JP2006025550A - Frequency detection device and distributed power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a frequency detection device that can exactly and easily detect the correct frequency of a system voltage, even if the system voltage to be detected is distorted in the vicinity of a zero point, and a distributed power supply device equipped with the detection device. <P>SOLUTION: In the frequency detection device that detects the system voltage of an AC power system 18 by a voltage detector 23, and detects a frequency from a zero point of a voltage detected by the voltage detector, frequency detection is performed by using a zero-point phase detection signal (a) that detects the frequency from the zero point of the voltage detected by the voltage detector, and an arbitrary-point phase detection signal (b) that detects the frequency from a point A of a phase α displaced from the zero pint of the voltage detected by the voltage detector. Here, the frequency detection device comprises a rectifier 37 that rectifies an AC voltage detected by the voltage detector and a potential divider 38 that divides a rectified DC voltage, to detect the frequency from the point, A displaced in phase from the zero point from its voltage dividing ratio. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a distributed power supply device interconnected to an AC power system, and more particularly to a frequency detection device that detects a frequency of a system voltage.

  For example, in a distributed power supply device that forms a three-phase AC voltage from a DC power source such as a solar cell or a fuel cell by an inverter and interconnects the system to a three-phase AC power system, It is necessary to accurately detect the frequency of the voltage. And based on the detected frequency, a grid connection operation by an inverter is performed, for example by forming a required voltage waveform with an inverter.

In such frequency detection, basically, an instantaneous amount of AC voltage is detected by a voltage detector (PT), sampled at a predetermined cycle, and the zero point (zero cross point of the voltage waveform) from the polarity change of the sampling value. Detect the presence of. And the period (time) of the area from the zero point detected last time to the zero point detected this time is calculated, and the frequency of the AC voltage is obtained from the reciprocal thereof (for example, refer to Patent Document 1).
Japanese Examined Patent Publication No. 63-46648

However, the method of detecting the frequency from the cycle between the zero points of the system voltage waveform has a problem that an accurate frequency cannot be detected if the voltage waveform near the zero point is distorted.
Temporary distortion of the voltage waveform can be prevented by averaging the detected frequency for the frequency detected several times before and making it the detected frequency. However, if a load or the like for improving the power factor is connected to the power system, the system voltage may be continuously distorted every cycle at the zero point. In that case, the detected frequency becomes an incorrect frequency, and if the operation is performed based on the incorrect frequency, a malfunction occurs in the grid connection.

  The present invention has been made in view of the circumstances described above, and a frequency detection device capable of accurately and easily detecting the correct frequency of the system voltage even if the system voltage to be detected is distorted near the zero point, and An object of the present invention is to provide a distributed power supply device including a detection device.

  The frequency detection device of the present invention is a frequency detection device that detects a system voltage of an AC power system with a voltage detector and detects a frequency from a zero point of the voltage detected by the voltage detector. The frequency detection is performed by the zero phase detection signal (a) for detecting the frequency by the zero point of the signal and the arbitrary point phase detection signal (b) for detecting the frequency by the phase point shifted from the zero point of the voltage detected by the voltage detector. It is characterized by doing.

  Further, the distributed power supply device of the present invention includes a frequency detection device that detects a system voltage of an AC power system with a voltage detector and detects a frequency based on a zero point of the voltage detected by the voltage detector, and the frequency detection device includes: The zero point phase detection signal (a) for detecting the frequency by the zero point of the voltage detected by the voltage detector and the arbitrary point phase detection for detecting the frequency by the phase point shifted from the zero point of the voltage detected by the voltage detector The frequency detection is performed with the signal (b).

  The frequency detection device includes a rectifier that rectifies the AC voltage detected by the voltage detector and a voltage divider that divides the rectified DC voltage, and detects a frequency from a point whose phase is shifted from the zero point by the voltage division ratio. It is preferable. Also, the AC voltage detected by the voltage detector is input to two comparators, one of the comparison values of the comparators is set to a zero point, and the other is set to a voltage value at a point shifted in phase from the zero point. It is preferable to do.

  According to the present invention, erroneous detection of frequency can be eliminated even when temporary distortion or continuous distortion occurs every period when the system voltage is zero. In particular, according to this frequency detection device, the phase detection signal (b) is output by the comparator at a phase angle α (preferably 10 to 20 °) at which waveform distortion is unlikely to occur, thereby causing a frequency due to waveform distortion. Can prevent the problem of false detection. A distributed power supply device including this frequency detection device can be realized only by adding a relatively simple circuit configuration (mainly realized by software).

