JPH06149397A - Direct current converter for system linkage - Google Patents

Abstract

PURPOSE:To prevent the power factor of a commercial power source from being decreased less than a prescribed value even when there is a load fluctuation generated at the time of operating a system linkage with the commercial power source. CONSTITUTION:Normally, a signal obtained by alternating current-converting the output of a direct current generator 1 by an alternating current converter 2 is system-linked with a commercial power source 5 by a high power factor, and supplied to a load 6. Then, when the power factor of the commercial power source is decreased to the prescribed value due to the load fluctuation, the power factor of the alternating current component outputted from the alternating current converter 2 is controlled so that the power factor of the commercial power source can be prevented from being decreased less than the prescribed value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC converter for system interconnection, which converts the output of a DC power generator into AC by an AC converter and systemically connects it to a commercial power source and supplies it to a load.

[0002]

2. Description of the Related Art In recent years, the demand for electric power has been increasing, and therefore electric power companies are increasing their power generation capacities to meet the demand. In order to avoid power shortage, it is desirable that some of the power required by the user be covered by themselves.

In this case, there are various power generation methods. For example, it is conceivable that power is generated by a fuel cell, the generated output is converted into alternating current, and the system is connected to a commercial power source.

A conventional basic control method in the case of using a fuel cell will be described with reference to FIG. 4 using an AC converter using a PWM inverter. In FIG. 4, 1 is a DC power generator, 2 is an AC converter, 5 is a commercial power source, and 6 is a load. The AC converter 2 includes a main converter 20, a reference oscillator 21, a phase setter 22, a sine wave waveform transmitter 23, an amplitude setter 24, a comparator 25, a gate drive circuit 26, a carrier triangular wave generator 27, and a comparator. 28, 29, 33, comparison
Calculator 30, power factor setting device 31, frequency / phase converter 3
2, the power setting device 34, and the interconnection reactor 35.

Symbols 36, 37 and 38 are detection points of the AC converter 2, symbols 51 and 52 are detection points on the commercial power source side.
Reference numeral 80 is a connection point between the commercial power supply and the output of the AC converter. In this system, the output of the DC generator 1 is connected to the commercial power source 5 at the interconnection point 80 via the main conversion means 20 of the AC converter 2 and the interconnection reactor 35, and is connected to the load 6. .

In the AC converter 2, the output of the reference oscillator 21 is supplied to the main converter 20 via the phase setter 22, the sine wave waveform transmitter 23, the amplitude setter 24, the comparator 25, and the gate drive circuit 26. It has become. The output of the carrier triangular wave generator 27 is output to the amplitude setting unit 2 in the comparator 25.
The output of 4 is compared.

The detection signal at the output power detection point 38 is compared with the output of the power setting unit 34 by the comparator 33, and the output is supplied to the frequency / phase converter 32. The frequency / phase detector 32 is also supplied with a signal from the detection point 51 of the commercial power supply 5, and its output is supplied to the phase setter 22.

The detection signal at the output detection point 37 is the power factor setting unit 3.
The output signal of 1 is supplied to the comparator / arithmetic unit 30, and its output is supplied to the comparator 29. The comparator 29 is supplied with a signal from the detection point 52 on the commercial power source side, and its output is the comparator 2
8 are supplied.

The comparator 28 is also supplied with a signal from the output detection point 36 of the main conversion means 20, and its output is the amplitude setter 24.
To be supplied to.

The operation of the AC converter 2 according to this system is as follows. The reference oscillator 21 sends out a frequency corresponding to 50 Hz (60 Hz) required for the AC converter 2,
The sine wave waveform transmitter 23 generates a sine wave based on the signal from the reference oscillator 21.

The amplitude of this sine wave is controlled by the output of the comparator 28. The comparator 28 outputs the voltage feedback signal from the voltage detection point 36 provided at the output of the main conversion means 20 and the output of the comparator 29. The result of comparing and is output. This sine wave is compared with the carrier signal supplied from the carrier triangular wave generator 27 in the comparator 25, the output thereof is amplified in the gate drive circuit 26, and the main conversion means 20 is obtained.
To the AC output.

