JPH0283459A - Current detection circuit - Google Patents

Abstract

PURPOSE:To prevent the irregularity of a measured value even when the time constant of a smoothing filter is reduced by making timing of the start of A/D conversion synchronous to a power supply. CONSTITUTION:The current of a line is detected by a current transformer 5 and converted to a digital value by an A/D conversion part 3 through a rectifying and smoothing circuit 8 consisting of a diode 7, a resistor C and a condenser R to be sent to a control part. A photocoupler 10 is connected to a power supply 9 and the pulse synchronous to the power supply 9 is generated and an A/D converter is driven in the timing matched with said pulse. Pulsating flow is generated when the time constant of the smoothing circuit becomes small but, since sampling is performed in synchronous relation to the power supply, the sampling point of the pulsating flow becomes same and the irregularity of a measured value is not generated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a current detection circuit used in inverter control of an air conditioner, etc., and more specifically, to a current detection circuit used in inverter control of an air conditioner, etc. This invention relates to a current detection circuit that improves current detection.

[Conventional Example] Conventionally, this type of current detection circuit has been provided, for example, in the power input stage of an outdoor unit, and as shown in FIG. 3(a), it detects the AC input current during compressor operation. The voltage is detected, subjected to half-wave rectification, converted to a digital value, and output to the control unit of an air conditioner, etc., as data for suppressing operating current. The control unit compares the operating current suppression data with preset regulation values, and if the operating current exceeds the rating of the breaker used in general households, it suppresses the AC input current. It looks like this.

[Problems to be Solved by the Invention] By the way, in the current detection circuit described above, the detected current is converted into a DC voltage by half-wave rectification.

As shown in Figure 3(b), the ripple of the DC voltage is reduced by a filter circuit consisting of a resistor and a capacitor.
This reduced DC voltage was converted into a digital value.

However, in order to perform more accurate detection, it is sufficient to reduce the ripple, but as shown by the broken line in FIG. 3(b), if the capacitance of the capacitor is increased to suppress the ripple, the filter There was a problem in that the time constant of the circuit became large and the responsiveness of the current suppression function deteriorated. That is, since the A/D conversion timing is delayed according to the time constant, the timing at which the control section suppresses the AC input current is delayed.

This invention was made in view of the above-mentioned problems, and its purpose is to convert the detected current into A in synchronization with the power supply of the above-mentioned AC input current.
An object of the present invention is to provide a current detection circuit that performs /D conversion and can prevent deterioration in responsiveness of an operating current suppression function.

[Means for Solving the Problem] In order to achieve the above object, the present invention provides a current detection circuit used for inverter control of an air conditioner, etc.
A current detection means for detecting the AC current, a power synchronization signal generation means for generating a signal synchronized with the power source of the AC current, and an A/C converter for converting the detected current into a digital value at the timing of the synchronization signal. D conversion means, the digital value obtained by the A/D conversion means is used as control data for the operating current of the air conditioner, etc., and responsiveness such as suppression of the operating current is increased. .

[Function] With the above configuration, the AC current detected by the current detection means is half-wave rectified and then smoothed.
The signal is converted into digital data by the D conversion means, and this conversion is performed at the timing of the signal synchronized with the power source of the AC current. At this time.

Regardless of the C-R time constant of the smoothing filter circuit,
The AC current is converted into digital data at regular intervals,
Current detection is performed. Namely.

Even if the time constant of the filter circuit ΦC-R is increased, the detection of the AC current will not be delayed, and the responsiveness of the suppressing function of the operating current of an air conditioner or the like will not deteriorate.

[Example] Embodiments of the present invention will be described below based on the drawings.

In Fig. 1, the current detection circuit includes a current detection unit 1 that detects the AC current flowing in the line as a DC voltage value, and a power supply synchronization signal that generates a signal synchronized with the power supply that supplies the AC current. With generation part 2.

An A/D converter 3 is provided which converts the detected current into digital value data at the timing of the power synchronization signal. In this current detection circuit, for example, in the case of an operating current suppression function of an air conditioner, etc.

