JPH08275399A - System-interconnected inverter device - Google Patents

Abstract

PURPOSE: To provide a system-interconnected inverter device which requires the less number of transformers when a voltage phase jump-off detecting method is used. CONSTITUTION: When a commercial power system 2 comes to an off-state, a transformer 13 takes out the AC output at an interconnection point 202. A phase comparing circuit 14 detects a phase difference between the AC output from the transformer 13 and the AC output from a voltage controlling and oscillating circuit 15 before the commercial power system 2 becomes the off- state. Immediately after the comercial power system 2 becomes the off-state, the AC output from the voltage controlling and oscillating circuit 15 is in phase with the commercial power system 2 before it becomes the off-state. Therefore, the comparison result of the phase comparing circuit 14 exceeds a specified value. As a result, a detecting circuit 16 generates a control signal. According to the control signal from the detecting circuit 16, a converting section 11 stops conversion of the DC output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grid-connected inverter device connected to an existing power system.

[0002]

2. Description of the Related Art Some grid-connected inverter devices are connected to a commercial power system as an existing power system. This grid-connected inverter device converts the power generated by the photovoltaic power generation system into a commercial frequency and supplies the converted power to a load that is a demand destination. When the power supplied to the load by the grid interconnection inverter device is insufficient, the commercial power system supplies the insufficient power to the load.

This system interconnection inverter device is shown in FIG. This system interconnection inverter device is connected to the commercial power system 2 and supplies the power generated by the solar cell 1 of the solar power generation system to the load 3.

In this system interconnection inverter device, the inverter circuit 101 converts the DC voltage from the solar cell 1 into an AC voltage of commercial frequency. As a result, the solar cell 1
DC power from is converted to AC power. On the other hand, the circuit breaker 102 is normally in the closed state, and the inverter circuit 101
The AC power from the power source is supplied to the load 3 via the circuit breaker 102. At this time, the phase-locked loop (PLL) circuit (not shown) of the control circuit 105 controls the inverter circuit 101 so that the internal oscillator (not shown) oscillates the phase of the voltage from the transformer 103. Match the phase of the reference frequency (the same frequency as the commercial frequency).

In the commercial power system, power supply may be stopped for maintenance or inspection of the power transmission system. In this case, it is necessary to stop the power supply from the grid interconnection inverter device in order to ensure the safety of workers. At this time, the grid interconnection inverter device detects a disconnection of the commercial power grid by, for example, examining a change in the voltage or frequency of the AC power supplied to the load.

By the way, when the electric power supplied from the grid interconnection inverter device is equal to the electric power consumed by the load,
That is, when the grid-connected inverter device operates independently, no change in voltage or frequency occurs, so it is difficult to detect disconnection of the commercial power system. Therefore, the voltage phase jump detection method is used to detect the disconnection of the commercial power system even in the isolated operation.

The voltage phase jump detection method detects an AC voltage and an AC current supplied to a load. When the commercial power system is cut off, it is detected that the phase of the AC voltage rapidly changes with respect to the AC current according to the power factor angle of the load.

The grid-connected inverter device shown in FIG. 6 adopts this method. That is, in the grid-connected inverter device, the transformer 103 detects the AC voltage supplied to the load 3, and the current transformer 104 detects the AC current. Control circuit 10
When the AC voltage and the AC current are received from the transformer 103 and the current transformer 104, respectively, 5 detects the phase difference of the AC voltage with respect to the AC current. When the phase difference increases,
The control circuit 105 sends a control signal to the inverter circuit 101 to stop the inverter circuit 101. As a result, the control circuit 105 cuts off the supply of AC power from the inverter circuit 101.

[0009]

By the way, the above-mentioned grid-connected inverter device includes the transformer 103 and the current transformer 10.
You need 4 and. Transformers such as the transformer 103 and the current transformer 104 are each made by winding a coil around an iron core, and have a heavy weight and a large shape. For this reason, when mounting the transformer 103 or the current transformer 104, a wide space and a mounting portion having high strength are required.

An object of the present invention is to eliminate the above drawbacks and to provide a grid interconnection inverter device capable of reducing the number of transformers when the voltage phase jump detection method is used.