When the commercial power source 5 is connected to the grid, the output capacity of the DC power generator 1 is usually smaller than the load facility capacity 6, so it is necessary to control the AC converter 2 to determine the output. The power setting device 34 sets the output of the AC converter 2, and the setting signal of the power setting device 34 and the power detection point 3 are set.
The feedback signal from 8 is compared by the comparator 33, and the comparison result is supplied to the frequency / phase converter 32.

The frequency / phase converter 32 is also supplied with the frequency signal supplied from the detection point 51 of the commercial power supply 5.
By the way, when the AC converter 2 and the commercial power source 5 are connected to each other, it is necessary to match the frequency, voltage and phase of both. Further, the load sharing between the commercial power supply 5 and the AC converter 2 is controlled by making the voltage phases of the two different. In this case, the AC converter 2 side is allocated by advancing the phase of the AC converter 2 in front of the interconnection reactor 35 with respect to the voltage phase of the commercial power supply 5.

Therefore, the phases of the commercial power supply 5 and the AC converter 2 are selected by fetching the output signal of the comparator 33 and the frequency signal of the commercial power supply 5 side into the frequency / phase converter 32, and the signals are set in phase. Input to the container 22. The phase setter 22 determines the reference phase for operating the main conversion means 20 based on the signal of the reference oscillator 21 and the signal from the frequency / phase converter 32.

Based on this signal, the sine wave waveform transmitter 23 creates an ideal sine wave and supplies it to the amplitude setting device 24. In addition, the amplitude setter 24 has a detection point 36 via a comparator 28.
Is also supplied, and the sine wave amplitude for setting the output voltage of the AC converter 2 is determined by the amplitude setter 24 by these signals.

A PWM signal for operating the main conversion circuit 20 is obtained by comparing this signal with the carrier signal from the carrier triangular wave generator 27 by the comparator 25. Actually, this PWM signal is amplified by the gate drive circuit 26 and used as the gate signal of the main conversion means 20 to send out the necessary AC output to the AC conversion device 2, and at the interconnection point 80 it is connected to the commercial power source 5 and the system. The load 6 is supplied with electric power.

By the way, as described above, the output capacity of the DC power generator 1 is finite and smaller than the load capacity, but reliability can be ensured by system interconnection with the commercial power source 5 and running from the commercial power source 5 is possible. Since the cost is low, it is necessary to maximize the effective use of the output of the DC generator 1. Therefore, when the output of the AC converter 2 having the DC power generator 1 as an input and the commercial power supply 5 are interconnected, the reactive power of the output of the AC converter 2 is controlled, and the AC converter has a high power factor (power factor). It is operated in 1).

In the control method in that case, the power factor is detected at the detection point 37 of the output of the interconnection reactor 35 in FIG. 4, and the power factor set by the power factor setting device 31 (for example, power factor 1) is compared. The arithmetic unit 30 compares. This signal and the signal from the detection point 52 for detecting the power factor on the commercial power source 5 side are compared by the comparator 29, and the output thereof is supplied to the comparator 28.

That is, the high power factor output of the AC converter 2 is achieved by controlling the output voltage value of the AC converter 2.

FIG. 5 shows an AC converter 2 when the system is interconnected.
And the vector of the relationship between voltage and current when the commercial power supply 5 is system-connected (actually, it is a three-phase output voltage, but here it is shown as one phase for simplification of description).

In FIG. 5, VC is a commercial power supply voltage, VI
(VI1, VI2) is the AC converter output voltage, VL is the interconnection reactor voltage, AC (AC1, AC2) is the commercial current, and AI (A
I1, AI2) is the output current of the AC converter, and AT is the load current. The load sharing between the commercial power supply and the AC converter is to provide a phase difference between the commercial power supply voltage VC and the AC converter output voltage VI. Specifically, the phase of the AC converter output voltage VI with respect to the commercial power supply voltage VC. Advance with angle α.

For example, as shown in FIG.
AC1 output voltage is VI1, the commercial power supply voltage is VC, and the phase angle is α, the AC converter output current is AI1, the commercial power supply current is AC1, and the load is shared with the total load current AT. There is.

