JP2006136037A - Circuit for detecting dc component of inverter output voltage - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive method for detecting a DC component of an inverter output voltage by eliminating the need for expensive components such as a detector. <P>SOLUTION: The circuit for detecting the DC component included in the AC output voltage of an inverter comprises a low-pass filter, a first operational amplifier, and a second operational amplifier. One power supply of the first operational amplifier has potential identical to the potential at one AC output terminal of the inverter, and the power supply of the second operational amplifier has potential different from the potential at one AC output terminal of the inverter. A detection signal is transmitted to the control circuit using a differential amplifier as the second operational amplifier. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a technique for preventing magnetic bias due to a DC component included in an applied voltage of a transformer supplied with electric power from an inverter, and more particularly to a circuit for detecting a DC component and a power supply method for the circuit.

  The inverter converts a DC voltage into an AC voltage and outputs it. However, a DC component may be slightly included in the output voltage due to a control error or a variation in characteristics of a semiconductor switching element to be used and its drive circuit. If there is a transformer in the load device of the inverter, this DC component will cause the magnet to become demagnetized, preventing normal power supply to the load on the secondary side of the transformer. The excitation current may increase abnormally and damage the inverter, transformer or other connected circuit components.

  Generation of a DC component due to a control error can be avoided to some extent by devising a control method, but generation of a DC component due to variations in characteristics of the semiconductor switching element and its drive circuit cannot be prevented. There is also a method of adjusting the direct current component to be zero first, but there is a concern that a deviation may occur due to a temperature change or a secular change. Therefore, in order to reliably suppress the generation of the DC component, it is necessary to detect the DC component actually generated and to control the inverter so as to reduce it.

  An example of a conventional DC component detection circuit is shown in FIGS.

FIG. 3 is described in Patent Document 1. The LC filter removes the AC component from the inverter output voltage, that is, the voltage between the AC output terminals U and V by the LC filter, detects only the DC component, and insulates by the insulation amplifier. It is amplified and transmitted to the control device.
In FIG. 3, 301 is an inverter, 302 is its control device, 303 is a reactor, 304 is a capacitor, and 305 is an insulation amplifier.

FIG. 4 is described in Patent Document 2, and has a configuration in which a reactor is connected in parallel with the inverter output. Since the reactor has a very small impedance with respect to the direct current, when a voltage including direct current is applied, the ratio of the direct current flowing through the reactor is increased, so that the direct current voltage component can be detected by detecting the current. .
In FIG. 4, 401 is an inverter, 402 is its control device, 403 is a reactor, and 404 is a current detector such as Hall CT.

FIG. 5 is described in Patent Document 3. A DC component is detected by a low-pass filter composed of a resistor and a capacitor, which is amplified by an amplifier using an operational amplifier (hereinafter referred to as an operational amplifier) and transmitted to a control device. To do.
In FIG. 5, 501 is an inverter, 502 is its control device, 503 is a low-pass filter, and 504 is an amplifier.
Japanese Patent No. 3228387 (FIGS. 1 to 4) JP-A-6-217559 (FIG. 1) JP-A-5-103483 (FIG. 1)

  In the circuits of FIG. 3 and FIG. 4, the signal is transmitted between the DC component detection unit and the control device, but expensive components such as an insulation amplifier and a current detector such as a Hall CT are used for this purpose. Is required. Further, when the inverter has a commercial frequency, the reactor to be used needs to have a large inductance and is similarly expensive.

  Although the circuit of FIG. 5 can be configured at a relatively low cost, the ground potential of the control circuit is fixed to one point of the inverter output (V terminal in the example of FIG. 5). For example, in recent years, in order to inexpensively drive the gate of an inverter, there are many examples using a non-insulated gate drive IC. For this purpose, the ground potential of the control circuit needs to be shared with the negative potential of the DC power supply.

  As described above, any of the methods is difficult to apply to a small capacity machine that is required to be particularly low cost.

  In order to solve the above problems, a voltage detection circuit for detecting a DC component included in an AC output voltage of an inverter includes at least a low-pass filter, a first operational amplifier, and a second operational amplifier, The potential of any one of the power supplies of the operational amplifier is the same as the potential of any of the AC output terminals of the inverter, and the potential of the power supply of the second operational amplifier is different from any of the AC output terminals of the inverter. A detection signal is transmitted to the control circuit using a differential amplifier as the second operational amplifier.

  For detecting the DC component of the inverter output voltage, expensive components such as a reactor and a current detector that have been conventionally used are not required, and a low-cost DC component detection circuit can be provided.

  The main point of the present invention is that, as a DC component detection of the inverter output, the potential of the power supply of the first operational amplifier is made the same as any of the inverter outputs, and a differential amplifier is used as the second operational amplifier for amplifying this output, This power supply is set to a potential different from that of the first operational amplifier.

