JP2000166247A - Inverter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten current detection sampling period for high-speed response by forming a current detector which obtains a load current detection signal with a resistor inserted between a reversed parallel connection circuit consisting of switching elements and diodes and positive and negative DC bus-bars and with the voltage across the resistor amplified and added. SOLUTION: A plurality of switching elements 31 to 36, and a plurality of diodes 7 to 12 are connected in reversed parallel so that the direction of current passing through the switching elements and the diodes may be opposite to form an upper arm and a lower arm of the U phase, V phase, and W phase of a main circuit in an inverter. Respective resistors SH11, SH12 and SH21, SH22 are inserted respectively between the reversed parallel connection circuit consisting of the switching elements 31 to 36 and the diodes 7 to 12, and a positive DC bus-bar 19 and a negative DC bus-bar 20. The voltage across the respective resistors SH11, SH12 and SH21, SH22 are amplified and added to form a current detector which obtains a load current detection signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device for driving a motor, and more particularly to an inverter device suitable for controlling the position, speed, torque and the like of a motor by detecting a current.

[0002]

2. Description of the Related Art A speed sensorless vector control for driving an induction motor by an inverter, a vector control with a speed sensor, and the like are used as power sources for performing variable speed operation of general industrial machines. Also, semiconductor manufacturing equipment, mounters,
AC servo motors with built-in position and speed sensors for robots and the like have come into wide use due to demands for automation and labor saving. These basic controls are speed, torque or position control.In response to recent demands for faster line speeds and faster tact times, the current of the induction motor is increased by a torque component current proportional to the torque and a torque component current Vector control is performed in which current is separated into orthogonal magnetic flux components and controlled. In the case of an AC servo motor, a rotating field type synchronous motor using a permanent magnet for the rotor performs high-speed current control by detecting the position of the permanent magnet with a magnetic pole position detector. It controls the instantaneous value of the current.

Japanese Patent Application Laid-Open No. Sho 63-178790 discloses a pulse width modulation control inverter having a current control loop inside a speed control loop. The inverter controls a two-phase current of a three-phase induction motor as a load. A current transformer for detecting insulated from an inverter main circuit is shown. Generally, the current of a three-phase induction motor changes in speed from zero to high speed, so that the current transformer for detection needs to detect DC current to AC current in a wide frequency band. For this reason, the current most widely used current detector is to wind an electric wire around an iron core, flow the inverter output current, and detect a magnetic flux proportional to the output current with a Hall element arranged in a gap in the magnetic circuit of the iron core. Thus, a signal obtained as a current detection signal insulated from the main circuit is adopted. Three-phase induction motors and AC servo motors require at least two current detectors,
The cost was high and the dimensions involved an iron core, which required considerable space. For this reason, there was a limit to downsizing the inverter.

In the prior art disclosed in Japanese Patent Application Laid-Open No. 8-149853, a switching element having a current sense terminal is used to insulate an analog output detected from a sense current through a photocoupler, thereby controlling the power module current. Had been detected. In this prior art, a current detection method using a resistor connected to a sense emitter terminal of a switching element with a sense emitter is used, which has solved the problem of small size, light weight, and cost. However, as described below, the detected current signal is intermittent, and there is a problem in sampling the current at high speed.

FIG. 4 shows a load current detector of a conventional three-phase inverter main circuit, and FIGS. 5 and 6 show operation timing charts. 4, reference numerals 1 to 6 denote switching elements with sense emitters, and reference numerals 7 to 12 denote diodes, which are connected in parallel in the opposite direction to the switching elements with sense emitters 1 to 6. Reference numerals 13 to 18 denote resistors for detecting a load current. The resistors 13 to 18 are connected to the sense emitter terminals of the switching elements 1 to 6 with a sense emitter. A current proportional to the collector current flows through the resistor. . Reference numeral 19 denotes a positive terminal of the DC bus, and reference numeral 20 denotes a negative terminal of the DC bus. A smoothing capacitor 21 is attached between both terminals, and the smoothing capacitor 21 is charged with an electric charge from an external DC power supply (not shown). Reference numerals 22, 23 and 24 denote U-phase, V-phase and W-phase inverter output terminals to which a motor 25 as a load is connected.