By the way, the AC converter 2 having the DC generator 1 as an input is operated at a high power factor as described above, and the control for maximally utilizing the active power from the DC generator 1 side is the interconnection point. In 80, the output voltage VI of the AC converter 2 is controlled so that the commercial power supply voltage VC and the phase of the AC converter output current AI match.

An example thereof is shown in FIG. 5, and the output voltage of the main conversion means 20 of the AC converter 2 is controlled so that the voltage VL of the interconnection reactor 35 becomes a right angle with respect to the commercial power supply voltage VC. This is because the voltage detection point 3 of the main conversion means 20.
The voltage signal detected in 6 and the power factor signal at the power factor detection point 37 of the output of the interconnection reactor 35 are fed back to set the voltage amplitude by the amplitude setter 24 to control.

Even when the output of the AC converter 2 is increased, as shown in FIG. 5, the AC converter VI (here, the vector of the voltage of the interconnection reactor 35 and the commercial power supply voltage VC are perpendicular to each other). It is possible by controlling VI2).
By maintaining this relationship, the AC converter 2 can always supply only active power to the load.

As described above, the method of supplying the output of the AC converter with a high power factor so as to extract as much active power as possible from the DC generator is a direct current using a fuel cell or a solar cell as an energy source. It is generally used as a power supply method for a power generator. This kind of supply method has no problem when the output capacity of the DC generator is smaller than the load capacity, but as shown in FIG. 5, the output current AI of the AC converter 2 increases from AI1 to AI2. Since the current AC on the commercial power source side changes from AC1 to AC2, the reactive power supply from the commercial power source 5 must be increased.

[0027]

However, as shown in FIG. 6 which shows the relationship between the output of the AC converter, the load, the load power amount of the commercial power source and the power factor, it is generally permissible that the commercial power source power factor falls below 0.85. Not required, but rather expensive. Therefore, maintaining the output of the AC converter 2 in the high power factor operation has a great effect of effectively using the output of the DC generator 1, but as a power supply system, the reliability and stability of the system are stable. There was a problem that it had an adverse effect on the power supply and other consumers.

That is, conventionally, in a system in which an AC converter is connected to the output of a DC generator to convert it into AC power and which is system-interconnected with a commercial power source to supply power to a load, DC power is generated with respect to load capacity. The equipment capacity was very small.
Therefore, no problem occurs even if the AC converter is supplied at a high power factor and the reactive power is supplied from the commercial power supply side.

In a general device, a method has been used in which the power factor setting of the output of the AC converter is manually changed only when the power factor on the commercial side is extremely reduced. However, when the ratio of the output of the DC generator becomes so large that it cannot be ignored with respect to the load capacity (generally 25% or more), if the AC converter is constantly operated at a high power factor, excessive reactive power will be supplied to the commercial power supply side. Will be needed.

On the other hand, in the present invention, in addition to the power factor of the output of the AC converter, the power factor of the commercial power source and the load is constantly monitored to reduce the energy cost on the DC generator side and to improve the reliability of the grid interconnection system. It is intended to be realized. The present invention solves such a problem by monitoring a commercial power source and a load power factor, controlling the power factor of the AC converter output before the commercial power source power factor decreases, and adversely affects the commercial power source. This is to maximize the amount of active power from the DC generator within the range that does not deteriorate the power factor. With this configuration, it is possible to reduce the energy cost on the side of the DC power generator and increase the reliability of the grid interconnection system.

[0031]

In order to solve such a problem, the present invention monitors the commercial power source power factor and the load power factor so that when the commercial power source power factor falls below a predetermined value. The power factor of the AC converter is adjusted so that the power factor on the commercial power source side does not fall below a predetermined value.

[0032]

[Operation] When the output of the DC power generator is AC-converted by the AC converter at all times and is supplied to the load in a system cooperation with the commercial power source at a high power factor, and the commercial power source power factor decreases to a predetermined value due to load fluctuation. Controls the power factor of the AC component output from the AC converter so that the commercial power source power factor does not fall below that value.

