JPH0772179A - Filter circuit for rectifier-type voltmeter - Google Patents

Abstract

PURPOSE:To reduce indication difference of a voltmeter due to the relative length of a distance between the generation source of an AC voltage and its measuring point when the AC voltage in which a harmonic component is superposed on its fundamental waves is measured by a rectifier-type voltmeter. CONSTITUTION:A capacitor 41 is connected in series with a resistance 42 to constitute a filter circuit 4, and it is connected in parallel with input terminals of a rectifier-type voltmeter 31. The impedance value of the filter circuit 4 is sufficiently small as compared with the input impedance value of the voltmeter 31 in the frequency distribution region of a harmonic component in an AC voltage to be measured. Thereby, the burden portion of the voltmeter 31 with reference to the harmonic component is lowered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rectifier type voltmeter for measuring an AC voltage in which a harmonic component is superimposed on its fundamental wave such as an output voltage of an inverter at a place distant from its source. The present invention relates to a rectifier voltmeter filter circuit that corrects an erroneous change in an input voltage signal due to an increase in the distance of an input path.

[0002]

2. Description of the Related Art Conventionally, a rectifier type voltmeter has been used as a comparatively accurate indicator of an effective value of a fundamental wave in measuring an AC voltage in which a harmonic component is superimposed on its fundamental wave such as an output voltage of an inverter. However, in this case, in order to maintain the measurement accuracy of the AC voltage, it is general to add no additional correction means related to the distance, type, etc. of the voltage signal input path to the voltmeter.

[0003]

However, when an AC voltage having a harmonic component superimposed on its fundamental wave is measured by a rectifier type voltmeter at a distance from its source, the fundamental wave component remains unchanged. However, the indication of the voltmeter tends to increase as the distance of the voltage signal input path increases.

Therefore, when the distance between the AC voltage generating source and the voltage measuring instrument is large as described above, the application of the rectification type voltmeter may be inappropriate. By the way, Figure 2
FIG. 3 is a system diagram of an induction motor drive system using an inverter that generates an AC voltage as described above, and FIG. 3 shows a voltage signal change pattern at the input terminal of a rectifier voltmeter that measures the output voltage of the inverter as a signal input path. It is a voltage signal waveform diagram which illustrates roughly according to the length.

In FIG. 2, reference numeral 1 is, for example, 3φ AC400.
An inverter panel for accommodating necessary equipment for converting AC power supplied from a / 440V AC power supply into required AC power and driving and controlling the induction motor of 2.
, Electromagnetic contactor 12, and ACL (AC reactor) 1
3 and a transistor-type inverter 14 as the main circuit device, and a P for 440 / 110V via a fuse 16.
A T (measuring transformer) 17 and a voltmeter 18 having an instructed range of 0 to 600 V are configured as measuring devices.

A field panel 3 is provided with a rectifier type voltmeter 31 having an instructed range of 0 to 600 V and is installed at a place distant from the inverter panel 1. Next, in the voltage signal waveform diagram of FIG. 3, when the voltage signal input path is short (for example, the voltmeter 18 of the inverter board is shown in FIG.
On the other hand, FIG. 6B shows a waveform diagram of the voltage signal at the voltmeter input terminal when the voltage signal input path is long (for example, for the voltmeter 31 on the site panel). In any case, the AC voltage to be measured forms a PWM-modulated pulse-shaped rectangular wave train output from the inverter 14.

As shown in the figure (a), it can be considered that there is no waveform difference between the inverter output terminal voltage and the voltmeter input terminal voltage, but in the figure (b) the voltmeter input terminal voltage waveform is It shows that the turbulence, especially its harmonic component, increased. Therefore, when the voltage shown in the above figures (a) and (b) is measured with a rectifier voltmeter, the indicated value in figure (b) is the same as that in figure (b) while measuring the same inverter output end voltage. Will be greater than.

In view of the above, according to the present invention, when an AC voltage in which a harmonic component is superposed on its fundamental wave like an inverter output voltage is measured by a rectifier voltmeter, the distance between the source of the AC voltage and its measurement point. It is an object of the present invention to provide a rectifier type voltmeter filter circuit which can make the difference in the indicated value of the voltmeter as small as possible depending on the length.

[0009]

In order to achieve the above object, in the rectifier type voltmeter filter circuit of the present invention, the first means is to measure an AC voltage in which a harmonic component is superimposed on its fundamental wave. A rectifier type voltmeter filter circuit is configured by connecting a capacitor and a resistor in series.
This series connection is connected in parallel to the input terminal of the rectifier voltmeter, and as a second means, with respect to each of the contained harmonic components, the impedance value of the series connection formed by the capacitor and the resistor is compared. The ratio of the input impedance value of the rectifier voltmeter is set to a value that allows a predetermined measurement accuracy with respect to the AC voltage to be maintained.

