JPS5963571A - Integrator for alternating current voltage - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for integrating an alternating current voltage by means of an operational amplifier with negative feedback via a capacitance. Such integrators are well known and are commonly used in measurement and control technology to process direct current flows. However, such an integrator is not suitable as it is for integrating alternating current voltage because there is always an output limit and drift occurs due to offset voltage.

It is therefore an object of the invention to design an integrator of the type mentioned at the outset in such a way that it is suitable for accurate and phase-fidelity integration of alternating voltages. This object is achieved according to the invention by an integrating device according to claim 1.

The present invention, including the embodiments described in claims 2 and below, will be explained in more detail with reference to the drawings.

The integrator 1 shown in FIG. 1 is negatively fed back via capacitor C1 in the usual manner and resistors R1 and R2.
It consists of an operational amplifier fed with an input voltage UE to be integrated via . The integration time constant of the integrator 1 is determined from the product of the capacitance value of the capacitor C1 and the sum of the resistance values of R1 and R2. If the input signal UE is sinusoidal,
At the output end of the integrator 1, a signal UA of the same sine wave plate appears, and its phase is exactly 90° more than the phase of the input voltage UE.
(electrical angle) is behind. However, in order to avoid this drift phenomenon, which always occurs due to a direct current source in the input circuit of an operational amplifier and a shift in zero point passage, a low-pass filter (smoothing circuit) consisting of a resistor R5 and a capacitor C2 is used. This DC component is taken out and given to an operational amplifier 2 located after the low-pass filter and connected as a PI circuit with resistors R6 and R7 and capacitor C3, and its output voltage is negatively fed back to the input side of the integrator 1. This PI circuit acts as a drift compensation regulator, and its output voltage is equal to the output signal UA since the DC component in the output signal UA disappears and the output signal UA becomes a pure sinusoidal voltage. changes in the direction of decreasing the DC component inside. The time constant of the smoothing circuit, which is determined by the resistance value of resistor R5 and the capacitance value of capacitor fC2, is suitably selected to be larger than the period T of alternating current voltage UE.

Now, since the output voltage UA of the integrator 1 is limited by the supply voltage of the operational amplifier, in the event of a large amplitude fluctuation of the input AC voltage UE, the output voltage UA will exceed the above limit unless special measures are taken. I bump into it. Thereby,
On the one hand, information about the amplitude of the input voltage UE or its time integral is lost, and on the other hand, phase errors occur in the output voltage UA. To avoid this phenomenon, resistor R2
By means of the bipolar electronic gate circuit 3 which bridges the integrator 1, the integration time constant of the integrator 1 is increased in time before the output limit is reached, such that the output voltage of the integrator 1 no longer hits this limit. For this purpose, a threshold circuit 4 is used which is provided with an output voltage UA. This threshold circuit has the characteristics as written in its block symbol. That is, if the input voltage e is within the range bounded by the settable threshold +Us and 10s, the signal a closes the opening/closing gap of the electronic gate circuit 3 and short-circuits the resistor R2.
If, on the other hand, the input voltage e exceeds the above range, this signal a disappears, thereby bringing the gate circuit into the open and closed position shown in FIG. 1, in which case the resistor R2 Current flows and the integral time constant increases. If the threshold value of the threshold circuit is lower than the output limit value of the operational amplifier, R1 and R2 are such that the output voltage UA of the integrator 1 does not exceed its output limit value upon amplitude fluctuations of the input voltage UB. That is, the operational amplifier can be chosen such that it is never overdriven. In FIG. 2, the effect of protection against overdriving is shown. Second
In the area marked ■ on the left side of the diagram, UA' is the virtual output voltage of the integrator that would occur if no output limit existed in this operational amplifier. This corresponds to a precise integration of the input voltage UE, as can be seen, for example, from the fact that the zero-point crossing of the voltage U8' takes place precisely at the extreme instant of the input voltage UE. However, since the output voltage UA is still limited to the value UAm -UAm, the output voltage U
An undesirable phase shift occurs in A. This phase shift is
According to the present invention, protection is provided against the auto (-) drive, so that it is avoided as shown in the right part (2) of FIG. After -Us has been exceeded, the time constant of the integrator 1 is increased so that the output voltage UA no longer reaches its limit and a phase-fidelity integration of the input voltage UE can subsequently be carried out without disturbances.

