JPH0340761A - Output voltage control circuit for inverter - Google Patents

Abstract

PURPOSE:To maintain a load input as a stabilized voltage having small distorsion by a method wherein the title circuit is provided with the output current detecting means of an inverter, the operating means of the impedance voltage drop of a wiring from an output terminal to a load and a correcting signal providing means. CONSTITUTION:A wiring voltage drop operating circuit 20 differentiates the signal of a current detector 25 by a differentiating circuit 21 and the result of the differentiation is given to an inductance voltage drop compensating amount regulator 22 to compensate the voltage drop of a power cable, which is due to an inductance. On the other hand, the signal of the current detector 25 is given to a resistance voltage drop compensating amount regulator 23 to compensate the voltage drop of a DC resistor. An impedance voltage drop compensating amount, outputted from the wiring voltage drop operating circuit 20, is outputted from a commanding sine wave generator 12 as a correcting signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inverter output voltage control circuit that can suppress waveform distortion caused by impedance of wiring to a load.

[Prior Art] FIG. 2 is a block diagram showing a conventional example of output voltage control of an uninterruptible power supply.

The uninterruptible power supply 3 is composed of a charger 4, an inverter 6, and a battery 5 connected to a DC intermediate circuit that connects these charging r&4 and the inverter 6. By supplying electric power to the uninterruptible power supply 3, the load 7 is supplied with alternating current power of a constant voltage and a constant frequency that will not cause a power outage.

In this way, AC power of constant voltage and constant frequency is applied to the load 7.
In order to supply power to the inverter 6, the inverter 6 detects its output voltage with the instrument transformer 11, and compares the command sine wave signal output by the command sine wave generator 12 with this detected voltage signal.

The voltage regulator 13 outputs a control signal to match both signals, and the pulse width modulation circuit 15 generates and outputs a pulse width modulation signal using the triangular wave signal from the carrier oscillator 14 and this control signal. Performs instantaneous voltage control.

As a result of instantaneous voltage control using such pulse width modulation, the output terminal voltage of the inverter 6 can be stabilized to a constant voltage with little waveform distortion.

[Problem to be solved by the invention]

By the way, the above-mentioned uninterruptible power supply 3 and the load 7 that will receive AC power are connected by a power cable, but since a voltage drop occurs due to the impedance of this power cable, the load 7 The input terminal voltage is
This value is different from the output end voltage of the uninterruptible power supply 3.

In particular, the load of the uninterruptible power supply 3 is often an electronic device such as a computer, and in the case of such a load, a distorted wave load current containing a large amount of harmonics flows, so the input voltage of the load 7 is based on that waveform. Distortion becomes large, and in some cases, there is a risk that the normal operation of electronic devices such as computers may be inhibited.

In order to compensate for such an impedance voltage drop of the power cable, a method was conventionally adopted in which the input terminal voltage of the load 7 was detected and this was fed back to the voltage control circuit of the inverter 6. 3 and the load 7 are installed apart from each other, there is a drawback that this voltage signal cannot be easily fed back.

Therefore, an object of the present invention is to maintain the input voltage of the load at a stable voltage with little waveform distortion by compensating for the voltage drop caused by the impedance of the wiring connecting the inverter and the load.

[Means for Solving the Problems] In order to achieve the above object, the output voltage control circuit of the present invention converts the output voltage signal of an inverter that converts direct current into alternating current and supplies power to a load into a command sine wave signal. In an inverter configured to perform instantaneous voltage control using a voltage regulating means, the output current causes impedance of the wiring from the output end of the inverter to the input end of the load. means for calculating a voltage drop, and this impedance voltage drop as the voltage il! ig! One means is provided with means for giving it as a correction signal.

[Effect]

The second invention provides a load current detection means at the output end of the inverter, detects a signal proportional to the load current as a voltage drop due to the DC resistance of the power cable, and detects a signal proportional to the differential value of the load current. , by detecting the voltage drop due to the inductance of the power cable and adding the sum of both to the command sine wave signal as a correction signal, the inverter will output a voltage that is higher by the voltage drop due to the impedance of the power cable. That is.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the present invention.

In FIG. 1, an uninterruptible power supply 3 consisting of a charger 4, a battery 5, and an inverter 6, an AC power supply 2 and a load 7 connected to the uninterruptible power supply 3 are shown.
, the names of the instrument transformer 11, the command sine wave generator 12, the voltage regulator 13, the carrier oscillator 14, and the pulse width modulation circuit 15 for controlling the output voltage of the inverter 6.
Since the application and functions are the same as those of the conventional circuit described in FIG. 2, a description thereof will be omitted.

In the present invention, a current detector 25 for detecting the load current to the load 7 is provided inside the uninterruptible T1 power supply device 3, and this detected current signal is guided to a wiring voltage drop circuit 20. .

The wiring voltage drop calculation circuit 20 includes a differentiating circuit 21, an inductance voltage drop compensation amount adjuster 22, a resistance voltage drop compensation N adjuster 23, and an adder 24, and receives a detected current signal from a current detector 25. By differentiating the voltage with the differentiating circuit 21 and applying the differential operation result to the inductance voltage drop compensation amount adjuster 22, the amount to compensate for the voltage drop caused by the inductance of the power cable can be obtained.

Further, by applying the detected current signal from the current detector 25 to the resistance voltage drop compensation amount adjuster 23, the amount to compensate for the voltage drop caused by the DC resistance of the power cable can be obtained.

The adder 24 adds up the voltage drop compensation it obtained due to the inductance and the voltage drop compensation amount due to the DC resistance, and outputs the impedance voltage drop compensation amount of the power cable.

This impedance voltage drop compensation amount output from the wiring voltage drop calculation circuit 20 is transmitted to the command sine wave generator 12 described above.
By adding it as a correction signal to the command sine wave signal from the inverter 6, the output voltage of the inverter 6 is increased by the impedance voltage drop of the power cable due to the current flowing to the load 7. Therefore, the input terminal voltage of the load 7 can be maintained at a predetermined value.

Note that most of the impedance voltage drop of the power cable is due to DC resistance, and the voltage drop due to inductance is small.

Therefore, the wiring voltage drop calculation circuit 20 can be configured only with the resistance voltage drop compensation amount adjuster 23, and the differentiating circuit 21, the inductance voltage drop compensation amount adjuster 22, and the adder 24 can be omitted.

[Effects of the Invention] According to the present invention, the load current output by the inverter is detected, and the detected current signal is used to calculate the amount of voltage drop caused by the impedance of the power cable connecting the inverter and the load. By calculating and adding this impedance voltage drop amount to the command sine wave signal as a correction signal, this inverter output voltage is increased by the voltage drop. As a result, the input terminal voltage of the load can be maintained at a constant voltage with little waveform distortion, regardless of the operating state of the load.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an embodiment of the present invention, Figure 2 is a block diagram showing an embodiment of the present invention.
The figure is a block diagram showing a conventional example of output voltage 1 control of an uninterruptible power supply.

Claims (1)

[Claims] 1) Detecting the output current of the inverter in an inverter configured to perform instantaneous voltage control using voltage adjustment means in order to match the output voltage signal of the inverter that converts direct current to alternating current and supplies power to a load with a command sine wave signal. means for calculating an impedance voltage drop of the wiring from the output end of the inverter to the input end of the load based on the output current, and means for applying the impedance voltage drop to the voltage adjustment means as a correction signal. An inverter output voltage control circuit characterized by: