JPS63131070A - Current detection circuit - Google Patents

Abstract

PURPOSE:To enable detection of current in a broad frequency range, by providing high and low frequency transformers. CONSTITUTION:A current detection circuit is provided with a low frequency transformer T1 composed of a saturable core and a high frequency transformer T2 composed of a current transformer. Because the transformer T1 is saturated by a fine magnetic field, a current I flows through a winding L for detection of current and as a bias point shifts to a positive level, a current IP flows to the positive level in average through a winding LP for biasing of pulses by a positive pulse voltage of a pulse generator OS. Therefore, when a current IB flows to a feedback winding LB so that the current IP is down to zero, it is balanced at a point of cancelling a magnetomotive force generated by the current I. Thus, current up to 0 - scores of kHz can be measured. This also allows a detection windings LS of the transformer T2 to measure a high frequency current up to tens of Hz - scores of kHz. Current with the frequency 0 - scores of kHz can be measured by adding up detection currents of both the transformers T1 and T2 with a compensation circuit 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement of an isolated current detection circuit used in an AC servo motor or the like.

[Prior Art] An example of a circuit for driving an AC servo motor is shown in FIG.

In the figure, 01 to Q4 are 1 to transistors for driving the servo motor.

The collectors of transistors Q1 and Q3 are connected to a potential V+ higher than common, and the emitters of transistors Q2 and 04 are connected to common. The emitter of transistor Q1 is connected to the collector of transistor Q2, and the emitter of transistor Q3 is connected to the collector of transistor Q4. A coil L1 of an AC servo motor M and a current detection circuit S are connected between these connection points.

The current detection circuit S generates a voltage according to the detected current.

P is a subtracter, which takes the difference between the voltage U corresponding to the command value of the motor rotation speed and the output voltage of the current detection circuit S.

A is an amplifier, which amplifies the difference voltage obtained by the subtracter P.

C is a comparator that performs pulse width modulation (hereinafter referred to as PWM) by comparing the output voltage of the amplifier Δ with a triangular wave voltage and generating a binary signal according to the comparison result. The PWM signal is applied to the gates of transistors Q1 and 04, and the inverted signal of the PWM signal is applied to the gates of transistors Q2 and 03. As a result, transistors Q1 and Q4, Q2 and Q3 are driven alternately, and motor M
rotates.

Since the potential of the current detection circuit S is floating, an insulated type is used for this circuit.

Conventionally, the current detection circuit S uses a Hall element and a DC-C
Some used a DC current transformer) and others used a magnetic amplifier.

[Problem that Kiseri is trying to solve] However, the former current detection circuit has poor temperature characteristics, which causes an offset of, for example, several percent in the detection signal, which causes unnecessary vibration in the motor. However, there was a problem that the frequency range of the current that could be detected was narrow. Further, the latter ffi current ratio detection circuit has a problem of poor responsiveness.

The present invention has been made in order to simultaneously solve the above-mentioned problems, and an object of the present invention is to realize a current detection circuit that can detect current with high precision over a wide range and has good responsiveness.

[Means for Solving the Problems] The present invention provides a pulse bias winding that is composed of a saturable core, has a current detection winding wound on its primary side, and has a pulsed voltage applied to its secondary side. A feedback winding is wound to generate a magnetic flux such that the magnetic flux of the saturable core becomes O based on the current flowing through the pulse bias winding, and the current is detected by the current flowing through the feedback winding. It consists of a low frequency transformer that detects the low frequency component of the current flowing through the current transformer, and a current transformer, with the current detecting winding being wound on the primary side and the current detecting winding being wound on the secondary side. a high-frequency transformer wound with a detection winding that detects high-frequency components of current flowing through the circuit; and compensation means for compensating the gain and phase of the current detected by the feedback winding and the detection winding to produce a summed measurement current. This is a current detection circuit equipped with the following.

[Example] Hereinafter, the present invention will be explained using the drawings.

FIG. 1 is a block diagram of one embodiment of a current detection circuit according to the present invention.

In the figure, 1.2 is an input terminal to which a current detection winding is connected.

T is a low frequency transformer composed of a saturable core, a current detection winding is wound on the primary side, and a pulse bias winding Lp and a feedback winding Le are wound on the secondary side. There is.

B-H characteristics of low frequency transformer T'+ (B: magnetic flux density,
H: strength of magnetic field) is as shown in FIG.

Connected to the pulse bias 1 m Lp are a pulse generator O8 that generates a pulse waveform voltage that is symmetrical in the positive and negative directions, and a resistor Rp that detects the current flowing through the winding LP.