The integrator according to the invention is well suited for use in conjunction with a Rogowski coil for the measurement of large conductor currents. The Rogowski coil is known in the art and consists of a winding surrounding seven conductors with a core of non-magnetic material.

The voltage induced in the Rogowski coil by the alternating current flowing through the conductor is applied as an input voltage to the integrator according to the invention, the output signal UA of which can be used as a mapping of the alternating current flowing through the conductor.

If integration with high amplitude fidelity of the input voltage is desired during the time when the response threshold +Us or -Us of the threshold circuit 4 is exceeded, an additional device as shown in FIG. 3 may be provided. . This is because even after increasing the integration time by opening s# of switch 3, the information about the input signal UE to be integrated is still fully present in the output voltage UA, and the weighting of the output signal UA is changed by changing the integration time. It is based on the recognition that by corresponding changes it is possible to obtain a mapping that is proportional to the voltage UA at each point in time over the entire time range. To that end, a bipolar electronic gate circuit 5 is driven by the output signal a of the threshold circuit 4. The gate circuit 5, which acts as a changeover switch, is shown in the position it occupies when the output voltage UA exceeds the response threshold 10s or -Us. In this case, the output terminal 6 is given a voltage obtained by subtracting the voltage obtained by multiplying the threshold voltage Us by the coefficient (V-1)/V by the mixing circuit 7 from the output voltage UA of the integrator l. On the other hand, if the output voltage UA is within the responsive threshold of the threshold circuit 4, the gate circuit 5 is switched and the proportional circuit 8 sets the amplification factor 1/V to the output voltage UA of the integrator 1. The multiplied voltage is applied to the output terminal 6. Amplification factor 1/
V is determined by the ratio of the smaller integration time and the larger integration time of the integrator 1, and in the example shown in FIG. 3, ldl/V=R1/(R1+R2)f. The signal Ua produced at the output terminal 6 as shown in FIG. 1 is a signal obtained by integrating the input voltage UE at each instant with high phase and amplitude fidelity. This is only guaranteed for the output voltage UA of the integrator 1 in the operating state in which it is within the response threshold of the threshold circuit 4. It is expedient that the output signal a of the threshold circuit 4 is derived from one output terminal in order to be able to indicate such an operating state.

FIG. 4 illustrates the above-mentioned reconstruction of the map U8 of the integrated voltage UE. During the time from tl to 12, the input voltage is by a factor V-(R1+'R2)/ Integration is performed with an integration time larger by R1. Therefore, the voltage Ua during the time to-H and t2 to T/2 is the output voltage UA of the integrator l by a factor of 1/
This is the voltage reduced by multiplying by V. During the period from 11 to t2 when integration is performed using the larger integration time, the signal Ua
is the difference between the voltage UA and the threshold voltage Us plus a voltage U s /V of a constant magnitude. As a result, the curve of the output voltage Ua becomes smooth 0, that is, at the time t1
There is no breaking point in the value of UA/V at t2, and the relational expression Ua=UA/■ holds true over the entire range from tQ to T/2i.

Frequently, the expected amplitude fluctuations of the input voltage UE do not drive the processing device to a sufficient value and therefore cannot be utilized well. In such cases, it is advantageous to carry out an adaptive amplification of the reconstructed voltage Ua. 5 and 6 each show a circuit which is added to the integration device according to FIG. 3 in order to constantly amplify the voltage Ua to a voltage with a predeterminable constant amplitude. This constant amplitude voltage is indicated by Un in FIG.

In FIG. 5, the multiplier 9 is supplied with the voltage Ua taken out from the terminal 6 and the output signal Fn of the regulator 10 having integral characteristics. The output signal of multiplier lO is provided to amplitude detector 11. An amplitude detector 11 detects the respective maximum value of the output voltage Un of the multiplier 9 and produces a corresponding DC voltage signal un at its output.