[0033]

Embodiments of the present invention will now be described in detail with reference to the drawings. In the figure, the same components as those described in the conventional technique are designated by the same reference numerals. FIG. 1 is a block diagram showing an embodiment of the present invention, in which 1 is a DC generator, 2 is an AC converter, 5 is a commercial power source, and 6 is a load. The AC converter 2 includes a main converter 20, a reference oscillator 21, a phase setter 22, a sine wave waveform transmitter 23, an amplitude setter 24,
Comparator 25, gate drive circuit 26, carrier triangular wave generator 27, comparators 28, 29, 33, 71, power factor setting device 3
1, a frequency / phase converter 32, a power setting device 34, an interconnection reactor 35, and comparison / operation devices 30 and 73. In addition, the comparison / arithmetic unit 30 and the power factor setting unit 3
Reference numeral 1 constitutes a converter side power factor monitoring means.

Further, symbols 36 and 52 are voltage detection points, symbols 37, 75 and 76 are power factor detection points, and symbols 38 and 5 are.
Reference numeral 1 is a power detection point, 72 is a commercial power supply side power factor setting device, 74 is a switching device, and symbol 80 is a connection point of the commercial power supply 5 AC conversion device 2. Of the power factor detection points 75 and 76, the symbol 75 is the commercial power source power factor detection point provided on the commercial power source side of the interconnection point 80, and the symbol 76 is the load power factor detection provided on the load side of the interconnection point 80. It is a point.

The comparator 71 is a commercial power source power factor detection point 7
When the power factor of 5 is reduced to the power factor set by the commercial power point power factor setting device 72, the output signal is sent out, and the comparison / calculation device 73 outputs the output signal from the comparator 71. A signal for controlling the power factor at the load power factor detection point 76 to be the power factor set by the commercial power source power factor setting device is output. However, the output of the comparison / calculation unit 73 is adapted to be output in conformity with the slope of the change in the load power factor, and the output signal of the comparison / calculation unit 73 prevents excessive power factor correction. ing. The comparator 71
The commercial power point power factor setting device 72 constitutes commercial power source power factor monitoring means.

In the configuration of this system, the output of the DC generator 1 is connected to the commercial power source 5 at the interconnection point 80 via the main conversion means 20 of the AC converter 2 and the interconnection reactor 35, and the load 6
It is designed to connect to.

In the AC converter 2, the output of the reference oscillator 21 is supplied to the main converter 20 through the phase setting device 22, the sine wave waveform sending device 23, the amplitude setting device 24, the comparator 25, and the gate drive circuit 26. It is like this. The output of the carrier triangular wave generator 27 is compared with the output of the amplitude setter 24 in the comparator 25.

The detection signal at the output power detection point 38 is compared with the output of the power setting unit 34 by the comparator 33, and the output is supplied to the frequency / phase converter 32. The frequency / phase detector 32 is also supplied with a signal from the detection point 51 of the commercial power supply 5, and its output is supplied to the phase setter 22.

The detection signal at the output detection point 37 is the power factor setting unit 3
The output signal of 1 is supplied to the comparator / arithmetic unit 30, and its output is supplied to the comparator 29. The comparator 29 is supplied with a signal from the detection point 52 on the commercial power source side, and its output is the comparator 2
8 are supplied.

The comparator 28 is also supplied with the signal from the output detection point 36 of the main conversion means 20, and its output is the amplitude setter 24.
To be supplied to.

A commercial power source power factor detection point 75 is provided between the commercial power source 5 and the interconnection point 80, and a load power factor detection point 76 is provided between the interconnection point 80 and the load 6. Rate detection point 7
The detection signal of No. 5 and the signal of the commercial power source power factor setting unit 72 are input to the comparator 71. The output of the comparator 71 is supplied to the comparator / arithmetic unit 73 together with the signal from the load power factor detection point 76.

Both the output of the comparison / operation unit 30 and the output of the comparator / operation unit 73 are supplied to the switching unit 74, and the switching unit 74 outputs the output signal from the comparison / operation unit 73 when the signal is output. The signal is selected and transmitted, and in other cases, comparison is performed and the output signal of the comparison / operation unit 30 is transmitted.

The operation of the AC converter 2 according to this system is as follows. The reference oscillator 21 sends out a frequency corresponding to 50 Hz (60 Hz) required for the AC converter 2,
The sine wave waveform transmitter 23 generates a sine wave based on the signal from the reference oscillator 21.

