JP2002078234A - Ac-feeding system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a power failure with high reliability inspite of a simple configuration, in a feeding system that feeds the mixture of commercial power and another AC power. SOLUTION: An AC-feeding system comprises a commercial power source 1, a DC power source 2 and an inverter 3 that converts DC power from the DC power source 1 to AC power. Power from the commercial power source 1 and power from the inverter 3 are exclusively switched by a switching means 5 and is supplied to a load 100 in time division. Furthermore, the system comprises an oscillator means 4 and a comparator means 7. The oscillator means 4 outputs a reference voltage of which the frequency, the phase and the amplitude are equal to those of the commercial power source 1 based on the voltage of the commercial power source. The inverter 3 converts DC power to an AC power of which the frequency, the phase and the amplitude are equal to those of the commercial power source 1 using the reference voltage from the oscillator means 4 as an original waveform. The comparator means 7 compares the voltage of the commercial power source 1 with the reference voltage of the oscillator means 4 and determines a power failure of the commercial power source when both voltages are different.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC power supply system that mixes power from a commercial power supply with power from another AC power supply and supplies the mixed power to a load.

[0002]

2. Description of the Related Art AC power from a commercial power supply and AC power from an inverter (another AC power supply) are supplied to a load.
In an AC power supply system that supplies a mixture, a means called system interconnection is used. Note that the inverter converts DC power from a DC power supply such as a solar cell, a fuel cell, and a secondary battery (storage battery) into AC power.

In the above system interconnection, a commercial power supply and an inverter are connected in parallel to a load. The inverter is
Control is performed based on the voltage or current of the commercial power supply, whereby an AC output having a frequency, a phase, and an amplitude substantially equal to that of the commercial power supply can be supplied to the load.

In the above-mentioned system interconnection, it is required to detect a power failure of a commercial power supply. For this reason, for example, a power failure detection device disclosed in Japanese Patent Application Laid-Open No. 7-154920 has been developed. In this device, the third harmonic component of the voltage at the interconnection point between the inverter and the commercial power supply is detected, and a power failure of the commercial power supply is detected based on the detected value.

[0005]

However, the power failure detection device disclosed in the above publication requires a very complicated circuit, and has disadvantages such as an increase in cost and a decrease in reliability.

[0006]

According to a first aspect of the present invention, there is provided:
(B) a commercial power supply; and (b) another AC power supply for generating AC power having substantially the same frequency, phase, and amplitude as the commercial power supply, and mixing the power of the commercial power supply with the power of the AC power supply. (C) switching means for exclusively switching between the commercial power supply and the AC power supply to supply the AC power to the load, and (d) the commercial power supply having a frequency, a phase, and an amplitude. And (e) comparing means for comparing the voltage of the commercial power supply with the reference voltage of the oscillating means, and judging that the commercial power supply has failed if the two are different. And an AC power supply system comprising:

According to a second aspect of the present invention, in the AC power supply system according to the first aspect, the oscillating means generates a reference voltage based on the voltage of the commercial power supply, and keeps the reference voltage for a limited time after the commercial power failure. This reference voltage is output continuously. According to a third aspect of the present invention, in the AC power supply system according to the second aspect, the oscillation means includes a phase lock loop. A fourth aspect of the present invention is the AC power supply system according to the second or third aspect, further comprising a DC power supply, wherein an inverter for converting DC power from the DC power supply to AC power is provided as the AC power supply. The inverter converts DC power to AC power based on the reference voltage from the oscillating means.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an AC power supply system according to an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the AC power supply system includes a commercial power supply 1 and a DC power supply 2. As the DC power supply 2, a solar cell, a fuel cell, a secondary battery (storage battery), or the like is used. DC power from DC power supply 2 is supplied to inverter 3
(Other AC power supply) is converted to AC power.

In order to make the frequency, phase and amplitude of the AC power (voltage) output from the inverter 3 equal to the AC power (voltage) from the commercial power supply 1, an oscillator 4 (oscillation means) for outputting a reference voltage ) Is used. The oscillator 4 has a PLL 40 (phase lock loop) and an amplitude adjuster 45, as shown in FIG.

The PLL 40 is a known PLL, and includes a frequency / phase comparator 41 and a voltage controlled oscillator 42 (VCO).
-Voltage control oscillator) and loop filter 4
3 The comparator 41 compares the frequency and phase between the output of the VCO 42 and the signal to be tracked (the voltage signal from the commercial power supply 1 in the present embodiment), and compares the comparison signal with the VCO 42 through the loop filter 43. By applying feedback, a voltage having the same frequency and phase as the tracked signal can be output from the VCO 42. The amplitude controller 45 receives a voltage signal from the commercial power supply 1 and
The voltage from O42 is adjusted to have the same amplitude as the voltage from commercial power supply 1. The amplitude-adjusted voltage signal is output as a reference voltage.

The inverter 3 refers to the DC power from the DC power supply 2 with reference to the reference voltage from the oscillator 4 (as an original waveform), and has the same frequency, phase, and amplitude as the AC power from the commercial power supply 1. Convert to AC power.

As shown in FIG. 1, the AC power supply system of the present embodiment further includes a switch 5 (switching means). The switch 5 exclusively switches the commercial power supply 1 and the inverter 2 with respect to the load 100, and
To supply AC power mixed in a time-division manner. The switching device 5 includes a mechanical relay, a solid state relay, a thyristor, a triac, a transistor, an I
Any one such as GBT may be used. In particular, thyristors,
In the case of a triac, it is cheap.

