JPH0733172Y2 - Current detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial field of application" The present invention relates to a current detector suitable for use in controlling a load current in, for example, high frequency heating or arc welding.

"Prior art" Conventionally, in arc welding power sources, etc., a current detector using a hall element is used, and the current flowing through the switching element is detected by this current detector, and the signal is fed back to the control circuit. This has provided load current control, protection against overcurrent, and the like.

FIG. 7 is a circuit diagram of a conventional arc welding power source. In this figure, 1 is a DC power source such as a battery, and 2-1 to 2-.
4 is a switching element, which is 2-1, 2-2 and 2-3,2-
4 are connected in series, and both ends thereof are connected in parallel to the DC power supply 1. Rectifiers 3-1 to 3-4 are connected to both ends of each of the switching elements 2-1 to 2-4 so as to have a polarity opposite to that of the DC power supply 1. Then, each of the switching elements 2-1 to 2-4 and each of the rectifying elements 3-1 to 3-4
The inverter INV is composed of. A load 5 is inserted in series between the output terminals of this inverter INV.

Next, the operation of the circuit shown in FIG.
Will be described as a resistance. FIG. 8 is a diagram showing the relationship between the on / off control timing of the switching elements 2-1 to 2-4 in the circuit and the current Id flowing in the circuit. In this figure, a section T1 is a section in which the current Id flows in the arrow Y1 direction shown in FIG. 7, and a section T2 is a section in which the current Id flows in the direction opposite to the arrow Y1. Therefore, the AC voltage is applied to the load 5. At this time, the current Id flowing in the circuit
Is detected by the DC current detector 4 using a Hall element.

[Problems to be solved by the invention] By the way, as described above, if the load 5 is a resistance, there is no problem. However, for example, in the case of an arc welding power source, the load 5 does not become a resistance load, and therefore, the current Is a current including pulsation. However, the conventional DC current detector 4 using the Hall element has a drawback that it generally has a slow response and it is difficult to detect a high frequency pulsating current with high accuracy.

The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to provide a current detector that can easily and highly accurately detect a high-frequency pulsating current.

"Means for Solving the Problem" The present invention relates to a current detector that detects a current flowing in a switching element used in an inverter, and a current transformer attached to a current path of the switching element and a switching element of the switching element. The storage device further includes a storage unit that stores the peak value of the current transformer during the off period, and an adder that adds the inverted value of the value stored in the storage unit to the output value of the current transformer. It is characterized by

[Operation] According to the present invention, the current transformer attached to the current path of the switching element generates a reverse voltage due to the exciting current when the switching element is turned off. By adding and, it becomes possible to ignore the exciting current,
It becomes possible to detect the high frequency pulsating current with high accuracy.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a current detector according to an embodiment of the present invention. In this figure, parts corresponding to those in FIG. 7 are designated by the same reference numerals, and their description will be omitted. In FIG. 1, 6-1, 6-2 are 2-3, 2-4 and 2-
The current transformers are respectively attached to the current paths of the switching elements 1 and 2-2. 7 and 8 are switching elements 2-
Signals S1 and S obtained by delaying the on / off control signals 1 to 2-4
2 is the terminal to which the voltage is applied. That is, as shown in FIG.
When (b) is an on / off control signal for the switching elements 2-1 and 2-4 and an on / off control signal for the switching elements 2-2 and 2-3, respectively, the signal S1 applied to the terminal 7 and the terminal 8 are applied. The signal S2 applied to the signal is a signal obtained by delaying the signals (a) and (b) by 1/4 cycle, as shown in FIGS. OM1 and OM2 are one-shot multivibrators, and output narrow pulse signals at the falling edges of the above-mentioned signals S1 and S2 (Fig. 2 (d) and (f)).
reference). S / H1 and S / H2 are sample and hold circuits,
They are connected to the current transformers 6-1 and 6-2, respectively, and each output of the current transformers 6-1 and 6-2 is read at the rising edge of each output signal of the one-shot multivibrator OM1, OM2.
9-1 and 9-2 are inverters, and sample and hold S / H1,
Inverts the S / H2 output and outputs it. 10-1 and 10-2 are adders, which are the outputs of the current transformers 6-1 and 6-2 and the inverter 9-.
Add the outputs of 1 and 9-2.

Next, for convenience of description of the operation of the embodiment having the above-described configuration, the operation will be described below assuming that the load 5 in FIG. 1 is a resistor. First, Fig. 3 (a), (b)
The ON / OFF control signal applied to each switching element is shown in FIG. Further, in FIG. 6C, the current flowing through the electric wire to which the current transformer 6-1 is attached, that is, the current transformer 6-1.
The primary current Ia is shown. Hereinafter, the output waveform of the current transformer 6-1 in this case will be examined. FIG. 4 is an equivalent circuit diagram of the current transformer 6-1. In this figure, I is the primary side current source of the current transformer 6-1 and the output impedance is almost infinite. L1 is the primary side leakage inductance of current transformer 6-1 and L2
Is a secondary side leakage inductance of the current transformer 6-1 and R is a secondary side load resistance of the current transformer 6-1 (not shown in FIG. 1). I0 is an exciting current, M is an exciting inductance, and this exciting inductance M is the primary side leakage inductance L1 and the secondary side leakage inductance L.
Much larger than two.