The operation of FIG. 4 will be described with reference to a time chart of FIG.

FIG. 5A is a diagram showing a relationship between a carrier (usually called a triangular wave or a carrier) for determining the switching frequency of the inverter and U-phase, V-phase and W-phase voltage commands. FIGS. 5 (b) and 5 (c) show ON and OFF timings of the switching elements 1 and 4 with sense emitters of the U-phase arm. FIG. 5D shows the current Iu flowing to the load at that time, that is, the U-phase load current. The switching elements with sense emitters 1 and 4 are alternately turned on and off alternately. The switching element with sense emitter 1 is turned on between A and B in FIG.
Is turned off, and conversely, between B and C, the gate signal GU or GX is input so that the switching element with sense emitter 1 is turned off and 4 is turned on. In order to prevent the upper and lower switching elements with sense emitters 1 and 4 from turning on at the same time, the switching elements with sensing emitters are turned on with a delay of a certain time (non-lap time) at the timing of turning on the command signal. . Assuming that the direction in which the load current flows from the inverter to the load side is positive, a current is supplied from the switching element with sense emitter 1 to the load 25 during the positive current D to E in FIG. A current is supplied from the diode 10 to the load 25 (the current flows back through the load 25). Next, FIG.
The current flows back from the load 25 to the diode 7 during the negative current GH, and flows from the load 25 to the switching element 4 with the sense emitter between HI. Therefore, the load current flows alternately and repeatedly through the switching element 1 with the sense emitter and the diode 10 in the positive direction and the switching element 4 and the diode 7 with the sense emitter in the negative direction.

FIG. 6 shows the U-phase current flowing in the motor as the load 25 in FIG. 4 and the voltage across the resistors 13 and 16 connected to the sense emitter terminals. FIG.
A) shows the U-phase current Iu. In a half cycle in which a positive current flows from the switching element with sense emitter 1 to the load 25, the U-phase current can be detected only when the switching element with sense emitter 1 is on, and the switching element with sense emitter 4 turns on. At the timing, no current flows through the switching element 4 with the sense emitter, and a current flows through the diode 10 connected in anti-parallel. However, since the diode has no resistance, the U-phase current cannot be detected. This situation is shown in FIG. 6B, in which the voltage across the resistor 13 is equal to the U-phase output terminal 2 of the inverter.
The sense emitter terminal of the switching element with sense emitter 1 is measured with the reference potential on the two sides. FIG. 6 b)
As shown in FIG. 7, an intermittent waveform is obtained as the voltage across the resistor 13. The switching elements 1 and 4 with sense emitters of the upper and lower arms are alternately turned on and off alternately depending on the direction of the load current. However, the load current is increased only when one of the switching elements with sense emitters (here, 1) is turned on. Can be detected. That is, the number of times that current can be detected per unit time is proportional to the carrier frequency (carrier frequency). This can be easily understood in FIGS. 5A and 5B because the number of times the switching element 1 with the sense emitter is turned on is the same as the number of vertices on the negative side of the triangular wave as the carrier wave. Next, in a) of FIG. 6, in the negative half cycle in which the current flows from the load 25 to the switching element 4 with the sense emitter, the U-phase current can be detected only when the switching element 4 with the sense emitter is on. At the timing when the switching element with sense emitter 1 is turned on, no current flows through the switching element with sense emitter 1 and a current flows through the diode 7 connected in anti-parallel, but the diode has no resistance and the U-phase current is Not detectable. The voltage across the resistor 16 is as shown in FIG. 6C when the sense emitter terminal of the switching element with sense emitter 4 is measured with the negative DC bus 20 as a reference potential. As shown in FIG. 6C), an intermittent waveform is obtained as the voltage across the resistor 16. The switching elements with sense emitters of the upper and lower arms are alternately turned on and off alternately, but the load current can be detected only when one of the switching elements with sense emitters (here, 4) is turned on. As described above, the number of times that current can be detected per unit time is proportional to the carrier frequency. This can be easily understood in FIGS. 5A and 5C because the number of times that the switching element 4 with the sense emitter is turned on is the same as the number of vertices on the positive side of the triangular wave that is the carrier wave.

