontinuous mode, it is desirable to make the capacity of the smoothing capacitor as small as possible so that the current continuous mode is achieved.

JP 2008-271687 A

  On the other hand, when the capacity of the smoothing capacitor is reduced, problems such as insufficient output torque and occurrence of torque ripple become a problem when attempting to output a large load current. In addition, regenerative energy is generated during the deceleration operation of the motor that is driven and controlled by the inverter device.However, if the capacity of the smoothing capacitor is insufficient, the regenerative energy cannot be sufficiently absorbed, and the DC power supply voltage rises and becomes overvoltage. It is necessary to lengthen the motor deceleration time. Therefore, the mode of operation applicable to the inverter device is limited.

  Therefore, an inverter device is provided that eliminates the need to limit the operating conditions even when a DC power source is set or deleted so that the capacity of the smoothing capacitor is reduced to the continuous current mode.

  According to the inverter device of the embodiment, a series circuit including a forward diode and a capacitor is connected between the DC power supply lines between the rectifier circuit that rectifies the AC voltage and the inverter circuit. Further, in parallel with the diode, a discharging means configured to discharge the charge of the capacitor to the positive side DC power supply line is connected. And a control means is controlled to discharge a capacitor | condenser via a discharge means.

The figure which is 1st Embodiment and shows the structure of an inverter apparatus Flow chart showing processing contents centering on control means The flowchart which is 2nd Embodiment and shows the processing content centering on a control means. The figure which shows the electric current or voltage waveform of each part at the time of supplying an electric current in order to identify a motor constant (the 1) The figure which shows the electric current or voltage waveform of each part at the time of supplying an electric current in order to identify a motor constant (the 2) The figure which is 3rd Embodiment and shows the structure of an inverter apparatus Flow chart showing processing contents centering on control means The figure which is 4th Embodiment and shows the structure of an inverter apparatus Flow chart showing processing contents centering on control means The figure which shows the simulation result when the motor performs power running / regenerative operation The figure which is 5th Embodiment and shows the structure of an inverter apparatus The figure which shows the input current waveform to the inverter device when the capacity of the smoothing capacitor is different

(First embodiment)
Hereinafter, the first embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 shows the configuration of the inverter device. Each phase terminal of the three-phase AC power source 1 is connected to an AC input terminal of a rectifier circuit 3 configured by bridge-connecting six diodes 2a to 2f. A DC output terminal of the rectifier circuit 3 is connected to an input terminal of the inverter circuit 6 through a positive power supply line (DC power supply line) 4 and a negative power supply line (DC power supply line) 5. The inverter circuit 6 is configured by connecting six IGBTs (switching elements) 7a to 7e in a three-phase bridge connection. Each phase output terminal of the inverter circuit 6 is connected to each phase stator winding (not shown) of the motor 8.

  A series circuit of a diode 9 and a capacitor 10 is connected between the positive power supply line 4 and the negative power supply line 5, and is inserted into the diode 9 as necessary to limit the current of the switch 12. A series circuit of a resistance element 11 (discharging means) and a switch 12 (discharging means, switching element) for which is determined is connected in parallel. The control means 13 is configured by hardware logic or a microcomputer, and detects the voltage + DC of the positive power supply line 4 with respect to the potential −DC of the negative power supply line 5 and the terminal voltage + DC2 of the capacitor 10. . Then, ON / OFF of the switch 12 is controlled according to the result of comparing the terminal voltage + DC2 with a predetermined threshold value. In the above, what remove | excluded the three-phase alternating current power supply 1 and the motor 8 comprises the inverter apparatus 14. FIG.

  Next, the operation of the present embodiment will be described with reference to FIG. In the initial state, the switch 12 is OFF. When the inverter device 14 is turned on, the capacitor 10 is charged through the diode 9 to the peak voltage of the DC power supply. Since the switch 12 is OFF, the discharge of the capacitor 10 charged to the peak voltage is blocked by the diode 9, and the inverter device 14 is operated in the current continuous mode.

  When the motor 8 is in the power generation mode, the DC voltage rises above the peak voltage of the power supply voltage due to the generated regenerative energy, and the voltage rise is absorbed by the capacitor 10 via the diode 9. At this time, no power source current flows, so no power source harmonics are generated. Thereafter, when the motor 8 enters the power running mode, the terminal voltage + DC2 of the capacitor 10 becomes higher than the voltage + DC of the positive power supply line 4.

  In the flowchart shown in FIG. 2, after the power is supplied to the inverter device 14, the time when the control unit 13 reads the voltage + DC of the positive power supply line 4 and the terminal voltage + DC2 of the capacitor 10 is “start”. The control means 13 uses a value obtained by adding the predetermined voltage α to the voltage + DC as a threshold value, and determines whether or not the voltage + DC2 is larger than the threshold value (+ DC + α) (S1). The value of α can be arbitrarily set by the control means 13, but the maximum value assumed from the power supply rated voltage range of the inverter device 14 for the purpose of preventing the voltage + DC2 from exceeding the threshold due to the DC ripple voltage in the power running mode. Set it to be higher than the DC ripple voltage.