The exclusive time-division switching control of the switching unit 5 is performed by a switching control unit 6. This switching control means 6 has a noise generator 61, a voltage generator 62 and a comparator 63. The noise generator 61 includes 0 to 1
A noise voltage of V is generated. The voltage generator 62
Generates a DC voltage of 1V. In the comparator 63, for example, when the voltage of the noise generator is higher than the voltage of the voltage generator 62, the switch 5 is connected to the commercial power supply 1, and in the opposite case, the switch is switched to the inverter 3. The voltage generator 62 receives the detection signal of the power from the DC power supply 2 or the power from the inverter 3 and controls the level of the DC voltage. For example, when the DC voltage level is 0.05 V, the AC output from the inverter 3 is 5% and the AC output from the commercial power source 1 is mixed in a time-division manner at a rate of 95%, and the load 10 is mixed.
0, and when the DC voltage level is 0.85 V, the AC output from the inverter 3 is 85% and the commercial power 1
Side AC output is supplied to the load 100 at a rate of 15%.

Further, the AC power supply system includes a comparator 7. The comparator 7 compares a voltage from the commercial power supply 1 with a reference voltage from the oscillator 4 and detects a power failure of the commercial power supply 1. More specifically, when the commercial power supply 1 fails, as shown in FIG. 3B, the voltage signal from the commercial power supply 1 becomes zero potential. On the other hand, the reference voltage from the oscillator 4 corresponds to the voltage from the commercial power supply 1, but as shown in FIG. Continue to be.
In other words, the response time of the loop filter 43 inside the PLL 40 is about 1 second when the frequency deviation is 1 Hz. Therefore, even if the commercial power supply 1 is cut off, the reference voltage remains at about 1 second (limited time). ), Just keep outputting.

The comparator 7 obtains a voltage difference between the voltage from the commercial power supply 1 and the reference voltage, as shown in FIG. Before the power failure of the commercial power supply 1, the voltage of the commercial power supply 1 and the reference voltage have the same cycle, phase, and amplitude, so that the voltage difference is substantially zero. On the contrary,
When the commercial power source 1 fails, the power difference is detected because the voltage difference signal includes the reference voltage or its inverted voltage. Specifically, a DC threshold voltage smaller than the amplitude of the reference voltage is compared with the voltage difference,
Perform power failure detection.

Since the electric wire of the commercial power supply 1 and the electric wire of the inverter 3 are always disconnected from each other by the exclusive switching by the switch 5, the one input terminal of the comparator 7 connected to the electric wire of the commercial power supply 1 , Only the voltage signal of the commercial power supply 1 is input, and the voltage signal from the inverter 3 is not input. Therefore, the power failure can be detected by comparing the voltage of the commercial power supply 1 input to one input terminal of the comparator 7 with the reference voltage input to the other input terminal. Further, since the reference voltage is used as a reference waveform when the inverter 5 converts DC power into AC power, the circuit configuration can be simplified.

The present invention is not limited to the above embodiment, and various modes are possible. For example, switching between the commercial power supply and the inverter may be performed at zero-cross timing without using noise, or may be performed every half-wave or every full-wave.

[0018]

As described above, according to the first aspect of the present invention, a highly reliable power failure detection can be performed with a simple configuration by comparing the voltage of the commercial power supply with the reference voltage. it can. According to the second aspect of the present invention, although the reference voltage is generated based on the voltage of the commercial power supply, the power failure can be detected more reliably by outputting the reference voltage for a limited time after the power failure of the commercial power supply. According to the third aspect of the present invention, since the configuration including the phase lock loop is employed, the power failure detection can be performed with a more inexpensive configuration. According to the fourth aspect of the present invention, since the reference voltage is used as the original waveform when converting DC power into AC power by the inverter, the circuit configuration of the entire power supply system can be simplified. .

[Brief description of the drawings]

FIG. 1 is a block diagram of an AC power supply system according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an oscillator used in the system.

FIG. 3 is a diagram illustrating a power failure detection method according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Commercial power supply 2 DC power supply 3 Inverter (AC power supply) 4 Oscillator (oscillation means) 40 Phase lock loop (PLL) 5 Switcher (switching means) 7 Comparator (comparing means) 100 Load

Claims (4)

[Claims] (1) A commercial power supply, (B) frequency, phase,
Another AC power supply that generates AC power having an amplitude substantially equal to the commercial power supply, comprising:
(C) switching means for exclusively switching between the commercial power supply and the AC power supply to supply AC power to the load; and (d) oscillation for outputting an AC reference voltage having substantially the same frequency, phase and amplitude as the commercial power supply. Means (e) comparing the voltage of the commercial power supply with the reference voltage of the oscillation means,
An AC power supply system comprising: a comparison unit that determines that a commercial power failure has occurred when the two are different. 2. The method according to claim 1, wherein the oscillating means generates a reference voltage based on the voltage of the commercial power supply, and outputs the reference voltage for a limited time after the commercial power failure. The AC power supply system according to claim 1. 3. The AC power supply system according to claim 2, wherein said oscillating means includes a phase lock loop. 4. An inverter further comprising a DC power supply for converting DC power from the DC power supply to AC power is provided as the AC power supply. The inverter is configured to supply DC power based on a reference voltage from the oscillating means. 4. The method according to claim 2, wherein the conversion is performed to AC power.
The AC power supply system according to 1.