GB1604602A

GB1604602A - Voltage monitoring circuit

Info

Publication number: GB1604602A
Application number: GB23628/78A
Authority: GB
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1977-06-10
Filing date: 1978-05-26
Publication date: 1981-12-09
Also published as: DE2726282A1; DE2726282B2; DE2726282C3; CA1129005A; SE7806369L

Description

(54) VOLTAGE MONITORING CIRCUIT (71) We, SIEMENS AKTIENGESELLSCHAFT, a German company of Berlin and Munich, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a voltage monitoring circuit.

Utilising the fact that A2 sin2wt + A2 cos2t = A2, it is known to form a corresponding cosine-wave voltage (orthogonal component) from a given sine-wave voltage by means of phase rotating elements and to square both voltages and sum the squares so as to theoretically determine the value A2.

The phase rotating elements involve either a non-negligible time delay of at least 1 ms (up to approximately 3 ms) and a frequency dependency (all-pass behaviour), or they exhibit powerful harmonic or relative harmonic sensitivity which has to be compensated for by supplementary time delay producing smoothing means.

According to the present invention, there is provided a circuit for continuously monitoring the peak value of an alternating voltage, which circuit comprises: (a) a multiplier for squaring the voltage; (b) an inverter for inverting the output signal from the multiplier; (c) a first adder for adding the output signal from the mulitplier to a further signal; (d) a second adder for adding the output signal from the inverter to a calculated signal and for supplying its output signal to the first adder as the said further signal; and (e) control means connected with the outputs of the first and second adders and with an input of the second adder, for producing the said calculated signal, which calculated signal is proportional to the square of the peak value, from a predetermined value and from signals obtained from the first and second adders.

The invention will now be described, by way of example, with reference to the single Figure of the accompanying drawing, which shows a block diagram of an embodiment of a voltage monitoring circuit according to the present invention.

Referring to the Figure, an alternating voltage Â sinot to be monitored is supplied to a zero-point-adjustable multiplier 1 in which the voltage is squared. The output value A2 sin2co t of the multiplier 1 is fed directly to a first input of a first adder 2 and also to an inverter 3 in the form of an operational amplifier having an amplification factor of "one". The output value -Â2sin2ott of the inverter 3 is fed to a first input of a second adder 4. To the second input of the second adder 4 there is fed a calculated signal. The calculated signal is supplied by control means comprising circuit elements 5 to 14 and connected between the output of the first adder 2 and the second input of the second adder 4. At the output of the second adder 4 there is produced a value which is supplied to the second input of the first adder 2. The resulting voltage at the output of the first adder 2 is supplied to the control means.

The control means comprises a third adder 5 having an input connected with the output of the first adder 2 and another input connected with a proportional amplifier 11 which has a variable amplification factor and which is arranged to feed-back - and effect sign reversal of - the calculated signal produced by the control means in use. The output of the third adder 5 is connected with a first input of a fourth adder 7 via a proportional amplifier 6 having a derivative function (a proportional-plus-derivative (PD) controller). A second input of the fourth adder 7 is connected with the output of the second adder 4 via a porportional amplifier 10 and a blocking diode 14.

The output of the fourth adder 7 is connected with the input of an integrating amplifier 8 (a J-controller) having a short integration time. The output of this integrating amplifier 8 is connected with an input of a further zero-point-adjustable multiplier 9.

A further input of the multiplier 9 is supplied by a maximum value generator 12 which, in use, generates a predetermined direct voltage Amax equal to the maximum peak value of the altemating voltage Â sinoat which is to be monitored. Thus, the voltage amplitude Â monitored may only be less than or equal to Amax.

The output of the multiplier 9, from which the calculated signal Is obtained in use, is connected with the second input of the second adder 4 via a further blocking diode 13. The output of the multiplier 9 is also connected with the third adder 5 via the proportional amplifier 11, as already described.

The voltage monitoring circuit is also suitable for monitoring currents insasmuch as these can be represented by currentproportional voltages.

Such a voltage monitoring circuit can be used not only for monitoring the peak value of a sinusoidally varying voltage but also for monitoring a variable which, independently of frequency variation, rapidly follows the peak value variations of a distorted alternating quantity.

In order to obtain an output from the circuit having only slight ripples, without supplementary smoothing outlay, the proportional amplifier 10 may be adjusted or adapted so as to have an amplification factor Vp between 1 and 10 and the proportional amplifier 6 may be adjusted or adapted so as to have an amplification factor Vp of approximately 2; furthermore, the proportional amplifier 11 may be adjusted or adapted so as to have an amplification factor V between zero and 2. p A rapidly integrating monitoring circuit 0. O. lms) for monitoring peak values within a range of -50% to +100% of the starting value, with a substitute-time con stant 5 < 0.1 ms and a unidirectional voltage ripple value of less than + 2% at 50 Hz, is therefore provided. With this circuit the d.c.

variable (precisely stated, the square there of) is formed by means of integration with separate sign control. The separate control sections for upward and downward control of the amplitude are produced by providing a weak counter-coupling, which influences the curve form as to the synchronous or unidirectional variable, thereby descreasing the ripple factor, despite the short integration time t < 0.its, which, alone, determines the time behaviour of the circuit, if the transfer behaviour of the integrating elements (operational amplifiers) in the MlIz range is neglected. The circuit is in particular advantageous for controlling static phase-shifters and also electronic protective and control devices.

The voltage monitoring circuit described is able to monitor the peak value of a voltage, or a value proportional to the peak value, with only a small time delay and to a considerable degree independently of frequency variations and the curve form of the voltage and within a large range of starting values, without utilizing supplementary smoothing means.