The amplitude of this sine wave is controlled by the amplitude setter 24 based on the output of the comparator 28.
8 is a voltage detection point 36 provided at the output of the main conversion means 20.
And outputs the result of comparing the voltage feedback signal from the output of the comparator 29 with the output of the comparator 29. Then, in the comparator 25, it is compared with the carrier signal supplied from the carrier triangular wave generator 27, and the output thereof is amplified by the gate drive circuit 26 and supplied to the main converting means 20 to obtain an AC output.

When the system is connected to the commercial power source 5, since the output capacity of the DC generator 1 is usually smaller than the load facility capacity 6, it is necessary to control the AC converter 2 to determine the output. The power setting device 34 sets the output of the AC converter 2, and the setting signal of the power setting device 34 and the power detection point 3 are set.
The feedback signal from 8 is compared by the comparator 33, and the comparison result is supplied to the frequency / phase converter 32.

The frequency / phase converter 32 is also supplied with the frequency signal supplied from the detection point 51 of the commercial power supply 5.
By the way, when the AC converter 2 and the commercial power source 5 are connected to each other, it is necessary to match the frequency, voltage and phase of both. Further, the load sharing between the commercial power supply 5 and the AC converter 2 is controlled by making the voltage phases of the two different. In this case, the AC converter 2 side is allocated by advancing the phase of the AC converter 2 in front of the interconnection reactor 35 with respect to the voltage phase of the commercial power supply 5.

Therefore, by taking the output signal of the comparator 33 and the frequency signal of the commercial power source 5 into the frequency / phase converter 32, the phases of the commercial power source 5 and the AC converter 2 are selected, and the signals are set in phase. Input to the container 22. The phase setter 22 determines the reference phase for operating the main conversion means 20 based on the signal of the reference oscillator 21 and the signal from the frequency / phase converter 32.

Based on this signal, the sine wave waveform transmitter 23 creates an ideal sine wave and supplies it to the amplitude setting device 24. In addition, the amplitude setter 24 has a detection point 36 via a comparator 28.
Is also supplied, and the amplitude setter 24 determines the sine wave amplitude for setting the output voltage of the AC converter 2 by these signals.

By comparing this signal with the carrier signal from the carrier triangular wave generator 27 by the comparator 25, a PWM signal for operating the main conversion circuit 20 is obtained. Actually, this PWM signal is amplified by the gate drive circuit 26 and used as the gate signal of the main conversion means 20 to send out the necessary AC output to the AC conversion device 2, and at the interconnection point 80 it is connected to the commercial power source 5 and the system. The load 6 is supplied with electric power.

As described above, although the output capacity of the DC power generator 1 is finite and smaller than the load capacity, reliability can be ensured by grid connection with the commercial power source 5 and running from the commercial power source 5 can be achieved. Since the cost is low, it is necessary to maximize the effective use of the output of the DC generator 1. Therefore, when the output of the AC converter 2 having the DC power generator 1 as an input and the commercial power supply 5 are interconnected, the reactive power of the output of the AC converter 2 is controlled, and the AC converter 2 has a high power factor (power factor). It is operated at a rate of 1).

The control method in that case is to detect the power factor at the detection point 37 of the output of the interconnection reactor 35 in FIG. 2 and compare the power factor set by the power factor setting device 31 (for example, 1). The arithmetic unit 30 compares. This signal and the signal from the detection point 52 for detecting the power factor on the commercial power source 5 side are compared by the comparator 29, and the output thereof is supplied to the comparator 28.

In other words, the high power factor output of the AC converter 2 is achieved by controlling the output voltage value of the AC converter 2.

FIG. 2 shows an AC converter 2 in the case of system interconnection.
And the vector of the relationship between voltage and current when the commercial power supply 5 is system-connected (actually, it is a three-phase output voltage, but here it is shown as one phase for simplification of description). In FIG. 2, VC is a commercial power supply voltage, VI (VI1, VI2) is an AC converter output voltage, VL is an interconnection reactor voltage, and AC (AC
1, AC2) is commercial current, AI is AC converter output current, A
T is the load current. Further, FIG. 3 shows the relationship among the load power, the AC converter 2, the commercial power supply, and the load power factor. Figure 2
In the above, the load sharing between the commercial power supply and the AC converter is to provide a phase difference between the commercial power supply voltage VC and the AC converter output voltage VI. Specifically, the commercial power supply voltage VC and the AC converter output voltage VI The phase angle α of is advanced.