Now, from the current source I to the primary side of the current transformer 6-1, the primary current Ia
During the initial T1 (Fig. 3) when the current flows, the exciting current I0 is small and the secondary current is small because the exciting inductance M is large.
A waveform similar to that of the primary current Ia can be detected for I2 (see FIG. 5 (a)). Next, during the period of T2, the exciting current I0 flows through the path of the broken line, so that the negative voltage v2 is applied to the load resistance R.
Occurs. However, this voltage v2 can be ignored because the exciting current I0 is small. This is because the ratio of the electromotive voltage that increases the exciting current I0 and the counter electromotive voltage that resets the exciting current I0 to zero is the ratio of the positive and negative detection voltages of the voltage v2 (ON /
When the off duty is 50%), it means that the exciting current I0 only increases and cannot be reset to zero. Therefore, the exciting current I0 continues to increase as shown in the area of FIG. 5 (b). When the exciting current I0 reaches the area shown in Fig. 5 (c), the negative voltage v2 generated during the T2 period due to the increased exciting current I0 becomes large and the exciting current I0 is quickly attenuated to a level at which the increase is canceled. It stabilizes when it reaches. At this time, voltage v2
The positive and negative average levels of are zero. (See FIG. 6).
That is, since the period areas of the signals obtained in the respective periods of T1 and T2 are equal, if a positive level equivalent to the negative level of the T2 period is added to the signal of the T1 period, the same DC component as the primary current Ia is included. An AC signal is obtained. Therefore, as shown in FIG. 2C, the one-shot multivibrator is provided with the signal S1 delayed by 1/4 period from the ON signal in FIG.
Converted to the trigger signal shown in (d) of Fig. 3 by OM1, and read the current transformer output voltage v2 during the T2 period by sample & hold S / H1. The value is inverted and output by the inverter 9-1,
A signal equivalent to the current Ia is obtained at the current detection output terminal d1 by adding the current transformer output voltage v2 and the adder 10-1. The same applies to the current transformer output voltage v3. If the value of the secondary side load resistance R (see FIG. 4) of the current transformers 6-1 and 6-2 is increased, the power consumption by the resistance R increases, so that the current waveform of FIG. However, if the resistance R is selected to be a sufficiently small value, the secondary current waveforms of the current transformers 6-1 and 6-2 become substantially rectangular waves, as shown in FIG. .

In the above description, the load 5 is described as a resistive load, but the present invention can of course be applied whether the load 5 is an inductive load or a capacitive load. . Further, the present invention is suitable for use as a high-frequency heating power source (resonance load), arc welding power source (inductive load), etc., but is not limited to these, and can be used for current detection of various inverters.

[Advantage of Device] As described above, according to the present invention, the current transformer attached to the current path of the switching element, and the storage means for storing the peak value of the current transformer during the OFF period of the switching element. Since it is provided with an adder that adds an inverted value obtained by inverting the positive and negative values stored in the storage means and the output value of the current transformer, the high-frequency pulsating current can be easily and accurately detected. It is possible.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing the construction of an embodiment of the present invention, FIGS. 2, 3, 5, and 6 are waveform diagrams showing the operation of the embodiment, and FIG. Equivalent circuit diagram of example current transformer, 7th
FIG. 8 is a circuit diagram showing a configuration of a conventional arc welding power source, and FIG. 8 is a waveform diagram showing an operation of the conventional arc welding power source. 2-1 to 2-4 ... Switching elements, 6-1, 6-2 ...
… Current transformer (output voltage v2, v3), 9-1, 9-2 …… Inverter,
10-1, 10-2 ... Adder, OM1, OM2 ... One-shot multivibrator, S / H1, S / H2 ... Sample & hold, INV ... Inverter.

Claims (3)

[Scope of utility model registration request] 1. A current detector for detecting a current flowing through a switching element used in an inverter, comprising: a current transformer attached to a current path of the switching element; and a current transformer in an off period of the switching element. A current detector, comprising: storage means for storing the peak value; and an adder for adding the inverted value of the value stored in the storage means, which is the inverted value of the positive and negative values, and the output value of the current transformer. . 2. The utility model registration, wherein the storage means is a sample & hold circuit for reading the output of the current transformer based on a timing signal generated at an arbitrary point during the switching element off period. Claim 1st
The current detector according to the item. 3. The current detection according to claim 2, wherein the timing signal is a signal output from a timer circuit triggered by a control signal for turning on the switching element. vessel.