In the positive half cycle shown in FIG. 6A, it can be detected every time the switching element 1 with the sense emitter is turned on, and in the negative half cycle, it can be detected every time the switching element 4 with the sense emitter is turned on. The frequency at which the current can be detected, that is, the number of detections per unit time, is the same as the carrier frequency, and a continuous current waveform cannot be obtained with the resistor attached to the sense emitter terminal of the switching element with the sense emitter. As described above, according to the conventional technique, the continuous current waveform shown in FIG. 5D flowing in the U-phase of the motor 25 can be obtained only as an intermittent waveform.

[0010]

As described above, the prior art in which the current on the load side is detected by a current transformer is disclosed in JP-A-63-1.
As disclosed in Japanese Patent Publication No. 78790, a load current is detected on the output side of an inverter, and a system using an iron core and a Hall element is generally used. In this conventional technique, it is difficult to reduce the size and weight of the current detector, and it is also difficult to reduce the cost. On the other hand, in the prior art disclosed in Japanese Patent Application Laid-Open No. 8-149853, a current detection method using a resistor connected to a sense emitter terminal of a switching element with a sense emitter is solved with respect to miniaturization, weight reduction, and cost. However, the load current has an intermittent waveform, and the current flowing to the diode side cannot be detected. When a high-speed response is required as in the case of an AC servo motor, the response of the current control loop needs to be improved, and the current detection sampling period needs to be further shortened. However, as described above, the load current has an intermittent waveform, and the current flowing to the diode cannot be detected.Therefore, sampling of the current flowing to the diode cannot be performed. There was a problem. In order to shorten the current detection sampling period, it is conceivable to increase the frequency of the carrier wave shown in FIG. 5A. However, the switching loss of the switching element with the sense emitter and the diode becomes large, and the temperature rise becomes large, and there is a limit. .

An object of the present invention is to secure a high-speed response by further shortening the current detection sampling period without increasing the carrier frequency.

[0012]

According to the present invention, a resistor is inserted between an anti-parallel connection circuit of a switching element and a diode and a positive DC bus, and an anti-parallel connection of the switching element and a diode. A resistor is inserted between the circuit and the negative DC bus, and the voltage between both ends of the resistor is amplified and added to constitute a current detector for obtaining a load current detection signal.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an inverter device with a built-in current detector according to the present invention will be described in detail with reference to the illustrated embodiments.

FIG. 1 shows a first embodiment of the present invention.
36 is a switching element and 7 to 12 are diodes. In this embodiment, as the switching element,
As shown, IGBT (Insulated Gate Bipolar Transformer)
istor). Switching elements 31 to 3
6 and the diodes 7 to 12 are connected in anti-parallel so that the directions of the currents flowing through the switching element and the diode are opposite to each other, as shown in FIG.
Phase, the upper arm and the lower arm of the W phase. The IGBT and the diode connected in antiparallel may be configured as an integrated element, or may be configured as separate elements and connected by wire bonding or the like.

SH11 and SH12 are first current detecting resistors of the upper arm of the U-phase and W-phase, one terminal of which is connected to the positive DC bus 19 and the other terminal of which is the switching element 31, It is connected to an anti-parallel circuit of 33 and diodes 7 and 9 as shown.

SH21 and SH22 are the second current detecting resistors of the lower arm of the U-phase and W-phase. One terminal of these resistors is connected to the negative DC bus 20, and the other terminal of these resistors is connected to the switching element 34. It is connected to an anti-parallel circuit of 36 and diodes 10 and 12 as shown.

Reference numeral 21 denotes a smoothing capacitor. 2
2, 23 and 24 are U-phase, V-phase and W-phase inverter output terminals, which are connected to a motor 25 as a load. A DC power supply such as a converter device (not shown) is connected to the positive DC bus 19 and the negative DC bus 20. This allows
The smoothing capacitor 21 is charged with the polarity shown, and a DC voltage is applied between the upper arm and the lower arm.

In this embodiment, a first current detection resistor and a second current detection resistor are provided on the upper arm and the lower arm of the U-phase and the W-phase, respectively. The reason is as follows.

That is, in the three-phase alternating current, since the sum of the respective phase currents is zero, the V-phase current can be obtained from the U-phase current and the W-phase current as follows.