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the member or element which has the same effect | action or function, and the overlapping description is abbreviate | omitted.

  FIG. 1 shows a distributed power supply device including a frequency detection device according to an embodiment of the present invention. A DC power source 11 such as a solar cell or a fuel cell is connected to the inverter system 10 by DC lines 11a and 11b, and the DC power is converted into AC power by the inverter system 10, and its output is passed through a switch 16 and a breaker 17. It is connected to the AC power system 18 and connected to the system.

  Here, the inverter system 10 receives the DC voltage of the DC power supply 11 as input, boosts the DC voltage by a booster circuit 12 such as a boost chopper, and forms a DC high voltage (link voltage) in the DC unit 13. The DC unit 13 has a plurality of capacitors C and a resistor r connected in series between the DC lines 13a and 13b, and has a function of smoothing the DC voltage while maintaining a DC high voltage.

  In the inverter 15, a three-phase AC voltage is formed from the DC link voltages input from the DC lines 13 a and 13 b, and connected to the AC power system 18 connected via the switch 16 and the breaker 17, and AC power is supplied to the load. Supply. In the inverter 15, the power switching element is turned on / off by a control command from the control device 21, and an AC voltage having an arbitrary voltage, frequency, and phase is formed by pulse width modulation control or the like.

  When forming an AC voltage waveform interconnected by the inverter 15, it is necessary to detect the voltage, phase and frequency on the AC power system 18 side. For this purpose, a three-phase voltage detection transformer (PT) 23 for detecting the voltage of the AC power system 18 connected via the breaker 17 is provided. The output of the three-phase voltage detection transformer (PT) 23 is connected to the control device 21, and the voltage, phase and frequency of the AC power system 18 are detected by a CPU circuit or the like provided in the control device 21.

  FIG. 2 shows a configuration example of a frequency detection device provided in this distributed power supply device. The system voltage of the AC power system 18 is detected by a voltage detector (PT) 23 and supplied to the control device 21, and the frequency of the system voltage is detected inside the control device 21.

  The output of the voltage detector (PT) 23 is connected to a noise cut filter 31 in the control device 21 where high frequency components such as noise are removed and only low frequency components pass. The voltage signal that has passed through the noise cut filter 31 is sampled at a predetermined sampling period by an A / D converter (not shown), and is sent to the two comparators 32 and 33 as digital signal data.

  The comparator 32 outputs a zero point phase detection signal (a) at the zero point of the voltage waveform, that is, the point at which the voltage waveform crosses the potential 0V. This signal (a) is input to the calculation unit 35 and measures the period (time = T) between the previous zero phase detection signal (a) and the current zero phase detection signal (a) after one cycle. Then, the frequency as the reciprocal is detected.

  That is, as shown in FIG. 3A, when the system voltage signal is positive at the zero point Z where the system voltage waveform crosses 0 V, the zero phase detection signal (a) outputs “1”. When the system voltage signal is negative, the zero point phase detection signal (a) outputs “0”. Therefore, the period (time = T) between the rising edge of the zero phase detection signal (a) and the next rising edge can be measured. And the frequency of system voltage is detectable by calculating | requiring the reciprocal number of this period (= T).

  The comparator 33 outputs an arbitrary point A other than the zero point of the voltage waveform, that is, an arbitrary point phase detection signal (b) at a point where the voltage waveform crosses the potential AV. This signal (b) is input to the calculation unit 35, and the period (time = T) between the previous arbitrary point phase detection signal (b) and the current arbitrary point phase detection signal (b) after one cycle. And the frequency as the reciprocal is detected.

  That is, as shown in FIG. 3B, when the system voltage signal is positive at an arbitrary point A where the system voltage waveform crosses AV, the arbitrary point phase detection signal (b) outputs “1”. To do. When the system voltage signal is negative, the arbitrary point phase detection signal (b) outputs “0”. Therefore, the period (time = T) between the rising edge of the arbitrary point phase detection signal (b) and the next rising edge can be measured. And the frequency of system voltage is detectable by calculating | requiring the reciprocal number of this period (= T).