For sinusoidal voltages, such an amplitude detector can in the simplest case consist of a rectifier followed by a low-pass filter. The output signal of the amplitude detector 11 is used as the actual value of the amplitude regulator 10 and is compared in a mixing circuit 12 with a certain setpoint value, for example an output voltage limit value UAm. The output quantity Fn of the integral regulator 10 causes the multiplier 9 to change the voltage Ua in the increasing direction until the voltage Un occurring at the output end of the multiplier 9 reaches a predetermined target value UAm.

In the device according to FIG. 6, the same amplitude detector 11 is provided and a ratio forming circuit t3 provides a ratio UAm/u1.
a is formed. The output signal Fn of the ratio forming circuit 13 is also changed by the multiplier 14 to increase the voltage Ua until the relational expression un = UAm 'where un is the amplitude of the AC voltage generated at the output terminal of the multiplier) is satisfied. let 6th
The device according to the figure operates dynamically more quickly than the device according to FIG. That is, there is an advantage that the voltage amplitude of Ua changes more quickly. In contrast, the advantage of the device according to FIG. 5 is that, since an integral adjustment circuit is used, the equilibrium condition, that is, the condition of UAm'''Ω, can be satisfied more precisely, especially in the event of a disturbance. With these devices, an output voltage Un with a normalized amplitude is obtained, and the normalization factor Fn is combined with the factor V to obtain the integrated input voltage from the relation UA' = U n - V/F n K. The exact value of the voltage UE is reached, so that the input voltage range of the downstream processing device can be better utilized.

[Brief explanation of the drawing]

Fig. 1 is a connection diagram of the integrator, Fig. 2 is a waveform diagram to explain the protection effect against overdrive, Fig. 3 is a connection diagram of the integrator when high amplitude fidelity is required, and Fig. 4 3 is a waveform diagram for explaining the operation of the integrating device of FIG. 3, and FIGS. 5 and 6 are connection diagrams of additional circuits when an output signal of a certain magnitude is required, respectively. ■, 2... operational amplifier, 3... gate circuit, 4
... Threshold circuit, 5... Gate circuit, 9...
- Multiplier, 10... Integral regulator, 11... Amplitude detector, 12... Mixing circuit, 13... Ratio forming circuit, 14... Multiplier.

Claims (1)

[Claims] 1) In a device for integrating an alternating current voltage using an operational amplifier which is negatively fed back through a capacitance and whose output is limited, a) a smoothing circuit connects an integrator in series with a PI circuit; an additional negative feedback circuit, b) driveable by the threshold circuit in order to extend the integration time when the output voltage of the FF amplifier exceeds a presettable threshold below the output limit value; 1. An alternating current voltage integrating device, characterized in that it is provided with a switching means. 2. An alternating current voltage integration device according to claim 1, characterized in that a bipolar electronic gate circuit for partially bridging the input resistance of an operational amplifier is provided as a switching means. . 3) An alternating current voltage integrating device, characterized in that it is used for integrating the output voltage of a Rogowski coil in the device according to claim 1 and claim 2. 4) In the device according to any one of claims 1 to 3, the output voltage of the integrator is related to the output signal of the threshold circuit and is amplified by an amplification factor of 1/■ through the proportional circuit.
(Here, ■ is the ratio of the larger integration time to the smaller integration time of the integrator) or the value obtained by multiplying the threshold value by the coefficient (V - 1)/V via a mixing circuit. An alternating current voltage integrator characterized in that a voltage corresponding to the subtracted voltage is applied to an output terminal. 5) In the device according to claim 4, the voltage occurring at the output terminal is modulated by the output signal of the PI regulator by the multiplier, and the PI regulator has a constant value as the target value and a constant value as the actual value. An alternating current voltage integration device characterized in that an amplitude value of a modulated voltage determined by an amplitude detector is provided. 6) The device according to claim 4, characterized in that the voltage appearing at the output terminal is modulated by a multiplier with a ratio between a constant value and its amplitude value determined by an amplitude detector. AC voltage integrator.