JPH05232157A - Voltage drop detection device - Google Patents

Abstract

PURPOSE:To simplify circuit configuration or software configuration while maintaining high-speed detection by multiplying a voltage waveform of each phase of three-phase AC by a three-phase sinusoidal signal of the same phases. CONSTITUTION:A PLL 22 is in synchronization with a detection voltage and generates a three-phase sinusoidal signal of a constant voltage. The PLL 22 is in synchronization with the detection voltage and generates N synchronization pulses in one period or half period of sinusoidal wave and a counter 23 is reset at a zero-cross point and counts the number of synchronization pulses. Multipliers 30-32 and an adder 33 constitute operation means, the voltage signal of each phase from a detector 21 and the sinusoidal signal of the corresponding phase from D/A converters 27-29 are multiplied by multipliers 30-32 and then the multiplication results are added by the adder 33. A comparator 34 and a timer 35 constitute a comparison means, the output and setting voltage of the adder 33 are compared by a comparator 34, the timer 35 starts counting when the output of the adder 33 is equal to or less than the setting voltage, and then an output change of the timer 35 is output as a voltage reduction signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage drop detecting device for detecting a power failure or an instantaneous voltage drop of a three-phase AC power supply.

[0002]

2. Description of the Related Art A constant commercial power supply type uninterruptible power supply, an uninterruptible different system switching device, etc. detect a three-phase AC voltage drop and switch to an inverter or a different system power source, and supply uninterruptible power to a load. To do. These devices require high-speed detection of voltage drop.

A conventional voltage drop detection method will be described below.

(1) Instantaneous value comparison and detection method FIG. 4 shows an absolute value type circuit diagram. The system voltage to be detected is sampled by the sample and hold circuit 1 and detected by the A / D converter 2 as a sampled digital signal. On the other hand, the system voltage is the waveform shaping circuit 3
Is converted into a square wave signal by and is taken out as a pulse signal of N times the system frequency synchronized by the PLL circuit 4.

The output pulse of the PLL circuit 4 is used for the sampling timing of the sample and hold circuit 1 and is also input to the counter 5 for counting. This counter 5
Is reset by the zero-crossing point timing signal of the system voltage waveform by the edge detection circuit 6 to obtain a count value synchronized with the sampling pulse of the system voltage. The ROM 7 obtains a sine wave sample value by using the count value of the counter 5 as an address. The comparator 8 uses the sample value of the ROM 7 as a comparison reference and detects whether the digital signal of the A / D converter 2 is lower than the comparison reference by a predetermined value or more (voltage drop). The counter 9 obtains a voltage drop detection output when the voltage drop detection by the comparator 8 continues for a certain period of time.

In contrast to the absolute value type described above, in order to compare the instantaneous value of the relative value type, the digital signal of the A / D converter 2 is written in the RAM as past data for half cycle or one cycle instead of the ROM 7. , And compares the sampled value with the current value of the A / D converter 2.

(2) Average value comparison / detection method In this method, three-phase alternating current is full-wave rectified and then converted into a DC signal from which ripple components have been removed by a CR filter, and this DC signal is more predetermined than the comparison reference DC signal. The voltage drop is detected when the voltage drops below the specified value.

(3) Three-phase voltage sum of squares method In this method, as shown in FIG.
sin ωt, E sin (ωt-2π / 3), E sin (ωt-4π
/ 3) is respectively squared by the multipliers 10, 11, and 12, the sum of these is calculated in the adder 13, and the result is compared with the comparison reference Vset by the comparator 14 to detect the voltage drop. .

The output Y of the adder 13 is

[0010]

[Equation 1]

[0011] obtain a DC value 3E ^2/2 proportional to the voltage E from.

[0012]

FIG. 6 shows the voltage drop detecting operation in the conventional instantaneous value comparison and detection method. Time t at the moment when the system voltage from the A / D converter 2 decreases and crosses the reference voltage with respect to the reference voltage from the ROM 7.
_{At 0} , the voltage drop detection output is obtained from the comparator 8.

When this detection output is used as a voltage drop detection signal, the detection time is shortened, but malfunctions are likely to occur due to the influence of noise and the like. Therefore, it is calculated by the counter 9 that the detection of the comparator 8 continues for a fixed time Δt, or the integrated value V of the difference ΔV between the system voltage and the reference voltage.

[0014]

[Equation 2]

The voltage drop is detected when the voltage exceeds a certain value.

In this detection method, the calculation of the integral value V requires an integral calculation to complicate the circuit, and the integral value depends on the timing of system voltage drop (for example, the 45-degree point and the 135-degree point of the sine wave). However, there is a problem that the time required for detection changes due to the change of the.

On the other hand, when the counter 9 continues for a certain period of time, there is almost no difference between the system voltage and the reference voltage at the zero crossing point of the sine wave and the zero crossing point of 180 degrees, and the level comparison by the comparator 8 is likely to be erroneous. In order to eliminate this error, it is necessary to suppress the application of the result of comparison near the zero cross to the counter 9. As described above, there is a problem that comparing the AC amounts with instantaneous values requires various corrections and compensations and complicates the circuit or software.