  If the voltage + DC2 is equal to or less than the threshold value (+ DC + α) (S1: NO), the switch 12 is kept OFF (S3). On the other hand, if the voltage + DC2 exceeds the threshold value (+ DC + α) (S1: YES), the switch 12 is turned ON. Thereby, the electric charge charged in the capacitor 10 is discharged via the resistance element 11. Then, it returns to step S1. If the voltage + DC2 falls below the threshold value (+ DC + α) while repeating this state (S1: NO), the switch 12 is turned off (S3), and the discharge of the capacitor 10 is stopped.

  In this way, the regenerative energy is appropriately discharged while being absorbed by the capacitor 10 selected to have a capacity capable of absorbing the regenerative energy. Therefore, the regenerative energy is equivalent to a general inverter device having a smoothing capacitor while maintaining the effect of reducing power harmonics. Performance can be maintained. Further, since a ripple current always flows through a smoothing capacitor of a general inverter device, a self-heating is high, and a capacitor having a large capacitance value is selected from the viewpoint of life. On the other hand, since a ripple current flows only under certain conditions such as during regeneration, the self-heating is greatly reduced, and a small and inexpensive capacitor can be used.

  As described above, according to the present embodiment, the rectifier circuit 3 that rectifies the AC voltage supplied from the AC power supply 1 and the inverter circuit 6 are connected between the positive power supply line 4 and the negative power supply line 5. The series circuit of the diode 9 and the capacitor 10 in the forward direction is connected. In parallel with the diode 9, a series circuit of a resistance element 11 and a switch 12 configured to be able to discharge the charge of the capacitor 10 to the positive power supply line 4 is connected.

  Then, the control means 13 performs control so that the capacitor 10 is discharged via the switch 12 during a period when the terminal voltage + DC2 of the capacitor 10 exceeds a threshold value set based on the ripple voltage of the DC power supply. Therefore, even in a configuration in which the capacity of the smoothing capacitor directly connected between the DC power supply + DC and -DC is set to be small so as to be in the continuous current mode in order to reduce distortion of the input current waveform, the operating conditions are not particularly limited. While the regenerative energy generated during the regenerative operation of the motor 8 is absorbed by the capacitor 10, the capacitor 10 can be appropriately discharged to reduce the ripple voltage.

(Second Embodiment)
Hereinafter, the same parts as those in the first embodiment are denoted by the same reference numerals, description thereof will be omitted, and different parts will be described. The second embodiment applies the configuration of the first embodiment when performing auto-tuning for identifying a constant of the inverter device motor 8 (for example, the resistance value or inductance of the stator winding). In general, a stable DC voltage is required when identifying motor constants. For example, the inductance L of the motor can be obtained from the slope of the current when a DC voltage is applied from V = L (di / dt). When a DC voltage is applied to the inductance, the current increases in proportion to time until magnetic saturation occurs. Therefore, the inductance value can be obtained if the gradient of the applied voltage and the current is known, but if the DC voltage is not stable, it causes an error in the inductance value.

  Therefore, when the motor constant is identified in the inverter device 14 shown in FIG. 1, the switch 12 is turned ON. By turning on the switch 12, the DC voltage can be smoothed and the ripple voltage can be reduced. FIG. 3 is a flowchart showing the procedure of the above operation. It is assumed that the inverter device 14 is turned on. If it is selected to identify the motor constant (S11: YES), the switch 12 is turned on (S12), and the motor constant is identified (S13). After the execution, the switch 12 is turned off (S14), and the motor constant identification is completed.

  In order to identify the motor constant, for example, by applying a stepped voltage to the motor, the current having the waveform shown in FIG. 4A is applied, and the motor constant is obtained from the waveform of the interphase terminal voltage at this time. is there. 4D and 4E show a conventional inverter device without the diode 9, the resistance element 11, the switch 12 and the control means 13 in the first embodiment, and there is no smoothing capacitor or the capacity of the smoothing capacitor is very large. For those having a small value, the inter-phase terminal voltage waveform and the DC voltage waveform at the time of identification are shown. The DC voltage shown in FIG. 4 (e) pulsates greatly, and this influence appears in the interphase terminal voltage waveform. In such a state, the motor constant cannot be obtained correctly.

  On the other hand, FIGS. 4B and 4C show the interphase terminal voltage waveform and the DC voltage waveform when the switch 12 is turned on in the inverter device 14 of the first embodiment. It is assumed that the control means 13 includes a voltage detection means and a control program necessary for identifying the motor constant. At this time, the capacitor 10 is connected to the positive power supply line 4 via the resistance element 11 and the switch 12, and there is almost no ripple in the DC voltage waveform, and accordingly there is almost no ripple in the interphase terminal voltage waveform. Thereby, a motor constant can be calculated | required correctly.