  Here, the arbitrary point A is a phase point shifted from the zero point of the system voltage. That is, the system voltage waveform is basically a sine wave, the zero point is a point with a phase angle of 0 °, and the arbitrary point A is a point with a phase angle α. Therefore, the comparison voltage AV in the comparator 33 is a voltage value proportional to the change in the amplitude of the system voltage. For this reason, even if the system voltage fluctuates, the comparison voltage AV at the point of the phase angle α varies in proportion to the system voltage so that the arbitrary point phase detection signal (b) at the point of the phase angle α is obtained. It has become.

  In order to form the comparison voltage AV in the comparator 33 that outputs the phase detection signal (b) at the arbitrary point A (phase angle α), the rectifier 37 that rectifies the AC voltage detected by the voltage detector 23, and the rectified DC And a voltage divider 38 for dividing the voltage. The voltage AV given by the voltage dividing ratio of the voltage divider 38 is used as the comparison voltage of the comparator 33.

  That is, the analog AC voltage (system voltage) after passing through the noise cut filter 31 is rectified by the rectifier 37, the DC voltage is divided by the voltage divider 38, and the phase angle α is shifted in phase from the zero point by the voltage dividing ratio. The frequency is detected by A. Therefore, even if the amplitude of the system voltage fluctuates, the divided voltage A can be obtained as a voltage having a voltage division ratio with respect to the amplitude of the AC voltage waveform. For this reason, when the amplitude of the voltage waveform varies, the comparison voltage A also varies, but the ratio of the comparison voltage A to the amplitude is constant, in other words, it corresponds to a voltage having a constant phase angle α. An arbitrary point phase detection signal (b) is output based on the comparison value. Therefore, the rising edge of the arbitrary point phase detection signal (b) is output at the point of the phase angle α that deviates from the zero point of the system voltage.

  Next, the operation of this frequency detection device will be described. As shown in FIG. 3, when the system voltage waveform is a normal sine wave without distortion, the period (= T) measured from the zero phase detection signal (a) is also an arbitrary point phase shifted by the phase angle α. The period (= T) of the detection signal (b) is also equal. For this reason, the frequency detected as the reciprocal of the period (= T) also matches.

  However, if a load for improving the power factor is connected to the power system, the system voltage may be continuously distorted every cycle in the vicinity of the zero point. This tendency is remarkable when a load having a low power factor such as an inverter is connected to the power supply system. In addition to the zero point, the waveform of the system voltage tends to collapse even in a sine wave phase such as 60 °.

  FIG. 5A shows a general three-phase voltage output inverter, and FIG. 5B shows the three-phase voltage output waveform. In the case of a single-phase AC output, the inverter output using the power switching element switches between positive and negative polarity. The output waveform is likely to be distorted by a waveform operation for power factor adjustment near the zero point of 0 ° and 180 °. However, in the case of three-phase alternating current, each phase is shifted by 120 °. Therefore, in the case of three-phase alternating current, the phase operation associated with switching between positive and negative polarity can be affected even at the point of sine wave phase of 0 °, 60 ° and 120 °. There is sex. That is, in the case of three-phase alternating current, distortion is likely to occur in the inverter output waveform with sine wave phases of 0 °, 60 °, 120 °, and 180 °. For this reason, it is empirically preferable that the phase α shifted from the zero point for generating the arbitrary point phase detection signal (b) is about 10 ° to 20 °. Therefore, the point A is preferably set to a point having a phase angle of 10 to 20 °.

FIG. 4 shows a case where the system voltage waveform is distorted near the zero point. That is, the system voltage is 0 V between the phase angles θ ₁ and θ ₂ , the system voltage is also 0 V between the phase angles θ ₃ and θ ₄ , and normal in other phase angles. In this case, the zero phase detection signal (a) becomes “1” at the phase angle θ ₂ as shown in the figure, becomes “0” at the phase angle 0 °, and becomes “1” again at the phase angle θ ₄ . For this reason, one period (θ ₂ to θ ₄ ) between both rising edges becomes a period T ′ different from the correct period (= T), and if a frequency is calculated by this period T ′, an incorrect frequency is obtained.

However, according to the arbitrary point phase detection signal (b) at the point A other than the zero point, the arbitrary point phase detection signal (b) becomes “1” at the phase angle θ ₅ (point A) crossing the voltage AV, and the voltage again The arbitrary point phase detection signal (b) becomes “0” at the phase angle θ ₆ that becomes AV, and the arbitrary point phase detection signal becomes “1” at the phase angle θ ₇ (point A) that crosses the voltage AV again. . Therefore, by outputting the “1” signal of the arbitrary point phase detection signal (b) at the point A, the period obtained can be a normal period (= T) even if the voltage waveform is distorted near the zero point. Therefore, the correct frequency can be obtained by calculating the reciprocal of the correct period (= T).

