JPS6039181B2 - Reactive power detection method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a reactive power detection method.

Detection of reactive power is important in various power devices.

The instantaneous value and effective value of the power supply voltage (load voltage) of one phase are represented by OR and E, respectively, and the instantaneous value and effective value of the load current are represented by IR and IR, respectively. Assuming that there is a delay by an angle, t of eR: ノ2E Sm
...E}IR=Nogen IR SIN (of t-)
...[21, and the reactive power QR of this phase is QR-EI
The RSN is represented by …[3} (
However, represents the angular frequency and t represents the time).

As a conventional reactive power detection method, the voltage expressed by the above equation '1} is passed through a bamboo/2 phase shifter, and a voltage e'=no2ES river (■t-m /2) and input this to the multiplier together with the current value expressed by the above formula {2}, q = e' x iR
．． A known method is to obtain the output {4}, pass it through a filter, remove the ripple component of the second term on the right side of equation (2), and extract only the first term on the right side of equation {4}.

This method has the disadvantage that it cannot follow sudden changes in load, such as in the arc furnace load, because a detection delay is caused by the filter. Note that in the case of a three-phase symmetrical load, the ripple component can be eliminated by adding the instantaneous values of the voltages of each phase, but since a general three-phase load (especially an arc furnace load) is asymmetrical, even in the case of a three-phase load, the filter component cannot be removed. As a result, a delay in detection is inevitable. The purpose of the present invention is to eliminate the drawbacks of the prior art as described above, eliminate detection delay, and eliminate the influence of waveform distortion! The object of the present invention is to provide a method for detecting high reactive power.

The present invention separately detects reactive power QR=EIRSIN as ESIN (or SIN) and IR, and calculates the value of reactive power by multiplying these detected values, and , ESIN and IR is a predictive detection method, i.e. the ESI is detected within a time period in which the sine wave of voltage E or current IR does not pass through one-half cycle.
This is done by a method of predictively obtaining values representative of N (or SIN) and IR. The present invention will be described below with reference to the drawings.

As mentioned above, the present invention provides reactive power QR=EIRSIN
is divided into ESIN and IR, predicted and detected separately, and obtained as the product of these predicted detection values.

Figure 1 illustrates an example of a predictive detection method for load current, in which the load current waveform is integrated from a cloud passage point B where the load current waveform changes from negative to positive or from positive to negative to a point at a predetermined time T. The fact that the value obtained is proportional to the effective value IR or peak value 21R of the load current is utilized.

That is, Paiso T (t) = ノ21R [1 COS (t-)] 2 hairs ≦ hair 10 T nino 21R
1-C.

6 T), and when T is constant, the integral value is proportional to R.

Further, as a method for detecting the power supply voltage plus SIN or ESIN, for example, in FIG. 1, a method may be used in which the instantaneous value of the power supply voltage at point B is sampled and held.

Another method is to detect the phase difference by utilizing the fact that the value obtained by integrating a certain constant voltage from the zero point A of the power supply voltage waveform to the zero point B of the load current is proportional to, for example,
It may be passed through a sine function generator to obtain the value of SIN◇, and the effective value E of the power supply voltage may be subtracted from this value. Normally, the obtained final detection signal is used to control the reactive power compensation bag counterfeit, but this control is performed in proportion to the detection signal, so the detection signal itself does not need to represent the actual value. A signal proportional to the actual value is sufficient, and whether or not control is performed correctly is a matter of setting the proportionality constant of the control device. For that reason, in practice, it is sufficient to find SIN without even finding ESm. Figure 2 shows a block diagram of a circuit configuration in which the predictive detection method as described above is used to detect IR and the instantaneous value sampling and holding method as described above is used to detect ES. A time diagram of the signals appearing at various points in the circuit of FIG. 2 is shown.

For example, a military pressure extraction means consisting of a voltage transformer PT, a heron current extraction means consisting of a current transformer CT, comparators CP(1) and CP(b), a logic circuit LOGIC, such as a monostable multipipelator MS. Time setting means, integrator I
NT, sample and hold circuit SH, and multiplier MULT are connected as shown in FIG. As shown in FIG. 3, comparators CP(1) and CP(b) generate polarity determination signals for voltage eR and current IR, respectively,
The logic circuit LOGIC controls the siple holding circuit SH and the integrator T in accordance with these polarity determination signals.

The sample holding circuit SH is the third one from the logic circuit LOGIQ.
It is controlled as shown in the waveform "LOGIC-SH" in the figure. That is, each time the voltage e passes through zero, the sample mode is set from that point A to the zero point B of the current i, and the voltage e is tracked during this period, and the current i is set to the zero point B.
is switched to the hold mode at the moment when the current i passes through the hold mode, and is therefore controlled to hold the instantaneous value at zero point B of the current i during the hold mode, i.e., the value proportional to ESIN, as shown in the waveform "SH". produces output like this.

The integrator INT is controlled by the logic circuit LOGIC and the monostable multipipulator MS as shown by the waveform "LOGIC-mT".