[0011]

In order to achieve the object, the present invention converts the DC output of a solar cell into an AC output and supplies it to a load, and the frequency of this AC output is the frequency of an existing power system. In a system interconnection inverter device having a conversion unit equal to the transformer, a transformer for extracting an AC output at an interconnection point between an existing power system and the conversion unit, a voltage controlled oscillator circuit for generating an AC output according to the input, and a transformer When the phase difference between the AC output from the voltage control oscillation circuit and the AC output from the voltage controlled oscillation circuit is detected and the detection result is used as the input of the voltage control circuit and the phase difference from the phase comparison circuit exceeds a predetermined value. And a detection circuit that generates a control signal, and the conversion unit stops conversion of the DC output according to the control signal from the detection circuit.

[0012]

With this configuration, when the existing power system is normal, the converter converts the DC output of the solar cell into an AC output, and makes the frequency of this AC output equal to the frequency of the existing power system.

When the existing power system is cut off, the transformer extracts the AC output at the interconnection point. The phase comparison circuit detects the phase difference between the AC output from the transformer and the AC output from the voltage controlled oscillation circuit before the existing power system is disconnected, and uses the detection result as the input of the voltage control circuit.

At this time, the phase of the AC output changes abruptly with respect to the phase before the disconnection according to the power factor angle of the load. Immediately after the disconnection, the AC output from the voltage controlled oscillator circuit is equal to the phase of the existing power system before the disconnection, so the comparison result in the phase comparison circuit exceeds the predetermined value.
The detection circuit generates a control signal. The conversion unit stops conversion of the DC output according to the control signal from the detection circuit.

As a result, even if only one transformer is used,
The control of the voltage phase jump detection method is performed.

[0016]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In this system interconnection inverter device, the solar cell 1 is connected to the input point 201 and is connected to the commercial power system 2 at the interconnection point 202. Then, the data integrating device detects the disconnection of the commercial power system 2 by the voltage phase jump detection method.

This system interconnection inverter device includes a conversion unit 1
1, circuit breaker 12, transformer 13, and phase comparison circuit 14
A voltage-controlled oscillation circuit 15 and a detection circuit 16.

As shown in FIG. 2, the conversion unit 11 includes a phase lock loop circuit 21, a generation circuit 22, a pulse width modulation circuit 23, and an inverter circuit 24.

Phase-locked loop circuit 2 of converter 11
1 is an AC signal a from the transformer 13 as shown in FIG.
A pulse signal b in phase with 1 is generated. The generation circuit 22 is
When the pulse signal b is received from the phase-locked loop circuit 21, a sine wave signal c equal to the cycle of the pulse signal b is received.
Occurs. Upon receiving the sine wave signal c, the pulse width modulation circuit 23 performs pulse width modulation that changes the duration of the pulse according to the amplitude of the sine wave signal c.

The pulse width modulation circuit 23 generates a modulation signal d by pulse width modulation. This modulation is performed by the phase comparison circuit 14
It is controlled by the control signal h from. That is, when the control signal h is at "L" level, the pulse width modulation circuit 23 generates the modulation signal d. Further, when the control signal h is at “H” level, the pulse width modulation circuit 23 does not output the modulation signal d.

The inverter circuit 24 converts the DC voltage from the solar cell 1 into an AC voltage a of commercial frequency by the modulation signal d. When the pulse width modulation circuit 23 does not output the modulation signal d, the inverter circuit 24 stops the conversion of the DC voltage and does not output the AC power.

The phase comparison circuit 14 detects the phase difference of the AC signal e from the voltage controlled oscillation circuit 15 with respect to the AC signal a1 from the transformer 13. Then, the phase comparison circuit 14
Generates a phase detection signal f according to this phase difference.
The voltage controlled oscillator circuit 15 generates an AC signal e having a frequency according to the phase difference signal f.

The detection circuit 16 detects a phase shift from the phase detection signal f of the phase comparison circuit 14. An example of this detection circuit 16 is shown in FIG. This detection circuit
A resistor 31, a capacitor 32, and NAD gates 33 to 3
5 and 5.

In this detection circuit, a signal of "H" level is usually applied to the reset terminal 37. Also,
As shown in FIG. 4, the dead band width t1 is set by the time constant determined by the resistor 31 and the capacitor 32. In this state, when the phase detection signal f is applied to the terminal 36 and the pulse width t2 of the phase detection signal f is smaller than the dead zone width t1, the NAD gate 33 outputs the signal g1 as the output signal g. Further, the pulse width t3 is the dead zone width t1.
If it is longer, the signal g2 is output. When the signal g2 is output, the flip-flop circuit composed of the NAD gates 34 and 35 inverts its state and outputs the control signal h to the terminal 3
Output from 8.

Next, the operation of this embodiment will be described.