  As another method for identifying the motor constant, for example, as shown in FIG. 5A, a rectangular wave current is applied to the motor, and the motor constant is obtained from the interphase terminal voltage waveform at this time. In the conventional inverter device, as shown in FIGS. 5D and 5E, the DC voltage greatly increases due to the influence of the motor inductance at the timing when the energization current becomes zero. For this reason, the overvoltage protection operation works on the inverter device.

On the other hand, in the inverter device 14 of the first embodiment, when the DC voltage rises, the capacitor 10 is charged regardless of the on / off state of the switch 12 and absorbs the voltage rise. Therefore, as shown in FIGS. 5B and 5C, the DC voltage does not increase or is reduced.
As described above, according to the second embodiment, the control unit 13 discharges the capacitor 10 via the resistance element 11 and the switch 12 during the period in which the process of identifying the motor constant for the motor 8 is executed. Thereby, the ripple of a DC voltage waveform and the ripple of an interphase terminal voltage waveform can be reduced, and a motor constant can be calculated | required more correctly.

(Third embodiment)
As shown in FIG. 6, the inverter device 21 of the third embodiment includes a current sensor 22 (current detection means) disposed on the positive power supply line 4 for detecting a load current, and the current sensor 22 outputs the current sensor 22. The sensor signal to be input is input to the control means 23. The control means 23 turns on the switch 12 when the load current energized to the motor 8 is equal to or greater than a certain value (threshold). Thus, if the switch 12 is turned on when the load current is greater than or equal to a certain value, the energy charged in the capacitor 10 at that time can be used, and an insufficient output torque of the motor 8 can be avoided.

  FIG. 7 shows a flowchart corresponding to the above operation. If the load current is greater than or equal to the threshold (S15: YES), the switch 12 is turned on (S12) and the process returns to step S15. When the load current becomes smaller than the threshold value (S15: NO), the switch 12 is turned off (S14).

  As described above, according to the third embodiment, the current sensor 22 that detects the load current is provided, and when the load current exceeds a predetermined threshold, the control unit 23 causes the capacitor 10 to be connected via the resistance element 11 and the switch 12. Discharge. Therefore, a shortage of output torque of the motor 8 can be avoided.

(Fourth embodiment)
As shown in FIG. 8, the inverter device 31 of the fourth embodiment is an example of a case where the switch 12 and the control means 13 in the first embodiment are specifically configured by respective elements. What corresponds to the switch 12 is a PNP transistor 32 whose collector (non-reference potential side conduction terminal) is connected in common with the resistance element 11. The control means 13 includes a Zener diode 33, a series circuit of resistance elements 34 and 35, and a diode 36 connected in parallel to the resistance element 35. The Zener diode 33 has an anode connected to the positive power supply line 4 and a cathode connected to the resistance element 34, and is forward-connected with respect to the positive power supply line 4. The base (conduction control terminal) of the PNP transistor 32 is connected to the common connection point of the resistance elements 34 and 35 and to the anode of the diode 36.

  Next, the operation of the fourth embodiment will be described. If the potentials of the DC voltage + DC and the terminal voltage + DC2 of the capacitor 10 are equal, the Zener diode 33 will not conduct. When the capacitor 10 absorbs the regenerative energy generated by the motor 8, the voltage + DC2 rises together with the voltage + DC. Thereafter, when the motor 8 enters the power running mode, the diode 9 prevents discharge from the capacitor 10, so that the terminal voltage + DC 2 of the capacitor 10 becomes higher than the voltage + DC of the positive power supply line 4. When the potential difference between the two voltages exceeds the Zener voltage of the Zener diode 33, the Zener diode 33 becomes reverse conducting.

  When the voltage + DC further decreases and the potential difference becomes equal to or higher than the voltage obtained by adding the base-emitter voltage to the base potential of the PNP transistor 32 (the Zener voltage plus the terminal voltage of the resistor 34), the PNP transistor 32 is turned on. Thus, the charge of the capacitor 10 is discharged through the resistance element 11. The diode 36 is disposed to protect the PNP transistor 32 when the voltage + DC rises excessively.

  FIG. 9 is a flowchart showing the above hardware operation. The voltage α for turning on the transistor 32 shown in step S21 can be set by selecting the Zener voltage of the Zener diode 33 in consideration of the base-emitter voltage and the voltage drop due to the resistance element 34.