FIG. 1 shows a first embodiment of the present invention.
In FIG. 1, 1 is an inverter, 2 is a DC power supply, 3 is a low-pass filter, 4 is a non-inverting amplifier using an operational amplifier and a resistor, 5 is a differential amplifier using an operational amplifier and a resistor, 6 is a control device, 7 is a resistor, Are diodes, 10 and 11 are capacitors, and 12 and 13 are zener diodes.

  The inverter AC output voltage, that is, the DC component included in the voltage between the U and V terminals is detected by the low-pass filter 3. In FIG. 1, since the ground potential of the control device is the same as the negative potential of the DC power supply 2, the differential amplifier 5 is used to extract only the voltage from different potential portions. Here, in order for the differential amplifier 5 to operate normally, the ground voltage of the −input terminal and the + input terminal of the operational amplifier needs to be smaller than the power supply voltage (usually ± 15 V or less) of the operational amplifier. Therefore, the amplification factor of the circuit, that is, R2 / R1 = R4 / R3 needs to be small according to the potential difference between the U and V terminals and the ground, for example, about 1/100.

 On the other hand, assuming that the output voltage of the inverter 1 is 100V, the DC component included is at most 1% of that, that is, 1V or less. The output becomes 10 mV or less, and sufficient accuracy cannot be obtained due to offset error or noise. Therefore, the non-inverting amplifier 4 amplifies the output of the low-pass filter 3 to about 10 times in advance, so that the output of the differential amplifier 5 has a practically no problem, for example, about 100 mV.

  Here, the power supplied to the operational amplifier of the non-inverting amplifier 4 needs to have a potential different from that of the differential amplifier 5 and the control device 6. However, since the power is very small, the power circuit is the output of the inverter 1. The voltage is rectified by the diodes 8 and 9 while limiting the current by the resistor 7, smoothed by the capacitors 10 and 11, and clamped to a predetermined value by the Zener diodes 12 and 13 to supply necessary positive and negative power supplies It can be configured at a low cost by such a method. The method of configuring the power supply is not limited to this. For example, in the power supply for operating the control device 6, a method of configuring power supplies having different potentials by adding, for example, a transformer winding and a rectifier circuit inside the power supply is also possible. It is.

FIG. 2 shows a second embodiment of the present invention.
This is an application example to a three-phase output inverter circuit, 21 is a three-phase inverter, 22 is a DC power supply, 23 and 24 are low-pass filters, 25 and 26 are non-inverting amplifiers, 27 and 28 are differential amplifiers, 29 is It is a control device.
30 and 31 are resistors, 32 to 35 are diodes, 36 and 37 are capacitors, and 38 and 39 are Zener diodes.

  In this configuration, the DC components of the U terminal and W terminal voltages are detected by the same method as in FIG. 1 with the V terminal potential as a reference. Since the voltage between the U terminal and the W terminal can be calculated from the U terminal and W terminal voltages, detection is omitted. Since the ground potentials of the operational amplifiers used for the non-inverting amplifiers 25 and 26 are both V terminal potentials, a common power source can be used. The power supply method is based on the same principle as that in FIG. 1 described in the first embodiment.

  The present invention can be applied to an uninterruptible power supply device including a transformer at the output of the inverter, an insulation type switching power supply using the transformer, and a variable speed drive inverter using a motor as a load. .

1 is a circuit example showing a first embodiment of the present invention. It is a circuit example which shows the 2nd Example of this invention. Shows conventional technology (example using LC filter) Shows conventional technology (example using DC current detector) Shows conventional technology (example using low-pass filter)

Explanation of symbols

・ 21, 301, 401, 501 ・ ・ ・ Inverter
2, 22 ... DC power supply 3, 23, 24, 503 ... Low-pass filter 4, 25, 26, 504 ... Operational amplifier 5, 27, 28 ... Differential amplifier 6, 29, 302, 402 , 502 ... Control device 7, R1 to R4, 30, 31 ... Resistor 8, 9, 32 to 35 ... Diode 10, 11, 36, 37, 304 ... Capacitor 305 ... Insulation amplifier
12, 13, 38, 39 ... Zener diode 404 ... Current detector 303, 403 ... Reactor

Claims (2)

A voltage detection circuit for detecting a DC component included in an AC output voltage of an inverter,
At least a low-pass filter, a first operational amplifier, and a second operational amplifier are included, and any potential of the power source of the first operational amplifier is the same as any potential of the AC output terminal of the inverter. A circuit for detecting a DC component of an inverter output voltage, wherein the potential of the power source of the second operational amplifier is different from any of the AC output terminals of the inverter.   2. The inverter output voltage direct current component detection circuit according to claim 1, wherein the second operational amplifier comprises a differential amplifier that amplifies the output of the first operational amplifier.

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