For example, as shown in FIG.
AC1 output voltage is VI1, the commercial power supply voltage is VC, and the phase angle is α, the AC converter output current is AI1, the commercial power supply current is AC1, and the load is shared with the total load current AT. There is.

By the way, the AC converter 2 which receives the DC power generator 1 as an input is operated at a high power factor as described above, and the control for maximally utilizing the effective power from the DC power generator 1 side is the interconnection point. In 80, the output voltage VI of the AC converter 2 is controlled so that the commercial power supply voltage VC and the phase of the AC converter output current AI match.

An example thereof is shown in FIG. 2, and the output voltage of the main conversion means 20 of the AC converter 2 is controlled so that the voltage VL of the interconnection reactor 35 becomes a right angle with respect to the commercial power supply voltage VC. This is because the voltage detection point 3 of the main conversion means 20.
The voltage signal detected in 6 and the power factor signal at the power factor detection point 37 of the output of the interconnection reactor 35 are fed back to set the voltage amplitude by the amplitude setter 24 to control.

That is, even when the output sharing of the AC converter 2 is increased, the AC power supply 2 should satisfy this condition.
Control the output voltage of. However, as shown in FIG. 3, when the output of the AC power supply device 2 is continuously supplied with a high power factor, the reactive power supply from the commercial power source 5 must be increased, so that the commercial power source power factor decreases. I will end up.

Therefore, in the present invention, as shown in FIG. 1, the power factor on the commercial power source side is detected at the power factor detection point 75, and the signal thereof together with the signal from the commercial power source power factor setting unit 72 is compared / calculated by the arithmetic unit 73. Compare with. Although the set value of the commercial power source power factor setting device 72 varies depending on the installation location of the present system, here, the case where it is set to 0.85 as shown in FIG.

That is, when the load sharing of the AC converter 2 is increased, the AC converter 2 receives the power factor of the AC converter 2 itself from the power factor detection point 37 until the commercial power source power factor reaches 0.85. Is detected and compared with the power factor setting device 31, the AC converter 2 controls the amplitude setting device 24 via the comparator 29 so as to maintain the high power factor.

In this case, the switch 74 is of course constructed so as to operate with the signal from the comparison / operation unit 30 of the AC converter 2. When the load is increased in this manner, the commercial power source power factor decreases and when the set value reaches 0.85, the switch 7
4 is switched to operate by the signal of the comparison / arithmetic unit 73.

In this case, as described above, the output signal from the comparator 71 is input to one input signal terminal of the comparison / calculation unit 73 so that the commercial power supply power factor can operate at the commercial power supply power factor set value. . The comparator / arithmetic unit 73 compares this signal with the load power factor and outputs the output signal via the switching unit 74 to the comparator 2
Enter in 9.

Here, the output of the commercial power source power factor signal and the load power factor are compared and calculated by the calculator 73 in order to make the output power factor of the AC converter 2 coincide with the slope of the load power factor. If the gradient of the load power factor is too large, the commercial power factor becomes larger than the set value, and the supply of reactive power from the AC conversion device 2 becomes too large, so that the active power utilization of the DC power generation device 1 decreases.

If the power factor gradient of the AC converter 2 is smaller than the load power factor gradient, the commercial power factor will be further reduced. Therefore, it is necessary to control the gradient of the power factor of the AC converter 2 to be parallel to the load power factor. Therefore, the comparison / calculation unit 73 compares the power factor on the commercial power source 5 side with the load power factor.

The actual control method will be described with reference to the vector diagram of FIG. When the commercial power factor is greater than 0.85, the output voltage VI1 of the AC converter 2 is controlled so that the output current AI1 of the AC converter 2 is in phase with the commercial voltage VC, and the load sharing amount is almost the same. , Commercial power supply voltage VC and AC converter 2
Is performed by changing the phase angle α of the output voltage VI1.