  FIG. 10 shows a waveform simulating the above hardware operation. A broken line in the figure indicates a section in which a regenerative operation is performed. First, in the section before the regenerative operation, the discharge current through the resistance element 11 does not flow, the voltage + DC2 is constant, and it can be confirmed that the capacitor 10 is not discharged by the potential difference due to the ripple voltage of the DC voltage + DC. Thereby, the input current waveform can maintain a rectangular wave with few harmonic components. That is, it can be confirmed that the level of the current harmonic is equivalent to that of the inverter device having no smoothing capacitor or having a smoothing capacitor having a very small capacity.

  In the regenerative operation section, since the capacitor 10 is charged via the diode 9 by regenerative power, the voltage + DC and the voltage + DC2 rise in the same manner. In the section after the regenerative operation, the PNP transistor 32 is turned on due to the decrease of the voltage + DC, the charge of the capacitor 10 is discharged, and it can be confirmed that the voltage + DC2 gradually decreases.

  As described above, according to the fourth embodiment, the collector of the PNP transistor 32 is connected in common with the resistance element 11, the control means 13 is configured by a series circuit of the Zener diode 33 and the resistance elements 34 and 35, and the PNP transistor 32. Was connected to the common connection point of the resistance elements 34 and 35. Therefore, the discharge of the capacitor 10 can be controlled by the control means 13 configured by hardware.

(Fifth embodiment)
As shown in FIG. 11, the inverter device 41 of the fifth embodiment is another example when the switch 12 and the control means 13 are configured by respective elements. Instead of the PNP transistor 32 of the fourth embodiment, An NPN transistor 42 is used. The resistive element 11 is connected between the collector of the NPN transistor 42 and the cathode of the diode 9.

  In the case of the fifth embodiment, similarly to the fourth embodiment, when the voltage + DC2 rises and the Zener diode 33 becomes reverse conducting, and the base potential of the NPN transistor 42 becomes higher than the emitter potential by the base-emitter voltage or higher, the NPN The transistor 42 is turned on. Then, the charged charge of the capacitor 10 is discharged through the resistance element 11.

  As described above, according to the fifth embodiment, the resistance element 11 is connected between the collector of the NPN transistor 42 and the cathode of the diode 9, and the control means 13 is a series circuit of the Zener diode 33 and the resistance elements 34 and 35. The base of the NPN transistor 42 is connected to the common connection point of the resistance elements 34 and 35. Therefore, similarly to the fourth embodiment, the discharge of the capacitor 10 can be controlled by the control means 13 configured by hardware.

(Other embodiments)
The PNP transistor 32 of the fourth embodiment may be replaced with a P-channel MOSFET in which the source is a reference potential side conduction terminal, the drain is a non-reference potential side conduction terminal, and the gate is a conduction control terminal.
In the fourth embodiment, the diode 36 may be omitted.
Further, the NPN transistor 42 of the fifth embodiment may be replaced with an N-channel MOSFET.

  Although several embodiments of the present invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  In the drawings, 1 is a three-phase AC power supply, 3 is a rectifier circuit, 4 is a positive power supply line (DC power supply line), 5 is a negative power supply line (DC power supply line), 6 is an inverter circuit, 8 is a motor, and 9 is Diode, 10 is a capacitor, 11 is a resistance element (discharge means), 12 is a switch (discharge means, switching element), 13 is a control means, 14 and 21 are inverter devices, 22 current sensors (current detection means), 23 Control means, 31 is an inverter device, 32 is a PNP transistor, 33 is a Zener diode, 34 and 35 are resistance elements, 41 is an inverter device, and 42 is an NPN transistor.

Claims (6)

A rectifier circuit for rectifying an alternating voltage;
An inverter circuit for converting the DC voltage rectified by the rectifier circuit into an AC voltage;
A series circuit of a forward diode and a capacitor connected between DC power supply lines between the rectifier circuit and the inverter circuit;
Discharging means connected in parallel to the diode and configured to be able to discharge the charge of the capacitor to a positive DC power supply line;
An inverter device comprising control means for controlling the capacitor to be discharged via the discharging means.   2. The inverter device according to claim 1, wherein the control unit discharges the capacitor through the discharge unit during a period in which a terminal voltage of the capacitor exceeds a threshold set for a ripple voltage of a DC power supply.   The inverter device according to claim 1, wherein the discharging unit is configured by a series circuit of a resistance element and a switching element.   The said control means discharges the said capacitor | condenser via the said discharge means during the period when the process which identifies a motor constant about the motor which is the drive object of the said inverter circuit is performed. The described inverter device. Provided with current detection means for detecting the load current,
5. The inverter device according to claim 1, wherein when the load current exceeds a predetermined threshold, the control unit discharges the capacitor via the discharge unit. 6. The switching element is composed of a transistor having a non-reference potential side conduction terminal connected in common with the resistance element,
The control means comprises a series circuit of a forward zener diode and two resistance elements connected in parallel to the discharge means,
The inverter device according to claim 3, wherein the conduction control terminal of the transistor is connected to a common connection point of the two resistance elements.

Images