Next, in the average value comparison and detection method, when trying to obtain high accuracy by increasing the detection level, the time constant of the CR filter for ripple removal becomes large, resulting in poor response and high-speed detection. Can not.

Next, in the voltage-squared sum method, when the three-phase voltage drops uniformly, the detection voltage Y has no ripple and can be detected at high speed. However, if there is variation in the rate of decrease in each phase voltage, the voltage drops. There is a problem that the detection time becomes long due to the influence of the slow phase.

It is an object of the present invention to provide a voltage drop detecting device which has a relatively simple circuit structure or software structure while achieving high speed detection.

[0021]

In order to solve the above-mentioned problems, the present invention provides a voltage detecting means for obtaining a voltage waveform of each phase of a three-phase alternating current to be detected, and a voltage detecting means for obtaining the voltage waveform. A sine wave generating means that generates a three-phase sine wave signal of a constant voltage in synchronization with the voltage waveform, and the three-phase sine wave signal and each phase voltage waveform of the three-phase alternating current are multiplied in the same phase, and each multiplication result is obtained. And a comparing means for obtaining the three-phase AC voltage drop detection signal when the calculation result of the calculating means reaches a set value or less and continues for a predetermined time.

[0022]

[Function] Vector V = for performing three-phase alternating current voltage waveforms
Represented by [Va, Vb, Vc], each element Va, Vb, Vc
To

[0023]

[Equation 3]

It is assumed that

A constant voltage of 3 is synchronized with the voltage waveform of each phase.
Vector C = [Ca, Cb, Cc] for performing phase sine wave signal
When the row vector V is multiplied by the transposed matrix C ^T of the row vector C, the three-phase voltage is converted to the synchronous rotation coordinate, and if the magnitude of the three-phase AC voltage is balanced, A constant DC amount is obtained as shown by.

[0026]

[Equation 4]

From the above, the three-phase sine wave of the above equation (3) is generated by the sine wave generating means, and the multiplication between the same phase and each multiplication result are added by the calculating means, and this is shown in the above equation (4). Obtain a constant DC amount. This DC amount is such that at a certain time, the row vector C is constant and the row vector V changes due to the voltage change of the three-phase AC, and the voltage drop appears as a DC level drop. The detection of the voltage drop is obtained from the DC level by detecting the decrease in the DC level by the comparison means.

Here, since the multiplication result between the same phase is added to the multiplication by the calculating means, even when one phase of the three-phase voltage is at the zero cross point, the other phases are at 120 degrees and 240 degrees. The calculation result does not become zero, and the comparison means does not require a means for suppressing the comparison in the vicinity of the zero-cross point even for the determination of continuation for a certain time by a counter or the like.

Further, by using the instantaneous voltage comparison, high-speed detection equivalent to the instantaneous value comparison detection method can be obtained. Further, as in the case of the sum-of-squares method, a DC amount with no pulsation in the detection signal is obtained to facilitate the determination of the voltage drop.

[0030]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. The voltage detector 21 detects a voltage waveform of each phase from a three-phase AC power supply to be detected such as a commercial power supply. This voltage signal corresponds to the above-mentioned equation (3).

PLL 22, counter 23, ROM 24,
25 and 26 and the D / A converters 27, 28 and 29 constitute a sine wave generating means and generate a three-phase sine wave signal of a constant voltage in synchronization with the detection voltage Vcos ωt. The PLL 22 generates N sync pulses in one cycle or a half cycle of the sine wave in synchronism with the detection voltage, the counter 23 is reset at the zero-cross point and counts the sync pulses, and the ROMs 24, 25, 2
Reference numeral 6 denotes a D / A converter in which half-cycle or one-cycle sample values of a sine wave are written with a phase difference of 120 degrees with each other and the sine wave sample value data is sequentially output using the count value of the counter 23 as an address. 27, 28 and 29 are ROMs 24 to 2
A sine wave signal is obtained by sequentially converting the sample value data from 6 into an analog signal. The outputs of the ROMs 24 to 26 are such that the voltage V is constant according to the above equation (3).

The multipliers 30, 31, 32 and the adder 33 constitute an arithmetic means, and each phase voltage signal from the detector 21 and D /
The in-phase sine wave signals from the A converters 27, 28 and 29 are multiplied in-phase by the multipliers 30 to 32, and the multiplication results are added by the adder 33. This calculation result shows that if the magnitude of the detected voltage is balanced from the equation (4), the constant DC amount is 3V.
/ 2.

The comparator 34 and the timer 35 constitute a comparing means, and the output of the adder 33 and the set voltage Vset are compared with each other by the comparator 34.
When the output of the adder 33 becomes equal to or lower than the set voltage, the timer 35 starts counting time, and this state is
When it continues beyond the time limit of, the output change of the timer 35 is taken out as a voltage drop detection signal.