WHAT WE CLAIM IS: 1. A circuit for continuously monitoring the peak value of an alternating voltage, which circuit comprises: (a) a multiplier for squaring the voltage; (b) an inverter for inverting the output signal from the multiplier; (c) a first adder for adding the output signal from the multiplier to a further signal; (d) a second adder for adding the output signal from the inverter to a calculated signal and for supplying its outputs signal to the first adder as the said further signal; and (e) control means connected with the outputs of the first and second adders and with an input of the second adder, for producing the said calculated signal, which calculated signal is proportional to the square of the peak value, from a predetermined value and from signals obtained from the first and second adders.

2. A circuit according to claim 1, for continuously monitoring the peak value of a substantially sinusoidally varying voltage.

3. A circuit according to claim 1 or 2, wherein the control means incorporates a third adder for adding the output signal from the first adder and the calculated signal inverted.

4. A circuit according to claim 3, wherein the control means further incorporates a first proportional amplifier coupled to the output of the third adder.

5. A circuit according to claim 4, wherein the first proportional amplifier is a PD-controller.

6. A circuit according to claim 4 or 5, wherein the control means further incorporates a fourth adder for adding the output signal from the first proportional amplifier to a signal derived via a diode and a second proportional amplifier from the output of the second adder.

7. A circuit according to claim 6, wherein the control means further incorporates an integrator for integrating the output signal from the fourth adder.

8. A circuit according to claim 7, wherein the control means further incorporates means for supplying a value proportional to the maximum value of the peak voltage, and a further multiplier for multiplying this

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The output of the fourth adder 7 is connected with the input of an integrating amplifier 8 (a J-controller) having a short integration time. The output of this integrating amplifier 8 is connected with an input of a further zero-point-adjustable multiplier 9. A further input of the multiplier 9 is supplied by a maximum value generator 12 which, in use, generates a predetermined direct voltage Amax equal to the maximum peak value of the altemating voltage Â sinoat which is to be monitored. Thus, the voltage amplitude Â monitored may only be less than or equal to Amax. The output of the multiplier 9, from which the calculated signal Is obtained in use, is connected with the second input of the second adder 4 via a further blocking diode 13. The output of the multiplier 9 is also connected with the third adder 5 via the proportional amplifier 11, as already described. The voltage monitoring circuit is also suitable for monitoring currents insasmuch as these can be represented by currentproportional voltages. Such a voltage monitoring circuit can be used not only for monitoring the peak value of a sinusoidally varying voltage but also for monitoring a variable which, independently of frequency variation, rapidly follows the peak value variations of a distorted alternating quantity. In order to obtain an output from the circuit having only slight ripples, without supplementary smoothing outlay, the proportional amplifier 10 may be adjusted or adapted so as to have an amplification factor Vp between 1 and 10 and the proportional amplifier 6 may be adjusted or adapted so as to have an amplification factor Vp of approximately 2; furthermore, the proportional amplifier 11 may be adjusted or adapted so as to have an amplification factor V between zero and 2. p A rapidly integrating monitoring circuit 0. O. lms) for monitoring peak values within a range of -50% to +100% of the starting value, with a substitute-time con stant 5 < 0.1 ms and a unidirectional voltage ripple value of less than + 2% at 50 Hz, is therefore provided. With this circuit the d.c. variable (precisely stated, the square there of) is formed by means of integration with separate sign control. The separate control sections for upward and downward control of the amplitude are produced by providing a weak counter-coupling, which influences the curve form as to the synchronous or unidirectional variable, thereby descreasing the ripple factor, despite the short integration time t < 0.its, which, alone, determines the time behaviour of the circuit, if the transfer behaviour of the integrating elements (operational amplifiers) in the MlIz range is neglected. The circuit is in particular advantageous for controlling static phase-shifters and also electronic protective and control devices. The voltage monitoring circuit described is able to monitor the peak value of a voltage, or a value proportional to the peak value, with only a small time delay and to a considerable degree independently of frequency variations and the curve form of the voltage and within a large range of starting values, without utilizing supplementary smoothing means. WHAT WE CLAIM IS:

1. A circuit for continuously monitoring the peak value of an alternating voltage, which circuit comprises: (a) a multiplier for squaring the voltage; (b) an inverter for inverting the output signal from the multiplier; (c) a first adder for adding the output signal from the multiplier to a further signal; (d) a second adder for adding the output signal from the inverter to a calculated signal and for supplying its outputs signal to the first adder as the said further signal; and (e) control means connected with the outputs of the first and second adders and with an input of the second adder, for producing the said calculated signal, which calculated signal is proportional to the square of the peak value, from a predetermined value and from signals obtained from the first and second adders.

value by the output signal from the integra tor to produce the calculated signal.

9. A circuit according to claim 8, where in the output of the further multiplier is coupled to the second adder by way of a further diode.

10. A circuit according to claim 8 or 9, wherein the control means further incopo rates a third proportional amplifier for deriving the inverted value of the calculated signal.

11. A circuit according to claim 8, 9 or 10, wherein the mulitpliers are zero-point adjustable.

12. A circuit according to claim 10, wherein the second proportional amplifier is 'adjusted or adapted so as to have an amplification factor 1 < Vp < 10, the third proporational amplifier is adjusted or adapted so as to have an amplification factor 0 < Vp < 2 and the first proportional amplifier is adjusted or adapted so as to have an amplification factor V > 2.

13. A circuit for continuously monitor ing the peak value of an alternating voltage, which circuit is substantially as hereinbefore described with reference to the accompany ing drawing.