In the control unit 4, the control data of the digital value is compared with a preset regulation value, and when it exceeds the regulation value, the operating current is suppressed so that the operating current does not exceed the rating of the breaker used in general households. It will be done like this.

By the way, in this example, the current detection unit 1 is a current transformer (Current) provided in the line of the power input stage of the air conditioner.
5, a load resistor 6 connected in parallel with the current transformer 5, a rectifier diode 7 that half-wave rectifies the current detected by the current transformer 5 and converts it into a DC voltage, and a rectifier diode 7 that converts the current detected by the current transformer 5 into a DC voltage A filter circuit 8 composed of a resistor R and a capacitor C is provided for smoothing. That is, the detected current on the line of the power supply input stage is converted to a DC voltage, and the C-R voltage of the filter circuit 8 is converted to a DC voltage.
Smoothed according to the time constant.

The power synchronization signal generating section 2 is equipped with a photocoupler 10 that obtains a signal at the peak value of the sine waveform of the power supply 9 supplied to the air conditioner.

That is, the light emitted by the photodiode of the photocoupler 10 turns on the phototransistor every cycle of the power supply (OFF at other times) t,, the photocoupler 10
A pulse signal is output from the phototransistor at ON/OFF timing.

Then, the pulse signal is input to the A/D converter 3,
The A/D converter 3 converts the detected current (voltage value) obtained by the current detector 1 into digital value data and outputs it to the controller 4. That is, the operation of the A/D converter 3 is always started at a constant timing regardless of the C/R time constant of the filter circuit 8, so it is not always affected by ripples contained in the DC voltage. Since the determination of whether to suppress the operating current is always made at a constant timing, the responsiveness of the operating current suppression is not deteriorated.

In the above embodiment, the case where the present invention is applied to the operating current suppression function of an air conditioner has been described, but the present invention can also be applied to current detection in other devices.

[Effects of the Invention] As explained above, according to the present invention, when detecting the current flowing through the power input stage of an air conditioner, etc., the operation start of the AID conversion unit that converts the detected current into a digital signal is activated by the power supply. Since the timing is synchronized, the A/D conversion operation always starts at a constant timing even if the C/R time constant of the filter circuit that smoothes the DC voltage obtained by half-wave rectification of the detection current is made small. Therefore, the responsiveness of the operating current suppressing function is not affected and the responsiveness is not deteriorated.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of a current detection circuit showing an embodiment of the present invention, FIG. 2 is a specific circuit block diagram of the current detection circuit, and FIG. 3 explains the operation of a conventional current detection circuit. This is a diagram for In the figure, 1 is a current detection section, 2 is a current synchronization signal generation section, 3 is an A/D conversion section, 4 is a control section, 5 is a current transformer, 6 is a load resistor, 7 is a rectifier diode, and 8 is a filter 9 is a power supply, and 10 is a photocoupler. Patent Appearance Fujitsu General Co., Ltd. Agent Patent Attorney Takuya Ohara

Claims (3)

[Claims] (1) In a current detection circuit used for inverter control of an air conditioner or the like, a current detection means for detecting an AC current, a power synchronization signal generation means for generating a signal synchronized with a power source of the AC current, and the above-mentioned. A/D conversion means for converting the detected current into a digital value at the timing of a synchronization signal, and the digital value obtained by the A/D conversion means is used as control data for the operating current of the air conditioner, etc. What is claimed is: 1. A current detection circuit characterized in that the responsiveness of operating current suppression, etc. is increased. (2) The current detecting means is composed of a current transformer, and the detected current obtained by the current transformer is passed through a rectifying diode and a C.
The current detection circuit according to claim 1, wherein the current is input to the A/D conversion means via a filter circuit with an R time constant. (3) The current detection circuit according to claim 1, wherein the power supply synchronization signal generating means is a photocoupler connected to the power supply side, and the synchronization signal is a signal for turning on and off a phototransistor of the photocoupler. .