[0010]

In general, in the rectifier type voltmeter, the rectifying surface of the rectifier acts as a kind of capacitor for a high frequency input signal and is affected by the frequency of the input signal. Therefore, when a high-frequency AC voltage is applied to the rectification type voltmeter through an electric wire that forms a voltage signal input path, the inductance and resistance of the coil in the voltmeter, the rectification surface capacitor portion as described above, and the resistance in the input path electric wire The inductance forms a kind of series resonance circuit.

Here, the inductance and capacitance of the rectifier type voltmeter and the electric wire are usually extremely small, so that the resonance frequency of the resonance circuit is sufficiently higher than the input signal frequency of the voltmeter. It becomes a value. Now, if the wire inductance increases as the distance of the input path increases, the resonance frequency of the series resonance circuit decreases, and accordingly, the frequency characteristic line of the resonance circuit shifts to the low frequency side, and the voltage The input terminal voltage of the meter increases.

That is, when an AC voltage in which a harmonic component is superimposed on its fundamental wave, such as an output voltage of a PWM-modulated inverter, is measured by a rectifier type voltmeter, the input of the voltmeter increases as the voltage signal input path length increases. The harmonic components in the AC voltage signal at the edges also increase, and the voltmeter reading obtained by rectifying this AC voltage signal is greater than the measurement reading of the AC voltage at its source.

In response to the above, according to the present invention, a series connection of a capacitor and a resistor is connected in parallel to an input terminal of a rectification type voltmeter as a filter circuit, and the impedance value of the series connection is as described above. In the frequency distribution range of the harmonic component in the AC voltage, it is not sufficiently small as compared with the input impedance value of the voltmeter to the extent that the predetermined measurement accuracy for the AC voltage can be maintained, and The burden on the voltmeter is reduced to avoid the adverse effect of the increase in the indicated value of the voltmeter due to the increase in the voltage signal input path as described above.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to the circuit diagram of FIG. It is assumed that the circuit configuration shown in FIG. 1 is installed on the site panel 3 shown in FIG. 31 in FIG.
Is a rectifier voltmeter that measures the output voltage of the inverter 14 applied via the PT 17, and the filter circuit 4 is constructed by connecting a capacitor 41 and a resistor 42 in series.

As described above, the impedance value of the filter circuit 4 is sufficiently smaller than the input impedance value of the voltmeter 31 in the frequency distribution range of the harmonic component in the output voltage of the inverter 14. As a result, the burden of the voltmeter 31 on the harmonic components is reduced, and the erroneous increase in the indicated value of the voltmeter 31 due to the increase in the distance between the inverter panel 1 and the field panel 3 is prevented. .

[0016]

According to the present invention, a filter circuit for a rectifier type voltmeter for measuring an AC voltage in which a harmonic component is superimposed on its fundamental wave, such as an inverter output voltage, is constructed by connecting a capacitor and a resistor in series. With this series connection in parallel with the input terminal of the voltmeter, in the frequency distribution range of the harmonic component, the ratio of the input impedance value of the voltmeter to the impedance value of the filter circuit, the AC voltage. When the AC voltage as described above is measured by the rectifier voltmeter, the AC voltage generation source (eg, inverter board) and the voltage measurement point Even when the distance to the (for example, the field panel) becomes large, it is possible to easily and surely prevent the erroneous increase in the indicated value of the voltmeter due to the increase in the distance. Can, also can provide this as being small and inexpensive with respect to the filter circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

[Fig. 2] System diagram of an induction motor drive system using an inverter

FIG. 3 is a voltage signal waveform diagram at the input terminal of a rectifier voltmeter.

[Explanation of symbols]

 1 Inverter panel 2 Induction motor 3 Field panel 4 Filter circuit 11 Power breaker 12 Magnetic contactor 13 ACL (AC reactor) 14 Inverter 15 Frequency meter 16 Fuse 17 PT (Voltage meter 31) 18 Voltmeter 31 (rectification type) Voltmeter 41 Capacitor 42 Resistance

Claims (2)

[Claims] 1. A filter circuit for a rectifier voltmeter, which measures an AC voltage having a harmonic component superimposed on its fundamental wave,
A rectifier type voltmeter filter circuit, comprising a capacitor and a resistor connected in series and connected in parallel to an input terminal of the rectifier type voltmeter. 2. A filter circuit for a rectifying voltmeter according to claim 1, wherein, with respect to each of the contained harmonic components, an input impedance of the rectifying voltmeter with respect to an impedance value of a series connection formed by the capacitor and a resistor. A filter circuit for a rectifying voltmeter, wherein the ratio of values is increased to a value that enables maintaining a predetermined measurement accuracy with respect to the AC voltage.