V-phase current =-(U-phase current + W-phase current) As is well known, in a polyphase AC circuit system having no neutral point path, if the number of phases is m, the minimum (m-1) ) All currents can be detected by the current detectors.

Next, a detection circuit for detecting a motor current as a load by the first current detection resistor and the second current detection resistor will be described. 37 and 38 are first amplifiers for inverting and amplifying the voltage between both ends of the U-phase and W-phase first current detection resistors SH11 and SH12, and 39 and 40 are U-phase and W-phase second current detection resistors SH21 and SH21, respectively. This is a second amplifier that inverts and amplifies the voltage across SH22. The upper amplifier first amplifier 37,
The reference voltage 38 is based on the positive DC bus 19, the reference voltage of the second lower amplifiers 39 and 40 is based on the negative DC bus 20, and the voltage across the current detection resistor is approximately 1
The voltage is amplified to 0 to 50 times, and the output voltage is reduced to about ± 5 V or less. Positive and negative power supplies V1 +, V1- for operating the first amplifiers 37, 38 and the second amplifiers 39, 4
The positive and negative power supplies V2 + and V2- for operating 0 are externally supplied. In the case of the first amplifier, the common of the power supply is the positive DC bus 19, and in the case of the second amplifier, the common of the power supply is the negative DC bus. 20. As another method, the positive and negative power supplies V1 +, V1-, V2
+ And V2- may be created and configured.

Here, the U phase will be described as an example (the same applies to the W phase). When the direction in which the current flows from the inverter to the motor 25, which is a load, is positive, and a positive current Iu flows through the motor as shown by the arrow in the figure, the upper-arm switching element 31 is turned on and the lower-arm switching element 34 is turned on. Is turned off, the first current detector SH11 is supplied from a DC power supply (not shown) to the positive DC bus 19.
A current flows through the switching element 31, the U-phase inverter output terminal 22, and the motor 25 through the switch. At this time, the voltage across the U-phase upper arm first current detection resistor SH11 is set to Vs1u, and the direction of the current is taken from the positive DC bus 19 to the switching element 31 as shown by the arrow in the figure. In this case, when the positive DC bus 19 is set to the reference potential, the voltage Vs1u between both ends becomes a negative voltage because the voltage decreases. When the switching element 31 of the upper arm is turned off and the switching element 34 of the lower arm is turned on, the diode 10, the U-phase from the DC power supply (not shown) passes through the second current detector SH21 from the negative DC bus 20. A current flows through the inverter output terminal 22 and the motor 25. At this time, the voltage across the U-phase lower arm second current detection resistor SH21 is set to Vs2u, and the direction of the current is from the negative DC bus 20 to the diode 10 as shown by the arrow in the figure. In this case, when the negative DC bus 20 is set to the reference potential, the voltage Vs2u between both ends becomes a negative voltage because the voltage decreases.

Next, when a negative current Iu flows in the motor in the direction opposite to the arrow in the figure, when the switching element 31 of the upper arm is off and the switching element 34 of the lower arm is on, the motor current becomes Motor 25 to U-phase inverter output terminal 22, lower arm switching element 3
4. The current flows from the U-phase lower arm second current detection resistor SH21 to the DC power supply (not shown) through the negative DC bus 20. When the upper-arm switching element 31 is on and the lower-arm switching element 34 is off, the motor current flows from the motor 25 to the U-phase inverter output terminal 22,
Diode 7, U-phase upper arm first current detection resistor SH1
1 flows through a positive DC bus 19 to a DC power supply (not shown).

U-phase upper arm first current detection resistor SH11
Are inverted and amplified by the U-phase upper arm first amplifier 37. Assuming that the amplification of this amplifier is K1,
Assuming that the output voltage of the U-phase upper arm first amplifier 37 is Vspu (p), the following is obtained.

Vspu (p) = − K1 · Vs1u (1) Similarly, the U-phase lower arm second The voltage across the terminals detected by the current detection resistor SH21 is inverted and amplified by the U-phase lower arm second amplifier 39. Assuming that the amplification degree of this amplifier is K1, the output voltage of the U-phase lower arm second amplifier 39 is Vsnu (n), as follows.