That is, each time the current i passes through the zero point B, the integral mode is set for a certain period of time T determined by the monostable multipipulator MS, and the holding mode is set for the rest of the time. To reset the integrator INT for the next integration near the end of each half-wave of the voltage waveform, e.g.
A reset signal ``RESET'' is generated using ``I''. In this way, a signal having a peak value of 21R (T of 1-COS) as shown in the waveform nNT is generated from the integrator state T. Therefore, the output of the multiplier MULT is a signal having a peak value proportional to EIRSm as shown by the waveform "MULT", which is directly or through another sample holding circuit as a reactive power detection output. taken out.

As is known from the above description, the present invention predicts and detects reactive power within an extremely short period of time, such as one-half cycle of a sine wave of current or voltage. The reactive power value obtained can be immediately used in the second half of the same half wave to control the reactive power compensator, and the adverse effects caused by the detection delay can be eliminated.

For example, when performing reactive power compensation with the configuration shown in FIG. 4, control without delay is possible by performing predictive detection as in the present invention. In FIG. 4, Qs is the reactive power of the system, Qc is the reactive power of the fixed phase advanced reactive power generating section consisting of capacitor 8, Q^ is the reactive power of load 5, and Qs
R represents the reactive power of the variable delayed phase reactive power generation section consisting of the thyristor 6 and the inductance 7, and 1 represents the Q
^ Prediction detector, 2 is the QsR command calculator, 3 is the thyristor firing angle adjuster, 4 is the pulse amplifier, 5 is the load, 6 is the thyristor, based on the information obtained by the QA prediction detector 1 The QsR command calculator 2 performs calculations, controls the signal of the thyristor firing angle regulator 3 according to the calculated value, and finally controls the firing angle of the thyristor 6 to maintain the Qs of the system constant. It is. Generally, the variation range of the phase of the load current is from 0 to 0/2, and the thyristor firing range Q of the compensator is from 0/2 to 0/2. growing. Therefore, according to the method of the present invention, the reactive component is detected in the first half period of a half-wave (1/2 cycle) of the load current, and the compensation device is used between Q; Compensation for each half wave is possible by firing the thyristor and passing the current to be compensated. This is illustrated in Figure 5. To explain briefly, the circuit shown in Fig. 2 responds to a change in Q within a range of 0 to m/2, Q changes within a range of m/2 to m, and according to the magnitude of Q, The current flowing through the thyristor is
The fundamental wave reactive component of R changes to keep Qs constant. As is known from the above description, the present invention detects reactive power within a time period in which the sine wave of the load current does not pass through one-half cycle.

Regarding the predictive detection of current, it is possible to consider a method of detecting the instantaneous value of the current after a certain period of time from point B in Fig. 1, for example, but this method causes distortion of the current waveform in loads such as arc furnaces. is significant, and the error becomes large. In contrast, in the present invention, since the integrated value of the current is used, the influence of harmonics is reduced, and malfunctions due to noise current are also prevented. For example, wT = electrical angle 3
60o/5=When electrical angle 7 is (50 days 2, T 4ms
), the influence of the fifth harmonic in the load current can be removed. (However, if T is chosen too large, compensation within half a wave will not be possible due to the ignition delay. Therefore, it is necessary to select an appropriate value to the extent that the ignition delay does not pose a problem in practice.) Therefore, the present invention is more useful than the conventional system in this respect as well.

[Brief explanation of drawings]

Figure 1 is a schematic diagram illustrating the load current predictive detection method;
FIG. 3 is a block diagram showing an example of a circuit configuration for implementing the present invention, FIG. 3 is a time diagram showing the timing of signals appearing at various points in the circuit of FIG. 2, and FIG. 4 is an example of a reactive power compensator. FIG. 5 is a schematic diagram showing the time relationship of the operation of the device of FIG. 4. PT: Potential transformer, CT: Current transformer, CP (1), CP
(D): Comparator, LOGIC: Logic circuit MS: Monostable multi/wave controller, SH: Sample holding circuit, I
NT: Integrator, MULT: Multiplier, 1: Q^ prediction detector, 2: QsR command calculator, 3: Thyristor firing angle adjuster, 4: Pulse amplifier, 5: Load, 6: Thyristor. Figure 5 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. In a method of detecting the reactive power of a load having a power factor angle ψ, a value proportional to the effective value of the load current and a value proportional to SINψ times the power supply voltage are respectively set to these load currents or power supply voltages. characterized in that it comprises respective means for detecting a sinusoidal wave of voltage within a time period which does not pass through one-half cycle, and means for receiving these detected values and generating a signal representative of their product. reactive power detection method. 2. In the reactive power detection method set forth in claim 1, the means for detecting a value proportional to the effective value of the load current is a predetermined value shorter than one-fourth cycle of the current waveform from the zero point passing point of the load current waveform. This is an integrating circuit that integrates the load current waveform up to a point in time, and the means for detecting a value proportional to SINψ times the power supply voltage is a sample holding circuit that samples and holds the instantaneous value at the above-mentioned zero point passing point of the load current waveform. A reactive power detection method characterized by a circuit.