A feedback path for the detection current of the resistor RP is connected to one end of the feedback winding La, and a resistor Ra for current detection of the winding La is connected to the other end. The feedback path includes a subtracter S that calculates the difference between the detected current of the resistor Rp and the current command value (0 [△]), and a subtracter S.
It consists of a low-pass filter F that averages the difference signal between the two, and an amplifier U that amplifies the output of the low-pass filter and feeds it back to the winding.

T2 is a high frequency transformer made up of a current transformer, a current detection circuit IL is wound on the primary side, and a detection winding Ls is wound on the secondary side.

3 is a compensation circuit that compensates and adds the gain and phase of the current signals detected by the high-frequency transformer and the low-frequency transformer to detect the measured current, and the current detected by the feedback winding La has a transfer function of 1/( The high frequency current detected by the detection winding III L s has a transfer function of TS/ (1+TS).
After passing through the circuit 5, it is detected by the resistor R.

The operation of such a circuit will be explained.

Since the low-frequency transformer T+, which is composed of a saturable core, is saturated by a minute magnetic field H, current r flows through the current detection winding, and when the bias point shifts in the positive direction, the positive voltage of the pulse generator O8 increases. Due to the pulse voltage in the direction, current 1p flows in the pulse bias winding LP in the positive direction on average.
If a current ■B flows through a, the magnetomotive force n generated by the current ■
Equilibrium occurs at the point where ((n is the number of turns of the winding) cancels out.

That is, nBIa = n I (na is the number of turns of the winding La). Since n and n9 are known and Ia can be measured, the current ■ can be determined. In this way, O to several tens of Hz
Measure the current I up to.

On the other hand, a high frequency transformer T composed of a current transformer
2 detection winding Ls has a frequency of several 1 Of-1 z to several 10 kHz
High-frequency currents up to

By adding the detection currents of both transformers in the compensation circuit 3, it is possible to measure a current with a frequency of 0 to several tens of kl-IZ.

Circuit 4 has a transfer characteristic as shown in FIG.
Since it has a transfer characteristic as shown in the figure (G is gain), the current detected by the resistor R is mainly occupied by the detection current of the low frequency transformer T1 in the low frequency range, and is mainly occupied by the detection current of the high frequency transformer T1 in the high frequency range. It is occupied by the detection current of T2.

FIG. 5 is a diagram showing an example of application of the current detection circuit according to the present invention.

The circuit shown in FIG. 5 is a drive circuit for a three-phase AC servo motor.

In the figure, CT is the current detection circuit according to the present invention! 1 is a motor coil, 6 is a rectifier circuit for rectifying a power source 7, 8 is a gate drive circuit, 9 is an insulating circuit in which a light emitting element and a light receiving element are opposed, and 10 is a pulse width modulation circuit.

In such a circuit, the current detected by the current detection circuit CT is fed back to the motor drive circuit.

[Effects] According to the present invention, since a high frequency transformer and a low frequency transformer are used, current can be detected over a wide frequency range. Furthermore, since the current is detected using a winding, responsiveness is improved.

Furthermore, since the detection is performed using the zero-level method, nonlinearity of the current detection means can be reduced. In addition, since detection is performed using pulse signals with positive and negative symmetry, Gt is less affected by the temperature characteristics of the saturable transformer.

Because of this, offset and drift are reduced, and current can be detected with high accuracy.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the current detection circuit according to the present invention, Fig. 2 is a graph of the B-H characteristics of the saturable transformer, and Figs. 3 and 4 show the transfer characteristics of the compensation circuit. 5 is a diagram showing an example of application of the current detection circuit according to the present invention, and FIG. 6 is a diagram showing an example of a motor drive circuit in which the current detection circuit is used. 1.2...Input terminal, 3...Compensation circuit, T,...
Low frequency transformer NT2... High frequency transformer, L.
...Current detection winding, LP...Pulse bias winding, LB...Feedback winding, Ls...Detection winding, O8...
・Pulse generator, S...depletion device, F...low pass filter, U...amplifier. Figure 1 Figure 3 Figure 4 Tokakan degree W- Figure 5 Figure 4

Claims (1)

[Claims] A pulse bias winding composed of a saturable core, a current detection winding wound on the primary side, and a pulse voltage applied to the secondary side, and the pulse bias winding A feedback winding is wound that generates a magnetic flux so as to reduce the magnetic flux of the saturable core to 0 based on the flowing current, and the current flowing to the feedback winding reduces the current flowing to the current detection winding. It consists of a low frequency transformer that detects frequency components and a current transformer, with the current detection winding wound on the primary side and the high frequency component of the current flowing through the current detection winding on the secondary side. A current detection circuit comprising: a high-frequency transformer around which a detection winding is wound; and compensation means for compensating the gain and phase of the current detected by the feedback winding and the detection winding to obtain a summed measurement current.