Vsnu (n) = − K1 · Vs2u (2) U-phase upper arm first amplifier 37 output voltage Vspu
The reference voltage of (p) is the DC bus 19 on the positive side, and the reference voltage of the output voltage Vsnu (n) of the U-phase lower arm second amplifier 39 is the DC bus 20 on the negative side. The reference voltage is
Since the voltage is viewed from the DC bus 19 on the positive side and the DC bus 20 on the negative side, a voltage Vspu, which uses VM that comes out later as a reference potential,
To distinguish it from Vsnu, add Vspu (p), Vsnu (n) and
(p) and (n) are attached.

Reference numeral 41 denotes a U-phase third amplifier for inverting and adding the output of the U-phase upper arm first amplifier 37 and the output of the U-phase lower arm second amplifier 39. Similarly, reference numeral 42 denotes a W-phase third amplifier for inverting and adding the output of the W-phase upper arm first amplifier 38 and the output of the W-phase lower arm second amplifier 40. The reference voltage of the U-phase and W-phase third amplifiers is an intermediate potential between the positive DC bus 19 and the negative DC bus 20.
In FIG. 1, resistors 46 and 47 are connected in series between the positive DC bus 19 and the negative DC bus 20 to divide the voltage between both ends of the positive DC bus 19 and the negative DC bus 20 by half, and Point VM
Has been established. The voltage across the positive DC bus 19 and the negative DC bus 20 is Vpn. The potential Vp of the positive DC bus 19 and the potential Vn of the negative DC bus 20 are determined by setting the reference point VM to the reference potential.
(Ie, zero potential)

Vp = + Vpn / 2 (3) Vn = −Vpn / 2 (4) U-phase upper arm viewed from reference point VM The output voltage Vspu of one amplifier 37 and the output voltage Vsnu of the U-phase lower arm second amplifier 39 as viewed from the reference point VM are expressed by the following equations (1) and (2).
By shifting the reference points of (p) and Vsnu (n), the following equations (5) and (6) can be obtained.

Vspu = Vp + Vspu (p) = + (Vpn / 2) −K1 · Vs1u (5) Vsnu = Vn + Vsnu (n) = − (Vpn / 2 ) −K1 · Vs2u (6) If the amplification of the third amplifier is set to one, the output Vu of the third amplifier becomes the above (5). , (6), the voltage Vspu,
Since Vsnu is added and inverted, equation (7) is obtained.

Vu = − (Vspu + Vsnu) = K1 (Vs1u + Vs2u) (7) The above (5) to (7) As shown by the equation, the voltage Vpn across the positive DC bus 19 and the negative DC bus 20 is canceled by using the reference point VM as the reference potential, and the output Vu of the third amplifier is detected by the first current detection. The voltage Vs1u between both ends of the resistor SH11
And the sum of the voltages Vs2u across the second current detection resistor SH21 and the amplification K1 of the first and second amplifiers. This means that even when the motor enters a regenerative state, energy is regenerated from the motor to the DC power supply of the inverter, and the voltage between the positive and negative DC buses increases, the reference point VM remains at the positive DC bus 19 and the negative DC bus 20. Resistance 46,4 between
7 are connected in series to divide the voltage between both ends of the positive DC bus 19 and the negative DC bus 20 by half, so that this relationship does not change. This situation is shown in the time chart of FIG.

A) shows the U-phase motor current Iu,
b) shows the voltage across the U-phase upper arm first current detection resistor SH11. In the positive half cycle of the U-phase motor current Iu, the current when the switching element 31 is on is detected. In a half cycle where a) is negative,
Current flows through the diode 7. c) shows a diode 1 in the half cycle in which the U-phase motor current Iu in a) is positive.
Current flows through 0, and in the negative half cycle, the current when the switching element 34 is on is detected.
d) is the output voltage VU of the U-phase third amplifier 41. As can be seen from the figure, the conventional current detection waveform, b) and c) in FIG.
Unlike the intermittent current shown in FIG. 2, in d) of FIG. 2, the current becomes a continuous current. Output voltages VU, VW of the third amplifiers 41, 42
Are read at the same timing by A / D converters 43 and 44, and are converted from analog voltage to digital signal.
It is sent to the microprocessor CPU45. By reading at the same timing, it is possible to prevent a temporal shift in detection between phases of current detection. The reference voltages of the A / D converters 43 and 44 and the microprocessor CPU 45 are based on VM similarly to the third amplifiers 41 and 42. However, the microprocessor CPU 45 can set the potential of the load side DC bus 20 by inserting an insulating means such as a photocoupler in the communication line with the A / D converters 43 and 44 without using VM as a reference. It is possible to prevent the occurrence of temperature drift and aging which are problems in analog transmission.