When the commercial power system 2 is normal, the frequency of the commercial power system 2 is stable, so that the frequency at the interconnection point 202 remains constant. The phase-locked loop circuit 21 of the converter 11 uses the AC signal a from the transformer 13.
1, that is, a pulse signal b having the same frequency as the commercial power system 2
Occurs. The generation circuit 22 generates a sine wave signal c equal to the period of the pulse signal b, and the pulse width modulation circuit 23
Generates a modulation signal d by pulse width modulation. The inverter circuit 24 converts the DC voltage from the solar cell 1 into the AC voltage a of the commercial frequency by the modulation signal d.

As a result, the converter 11 converts the AC power having the same frequency and the same phase as the commercial power system 2 into the circuit breaker 1.
Supply to the load 3 via 2.

At the same time, the phase comparison circuit 14 includes a transformer 13
The phase of the AC signal e from the voltage controlled oscillator circuit 15 is compared with the AC signal a1 from. According to this comparison, if the phases are the same, that is, if the frequency of the pulse signal b of the voltage controlled oscillator circuit 19 is the same as that of the commercial power system 2,
A predetermined phase detection signal f is generated.

This phase detection signal f is applied to the detection circuit 16. In the detection circuit 16, the NAD gate 33 generates the signal g1 according to the phase detection signal f. For this,
Since the NAD gates 34 and 35 do not invert their states, they generate the control signal h of "L" level. With this control signal h, the pulse width modulation circuit 23 continues to output the modulation signal d, so that the inverter circuit 24 of the conversion unit 11
The conversion of the DC power from the solar cell 1 is continued.

When the commercial power system 2 is disconnected, the phase of the AC voltage at the interconnection point 202 after the disconnection is sharper than that before the disconnection according to the power factor angle of the load 3. Changes to. This change is transmitted via the transformer 13 to the AC signal a1.
Is added to the phase comparison circuit 14.

On the other hand, the voltage controlled oscillator circuit 15 applies the AC signal e of the phase before the disconnection to the phase comparison circuit 14. Since the phase comparison circuit 14 generates the phase detection signal f corresponding to the phase difference, the pulse width of the phase detection signal f becomes large. Therefore, the phase detection signal f having a pulse width larger than the dead zone width t1 is output to the detection circuit 16. Detection circuit 16
From the phase detection signal f as an output signal g
2 is output.

When the signal g2 is output, the NAD gate 3
The flip-flop circuit composed of 4, 35 inverts its state and outputs the control signal h of "H" level. Due to this control signal h, the pulse width modulation circuit 23 does not output the modulation signal d, so the inverter circuit 2 of the conversion unit 11
4 stops the conversion of the DC power from the solar cell 1.

In this way, according to this embodiment, when the commercial power system 2 is cut off, the supply of the AC power from the converter 11 can be stopped.

Further, this embodiment uses only the transformer 13 for detecting the AC voltage. As a result, this embodiment can reduce the number of transformers as compared with the conventional one.

[0036]

As described above, according to the present invention, even if only one transformer is used, when the existing power system is disconnected, a rapid phase change is detected and the AC output from the converter is detected. Stop the supply. As a result, the number of transformers to be used can be reduced as compared with the conventional voltage phase jump detection method.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing an example of a conversion unit.

FIG. 3 is a block diagram showing an example of a detection circuit.

FIG. 4 is a diagram showing waveforms of the detection circuit of FIG.

FIG. 5 is a waveform diagram showing a waveform in a conversion unit.

FIG. 6 is a block diagram showing a conventional grid interconnection inverter device.

[Explanation of symbols]

 2 Commercial Power System 11 Converter 13 Transformer 14 Phase Comparison Circuit 15 Voltage Controlled Oscillation Circuit 16 Detection Circuit 202 Connection Point

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H02M 7/48 H01L 31/04 K

Claims (1)

[Claims] 1. A system interconnection inverter device, comprising: a conversion unit for converting a DC output of a solar cell into an AC output and supplying the AC output to a load, and for making the frequency of the AC output equal to the frequency of an existing power system. The transformer that takes out the AC output at the interconnection point between the power system and the converter, the voltage controlled oscillator that generates the AC output according to the input, the AC output from the transformer, and the AC output from the voltage controlled oscillator The converter includes a phase comparison circuit that detects the phase difference of and the detection result is input to the voltage control circuit, and a detection circuit that generates a control signal when the phase difference from the phase comparison circuit exceeds a predetermined value. A system interconnection inverter device characterized in that conversion of DC output is stopped by a control signal from a detection circuit.