According to the present embodiment, the detection speed of the voltage drop is as high as that of the instantaneous value comparison method, and the sine wave generating means is added to the voltage square sum circuit in terms of the circuit configuration. Unlike the value comparison method, there is no need for means for suppressing calculation at the zero-cross point or means for integration, and the structure is relatively simple.

In this embodiment, the hardware configuration is shown, but most of it can be realized by a software configuration by a computer. For example, each phase voltage waveform from the voltage detector 21 is taken into a computer as sampling data by a sample hold circuit, a multiplexer circuit, and an A / D converter, and multiplication, addition, comparison with a sine wave sample data held as table data and a timer are performed. It is realized by preparing a computer with software that repeats each processing of calculation.

The voltage drop detection test based on the present invention was carried out together with the conventional instantaneous value comparison detection system and voltage square sum system tests. As a test target, the pole switch at a certain point in the high-voltage distribution system was opened, and the response waveform to the voltage drop (blackout) on the load side from this point at this time was obtained by simulation with EMTP.

Tests were conducted both when the phase advancing capacitor was coupled to the load side and it took time to reduce the residual voltage, and when the phase advancing capacitor was not connected. In addition, the comparison between the reference value and the detection signal is performed by software, and the judgment level (reference value) is 80% of the steady value of the detection signal.
And

FIG. 2 shows a simulation waveform diagram when there is no capacitor on the load side. FIG. 2 (a) shows the line voltage waveform, and FIG. 2 (b) shows the voltage detection signal and the voltage drop discrimination according to the method of the present invention. The signals are shown in (c) of the voltage detection signal and the voltage drop determination signal in the voltage sum of squares method.

FIG. 3 shows a simulation waveform diagram when there is a capacitor on the load side. FIG. 3 (a) shows the line voltage waveform, and FIG. 3 (b) shows the voltage detection signal and the voltage drop discrimination according to the method of the present invention. The signals are shown in (c), and the respective signals in the sum of voltage squares method are shown.

The simulation result and the calculation result of the instantaneous value comparison method become the discrimination time in the following table.

[0041]

[Table 1]

In the instantaneous value comparison method, the time required for the waveform of each phase voltage to be synchronized with it and for the magnitude to fall below the sine wave signal of 80% of the phase voltage was calculated.

From this result, the method of the present invention has almost the same responsiveness as the instantaneous value comparison method regardless of the presence or absence of the capacitor,
Compared to the sum of squared voltage method, it is possible to detect a voltage drop with faster response. In particular, when a capacitor is connected to the system and the residual voltage between the lines is large, the difference in response becomes large.

[0044]

As described above, according to the present invention, each phase voltage of the three-phase alternating current and the three-phase sine wave signal generated in synchronization with this are multiplied in-phase, and the respective multiplication results are added. By converting the three-phase AC voltage on the synchronous rotation coordinate to obtain a detection voltage with a constant DC amount, and detecting the voltage drop by comparing this voltage with the comparison reference voltage, the instantaneous value comparison method is used. The high-speed detection is equivalent to that of the above method, and there is an effect that the circuit configuration or the software configuration can be simplified by eliminating the need for integral calculation and zero-cross point detection suppressing means as compared with the instantaneous value comparison method.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a voltage drop detection waveform diagram.

FIG. 3 is a voltage drop detection waveform diagram.

FIG. 4 is a circuit diagram of an instantaneous value comparison detection method.

FIG. 5 is a circuit diagram of a three-phase voltage sum of squares method.

FIG. 6 is an instantaneous value comparison detection waveform diagram.

[Explanation of symbols]

21 ... Voltage detector, 22 ... PLL, 23 ... Counter, 2
4, 25, 26 ... ROM, 27, 28, 29 ... D / A converter, 30, 31, 32 ... Multiplier, 33 ... Adder, 34
... comparator, 35 ... timer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masato Fuchikawa 2109 Yashima Nishimachi, Takamatsu City, Kagawa 8 Shikoku Research Institute (72) Inventor Yasuo Kataoka 2-1-117 Osaki, Shinagawa-ku, Tokyo Stock Association Shameidensha (72) Inventor Masayuki Terashima 2-17 Osaki, Shinagawa-ku, Tokyo Stock company Shameidensha

Claims (1)

[Claims] 1. A voltage detecting means for obtaining a voltage waveform of each phase of a three-phase alternating current to be detected, a sine wave generating means for generating a three-phase sine wave signal of a constant voltage in synchronization with the voltage waveform, and the three. When the voltage waveform of each phase of the alternating current and the three-phase sine wave signal are respectively multiplied in the same phase and each multiplication result is added, and the calculation result of this calculation means reaches the set value or less and continues for a predetermined time. A voltage drop detection device comprising: a comparison unit that obtains the voltage drop detection signal of the three-phase AC.