The power supply 48 is a + 5V power supply for the A / D converters 43 and 44 and the microprocessor CPU 45, 50 is a positive power supply for the third amplifier, and 49 is a negative power supply for the third amplifier.

First amplifier 37, 38, second amplifier 3
9 and 40 are constituted by the same circuit, and the detailed circuit is shown in FIG. R1, R2, R3 are resistors, OP1, O
P2 is an operational amplifier and constitutes an inverting amplifier.
It is not necessarily limited to the inverting amplifier, but may be a non-inverting amplifier or a differential amplifier. The third amplifiers 41 and 42 are formed of the same circuit, R4, R5, R6, and R7 are resistors, and OP3 is an operational amplifier, forming an inverting adder. This is not limited to the inverting amplifier, but may be a non-inverting adder. Although the amplification degree of the third amplifier is set to 1 in the above description, the invention is not limited to this. Also,
In FIG. 1, the load current detection phase is a U phase and a W phase.
There is no problem even if the phase is U-phase, V-phase or V-phase or W-phase. Although the figure shows a three-phase inverter, a multi-phase (m-phase) inverter can also realize a load current detection from the (m-1) phase with a similar configuration.

Further, since the detected motor current signal can be detected not as an intermittent waveform but as a continuous waveform as shown in FIG. 2D, the number of times of current detection sampling can be doubled without increasing the carrier frequency of the carrier wave. it can. Therefore, a high-speed current control response can be realized. That is, the upper and lower switching elements are turned on and off alternately, and the current can be detected even in the portion where the current cannot be detected as shown in FIGS. It is possible to do so, and the responsiveness can be improved accordingly. Also, since the voltages detected by the current detection resistors are not insulated and combined, there is no influence of temperature drift of the photocoupler or the like, aging, etc., and highly accurate current detection with good linearity can be obtained. .

FIG. 3 shows an embodiment of an inverter module for an inverter device according to the present invention. The module 53 according to this embodiment is a module that incorporates a first current detection resistor and a second current detection resistor in an inverter main circuit including a switching element and a diode.

The inverter module 53 for the inverter device shown in FIG. 3 includes an inverter main circuit, current detection resistors SH11, SH12, SH21, and SH22, and further includes a first and second amplifier 3 shown in FIG.
7, 38, 39, 40 and third amplifiers 41, 42
And resistors 46 and 47 for obtaining reference voltages of the third amplifiers 41 and 42, A / D converters 43 and 44, and a microprocessor CPU45. Note that the microprocessor CPU 45 can be provided externally without being mounted in the module.
Here, the smoothing capacitor 21 is arranged outside the module and is mounted in the inverter device. Also, the first and second amplifiers 37, 38, 39,
The control power supply 40 is generated inside the module 53 using positive and negative DC bus voltages.

More specifically, the module 53 uses a metal base 51 also serving as a heat radiator, forms an insulating layer (not shown) on the metal base 51, and further forms an inverter main circuit including a switching element and a diode thereon. In addition, a current detection resistor and an amplifier circuit are mounted and insulated and sealed with a mold resin or equivalent. FIG. 3 illustrates a case where the circuit of the embodiment of FIG. 1 is modularized. Terminals on the mold resin are denoted by the same reference numerals as those assigned to the circuit. . The module 53 is used by being attached to a heat radiating member or the like of the inverter device through an attachment hole 52 provided in the metal base 51. Therefore, according to the inverter module 53 for the inverter shown in FIG. 3, since the modules including the wiring around the inverter main circuit and the wiring around the load current detection are modularized, there is no need to separately provide a current detector. In addition, the configuration of the inverter device can be greatly simplified, and the size can be sufficiently reduced.

[0038]

As described above, according to the present invention, since the current detection sampling period can be further shortened, a high-speed response can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a main circuit and a detection circuit according to an embodiment of the present invention.

