JP3625889B2 - Grid-connected inverter device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a grid-connected inverter device linked to an existing power system.
[0002]
[Prior art]
Some grid-connected inverter devices are linked to a commercial power system as an existing power system. This grid-connected inverter device converts the generated power of 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-connected inverter device is insufficient, the commercial power system supplies the insufficient power to the load.
[0003]
This system interconnection inverter device is shown in FIG. This grid-connected inverter device is linked to the commercial power system 2 and supplies the generated power of the solar cell 1 of the photovoltaic power generation system to the load 3.
[0004]
In this grid-connected inverter device, the inverter circuit 101 converts the DC voltage from the solar cell 1 into an AC voltage having a commercial frequency. Thereby, the DC power from the solar cell 1 is converted into AC power. On the other hand, the circuit breaker 102 is normally closed, and AC power from the inverter circuit 101 is supplied to the load 3 via the circuit breaker 102. At this time, a phase-locked loop (PLL) circuit (not shown) of the control circuit 105 controls the inverter circuit 101, and a built-in oscillator (not shown) oscillates the phase of the voltage from the transformer 103. Match the phase of the reference frequency (same frequency as the commercial frequency).
[0005]
In a 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-connected inverter device in order to ensure the safety of the worker. At this time, the grid interconnection inverter device detects, for example, a disconnection of the commercial power system by examining changes in the voltage or frequency of the AC power supplied to the load.
[0006]
By the way, when the power supplied from the grid-connected inverter device is equal to the power consumed by the load, that is, when the grid-connected inverter device operates alone, no voltage or frequency change occurs. It is difficult to detect system disconnection. Therefore, a voltage phase jump detection method is used to detect the disconnection of the commercial power system even in the case of single operation.
[0007]
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 changes rapidly with respect to the AC current according to the power factor angle of the load.
[0008]
The grid interconnection inverter device of FIG. 6 employs 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. When control circuit 105 receives AC voltage and AC current from transformer 103 and current transformer 104, respectively, it detects the phase difference of AC voltage with respect to 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]
[Problems to be solved by the invention]
By the way, the grid interconnection inverter apparatus described above requires the transformer 103 and the current transformer 104. Transformers such as the transformer 103 and the current transformer 104 are obtained by winding a coil around an iron core, which increases in weight and shape. For this reason, when mounting the transformer 103 and the current transformer 104, a large space and an attachment part with high strength are required.
[0010]
An object of the present invention is to provide a grid-connected inverter device that can reduce the number of transformers when the voltage phase jump detection method is used, excluding such drawbacks.
[0011]
[Means for Solving the Problems]
In order to achieve the object, the present invention converts a DC output of a solar cell into an AC output and supplies it to a load, and has a grid connection including a conversion unit that makes the frequency of the AC output equal to the frequency of an existing power system. in the system inverter device, a transformer for taking out the AC output of the interconnection point between the power system and the conversion unit, and a voltage controlled oscillator for generating an AC output corresponding to the input, the voltage control and the AC output from the transformer detecting a phase difference between the AC output from the oscillation circuit, a phase comparison circuit output a detection result to the input terminal of the voltage controlled oscillator circuit in order to the input of the voltage controlled oscillator circuit is connected, said phase comparator When the phase difference from the circuit exceeds a predetermined value, generating a control signal Subeku, the output of the phase comparator between the input terminal and the output terminal of the phase comparator circuit and the input terminal of the voltage controlled oscillator And a connected detection circuit, the converter unit by the control signal from the detecting circuit, stops the conversion of the DC output.
[0012]
[Action]
With this configuration, when the existing power system is normal, the conversion unit converts the direct current output of the solar cell into an alternating current output, and makes the frequency of the alternating current output equal to the frequency of the existing power system.
[0013]
When the existing power system is cut off, the transformer takes out the AC output at the connection point. The phase comparison circuit detects a 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 an input to the voltage control circuit.
[0014]
At this time, according to the power factor angle of the load, the phase of the AC output changes abruptly with respect to the phase before the disconnection. Immediately after the disconnection, the AC output from the voltage controlled oscillation circuit is equal to the phase of the existing power system before the disconnection, so the comparison result in the phase comparison circuit exceeds a predetermined value. The detection circuit generates a control signal. The conversion unit stops the conversion of the DC output according to the control signal from the detection circuit.
[0015]
Thereby, even if one transformer is used, the voltage phase jump detection method is controlled.
[0016]
【Example】
Next, embodiments of the present invention will be described with reference to the drawings.
[0017]
FIG. 1 is a block diagram showing an embodiment of the present invention. In this grid-connected inverter device, the solar cell 1 is connected to the input point 201 and linked to the commercial power grid 2 at the grid point 202. Then, the data integrating device detects the disconnection of the commercial power system 2 by the voltage phase jump detection method.
[0018]
This grid-connected inverter device includes a conversion unit 11, a circuit breaker 12, a transformer 13, a phase comparison circuit 14, a voltage control oscillation circuit 15, and a detection circuit 16.
[0019]
As shown in FIG. 2, the conversion unit 11 includes a phase-locked loop circuit 21, a generation circuit 22, a pulse width modulation circuit 23, and an inverter circuit 24.
[0020]
As shown in FIG. 5, the phase-locked loop circuit 21 of the conversion unit 11 generates a pulse signal b having the same phase as the AC signal a <b> 1 from the transformer 13. When the generation circuit 22 receives the pulse signal b from the phase lock loop circuit 21, the generation circuit 22 generates a sine wave signal c equal to the period of the pulse signal b. When the pulse width modulation circuit 23 receives the sine wave signal c, the pulse width modulation circuit 23 performs pulse width modulation to change the pulse duration according to the amplitude of the sine wave signal c.