This phase angle is calculated by the frequency / phase converter 3
The phase setting device 22 determines the phase of the AC converter 2 with respect to the phase of the commercial power supply 5 based on the output signal of 2. In this way, when the AC converter 2 increases the load sharing amount with a high power factor, the commercial power source power factor is set to a set value (in this case,
0.85) is detected, up to now, only the active power was supplied from the AC converter 2 by the high power factor operation, but since the commercial power factor is not lowered below the set value, the AC converter 2
It is necessary to supply reactive power from.

As control in this case, the AC converter voltage VI has been controlled so far so that the commercial power supply voltage VC and the AC converter current AI are in phase, but in addition to this control,
The output voltage VI of the AC converter is controlled so that the AC converter current AI is delayed in phase from the commercial power supply voltage VC.

For this control, as shown in FIG. 2, the phase angle α between the commercial power source voltage VC and the AC converter output voltage VI is shown.
Does not change, and only the AC converter 2 output voltage VI is controlled. That is, as shown in FIG. 2, the output voltage VI of the AC converter 2 is changed from VI1 to VI2. As a result, the AC converter current AI is delayed in phase from AI1 to AI2 and supplies a reactive current.

In this case, when the load current AT increases,
The commercial power supply current AC changes from AC1 to AC2 and the power factor does not change. That is, it is possible to control the change of the commercial power factor by controlling the output voltage of the AC converter 2.

This is possible by adding the voltage element of the power factor control loop to the voltage control loop of the AC converter 2. Although the case where the load increases and the commercial power factor decreases is described here, the control according to the present invention is naturally possible even when the commercial power source power factor decreases due to the load condition even when the load is constant.

[0070]

As described above, according to the present invention, when power is supplied to the load by system interconnection with the output obtained by converting the output of the DC generator to the AC power source and the commercial power source, the power factor of the commercial power source falls below a predetermined value. Since the AC conversion output power factor is controlled so as not to prevent it, it becomes possible to reduce the energy cost and prevent the commercial power factor from being excessively lowered. It has an effect that a great effect can be exerted in preventing the adverse effect of.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a vector relationship of the apparatus of FIG.

FIG. 3 is a diagram showing a power factor characteristic of the device of FIG.

FIG. 4 is a block diagram showing a configuration of a conventional example.

5 is a diagram showing a vector relationship of the apparatus of FIG.

6 is a diagram showing a power factor characteristic of the device of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC generator 2 AC converter 5 Commercial power supply 6 Load 20 Main conversion means 21 Reference oscillator 22 Phase setting device 23 Sine wave waveform transmitter 24 Amplitude setting device 26 Gate drive circuit 27 Carrier triangular wave generator 31 Power factor setting device 34 Electric power Setting device 32 Frequency / phase converter 35 Interconnection reactor 74 Switching device 25, 28, 29, 33, 71, 73 Comparator 36, 37, 38, 51, 52, 75, 76 Detection point 30, 73 Comparison / arithmetic unit 80 interconnection points

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiaki Takasago 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Within Nippon Telegraph and Telephone Corporation (72) Toru Otani 1-1-6 Uchiyuki-cho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corp. (72) Inventor Noritaka Tazawa 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corp.

Claims (1)

[Claims] 1. An interconnection point is provided on a commercial power receiving path connected to a load, and an output obtained by converting an output of a DC generator into an AC component by an AC converter is connected to the interconnection point for grid interconnection operation. In an AC conversion device for grid interconnection, a commercial power source power factor monitoring means for outputting an output signal when the power factor at a commercial power source power factor detection point provided on the commercial power source side from the interconnection point drops to a preset power factor And when the output signal from the commercial power source power factor monitoring means is supplied, control is performed so that the power factor at the load power factor detection point provided on the load side from the interconnection point does not fall below the preset power factor. A comparing / calculating unit that outputs a signal to the AC converting device, wherein the AC converting device sets the power factor at the commercial power source power factor detection point when the output signal is supplied from the comparing / calculating unit. Load force so that it does not fall below the power factor An AC converter for grid interconnection, which is characterized in that power factor control is performed according to a change in the power factor.