FIG. 2 is a time chart for explaining an embodiment according to the present invention.

FIG. 3 is an external view of an inverter module according to an embodiment of the present invention.

FIG. 4 is a configuration diagram of a conventional main circuit.

FIG. 5 is a time chart for explaining the operation of a conventional main circuit.

FIG. 6 is a time chart for explaining conventional current detection.

[Explanation of symbols]

1-6: Switching element with sense emitter, 7-1
2 Diode, 13 to 18 Resistance, 19 DC bus positive terminal, 20 DC bus negative terminal, 21 Smoothing capacitor, 22 U-phase inverter output terminal, 23 V-phase inverter output terminal, 24 W Phase inverter output terminals, 25 ...
Load (motor or induction motor), 31 to 36: switching element, SH11: U-phase upper arm first current detection resistor, SH12: W-phase upper arm first current detection resistor, S
H21: U-phase lower arm second current detection resistor, SH22:
W-phase lower arm second current detection resistor, 37 ... U-phase upper arm first amplifier, 38 ... W-phase upper arm first amplifier, 39
... U-phase lower arm second amplifier, 40 ... W-phase lower arm second amplifier, 41 ... U-phase third amplifier, 42 ... W-phase third amplifier, 43-44 ... A / D converter, 45 ... Microprocessor CPU, 46-47 ... resistance, R1-R3 ...
Resistors, R4 to R7: resistors, OP1 to OP3: operational amplifiers, 48: DC power supply for A / D converter, 49: negative power supply of third amplifier, 50: positive power supply of third amplifier, 51 ...
Metal base, 52 mounting holes, 53 inverter module.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Masato Takase 7-1-1 Higashi Narashino, Narashino-shi, Chiba F-term in the Industrial Equipment Division, Hitachi, Ltd. 5H007 AA04 AA06 AA12 BB06 CA01 CB05 DA05 DB12 DC02 EA13 HA04

Claims (5)

[Claims] A first antiparallel circuit in which a first switching element and a first diode are connected in parallel in a reverse direction; a second antiparallel circuit in which a second switching element and a second diode are connected in parallel in a reverse direction; A first arm connected in series between the first antiparallel circuit and the second antiparallel circuit and the first and second switching elements such that the second switching element is in the forward direction and connected between the DC buses, and the first arm and In the inverter device, in which a plurality of arms having the same configuration as the arm are connected in parallel and an intermediate point between the first anti-parallel circuit and the second anti-parallel circuit of each arm is connected to a load, the positive side of the DC bus and the A first current detection resistor connected between a first anti-parallel circuit, a second current detection resistor connected between the negative side of the DC bus and the second anti-parallel circuit, A first amplifier that amplifies the voltage across one current sensing resistor A device, a second amplifier for amplifying the voltage across the second current detection resistor, and a potential obtained by equally dividing the positive / negative voltage of the DC bus as a reference potential, the first amplifier and An inverter device comprising: a third amplifier for adding the second amplifier. 2. An A / D converter for converting an analog value into a digital value using the output voltage of the third amplifier as the same reference potential as the reference potential of the third amplifier. Item 3. The inverter device according to Item 1. 3. The first and second current detection resistors, the first, second, and third amplifiers, the A / D converter, the first antiparallel circuit, and the second antiparallel. 3. The inverter device according to claim 2, wherein the inverter main circuit formed of a circuit is mounted in the inverter module. 4. An anti-parallel circuit in which a switching element and a diode are connected in parallel in a reverse direction is provided, and the anti-parallel circuit is a series body in which two switching elements are connected in series such that the switching element is in a forward direction. In the inverter device, a plurality of DC power supplies are connected in parallel, and a connection point between the anti-parallel circuits in each of the series bodies is connected to a load. Current detecting means respectively inserted at the connection points on the negative and positive sides, amplifying means for amplifying the voltages at both ends of the positive current detecting means and the negative current detecting means, respectively, and the positive / negative voltage of the DC bus. The potential obtained by equally dividing the voltage
An inverter device comprising voltage adding means for adding the positive side and negative side amplified voltages. 5. The inverter device according to claim 4, wherein said series body, said current detecting means, said amplifying means, and said voltage adding means are constituted as an integrated module.