[0021]
The pulse width modulation circuit 23 generates a modulation signal d by pulse width modulation. This modulation is controlled by a control signal h from the phase comparison circuit 14. That is, when the control signal h is at the “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.
[0022]
The inverter circuit 24 converts the DC voltage from the solar cell 1 into an AC voltage a having a commercial frequency according to the modulation signal d. Further, 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.
[0023]
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 oscillation circuit 15 generates an AC signal e having a frequency corresponding to the phase difference signal f.
[0024]
The detection circuit 16 detects a phase shift from the phase detection signal f of the phase comparison circuit 14. An example of the detection circuit 16 is shown in FIG. This detection circuit includes a resistor 31, a capacitor 32, and NAD gates 33 to 35.
[0025]
In this detection circuit, a signal of “H” level is normally applied to the reset terminal 37. Further, as shown in FIG. 4, the dead zone width t1 is set by a time constant determined by the resistor 31 and the capacitor 32. When the phase detection signal f is applied to the terminal 36 in this state, if the pulse width t2 of the phase detection signal f is smaller than the dead band width t1, the NAD gate 33 outputs the signal g1 as the output signal g. If the pulse width t3 is longer than the dead band width t1, the signal g2 is output. When the signal g2 is output, the flip-flop circuit composed of the NAD gates 34 and 35 inverts the state and outputs the control signal h from the terminal 38.
[0026]
Next, the operation of this embodiment will be described.
[0027]
When the commercial power system 2 is normal, since the frequency of the commercial power system 2 is stable, the frequency of the interconnection point 202 is kept constant. The phase lock loop circuit 21 of the converter 11 generates the AC signal a1 from the transformer 13, that is, the pulse signal b having the same frequency as that of the commercial power system 2. 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 an AC voltage a having a commercial frequency by using the modulation signal d.
[0028]
Thereby, the converter 11 supplies AC power having the same frequency and the same phase as the commercial power system 2 to the load 3 via the circuit breaker 12.
[0029]
At the same time, the phase comparison circuit 14 compares the phase of the AC signal e from the voltage controlled oscillation circuit 15 with the AC signal a1 from the transformer 13. From this comparison, if the phase is the same, that is, if the frequency of the pulse signal b of the voltage controlled oscillation circuit 19 is the same as that of the commercial power system 2, a predetermined phase detection signal f is generated.
[0030]
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 by the phase detection signal f. For this reason, the NAD gates 34 and 35 do not invert the state, and therefore generate the control signal h at the “L” level. Due to 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 converter 11 continues the conversion of the DC power from the solar cell 1.
[0031]
By the way, when the commercial power system 2 is disconnected, the phase of the AC voltage at the interconnection point 202 after the disconnection changes abruptly according to the power factor angle of the load 3 compared to the phase before the disconnection. . This change is applied to the phase comparison circuit 14 through the transformer 13 as an AC signal a1.
[0032]
On the other hand, the voltage controlled oscillation circuit 15 adds the AC signal e having the phase before the interruption 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 increases. Therefore, a phase detection signal f having a pulse width larger than the dead band width t1 is output to the detection circuit 16. The detection circuit 16 outputs a signal g2 as an output signal g from the phase detection signal f.
[0033]
When the signal g2 is output, the flip-flop circuit composed of the NAD gates 34 and 35 inverts the 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 that the inverter circuit 24 of the converter 11 stops the conversion of the DC power from the solar cell 1.
[0034]
Thus, according to this embodiment, when the commercial power system 2 is cut off, the supply of AC power from the conversion unit 11 can be stopped.
[0035]
In addition, this embodiment uses only the transformer 13 for detecting the AC voltage. As a result, according to this embodiment, the number of transformers can be reduced as compared with the prior art.
[0036]
【The invention's effect】
As described above, according to the present invention, even if only one transformer is used, when the existing power system is cut off, a sudden phase change is detected and the supply of AC output from the conversion unit is stopped. 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 the drawings]
FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a block diagram illustrating an example of a conversion unit.
FIG. 3 is a block diagram illustrating an example of a detection circuit.
4 is a diagram showing waveforms of the detection circuit of FIG. 3;
FIG. 5 is a waveform diagram showing waveforms in a conversion unit.
FIG. 6 is a block diagram showing a conventional grid-connected inverter device.
[Explanation of symbols]
2 Commercial Power System 11 Conversion Unit 13 Transformer 14 Phase Comparison Circuit 15 Voltage Control Oscillation Circuit 16 Detection Circuit 202 Connection Point

Claims (1)

In the grid-connected inverter device comprising a conversion unit that converts the DC output of the solar cell into an AC output and supplies it to the load, and equalizes the frequency of this AC output with the frequency of the existing power system,
A transformer for taking out the AC output of the interconnection point between the power system and the conversion unit,
A voltage controlled oscillation circuit that generates an AC output according to the input;
Wherein detecting a phase difference between the AC output from the transformer and the AC output from the voltage controlled oscillator circuit, the detection result to connect the output terminal to the input terminal of the voltage controlled oscillator circuit in order to the input of the voltage controlled oscillator a phase comparator circuit which is,
When the phase difference from the phase comparator circuit exceeds a predetermined value, the phase comparison circuit between the input terminals in order to generate the control signal and the output terminal of the phase comparator circuit and the input of the voltage controlled oscillator And a detection circuit connected to the output terminal of
The conversion unit wherein a control signal from the detection circuit, system interconnection inverter apparatus characterized by stopping the conversion of the DC output.

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