  FIG. 6 shows a flow for determining the finally detected frequency from the frequency (a) detected by the comparator 32 and the frequency (b) detected by the comparator 33. That is, the frequency (a) is detected from the zero point phase detection signal (a), the frequency (b) is detected from the arbitrary point phase detection signal (b), and both frequencies are compared and judged, and the final detection frequency Is determined.

  First, when the determination unit 40 determines that the frequency (a) is equal to the frequency (b), it is a normal state, and this coincident frequency becomes the final detection frequency. Then, the determination unit 40 stores this frequency as the previous determination frequency. If the frequency (a) and the frequency (b) do not match, the determination unit 40 determines the detection frequency with reference to the previous determination frequency.

  For example, when the voltage waveform distortion as shown in FIG. 4 occurs near the zero point, the frequency (a) becomes abnormal, but the detection frequency (b) by the arbitrary point phase detection signal matches the previous determination frequency. If so, the frequency (b) is determined as the final detection frequency. This makes it possible to detect the correct frequency even when the voltage waveform of the system voltage is distorted near the zero point.

  Thus, according to this frequency detection apparatus, the phase detection signal (b) is output by the comparator 33 at the point A at the phase angle α (preferably 10 to 20 °) where waveform distortion is unlikely to occur. By adding a simple circuit configuration (mainly realized by software), it is possible to prevent the problem of erroneous frequency detection due to waveform distortion.

  In the above-described embodiment, two comparators are used to detect a zero point phase detection signal and an arbitrary point phase detection signal. However, three or more comparators are used and an arbitrary point phase with a plurality of phase angles is used. A detection signal may be obtained. As a result, the determination unit can perform more accurate frequency detection.

  Although one embodiment of the present invention has been described so far, it is needless to say that the present invention is not limited to the above-described embodiment, and may be implemented in various forms within the scope of the technical idea.

It is a circuit diagram which shows the structural example of a distributed power supply system. It is a block diagram which shows schematic structure of the frequency detection apparatus of this invention. It is a wave form diagram in case a system | strain voltage is normal. It is a wave form diagram in case there exists distortion in the zero point vicinity of a system voltage. (A) is a circuit diagram which shows the structural example of an inverter, (b) is a wave form diagram of the three-phase output voltage. It is a flowchart which determines a final detection frequency from two detected frequencies (a) and (b).

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Inverter system 11 DC power supply 12 Booster circuit 13 DC part 15 Inverter 16 Switch 17 Breaker 18 AC power system 21 Controller 23 Voltage detector 31 Noise cut filter 32, 33 Comparator 35 Operation part 37 Rectifier 38 Voltage divider 40 Determination part

Claims (5)

In the frequency detection device that detects the system voltage of the AC power system with a voltage detector and detects the frequency by the zero point of the voltage detected by the voltage detector,
A zero-point phase detection signal (a) for detecting the frequency from the zero point of the voltage detected by the voltage detector, and an arbitrary point phase detection signal for detecting the frequency by a phase point shifted from the zero point of the voltage detected by the voltage detector And (b) performing frequency detection.   The frequency detection device includes a rectifier that rectifies the AC voltage detected by the voltage detector, and a voltage divider that divides the rectified DC voltage, and detects a frequency from a point shifted in phase from the zero point by the voltage division ratio. The frequency detection apparatus according to claim 1.   AC voltage detected by the voltage detector is input to two comparators, one of which is set to a zero point, and the other is set to a voltage value at a point shifted in phase from the zero point. The frequency detection apparatus according to claim 1.   The frequency detection apparatus according to claim 1, wherein the phase point shifted from the zero point is a phase angle of 10 ° to 20 °. In the distributed power supply system connected to the AC power system,
A frequency detector for detecting the system voltage of the AC power system with a voltage detector and detecting the frequency by the zero point of the voltage detected by the voltage detector;
The frequency detection device detects a frequency by a zero point phase detection signal (a) for detecting a frequency from a zero point of a voltage detected by the voltage detector and a phase point shifted from the zero point of the voltage detected by the voltage detector. A distributed power supply apparatus that performs frequency detection with an arbitrary point phase detection signal (b).

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